Proposed Generic Communication; Managing Gas Intrusion in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems, 29010-29015 [07-2557]

Download as PDF 29010 Federal Register / Vol. 72, No. 99 / Wednesday, May 23, 2007 / Notices Appendix A to 10 CFR Part 50 as its regulatory requirement. The TSTF stated the improved BPWS provides the following benefits: (1) Allows the plant to reach the all-rods-in condition prior to significant reactor cool down, which reduces the potential for re-criticality as the reactor cools down; (2) reduces the potential for an operator reactivity control error by reducing the total number of control rod manipulations; (3) minimizes the need for manual scrams during plant shutdowns, resulting in less wear on control rod drive (CRD) system components and CRD mechanisms; and (4) eliminates unnecessary control rod manipulations at low power, resulting in less wear on reactor manual control and CRD system components. The addition of procedural requirements and verifications specified in NEDO–33091–A, along with the proper use of the BPWS will prevent a control rod drop accident (CRDA) from occurring while power is below the low power setpoint (LPSP). The net change to the margin of safety is insignificant. Therefore, this change does not involve a significant reduction in a margin of safety. Based upon the above discussion of the amendment request, the requested change does not involve a significant hazards consideration. Dated at Rockville, Maryland, this 10th day of May 2007. For the Nuclear Regulatory Commission. Timothy J. Kobetz, Branch Chief, Technical Specifications Branch, Division of Inspection & Regional Support, Office of Nuclear Reactor Regulation. [FR Doc. 07–2563 Filed 5–22–07; 8:45 am] BILLING CODE 7590–01–P NUCLEAR REGULATORY COMMISSION Addresses Proposed Generic Communication; Managing Gas Intrusion in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems Nuclear Regulatory Commission. AGENCY: Notice of opportunity for public comment. pwalker on PROD1PC71 with NOTICES ACTION: SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is proposing to issue a generic letter (GL) to address the issue of gas intrusion into the emergency core cooling, decay heat removal, and containment spray systems (hereinafter referred to as the ‘‘subject systems’’). Specifically, the NRC is issuing this GL for the following two purposes: VerDate Aug<31>2005 18:32 May 22, 2007 (1) to request addressees to submit information demonstrating that the subject systems are in compliance with the current licensing and design bases, and applicable regulatory requirements, and that suitable design, operational, and testing control measures are in place for maintaining this compliance, and (2) to collect the requested information to determine if additional regulatory action is required. This Federal Register notice is available through the NRC’s Agencywide Documents Access and Management System (ADAMS) under accession number ML0704001003. DATES: Comment period expires July 23, 2007. Comments submitted after this date will be considered if it is practical to do so, but assurance of consideration cannot be given except for comments received on or before this date. ADDRESSES: Submit written comments to the Chief, Rulemaking, Directives, and Editing Branch, Division of Administrative Services, Office of Administration, U.S. Nuclear Regulatory Commission, Mail Stop T6–D59, Washington, DC 20555–0001, and cite the publication date and page number of this Federal Register notice. Written comments may also be delivered to NRC Headquarters, 11545 Rockville Pike (Room T–6D59), Rockville, Maryland, between 7:30 a.m. and 4:15 p.m. on Federal workdays. FOR FURTHER INFORMATION, CONTACT: Warren C. Lyon, NRR, at 301–415–2897 or by e-mail: wcl@nrc.gov or David P. Beaulieu, NRR, at 301–415–3243 or by e-mail: dpb@nrc.gov. SUPPLEMENTARY INFORMATION: NRC Generic Letter 2007–XX, Managing Gas Intrusion in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems Jkt 211001 All holders of operating licenses for nuclear power reactors, except those who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this generic letter (GL) to address the issue of gas 1 intrusion into the emergency core cooling, decay heat removal 2, and 1 Gas as used here includes, air, nitrogen, hydrogen, water vapor, or any other void that is not filled with liquid water. 2 Decay heat removal (DHR), residual heat removal (RHR), and shutdown cooling (SDC) are common names for systems used to cool the reactor PO 00000 Frm 00066 Fmt 4703 Sfmt 4703 containment spray systems (hereinafter referred to as the ‘‘subject systems’’). Specifically, the NRC is issuing this GL: (1) To request addressees to submit information to demonstrate that the subject systems are in compliance with the current licensing and design bases and applicable regulatory requirements, and that suitable design, operational, and testing control measures are in place for maintaining this compliance, and (2) to collect the requested information to determine if additional regulatory action is required. Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.54(f), addressees are required to submit a written response to this GL. Background Instances of gas intrusion into the subject systems have occurred since the beginning of commercial nuclear power plant operation. The NRC has published 20 information notices (INs), two GLs, and a NUREG 3 that are related to this issue and has interacted with the nuclear industry many times in relation to these publications and in response to gas intrusion events. The following paragraphs summarize a few events to illustrate some of the technical and regulatory requirements issues. In May 1997, at Oconee Nuclear Station Unit 3, hydrogen ingestion during plant cooldown damaged and rendered nonfunctional two highpressure injection (HPI) pumps. If the operators had started the remaining HPI pump, it too would have been damaged. The NRC responded with an augmented inspection team (IN 97–38, ‘‘LevelSensing System Initiates Common-Mode Failure of High-Pressure-Injection Pumps,’’ Agencywide Documents Access and Management System (ADAMS) Accession No. ML031050514, June 24, 1997). The NRC team reported that there had been a total lack of HPI capability during power operation, a failure to meet technical specification (TS) HPI operability requirements, design deficiencies, inadequate maintenance practices, operators that were less than attentive to plant parameters, a failure to adequately assess operating experience, and a violation of 10 CFR part 50, Appendix coolant system (RCS) during some phases of shutdown operation. The NRC staff generally uses DHR here. 3 GL 88–17, ‘‘Loss of Decay Heat Removal,’’ October 17, 1988 (ML031200496); GL 97–04, ‘‘Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps,’’ October 7, 1997 (ML031110062); and NUREG–0897, Revision 1, ‘‘Containment Emergency Sump Performance—Technical Findings Related to USI A–43,’’ October 1985. E:\FR\FM\23MYN1.SGM 23MYN1 Federal Register / Vol. 72, No. 99 / Wednesday, May 23, 2007 / Notices pwalker on PROD1PC71 with NOTICES B, Criterion III (‘‘Notice of Violation and Proposed Imposition of Civil Penalties —$330,000,’’ August 27, 1997, http:// www.nrc.gov/reading-rm/doccollections/enforcement/actions/ reactors/ea97297.html). As a result of this Oconee Unit 3 event, the industry initiated an industry-wide improvement activity to address the gas issue. Based on the industry actions, the NRC concluded that no generic action was necessary. However, significant gas events that jeopardized the operability of the subject systems continued to occur, as illustrated in the following paragraphs. Dresden Nuclear Power Station Unit 3 experienced a reactor scram on July 5, 2001, that was accompanied by a water hammer as a result of high pressure coolant injection (HPCI) system voids due to inadequate pipe venting. The licensee discovered a damaged pipe support that rendered the HPCI system inoperable on July 19, 2001. On September 28, 2001, NRC inspectors discovered discrepancies in another HPCI hanger that may have been caused by the water hammer. The licensee repaired the hangers on September 30, 2001, and vented the system. An NRC inspector identified a high point that had not been vented and air was removed when the licensee vented that location. The HPCI system was inoperable from July 5, 2001, to September 30, 2001 (NRC Supplemental Inspection Report 50–237, 50–239/ 2003–012, ML033530204, December 18, 2003). The NRC found violations of 10 CFR 50.9, a TS, and 10 CFR part 50, Appendix B, Criterion XVI (‘‘Notice of Violation and Proposed Imposition of Civil Penalty—$60,000, and Final Significance Determination for a White Finding,’’ ML031740755, June 23, 2003). On August 14, 2003, the Perry Nuclear Power Plant scrammed from 100 percent power due to a loss of offsite power. This caused a momentary loss of common water leg pumps 4 and a discharge pressure decrease from 44 psig to 7 psig allowed accumulated gas to completely void a water leg pump and the associated feedwater leakage control system piping. Pump operation was restored by venting the pump casing but a piping high point that was not included in fill and vent procedures was not vented. On September 10, 2003, the licensee vented enough gas from the high point that would have caused the pump to be non-functional if another 4 These are 40 gpm pumps used to compensate for back-leakage through check valves in RHR and LPSI piping into the suppression pool. The purpose is to keep piping full of water where the pipe elevation is higher than the suppression pool. The system is often referred to as a ‘‘keep-full’’ system. VerDate Aug<31>2005 18:32 May 22, 2007 Jkt 211001 loss of offsite power would occur. If the RHR and/or the LPCS pumps had started while the leakage control system piping was voided, the resulting water hammer could have caused the system piping to rupture. The NRC characterized the inspection finding as white; the finding resulted in a TS violation, escalated enforcement action, and a supplemental inspection (NRC Inspection Report 50–440/2003–009, ML032880107, October 10, 2003, and ML040330980, January 30, 2004). On July 28, 2004, the Palo Verde licensee identified that emergency core cooling system (ECCS) suction piping voids in all three Palo Verde units could have resulted in a loss of the ECCS during transfer to the recirculation mode for some loss-of-coolant accident (LOCA) conditions. The condition had existed since plant startups in 1986, was contrary to the Palo Verde final safety analysis reports (FSARs), and would not be identified during testing because water is not drawn from the containment emergency sumps. The NRC inspectors identified multiple violations of 10 CFR part 50, Appendix B, Criteria III and V, and violations of 10 CFR 50.59. The NRC responded with a special inspection, issued a yellow finding, and imposed a civil penalty of $50,000 (NRC Special Inspection Report 50–328, 50–329, 50–330/2004–014, ML050050287, January 5, 2005). The Palo Verde licensee identified the ECCS piping suction voids after being contacted by engineer from another plant where an NRC inspector identified the same problem. In February 2005, an HPI pump at Indian Point Energy Center Unit 2 was found inoperable because the pump casing was filled with gas. The licensee then found numerous locations in the ECCS piping with gas accumulation. The licensee did not initially understand the implications of the gas condition, and the licensee’s early assessments were inadequate, particularly with respect to assessing the operability of the other two HPI pumps. The NRC conducted a special inspection that found one HPI pump was not functional and the other two HPI pumps had a 75 percent failure probability. The NRC found several violations of 10 CFR part 50, Appendix B, Criterion XVI, and issued a white finding (NRC Inspection Report 50–247/ 2005–006, ML051680119, June 17, 2005). In March 2005, the NRC reported that Diablo Canyon had a sustained history of gas voiding in piping that could possibly result in gas binding or damage to the centrifugal charging pumps or the HPSI pumps during switchover from PO 00000 Frm 00067 Fmt 4703 Sfmt 4703 29011 cold-leg to hot-leg injection.5 The NRC inspectors concluded that the licensee focused on managing the symptom of the problem rather than finding and eliminating the cause, which is contrary to 10 CFR part 50, Appendix B, Criterion XVI (NRC Inspection Report 50–275, 50–323/2005–006, ML050910120, March 31, 2005). In September 2005, operators discovered a void in the HPCI pump discharge piping at the Duane Arnold Energy Center due to ‘‘turbulent penetration’’ that caused hot water from the feedwater pipe to penetrate downward into the HPCI discharge pipe. This heated the HPCI pipe on the low pressure side of a closed valve to greater than the saturation temperature and caused steam to be generated in the low pressure pipe as fast as it was vented. The condition had existed since plant startup (Licensee Event Report 50– 331/2005–004, ML053360261, November 28, 2005). The NRC opened an unresolved item (URI 05000331/ 2006002–03) for further NRC review of the licensee’s piping analysis that evaluated HPSI system operability with the voided piping (NRC Inspection Report 50–331/2006–002, ML061210448, April 27, 2006, and NRC Inspection Report 50–331/2006–008, ML070640515, March 2, 2007). In October 2005, an NRC inspection team at the Palo Verde Nuclear Generating Station identified that, following a postulated accident when refueling water tank (RWT) level reached the setpoint for containment sump recirculation, the licensee’s design basis credited containment pressure for preventing the ECCS pumps from continuing to reduce RWT level and drawing air into the ECCS. However, a recent licensee analysis showed that the minimum containment pressure would be less than needed. The licensee declared the ECCS inoperable at all three units, requiring a shutdown of Units 2 and 3 (Unit 1 was already shut down). The NRC found multiple violations of 10 CFR part 50, Appendix B, Criteria III and V (NRC Supplemental Inspection Report 50– 528, 50–529, 50–530/2005–012, ML060300193, January 27, 2006). These are a few of the more than 60 gas intrusion events reported during recent years involving the subject 5 A similar gas accumulation problem under closed valves in the recirculation piping from the DHR discharge to the HPSI and charging pump suctions has occurred at several plants. This has the potential to cause loss of all high pressure RCS makeup capability when shifting suction to the emergency containment sump from the refueling water or borated water storage tank following a LOCA. E:\FR\FM\23MYN1.SGM 23MYN1 29012 Federal Register / Vol. 72, No. 99 / Wednesday, May 23, 2007 / Notices pwalker on PROD1PC71 with NOTICES systems. The number is larger if other similar events at the same plant are counted. Further, many events do not have to be reported to the NRC, and many of them have not been addressed during the NRC’s inspections. For example, at least 40 RHR water hammer events have occurred at the Sequoyah Nuclear Plant, although none of them rendered the RHR system inoperable. Additionally, if an ECCS pump has been damaged because of gas but is repaired and tested operable within the TS completion time (typically, 72 hours), the licensee is not required to report the occurrence to the NRC. The frequency and the significance of these events and the likelihood that unidentified gas issues exist require licensee action to ensure compliance with regulatory requirements that will maintain operability of the subject systems. Applicable Regulatory Requirements 10 CFR part 50 Appendix A or similar plant-specific principal design criteria 6 provide design requirements, and 10 CFR part 50 Appendix B, TSs, and licensee quality assurance programs provide operating requirements. Appendix A requirements applicable to gas management in the subject systems include the following: • General Design Criterion (GDC) 1 requires that the subject systems be designed, fabricated, erected, and tested to quality standards. • GDC 34 requires an RHR system designed to maintain specified acceptable fuel design limits and to meet design conditions that are not exceeded if a single failure occurs and specified electrical power systems fail. • GDC 35, 36, and 37 require an ECCS design that meets performance, inspection, and testing requirements. Specified performance criteria are provided in 10 CFR 50.46. • GDC 38, 39, and 40 require a containment heat removal system design that meets performance, inspection, and testing requirements. Quality assurance criteria provided in Appendix B that apply to gas management in the subject systems include the following: • Criteria III and V require measures to assure that applicable regulatory requirements and the design basis, as defined in 10 CFR 50.2, ‘‘Definitions,’’ and as specified in the license application, are correctly translated into controlled specifications, drawings, procedures, and instructions. • Criterion XI requires a test program to assure that the subject systems will 6 For facilities with a construction permit issued prior to May 21, 1972, that are not licensed to Appendix A. VerDate Aug<31>2005 18:32 May 22, 2007 Jkt 211001 perform satisfactorily in service. Test results shall be documented and evaluated to assure that test requirements have been satisfied. • Criterion XVI requires measures to assure that conditions adverse to quality, such as failures, malfunctions, deficiencies, deviations, defective material and equipment, and nonconformances, are promptly identified, corrected, documented, and reported to management. • Criterion XVII requires maintenance of records of activities affecting quality. Further, as part of the licensing basis, licensees have committed to certain quality assurance provisions that are identified in both their TSs and quality assurance programs. Licensees have committed to use the guidance of Regulatory Guide (RG) 1.33, ‘‘Quality Assurance Requirements (Operation),’’ which endorses American National Standards Institute (ANSI) N18.7–1976/ American Nuclear Society 3.2, ‘‘Administrative Controls and Quality Assurance for the Operational Phase of Nuclear Power Plants,’’ or equivalent licensee-specific guidance. Section 5.3.4.4, ‘‘Process Monitoring Procedures,’’ of ANSI N18.7 that states that procedures for monitoring performance of plant systems shall be required to assure that engineered safety features and emergency equipment are in a state of readiness to maintain the plant in a safe condition if needed. The limits (maximum and minimum) for significant process parameters shall be identified. Operating procedures shall address the nature and frequency of this monitoring, as appropriate. 10 CFR 50.36(c)(3) defines TS surveillance requirements (SRs) as ‘‘relating to test, calibration, or inspection to assure’’ maintenance of quality, operation within safety limits, and operability. Typically, TS Section 5 or 6 requires that licensees establish, implement, and maintain written procedures covering the applicable procedures recommended in Appendix A to RG 1.33, Revision 2 (February 1978). Appendix A to RG 1.33 identifies instructions for filling and venting the ECCS and DHR system, as well as for draining and refilling heat exchangers. Surveillance requirements to verify that at least some of the subject system piping is filled are provided in standard technical specifications (STSs) and in most licensee TSs. Discussion The events discussed in the BACKGROUND section illustrate that many of the regulatory requirements identified in the APPLICABLE REGULATORY REQUIREMENTS PO 00000 Frm 00068 Fmt 4703 Sfmt 4703 section are not being met. The NRC inspectors often find that the 10 CFR part 50 Appendix B criteria identified above are not adequately addressed in plant venting procedures. In some cases, venting procedures were almost nonexistent, there were no records of gas quantities that were vented and licensees unsuccessfully attempted to recreate the history by asking operators for their recollections. Consequently, there was no foundation for establishing that the subject systems were operable prior to venting. In addition, the venting processes sometimes did not ensure that all gas was removed from the venting location and often did not adequately establish the quantity of vented gas. Further, examination of ultrasonic test (UT) processes at several licensee sites established that one licensee initially did not know how to acceptably determine liquid level via UT. Additional issues include TSs, which often do not require venting of suction piping despite voids in suction pipes generally being of more concern than in discharge piping, and do not adequately address operability of the subject systems prior to surveillance and for the time span until the next surveillance. This GL and the anticipated NRC followup to this GL are intended to correct such conditions. It is important that the subject systems are sufficiently filled with water to ensure that they can reliably perform their intended functions under all LOCA and non-LOCA conditions that require makeup to the RCS. Portions of these systems and some of the associated pumps are normally in a standby condition while other pumps provide both ECCS and operational functions. For example, some highpressure pumps are used for normal RCS makeup, and some low-pressure pumps provide a normal DHR capability. The following safety issues are associated with gas intrusion into the subject systems: (1) The introduction of gas into a pump can cause the pump to become air-bound with little or no flow, rendering the pump inoperable. Airbinding can render more than one pump inoperable when pumps share common discharge or suction headers, or when the gas accumulation process affects more than one train, greatly increasing the risk significance. Such a commonmode failure would result in the inability of the ECCS or the DHR system to provide adequate core cooling and the inability of the containment spray system to maintain the containment pressure and temperature below design limits. An air-bound pump can become E:\FR\FM\23MYN1.SGM 23MYN1 pwalker on PROD1PC71 with NOTICES Federal Register / Vol. 72, No. 99 / Wednesday, May 23, 2007 / Notices damaged quickly, eliminating the possibility of recovering the pump during an event by simply subsequently venting the pump and suction piping. (2) Gas introduced into a pump can render the pump inoperable, even if the gas does not air bind the pump, because the gas can reduce the pump discharge pressure and flow capacity to the point that the pump cannot perform its design function. For example, an HPI pump that is pumping air-entrained water may not develop sufficient discharge pressure to inject under certain small break LOCA scenarios. (3) Gas accumulation can result in water hammer or a system pressure transient, particularly in pump discharge piping following a pump start, which can cause piping and component damage or failure. Gas accumulation in the DHR system has resulted in pressure transients that have caused DHR system relief valves to open. In some plants, the relief valve reseating pressure is less than the existing RCS pressure, a condition that complicates recovery. (4) Pump cavitation caused by entrained gas results in additional stresses that can lead to premature failure of pump components that can render the pump inoperable. (5) Gas intrusion can result in pumping noncondensible gas into the reactor vessel that may affect core cooling flow. (6) The time needed to fill voided discharge piping can delay delivery of water beyond the time frame assumed in the accident analysis. The scope and number of identified gas intrusion problems at some facilities raise concerns about whether similar unrecognized design, configuration, and operability problems exist at other reactor facilities. A review of the operating experience has identified the following concerns, which are the focus of this GL: (1) TS SRs, as implemented by associated surveillance procedures, have not reliably precluded gas problems. Operating experience shows many instances in which substantive gas voiding in the system piping has not been identified. The surveillance procedures may not reliably reveal asfound conditions in which the system may be inoperable or degraded because of gas. Additionally, some plants have no TS SR to verify that the subject systems’ piping is sufficiently full of water. Still other plants have incomplete TS SRs that cover only portions of the system. For example, the TS may require verifying that ECCS discharge piping is full of water but may not include verification of the suction piping or containment spray piping. VerDate Aug<31>2005 18:32 May 22, 2007 Jkt 211001 Although the TS and FSAR at many facilities indicate that the subject systems are full of water, in practice it is not uncommon for licensees to vent some gas during periodic surveillances. Further, there may be some parts of these systems where it is not possible or practical to verify them to be full of water. Hence, the current TS and FSAR may establish a standard that may not be realistic to establish system operability. A realistic standard should bound the volume of gas that may impact pump operability and the volume for which water-hammerinduced stress limits may be exceeded. Criterion XI of Appendix B to 10 CFR part 50 requires licensees to perform testing using written test procedures, which include but are not limited to procedures for TS SRs, that incorporate the requirements and acceptance limits contained in applicable design documents. TSs often require surveillance of discharge piping but do not mention suction piping. Consequently, suction piping surveillances may not be performed. However, since the subject systems may be rendered inoperable or degraded because of gas in suction piping, the regulations require that presence of gas in all piping be assessed to establish operability. (2) Typically the FSAR describes that the subject systems are filled with water. The wording of TS SRs further confirms that the design-basis configuration calls for the specified piping to be filled with water. Operating experience provides many examples of licensees treating the accumulation of gas as an expected condition (rather than a nonconforming condition) that was not documented even when it involved a substantial volume of gas that clearly constituted a significant condition adverse to quality. In such cases, Criterion XVI of Appendix B to 10 CFR part 50 requires that the cause of the condition be determined and corrective action taken to preclude repetition. Based on the as-found volume and location of gas, corrective actions beyond simply refilling a system may be necessary to provide reasonable assurance that the affected system will remain operable until the next surveillance. (3) Although the subject systems are often susceptible to gas intrusion, not all plants have vent valves at one or more system high points. Some licensees have installed additional vent valves at system high points after operational events. For example, one licensee installed an additional 21 high-point vent valves. Another licensee, who installed an additional 17 vent valves, PO 00000 Frm 00069 Fmt 4703 Sfmt 4703 29013 determined that the primary cause of the gas voiding problem was that the original design specification did not call for a sufficient number of vent valves. No specific NRC requirement mandates the installation of vent valves on the subject systems. However, failure to translate the design basis of assuring the system is maintained sufficiently full of water to maintain operability into drawings, specifications, procedures, and instructions is a violation of Criterion III in Appendix B of 10 CFR part 50. Further, Criterion V requires documented instructions, procedures, or drawings that include appropriate quantitative or qualitative acceptance criteria for determining that important activities have been satisfactorily accomplished. This means that each addressee must have suitable documentation and records, including acceptance criteria, to establish that the subject systems have been and are maintained sufficiently full of water to ensure system operability. Vent valves and their use are often a key ingredient for satisfying these requirements. The NRC staff is initiating a Technical Specifications Task Force (TSTF) activity to address the recognized TS weaknesses associated with gas intrusion concerns. In the interim, until new TSs are developed, the NRC staff will treat a SR that the piping be full of water as satisfied if the piping and pumps of the subject systems are maintained sufficiently full of water to ensure system operability when operability is required. This condition must be shown to be satisfied during the time between surveillances, and either venting or UT surveillances are acceptable means of obtaining void data. Further, the NRC staff will consider justification for not conducting a periodic surveillance or for extending the time between surveillances of certain sections of piping if an addressee considers surveillance to be unnecessary. For example, some three loop plants designed by Westinghouse maintain HPSI discharge lines at a pressure greater than the RCS operating pressure. This eliminates the potential for leakage from the accumulators or the RCS as a possible means to introduce gas into the discharge lines. An assessment for such plants that (1) acceptably eliminates other means of introducing gas, (2) establishes acceptable verification that the lines are essentially full following a condition that reduces the discharge line pressure, and (3) establishes an operating history confirming that gas has not accumulated will be adequate justification for not conducting surveillances inside E:\FR\FM\23MYN1.SGM 23MYN1 29014 Federal Register / Vol. 72, No. 99 / Wednesday, May 23, 2007 / Notices containment or at locations that constitute a hazard to personnel performing the assessment. The NRC memorandum, ‘‘Technical Considerations for Reasonably Assuring Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems Operability,’’ ML071030382, April 17, 2007, provides some operating experience insights. The NRC staff plans to use this information during inspection activities that are planned as a followup to this GL and for guidance in the TSTF program to develop improved TSs. Requested Actions Each addressee is requested to evaluate their ECCS, DHR system, and containment spray system designs, operation, and test procedures to assure that gas intrusion is minimized and monitored in order to maintain system operability and compliance with the requirements of Appendix B to 10 CFR part 50. Requested Information Each addressee is requested to provide a summary description of how the REQUESTED ACTIONS have been addressed within 6 months of the date of this GL. This summary description should specifically address the quality assurance criteria in 10 CFR part 50, Appendix B, Sections III, V, XI, XVI, and XVII and the TSs that apply to the subject systems. This summary should include a general description of: (1) The design, (2) the operating procedures, and (3) the test procedures to assure that gas intrusion does not affect the ability of the subject systems to perform their intended functions. If an addressee determines that system or procedure modifications are necessary based on the review of the requested actions and these changes cannot be accomplished within 6 months of the date of this GL, then the addressee should also provide a plan and schedule for completion of these actions. generic letter, an addressee is required to submit a written response if they are unable to provide the information or they cannot meet the requested completion date. The addressee must address in its response any alternative course of action that it proposes to take, including the basis for the acceptability of the proposed alternative course of action. The required written response should be addressed to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, 11555 Rockville Pike, Rockville, MD 20852, under oath or affirmation under the provisions of section 182a of the Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f). In addition, submit a copy of the response to the appropriate regional administrator. Required Response In accordance with 10 CFR 50.54(f), in order to determine whether a facility license should be modified, suspended, or revoked, or whether other action should be taken, an addressee is required to respond as described below. Within 6 months of the date of this Reasons for Information Request The NRC is requesting this information because a review of operating experience shows numerous instances of gas intrusion events involving the subject systems that have rendered or potentially rendered these risk-significant systems inoperable. RELATED GENERIC COMMUNICATIONS ADAMS accession No. Document No. Document name GL 88–17 ..................... GL 97–04 ..................... Loss of Decay Heat Removal ................................................................................................................. Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps. Loss of Safety Injection Capability .......................................................................................................... Unit Startup with Degraded High Pressure Safety Injection System ..................................................... Inadequate Net Positive Suction Head in Low Pressure Safety Systems ............................................. Potential for Gas Binding of High-Pressure Safety ................................................................................ Injection Pumps During a Loss-of-Coolant Accident .............................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. Potentially Inadequate Performance of ECCS in PWRs during Recirculation Operation Following a LOCA. Loss of Residual Heat Removal Caused by Accumulator Nitrogen Injection ........................................ Potential for Water Hammer, Thermal Stratification, and Steam Binding in High-Pressure Coolant Injection Piping. Potential for Common-Mode Failure of High Pressure Safety Injection Pumps or Release of Reactor Coolant Outside Containment During a Loss-of-Coolant Accident. A Review of Water Hammer Events after 1985 ..................................................................................... Undetected Accumulation of Gas in Reactor System ............................................................................ Recent Failures of Charging/Safety Injection Pump Shafts ................................................................... Loss of Reactor Coolant Inventory and Potential Loss of Emergency Mitigation Functions While in a Shutdown Condition. Inadequate Net Positive Suction Head of Emergency Core Cooling and Containment Heat Removal Pumps under Design Basis Accident Conditions. Undetected Accumulation of Gas in Reactor Coolant System and Inaccurate Reactor Water Level Indication During Shutdown. Level-Sensing System Initiates Common-Mode Failure of High Pressure Injection Pumps ................. Potential Nitrogen Accumulation Resulting from Back-Leakage from Safety Injection Tanks ............... Design Deficiencies Can Lead to Reduced ECCS Pump Net Positive Suction Head During DesignBasis Accidents. Potential Hydrogen Combustion Events in BWR Piping ........................................................................ .................................................................................................................................................................. Effect of Adding Gas Into Water Storage Tanks on the Net Positive Suction Head for Pumps ........... IN IN IN IN IN IN IN IN IN 86–63 ...................... 86–80 ...................... 87–63 ...................... 88–23 ...................... 88–23, Supp. 1 ....... 88–23, Supp. 2 ....... 88–23, Supp. 3 ....... 88–23, Supp. 4 ....... 88–74 ...................... IN 89–67 ...................... IN 89–80 ...................... IN 90–64 ...................... IN IN IN IN 91–50 94–36 94–76 95–03 ...................... ...................... ...................... ...................... IN 96–55 ...................... pwalker on PROD1PC71 with NOTICES IN 96–65 ...................... IN 97–38 ...................... IN 97–40 ...................... IN 98–40 ...................... IN 02–15 ...................... IN 02–15, Supp. 1 ....... IN 02–18 ...................... VerDate Aug<31>2005 18:32 May 22, 2007 Jkt 211001 PO 00000 Frm 00070 Fmt 4703 Sfmt 4703 E:\FR\FM\23MYN1.SGM 23MYN1 ML031200496 ML031110062 ML031250058 ML031250214 ML031180034 ML031150208 ML881230018 ML900125002 ML901204023 ML921215001 ML031150118 ML031180745 ML031190089 ML031103251 ML031190397 ML031060539 ML031060430 ML031060404 ML031050598 ML031050500 ML031050514 ML031050497 ML031040547 ML020980466 ML031210054 ML021570158 29015 Federal Register / Vol. 72, No. 99 / Wednesday, May 23, 2007 / Notices RELATED GENERIC COMMUNICATIONS—Continued ADAMS accession No. Document No. Document name IN 06–21 ...................... Operating Experience Regarding Entrainment of Air Into Emergency Core Cooling and Containment Spray Systems. Backfit Discussion Under the provisions of Section 182a of the Atomic Energy Act of 1954, as amended, this GL requests a review and appropriate resulting actions for the purpose of assuring compliance with applicable existing requirements. No backfit is either intended or approved by the issuance of this GL. Therefore, the NRC staff has not performed a backfit analysis. Federal Register Notification To be done after the public comment period. Congressional Review Act In accordance with the Congressional Review Act, the NRC has determined that this GL is not a major rule and the Office of Information and Regulatory Affairs of the Office of Management and Budget has confirmed this determination. pwalker on PROD1PC71 with NOTICES Paperwork Reduction Act Statement This GL contains an information collection that is subject to the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.). The Office of Management and Budget approved this information collection under clearance number 3150–0011. The burden to the public for this mandatory information collection is estimated to average 300 hours per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the information collection. The NRC is seeking public comment on the potential impact of the information collection contained in the GL and on the following issues: 1. Is the proposed information collection necessary for the proper performance of the functions of the NRC, including whether the information will have practical utility? 2. Is the estimate of burden accurate? 3. Is there a way to enhance the quality, utility, and clarity of the information collected? 4. How can the burden of the information collection be minimized, including the use of automated collection techniques? VerDate Aug<31>2005 18:32 May 22, 2007 Jkt 211001 Send comments on any aspect of this information collection, including suggestions for reducing the burden, to the Records and FOIA/Privacy Services Branch (T5–F52), U.S. Nuclear Regulatory Commission, Washington, DC 20555–0001, or by Internet electronic mail to infocollects@nrc.gov; and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB–10202 (3150–0011), Office of Management and Budget, Washington, DC 20503. Public Protection Notification: The NRC may not conduct or sponsor, and a person is not required to respond to, an information collection unless the requesting document displays a currently valid OMB control number. Contact: Please direct any questions about this matter to the technical contact or the Lead Project Manager listed below, or to the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. Michael J. Case, Director, Division of Policy and Rulemaking, Office of Nuclear Reactor Regulation. Technical Contact: Warren C. Lyon, NRR, 301–415–2897, e-mail: wcl@nrc.gov. Lead Project Manager: David P. Beaulieu, NRR, 301–415–3243, e-mail: dpb@nrc.gov. Note: NRC generic communications may be found on the NRC public Web site, http:// www.nrc.gov, under Electronic Reading Room/Document Collections. End of Draft Generic Letter Documents may be examined, and/or copied for a fee, at the NRC’s Public Document Room at One White Flint North, 11555 Rockville Pike (first floor), Rockville, Maryland. Publicly available records will be accessible electronically from the Agencywide Documents Access and Management System (ADAMS) Public Electronic Reading Room on the Internet at the NRC Web site, http://www.nrc.gov/NRC/ADAMS/ index.html. If you do not have access to ADAMS or if you have problems in accessing the documents in ADAMS, contact the NRC Public Document Room (PDR) reference staff at 1–800–397–4209 or 301–415–4737 or by e-mail to pdr@nrc.gov. Dated at Rockville, Maryland, this 16th day of May 2007. PO 00000 Frm 00071 Fmt 4703 Sfmt 4703 ML062570468 For the Nuclear Regulatory Commission. Jennifer Golder, Acting Director, Division of Policy and Rulemaking, Office of Nuclear Reactor Regulation. [FR Doc. 07–2557 Filed 5–22–07; 8:45 am] BILLING CODE 7590–01–P SECURITIES AND EXCHANGE COMMISSION [Release No. 34–55776; File No. SR–Amex– 2007–29] Self-Regulatory Organizations; American Stock Exchange LLC; Order Granting Accelerated Approval of a Proposed Rule Change, as Modified by Amendment No. 1 Thereto, Relating to the Listing and Trading of Notes Linked to the Performance of the Dow Jones-AIG Commodity Index Total Return May 17, 2007. I. Introduction On March 2, 2007, the American Stock Exchange LLC (‘‘Amex’’ or ‘‘Exchange’’) filed with the Securities and Exchange Commission (‘‘Commission’’) a proposed rule change pursuant to Section 19(b)(1) of the Securities Exchange Act of 1934 (‘‘Act’’) 1 and Rule 19b–4 thereunder.2 On April 5, 2007, Amex filed Amendment No. 1 to the proposed rule change. The proposed rule change, as amended, was published for comment in the Federal Register on May 1, 2007 for a 15-day comment period.3 The Commission received no comments on the proposal. This order approves the proposed rule change, as modified by Amendment No. 1, on an accelerated basis. II. Description of the Proposal Under Section 107A of the Amex Company Guide (‘‘Company Guide’’), the Exchange may approve for listing and trading securities which cannot be readily categorized under the listing criteria for common and preferred stocks, bonds, debentures, or warrants, including index and currency warrants. Amex proposes to list for trading under 1 15 U.S.C. 78s(b)(1). CFR 240.19b–4. 3 See Securities Exchange Act Release No. 55661 (April 24, 2007), 72 FR 23862 (‘‘Notice’’). 2 17 E:\FR\FM\23MYN1.SGM 23MYN1

Agencies

[Federal Register Volume 72, Number 99 (Wednesday, May 23, 2007)]
[Notices]
[Pages 29010-29015]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 07-2557]


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NUCLEAR REGULATORY COMMISSION


Proposed Generic Communication; Managing Gas Intrusion in 
Emergency Core Cooling, Decay Heat Removal, and Containment Spray 
Systems

AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of opportunity for public comment.

-----------------------------------------------------------------------

SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is proposing to 
issue a generic letter (GL) to address the issue of gas intrusion into 
the emergency core cooling, decay heat removal, and containment spray 
systems (hereinafter referred to as the ``subject systems''). 
Specifically, the NRC is issuing this GL for the following two 
purposes:
    (1) to request addressees to submit information demonstrating that 
the subject systems are in compliance with the current licensing and 
design bases, and applicable regulatory requirements, and that suitable 
design, operational, and testing control measures are in place for 
maintaining this compliance, and
    (2) to collect the requested information to determine if additional 
regulatory action is required.
    This Federal Register notice is available through the NRC's 
Agencywide Documents Access and Management System (ADAMS) under 
accession number ML0704001003.

DATES: Comment period expires July 23, 2007. Comments submitted after 
this date will be considered if it is practical to do so, but assurance 
of consideration cannot be given except for comments received on or 
before this date.

ADDRESSES: Submit written comments to the Chief, Rulemaking, 
Directives, and Editing Branch, Division of Administrative Services, 
Office of Administration, U.S. Nuclear Regulatory Commission, Mail Stop 
T6-D59, Washington, DC 20555-0001, and cite the publication date and 
page number of this Federal Register notice. Written comments may also 
be delivered to NRC Headquarters, 11545 Rockville Pike (Room T-6D59), 
Rockville, Maryland, between 7:30 a.m. and 4:15 p.m. on Federal 
workdays.

FOR FURTHER INFORMATION, CONTACT: Warren C. Lyon, NRR, at 301-415-2897 
or by e-mail: wcl@nrc.gov or David P. Beaulieu, NRR, at 301-415-3243 or 
by e-mail: dpb@nrc.gov.

SUPPLEMENTARY INFORMATION:
    NRC Generic Letter 2007-XX, Managing Gas Intrusion in Emergency 
Core Cooling, Decay Heat Removal, and Containment Spray Systems

Addresses

    All holders of operating licenses for nuclear power reactors, 
except those who have permanently ceased operations and have certified 
that fuel has been permanently removed from the reactor vessel.

Purpose

    The U.S. Nuclear Regulatory Commission (NRC) is issuing this 
generic letter (GL) to address the issue of gas \1\ intrusion into the 
emergency core cooling, decay heat removal \2\, and containment spray 
systems (hereinafter referred to as the ``subject systems''). 
Specifically, the NRC is issuing this GL:
---------------------------------------------------------------------------

    \1\ Gas as used here includes, air, nitrogen, hydrogen, water 
vapor, or any other void that is not filled with liquid water.
    \2\ Decay heat removal (DHR), residual heat removal (RHR), and 
shutdown cooling (SDC) are common names for systems used to cool the 
reactor coolant system (RCS) during some phases of shutdown 
operation. The NRC staff generally uses DHR here.
---------------------------------------------------------------------------

    (1) To request addressees to submit information to demonstrate that 
the subject systems are in compliance with the current licensing and 
design bases and applicable regulatory requirements, and that suitable 
design, operational, and testing control measures are in place for 
maintaining this compliance, and
    (2) to collect the requested information to determine if additional 
regulatory action is required.
    Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 
Section 50.54(f), addressees are required to submit a written response 
to this GL.

Background

    Instances of gas intrusion into the subject systems have occurred 
since the beginning of commercial nuclear power plant operation. The 
NRC has published 20 information notices (INs), two GLs, and a NUREG 
\3\ that are related to this issue and has interacted with the nuclear 
industry many times in relation to these publications and in response 
to gas intrusion events. The following paragraphs summarize a few 
events to illustrate some of the technical and regulatory requirements 
issues.
---------------------------------------------------------------------------

    \3\ GL 88-17, ``Loss of Decay Heat Removal,'' October 17, 1988 
(ML031200496); GL 97-04, ``Assurance of Sufficient Net Positive 
Suction Head for Emergency Core Cooling and Containment Heat Removal 
Pumps,'' October 7, 1997 (ML031110062); and NUREG-0897, Revision 1, 
``Containment Emergency Sump Performance--Technical Findings Related 
to USI A-43,'' October 1985.
---------------------------------------------------------------------------

    In May 1997, at Oconee Nuclear Station Unit 3, hydrogen ingestion 
during plant cooldown damaged and rendered nonfunctional two high-
pressure injection (HPI) pumps. If the operators had started the 
remaining HPI pump, it too would have been damaged. The NRC responded 
with an augmented inspection team (IN 97-38, ``Level-Sensing System 
Initiates Common-Mode Failure of High-Pressure-Injection Pumps,'' 
Agencywide Documents Access and Management System (ADAMS) Accession No. 
ML031050514, June 24, 1997). The NRC team reported that there had been 
a total lack of HPI capability during power operation, a failure to 
meet technical specification (TS) HPI operability requirements, design 
deficiencies, inadequate maintenance practices, operators that were 
less than attentive to plant parameters, a failure to adequately assess 
operating experience, and a violation of 10 CFR part 50, Appendix

[[Page 29011]]

B, Criterion III (``Notice of Violation and Proposed Imposition of 
Civil Penalties --$330,000,'' August 27, 1997, http://www.nrc.gov/
reading-rm/doc-collections/enforcement/actions/reactors/ea97297.html).
    As a result of this Oconee Unit 3 event, the industry initiated an 
industry-wide improvement activity to address the gas issue. Based on 
the industry actions, the NRC concluded that no generic action was 
necessary. However, significant gas events that jeopardized the 
operability of the subject systems continued to occur, as illustrated 
in the following paragraphs. Dresden Nuclear Power Station Unit 3 
experienced a reactor scram on July 5, 2001, that was accompanied by a 
water hammer as a result of high pressure coolant injection (HPCI) 
system voids due to inadequate pipe venting. The licensee discovered a 
damaged pipe support that rendered the HPCI system inoperable on July 
19, 2001. On September 28, 2001, NRC inspectors discovered 
discrepancies in another HPCI hanger that may have been caused by the 
water hammer. The licensee repaired the hangers on September 30, 2001, 
and vented the system. An NRC inspector identified a high point that 
had not been vented and air was removed when the licensee vented that 
location. The HPCI system was inoperable from July 5, 2001, to 
September 30, 2001 (NRC Supplemental Inspection Report 50-237, 50-239/
2003-012, ML033530204, December 18, 2003). The NRC found violations of 
10 CFR 50.9, a TS, and 10 CFR part 50, Appendix B, Criterion XVI 
(``Notice of Violation and Proposed Imposition of Civil Penalty--
$60,000, and Final Significance Determination for a White Finding,'' 
ML031740755, June 23, 2003).
    On August 14, 2003, the Perry Nuclear Power Plant scrammed from 100 
percent power due to a loss of offsite power. This caused a momentary 
loss of common water leg pumps \4\ and a discharge pressure decrease 
from 44 psig to 7 psig allowed accumulated gas to completely void a 
water leg pump and the associated feedwater leakage control system 
piping. Pump operation was restored by venting the pump casing but a 
piping high point that was not included in fill and vent procedures was 
not vented. On September 10, 2003, the licensee vented enough gas from 
the high point that would have caused the pump to be non-functional if 
another loss of offsite power would occur. If the RHR and/or the LPCS 
pumps had started while the leakage control system piping was voided, 
the resulting water hammer could have caused the system piping to 
rupture. The NRC characterized the inspection finding as white; the 
finding resulted in a TS violation, escalated enforcement action, and a 
supplemental inspection (NRC Inspection Report 50-440/2003-009, 
ML032880107, October 10, 2003, and ML040330980, January 30, 2004).
---------------------------------------------------------------------------

    \4\ These are 40 gpm pumps used to compensate for back-leakage 
through check valves in RHR and LPSI piping into the suppression 
pool. The purpose is to keep piping full of water where the pipe 
elevation is higher than the suppression pool. The system is often 
referred to as a ``keep-full'' system.
---------------------------------------------------------------------------

    On July 28, 2004, the Palo Verde licensee identified that emergency 
core cooling system (ECCS) suction piping voids in all three Palo Verde 
units could have resulted in a loss of the ECCS during transfer to the 
recirculation mode for some loss-of-coolant accident (LOCA) conditions. 
The condition had existed since plant startups in 1986, was contrary to 
the Palo Verde final safety analysis reports (FSARs), and would not be 
identified during testing because water is not drawn from the 
containment emergency sumps. The NRC inspectors identified multiple 
violations of 10 CFR part 50, Appendix B, Criteria III and V, and 
violations of 10 CFR 50.59. The NRC responded with a special 
inspection, issued a yellow finding, and imposed a civil penalty of 
$50,000 (NRC Special Inspection Report 50-328, 50-329, 50-330/2004-014, 
ML050050287, January 5, 2005). The Palo Verde licensee identified the 
ECCS piping suction voids after being contacted by engineer from 
another plant where an NRC inspector identified the same problem.
    In February 2005, an HPI pump at Indian Point Energy Center Unit 2 
was found inoperable because the pump casing was filled with gas. The 
licensee then found numerous locations in the ECCS piping with gas 
accumulation. The licensee did not initially understand the 
implications of the gas condition, and the licensee's early assessments 
were inadequate, particularly with respect to assessing the operability 
of the other two HPI pumps. The NRC conducted a special inspection that 
found one HPI pump was not functional and the other two HPI pumps had a 
75 percent failure probability. The NRC found several violations of 10 
CFR part 50, Appendix B, Criterion XVI, and issued a white finding (NRC 
Inspection Report 50-247/2005-006, ML051680119, June 17, 2005).
    In March 2005, the NRC reported that Diablo Canyon had a sustained 
history of gas voiding in piping that could possibly result in gas 
binding or damage to the centrifugal charging pumps or the HPSI pumps 
during switchover from cold-leg to hot-leg injection.\5\ The NRC 
inspectors concluded that the licensee focused on managing the symptom 
of the problem rather than finding and eliminating the cause, which is 
contrary to 10 CFR part 50, Appendix B, Criterion XVI (NRC Inspection 
Report 50-275, 50-323/2005-006, ML050910120, March 31, 2005).
---------------------------------------------------------------------------

    \5\ A similar gas accumulation problem under closed valves in 
the recirculation piping from the DHR discharge to the HPSI and 
charging pump suctions has occurred at several plants. This has the 
potential to cause loss of all high pressure RCS makeup capability 
when shifting suction to the emergency containment sump from the 
refueling water or borated water storage tank following a LOCA.
---------------------------------------------------------------------------

    In September 2005, operators discovered a void in the HPCI pump 
discharge piping at the Duane Arnold Energy Center due to ``turbulent 
penetration'' that caused hot water from the feedwater pipe to 
penetrate downward into the HPCI discharge pipe. This heated the HPCI 
pipe on the low pressure side of a closed valve to greater than the 
saturation temperature and caused steam to be generated in the low 
pressure pipe as fast as it was vented. The condition had existed since 
plant startup (Licensee Event Report 50-331/2005-004, ML053360261, 
November 28, 2005). The NRC opened an unresolved item (URI 05000331/
2006002-03) for further NRC review of the licensee's piping analysis 
that evaluated HPSI system operability with the voided piping (NRC 
Inspection Report 50-331/2006-002, ML061210448, April 27, 2006, and NRC 
Inspection Report 50-331/2006-008, ML070640515, March 2, 2007).
    In October 2005, an NRC inspection team at the Palo Verde Nuclear 
Generating Station identified that, following a postulated accident 
when refueling water tank (RWT) level reached the setpoint for 
containment sump recirculation, the licensee's design basis credited 
containment pressure for preventing the ECCS pumps from continuing to 
reduce RWT level and drawing air into the ECCS. However, a recent 
licensee analysis showed that the minimum containment pressure would be 
less than needed. The licensee declared the ECCS inoperable at all 
three units, requiring a shutdown of Units 2 and 3 (Unit 1 was already 
shut down). The NRC found multiple violations of 10 CFR part 50, 
Appendix B, Criteria III and V (NRC Supplemental Inspection Report 50-
528, 50-529, 50-530/2005-012, ML060300193, January 27, 2006).
    These are a few of the more than 60 gas intrusion events reported 
during recent years involving the subject

[[Page 29012]]

systems. The number is larger if other similar events at the same plant 
are counted. Further, many events do not have to be reported to the 
NRC, and many of them have not been addressed during the NRC's 
inspections. For example, at least 40 RHR water hammer events have 
occurred at the Sequoyah Nuclear Plant, although none of them rendered 
the RHR system inoperable. Additionally, if an ECCS pump has been 
damaged because of gas but is repaired and tested operable within the 
TS completion time (typically, 72 hours), the licensee is not required 
to report the occurrence to the NRC. The frequency and the significance 
of these events and the likelihood that unidentified gas issues exist 
require licensee action to ensure compliance with regulatory 
requirements that will maintain operability of the subject systems.

Applicable Regulatory Requirements

    10 CFR part 50 Appendix A or similar plant-specific principal 
design criteria \6\ provide design requirements, and 10 CFR part 50 
Appendix B, TSs, and licensee quality assurance programs provide 
operating requirements. Appendix A requirements applicable to gas 
management in the subject systems include the following:
---------------------------------------------------------------------------

    \6\ For facilities with a construction permit issued prior to 
May 21, 1972, that are not licensed to Appendix A.
---------------------------------------------------------------------------

     General Design Criterion (GDC) 1 requires that the subject 
systems be designed, fabricated, erected, and tested to quality 
standards.
     GDC 34 requires an RHR system designed to maintain 
specified acceptable fuel design limits and to meet design conditions 
that are not exceeded if a single failure occurs and specified 
electrical power systems fail.
     GDC 35, 36, and 37 require an ECCS design that meets 
performance, inspection, and testing requirements. Specified 
performance criteria are provided in 10 CFR 50.46.
     GDC 38, 39, and 40 require a containment heat removal 
system design that meets performance, inspection, and testing 
requirements.
    Quality assurance criteria provided in Appendix B that apply to gas 
management in the subject systems include the following:
     Criteria III and V require measures to assure that 
applicable regulatory requirements and the design basis, as defined in 
10 CFR 50.2, ``Definitions,'' and as specified in the license 
application, are correctly translated into controlled specifications, 
drawings, procedures, and instructions.
     Criterion XI requires a test program to assure that the 
subject systems will perform satisfactorily in service. Test results 
shall be documented and evaluated to assure that test requirements have 
been satisfied.
     Criterion XVI requires measures to assure that conditions 
adverse to quality, such as failures, malfunctions, deficiencies, 
deviations, defective material and equipment, and nonconformances, are 
promptly identified, corrected, documented, and reported to management.
     Criterion XVII requires maintenance of records of 
activities affecting quality.
    Further, as part of the licensing basis, licensees have committed 
to certain quality assurance provisions that are identified in both 
their TSs and quality assurance programs. Licensees have committed to 
use the guidance of Regulatory Guide (RG) 1.33, ``Quality Assurance 
Requirements (Operation),'' which endorses American National Standards 
Institute (ANSI) N18.7-1976/American Nuclear Society 3.2, 
``Administrative Controls and Quality Assurance for the Operational 
Phase of Nuclear Power Plants,'' or equivalent licensee-specific 
guidance. Section 5.3.4.4, ``Process Monitoring Procedures,'' of ANSI 
N18.7 that states that procedures for monitoring performance of plant 
systems shall be required to assure that engineered safety features and 
emergency equipment are in a state of readiness to maintain the plant 
in a safe condition if needed. The limits (maximum and minimum) for 
significant process parameters shall be identified. Operating 
procedures shall address the nature and frequency of this monitoring, 
as appropriate.
    10 CFR 50.36(c)(3) defines TS surveillance requirements (SRs) as 
``relating to test, calibration, or inspection to assure'' maintenance 
of quality, operation within safety limits, and operability. Typically, 
TS Section 5 or 6 requires that licensees establish, implement, and 
maintain written procedures covering the applicable procedures 
recommended in Appendix A to RG 1.33, Revision 2 (February 1978). 
Appendix A to RG 1.33 identifies instructions for filling and venting 
the ECCS and DHR system, as well as for draining and refilling heat 
exchangers. Surveillance requirements to verify that at least some of 
the subject system piping is filled are provided in standard technical 
specifications (STSs) and in most licensee TSs.

Discussion

    The events discussed in the BACKGROUND section illustrate that many 
of the regulatory requirements identified in the APPLICABLE REGULATORY 
REQUIREMENTS section are not being met. The NRC inspectors often find 
that the 10 CFR part 50 Appendix B criteria identified above are not 
adequately addressed in plant venting procedures. In some cases, 
venting procedures were almost nonexistent, there were no records of 
gas quantities that were vented and licensees unsuccessfully attempted 
to recreate the history by asking operators for their recollections. 
Consequently, there was no foundation for establishing that the subject 
systems were operable prior to venting. In addition, the venting 
processes sometimes did not ensure that all gas was removed from the 
venting location and often did not adequately establish the quantity of 
vented gas. Further, examination of ultrasonic test (UT) processes at 
several licensee sites established that one licensee initially did not 
know how to acceptably determine liquid level via UT. Additional issues 
include TSs, which often do not require venting of suction piping 
despite voids in suction pipes generally being of more concern than in 
discharge piping, and do not adequately address operability of the 
subject systems prior to surveillance and for the time span until the 
next surveillance. This GL and the anticipated NRC followup to this GL 
are intended to correct such conditions.
    It is important that the subject systems are sufficiently filled 
with water to ensure that they can reliably perform their intended 
functions under all LOCA and non-LOCA conditions that require makeup to 
the RCS. Portions of these systems and some of the associated pumps are 
normally in a standby condition while other pumps provide both ECCS and 
operational functions. For example, some high-pressure pumps are used 
for normal RCS makeup, and some low-pressure pumps provide a normal DHR 
capability.
    The following safety issues are associated with gas intrusion into 
the subject systems:
    (1) The introduction of gas into a pump can cause the pump to 
become air-bound with little or no flow, rendering the pump inoperable. 
Air-binding can render more than one pump inoperable when pumps share 
common discharge or suction headers, or when the gas accumulation 
process affects more than one train, greatly increasing the risk 
significance. Such a common-mode failure would result in the inability 
of the ECCS or the DHR system to provide adequate core cooling and the 
inability of the containment spray system to maintain the containment 
pressure and temperature below design limits. An air-bound pump can 
become

[[Page 29013]]

damaged quickly, eliminating the possibility of recovering the pump 
during an event by simply subsequently venting the pump and suction 
piping.
    (2) Gas introduced into a pump can render the pump inoperable, even 
if the gas does not air bind the pump, because the gas can reduce the 
pump discharge pressure and flow capacity to the point that the pump 
cannot perform its design function. For example, an HPI pump that is 
pumping air-entrained water may not develop sufficient discharge 
pressure to inject under certain small break LOCA scenarios.
    (3) Gas accumulation can result in water hammer or a system 
pressure transient, particularly in pump discharge piping following a 
pump start, which can cause piping and component damage or failure. Gas 
accumulation in the DHR system has resulted in pressure transients that 
have caused DHR system relief valves to open. In some plants, the 
relief valve reseating pressure is less than the existing RCS pressure, 
a condition that complicates recovery.
    (4) Pump cavitation caused by entrained gas results in additional 
stresses that can lead to premature failure of pump components that can 
render the pump inoperable.
    (5) Gas intrusion can result in pumping noncondensible gas into the 
reactor vessel that may affect core cooling flow.
    (6) The time needed to fill voided discharge piping can delay 
delivery of water beyond the time frame assumed in the accident 
analysis.
    The scope and number of identified gas intrusion problems at some 
facilities raise concerns about whether similar unrecognized design, 
configuration, and operability problems exist at other reactor 
facilities.
    A review of the operating experience has identified the following 
concerns, which are the focus of this GL:
    (1) TS SRs, as implemented by associated surveillance procedures, 
have not reliably precluded gas problems. Operating experience shows 
many instances in which substantive gas voiding in the system piping 
has not been identified. The surveillance procedures may not reliably 
reveal as-found conditions in which the system may be inoperable or 
degraded because of gas. Additionally, some plants have no TS SR to 
verify that the subject systems' piping is sufficiently full of water. 
Still other plants have incomplete TS SRs that cover only portions of 
the system. For example, the TS may require verifying that ECCS 
discharge piping is full of water but may not include verification of 
the suction piping or containment spray piping. Although the TS and 
FSAR at many facilities indicate that the subject systems are full of 
water, in practice it is not uncommon for licensees to vent some gas 
during periodic surveillances. Further, there may be some parts of 
these systems where it is not possible or practical to verify them to 
be full of water. Hence, the current TS and FSAR may establish a 
standard that may not be realistic to establish system operability. A 
realistic standard should bound the volume of gas that may impact pump 
operability and the volume for which water-hammer-induced stress limits 
may be exceeded.
    Criterion XI of Appendix B to 10 CFR part 50 requires licensees to 
perform testing using written test procedures, which include but are 
not limited to procedures for TS SRs, that incorporate the requirements 
and acceptance limits contained in applicable design documents. TSs 
often require surveillance of discharge piping but do not mention 
suction piping. Consequently, suction piping surveillances may not be 
performed. However, since the subject systems may be rendered 
inoperable or degraded because of gas in suction piping, the 
regulations require that presence of gas in all piping be assessed to 
establish operability.
    (2) Typically the FSAR describes that the subject systems are 
filled with water. The wording of TS SRs further confirms that the 
design-basis configuration calls for the specified piping to be filled 
with water. Operating experience provides many examples of licensees 
treating the accumulation of gas as an expected condition (rather than 
a nonconforming condition) that was not documented even when it 
involved a substantial volume of gas that clearly constituted a 
significant condition adverse to quality. In such cases, Criterion XVI 
of Appendix B to 10 CFR part 50 requires that the cause of the 
condition be determined and corrective action taken to preclude 
repetition. Based on the as-found volume and location of gas, 
corrective actions beyond simply refilling a system may be necessary to 
provide reasonable assurance that the affected system will remain 
operable until the next surveillance.
    (3) Although the subject systems are often susceptible to gas 
intrusion, not all plants have vent valves at one or more system high 
points. Some licensees have installed additional vent valves at system 
high points after operational events. For example, one licensee 
installed an additional 21 high-point vent valves. Another licensee, 
who installed an additional 17 vent valves, determined that the primary 
cause of the gas voiding problem was that the original design 
specification did not call for a sufficient number of vent valves. No 
specific NRC requirement mandates the installation of vent valves on 
the subject systems. However, failure to translate the design basis of 
assuring the system is maintained sufficiently full of water to 
maintain operability into drawings, specifications, procedures, and 
instructions is a violation of Criterion III in Appendix B of 10 CFR 
part 50.
    Further, Criterion V requires documented instructions, procedures, 
or drawings that include appropriate quantitative or qualitative 
acceptance criteria for determining that important activities have been 
satisfactorily accomplished. This means that each addressee must have 
suitable documentation and records, including acceptance criteria, to 
establish that the subject systems have been and are maintained 
sufficiently full of water to ensure system operability. Vent valves 
and their use are often a key ingredient for satisfying these 
requirements.
    The NRC staff is initiating a Technical Specifications Task Force 
(TSTF) activity to address the recognized TS weaknesses associated with 
gas intrusion concerns. In the interim, until new TSs are developed, 
the NRC staff will treat a SR that the piping be full of water as 
satisfied if the piping and pumps of the subject systems are maintained 
sufficiently full of water to ensure system operability when 
operability is required. This condition must be shown to be satisfied 
during the time between surveillances, and either venting or UT 
surveillances are acceptable means of obtaining void data. Further, the 
NRC staff will consider justification for not conducting a periodic 
surveillance or for extending the time between surveillances of certain 
sections of piping if an addressee considers surveillance to be 
unnecessary. For example, some three loop plants designed by 
Westinghouse maintain HPSI discharge lines at a pressure greater than 
the RCS operating pressure. This eliminates the potential for leakage 
from the accumulators or the RCS as a possible means to introduce gas 
into the discharge lines. An assessment for such plants that (1) 
acceptably eliminates other means of introducing gas, (2) establishes 
acceptable verification that the lines are essentially full following a 
condition that reduces the discharge line pressure, and (3) establishes 
an operating history confirming that gas has not accumulated will be 
adequate justification for not conducting surveillances inside

[[Page 29014]]

containment or at locations that constitute a hazard to personnel 
performing the assessment. The NRC memorandum, ``Technical 
Considerations for Reasonably Assuring Emergency Core Cooling, Decay 
Heat Removal, and Containment Spray Systems Operability,'' ML071030382, 
April 17, 2007, provides some operating experience insights. The NRC 
staff plans to use this information during inspection activities that 
are planned as a followup to this GL and for guidance in the TSTF 
program to develop improved TSs.

Requested Actions

    Each addressee is requested to evaluate their ECCS, DHR system, and 
containment spray system designs, operation, and test procedures to 
assure that gas intrusion is minimized and monitored in order to 
maintain system operability and compliance with the requirements of 
Appendix B to 10 CFR part 50.

Requested Information

    Each addressee is requested to provide a summary description of how 
the REQUESTED ACTIONS have been addressed within 6 months of the date 
of this GL. This summary description should specifically address the 
quality assurance criteria in 10 CFR part 50, Appendix B, Sections III, 
V, XI, XVI, and XVII and the TSs that apply to the subject systems. 
This summary should include a general description of: (1) The design, 
(2) the operating procedures, and (3) the test procedures to assure 
that gas intrusion does not affect the ability of the subject systems 
to perform their intended functions.
    If an addressee determines that system or procedure modifications 
are necessary based on the review of the requested actions and these 
changes cannot be accomplished within 6 months of the date of this GL, 
then the addressee should also provide a plan and schedule for 
completion of these actions.

Required Response

    In accordance with 10 CFR 50.54(f), in order to determine whether a 
facility license should be modified, suspended, or revoked, or whether 
other action should be taken, an addressee is required to respond as 
described below. Within 6 months of the date of this generic letter, an 
addressee is required to submit a written response if they are unable 
to provide the information or they cannot meet the requested completion 
date. The addressee must address in its response any alternative course 
of action that it proposes to take, including the basis for the 
acceptability of the proposed alternative course of action.
    The required written response should be addressed to the U.S. 
Nuclear Regulatory Commission, ATTN: Document Control Desk, 11555 
Rockville Pike, Rockville, MD 20852, under oath or affirmation under 
the provisions of section 182a of the Atomic Energy Act of 1954, as 
amended, and 10 CFR 50.54(f). In addition, submit a copy of the 
response to the appropriate regional administrator.

Reasons for Information Request

    The NRC is requesting this information because a review of 
operating experience shows numerous instances of gas intrusion events 
involving the subject systems that have rendered or potentially 
rendered these risk-significant systems inoperable.

                     Related Generic Communications
------------------------------------------------------------------------
                                                              ADAMS
          Document No.                Document name       accession No.
------------------------------------------------------------------------
GL 88-17.......................  Loss of Decay Heat          ML031200496
                                  Removal.
GL 97-04.......................  Assurance of                ML031110062
                                  Sufficient Net
                                  Positive Suction Head
                                  for Emergency Core
                                  Cooling and
                                  Containment Heat
                                  Removal Pumps.
IN 86-63.......................  Loss of Safety              ML031250058
                                  Injection Capability.
IN 86-80.......................  Unit Startup with           ML031250214
                                  Degraded High
                                  Pressure Safety
                                  Injection System.
IN 87-63.......................  Inadequate Net              ML031180034
                                  Positive Suction Head
                                  in Low Pressure
                                  Safety Systems.
IN 88-23.......................  Potential for Gas           ML031150208
                                  Binding of High-
                                  Pressure Safety.
IN 88-23, Supp. 1..............  Injection Pumps During      ML881230018
                                  a Loss-of-Coolant
                                  Accident.
IN 88-23, Supp. 2..............  ......................      ML900125002
IN 88-23, Supp. 3..............  ......................      ML901204023
IN 88-23, Supp. 4..............  ......................      ML921215001
IN 88-74.......................  Potentially Inadequate      ML031150118
                                  Performance of ECCS
                                  in PWRs during
                                  Recirculation
                                  Operation Following a
                                  LOCA.
IN 89-67.......................  Loss of Residual Heat       ML031180745
                                  Removal Caused by
                                  Accumulator Nitrogen
                                  Injection.
IN 89-80.......................  Potential for Water         ML031190089
                                  Hammer, Thermal
                                  Stratification, and
                                  Steam Binding in High-
                                  Pressure Coolant
                                  Injection Piping.
IN 90-64.......................  Potential for Common-       ML031103251
                                  Mode Failure of High
                                  Pressure Safety
                                  Injection Pumps or
                                  Release of Reactor
                                  Coolant Outside
                                  Containment During a
                                  Loss-of-Coolant
                                  Accident.
IN 91-50.......................  A Review of Water           ML031190397
                                  Hammer Events after
                                  1985.
IN 94-36.......................  Undetected                  ML031060539
                                  Accumulation of Gas
                                  in Reactor System.
IN 94-76.......................  Recent Failures of          ML031060430
                                  Charging/Safety
                                  Injection Pump Shafts.
IN 95-03.......................  Loss of Reactor             ML031060404
                                  Coolant Inventory and
                                  Potential Loss of
                                  Emergency Mitigation
                                  Functions While in a
                                  Shutdown Condition.
IN 96-55.......................  Inadequate Net              ML031050598
                                  Positive Suction Head
                                  of Emergency Core
                                  Cooling and
                                  Containment Heat
                                  Removal Pumps under
                                  Design Basis Accident
                                  Conditions.
IN 96-65.......................  Undetected                  ML031050500
                                  Accumulation of Gas
                                  in Reactor Coolant
                                  System and Inaccurate
                                  Reactor Water Level
                                  Indication During
                                  Shutdown.
IN 97-38.......................  Level-Sensing System        ML031050514
                                  Initiates Common-Mode
                                  Failure of High
                                  Pressure Injection
                                  Pumps.
IN 97-40.......................  Potential Nitrogen          ML031050497
                                  Accumulation
                                  Resulting from Back-
                                  Leakage from Safety
                                  Injection Tanks.
IN 98-40.......................  Design Deficiencies         ML031040547
                                  Can Lead to Reduced
                                  ECCS Pump Net
                                  Positive Suction Head
                                  During Design-Basis
                                  Accidents.
IN 02-15.......................  Potential Hydrogen          ML020980466
                                  Combustion Events in
                                  BWR Piping.
IN 02-15, Supp. 1..............  ......................      ML031210054
IN 02-18.......................  Effect of Adding Gas        ML021570158
                                  Into Water Storage
                                  Tanks on the Net
                                  Positive Suction Head
                                  for Pumps.

[[Page 29015]]

 
IN 06-21.......................  Operating Experience        ML062570468
                                  Regarding Entrainment
                                  of Air Into Emergency
                                  Core Cooling and
                                  Containment Spray
                                  Systems.
------------------------------------------------------------------------

Backfit Discussion

    Under the provisions of Section 182a of the Atomic Energy Act of 
1954, as amended, this GL requests a review and appropriate resulting 
actions for the purpose of assuring compliance with applicable existing 
requirements. No backfit is either intended or approved by the issuance 
of this GL. Therefore, the NRC staff has not performed a backfit 
analysis.

Federal Register Notification

    To be done after the public comment period.

Congressional Review Act

    In accordance with the Congressional Review Act, the NRC has 
determined that this GL is not a major rule and the Office of 
Information and Regulatory Affairs of the Office of Management and 
Budget has confirmed this determination.

Paperwork Reduction Act Statement

    This GL contains an information collection that is subject to the 
Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.). The Office of 
Management and Budget approved this information collection under 
clearance number 3150-0011.
    The burden to the public for this mandatory information collection 
is estimated to average 300 hours per response, including the time for 
reviewing instructions, searching existing data sources, gathering and 
maintaining the data needed, and completing and reviewing the 
information collection. The NRC is seeking public comment on the 
potential impact of the information collection contained in the GL and 
on the following issues:
    1. Is the proposed information collection necessary for the proper 
performance of the functions of the NRC, including whether the 
information will have practical utility?
    2. Is the estimate of burden accurate?
    3. Is there a way to enhance the quality, utility, and clarity of 
the information collected?
    4. How can the burden of the information collection be minimized, 
including the use of automated collection techniques?
    Send comments on any aspect of this information collection, 
including suggestions for reducing the burden, to the Records and FOIA/
Privacy Services Branch (T5-F52), U.S. Nuclear Regulatory Commission, 
Washington, DC 20555-0001, or by Internet electronic mail to 
infocollects@nrc.gov; and to the Desk Officer, Office of Information 
and Regulatory Affairs, NEOB-10202 (3150-0011), Office of Management 
and Budget, Washington, DC 20503.
    Public Protection Notification: The NRC may not conduct or sponsor, 
and a person is not required to respond to, an information collection 
unless the requesting document displays a currently valid OMB control 
number.
    Contact: Please direct any questions about this matter to the 
technical contact or the Lead Project Manager listed below, or to the 
appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
    Michael J. Case, Director, Division of Policy and Rulemaking, 
Office of Nuclear Reactor Regulation.
    Technical Contact: Warren C. Lyon, NRR, 301-415-2897, e-mail: 
wcl@nrc.gov.
    Lead Project Manager: David P. Beaulieu, NRR, 301-415-3243, e-mail: 
dpb@nrc.gov.

    Note: NRC generic communications may be found on the NRC public 
Web site, http://www.nrc.gov, under Electronic Reading Room/Document 
Collections.

End of Draft Generic Letter
    Documents may be examined, and/or copied for a fee, at the NRC's 
Public Document Room at One White Flint North, 11555 Rockville Pike 
(first floor), Rockville, Maryland. Publicly available records will be 
accessible electronically from the Agencywide Documents Access and 
Management System (ADAMS) Public Electronic Reading Room on the 
Internet at the NRC Web site, http://www.nrc.gov/NRC/ADAMS/index.html. 
If you do not have access to ADAMS or if you have problems in accessing 
the documents in ADAMS, contact the NRC Public Document Room (PDR) 
reference staff at 1-800-397-4209 or 301-415-4737 or by e-mail to 
pdr@nrc.gov.

    Dated at Rockville, Maryland, this 16th day of May 2007.
    For the Nuclear Regulatory Commission.
Jennifer Golder, Acting Director, Division of Policy and Rulemaking, 
Office of Nuclear Reactor Regulation.
[FR Doc. 07-2557 Filed 5-22-07; 8:45 am]
BILLING CODE 7590-01-P