South Carolina Electric & Gas Company, Virgil C. Summer Nuclear Station; Exemption, 5224-5226 [05-1772]

Agencies

• NUCLEAR REGULATORY COMMISSION

[Federal Register Volume 70, Number 20 (Tuesday, February 1, 2005)]
[Notices]
[Pages 5224-5226]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-1772]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-395]


South Carolina Electric & Gas Company, Virgil C. Summer Nuclear 
Station; Exemption

1.0 Background

    The South Carolina Electric & Gas Company (SCE&G, the licensee) is 
the holder of the Renewed Facility Operating License No. NPF-12 which 
authorizes operation of the Virgil C. Summer Nuclear Station (VSNS). 
The license provides, among other things, that the facility is subject 
to all rules, regulations, and orders of the Nuclear Regulatory 
Commission (NRC or the Commission) now or hereafter in effect.
    The facility consists of a pressurized-water reactor located in 
Fairfield County in South Carolina.

2.0 Request/Action

    Title 10 of the Code of Federal Regulations (10 CFR), part 50, 
section 50.44 specifies requirements for the control of hydrogen gas 
generated after a postulated loss-of-coolant accident (LOCA) for 
reactors fueled with zirconium cladding. Acceptance criteria contained 
in 10 CFR 50.46 are for emergency core cooling systems (ECCSs) for 
reactors fueled with zircaloy or ZIRLO\TM\ cladding. In addition, 
Appendix K to 10 CFR part 50 requires that the Baker-Just equation be 
used to predict the rates of energy release, hydrogen concentration, 
and cladding oxidation from the metal-water reaction.
    In summary, the exemption request relates solely to the specific 
types of cladding material specified in these regulations. As written, 
the regulations presume the use of zircaloy or ZIRLO\TM\ fuel rod 
cladding. Thus, an exemption from the requirements of 10 CFR 50.44, 10 
CFR 50.46, and Appendix K to 10 CFR part 50 is needed to irradiate lead 
test assemblies (LTAs) consisting of developmental clad alloys at VSNS.

[[Page 5225]]

3.0 Discussion

3.1 Fuel Mechanical Design

Optimized ZIRLO\TM\
    Optimized ZIRLO\TM\ has a lower tin content than the licensed 
ZIRLO\TM\. Tin is a solid solution strengthener and [alpha]-phase 
stabilizer present entirely in the base [alpha]-phase zirconium 
crystalline structure. Potential impacts of a reduced tin content on 
material properties include (1) a reduced tensile strength, (2) an 
increased thermal creep rate, (3) an increased irradiation growth rate, 
(4) a reduced [alpha][rarr][alpha]+[beta] phase transition temperature, 
and (5) an improved corrosion resistance. The slight reduction in tin 
content will not effect the size, shape, or distribution of any second 
phase or inter-metallic precipitates, nor the overall microstructure of 
this developmental zirconium alloy. With a consistent microstructure, 
low tin ZIRLO\TM\ will exhibit many similar material characteristics as 
the licensed ZIRLO\TM\. Further, the final annealing of Optimized 
ZIRLO\TM\ has been designed to improve mechanical performance.
    In the exemption request, SCE&G provides details of the planned 
post-irradiation examinations (PIEs) of the LTAs. Examinations include 
rod profilometry, rod growth, rod oxidation, and visual inspection. In 
response to a request for additional information, the licensee stated 
that PIE data, as well as data from other Westinghouse LTA programs, 
will be used to ensure existing design models remain valid.
    As a result of the PIEs, any negative aspects of the low tin 
alloy's performance, including the potential impacts of a reduced tin 
content identified above, will be identified and resolved. Furthermore, 
significant deviations from model predictions will be reconciled.
    The fuel rod burnup and fuel duty experienced by the LTAs in VSNS 
will remain well within the operating experience base and applicable 
licensed limits for ZIRLO\TM\.
    Utilizing currently approved fuel performance and fuel mechanical 
design models and methods, SCE&G and Westinghouse will perform cycle-
specific reload evaluations to ensure that the LTAs satisfy existing 
design criteria.
    Based upon LTA irradiation experience of similar low tin versions 
of ZIRLO\TM\, expected performance due to similar material properties, 
and an LTA PIE program aimed at qualifying model predictions, the staff 
finds the LTA mechanical design acceptable for VSNS.

3.2 Core Physics and Non-LOCA Safety Analysis

    The SCE&G exemption request relates solely to the specific types of 
cladding material specified in the regulations. No new or altered 
design limits for purposes of 10 CFR part 50, Appendix A, General 
Design Criterion 10, ``Reactor Design,'' need to be applied or are 
required for this program.
Optimized ZIRLO\TM\
    Due to similar material properties, any impact of low tin ZIRLO\TM\ 
on the safety analysis models and methods is expected to be minimal. 
Utilizing currently approved core physics, core thermal-hydraulics, and 
non-LOCA safety analysis models and methods, SCE&G and Westinghouse 
will perform cycle-specific reload evaluations to ensure that the LTAs 
satisfy design criteria.
    Nuclear design evaluations will ensure that LTAs be placed in 
nonlimiting core locations. As such, additional thermal margin to 
design limits will be maintained between LTA fuel rods and the hot rod 
evaluated in safety analyses. Thermal-hydraulic and non-LOCA 
evaluations will confirm that the LTAs are bounded by the current 
analysis of record.
    Based upon the use of approved models and methods, expected 
material performance, and the placement of LTAs in nonlimiting core 
locations, the staff finds that the irradiation of up to four LTAs in 
VSNS will not result in unsafe operation nor violation of Specified 
Acceptable Fuel Design Limits. Furthermore, in the event of a Design 
Basis Accident, these LTAs will not promote consequences beyond those 
currently analyzed.

3.3 Regulatory Evaluation

    Pursuant to 10 CFR 50.12, the Commission may, upon application by 
any interested person or upon its own initiative, grant exemptions from 
the requirements of 10 CFR part 50 if, (1) the exemptions are 
authorized by law, will not present an undue risk to public health or 
safety, and are consistent with the common defense and security; and 
(2) special circumstances are present.
3.3.1 10 CFR 50.44
    The underlying purpose of 10 CFR 50.44 is to ensure that means are 
provided for the control of hydrogen gas that may be generated 
following a LOCA. The licensee has provided means for controlling 
hydrogen gas and has previously considered the potential for hydrogen 
gas generation stemming from a metal-water reaction. The LTA rods 
containing a low tin version of ZIRLO\TM\ cladding are similar in 
chemical composition to zircaloy cladding. Metal-water reaction tests 
performed by Westinghouse on low tin versions of ZIRLO\TM\ (documented 
in Appendix B of Addendum 1 to WCAP-12610-P-A) demonstrate comparable 
reaction rates. Accordingly, the previous calculations of hydrogen 
production resulting from a metal-water reaction will not be 
significantly changed. As such, application of 10 CFR 50.44 is not 
necessary for the licensee to achieve its underlying purpose in these 
circumstances.
3.3.2 10 CFR 50.46
    The underlying purpose of 10 CFR 50.46 is to establish acceptance 
criteria for ECCS performance. The applicability of these ECCS 
acceptance criteria has been demonstrated by Westinghouse. Ring 
compression tests performed by Westinghouse on low tin versions of 
ZIRLO\TM\ (documented in Appendix B of Addendum 1 to WCAP-12610-P-A) 
demonstrate an acceptable retention of post-LOCA ductility up to 10 CFR 
50.46 limits of 2200 [deg]F and 17 percent Equivalent Cladding Reacted. 
Utilizing currently approved LOCA models and methods, Westinghouse will 
perform cycle-specific reload evaluations prior to use to ensure that 
the LTAs satisfy 10 CFR 50.46 acceptance criteria. Therefore, the 
exemption to expand the application of 10 CFR 50.46 to include 
Optimized ZIRLO\TM\ is acceptable.
3.3.3 10 CFR Part 50, Appendix K
    Paragraph I.A.5 of Appendix K to 10 CFR part 50 states that the 
rates of energy, hydrogen concentration, and cladding oxidation from 
the metal-water reaction shall be calculated using the Baker-Just 
equation. Since the Baker-Just equation presumes the use of zircaloy 
clad fuel, strict application of the rule would not permit use of the 
equation for the LTA cladding for determining acceptable fuel 
performance. Metal-water reaction tests performed by Westinghouse on 
low tin versions of ZIRLO\TM\ (documented in Appendix B of Addendum 1 
to WCAP-12610-P-A) demonstrate conservative reaction rates relative to 
the Baker-Just equation. Thus, application of Appendix K, Paragraph 
I.A.5 is not necessary for the licensee to achieve its underlying 
purpose in these circumstances.
3.3.4 Special Circumstances
    In summary, the staff reviewed the licensee's request of proposed 
exemption to allow up to four LTAs containing fuel rods, guide thimble 
tubes, and instrumentation tubes

[[Page 5226]]

fabricated with Optimized ZIRLO\TM\. Based on the staff's evaluation, 
as set forth above, the staff considers that granting the proposed 
exemption will not defeat the underlying purpose of 10 CFR 50.44, 10 
CFR 50.46, or Appendix K to 10 CFR part 50. Accordingly, special 
circumstances, are present pursuant to 10 CFR 50.12(a)(2)(ii).
3.3.5. Other Standards in 10 CFR 50.12
    The staff examined the rest of the licensee's rationale to support 
the exemption request, and concluded that the use of Optimized 
ZIRLO\TM\ would satisfy 10 CFR 50.12(a) as follows:
    (1) The requested exemption is authorized by law:
    No law precludes the activities covered by this exemption request. 
The Commission, based on technical reasons set forth in rulemaking 
records, specified the specific cladding materials identified in 10 CFR 
50.44, 10 CFR 50.46, and 10 CFR part 50, Appendix K. Cladding materials 
are not specified by statute.
    (2) The requested exemption does not present an undue risk to the 
public health and safety as stated by the licensee:

    The LTA safety evaluation will ensure that these acceptance 
criteria [in the Commission's regulations] are met following the 
insertion of LTAs containing Optimized ZIRLO\TM\ material. Fuel 
assemblies using Optimized ZIRLO\TM\ cladding will be evaluated 
using NRC-approved analytical methods and plant specific models to 
address the changes in the cladding material properties. The safety 
analysis for VSNS is supported by the applicable technical 
specification. The VSNS reload cores containing Optimized ZIRLO\TM\ 
cladding will continue to be operated in accordance with the 
operating limits specified in the technical specifications. LTAs 
utilizing Optimized ZIRLO\TM\ cladding will be placed in non-
limiting core locations. Thus, the granting of this exemption 
request will not pose an undue risk to public health and safety.

    The NRC staff has evaluated these considerations as set forth in 
Section 3.1 of this exemption. For the reasons set forth in that 
section, the staff concludes that Optimized ZIRLO\TM\ may be used as a 
cladding material for no more than four LTAs to be placed in 
nonlimiting core locations during VSNS's next refueling outage, and 
that an exemption from the requirements of 10 CFR 50.44, 10 CFR 50.46, 
and 10 CFR part 50, Appendix K does not pose an undue risk to the 
public health and safety.

4.0 Conclusion

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), the exemption is authorized by law, will not present an undue 
risk to the public health and safety, and is consistent with the common 
defense and security. Also, special circumstances are present. 
Therefore, the Commission hereby grants SCE&G exemptions from the 
requirements of 10 CFR 50.44, 10 CFR 50.46, and 10 CFR part 50, 
Appendix K, to allow four LTAs containing fuel rods with Optimized 
ZIRLO\TM\ and several different developmental clad alloys.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not have a significant effect on the 
quality of the human environment (70 FR 1742).
    This exemption is effective upon issuance.

    Dated in Rockville, Maryland, this 14th day of January 2005.

    For the Nuclear Regulatory Commission.
James E. Lyons,
Deputy Director, Division of Licensing Project Management, Office of 
Nuclear Reactor Regulation.
[FR Doc. 05-1772 Filed 1-31-05; 8:45 am]
BILLING CODE 7590-01-P