Mark Edward Leyse; Consideration of Petition in Rulemaking Process, 71564-71569 [E8-27938]

Agencies

• NUCLEAR REGULATORY COMMISSION

[Federal Register Volume 73, Number 228 (Tuesday, November 25, 2008)]
[Proposed Rules]
[Pages 71564-71569]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-27938]


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NUCLEAR REGULATORY COMMISSION

10 CFR Part 50

[Docket No. PRM-50-84; NRC-2007-0013]


Mark Edward Leyse; Consideration of Petition in Rulemaking 
Process

AGENCY: Nuclear Regulatory Commission.

ACTION: Resolution of petition for rulemaking and closure of petition 
docket.

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SUMMARY: The Nuclear Regulatory Commission (NRC) will consider the 
issues raised in a petition for rulemaking (PRM) submitted by Mark 
Edward Leyse in the NRC's rulemaking process. The petition was dated 
March 15, 2007, and was docketed as PRM-50-84. The petitioner requests 
that the NRC amend its regulations to require that nuclear power 
reactors be operated in a manner to limit the thickness of crud layers 
and/or the thickness of oxide layers on fuel rod cladding surfaces to 
ensure that the facilities operate in compliance with the emergency 
core cooling system (ECCS) acceptance criteria. The petitioner also 
requests that the requirements pertaining to ECCS evaluation models be 
amended to explicitly require that the steady-state temperature 
distribution and stored energy in reactor fuel at the onset of a 
postulated loss-of-coolant accident (LOCA) be calculated by factoring 
in the role that the thermal resistance of crud and/or oxide layers on 
fuel cladding plays in increasing the stored energy of the fuel. 
Lastly, the petitioner requests that the acceptance criteria for 
analyses of ECCS cooling performance for light-water nuclear power 
reactors be amended to stipulate a maximum allowable percentage of 
hydrogen content in the cladding of fuel rods. The NRC will consider 
the petitioner's first two requests in PRM-50-84 because the underlying 
technical considerations regarding the effects of crud and oxide growth 
on ECCS analyses noted by the petitioner are sufficiently related to an 
ongoing NRC rulemaking activity on ECCS analysis acceptance criteria. 
The NRC will consider the petitioner's third request because the NRC 
has already initiated rulemaking activities that will address the 
petitioner's underlying technical concerns on fuel cladding 
embrittlement.
    While the NRC will consider the issues raised in the petition in 
its rulemaking process, the petitioner's concerns may not be addressed 
exactly as the petitioner has requested. During the rulemaking process, 
the NRC will solicit comments from the public and will consider all 
comments before issuing a final rule.

DATES: The docket for the petition for rulemaking PRM-50-84 is closed 
on November 25, 2008.

ADDRESSES: You can access publicly available documents related to this 
petition for rulemaking using the following methods:
    Federal e-Rulemaking Portal: Documents related to the evaluation of 
this petition are assigned to rulemaking docket ID: NRC-2006-0013. 
Further NRC action on the issues raised by this petition will be 
considered in the rulemaking to establish Performance-based ECCS 
Cladding Acceptance Criteria, (RIN 3150-AH42) which has been assigned 
rulemaking docket ID: NRC-2008-0332. Information on this petition and 
the related rulemaking can be accessed at the Federal rulemaking 
portal, https://www.regulations.gov; search on rulemaking docket ID: 
NRC-2007-0013 and NRC-2008-0332. The NRC also tracks all rulemaking 
actions in the ``NRC Regulatory Agenda: Semiannual Report (NUREG-
0936).''
    NRC's Public Document Room (PDR): The public may examine and have 
copied for a fee, publicly available documents at the NRC's PDR, Public 
File Area, Room O1-F21, One White Flint North, 11555 Rockville Pike, 
Rockville, Maryland.
    NRC's Agencywide Document Access and Management System (ADAMS): 
Publicly available documents created or received at the NRC are 
available electronically at the NRC's Electronic Reading Room at http:/
/www.nrc.gov/NRC/reading-rm/adams.html. From this page, the public can 
gain entry into ADAMS, which provides text and image files of NRC's 
public documents. If you do not have access to ADAMS or if there are 
any problems in accessing the documents located in ADAMS, contact the 
NRC PDR Reference staff at 1-800-397-4209, 301-415-4737 or by e-mail to 
PDR.resource@nrc.gov.

FOR FURTHER INFORMATION CONTACT: Richard Dudley, Mail Stop O12-D3, 
Office of Nuclear Reactor Regulation, United States Nuclear Regulatory 
Commission, Washington, DC 20555-0001; telephone (301) 415-1116, or e-
mail richard.dudley@nrc.gov.

SUPPLEMENTARY INFORMATION:

The Petition

    The NRC received a petition for rulemaking (ADAMS Accession No. 
ML070871368) from Mark Edward Leyse (the petitioner) dated March 15, 
2007, which was docketed as PRM-50-84. The petitioner requested that 
all holders of operating licenses for nuclear power plants be required 
to operate such plants at operating conditions (e.g., levels of power 
production, and light-water coolant chemistries) necessary to 
effectively limit the thickness of crud and/or oxide layers on fuel rod 
cladding surfaces. On May 23, 2007, the NRC published a notice of 
receipt for this petition in the Federal Register (72 FR 28902) and 
requested public comment. The public comment period ended on August 6, 
2007.

NRC Evaluation

    The NRC review of this petition and evaluation of public comments 
are based upon NRC's understanding of several terms used by the 
petitioner:
    1. Crud is any foreign substance which may become deposited on the 
surface of fuel cladding. This layer can impede the transfer of heat. 
The NRC believes that the word ``crud'' originated as an acronym for 
``Chalk River

[[Page 71565]]

Unidentified Deposit'', based upon deposits on early test fuels 
observed at Chalk River Laboratories in Canada. Crud most frequently 
refers to deposits of tiny iron or nickel metallic particles eroded 
from pipe and valve surfaces. These particles of stable isotopes may 
become ``activated'' or irradiated and transform into radioactive 
isotopes, such as cobalt-60. In fouling technology today, the term 
``crud'' is generally applied to solid deposits on fuel element heat 
transfer surfaces (cladding). The NRC staff makes a clear distinction 
between crud and pure zirconium oxidation layers. Although both 
materials contain metal oxides, crud does not originate at the fuel 
rod, while zirconium oxide forms on fuel when the cladding material 
reacts with oxygen.
    2. Oxide is a product of the reaction of oxygen with the zirconium 
cladding material itself. Zirconia, or zirconium dioxide 
(ZrO2) is one oxidation product which may be found on the 
exterior surface (and sometimes the interior surface) of zirconium fuel 
cladding. Although it may be an additional surface layer, formation of 
oxides also consumes some cladding base material, thereby decreasing 
metal cladding thickness. Compared to the original metal cladding 
material, metal oxides usually are more brittle and conduct heat less 
effectively. In this discussion, the terms ``corrosion'' and 
``oxidation'' are considered one and the same.
    3. Hydrogen in a nuclear reactor may be produced by the breakup of 
coolant water molecules during the oxidation process described 
previously. Hydrogen may not only be present in the reactor coolant, 
but may also diffuse into the fuel cladding. It may then either remain 
in solution or be precipitated as a zirconium hydride. Hydrogen in 
either form has been found to alter both the material properties and 
behavior of the cladding material. Formation of zirconium hydrides, 
such as ZrH2, has been found to cause embrittlement of zirconium fuel 
cladding.
    The NRC understands the petitioner as requesting the NRC to conduct 
rulemaking in three specific areas:
    1. Establish regulations that require licensees to operate light 
water power reactors under conditions that are effective in limiting 
the thickness of crud and/or oxide layers on zirconium-clad fuel in 
order to ensure compliance with 10 CFR 50.46(b) ECCS acceptance 
criteria;
    2. Amend current regulations in Appendix K to 10 CFR Part 50 to 
explicitly require that the steady-state temperature distribution and 
stored energy in the reactor fuel at the onset of a postulated LOCA be 
calculated by factoring in the role that the thermal resistance of crud 
deposits and/or oxide layers plays in increasing the stored energy in 
the fuel (these requirements also need to apply to any NRC-approved, 
best-estimate ECCS evaluation models used in lieu of Appendix K 
calculations); and
    3. Amend Sec.  50.46 to specify a maximum allowable percentage of 
hydrogen content in cladding.
    The NRC will address each of the petitioner's requests below. The 
NRC will first address the petitioner's third request because the logic 
used to evaluate the other requests can be more easily understood.
    Proposal 3--Amendment of 10 CFR 50.46, Acceptance Criteria for 
Emergency Core Cooling Systems for Light-water Nuclear Power Reactors, 
to include a limit on maximum hydrogen content in cladding.
    The petitioner states that an increase in hydrogen content in 
cladding contributes to cladding embrittlement. The petitioner cites an 
April 4, 2001, NRC Advisory Committee on Reactor Safeguards (ACRS) 
subcommittee meeting on reactor fuels during which an expert from 
Argonne National Laboratory stated that a reduction of ductility occurs 
when hydrogen levels reach about 600 to 700 parts-per-million (ppm) in 
Zircaloy cladding. According to the petitioner, another expert from the 
Atomic Energy Research Institute stated that a threshold for a 
reduction of ductility in Zircaloy cladding occurs at even a lower 
hydrogen level of about 150 to 200 ppm. The petitioner also references 
an event at Three Mile Island, Unit 1 (TMI-1) during refueling Cycle 10 
that involved hydrogen absorption in fuel cladding. The petitioner 
notes that hydrogen content in the cladding of a rod that did not fail 
measured 700 ppm at TMI-1 and that this level of hydrogen content in 
one-cycle cladding is similar to the 800 ppm level measured in fuel 
cladding at the H.B. Robinson, Unit 2 facility, a pressurized water 
reactor (PWR). The petitioner states that some of the cladding in TMI-1 
Cycle 10 contained levels of hydrogen that Argonne National Laboratory 
found would have caused a loss of cladding ductility in addition to the 
embrittlement resulting from excessive oxide levels.
    The petitioner also states that absorption of hydrogen would 
contribute to a loss of cladding ductility during a LOCA along with 
cladding degradation and massive oxidation. The petitioner cites a 
failed fuel rod from the TMI-1, Cycle 10 event when hydrogen absorption 
caused hydrided material to break away from the outer portions of the 
cladding. The petitioner believes that the effects of increased stored 
energy due to a heavy crud layer in the fuel and the severity of 
cladding oxidation, embrittlement, and resulting fuel degradation 
during an actual event would be substantially greater than in an ECCS 
calculation based on clean cladding.
    In 2003, the Commissioners directed the NRC staff to undertake 
rulemaking to amend 10 CFR 50.46 to provide for a more performance-
based approach to meeting the ECCS acceptance criteria in Sec.  
50.46(b). Technical work to finalize the technical basis for this 
rulemaking is currently proceeding and includes a study (Research 
Information Letter 0801, ``Technical Basis for Revision of 
Embrittlement Criteria in 10 CFR 50.46,'' May 30, 2008, ADAMS accession 
no. ML081350225; NUREG/CR-6967, ``Cladding Embrittlement During 
Postulated Loss-of-Coolant Accidents,'' July 2008, ADAMS accession no. 
ML082130389) of the effects on cladding embrittlement caused by 
cladding oxidation and hydrogen. Because the NRC is already 
investigating the need to amend Sec.  50.46 to address hydrogen effects 
on cladding, the petitioner's request in Proposal 3 will be considered 
during the current rulemaking. This rulemaking is designated as RIN 
3150-AH42 in the ``NRC Regulatory Agenda: Semiannual Report (NUREG-
0936).'' Documents associated with this rule are posted under docket 
ID: NRC-2008-0332 on the Regulations.gov Web site. Rulemaking will 
begin when a consensus is reached on the technical basis for the 
amendments.
    Proposal 1--Establish regulations that require licensees to operate 
light water power reactors under conditions that effectively limit the 
thickness of crud and oxide layers on zirconium-clad fuel to ensure 
compliance with 10 CFR 50.46(b) ECCS acceptance criteria.
    To support the rulemaking request in Proposal 1 of the petition, 
the petitioner lists sources, such as the Electric Power Research 
Institute (EPRI) reports, ACRS transcripts, and several journal 
articles to show that the thermal conductivities of the crud and oxide 
layers are lower than the thermal conductivity of zirconium metal 
cladding. The petitioner asserts that because of these lower heat 
transfer rates, the stored energy within the fuel and the time to 
transfer stored energy will increase. The petitioner cites several 
operating instances to support the contention that safety issues can 
arise from the thermal resistance of crud and oxide layers on fuel 
cladding. Finally, the petitioner

[[Page 71566]]

lists several examples to show that incidents of fuel failures have 
increased in recent years.
    The petitioner's request in Proposal 1 is founded on the potential 
impact of crud and oxide on ECCS performance evaluations. The NRC 
generally agrees with the petitioner that crud and oxide formation can 
impact the thermal response of the fuel system. Hydrogen embrittlement 
is also an issue in the ongoing rulemaking to revise the ECCS 
acceptance criteria discussed in Proposal 3 above. The need for any 
operational restrictions, as requested by the petitioner, would 
presumably be determined (in part) from these considerations. The NRC 
believes that the petitioner's Proposal 1 is sufficiently relevant to 
the ongoing cladding embrittlement rulemaking to warrant consideration 
in that proceeding. The NRC is accepting the petitioner's Proposal 1 
for consideration during the current rulemaking to revise Sec.  
50.46(b). In deciding to consider the petitioner's concern in the Sec.  
50.46(b) rulemaking, the NRC expresses no position on the specific 
merits of the petitioner's request and underlying bases. These issues 
will be addressed separately as part of the rulemaking.
    Proposal 2--Amendment of Appendix K to 10 CFR Part 50, ECCS 
Evaluation Models I(A)(l), The Initial Stored Energy in the Fuel, to 
also require the thermal resistance of crud deposits and/or oxide 
layers as factors in calculations of steady-state temperature 
distribution and stored energy in the reactor fuel at the onset of a 
postulated LOCA.
    In this proposal, the petitioner requested that Appendix K to 10 
CFR Part 50 be amended to include explicit instructions on how to 
perform the ECCS performance calculations mentioned above. Also, in 
lieu of Appendix K calculations, the petitioner requested establishment 
of a regulation stating that these requirements must also apply to any 
NRC-approved, best-estimate ECCS evaluation model, as described in NRC 
Regulatory Guide 1.157. The petitioner states that because layers of 
crud and/or oxide increase the quantity of stored energy in the fuel, 
Appendix K to Part 50 should explicitly require that the thermal 
conductivity of layers of crud and/or oxide be factored into 
calculations of the stored energy in the fuel. In support of the 
petition, several references are cited. For example, the petitioner 
quotes from a letter to the NRC from James F. Klapproth, Manager, 
Engineering and Technology at General Electric Nuclear Energy (April 8, 
2002, ADAMS accession no. ML021020383): ``The primary effects of [a] 
heavy crud layer during a postulated LOCA would be an increase in the 
fuel stored energy at the onset of the event, and a delay in the 
transfer of that stored energy to the coolant during the blowdown phase 
of the event.''
    Proposal 2 requests that Appendix K explicitly require 
consideration of crud and/or oxide layers in the calculation of stored 
energy used in ECCS performance calculations required by Sec.  50.46. 
Appendix K provides requirements for one acceptable methodology for 
performing Sec.  50.46 ECCS performance calculations that must meet the 
acceptance criteria in Sec.  50.46(b). Similar to Proposal 1 above, the 
petitioner's request in Proposal 2 is founded on the potential impact 
of crud and oxide on ECCS performance evaluations. Because the NRC 
agrees with the petitioner that crud and oxide formation can change the 
thermal response of the fuel system, it is possible that crud and 
oxidation layers could also have an impact on cladding hydrogen 
concentration. Also, because hydrogen uptake and concentration are 
being considered in the ongoing rulemaking to establish new 
performance-based ECCS acceptance criteria, consideration of crud and 
oxidation in that context is appropriate. Thus, the NRC concludes that 
Proposal 2 is likewise sufficiently relevant to the ongoing rulemaking 
to warrant consideration in that proceeding. As in the case of the 
petitioner's Proposal 1, the NRC expresses no position on the specific 
merits of the petitioner's Proposal 2 and its underlying bases. These 
issues will be addressed separately as part of the Sec.  50.46(b) 
rulemaking.

Comparison of PRM-50-84 With Previous Similar Petitions

    PRM-50-84 is the fifth in a series of petitions for rulemaking 
submitted to the NRC regarding the build-up, analysis, and release of 
crud on nuclear power plant heat exchange surfaces, and the oxidation 
of zirconium fuel cladding. Each of the four previous petitions (PRM-
50-73 and PRM-50-73A (68 FR 41963; July 16, 2003); PRM-50-76 (70 FR 
52893; September 9, 2005); and PRM-50-78 (69 FR 56958; September 23, 
2004)) have been denied by the Commission. The NRC evaluated each of 
the previous petitions and concluded that the requested actions would 
not contribute to maintaining the public safety or security, nor would 
it improve the regulatory efficiently and effectiveness. The current 
petition is being considered because it includes the assertion that the 
accumulation of crud and oxide deposits will interfere with effective 
heat exchange between the cladding and coolant, increase fuel 
temperatures, and thus, lead to safety problems. Additionally, the 
NRC's knowledge of the effects of crud, oxidation, and hydrogen content 
on cladding integrity has increased in the last few years.
    In 2003, the NRC initiated work to develop the technical basis for 
new, performance-based ECCS acceptance criteria that would apply to all 
zirconium cladding alloys.\1\ Laboratory testing was performed on non-
irradiated and irradiated zirconium alloys with different burnups to 
determine what parameters affected cladding embrittlement. On May 30, 
2008, the NRC summarized the results of this research effort in a 
letter (Research Information Letter 0801, ``Technical Basis for 
Revision of Embrittlement Criteria in 10 CFR 50.46,'' May 30, 2008, 
ADAMS accession no. ML081350225). The NRC is now evaluating this 
information to determine if it provides an adequate basis for 
establishing the new, performance-based ECCS acceptance criteria. Two 
significant conclusions of this work are that hydrogen content of 
cladding is an important factor in causing cladding embrittlement and 
that cladding oxidation is a key contributor to cladding hydrogen 
content. Because crud and oxide formation can impact the thermal 
response of the fuel system, it is possible that crud and oxidation 
layers could also have direct or indirect impacts on cladding hydrogen 
concentration. Also, because all these factors appear to be 
interrelated, the NRC will consider all of the phenomena addressed in 
PRM-50-84 (crud, oxidation, and hydrogen content) in the ongoing 
rulemaking to establish new performance-based ECCS acceptance criteria 
in Sec.  50.46(b).
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    \1\ The acceptance criteria in the current regulations are 
specifically applicable to only two cladding alloys, Zircaloy and 
Zirlo. Fuel designs with other, more advanced cladding alloys must 
be reviewed on a case-by-case basis and require NRC approval of an 
exemption to the existing requirements.
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Analysis of Public Comments

    Comments in support of PRM-50-84 were provided by the Union of 
Concerned Scientists (UCS), two individuals, and the petitioner. The 
Nuclear Energy Institute and Strategic Teaming and Resource Sharing 
organization submitted comments in opposition to the petition. A 
summary of the comments and the NRC's evaluation of those comments 
follow.
    Comment: A commenter referenced various technical reports and

[[Page 71567]]

operational events to demonstrate that the accumulated hydrogen content 
of zirconium fuel cladding reduces the ductility of the cladding and 
increases the possibility that core geometry could change during a LOCA 
and reduce fuel cooling. (MEL 7-1)
    NRC Response:
    The NRC agrees with the commenter that cladding ductility can be 
reduced by hydrogen absorption in zirconium cladding. Since 2003, the 
NRC has been working to develop the technical basis for a new 
regulation on performance-based ECCS acceptance criteria applicable to 
the various zirconium cladding alloys. The NRC accepts this aspect of 
the petitioner's request and will consider hydrogen embrittlement 
issues during the ongoing rulemaking.
    Comment: Several commenters referred to numerous technical reports, 
papers, and articles to document the existence of crud and oxidation 
layers on light-water reactor fuel cladding and show that the thermal 
resistance associated with the crud and oxidation layers significantly 
affects fuel temperatures and ECCS performance. (RHL-1, RHL-2, MEL 6-1, 
MEL 6-2, MEL 7-1, MEL 7-2, MEL 7-3, RHL 8-2, RHL-10)
    NRC Response:
    The NRC reviewed the technical information provided or referenced 
by the commenters. The NRC agrees with the commenters that formation of 
cladding crud and oxide layers is an expected condition at nuclear 
power plants. However, the amount of accumulated crud and oxidation 
varies from plant to plant and from one fuel cycle to another. The NRC 
agrees that crud and/or oxide layers may directly affect the stored 
energy in the fuel by their thermal resistance as well as indirectly 
affecting the stored energy through an increase in the fuel rod 
internal pressure. In addition to the thermal insulating effect of 
crud, the NRC notes that a crud layer can also change surface 
topography, which has also been shown to affect cladding oxidation. As 
part of the ongoing rulemaking on performance-based ECCS analysis 
acceptance criteria, the NRC will evaluate the effects of these 
phenomena on cladding hydrogen content and embrittlement to determine 
their overall significance and if the regulations should be amended in 
this area.
    Comment: A commenter asserted that the need to implement PRM-50-84 
is shown by analysis of the NRC's February 28, 2006 inspection report 
on the River Bend Station (ML060600503). The inspection reviewed 
activities conducted by the licensee related to the identification and 
resolution of problems, including calculated higher cladding 
temperatures in fuel Cycle 8 and the formation of tenacious crud on the 
fuel rod cladding and fuel rod bowing in River Bend Cycle 11. (RHL-2)
    NRC Response:
    The NRC agrees with the commenter that the River Bend experience 
shows that exceptionally large accumulations of oxide and crud can have 
an impact on thermal hydraulic analyses. As part of the ongoing 
rulemaking on performance-based ECCS analysis acceptance criteria, the 
NRC will evaluate: (i) The effects of these phenomena on cladding 
hydrogen content and embrittlement to determine their overall 
significance, (ii) if such large accumulations are likely to occur 
under current NRC requirements and industry practices, and (iii) if the 
NRC's requirements should be amended in this area.
    Comment: Thermal-hydraulic analyses of ECCS performance approved by 
the NRC are often inadequate because they may not consider or 
improperly consider the thermal resistance of accumulated crud and/or 
oxidation on fuel cladding. Commenters cited examples of plant-specific 
ECCS analyses and asserted that had crud been properly considered, it 
is likely that the licensee would not be in compliance with the ECCS 
analysis acceptance criteria in Sec.  50.46(b). (RHL-2, MEL 7-1, MEL 7-
2, MEL 7-3)
    NRC Response:
    Assertions regarding potentially non-compliant ECCS analyses at the 
facilities mentioned are issues which are separate from resolving a 
petition for rulemaking on the adequacy of existing regulations. These 
assertions are not appropriate for consideration in a rulemaking 
context and are outside the scope of review of this PRM. This 
information has been referred to the Office Allegation Coordinator to 
determine the need for additional plant-specific regulatory review.
    Comment: A commenter cited Generic Safety Issue No. 191 (GSI-191) 
regarding pressurized water reactors (PWRs), ``Assessment of Debris 
Accumulation on PWR Sump Performance,'' and a related document, ``Peer 
Review of GSI-191 Chemical Effects Research Program'' (NUREG-1861), as 
justification for the petitioner's conclusion that the current 
regulations in Sec.  50.46 should be amended. The commenter asserts 
that these documents discuss the possibilities of incomplete modeling 
of crud-related thermal properties of fuel cladding. (UCS 3-4)
    NRC Response:
    In GSI-191, the NRC is addressing issues involving PWR containment 
sump performance and related chemical effects during a loss-of-coolant 
accident. The GSI-191 issues are different from the long-term buildup 
of crud and oxidation on reactor fuel which typically occurs during 
plant operation. The NRC agrees with the commenter that dissolved 
solids in post-accident cooling water that impinges on hot fuel 
surfaces could be deposited or precipitated out and could impede heat 
transfer from the fuel. The evaluation of GSI-191 by the NRC is a 
separate issue.
    Comment: A commenter identified two distinguishable layers in BWR 
fuel cladding deposits: an inner spinel structure and an outer iron 
oxide structure. The commenter further described the use of zinc in the 
coolant chemistry of some reactors to reduce radiation buildup on out-
of-core surfaces and stated that the potential culprit in cladding 
overheating could be the tenacious ferrite deposit. Because the thermal 
conductivity of the ferrite is not known, the commenter concluded that 
the potential effects of the tenacious layer should be seriously 
evaluated. (LIN-4)
    NRC Response:
    The NRC has considered the comment and agrees with much of the 
information provided. The structure and the composition of crud 
deposits may be complex. Also, the relationship between crud deposition 
and coolant chemistry is difficult to completely characterize. As part 
of the ongoing rulemaking on performance-based ECCS analysis acceptance 
criteria, the NRC will evaluate the effects of these phenomena on 
cladding hydrogen content and embrittlement to determine their overall 
significance and if the regulations should be amended in this area.
    Comment: A commenter referred to an NRC press release regarding an 
order issued to First Energy Nuclear Operating Company. The order 
addresses the prompt sharing of information that may be relevant to 
regulatory activities. The commenter asserted that a proprietary EPRI 
report, ``BWR Fuel Deposit Sample Evaluation, River Bend Cycle 11 Crud 
Flakes,'' has information relevant to regulatory activities associated 
with PRM-50-84. The commenter implied that the River Bend Station 
licensee should be subject to a similar NRC order requiring that it 
provide information, such as the EPRI report, to the NRC. (RHL-9)
    NRC Response:
    The NRC reviewed the information about River Bend Cycle 11 provided 
by the petitioner and commenters and the inspection report 
(ML060600503)

[[Page 71568]]

prepared by the NRC inspection team that investigated the crud 
occurrences in River Bend Cycles 8 and 11. Although the NRC inspection 
report referenced the proprietary EPRI report, the NRC staff evaluating 
PRM-50-84 did not review the EPRI report. Nevertheless, the NRC agrees 
with the commenter that the River Bend experience shows that 
exceptionally large accumulations of oxide and crud can have an impact 
on thermal hydraulic analyses. As part of the ongoing rulemaking on 
performance-based ECCS analysis acceptance criteria, the NRC will 
evaluate the effects of these phenomena on cladding hydrogen content 
and embrittlement to determine their overall significance and if the 
regulations should be amended in this area.
    Comment: A commenter opposed granting the petition because the 
petition relies heavily on abnormal operating experiences at four 
plants: River Bend (1998-1999 and 2001-2003), Three Mile Island 1 
(1995), Palo Verde Unit 2 (1997), and Seabrook (1997), when localized 
sections of thick crud developed during normal operation. The commenter 
stated that NRC guidelines in Section 4.2 of the Standard Review Plan 
(NUREG-0800) do not specify a specific limit on the maximum allowable 
corrosion thickness, but require the impact of corrosion on the thermal 
and mechanical performance to be considered in fuel design analysis 
regarding the design stress and strain limits.
    The commenter stated that cladding hydrogen content can have an 
adverse effect on ductile/brittle behavior of zirconium alloys heated 
into the beta phase and quenched (as would occur in a LOCA). The 
hydrogen impact on post-quench cladding ductility is a complex function 
of the oxidation temperature and pre-quench cooling path. The potential 
impact of hydrogen on the Sec.  50.46(b) fuel acceptance criteria has 
been recognized for several years. Experimental programs are underway 
to assess this impact on current and newer cladding alloys developed to 
minimize hydrogen build-up during irradiation. The commenter further 
states that, based on these data, the NRC Office of Nuclear Regulatory 
Research is developing the technical basis for new performance-based 
fuel acceptance criteria in Sec.  50.46(b) that include the effects of 
hydrogen.
    In summary, the commenter states that the incidents cited by the 
petitioner were isolated operational events and would not have been 
prevented by imposing specific regulatory limits on crud thickness. The 
industry is actively pursuing root cause evaluations and has developed 
corrective actions to mitigate further cases of excessive crud 
formation. The separate effects of hydrogen on cladding embrittlement 
will be addressed in future rulemaking to implement new acceptance 
criteria that are already being developed by the NRC. (NEI 5-1, NEI 5-
2, NEI 5-3, NEI 5-4, NEI 5-5, NEI 5-6, NEI 5-7)
    NRC Response:
    The NRC agrees with a great deal of the technical information 
provided by the commenter and with the commenter's view that new 
regulations imposing specific regulatory limits on crud thickness would 
not necessarily have prevented the occurrences of heavy crud deposits 
resulting from the operational events cited by the petitioner. 
Nevertheless, formation of cladding crud and oxide layers is an 
expected condition at nuclear power plants. The thickness of these 
layers varies from plant to plant. The commenter acknowledged that the 
hydrogen impact on post-quench cladding ductility is a complex function 
of the oxidation temperature and pre-quench cooling path, and that 
these effects will be evaluated in the ongoing rulemaking to develop 
more performance-based cladding acceptance criteria. Because crud and 
oxide considerations also have potential impact on these new criteria, 
the NRC has determined that the petitioner's issues are sufficiently 
related to the ongoing cladding acceptance criteria rulemaking and 
should be considered in that proceeding.
    Comment: Commenters stated that industry-funded research has 
resulted in chemistry controls, core design constraints, and 
operational guidance that reduce the susceptibility to heavy crud 
deposition and that many pressurized water reactors, especially those 
most susceptible to heavy crud deposition, make extensive use of the 
industry guidance. Commenters stated that the requested rulemaking 
would not make a significant contribution to safety because existing 
regulations and guidance already address consideration of crud-related 
parameters for core cooling. A commenter stated that NRC and licensee 
efficiency and effectiveness would be decreased by the requested 
regulations because significant resources would be required for the NRC 
to promulgate the rule, for licensees to generate additional 
information as part of the development of their ECCS evaluation models, 
and for the NRC to evaluate the licensees' data and analysis. (NEI 5-1, 
STARS 11-1, NEI 5-2, STARS 11-2, STARS 11-3)
    NRC Response:
    The NRC acknowledges that voluntary industry guidance, if properly 
implemented by licensees, can be effective in reducing the 
susceptibility to heavy crud deposition. However, the NRC has 
determined that crud and oxidation layers can have an impact on 
cladding hydrogen concentration. Because hydrogen uptake and 
concentration are being considered in the ongoing rulemaking to 
establish new performance-based ECCS acceptance criteria, consideration 
of crud and oxidation in that context is appropriate. If the NRC 
decides that additional regulations are needed regarding the 
accumulation of crud and oxidation, the NRC will estimate the 
additional NRC and licensee burden associated with the proposed changes 
and evaluate the overall cost-effectiveness of the requirements.
    Late Comment: On September 5, 2008, after the close of the public 
comment period on PRM-50-84, the NRC received an additional public 
comment from Mr. Mark Leyse. The NRC reviewed the information contained 
in the late comment and determined that it provided no additional 
information that would affect the NRC's decision to address the issues 
raised in PRM-50-84 in the ongoing Sec.  50.46(b) rulemaking.

Resolution of Petition

    The NRC will consider the petitioner's requested rulemaking 
changes, the underlying issues relevant to the petition, and the 
comments submitted on PRM-50-84, in the ongoing rulemaking to revise 
Sec.  50.46(b). This rulemaking is directed at establishing 
performance-based ECCS acceptance criteria to prevent fuel cladding 
embrittlement. The petitioner's requested changes and the underlying 
issues address crud, oxidation, and hydrogen content. These parameters 
may be factors in hydrogen embrittlement of zirconium cladding, which 
is being addressed in the Sec.  50.46(b) rulemaking. After the 
conclusion of the NRC's technical evaluation of the factors relevant to 
fuel cladding embrittlement, the NRC will determine whether to adopt 
the petitioner's requested rulemaking changes in the Sec.  50.46(b) 
rule. If the ongoing work to establish the technical basis for this 
rulemaking does not support the issuance of a proposed rule, the NRC 
will issue a supplemental Federal Register notice that addresses why 
the petitioner's requested rulemaking changes were not adopted by the 
NRC. With this resolution of the petition, the NRC closes the docket 
for PRM-50-84.


[[Page 71569]]


    Dated at Rockville, Maryland, this 5th day of November 2008.

    For the Nuclear Regulatory Commission.
Martin J. Virgilio,
Acting Executive Director for Operations.
[FR Doc. E8-27938 Filed 11-24-08; 8:45 am]
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