[Federal Register Volume 71, Number 130 (Friday, July 7, 2006)]
[Notices]
[Pages 38673-38675]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E6-10623]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. STN 50-454 and STN 50-455]


Exelon Generation Company, LLC; Byron Station, Unit Nos. 1 and 2; 
Exemption

1.0 Background

    The Exelon Generation Company, LLC (Exelon, licensee) is the holder 
of Facility Operating License Nos. NPF-37 and NPF-66 which authorize 
operation of the Byron Station Unit 1 and Unit 2, respectively. The 
licenses provide, among other things, that the facility is subject to 
all rules, regulations, and orders of the Nuclear Regulatory Commission 
(NRC, Commission) now or hereafter in effect.
    The facility consists of two pressurized-water reactors located in 
Ogle County, Illinois.

2.0 Request/Action

    Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 
Section 50.12, ``Specific exemptions,'' Exelon has requested an 
exemption from 10 CFR 50.44, ``Combustible gas control system for 
nuclear power reactors''; 10 CFR 50.46, ``Acceptance criteria for 
emergency core cooling systems [ECCS] for light-water nuclear power 
reactors'';

[[Page 38674]]

and Appendix K to 10 CFR part 50, ``ECCS Evaluation Models.'' The 
regulation at 10 CFR 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. Section 50.46 
contains acceptance criteria for ECCS for reactors fueled with zircaloy 
or ZIRLOTM cladding. 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.
    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 ZIRLOTM 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) comprised of the AXIOMTM 
developmental clad alloys at Byron Station, Unit Nos. 1 and 2.

3.0 Discussion

3.1 Material Design

3.1.1 Fuel Material Design
    In order to meet future demands of the nuclear industry, 
Westinghouse is evaluating the in-reactor performance of several 
developmental alloys. The licensee states that the material properties 
and mechanical performance of the advanced cladding alloys are expected 
to be similar to Zircaloy-4 and ZIRLOTM, and that any 
difference in phase transition temperatures and mechanical strength 
will be considered in the LTA fuel rod design evaluation. Further, 
preliminary autoclave testing indicates that the advanced alloys 
exhibit acceptable corrosion resistance. This is consistent with the 
NRC staff's expectation that unirradiated properties of any advanced 
cladding alloy will be accounted for in the LTA fuel rod design 
evaluation.
    The licensee's September 23, 2005, letter stated:

    The current licensed fuel performance code predictions for the 
developmental cladding will be compared to post-irradiation 
examination data at Byron Station. If significantly adverse 
observations are found relative to predictions, the adverse rod(s) 
will either be removed and the fuel assembly will be reconstituted 
with suitable replacement rods, or the entire fuel assembly will be 
removed from the following fuel cycle(s) until deviations are 
understood and addressed.
    Where appropriate, concurrent data obtained from other LTA 
programs for the same developmental claddings will be factored into 
the assessment of the LTAs at Byron Station. Specifically, before 
the assemblies are reinserted, all available information will be 
reviewed to ensure existing design assumptions remain valid.

    Based upon the limited number of advanced alloy fuel rods placed in 
non-limiting core locations, specifically accounting for significant 
deviations in unirradiated material and mechanical properties, and an 
LTA post-irradiation examination program aimed at qualifying model 
predictions and understanding deviations, the NRC staff finds the LTA 
mechanical design acceptable for Byron Station Unit Nos. 1 and 2.
3.1.2 Core Physics and Non-LOCA Analysis
    The 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.
    The standard reload methodologies will be applied to the advanced 
cladding alloys. Nuclear design evaluations will assure that LTAs will 
be placed in non-limiting 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 testing to date it is not anticipated that any of the 
advanced cladding fuel rods would fail during normal operation. 
However, if any failures occurred, their effects would be well within 
technical specification limits for doses and, in all cases, core 
coolable geometry would be maintained. The NRC staff agrees that the 
placement of a limited number of advanced alloy fuel rods in non-
limiting locations would not challenge reported dose consequences nor 
core coolability.
    Based upon the limited number of advanced alloy fuel rods placed in 
non-limiting core locations, the use of approved models and methods, 
and expected material performance, the NRC staff finds that the 
irradiation of up to four LTAs at the Byron Station 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.

3.2 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 when (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) when special circumstances are present.
3.2.1 10 CFR 50.44
    The underlying purpose of 10 CFR 50.44 is to assure that means are 
provided for the control of hydrogen gas that may be generated 
following a LOCA. The licensee has provided a means for controlling 
hydrogen gas and has previously considered the potential for hydrogen 
gas generation stemming from a metal-water reaction. Based upon the 
material composition of these alloys, which is similar to other 
licensed zirconium alloys, the high temperature metal-water reaction 
rates are expected to be similar. Due to the limited number and 
anticipated performance of the advanced cladding fuel rods, the 
previous calculations of hydrogen production resulting from a metal-
water reaction will not be significantly changed. As such, the 
limitations of 10 CFR 50.44 related to cladding material is not 
necessary for the licensee to achieve the underlying purpose of the 
rule in these circumstances.
3.2.2 10 CFR 50.46
    The underlying purpose of 10 CFR 50.46 is to establish acceptance 
criteria for ECCS performance in response to LOCAs. Due to the limited 
number of advanced alloy fuel rods, any change in the post-LOCA 
ductility characteristics of the advanced alloy fuel rods (relative to 
the 2200 [deg]F peak cladding temperature and 17 percent effective 
cladding reacted) would not challenge core coolable geometry. 
Westinghouse performs cycle-specific reload evaluations to assure that 
10 CFR 50.46 acceptance criteria are satisfied and will include the 
LTAs in such analyses. Thus, the limitations of 10 CFR 50.46 related to 
cladding material are not necessary for the licensee to achieve the 
underlying purpose of the rule in these circumstances.
3.2.3 10 CFR 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 advanced cladding

[[Page 38675]]

alloys for determining acceptable fuel performance. Based upon the 
material composition of these alloys, which is similar to other 
licensed zirconium alloys, the high temperature metal-water reaction 
rates are expected to be similar. Because of the limited number of 
AXIOMTM clad fuel rods and the similarity in material 
composition to other advanced cladding fuel rods, the NRC staff 
concludes that the application of the Baker-Just equation in these 
conditions is acceptable. Thus, application of 10 CFR Part 50 Appendix 
K, Paragraph I.A.5 is not necessary for the licensee to achieve the 
underlying purpose of the rule in these circumstances.
3.2.4 Special Circumstances
    In summary, the NRC staff reviewed the licensee's request of 
proposed exemption to allow up to four LTAs containing fuel rods with 
AXIOMTM cladding. Based on the NRC staff's evaluation, as 
set forth above, the NRC staff considers that granting the proposed 
exemption will not defeat the underlying purpose of 10 CFR 50.46, 10 
CFR 50.44, or Appendix K to 10 CFR Part 50. Accordingly, special 
circumstances, are present pursuant to 10 CFR 50.12(a)(2)(ii).
3.2.5 Other Standards in 10 CFR 50.12
    The NRC staff examined the rest of the licensee's rationale to 
support the exemption request, and concluded that the use of 
AXIOMTM 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 in the licensee's exemption request:

    The LTA safety evaluation will ensure that the acceptance 
criteria of 10 CFR 50.46, 10 CFR 50.44, and 10 CFR 50 Appendix K are 
met following insertion of the assemblies containing 
AXIOMTM material. Fuel assemblies using 
AXIOMTM cladding will be evaluated using NRC-approved 
analytical methods and will address the changes in the cladding 
material properties. The safety analysis for Byron Station Units 1 
and 2 is supported by the applicable Technical Specifications. The 
Byron Station Units 1 and 2 reload cores containing 
AXIOMTM cladding will continue to be operated in 
accordance with the operating limits specified in the Technical 
Specifications. LTAs using AXIOMTM cladding will be 
placed in non-limiting core locations. Therefore, this exemption 
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 NRC staff concludes that AXIOMTM may be used as 
a cladding material for no more than four LTAs to be placed in non-
limiting core locations during Byron'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.
    (3) The requested exemption will not endanger the common defense 
and security:
    The common defense and security are not affected and, therefore, 
not endangered by this exemption.

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 Exelon an exemption from the 
requirements of 10 CFR 50.44, 10 CFR 50.46 and 10 CFR Part 50, Appendix 
K, for Byron Station, Unit Nos. 1 and 2.
    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 (71 FR 32144).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 30th day of June 2006.

    For the Nuclear Regulatory Commission.
Catherine Haney,
Director, Division of Operating Reactor Licensing, Office of Nuclear 
Reactor Regulation.
 [FR Doc. E6-10623 Filed 7-6-06; 8:45 am]
BILLING CODE 7590-01-P