[Federal Register Volume 74, Number 87 (Thursday, May 7, 2009)]
[Notices]
[Pages 21418-21421]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E9-10619]



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NUCLEAR REGULATORY COMMISSION

[NRC-2009-0198; Docket No. 50-455]


Exelon Generation Company, LLC; Byron Station, Unit No. 2; 
Exemption

1.0 Background

    Exelon Generation Company, LLC (Exelon, the licensee) is the holder 
of Facility Operating License No. NPF-66 which authorizes operation of 
the Byron Station, Unit No. 2 (Byron 2). The license provides, among 
other things, that the facility is subject to all rules, regulations, 
and orders of the Nuclear Regulatory Commission (NRC, the Commission) 
now or hereafter in effect.
    The facility is one unit of a two-unit pressurized-water reactor 
station 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,'' the licensee has, by letter 
dated March 24, 2008 (Agencywide Documents Access and Management System 
(ADAMS) Accession No. ML080850235), requested an exemption from the 
requirements of 10 CFR 50.46, ``Acceptance criteria for emergency core 
cooling systems for light-water nuclear power reactors,'' and 10 CFR 
Part 50, Appendix K, ``ECCS Evaluation Models,'' for one lead test 
assembly (LTA) using Westinghouse AXIOMTM cladding.
    The regulation at 10 CFR 50.46(a)(1)(i) requires that ``[e]ach 
boiling or pressurized light-water nuclear power reactor fueled with 
uranium oxide pellets within cylindrical zircaloy or ZIRLOTM 
cladding must be provided with an emergency core cooling system (ECCS) 
that must be designed so that its calculated cooling performance 
following postulated loss-of-coolant accidents conforms to the criteria 
set forth in paragraph (b) of this section.'' The regulation at 10 CFR 
50.46(a)(1)(ii) requires that, ``[a]lternatively, an ECCS evaluation 
model may be developed in conformance with the required and acceptable 
features of appendix K ECCS Evaluation Models.'' Appendix K of 10 CFR 
Part 50 requires, in paragraph I.A.5, that ``[t]he rate of energy 
release, hydrogen generation, and cladding oxidation from the metal/
water reaction shall be calculated using the Baker-Just equation 
(Baker, L., Just, L.C., ``Studies of Metal Water Reactions at High 
Temperatures, III. Experimental and Theoretical Studies of the 
Zirconium-Water Reaction,'' ANL-6548, page 7, May 1962).'' The 
regulations make no provisions for use of fuel rods clad in a material 
other than zircaloy or ZIRLOTM. The licensee plans to 
irradiate one LTA using fuel rods clad with AXIOMTM alloy in 
Byron 2. Because the material specification of the AXIOMTM 
alloy differs from the specification for zircaloy or 
ZIRLOTM, the licensee requested a plant-specific exemption 
from the requirements of 10 CFR 50.46 and 10 CFR Part 50, Appendix K, 
to support the use of the LTA for Byron 2. However, as discussed 
subsequently in Sections 3.0 and 4.0, the NRC staff determined that a 
broad exemption from all the requirements of 10 CFR 50.46 and 10 CFR 
Part 50, Appendix K, is not required in this particular circumstance.
    The licensee plans to use one LTA, containing fresh and twice-
burned AXIOMTM clad fuel rods, in the Byron 2 Cycle 16 
reactor core. The twice-burned AXIOMTM clad fuel rods would 
continue to be irradiated up to a lead rod average burnup of up to 
75,000 megawatt days per metric ton uranium (MWD/MTU).
    Previously, by letter dated June 30, 2006 (ADAMS Accession No. 
ML061380518), the NRC staff approved the irradiation of four LTAs 
containing AXIOMTM clad fuel rods in the Byron Station, Unit 
No. 1 (Byron 1), Cycle 15 core. In the same letter, the NRC staff also 
approved the re-insertion of two of the four LTAs into the Byron 1 
Cycle 16 core and the other two LTAs into the Byron 2 Cycle 15 core. 
Byron 1 is currently operating in Cycle 16; Byron 2 is currently 
operating in Cycle 15. Prior to re-insertion of the LTAs into the Cycle 
16 and Cycle 15 cores, respectively, for the second cycle of 
irradiation, the licensee performed post-irradiation examination (PIE) 
for the LTAs. During the spring 2010, Byron 2 refueling outage, the 
licensee plans to perform PIE for the two LTAs, then re-insert one LTA 
into the Byron 2 Cycle 16 core to gain high burnup data. The LTA will 
consist of fresh fuel rods in AXIOMTM cladding along with up 
to 16 twice-burned fuel rods in AXIOMTM cladding selected 
from the irradiated LTAs. During this third cycle, the twice-burned 
fuel rods will reach a peak rod average burnup of 75,000 MWD/MTU, which 
exceeds the NRC staff's burnup limit of 62,000 MWD/MTU (ADAMS Accession 
No. ML061420458), based on the capabilities of the fuel performance and 
design models for Westinghouse VANTAGE+ fuel, which is used in the 
Byron 2 reactor core.

3.0 Discussion

    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. The Commission will not 
consider granting an exemption unless special circumstances are 
present.

Authorized by Law

    This exemption would allow the licensee to re-insert one LTA 
containing AXIOMTM fuel rod cladding that is neither 
Zircaloy nor ZIRLOTM, which are the cladding materials 
contemplated by 10 CFR 50.46(a)(1)(i) and by 10 CFR Part 50, Appendix 
K, paragraph I.A.5. Selection of a specific cladding material in 10 CFR 
50.46(a)(1)(i) and in 10 CFR Part 50, Appendix K, paragraph I.A.5 was 
at the discretion of the Commission consistent with its statutory 
authority. No statute required the NRC to adopt this specification. As 
stated above, 10 CFR 50.12 allows the Commission to grant exemptions 
from the requirements of 10 CFR Part 50. The NRC staff has determined 
that granting of an exemption from 10 CFR 50.46(a)(1)(i) and from 10 
CFR Part 50, Appendix K, paragraph I.A.5 related to AXIOMTM 
fuel rod cladding, which is neither Zircaloy nor ZIRLOTM, 
will not result in a violation of the Atomic Energy Act of 1954, as 
amended, or the Commission's regulations. Therefore, the exemption is 
authorized by law. Furthermore, the NRC staff has determined that, 
because the licensee plans to ensure that the acceptance and analytical 
criteria of 10 CFR 50.46 and 10 CFR Part 50, Appendix K are met 
following the insertion of the subject LTA, exemption from the 
remaining requirements of 10 CFR 50.46 and 10 CFR Part 50, Appendix K 
is not required.

No Undue Risk to Public Health and Safety

    In its March 24, 2008 letter, the licensee provided technical 
justification to support its conclusion that irradiating one LTA, 
containing fresh and twice-burned AXIOMTM clad fuel rods, in 
the Byron 2 Cycle 16 reactor core, up to a lead rod average burnup of 
up to 75,000 MWD/MTU would result in no undue risk to public health and 
safety. The licensee's technical justification and the NRC staff's 
associated conclusions follow.
Fuel Mechanical Design Considerations
    Prior to Byron 2 Cycle 16, characterization of the twice-burned 
AXIOMTM fuel rods will be performed

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to include an overall visual examination and measurements of cladding 
oxide, fuel rod growth, and diameter profile. Prior to irradiating the 
LTA during Byron 2 Cycle 16, the twice-burned AXIOMTM clad 
fuel rods will be evaluated with current fuel performance methods and 
codes to ensure that all current design criteria are met for the 
projected burnup. The licensee stated that if some of the 
AXIOMTM clad twice-burned rods scheduled for reconstitution 
exhibit anomalous behavior, have measured characteristics of oxide 
thickness or rod length that are outside acceptable bounds, or are 
determined incapable of meeting all current design requirements, those 
twice-burned rods will not be used for reconstitution and will be 
replaced with rods meeting the reload requirements. The licensee also 
stated that, to ensure that the acceptance criteria of 10 CFR 50.46 and 
10 CFR Part 50, Appendix K, are met, the LTA using AXIOMTM 
cladding will be evaluated using NRC-approved analytical methods and 
will address the changes in the cladding material properties and that 
the reload core containing AXIOMTM cladding will continue to 
be operated in accordance with the operating limits specified in the 
Byron Station Technical Specifications (TS). Based upon the limited 
number of AXIOMTM clad fuel rods, the PIE and 
characterization which would detect anomalous behavior, the use of NRC-
approved models to ensure that all design criteria remain satisfied, 
and the requirement to operate the Byron Cycle 16 core within TS 
limits, the NRC staff finds the LTA mechanical design acceptable for 
Byron 2 Cycle 16.
    Traditionally, the NRC staff had two criteria for LTA programs: (1) 
The number of LTAs should be limited, and (2) the core locations of 
LTAs should be non-limiting (i.e., not in the highest power regions). 
In 2003, the NRC staff endorsed the concept of locating LTAs next to 
the highest power or high-duty regions for simulating typical reactor 
operations. By letters dated January 8 and August 29, 2003 (ADAMS 
Accession Nos. ML030070476 and ML032410054, respectively), the NRC 
staff approved Westinghouse Topical Report WCAP-15604-NP, Revision 1, 
``Limited Scope High Burnup Lead Test Assemblies,'' which provides the 
basis and guidelines for the operation of a limited number of LTAs for 
a high burnup irradiation program. Based on the licensee's planned LTA 
program, the NRC staff considers that the burnup extension is 
consistent with the approved report. Based on the approved report, 
acceptable PIEs for the Byron LTAs prior to the second cycle of 
irradiation, and the licensee's plans for PIE and characterization of 
the twice-burned fuel rods prior to the third cycle of irradiation, the 
NRC staff concludes that it is acceptable to extend the LTA burnup 
limit to a peak rod average of 75,000 MWD/MTU for Byron Unit 2.
    The Byron 2 reactor core contains a total of 193 fuel assemblies; 
each fuel assembly contains 264 fuel rods. As mentioned previously, the 
Byron 2 Cycle 16 LTA, which is the subject of the licensee's exemption 
request, will consist of up to 16 twice-burned fuel rods in 
AXIOMTM cladding with the remainder (and the majority) being 
fresh fuel rods in AXIOMTM cladding, and will be placed in 
the Cycle 16 reactor core in a non-limiting core location. The licensee 
stated that setting the number of AXIOMTM clad rods at this 
level restricts the portion of such rods to a value of 0.52 percent, 
which, even if failed, is well within the postulated core damage in the 
Byron Station's current licensing basis. The licensee also stated that, 
even though there have been no AXIOMTM clad fuel rod 
failures in the industry to date, if a failure were to occur, the 
effects would be well within the TS limits for doses and core coolable 
geometry would be maintained. Based upon the limited number of 
AXIOMTM clad fuel rods placed in non-limiting core 
locations, the use of approved models and methods, and the acceptable 
performance to date of the AXIOMTM cladding, the NRC staff 
finds that the irradiation of the subject LTA in the Byron 2 Cycle 16 
core 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, as discussed next.
Dose Analyses Considerations for Extended Burnup
    The licensee stated in its March 24, 2008 letter, that the 
assessment contained in Westinghouse Topical Report WCAP-12610-P-A, 
``VANTAGE + Fuel Assembly Reference Core Report,'' April 1995, 
concluded that the fuel-handling accident (FHA) total effective dose 
equivalent doses are not adversely affected by extended burnup up to 
75,000 MWD/MTU. However, the licensee recognized that there is 
uncertainty in fission product gap inventory, due to the limited 
fission gas release measurements on high burnup fuel, and provided a 
discussion of the conservatisms in the Byron FHA dose calculation. 
These included use of the alternative source term (AST) methodology, 
the relative power for this particular LTA in Cycle 16, offloading 
time, containment isolation, and mechanical fuel damage due to impact.
AST Methodology
    The NRC approved the use of an AST methodology for Byron Station in 
License Amendment No. 147, dated September 8, 2006 (ADAMS Accession No. 
ML062340420). The analyses provided by the licensee in support of the 
amendment and approved by the NRC staff used gap release fractions for 
accidents other than the loss-of-coolant accident (LOCA), which are two 
times the values in Table 3 of Regulatory Guide (RG) 1.183, 
``Alternative Radiological Source Terms for Evaluating Design Basis 
Accidents at Nuclear Power Reactors,'' July 2000. The factor of two was 
used to offset the fact that some fuel assemblies would exceed the rod 
power/burnup criteria in RG 1.183. For the FHA, all of the fuel rods in 
the limiting assembly were assumed to fail, releasing their fuel/clad 
gap fission product inventory. The NRC staff has previously found this 
approach acceptable in the safety evaluation accompanying the above-
cited amendment.
LTA Relative Power
    The licensee stated that, due to its high burnup, the LTA's 
relative power will not approach the 1.7 peaking limit assumed in the 
Updated Final Safety Analysis Report (UFSAR). The Byron 2 Cycle 16 
reactor core will be designed such that the LTA will remain in a non-
limiting location. Therefore, with more appropriate relative assembly 
powers credited for both the LTA and other potentially-impacted 
assemblies, the calculated dose would decrease. Although relative 
assembly powers are not generally credited in design-basis accident 
(DBA) radiological consequences analyses, the NRC staff finds that the 
specific situation described above does show that conservatism exists 
in the current licensing basis FHA analysis when compared to the 
expected impact of dropping the extended burnup LTA.
Offloading Time
    The licensee stated that, although the FHA calculation assumes that 
core offload begins no sooner than 48 hours after shutdown, in 
practice, core offload typically commences much later than 48 hours 
after entry into Mode 3. However, because the licensee did not provide 
supporting documentation on how it would assure the expected >48 hours 
to start core offload (i.e., TS, physical constraints, procedures, 
etc.), the NRC staff finds that this conservatism cannot

[[Page 21420]]

be credited as a conservatism related to this exemption request for the 
subject LTA. However, the NRC staff notes that other conservatisms in 
the FHA, discussed previously and below, more than offset this non-
credited core offload time.
Containment Isolation
    In accordance with Byron Station TS 3.9.4, the movement of recently 
irradiated fuel (i.e., fuel that has occupied part of a critical 
reactor core within the previous 48 hours) requires that containment 
integrity be in effect. Fuel with additional decay can be moved without 
containment integrity or exhaust filtration. Compensatory measures to 
close any openings and ensure exhaust is in the proper direction within 
1 hour after a FHA are required procedurally as defense-in-depth 
measures; however, they are not credited in the analysis in accordance 
with RG 1.183. The NRC staff, in its review of the licensee's AST 
methodology, has previously found this approach acceptable and would, 
therefore, apply to movement of the LTA.
Mechanical Fuel Damage Due to Impact
    The Byron Station UFSAR analysis assumes all rods of the dropped 
assembly fail. The licensee stated that this is a very conservative 
assumption given the broad spectrum of loads considered and the 
resulting high structural strength of the fuel assembly and other core 
components. The licensee also stated that irradiated fuel assembly drop 
events (e.g., Fort Calhoun in 2003, North Anna in 2001, and Haddam Neck 
in 1986) have also yielded no increase in local area dose rates. The 
NRC staff concludes that the amount of assumed fuel damage in the 
current licensing basis is conservative based on fuel mechanical design 
and actual industry experience, even if the FHA were to involve the 
subject LTA.
    The NRC staff finds that the conservatisms associated with the AST 
analysis, LTA relative power, compensatory measures during irradiated 
fuel movement, and FHA fuel damage assumptions compensate for the 
uncertainties in the gap fractions. Therefore, the fission product gap 
inventory assumed in the current licensing basis FHA radiological 
assessment remains bounding for the extended burnup LTA.
    For other DBAs, even though extended burnup to 75,000 MWD/MTU for 
the one LTA would cause a variation in the core inventory compared to 
the current fuel, there are no significant increases to isotopes that 
are major contributors to accident doses. Therefore, the NRC staff 
finds that current licensing basis DBA results remain bounding for 
estimated offsite and control room operator doses and the radiation 
dose limitations of 10 CFR 50.67, ``Accident Source term,'' and 10 CFR 
Part 50, Appendix A, GDC-19, ``Control Room,'' will not be exceeded. 
The NRC staff finds that the licensee used assumptions, inputs, and 
methods that are consistent with the conservative regulatory 
requirements and guidance identified above. Based on the Byron Station 
current licensing bases and the acceptable conservatisms discussed 
above, the NRC staff finds with reasonable assurance that the 
licensee's estimates of the exclusion area boundary, low-population 
zone, and control room doses will continue to comply with the 
applicable regulatory criteria. Therefore, the proposed extension of 
the fuel rod average burnup limit for one LTA is acceptable with regard 
to the radiological consequences of postulated DBAs.
Conclusion
    Based upon the limited number and anticipated performance of the 
AXIOMTM clad fuel rods, the use of PIE and characterization 
to detect anomalous behavior to preclude further irradiation damage, 
and the use of NRC-approved models to ensure that all design criteria 
remain satisfied, the NRC staff finds the use of the subject LTA up to 
75,000 MWD/MTU in the Byron 2 Cycle 16 reactor core to be acceptable.

Consistent With Common Defense and Security

    The proposed exemption would allow the use of one LTA with a 
variant cladding material. This change to the plant core configuration 
has no impact on security issues. Special nuclear material in the LTA 
will continue to be handled and controlled in accordance with 
applicable regulations. Therefore, the common defense and security is 
not impacted by this exemption.

Special Circumstances

    In accordance with 10 CFR 50.12(a)(2)(ii), special circumstances 
are present whenever application of the regulation in the particular 
circumstances would not serve the underlying purpose of the rule or is 
not necessary to achieve the underlying purpose of the rule.
    The underlying purpose of 10 CFR 50.46(a)(1)(i) is to establish 
acceptance criteria for ECCS performance. Previously, on June 30, 2006, 
the NRC staff approved an exemption for four Byron LTAs that 
demonstrated the acceptability of the AXIOMTM cladding under 
LOCA conditions (ADAMS Accession No. ML061380518). The unique features 
of the LTAs were evaluated for effects on the LOCA analyses. The 
results showed that the LTAs would not adversely affect ECCS 
performance. Because the current LTA will be located in a non-limiting 
core location, the licensee concluded and the NRC staff agrees that the 
LOCA safety analyses will remain bounding for the Cycle 16 LTA for 
Byron 2. Therefore, the NRC staff concludes that application of 10 CFR 
50.46(a)(1)(i) in this particular circumstance is not necessary for the 
licensee to achieve the underlying purpose of the rule.

10 CFR Part 50, Appendix K

    Paragraph I.A.5 of Appendix K to 10 CFR Part 50 states that ``[t]he 
rate of energy release, hydrogen generation, and cladding oxidation 
from the metal/water reaction shall be calculated using the Baker-Just 
equation.'' The Baker-Just equation, developed in 1962, presumed the 
use of zircaloy clad fuel, and thus did not address AXIOMTM 
clad fuel for determining acceptable fuel performance. The underlying 
intent of this portion of Appendix K is to ensure that analysis of fuel 
response to LOCAs is conservatively calculated. Previously, in its June 
30, 2006, exemption for four Byron LTAs with AXIOMTM clad 
fuel rods (ADAMS Accession No. ML061380518), the NRC staff concluded 
that, based on the material composition of the AXIOMTM 
alloy, which is similar to other licensed zirconium alloys, the high 
temperature metal-water reaction rates are expected to be similar. The 
NRC staff also concluded that, because of the limited number of 
AXIOMTM clad fuel rods and the similarity in material 
composition to other advanced cladding materials, the application of 
the Baker-Just equation in the analysis of the four Byron LTAs with 
AXIOMTM clad fuel rods was acceptable. Based on the NRC 
staff's previous conclusions for four LTAs with AXIOMTM clad 
fuel rods, the NRC staff concludes that an exemption from 10 CFR Part 
50, Appendix K, as requested by the licensee, is not necessary for the 
licensee's request to apply the Baker-Just equation to the one LTA with 
AXIOMTM clad fuel rods planned for insertion in the Byron 2 
Cycle 16 reactor core, because application of the Baker-Just equation 
in this circumstance will achieve the underlying purpose of the rule.

4.0 Conclusion

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), an exemption from the

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requirements of 10 CFR 50.46(a)(1)(i) 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 the 
licensee an exemption from the requirement of 10 CFR 46(a)(1)(i) 
related to fuel cladding material to allow one LTA containing 
AXIOMTM clad fuel rods to be irradiated in Byron 2 during 
Cycle 16 up to a lead rod average burnup of up to 75,000 MWD/MTU. The 
remaining requirements of 10 CFR 50.46 remain in effect for the Byron 2 
Cycle 16 reactor core.
    Furthermore, for the reasons stated in the previous section, the 
Commission has determined that an exemption from the requirements of 10 
CFR Part 50, Appendix K, is not required. Therefore, the Commission is 
not issuing an exemption from 10 CFR Part 50, Appendix K for the Byron 
2 Cycle 16 reactor core.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of the exemption from 10 CFR 46(a)(1)(i) will not have a 
significant effect on the quality of the human environment (74 FR 
20000; April 30, 2009).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 30th day of April 2009.

    For the Nuclear Regulatory Commission.
Joseph Giitter,
Director, Division of Operating Reactor Licensing, Office of Nuclear 
Reactor Regulation.
[FR Doc. E9-10619 Filed 5-6-09; 8:45 am]
BILLING CODE 7590-01-P