[Federal Register Volume 68, Number 189 (Tuesday, September 30, 2003)]
[Notices]
[Pages 56337-56338]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-24670]


=======================================================================
-----------------------------------------------------------------------

NUCLEAR REGULATORY COMMISSION

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


Exelon Generation Company, LLC, Byron Station, Units 1 and 2; 
Exemption

1.0 Background

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

2.0 Request/Action

    Title 10 of the Code of Federal Regulations (10 CFR), part 50, 
requires, among other items, that each boiling or pressurized light-
water nuclear power reactor fueled with oxide pellets within 
cylindrical zircaloy or ZIRLO cladding, must, as provided in paragraphs 
(b) through (d) of 10 CFR 50.44, include means for control of hydrogen 
gas that may be generated, following a postulated loss-of-coolant 
accident (LOCA) by:
    (1) Metal-water reaction involving the fuel cladding and the 
reactor coolant.
    (2) Radiolytic decomposition of the reactor coolant, and
    (3) Corrosion of metals.

Section 50.46 of Title 10 of the Code of Federal Regulations, 
``Acceptance Criteria for Emergency Core Cooling Systems for Light-
Water Nuclear Power Reactors,'' requires, among other items, that each 
boiling or pressurized light-water nuclear power reactor fueled with 
uranium oxide pellets within cylindrical zircaloy or ZIRLO cladding, 
must be provided with an emergency core cooling system (ECCS) that must 
be designed so that its calculated cooling performance following 
postulated LOCAs conforms to the criteria set forth in paragraph (b) of 
10 CFR 50.46. Section 50.46 also requires that ECCS cooling performance 
must be calculated in accordance with an acceptable evaluation model 
and must be calculated for a number of postulated LOCAs of different 
sizes, locations, and other properties sufficient to provide assurance 
that the most severe postulated LOCAs are calculated. Section 50.46 
provides further that an acceptable evaluation model may be developed 
in conformance with the features of 10 CFR part 50, appendix K models.
    Appendix K to part 50 of Title 10 of the Code of Federal 
Regulations, ``ECCS Evaluation Models,'' requires, among other items, 
that the rate of energy release, hydrogen generation, and cladding 
oxidation from the metal/water reaction shall be calculated using the 
Baker-Just equation.
    In summary, 10 CFR 50.44, 10 CFR 50.46, and 10 CFR part 50, 
appendix K, make no provisions for use of fuel rods clad in a material 
other than Zircaloy or ZIRLO. The licensee has requested the use of a 
limited number of ``lower tin'' ZIRLO clad replacement fuel rods in one 
lead test assembly (LTA) with a tin composition that is less than the 
licensing basis for ZIRLO tin composition, as defined in Westinghouse 
design specifications.

3.0 Discussion

    Pursuant to 10 CFR 50.12, the Commission may, upon application by 
any interested person or upon its own initiative, grant an exemption 
from the requirements of 10 CFR part 50 only if (1) the exemption is 
authorized by law, will not present an undue risk to public health or 
safety, and is consistent with the common defense and security; and (2) 
special circumstances are present. Special circumstances are present if 
application of the regulation is not necessary to achieve the 
underlying purpose of the rule.
    The licensee here requests an exemption in order to use newly 
developed low tin ZIRLO that is an improved version of the ZIRLO 
material, and is not described in WCAP-12610-P-A, ``VANTAGE+ Fuel 
Assembly Reference Core Report,'' which describes the use of ZIRLO clad 
fuel. The staff examined the licensee's rationale to support the 
exemption request(s) and, for the reasons set forth below, concludes 
that the licensee would meet the underlying purpose of 10 CFR 50.44, 
50.46 and part 50, appendix K.
    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 the lower tin ZIRLO (LT-2) cladding are similar in chemical 
composition to zircaloy cladding. Accordingly, 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.
    The underlying purpose of 10 CFR 50.46, and 10 CFR part 50, 
appendix K, is to establish requirements for the calculation of ECCS 
performance. The ECCS performance requirements include peak cladding 
temperature, maximum cladding oxidation, hydrogen generation, and 
coolable geometry. With respect to 10 CFR 50.46, the licensee has 
previously performed a LOCA safety analysis using the approved 
Westinghouse methodology including the Byron Station ECCS Model Safety 
Analysis of Record for LTAs of lower tin ZIRLO (LT-1) cladding. The 
unique features of the LTAs were evaluated for

[[Page 56338]]

effects on the LOCA analysis. The result showed that the Byron Station 
ECCS Model Safety Analysis of Record remained bounding for those LTAs. 
The staff recognizes that the current LTAs will be located at non-
limiting core locations, and the ZIRLO (LT-2) is very similar to the 
approved ZIRLO and the previously exempted ZIRLO (LT-1) in chemical 
composition and mechanical behavior. Accordingly, the currently 
approved methodology for analyzing ECCS performance is acceptable to 
apply for the low tin ZIRLO (LT-2) LTAs, as is further discussed below 
with respect to the Baker-Just equation. As also discussed below, 
results of comparative LOCA calculations with the same plant operating 
parameters will be performed in the reload analysis for Cycle 13 to 
verify that the current ECCS Model Safety Analysis of Record remains 
bounding for these four LTAs for Byron Station Unit 1 Cycle 13.
    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 ZIRLO (LT-2) cladding for determining acceptable fuel 
performance. The underlying intent of this portion of the Appendix K, 
however, is to ensure that analysis of fuel response to LOCAs is 
conservatively calculated. Due to the similarities in the chemical 
composition of the ZIRLO (LT-2) and zircaloy, the application of the 
Baker-Just equation in the analysis of the improved ZIRLO (LT-2) clad 
fuel will conservatively bound all post-LOCA scenarios. Thus, 
application of appendix K, paragraph I.A.5, is not necessary for the 
licensee to achieve the underlying purpose of the rule in these 
circumstance.
    According to the submittal, the licensee will perform reload 
analysis to demonstrate adequate ECCS performance, and show that the 
LTAs do not have a significant impact upon the analysis for Byron 
Station Unit 1. In the Cycle 13 reload analyses, the licensee will 
verify that the predicted peak cladding temperature of the LTAs are 
significantly lower than that predicted for the resident fuel. The 
licensee will also verify that the Baker-Just equation conservatively 
predicts local cladding oxidation of the LTAs of only a few percent. 
Also, the licensee will verify that maximum hydrogen generation is 
unchanged with the inclusion of the LTAs, and the coolable geometry is 
maintained following a LOCA. As such, application of 10 CFR 50.46 and 
10 CFR part 50, appendix K is not necessary to achieve their underlying 
purposes in these circumstances.
    To summarize, based on the previously acceptable performance of the 
LTAs in Byron Station Units 1 and 2, the staff concludes that the 
licensee has demonstrated that the LTAs will perform adequately under 
LOCA conditions, and thus the LTAs are acceptable for operation in 
Byron Station Unit 1 Cycle 13.
    Therefore, application of 10 CFR 50.44, 10 CFR 50.46, and appendix 
K to 10 CFR part 50 is not necessary to achieve their underlying 
purposes and that special circumstances are present. Thus, it is 
acceptable to grant an exemption, pursuant to 10 CFR 50.12(a)(2), from 
the requirements of 10 CFR 50.44, 10 CFR 50.46, and Appendix K to 10 
CFR Part 50 for the irradiation of the lower tin ZIRLO (LT-2) clad fuel 
rods in Byron Station Unit 1 during Cycle 13.

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 Generation Company, LLC, 
an exemption from the requirements of 10 CFR 50.44, 10 CFR 50.46, and 
10 CFR part 50, appendix K, for irradiation of low tin ZIRLO (LT-2) 
clad fuel rods in Byron Station Unit 1 during Cycle 13.
    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 (68 FR 54246).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 22nd day of September, 2003.

    For the Nuclear Regulatory Commission.
Eric J. Leeds,
Deputy Director, Division of Licensing Project Management, Office of 
Nuclear Reactor Regulation.
[FR Doc. 03-24670 Filed 9-29-03; 8:45 am]
BILLING CODE 7590-01-P