[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]
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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