[Federal Register Volume 62, Number 94 (Thursday, May 15, 1997)]
[Notices]
[Pages 26828-26829]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-12737]
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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-338 and 50-339]
Virginia Electric and Power Company; North Anna Power Station,
Units 1 and 2; Exemption
I
Virginia Electric and Power Company (the licensee) is the holder of
Facility Operating License Nos. NPF-4 and NPF-7, which authorize
operation of North Anna Power Station, Unit Nos. 1 and 2 (NPS1&2). The
licenses provide, among other things, that the licensee be subject to
all rules, regulations, and Orders of the Nuclear Regulatory Commission
(the Commission) now or hereafter in effect.
The facility consists of two pressurized water reactors at the
licensee's site located in Louisa County, Virginia.
II
By letter dated September 4, 1996, as supplemented February 3,
1997, the licensee requested an exemption to 10 CFR 50.44, 10 CFR
50.46, and Appendix K to 10 CFR Part 50 that would enable the use of
four demonstration fuel assemblies for three cycles, with the initial
irradiation planned for North Anna 1 Cycle 13. Irradiation of these
four fuel assemblies may occur in either North Anna Unit 1 or North
Anna Unit 2, or a combination of the two units, subject to the
following constraints:
(1) The assemblies are not to be irradiated for more than three
full operating cycles, and
(2) The maximum rod average burnup of any fuel rod in these
assemblies shall not exceed the North Anna Units 1 and 2 lead rod
burnup restriction of 60,000 megawatt days per metric ton uranium (MWD/
MTU).
The regulations cited above refer to pressurized water reactors
fueled with uranium oxide pellets within cylindrical zircaloy or ZIRLO
cladding. The four demonstration assemblies to be used during these
fuel cycles contain fuel rods with zirconium-based claddings that are
not chemically identical to zircaloy or ZIRLO.
Since 10 CFR 50.46 and Appendix K to 10 CFR Part 50 identify
requirements for calculating emergency core cooling system (ECCS)
performance for reactors containing fuel with zircaloy or ZIRLO
cladding, and 10 CFR 50.44 relates to the generation of hydrogen gas
from a metal-water reaction with reactor fuel having zircaloy or ZIRLO
cladding, an exemption is needed to place the four demonstration
assemblies containing fuel rods with advanced zirconium-based cladding
in the core.
III
Title 10 of the Code of Federal Regulations at 50.12(a)(2)(ii)
enables the Commission to grant an exemption from the requirements of
Part 50 when special circumstances are present such that 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
and 10 CFR Part 50, Appendix K, is to establish requirements for the
calculation of ECCS performance. The licensee has performed a
calculation demonstrating adequate ECCS performance for NPS1&2 and has
shown that the four demonstration assemblies do not have a significant
impact on that previous calculation. The peak cladding temperature of
the demonstration
[[Page 26829]]
assemblies was significantly lower than the resident Westinghouse fuel.
Using the Baker-Just equation, the local cladding oxidation of the
demonstration assemblies was less than 5%. Also, the maximum hydrogen
generation was unchanged with the inclusion of four demonstration
assemblies. Therefore, the coolable geometry was maintained following a
loss-of-coolant accident (LOCA).
Paragraph I.A.5 of Appendix K to 10 CFR part 50 states that the
rates of energy release, 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 advanced zirconium-based alloys for determining acceptable
fuel performance. The underlying intent of this portion of the
Appendix, however, is to ensure that analysis of fuel response to LOCAs
is conservatively calculated. Due to the similarities in the
composition of the advanced zirconium-based alloys and Zircaloy/ZIRLO,
the application of the Baker-Just equation in the analysis of advanced
zirconium-based clad fuel will conservatively bound all post-LOCA
scenarios. Thus, the underlying purpose of the rule will be met. Thus,
special circumstances exist to grant an exemption from Appendix K to 10
CFR part 50 that would allow the licensee to apply the Baker-Just
equation to advanced zirconium-based alloys. Only LOCA methods approved
by NRC were used to perform the calculations which demonstrated
adequate safety performance of ECCS systems. These include: (1) RSG
LOCA-B&W LOCA evaluation model, (BAW 10168, Rev. 3), (2) RELAP5/MOD2-
B&W code, (BAW 10164, Rev. 3), (3) the BEACH implementation of RELAP 5,
(BAW-10166, Rev. 4), and (4) REFLOD3B (BAW-10171-PA, Rev. 3). The
licensee documented calculations which demonstrate that existing North
Anna calculations based on the current fuel design conservatively bound
the LOCA performance of the demonstration assemblies as calculated by
NRC-approved methods. Results of comparative LOCA calculations with the
same plant operating parameters demonstrated that the LOCA
calculational methods used are acceptable for the demonstration
assemblies at North Anna. As such, the licensee has achieved the
underlying purpose of 10 CFR 50.46 and 10 CFR 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
postulated LOCA accident. 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
small number of fuel rods in the four demonstration assemblies
containing advanced zirconium-based claddings in conjunction with the
chemical similarity of the advanced claddings to zircaloy and ZIRLO
ensures that previous calculations of hydrogen production resulting
from a metal-water reaction would not be significantly changed. As
such, the licensee has achieved the underlying purpose of 10 CFR 50.44.
The four demonstration assemblies that will be placed in the NPS-1
reactor during Cycles 13, 14, and 15, or in NPS-2 under constraints
previously described, meet the same design bases as the fuel in the
reactor during previous cycles. No safety limits or setpoints have been
altered as a result of the use of the four demonstration assemblies.
The demonstration assemblies will be placed in core locations that will
not experience limiting power peaking during the aforementioned
operating cycles. The advanced claddings have been tested for corrosion
resistance, tensile and burst strength, and creep characteristics. The
results indicate that the advanced claddings are safe for reactor
service.
IV
For the foregoing reasons, the NRC staff has concluded that the use
of the four demonstration assemblies in the NPS-1 reactor during Cycles
13, 14, and 15, or in NPS-2 under constraints previously described,
will not present an undue risk to public health and safety and is
consistent with the common defense and security. The NRC staff has
determined that there are special circumstances present as specified in
10 CFR 50.12(a)(2)(ii) such that application of 10 CFR 50.46, 10 CFR
Part 50, Appendix K, and 10 CFR 50.44 to only apply to zircaloy or
ZIRLO is not necessary in order to achieve the underlying purpose of
these regulations.
Accordingly, the Commission has determined that pursuant to 10 CFR
50.12, an exemption is authorized by law and will not endanger life or
property or common defense and security and is otherwise in the public
interest, and hereby grants Virginia Electric and Power Company an
exemption from the requirements of 10 CFR 50.44, 10 CFR 50.46, and
Appendix K to 10 CFR Part 50 in that explicit consideration of the
advanced zirconium-based clad fuel present within the four
demonstration assemblies is not required in order to be in compliance
with these regulations. This exemption applies only to the four
demonstration assemblies for the three total operating cycles for which
these assemblies will be in the NPS-1 and NPS-2 reactor cores under the
constraints stated in Section II above.
Pursuant to 10 CFR 51.32, the Commission has determined that the
granting of this exemption will have no significant impact on the
quality of the human environment (62 FR 23504).
This exemption is effective upon issuance.
Dated at Rockville, Maryland this 9th day of May 1997.
For the Nuclear Regulatory Commission.
Samuel J. Collins,
Director, Office of Nuclear Reactor Regulation.
[FR Doc. 97-12737 Filed 5-14-97; 8:45 am]
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