[Federal Register Volume 69, Number 212 (Wednesday, November 3, 2004)]
[Notices]
[Pages 64113-64115]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-24493]
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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-498 and 50-499]
STP Nuclear Operating Company; South Texas Project, Unit No. 1
and 2; Exemption
1.0 Background
The STP Nuclear Operating Company (STPNOC or the licensee) is the
holder of Facility Operating License Nos. NPF-76 and NPF-80, which
authorize operation of South Texas Project (STP), Units 1 and 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, the Commission) now or hereafter in
effect.
The facility consists of two pressurized water reactors located in
Matagorda County, Texas.
2.0 Request/Action
Title 10 of the Code of Federal Regulations (10 CFR) part 50,
section 50.44, specifies requirements for the control of hydrogen gas
generated after a postulated loss-of-coolant accident (LOCA). Section
50.46 of 10 CFR contains acceptance criteria for the emergency core
cooling system (ECCS) for reactors with zircaloy or ZIRLO\TM\ clad
fuel. Appendix K to 10 CFR part 50 requires, among other things, that
the Baker-Just equation be used to predict the rates of energy release,
hydrogen concentration, and cladding oxidation from the metal-water
reaction. Of these three regulations (10 CFR 50.44, 50.46, and Appendix
K to 10 CFR part 50), 10 CFR 50.44 is the only one that has undergone
considerable changes relative to its previous version, changes that
became effective on January 1, 2004.
[[Page 64114]]
Prior to that date, 10 CFR 50.44 specified requirements for the control
of hydrogen gas generated after a postulated LOCA for reactors with
zircaloy or ZIRLO\TM\ clad fuel. The new regulation in 10 CFR 50.44 no
longer identifies zircaloy or ZIRLO\TM\ as requisite fuel cladding, nor
does it identify the LOCA or 10 CFR 50.46 as bases. Because the intent
of this exemption request relates solely to the specific types of
cladding material specified in these regulations, no exemption is
needed from the requirements of 10 CFR 50.44. As written, zircaloy or
ZIRLO\TM\ cladding continues to be the requisite fuel cladding that is
explicitly identified in 10 CFR 50.46 and Appendix K to 10 CFR part 50.
Therefore, an exemption from the requirements of 10 CFR 50.46 and
Appendix K to 10 CFR part 50 is needed in order to irradiate up to
eight lead test assemblies (LTAs) comprised of low tin (Optimized)
ZIRLO\TM\ at the STP, Units 1 and/or 2.
In summary, in a letter dated May 27, 2004 (Reference 1)\1\, as
supplemented by letter dated August 23, 2004 (Reference 2)\2\, STPNOC
requested an exemption from 10 CFR 50.44, ``Standards for Combustible
Gas Control System in Light-Water-Cooled Power Reactors``; 10 CFR
50.46, ``Acceptance Criteria for Emergency Core Cooling Systems for
Light-Water Nuclear Power Reactors''; and Appendix K to 10 CFR part 50,
``ECCS Evaluation Models,'' which would allow irradiation of up to
eight LTAs containing fuel rods, guide tubes, and instrumentation tubes
fabricated with Optimized ZIRLOTM. Optimized
ZIRLOTM is not within the licensing basis of the approved
ZIRLOTM as described in WCAP-12610-P-A (Reference 3)\3\ for
STP, Units 1 and 2. Irradiation of up to eight Optimized
ZIRLOTM LTAs in STP Units 1 and/or 2 will provide data on
fuel and material performance to support future licensing activities.
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\1\ Letter from T.J. Jordan (South Texas) to U.S. Nuclear
Regulatory Commission, ``The South Texas Project, Units 1 and 2
Request for Exemption Pursuant to 10 CFR 50.12 Exemption to the Fuel
Cladding Material Specified in 10 CFR 50.44, 10 CFR 50.46, and 10
CFR 50 Appendix K,'' Docket Nos. STN 50-498 and STN 50-499, May 27,
2004, ADAMS Accession No. ML041590200.
\2\ Letter from T.J. Jordan (South Texas) to U.S. Nuclear
Regulatory Commission, ``The South Texas Project, Units 1 and 2
Response to Request for Additional Information Regarding Exemption
to Use a Low Tin Cladding,'' Docket Nos. STN 50-498 and STN 50-499,
August 23, 2004, ADAMS Accession No. ML042430272.
\3\ Westinghouse Electric Company Topical Report, WCAP-12610-P-
A, ``VANTAGE+ Fuel Assembly Reference Core Report,'' April 1995.
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3.0 Discussion
The staff has previously reviewed exemption requests for LTA
programs comprised of fuel with Optimized ZIRLOTM cladding
material manufactured by Westinghouse Electric Company (Westinghouse).
Exemptions from 10 CFR 50.46 and Appendix K to 10 CFR part 50 for use
of Optimized ZIRLOTM have been issued by the NRC staff for
Millstone, Unit 3 (Reference 4)\4\, Catawba Station (Reference 5)\5\,
and Calvert Cliffs, Unit 2 (Reference 6)\6\.
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\4\ Letter from U.S. Nuclear Regulatory Commission to D.A.
Christian (Dominion), ``Millstone Power Station, Unit No. 3,
Exemption from the Requirements of Title 10 of the Code of Federal
Regulations (10 CFR) Part 50.44, 10 CFR 50.46, and 10 CFR part 50,
Appendix K,'' Docket No. 50-423, February 11, 2004, ADAMS Accession
No. ML040070238.
\5\ Letter from U.S. Nuclear Regulatory Commission to D.M. Jamil
(Duke), ``Catawba Nuclear Station, Units 1 and 2 RE: Exemption from
the Requirements of 10 CFR 50.44, 10 CFR 50.46, and 10 CFR 50
Appendix K,'' August 4, 2003, ADAMS Accession No. ML032060473.
\6\ Letter from U.S. Nuclear Regulatory Commission to P.E. Katz
(Constellation), ``Calvert Cliffs Nuclear Power Plant, Unit No. 2,''
December 3, 2002, ADAMS Accession No. ML022540002.
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3.1 Material Evaluation
3.1.1 Fuel Mechanical Design
Tin is a solid solution strengthener and [alpha]-phase stabilizer
present entirely in the base [alpha]-phase zirconium crystalline
structure. Potential impacts of a reduced tin content on material
properties include (1) a reduced tensile strength, (2) an increased
thermal creep rate, (3) an increased irradiation growth rate, (4) a
reduced [alpha][harr][alpha]+[beta] phase transition temperature, and
(5) an improved corrosion resistance. The slight reduction in tin
content will not affect the size, shape, or distribution of any second
phase or inter-metallic precipitates nor the overall microstructure of
this developmental zirconium alloy. With a consistent microstructure,
Optimized ZIRLOTM will exhibit material characteristics very
similar to that of ZIRLOTM.
In Reference 2, the licensee provided information concerning their
post-irradiation examination plan. In Reference 2, the licensee stated
that their plan would be consistent with those of the other Optimized
ZIRLOTM irradiation programs currently underway. As with the
post-irradiation examinations involved in the other irradiation
programs, the detailed examinations in the licensee's Optimized
ZIRLOTM irradiation program will be based on the fuel duty,
cycle performance, need for specific information, and time available on
site during refueling outages. The measured parameters will include rod
profilometry, rod wear, assembly and rod growth, assembly bow, grid
cell dimensions, and oxide thickness. As a result of these post-
irradiation examinations, any negative aspects of the Optimized
ZIRLOTM performance, including the potential impacts of
reduced tin content identified above, will be identified and resolved.
Furthermore, significant deviations from model predictions will be
reconciled.
The fuel rod burnup and fuel duty experienced by the Optimized
ZIRLOTM LTAs in STP, Units 1 and 2, will remain well within
the operating experience base and applicable licensed limits for
ZIRLOTM.
Utilizing currently approved fuel performance and fuel mechanical
design models and methods, the STP, Units 1 and 2, and Westinghouse
will perform cycle-specific reload evaluations to ensure that the
Optimized ZIRLOTM LTAs satisfy design criteria.
Based upon the irradiation experience of LTAs with
ZIRLOTM of a similar low tin content, expected performance
due to similar material properties, and an extensive LTA post-
irradiation examination program aimed at qualifying model predictions,
the NRC staff finds the Optimized ZIRLOTM LTA mechanical
design acceptable for STP, Units 1 and 2.
3.1.2 Core Physics and Non-LOCA Safety Analysis
The STP, Units 1 and 2, exemption request relates solely to the
specific types of cladding material specified in the regulations. Due
to similar material properties, any impact of Optimized
ZIRLOTM on the safety analysis models and methods is
expected to be minimal. Utilizing currently approved core physics, core
thermal-hydraulics, and non-LOCA safety analysis models and methods,
the licensee and Westinghouse will perform cycle-specific reload
evaluations to ensure that the LTAs satisfy design criteria. Fuel
management guidelines will require that LTAs be placed in non-limiting
core locations. In Reference 2, the licensee described how the power
peaking margin would be used to ensure that LTAs will not be limiting.
Based upon the use of approved models and methods, expected
material performance, and the placement of LTAs in non-limiting core
locations, the NRC staff finds that the irradiation of up to eight
Optimized ZIRLOTM LTAs in STP, Units 1 and 2, 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
[[Page 64115]]
promote consequences beyond those currently analyzed.
3.2 ECCS Performance and Exemptions
Pursuant to 10 CFR 50.12, the Commission may, upon application by
any interested person or 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) special
circumstances are present. Special circumstances are present if
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 is to establish acceptance
criteria for ECCS performance. In Addendum 1 to WCAP-12610-P-A
(Reference 7)\7\, Westinghouse demonstrates that the material
properties of Optimized ZIRLOTM are similar to those of the
currently approved ZIRLOTM cladding and that the ECCS
acceptance criteria for ZIRLOTM clad fuel are also
applicable to fuel with Optimized ZIRLOTM cladding. Ring
compression tests performed by Westinghouse on Optimized
ZIRLOTM demonstrate an acceptable retention of ductility up
to 10 CFR 50.46 limits of 2200 [deg]F peak cladding temperature and 17
percent total oxidation. Utilizing currently approved LOCA models and
methods, Westinghouse will perform cycle-specific reload evaluations to
ensure that the Optimized ZIRLOTM LTAs satisfy 10 CFR 50.46
acceptance criteria.
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\7\ Westinghouse Electric Company Topical Report, Addendum 1 to
WCAP-12610-P-A and CENPD-404-P-A, ``Optimized ZIRLO'', February
2003.
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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 Optimized ZIRLOTM LTA cladding for
determining acceptable fuel performance. Metal-water reaction tests
performed by Westinghouse on Optimized ZIRLOTM (documented
in Appendix B of Addendum 1 to WCAP-12610-P-A) demonstrate conservative
reaction rates relative to the Baker-Just equation. Thus, application
of Appendix K, Paragraph I.A.5, in these circumstances, is not
necessary for the licensee to achieve the underlying purpose of the
regulation.
Based upon the results of metal-water reaction tests and ring-
compression tests, which ensure the applicability of ECCS models and
acceptance criteria and the use of approved LOCA models to ensure that
the Optimized ZIRLOTM LTAs satisfy 10 CFR 50.46 acceptance
criteria, the NRC staff finds it acceptable to grant an exemption from
the requirements of 10 CFR 50.46 and Appendix K to 10 CFR part 50 for
the use of up to eight LTAs in STP, Units 1 and 2.
3.3 Special Circumstances
In summary, the NRC staff has reviewed the licensee's request for
an exemption to allow up to eight LTAs containing fuel rods, guide
thimble tubes, and instrumentation tubes fabricated with Optimized
ZIRLOTM to be used in STP, Units 1 and 2. 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, or Appendix K to 10 CFR part 50. Accordingly, special
circumstances, are present pursuant to 10 CFR 50.12(a)(2)(ii).
3.4 Other Standards in 10 CFR 50.12
The NRC staff reviewed information provided by the licensee in
References 1 and 2 to support the exemption request, and concluded that
the use of Optimized ZIRLOTM 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
50.46 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 by the licensee in Reference 1:
The lead test assembly safety evaluation will ensure that these
acceptance criteria are met following insertion of the assemblies
containing Optimized ZIRLOTM material. Fuel assemblies
using Optimized ZIRLOTM cladding will be evaluated using
NRC-approved analytical methods and will address the changes in the
cladding material properties. The safety analysis for the South
Texas Project is supported by the applicable technical
specifications. The South Texas Project reload cores containing
Optimized ZIRLOTM cladding will continue to be operated
in accordance with the operating limits specified in the technical
specifications. Lead test assemblies using Optimized
ZIRLOTM 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 and 3.2 of this Exemption. For the reasons set forth in
Sections 3.1 and 3.2, the NRC staff concludes that Optimized
ZIRLOTM may be used as a cladding material for up to eight
LTAs to be placed in non-limiting core locations in STP, Units 1 and 2,
and that an exemption from the requirements of 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 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 STPNOC an exemption from the
requirements of 10 CFR part 50, Appendix K and Section 50.46, for the
use of up to eight LTAs containing Optimized ZIRLOTM in STP,
Units 1 and 2, up to a lead rod average burnup of 62,000 megawatt days
per metric ton of uranium.
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 (69 FR 45352).
This exemption is effective upon issuance.
For the Nuclear Regulatory Commission.
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear
Reactor Regulation.
[FR Doc. 04-24493 Filed 11-2-04; 8:45 am]
BILLING CODE 7590-01-P