[Federal Register Volume 70, Number 20 (Tuesday, February 1, 2005)]
[Notices]
[Pages 5224-5226]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-1772]
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NUCLEAR REGULATORY COMMISSION
[Docket No. 50-395]
South Carolina Electric & Gas Company, Virgil C. Summer Nuclear
Station; Exemption
1.0 Background
The South Carolina Electric & Gas Company (SCE&G, the licensee) is
the holder of the Renewed Facility Operating License No. NPF-12 which
authorizes operation of the Virgil C. Summer Nuclear Station (VSNS).
The license provides, among other things, that the facility is subject
to all rules, regulations, and orders of the Nuclear Regulatory
Commission (NRC or the Commission) now or hereafter in effect.
The facility consists of a pressurized-water reactor located in
Fairfield County in South Carolina.
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) for
reactors fueled with zirconium cladding. Acceptance criteria contained
in 10 CFR 50.46 are for emergency core cooling systems (ECCSs) for
reactors fueled with zircaloy or ZIRLO\TM\ cladding. In addition,
Appendix K to 10 CFR part 50 requires that the Baker-Just equation be
used to predict the rates of energy release, hydrogen concentration,
and cladding oxidation from the metal-water reaction.
In summary, the exemption request relates solely to the specific
types of cladding material specified in these regulations. As written,
the regulations presume the use of zircaloy or ZIRLO\TM\ fuel rod
cladding. Thus, an exemption from the requirements of 10 CFR 50.44, 10
CFR 50.46, and Appendix K to 10 CFR part 50 is needed to irradiate lead
test assemblies (LTAs) consisting of developmental clad alloys at VSNS.
[[Page 5225]]
3.0 Discussion
3.1 Fuel Mechanical Design
Optimized ZIRLO\TM\
Optimized ZIRLO\TM\ has a lower tin content than the licensed
ZIRLO\TM\. 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][rarr][alpha]+[beta] phase transition temperature,
and (5) an improved corrosion resistance. The slight reduction in tin
content will not effect 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,
low tin ZIRLO\TM\ will exhibit many similar material characteristics as
the licensed ZIRLO\TM\. Further, the final annealing of Optimized
ZIRLO\TM\ has been designed to improve mechanical performance.
In the exemption request, SCE&G provides details of the planned
post-irradiation examinations (PIEs) of the LTAs. Examinations include
rod profilometry, rod growth, rod oxidation, and visual inspection. In
response to a request for additional information, the licensee stated
that PIE data, as well as data from other Westinghouse LTA programs,
will be used to ensure existing design models remain valid.
As a result of the PIEs, any negative aspects of the low tin
alloy's performance, including the potential impacts of a 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 LTAs in VSNS
will remain well within the operating experience base and applicable
licensed limits for ZIRLO\TM\.
Utilizing currently approved fuel performance and fuel mechanical
design models and methods, SCE&G and Westinghouse will perform cycle-
specific reload evaluations to ensure that the LTAs satisfy existing
design criteria.
Based upon LTA irradiation experience of similar low tin versions
of ZIRLO\TM\, expected performance due to similar material properties,
and an LTA PIE program aimed at qualifying model predictions, the staff
finds the LTA mechanical design acceptable for VSNS.
3.2 Core Physics and Non-LOCA Safety Analysis
The SCE&G exemption request relates solely to the specific types of
cladding material specified in the regulations. No new or altered
design limits for purposes of 10 CFR part 50, Appendix A, General
Design Criterion 10, ``Reactor Design,'' need to be applied or are
required for this program.
Optimized ZIRLO\TM\
Due to similar material properties, any impact of low tin ZIRLO\TM\
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, SCE&G and Westinghouse
will perform cycle-specific reload evaluations to ensure that the LTAs
satisfy design criteria.
Nuclear design evaluations will ensure that LTAs be placed in
nonlimiting core locations. As such, additional thermal margin to
design limits will be maintained between LTA fuel rods and the hot rod
evaluated in safety analyses. Thermal-hydraulic and non-LOCA
evaluations will confirm that the LTAs are bounded by the current
analysis of record.
Based upon the use of approved models and methods, expected
material performance, and the placement of LTAs in nonlimiting core
locations, the staff finds that the irradiation of up to four LTAs in
VSNS 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.
3.3 Regulatory Evaluation
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 if, (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.
3.3.1 10 CFR 50.44
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 a low tin version of ZIRLO\TM\ cladding are similar in
chemical composition to zircaloy cladding. Metal-water reaction tests
performed by Westinghouse on low tin versions of ZIRLO\TM\ (documented
in Appendix B of Addendum 1 to WCAP-12610-P-A) demonstrate comparable
reaction rates. Accordingly, the 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.
3.3.2 10 CFR 50.46
The underlying purpose of 10 CFR 50.46 is to establish acceptance
criteria for ECCS performance. The applicability of these ECCS
acceptance criteria has been demonstrated by Westinghouse. Ring
compression tests performed by Westinghouse on low tin versions of
ZIRLO\TM\ (documented in Appendix B of Addendum 1 to WCAP-12610-P-A)
demonstrate an acceptable retention of post-LOCA ductility up to 10 CFR
50.46 limits of 2200 [deg]F and 17 percent Equivalent Cladding Reacted.
Utilizing currently approved LOCA models and methods, Westinghouse will
perform cycle-specific reload evaluations prior to use to ensure that
the LTAs satisfy 10 CFR 50.46 acceptance criteria. Therefore, the
exemption to expand the application of 10 CFR 50.46 to include
Optimized ZIRLO\TM\ is acceptable.
3.3.3 10 CFR Part 50, Appendix K
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 LTA cladding for determining acceptable fuel
performance. Metal-water reaction tests performed by Westinghouse on
low tin versions of ZIRLO\TM\ (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 is not necessary for the licensee to achieve its underlying
purpose in these circumstances.
3.3.4 Special Circumstances
In summary, the staff reviewed the licensee's request of proposed
exemption to allow up to four LTAs containing fuel rods, guide thimble
tubes, and instrumentation tubes
[[Page 5226]]
fabricated with Optimized ZIRLO\TM\. Based on the staff's evaluation,
as set forth above, the staff considers that granting the proposed
exemption will not defeat the underlying purpose of 10 CFR 50.44, 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).
3.3.5. Other Standards in 10 CFR 50.12
The staff examined the rest of the licensee's rationale to support
the exemption request, and concluded that the use of Optimized
ZIRLO\TM\ 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
50.44, 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:
The LTA safety evaluation will ensure that these acceptance
criteria [in the Commission's regulations] are met following the
insertion of LTAs containing Optimized ZIRLO\TM\ material. Fuel
assemblies using Optimized ZIRLO\TM\ cladding will be evaluated
using NRC-approved analytical methods and plant specific models to
address the changes in the cladding material properties. The safety
analysis for VSNS is supported by the applicable technical
specification. The VSNS reload cores containing Optimized ZIRLO\TM\
cladding will continue to be operated in accordance with the
operating limits specified in the technical specifications. LTAs
utilizing Optimized ZIRLO\TM\ cladding will be placed in non-
limiting core locations. Thus, the granting of this exemption
request 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 of this exemption. For the reasons set forth in that
section, the staff concludes that Optimized ZIRLO\TM\ may be used as a
cladding material for no more than four LTAs to be placed in
nonlimiting core locations during VSNS's next refueling outage, and
that an exemption from the requirements of 10 CFR 50.44, 10 CFR 50.46,
and 10 CFR part 50, Appendix K does not pose an undue risk to the
public health and safety.
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 SCE&G exemptions from the
requirements of 10 CFR 50.44, 10 CFR 50.46, and 10 CFR part 50,
Appendix K, to allow four LTAs containing fuel rods with Optimized
ZIRLO\TM\ and several different developmental clad alloys.
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 (70 FR 1742).
This exemption is effective upon issuance.
Dated in Rockville, Maryland, this 14th day of January 2005.
For the Nuclear Regulatory Commission.
James E. Lyons,
Deputy Director, Division of Licensing Project Management, Office of
Nuclear Reactor Regulation.
[FR Doc. 05-1772 Filed 1-31-05; 8:45 am]
BILLING CODE 7590-01-P