[Federal Register Volume 68, Number 150 (Tuesday, August 5, 2003)]
[Notices]
[Pages 46238-46239]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-19886]
[[Page 46238]]
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
[Docket No. 50-328]
Tennessee Valley Authority, Sequoyah Nuclear Plant, Unit 2;
Exemption
1.0 Background
Tennessee Valley Authority (TVA, the licensee) is the holder of
Facility Operating License No. DRP-79 which authorizes operation of
Sequoyah Nuclear Power Station, Unit 2 (SQN2). The license provides,
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 a pressurized water-reactor located on
TVA's Sequoyah site, which is located in Hamilton County, Tennessee.
2.0 Request/Action
Title 10 of the Code of Federal Regulations (10 CFR), part 50,
appendix G, which is invoked by 10 CFR 50.60, requires that pressure-
temperature (P-T) limits be established for reactor pressure vessels
(RPVs) during normal operating and hydrostatic or leak rate testing
conditions. Specifically, appendix G to 10 CFR part 50 states that
``[t]he appropriate requirements on . . . the pressure-temperature
limits and minimum permissible temperature must be met for all
conditions,'' and ``[t]he pressure-temperature limits identified as
`ASME Appendix G limits' . . . require that the limits must be at least
as conservative as limits obtained by following the methods of analysis
and the margins of safety of Appendix G of Section XI of the ASME
Code.'' Appendix G of 10 CFR part 50 also specifies that the Editions
and Addenda of the ASME Boiler and Pressure Vessel (B&PV) Code which
are incorporated by reference in 10 CFR 50.55a apply to the
requirements in appendix G to 10 CFR part 50. The NRC endorsed Editions
and Addenda of the ASME B&PV Code through the 1998 Edition and 2000
Addenda. However, TVA has currently incorporated the 1995 Edition
through the 1996 Addenda of the ASME B&PV Code into the SQN2 licensing
basis for defining the ASME B&PV Code requirements which apply to the
unit's ASME B&PV Code, Section XI program. Hence, with respect to the
statements from appendix G to 10 CFR part 50 referenced above, it is
the 1995 Edition through 1996 Addenda of ASME B&PV Code, Section XI,
Appendix G which apply for SQN2. Finally, 10 CFR 50.60(b) states that,
``[p]roposed alternatives to the described requirements in [Appendix G]
of this part or portions thereof may be used when an exemption is
granted by the Commission under [10 CFR 50.12].''
TVA requested in its submittal dated September 6, 2002, as
supplemented by letters dated December 19, 2002, and June 24, 2003,
that the staff exempt SQN2 from application of specific requirements of
appendix G to 10 CFR part 50, and substitute use of ASME B&PV Code Case
N-640. ASME B&PV Code Case N-640 permits the use of an alternate
reference fracture toughness curve for RPV materials for use in
determining the P-T limits. The exemption request is consistent with,
and needed to support, a SQN2 license amendment request that was
submitted on June 5, 2003, to modify the P-T limit curves in the
facility's Technical Specifications (TS). The SQN2 license amendment
request will revise the P-T limits for heatup, cooldown, and inservice
test limitations for the reactor coolant system (RCS) to 32 effective
full power years of operation.
Code Case N-640
The licensee has proposed an exemption to allow use of ASME Code
Case N-640 in conjunction with ASME Section XI, Appendix G, 10 CFR
50.60(a) and 10 CFR part 50, appendix G, to establish P-T limits for
the SQN2 RPV. The revised P-T limits have been developed using the
lower bound KIC fracture toughness curve shown in ASME
Section XI, Appendix A, Figure A-2200-1, in lieu of the lower bound
KIA fracture toughness curve of ASME Section XI, Appendix G,
Figure G-2210-1, as the basis fracture toughness curve for defining the
SQN2 P-T limits. The other margins involved with the ASME Section XI,
Appendix G process of determining P-T limit curves remain unchanged.
Use of the KIC curve as the basis fracture toughness
curve for the development of P-T operating limits is more technically
correct than use of the KIA curve. The KIC curve
appropriately implements the use of a relationship based on static
initiation fracture toughness behavior to evaluate the controlled
heatup and cooldown process of an RPV, whereas the KIA
fracture toughness curve codified into Appendix G to Section XI of the
ASME Code was developed from more conservative crack arrest and dynamic
fracture toughness test data. The application of the KIA
fracture toughness curve was initially codified in Appendix G to
Section XI of the ASME Code in 1974 to provide a conservative
representation of RPV material fracture toughness. This initial
conservatism was necessary due to the limited knowledge of RPV material
behavior in 1974. However, additional knowledge has been gained about
RPV materials which demonstrates that the lower bound on fracture
toughness provided by the KIA fracture toughness curve is
well beyond the margin of safety required to protect the public health
and safety from potential RPV brittle failure. Application of the
provisions of ASME Code Case N-640 will result in the implementation of
P-T limit curves having sufficient margin to ensure that, when
stressed, the reactor pressure vessel will behave in a nonbrittle
manner and that the probability of rapidly propagating brittle fracture
is extremely low.
In addition, P-T limit curves based on the KIC fracture
toughness curve will enhance overall plant safety by opening the P-T
operating window with the greatest safety benefit in the region of low
temperature operations. The operating window through which the operator
heats up and cools down the RCS is determined by the difference between
the maximum allowable pressure determined by Appendix G of ASME Section
XI, and the minimum required pressure for the reactor coolant pump
seals adjusted for instrument uncertainties. A narrow operating window
could potentially have an adverse safety impact by increasing the
possibility of inadvertent overpressure protection system actuation due
to pressure surges associated with normal plant evolutions such as RCS
pump starts or swapping operating charging pumps with the RCS in a
water-solid condition.
Therefore, the licensee concluded that these considerations were
special circumstances pursuant to 10 CFR 50.12(a)(2)(ii), and supported
the requested exemption to utilize the provisions of ASME B&PV Code
Case N-640 in the development of SQN2 RPV P-T limit curves.
The NRC staff has reviewed the exemption request submitted by TVA
and has concluded that an exemption should be granted to permit the
licensee to utilize the provisions of ASME B&PV Code Case N-640 for the
purpose of developing SQN2 RPV P-T limit curves. The NRC staff agrees
that special circumstances pursuant to 10 CFR 50.12(a)(2)(ii),
``[a]pplication 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,'' exist. The NRC staff
concurs that the licensee may acceptably apply the provisions of
[[Page 46239]]
ASME Code Case N-640 to relax the requirements found in the 1995
Edition through 1996 Addenda of the ASME B&PV Code, Section XI,
Appendix G, while maintaining, pursuant to 10 CFR50.12(a)(2)(ii), the
underlying purpose of the ASME B&PV Code and the NRC regulations to
ensure that adequate margins of safety exist to protect the RCS from
the potential for brittle failure.
3.0 Discussion
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, 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) when special circumstances are present. The NRC staff accepts the
licensee's determination that an exemption would be required to approve
the use of ASME B&PV Code Case N-640. The NRC staff concluded that the
use of ASME B&PV Code Case N-640 would meet the underlying intent of
appendix G to 10 CFR part 50. Based upon a consideration of the
conservatism that is explicitly incorporated into the methodologies of
appendix G to 10 CFR part 50, the staff concluded that application of
ASME Code Case N-640 as described would provide an adequate margin of
safety against brittle failure of the RPV. This is also consistent with
the determination that the staff has reached for other licensees under
similar conditions based on the same considerations. Therefore, the
staff concludes that requesting the exemption under the special
circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate and that the
methodology of Code Case N-640 may be used to revise the P-T limits for
the SQN2 RPV.
4.0 Conclusion
Accordingly, the Commission has determined that, pursuant to 10 CFR
50.12(a), the exemption is authorized by law, will not endanger life or
property or common defense and security. Also, special circumstances
are present. Therefore, the Commission hereby grants Tennessee Valley
Authority an exemption from the requirements of appendix G to 10 CFR
part 50 for the development of P-T limit curves for the SQN2 RPV.
Pursuant to 10 CFR 51.32, the Commission has determined that the
granting of this exemption will not result in any significant effect on
the quality of the human environment (68 FR 44550).
This exemption is effective upon issuance.
Dated at Rockville, Maryland, this 30th Day of July 2003.
For The Nuclear Regulatory Commission.
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear
Reactor Regulation.
[FR Doc. 03-19886 Filed 8-4-03; 8:45 am]
BILLING CODE 7590-01-P