[Federal Register Volume 60, Number 75 (Wednesday, April 19, 1995)]
[Notices]
[Pages 19610-19611]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-9637]
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NUCLEAR REGULATORY COMMISSION
[Docket No. 50-306]
Northern States Power Company (Prairie Island Unit 2); Exemption
I
Northern States Power Company (NSP, the licensee) is the holder of
Facility Operating License No. DPR-60 which authorizes operation of
Prairie Island Nuclear Generating Plant, Unit No. 2. The unit is a
pressurized water reactor (PWR) located in Goodhue County, Minnesota.
The license provides, among other things, that the facility is subject
to all rules, regulations, and orders of the Nuclear Regulatory
Commission (the Commission) now or hereafter in effect.
II
Pursuant to 10 CFR 50.12(a), the NRC may grant exemptions from the
requirements of the regulations (1) which are authorized by law, will
not present an undue risk to the public health and safety, and are
consistent with the common defense and security; and (2) where special
circumstances are present.
Section III.D.1.(a) of Appendix J to 10 CFR Part 50 requires the
performance of three Type A containment integrated leakage rate tests
(ILRTs), at approximately equal intervals during each 10-year service
period of the primary containment. The third test of each set shall be
conducted when the plant is shut down for the 10-year inservice
inspection of the primary containment.
III
By letters dated February 23 and March 3, 1995, NSP requested
temporary relief from the requirement to perform a set of three Type A
tests at approximately equal intervals during each 10-year service
period of the primary containment. The requested exemption would permit
a one-time interval extension of the third Type A test by approximately
24 months (from the 1995 refueling outage, currently scheduled to begin
in May 1995, to the 1997 refueling outage) and would permit the third
Type A test of the second 10-year inservice inspection period to not
correspond with the end of the current American Society of Mechanical
Engineers Boiler and Pressure Vessel Code (ASME Code) inservice
inspection interval.
The licensee's request cites the special circumstances of 10 CFR
50.12, paragraph (a)(2)(ii), as the basis for the exemption. NSP points
out that the existing Type B and C testing programs are not being
modified by this request and will continue to effectively detect
containment leakage caused by the degradation of active containment
isolation components as well as containment penetrations. It has been
the consistent and uniform experience at Prairie Island Nuclear
Generating Plant, Unit No. 2, during the five Type A tests conducted
from 1977 to date, that any significant containment leakage paths are
detected by the Type B and C testing. The Type A test results have only
been confirmatory of the results of the Type B and C test results.
IV
Section III.D.1.(a) of Appendix J to 10 CFR Part 50 states that a
set of three Type A leakage rate tests shall be performed at
approximately equal intervals during each 10-year service period.
The licensee proposes an exemption to this section which would
provide a one-time interval extension for the Type A test by
approximately 24 months. The Commission has determined, for the reasons
discussed below, that pursuant to 10 CFR 50.12(a)(1) this 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. The
Commission further determines that special circumstances, as provided
in 10 CFR 50.12(a)(2)(ii), are present justifying the exemption;
namely, that application of the regulation in the particular
circumstances is not necessary to achieve the underlying purpose of the
rule.
The underlying purpose of the requirement to perform Type A
containment leak rate tests at intervals during the 10-year service
period is to ensure that any potential leakage pathways through the
containment boundary are identified within a time span that prevents
significant degradation from continuing or becoming unknown. The NRC
staff has reviewed the basis and supporting information provided by the
licensee in the exemption request. The NRC staff has noted that the
licensee has a good record of ensuring a leak-tight containment. All
Type A tests have passed with significant margin and the licensee has
noted that the results of the Type A testing have been confirmatory of
the Type B and C tests which will continue to be performed. The
licensee has stated that it will perform the general containment
inspection although it is only required by Appendix J (Section V.A.) to
be performed in conjunction with Type A tests. The NRC staff considers
that these inspections, though limited in scope, provide an important
added level of confidence in the continued integrity of the containment
boundary. The Prairie Island containment vessels are free-standing
steel structures designed for the peak pressure of the design basis
accident and low leakage. A concrete shield building surrounds the
containment vessel, providing a shield building annulus between the two
structures. Penetrations of the containment vessel for piping,
electrical conductors, ducts and access hatches are provided with
double barriers against leakage. The NRC staff also notes that due to
the free-standing design of the containment structure, the vessel shell
and penetrations are accessible for inspection from both inside
containment and outside in the shield building annulus.
The NRC staff has also made use of the information in a draft staff
report, NUREG-1493, ``Performance-Based Containment Leak-Test
Program,'' which provides the technical justification for the present
Appendix J rulemaking effort which also includes a 10-year test
interval for Type A tests. The integrated leakage rate test, or Type A
test, measures overall containment leakage. However, operating
experience [[Page 19611]] with all types of containments used in this
country demonstrates that essentially all containment leakage can be
detected by local leakage rate tests (Type B and C). According to
results given in NUREG-1493, out of 180 ILRT reports covering 110
individual reactors and approximately 770 years of operating history,
only 5 ILRT failures were found which local leakage rate testing could
not detect. This is 3% of all failures. This study agrees well with
previous NRC staff studies which show that Type B and C testing can
detect a very large percentage of containment leaks. The Prairie Island
Nuclear Generating Plant, Unit No. 2, experience has also been
consistent with these results.
The Nuclear Management and Resources Council (NUMARC), now the
Nuclear Energy Institute (NEI), collected and provided the NRC staff
with summaries of data to assist in the Appendix J rulemaking effort.
NUMARC collected results of 144 ILRTs from 33 units; 23 ILRTs exceeded
1La. Of these, only nine were not type B or C leakage penalties.
The NEI data also added another perspective. The NEI data show that in
about one-third of the cases exceeding allowable leakage, the as-found
leakage was less than 2La; in one case the leakage was found to be
approximately 2La; in one case the as-found leakage was less than
3La; one case approached 10La; and in one case the leakage
was found to be approximately 21La. For about half of the failed
ILRTs the as-found leakage was not quantified. These data show that,
for those ILRTs for which the leakage was quantified, the leakage
values are small in comparison to the leakage value at which the risk
to the public starts to increase over the value of risk corresponding
to La (approximately 200La, as discussed in NUREG-1493).
Therefore, based on these considerations, it is unlikely that an
extension of one cycle for the performance of the Appendix J, Type A
test at Prairie Island Nuclear Generating Plant, Unit No. 2, would
result in significant degradation of the overall containment integrity.
As a result, the application of the regulation in these particular
circumstances is not necessary to achieve the underlying purpose of the
rule. Based on the generic and plant-specific data, the NRC staff finds
the basis for the licensee's proposed one-time schedular exemption to
allow an extension of one cycle for the performance of the Appendix J,
Type A test, provided that the general containment inspection is
performed, to be acceptable.
Pursuant to 10 CFR 51.32, the Commission has determined that
granting this exemption will not have a significant effect on the
quality of the human environment (60 FR 18428).
This exemption is effective upon issuance.
Dated at Rockville, Maryland, this 12th day of April 1995.
For the Nuclear Regulatory Commission.
Elinor G. Adensam,
Acting Director, Division of Reactor Projects III/IV, Office of Nuclear
Reactor Regulation.
[FR Doc. 95-9637 Filed 4-18-95; 8:45 am]
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