[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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