ML20087H033
| ML20087H033 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/12/1995 |
| From: | Adensam E NRC (Affiliation Not Assigned) |
| To: | NORTHERN STATES POWER CO. |
| Shared Package | |
| ML20087H036 | List: |
| References | |
| NUDOCS 9504180179 | |
| Download: ML20087H033 (6) | |
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
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) Docket No 50-306 Northern States Power Company
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(Prairie Island Unit 2)
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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.l.(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.
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.. 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 1sland 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.
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Section'I!!.D.I.(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.
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..The licensee proposes an exemption to this.section which would provide _a l
1 one-time interval extensiori for the Type' A test by approximately'24 months.
I 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 i
i 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 a
the exemption; namely, that' application of the regulation in the particular circumstances is not necessary to achieve th underlying purpose of the rule.
1 The underlying purpose of the requirement to perform Type A containment i
leak rate' tests at intervals during the 10-year service period is to' en'sure l
that any potential leakage pathways through the containment boundary are j
l identified within a time span that prevents significant degra'dation from-i continuing or becoming unknown. The NRC-staff has reviewed the basi: and-supporting information provided by the licensee in the exemption request.
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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 j
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 I
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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 I
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-t 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 i
provided with double barriers against leakage.
The NRC staff also notes that-v
.i due to the free-standing design of the containment structure, the vessel shell i
and penetratMns are-accessible for inspection from both inside containment i
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
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provides the technical justification for the present Appendix-J rulemaking effort which also includes a 10-year test interval-for Type A tests. The-j integrated leakage rate test, or Type A test, measures overall containment leakage.
However, operating experienew 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 con'tainment l
leaks. The Prait ie' Island Nuclear Generating Plant, Unit No. 2, experience 5
hn 4h o been consistent with these results.
ihe doclear 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 IL,.
Of these, only nine were i
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- p 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 2L,; in one case the leakage was found to be approximately 2L,; in one case the as-found leakage was less than 3L,; one case approached 10L,;' and in one case the leakage was found to be approximately 21L,.
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 L, ' approximately 200L,, as discussed in
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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
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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.
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Pursuant,to 10 CFR 51.32,'the! Commission has determined that granting this
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exemptioniwill not have'a1significant effect on the quality of the human L-x g. 7_. w s-j environment.{(60 F,R 18428).
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,~c This' exemption'isieffectiv'e! upon, issuance.. "
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.FOR THE NUCLEAR REGULATORY COMMISSION
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', Original signed by
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Elinor G. Adensam, Acting Director l
Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Dated at Rockville, Maryland, 4
this12thday of April 1995 i
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- See previous concurrence
~ DOCUMENT NAME: G:\\WPDOCS\\WPDOCS\\ PRAIRIE \\PI91634.EXM Ta seesive e sepy of thle deem indlesee in the hem: "C* = Copy without ettechment/ enclosure "E' = Copy with ettechment/ enclosure, "N* = No copy 0FFICE LA:PD31 [ E (A)PM:PD31 [ E D:PD31 l C/ *BC:SCSB l E
- 0GC-lE (A)JPARJ% l NAME-CJamers(it fCThomasr:Ag CCarpenter RBarrett EHoller EAdepsam DATE 4/ 5 /9517 4/ f/95 ~'
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