ML20205A841
| ML20205A841 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/21/1988 |
| From: | Holahan G Office of Nuclear Reactor Regulation |
| To: | NORTHERN STATES POWER CO. |
| Shared Package | |
| ML20205A848 | List: |
| References | |
| NUDOCS 8810260112 | |
| Download: ML20205A841 (6) | |
Text
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D 7590-01 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
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LORTHERN STATES POWER
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Docket No. 50-263 COMPANY
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(Monticello Nuclear
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Generating Plant)
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EXEMPTION I.
The Northern States Power Company (NSP, the licensee) is the holder of Facility Operating License No. DPR-22, which authorizes operation of the Monticello Nuclear Generating Plant (Monticello) at a steady-state power level not in excess of 1670 megawatts thermal.
The plant is a boiling water reactor located at the licensee's site in Wright County, Minnesota.
The license provides, among other things, that Monticello is subject to all rules, regulations, and ordsrs of the Nuclear Regulatory Commission (tne Commission) now or hereafter in effect.
II.
if The Code of Federal Regulations, 10 CFR 50.54(o), spect'ies that primary reactor containments for water-cooled powcr reactors shall comply with Appendix J, "Primary Reactor Containment Leakape Testing for Water-Cooled Power Reactors." Paragraph II'.. A.3 of Appendix J incorporates by reference the Americtn National Standard ANSI N45.4-1972, "Leakage Rate Testing of Containment Structures for Nuclear Reactors." This standard requires that containment leakage rate calculations for containment intc; rated leakage rate es10260112 8s:021 ADOCKOi/00gg3 DR
tests (CILRTS) be perforned using either the Point-to-Point method or Total Tine method.
Further adyrnces in leakage rate testing technology have provided improved test nethods, including a newer method of evaluating test data called the Pass Point method. This Mass Point nethod was incorporated in a newer standard, ANSI /ANS-56.8-1981, "Containment System Leakage Testing Requirements" (revised 1987) and in fact has been accepted by the Ccmmission's staff as an inproved alternative cethod of calculating containnent leakage rates. However, a strict interpretation cf the specific wording of App,ndix J III.A.3, by referencing only the older ANSI standard, precludes use of the r. ewer improved rethed, unless the licensees who wish to use this nethod receive an exenption from tne Appendix J requirenent of conforming to this provision of ANSI N45.4-1972.
i III.
1 By letter dated August 1, 1988, as supplemented by letter dated August ?3, IgEF, the licensee requested an exeniption from 10 CFR Par t 50, Appendir J, Paragraph !!I.A.3, which requires that all CILRTs be performed in accordance with ANSI N45.4-1972. ANSI N45.4-1972 requires that leakage rate calculations be perforred using either the Total Tine method or the Point to-Point method.
The licensee indicated that since the issusnce of ANSI N45.4-1972, a more accurate method of detern.ining containment leakage rates, the Pass Point nethod, has been developed as described in ANSI /ANS-56.8. Therefore, the Itcensee has requested an exemptien to allow the use of the Pass Point rethod for calculating containrent Inakage rates.
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w It has been recognized by the professional community that the Mass Point method is superior to the Point-to-Point and Total Time nethods which are referenced in ANS? N45.4-1972 and endorsed by the preser,t regulations.
The Mass Point method calculates the air mass at a series of points in time, and plots it against time.
A linear regression line is plotted through the mass-time points using a least squares fit.
The slope of this line is divided by the intercept of this line, and the result is multiplied by an appropriate constant to obtain the calculated leakage rate.
The superiority of the Mass Point method becomes apparent when it is compared with the two other methods.
In the Total Time method, a series of leakage rates are calculated on the basis of containment air mass differences between an initial data point and each individual data point thereafter, and an average of these leakage rates is then determined.
If for any reason (e.g., instrument error, lack of temperature equilibrium, ingassing, or outgassing) the initial data point is not accurate, the results of the test will be affected.
In the Point-to-Point method, the leak rates are based on the mass difference between eac.h pair of consecutive data points, and these leakage rates are then averaged to yield a single leakage rate estimate.
Mathematically, this can be shown to be the difference between the air mass at the beginning of the test and the air mass at the end of the test expressed as a percentage of the contair. ment air mass.
It follows from the above that the Point-to-Point method ignores any mass readings taken during the test and thus the leakage rate is calculated on the basis of the difference in mass between two measurements taken at the beginning and at the end of the test, which art 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> apart.
On February 29,1988 (53 FR 5985), the Cormiission pubitsbed a proposed amendcent to Appendix J to erplicitly permit the use of the Pass Point rethod, subject to certain conditions that have been accepted by the Commission's staff since approximately 1976, as well as to permit the use of the prior retheds referenced in ANSI N45.4-1972.
In addition to the nethod of c6iculation, consideration of the length of the test should also be included in the overall program.
In accordance with Section 7.6 of ANSI N45.4-1972, a test duration of less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is only allcked if approved by the Conmission, and the only currently apprcved methodology for such a test is certained in Eechtel Topical Report SN-TOP-1, Revision 1, "Testing Criteria for Integrated Leakage Rate Testing of Primary Containnent Structures for Nuclear Power Plants," dated November 1,1972.
This approach cr.ly alicks use of the Tctal Tire method.
Therefore, the Cencission conditions the exenption to require a minin.un test duration cf 24 Scurs when the Pass Point method is used.
By letter Jated August 23, 1980, the 1tctnsee confirned that a mininun test duration of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> will be utilized when the Pass Point rethod is used.
It the August 1, 19ff letter, the licensee also subritted infernation to idtntify the special circur. stances for granting this exemption for Monticello pursuant to 10 CFR 50.12. The purpose of Appendix J to 10 CFR Part 50 is te assure that containrent leak-tight integrity can be verified periodically throughout the service lifetime in order to maintain containnent leakage rate within the Ifmit specified in the facility Technical Specificatters. The underlying rurpose of the rule, in specifying particular rethods for calculating leakage rates, is to assure that accurate and conservatise nethods are used to assess the results of contafonent leakage rate tests. The
Commission's staff has determined that the Mass Point method is an acceptable method for calculating containment leakage rates and satisfies the purpose of the rule.
Based on the above discussion, the licensee's proposed exemption from paragraph III.A.3 of Appendix J to allow use of the Mass Point method as requested in the submittal dated August 1, 1988, as revised by letter dated August 23, 1988, is acceptable, until such provision of Appendix J is modified.
Thereafter, the licensee shall comply with the provisions of such rule.
The exemption applies only to the method of calculating leakage rates
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use of the Mass Point method) and not to any other aspects of the tests.
IV.
Accordingly, the Commission has determined pursuant to 10 CFR 50.12(a)(1),
that this exemption is authorized by law, will not present an ur.due risk to the public health and safety, and is consistent with the common defense and security.
The Commission has further determined that special circumstances, as set fcrth in 10 CFR 50.12(a)(2)(ii), are present juttifying the exemption, namely that application of the regulation in the parti mlar circumstances is not necessary to achieve the underlying purpose of the rule.
Accordingly, the Commission hereby grants an exemption as described in Sectici III above from Paragraph III.A.3 of Appendix J to the extent that the Mass Point method may be used for containment leakage rate calculations, providing it is used with a minimum test duration of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
The exemption is granted ur,til such provision of Appendix J is modified.
Thcreafter, the licensee shall comply f
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I with the provisions of such rule. The exemption applies only to the methoc' of calculating leakage rate (using the Mass Point method) and not to any other aspects of the tests.
Pursuant to 10 CFR 51.32, the Commission has determined that granting of I
this exemption will not have a significant effect on the quality of the human
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environment (October 4 1988, 53 FR38994 ).
i This exemption is effective upon issuance, FOR THE NUCLEAR REGULATORY COMMISSION W h
& 9 Gary M. Holahan, Acting Director Division of Reactor Projects - III IV, Y and Special Projects Office of Nuclear Reactor Regulation Dated at 1 Sckville, Maryland this 21std y of October 1988.
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