ML20214N037

Exemption from Paragraph III.A.3 of 10CFR50,App J, Authorizing Use of Mass Point Method in Containment Leak Rate Testing w/24-h Min Test Duration Until App J Modified, Per Util 870417 Request

ML20214N037
Person / Time
Site:	Yankee Rowe
Issue date:	05/26/1987
From:	Varga S Office of Nuclear Reactor Regulation
To:	YANKEE ATOMIC ELECTRIC CO.
Shared Package
ML20214M582	List: ML20214M581 ML20214N037
References
NUDOCS 8706020033
Download: ML20214N037 (6)

Text

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s 7590-01 UNITED STATES NUCLEAR REGULATORY COMMISSION In the Matter of )

)

YANKEE ATOMIC ELECTRIC COMPANY ) Docket No.50-029

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(Yankee Nuclear Power Station) )

, EXEMPTION I.

Yankee Atomic Electric Company (YAEC or the licensee) hol'ds Facility Operating License No. DPR-3 which authorizes the operation of the Yankee Nuclear Power Station (Yankee or the facility) at steady-state power levels not in excess of 600 megawatts thermal. This license provides, among other things, that the facility is subject to all rules, regulations and Orders of

., the U.S. Nuclear Regulatory Comission (the Comission) now or here'after in effect.

The facility is a pressurized water reactor located at the licensee's site near Rowe, Massachusetts.

II.

The Code of Federal Regulations,10 CFR 50.54(o), specifies that primary reactor containments for water-cooled power reactors shall comply with '

Appendix J, " Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors." Paragraph III.A.3 of Appendix J incorporates by reference the American National Standard (ANSI) N45.4-1972, " Leakage Rate Testing of Containment Structures for Nuclear Reactors." This standard requires that containment leakage calculations for Containment Integrated Leakage Rate Tests (CILRTs) be perfonned using either the Point-to-Point method or the Total Time method. 8706020033 870526 PDR P ADOCK 05000029 ppg.

s A more recent standard, ANSI /ANS 56.8-1981, " Containment System Leakage Testing," which was intended to replace ANSI N45.4-1972, specifies the use of the Mass Point method, to the exclusion of the two older methods. A proposed revision to Appendix J, which has been published for public comment (51 FR 39538, dated October 29,1986), refers to a proposed Regulatory Guide (MS 021-5, October,1986), which endorses, with certain exceptions, the ANSI /ANS 56.8-1981

. standard.

In April 1987, the licensee was notified that the Mass Point method was not in conformance with the current Appendix J and was, therefore, not permitted without exemption. Pending revision of Appendix J which would permit the Mass Point analysis, licensees who wish to use the Mass Point technique must submit an application for exemption from the Appendix J requirement that test calcu-lation for CILRTs will conform with ANSI N45.4-1972.

III.

By letter dated April 17, 1987, the licensee requested an exemption from 10 CFR Part 50, Appendix J, Paragraph III. A.3, which requires that all CILRTs be performed in accordance with ANSI N45.4-1972, " Leakage Rate Testing of Containment Structures for Nuclear Reactors." ANSI N45.4-1972 requires that leakage calculations be performed using either the Total Time method or the Point-to-Point method. The April 17, 1987 letter also noted that the licensee will propose an anendment to the Technical Specifications (TSs) to maintain consistency between the TSs and the requested exemption. The Commission will respond to the proposed amendment by separate correspondence.

The licensee indicated that in 1976 the Commission's staff unofficially recognized the merits of the Mass Point technique and that this was the recommended method to use. On this basis, the licensee has been performing calculations using the Mass Point method. The licensee was recently informed

by the Staff that with regard to the Mass Point method, the method has not been incorporated into the current provisions of 10 CFR Part 50 Appendix J, and its use requires an exemption. In response to this staff position the licensee has

requested an exemption. The licensee has stated in support of the application for exemption from Appendix J that the Mass Point method is a more accurate method of calculating containment leakage.

It has been recognized by the professional comunity that the Mass Point method is superior to the two other methods, Point-to-Point and Total Time, which are referenced in ANSI N45.4-1972 and endorsed by the present regulations.

The Mass Point method calculates the air mass at each point in time, and plots it against time. A linear regression line is plotted through the mass-time

{

! points using a least square fit. The slope of this line is the leakage rate. .The 4

staff believes that the Mass Point method was not specified in ANSI N45.4-1972 because the other more conservative methods (Point-to-Point and Total Time) were I adequate and suitable for the sensitivity levels of the instrumentation in use at that time. However, with the present developments in technology, the Mass'  !

! Point method has gained recognition as the proper one to use. The superiority of the Mass Point method becomes apparent when it is compared with the two other f

methods. In the Total Time method, a series of leakage rates are calculated on the basis of air mass differences between an initial data point and each individual

, data point thereafter. If for any reason (such as instrument error, lack of l temperature equilibrium, ingassing, or outgassing) the initial data point is 4

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 each pair of i

_ _ _ . _ _ _ _ _ _ _ _ _ - - - - ,. _ _ - - , _ _ - ~ _ _ _ _ , - _ _ _ _ _ _

O consecutive points which 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 1

a percentage of the containment air mass.

1 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 j ,

basis of the difference in mass between two measurements taken at the beginning i and at the end of the test, which are 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> apart.

Draft Regulatory Guide MS 021-5, which was published for coment in October 1986, endorses, with exceptions, the ANSI /ANS 56.8-1981 standard and the Mass

] Point Method.

In addition to the method of calculation, 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 less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is only allowed if approved by the NRC staff, and the only currently approved methodology for such a test is contained in Bechtel Topical Report BN-TOP-1,

Revision 1. " Testing Criteria for Integrated Leakage Rate Testing of Primary -

Containment Structures for Nuclear Power Plants," dated November 1,1972. This I

approach only allows use of the Total Time method. Therefore, the staff will

condition the exemption to require 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 /> .when .

the Mass Point method is used.

The licensee's letter also submitted information to identify the special l circumstances for granting this exemption for Yankee pursuant to 10 CFR 50.12.

l The purpnse of Appendix J to 10 CFR Part 50 is to assure that containment leak-tight integrity can be verified periodically throughout the service lifetime so as to maintain containment leakage within the limit'specified in )

1 l 4

4

s the facility TSs. The underlying purpose of the rule specifying particular methods for calculating leakage rates is to assure that accurate and conservative methods are used to assess the results of containment leak rate tests. As set forth above, the Mass Point method has been a widely used method providing accurate results and thus 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 re-quested in the submittal dated April 17, 1987, is acceptable with the condition of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> minimum test duration, until such provision of Appendix J is modified. Thereafter, the licensee shall comply with the provisions of such rule (or may renew its request for exemption). The exemption applies only to the method of calculating leakage by use of the Mass Point method and not to any other aspects of the tests. + -

IV.

Accordingly, the Commission has determined that, pursuant to 10 CFR Part 50.12, 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 Convaission has further detennined that special circumstances, as set forth in 10 CFR 50.12(1)(2)(11), 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. Accordingly, the Commission hereby grants an exemption as described in Section 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 until such pro-vision of Appendix J is modified. Thereafter, the licensee shall comply with the provisions of such rule. The exemption applies only to the method of

s calculating leakage by use of the Mass Point method and not to any other aspects of the tests.

Pursuant to 10 CFR 51.32, the Commission has determined that the granting of this exemption will have no significant impact on the environment (52FR17651).

This exemption is effective upon issuance.

FOR THE NUCLEAR REGULATORY COMMISSION 0

ev n . Var a c r s Division of Reactor cts I/II Dated at Bethesda, Maryland this

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