ML20127P315

Evaluation of Containment Leak Testing Program for Monticello Nuclear Generating Plant

ML20127P315
Person / Time
Site:	Monticello
Issue date:	07/30/1976
From:	Office of Nuclear Reactor Regulation
To:
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ML20127P299	List: ML20127P293 ML20127P315
References
NUDOCS 9212020187
Download: ML20127P315 (12)

Text

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JUL. 3 01970 EVALUATION OF Ti!E CONTAINMENT LEAK TESTING PROGRAM FOR Tile MONTICELLO NUCLEAR GENERATING PLANT INTRODUCTION Dy our letter, dated August 5, 1975, the Northern States Power Company (NSP) was requested to review the Monticello Plant in terms of the current containment leak testing pro-gram, and the associated Technical Specifications, for com-pliance with the requirements of Appendix J to 10 CFR Part 50.

As part of this request, NSP was to determine the planned actions and schedule necessary to attain conformance with the above cited regulation.

Appendix J to 10 CPR 50 was published on February 14, 1973.'

Since many operating nuclear plants had either received an operat-ing license or were in advanced stages of design or construction at that time, some plants may not now be in full compliance with the requirements of this regulation. Therefore, beginning in l

August 1975, requests for review of the extent of compliance with the requirements of Appendix J were made of each licensee.

} Following the initial responses to these requests, NRC staff t

positions were developed regarding the extent to which current leak testing practices generally satisfy the intent, rather than

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JUL 301976 the letter of the requirements of the regulation. These

. staff positions have since been applied in our review of reports filed by the Monticello licensee and the results are reflected in the following evaluation.

The Northern States Power Company (NSP) submitted responses on September 19, 1975, January 30, May 4, and May 5, 1976. In the most recent submittals, NSP requested 4 a number of specific exemptions and proposed syster., modifi-l cations to attain full compliance with the requirements of i

Appendix J. In the following evaluation, the Appendix J l requirement is identified along with the exemption or ..

modification proposed by NSP.

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EVALUATION Section II.G of Appendix J 1equires that local leakage tests (Type B) be performed to determine the leakage through containment penetrations whose design incoporates resilient l seals, gaskets, or scalant compounds. These local tests are

! performed to provide periodic surveillance of reactor contain-ment penetrations so that proper maintenance and repairs are made during the service life of the plant. NSP has identified nine (9) instrument lines for which no provision for local leak-testing _was-made in-the original plant design, and has requested that these lines be exempted from the requirements of Type B testing. These instrument lines consist of small diameter i

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JUL'. 3 01976 piping located outside containment and connecting to a scaled transducer. The signals generated by these instruments are drywell pressure (x29E, x29F, x50E and x50F), torus pressure and temperature (x206A, x206D, x209A and x209D), and drywell flood level (x32C). Any modification of these lines to per-mit local leak testing may result in a degradation in perfor-mance of their safety related functions. These instrument lines are passive systems, which can be manually isolated.

Since each of these lines is exposed to the containment atmosphere, they are tested, in situ, as part of the integ-rated (Type A) leakage test program. Based on the foregoing t

arguments, we find the proposed exemption acceptable. '

Section II.H.3 of Appendix J requires that containment isolation valves, which include those valves which operate intermittently under post-accident conditions, be locally leak tested (Type C). NSP has identified four (4) air operated testable check valves and ten (10) motor operated globe and gate valves which meet the defir.ition of a' con-tainment isolation valve (operate intermittently, post-f accident) and for which an exemption from local leak testing j has been requested.

I The four air operated testable check valves are located 4

on redundant-lines of.the core spray system and the low pres-I sure coolant injection subsystem (LPCI) . In-each case, the

-check valve is located inside containment.in series with two

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motor operated gate or globe " aloes outside containment.

l In the event of a postulated loss-of-coolant accident, the two motor operated valves would receive a signal to open to allow suppression pool water to be injected into the sg reactor vessel. Should either a core spray pump fail to start, or an RHR train (LPCI source) be isolated, these lines would have to be isolatet to limit leakage through i the idle loop. NSP has proposed to exclude the check valves from local leak testing because: (1)-redundant isolation is provided by the two motor operated valves outside containment; and (2) the check valves were not _

intended to meet gas leakage acceptance criteria in the original plant design. However, in order to isolate a line with the motor operated valves, manual action would have to be taken by the operator, while the check valves automatically close to limit leakage from the vessel. ' We  :

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< find that this is sufficient justification for continuing j

to maintain the leakage integrity of the check valves.

Therefore, we conclude that the proposed exemption is not acceptable for the check valves.

I The ten motor operated globe and gate valves, for Which NSP has requested an exemption from Type C testing,

,4 are located in the drywell spray, torus spray and RHR

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recirculation lines. In each case NSP has indicated that leakage cannot occur since the RFIR system is always at a higher pressure than the containment, even considering f the most limiting single active failure in the syster l Ilowever , as with the LPCI mode of the Ri!R system, there is a high probability that following the initial phase of a loss of coolant accident, the redundant train of the.RilR

system may be shutdown and isolated. This would neccessi-J tate containment isolation of the drywell and toras spray lines and the RIIR recirculation line for that train.

Therefore, we conclude that the proposed exemption is not i

acceptable for the motor operate'd valves.

4 l Section III.C.1 of Appendix J requires that Type C 1

tests (isolation valves) be performed by local pressuriza-t i tion applied in the same direction as that required to perform the safety function, unless it can be determined that pressurizing in the reverse direction will yield equivalent or conservative results. .NSP has identified

- eleven (11) isolation valves for which an exemption for the direction of-test pressure has been requested. This exemption is not necessary, since Appendix J clearly.

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allows reverse direction testing. Documentation of the determination that reverse direction testing for these 4

valves will yield conservative or equivalent results shall 1

1 be kept on file at the plant site.

Section III.C.2 of Appendix J requires that contain-

! ment isolation valves be locally leak tested (Type C) at.

the peak calculated containment' pressure (Pa). The licensee has requested an exemption to ellow a continuation of a 25 psig test pressure for the main steam isolation valves (MSIVs). The main steam system design in most operating BWR plants necessitates leak testing of the

MSIVs by pressurizing between the. valves. The MSIVs are angled in the main steam lines to afford better sealing in the direction of accident leakage. A test

! pressure of Pa acting on the inboard disc lifts the i

disc off the seat resulting in excessive leakage into the reactor vessel. This consideration was given when the original test pressure of 25 psig was established for O

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the MSIVs at the design stage of the plant. Since testing 2

of the MSIVs at a reduced pressure results in a conservative J

determination of the leakage rate through the valves, we find 4

the proposed exemption acceptable.

• Section III.B.2 and III.D.2 of Appendix J specify the I local leak testing requirements for containment airlocks.

Together, these sections require that containment airlocks be leak tested at six month intervals and following each airlock opening during such intervals, and that these tests

(Type B) be conducted at the peak calculated containment pressure (Pa). The intent of the tests following each opening is to demonstrate that the doors have been properly resealed following airlock use. The six month interval establishes the frequency at which the leakage integrity of the air _ lock

, assembly shall be determined.

l The airlock design for the Monticello plant includes an 4

inner and outer door, each equipped with a single seal, which seat with containment pressure. Pressurizing the airlock to Pa lifts the inner airlock door off its seat which results in excessive leakage into the containment. This condition does not reflect the post-accident condition of the airlock.

In order to leak test the airlock at Pa, a strongback must be installed, inside the containment, on the inner airlock

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1 door. The strongback prevents the inner door from lifting off its seat. To conduct the test, the airlock doors must be opened both before and after the test to install and remove the strongback. Consequently, NSP has requested'an exemption to allow testing the airlock at a reduced pres-i t sure (10 psig) which would not require the use of strongback.

In addition, they have requested an exemption to allow leak testing within three days following the first of a series of airlocks openings, rather than after each opening.

We agree with the licensee's approa*ch regarding the I tests used to demonstrate that the airlock doors have been properly resealed. Conducting tho test at Pa would neces-j sitate breaking the door seals to remove the strongback, thus defeating the purpose the test. However, before we

! can conclude our reiiew of the acceptability of the proposed exemption for the "after opening" tests, the licensee must 1

propose an acceptance criterion for the reduced pressure tests that has been determined by relating the leakage rate at the test pressure (10 psig) to the leakage rate at Pa. The Appendix J requirement to test the airlock following each opening is impractical considering the time required to perform the test in relation to the frequency 2

of airlock use. Therefore, we agree that testing within i

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three days following the first of a series of openings adequately demonstrates the continuing integrity of the i '

! airlock door seals.

i The intent of the six-month interval tests is to provide j an accurate accounting of the leakage integrity of the airlock assembly. The licensee has proposed to conduct this test at the reduced pressure alse. Since the test pressure may

influence the leakage rate through various components in the airlock, the six month tests shall be performed at a pressure 1

of Pa using strongback. After the strongback has been removed, the door seals can be verified using the reduced pressure test.

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PROPOSED MODIFICATIONS NSP has submitted a description of a number of proposed modifications to permit local leak testing of isolation valves which were originally considered exempt from testing when the plant was designed. The acceptability of these proposed mod-i ifications is dependent upon proper identification of the

- valves which require Type C testing.

Appendix J,Section II.H states that the containment isolation valves included in the'" Type C Tests" are those .

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that:

(1) Provide a direct connection between the inside and outside atmospheres of the primary reactor containment under normal 4

operation, such as purge, and ventilation, vacuum relief, 8

and instrument valves;

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1 (2) Are required to close automatically upon receipt of a containment isolation signal in response to controls intended to effect containment isolation;

] (3) Are required to operate intermittently under post-accident I conditions; and 1

(4) Are in main steam and feedwater piping and other systems which penetrate containment of direct-cycle boiling water power reactors.

NSP has not identified the manner by which this definition has been applied to determine which valves require or do not 4 require Type C testing. For example, NSP has excluded 17 isolation valves from Type C testing because the lines ter-4 i

minate below the surface of the suppression pool and, therefore, I However, do not communicate with the containment atmosphere.

the suppression pool serves as a blowdown sink and will, there-fore, be contaminated. Any valve in one of these lines which closes automatically or operates intermittently following an accident-should be Type C tested based on definition 2 or 3.

In this regard, an exemption from the requirement for leak i

testing with air may be justified, since these valves would not be exposed to the containment atmosphere.

Therefore,_ we will be unable to conclude our review of the acceptability of the proposed modifications until a more 1

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testing has been made.

CONCLUSION 4

The Northern States Power Company has requested certain J

j exemptions and proposed certain modifications to attain con-formance with the requirements of Appendix J to 10 CFR 50.

l The status of each of these items is as follows:

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1) the proposal to exclude, from Type B-testing, those instrument lines for which no provision for local leak testing exists is acceptable;

2) sufficent justification has not been provided in support e

of the proposed exemption of the core spray and LPCI

! check valves, drywell spray valves, torus spray valves, and the RHR recirculation valves from Type C testing;

3) an exemption is not necessary for reverse direction

! testing;

4) reduced pressure testing of the MSIV's is acceptable;

, 5) reduced pressure testing of the airlock is acceptable i

provided an adequate acceptance criterion is demonstrated; l

6) testing the airlock within three days following the-first i of-a series of openings is acceptable;

7) we will require that integrated leakage tests of the.

airlock at the six month intervals be. conducted at a pressure of Pa; and L

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8) the licensee has not provided an adequate basis for the selective proposed modifications to permit local leak testing. A methodical determination of those isolation valves which require Type C testing should precede such i a proposal.

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