ML20030D634

Safety Evaluation Re Containment Purging & Venting During Normal Operation

ML20030D634
Person / Time
Site:	Yankee Rowe
Issue date:	08/27/1981
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20030D633	List: ML20030D632 ML20030D634
References
NUDOCS 8109140072
Download: ML20030D634 (8)

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SAFETY EVALUATION REPORT

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FOR CONTAINMENT PURGING / VENTING DURING NORMAL OPERATION YANKEE-ROWE NUCLEAR > POWER ST'ATION -

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INTRODUCTION

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A number of events have occurred over the past several years which directly relate to the practice of containment purging and vent,ing during, normal plant operation. These events have raised concerns relative to potential failures affecting the purge penetrations which could lead to degradation in containment integrity, and, for PWR's, a degradation in U.CS performance.

By letter, dated November 28, 1978, the Commission (NRC) requested all

. licensees of operating reactors to respond to certain generic concerns about l

containment purging or venting during normal plant operation. The generic concerns were twofold:

(1) Events had occurred where licensees overrode o-bypassed the safety l

actuation isolation signals to the containment isolation valves.

These events were determined to be abnormal occurrences and were so characterized in our report to Congress in January 1979.

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(2) Recent licensing reviews have required tests or analyses to show that containment purge or vent valves would shut without degrading containment integrity during the dynamic loads of a design basis loss-of-coohnt accident (DBA-LOCA).

The ARC position of the November 1978 letter requested licensees to cease purging (or venting) of containment or limit purging (or venting) to an absolute minimum. Licensees who elected to purge (or vent) the contain.nent were requested to demonstrate that the containment purge (or vent) system 8109140072 010827 PDR ADOCK 05000029 p

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2-design met the criteria outlined in the N?C Standard Review Plan (SRP) 6.2.4, Revision 1 and the associated Branch Technical Position (BTP) CSB 6-4.

II. DISCUSSION AND EVALUATION' The purge and vent system at the Yankee Rowe Nuclear Powe P1 tlLconisting of_ two 30 inch lines, was designed to purge and vent the containment atmosphere to :;mprove working conditions for personnel.

The licensee stated, in a letter dated November 1, 1979, that the 30 inch purge / vent valves in the,' Yankee-Rowe Plant are manually operated valves, and that purging / venting through them"is prohibited during plant operation in Modes 1 through 4 by Technic ~al Specifications.

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Also, there are no pneumatic equipment operators or instrumentation inside"the a

containment; therefore, venting ~of the containment; during ' lailtjpetat' ion]n*

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l modes 1 through 4 is not necessary.

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l' III. CONCLUSION We agree with the licensee's_ view that maintaining the 30 inch purge values i-l closed during plant operation in Modes 1 througn 4'will preclude the release of radioactivity to the environs via the containment purge / vent system should a loss-of-coolant accident occur. We, therefore, conclude that the purge / vent

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system design and use for the Yankee-Rovo Plart are acceptable. However, as a result of the numerous reports on unsatisfactory performance of the resilient seats for butterfly-type isolation valves in containment purge and ventlines,periodicleakageintegrity.testsoftheabove30hinchbutterfly.

isolation valves have been found necessary (see' Enclosure 2). We, there' fore, request that the licensee propose a technical specification for testing these valves in accordance with the following ~ recommended testing frequencyt "The leakage integrity tests of the isolation valves in the containment purge lines shall be conducted at least once every six months."

3-The-purpose of the leakage integrity tests of the isolation valves in the containment. purge lines is to identify excessive degradation of the resilient seats for-these valves.

Therefore, they need not be conducted with the pre-

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m cision rdckuired:for the Type: C. isolation. valve' tests in 10 CFR Part 50, Ap-pendix J.

These tests wouldie perfonned in addition to the quentitative Type C tests required.by Appendix J and would not relieve the licensee of the

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responsibility to conform to-the requirements of Appendix J.

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l PURGE / VENT VALVE LEAKAGE TESTS The long term resolution of Generic Issue B-24, " Containment Purging During Normal Plant Operation," includes, in part, the implementation of.

that provisions should be made for leakage rate testing of the (pecif Item B.4.of Branch Technical Position (BTP) CSB 6-4.

Item B.4 s purge / vent Although system) isolation valves, individually, during reactor operation.

Item B.4 does not address the testing frequency, Appendix J to 10 CFR Part 50 specifies a maximum test interval of 2 years.

As a result of the numerous reports on unsatisfactory performance of the resilient seats for the isolation valves in containment purge and vent lines (addressed in CIE Circular 77-11, dated 3eptember 6,1977), Generic Issue B-20, " Containment Leakage Due to Seal 9eterioration," was established' to evaluate the matter and establish an appropriate testing frequency for the isolation valves. Excessive leakage past the resilient seats.of isolation valves in purge / vent lines is typically caused by severe environmental con-

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ditions and/or wear due to frequent use. Consequently, the leakage test.

frequency for these valves should be keyed-to' the' occurrence of severefenviron-mental conditions and the'use of the valves, rather than'the' current reqdire-ments of 10 CFR 50, Appendix J.

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It is recommended that the following provision be added.to the Technical -

Specifications for the leak testing of purge / vent line isolation valves:-

" Leakage integrity tests shall be performed on the containment isolation valves with resilient material seals.in (a) active purge / vent systems (i.e., those which may be operated during plant operating, Modes 1 through 4) at least once every three months and (b) passive purge systems.(i.e., those which must be administratively controlled closed during reactor operating Modes 1 through 4) at least once every six months."

By way of clarification, the above proposed surveillance specification is predicated on our expectation that a plant would have a need to go to cold

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shutdown several times a yecr. To cover the possibility that this may not occur, a maximum test interval of 6 months is specified. However, it is 'not our intent to require a plant to shutdown just to conduct the valve leakoge integr.ity tests.

If licensees anticipate long duration power oper -

ations with infrequent shutdown, then installation of a leak test connection-that is' accessible from outside containment may be appropriate. This will permit simultaneous testing of the redundant valves.

It will not be possible to satisfy explicitly the guidance of Item B.4 of BTP CSB 6-4 (which states that valves should be tested individually), but at least some testing of the valves during reactor operation will be possible.

y v:,;i.;j,i It is: intended that the above proposed surveillance specification be applied to the t.ctive purge / vent lines, as well as passive purge lines:

1.e., the purge lines that are administratively controlled closed during reactor oper-ating modes 1-4.

The reason for including the passive purge lines is that B-20 is concerned wtih the potential adverse effect of.. seasonal weather. con-ditions on the integrity of the isolation valves. Consequently, passive purge lines must also be included in the surveillance program.

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The purpose of the leakage integrity tests of the isolation valves in the

- containment purge and vent lines is to identify excessive degradation of the resilient seats for these valves. Therefore, they need not be conducted with the precision required for the Type C isolation valve tests in 10 CFR..

These tests would be performed in addition to the 1 Part 50, Appendix J.

quantitative Type C tests required by Appendix J and would not relieve the licensee of the responsibility to conform to the requirements of Appendix J.

In view of the wide variety of valve types and seating materials, the:,. -

acceptance criteria for such tests should be developed on a plant-specific basis.

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'l MODEL TECHNICAL SPECIFICATIONS CONTAINMENT SYSTEMS x

LigQINGCONDITIONFOROPERATION 3.6.1.7 The containment purge supply and exhaust isolation valves may be open for safety-related reasons or shall be closed. The containment vent line Lisolation valves _may be open for safety-related reasons or shall -

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APPLICABILITY: MODES 1, 2, 3, and 4.

ACTION:

(For plants with valves closed by technical specification)

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With one containment purge supply-and/or one exhaust isolation va1ve open, close the open valve (s) within one hour or be in at least HOT STANDY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUIDOWN within the.following

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30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.-

(For plants with valves that may be opened by technical specifications)

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,v, With one containment purge. supply and/o, r' one exhaust isolation'.or" venti.'

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valve inoperable,.close the associated OPERABLE valve and either4estore 1.

the inoperable valve to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or. lock' the '" *W W

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- OPERABLE. valve closed.a

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2.. Operation may then continue 'until performa.nce' 'of' the 'next requiie'd ' W -

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, valve test provided that the OPERABLE valve is ver closed at least once per 31 days.

Otherwise, be in at least HOT STANDBY within the next six hous and 3.

in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

The provisions of Specification 3.0.4 are not applicable.

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SURVEILLANCE REQUIREMENTS

-inch containment purge supply and exhaust isolation valves The

-incTvent line isolation valves shall be determined closed at 4.6.1.7.1 and the least once per 31 days.

The valve seals of the purge supply and exhaust isolation valves 4.6.1.7.2 and the vent line isolation valves shall be replaced at least one per _ years.

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3/4 4.6.3 CONTAINMENT ISOLATION VAL _VES LIMITING CONDITION FOR OPERATION 3.6.3 The containment isolation valve:. ecified in Table 3.6-1 shall be OPERABLE with isolation times as shown in Table 3.6-1.

APPLICABILITY:

MODES 1, 2, 3 and 4.

ACTION:

With one or more of the isolation valves (s) specified in Table 3.6-1 inoperable, maintain at least one isolation valve OPERABLE in each affected penetration that is open and either:

', La. Restore the inoperable valve (s) to OPERABLE status within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or.

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Isolate each affected penetration within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> by.use-of at.least one deactivated automatic valve secured _in the isolation position, or: :- : ~7::-

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,, m Isolate each affected' penetration within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> by use of at least c.

one closed manual valve or blind flange; or d.

Be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

SURVEILLANCE REQUIREMENTS The isolation valves specified in Table 3.6-1 shall be demonstated 4.6.3.1 OPERABLE prior to returning the valve to service after maintenance, repair or replacement work is performed on the valve or its associated actuator, control or power circuit by performance of a cycling test, and verification of isola-tion time.

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SURVEILLANCE REQUIREMENTS (Continued) 4.6.3.2 Each isolation valve specified in Table 3.6'-1 shall be demonstrated.

OPERABLE during the COLD SHUTDOWN or REFUELING MODE at least once per 18 months by:-

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Verifying that on a Phase A containment isolation test signal, each Phase A isolation valve actuates to its isolation position.

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Verifying that on a Phasa B containment isolation test sigr.al, each Phase B isolation valve actuates to its isolation position.

4.6.3.3 The isolation time of each power operated or automatic valve of Table 3.6-1 shall be determined to be within its limit when tested pursuant to.

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, g 4.6.3.4 The containment purge and vent isolation valves shall be demonstated OPERABLE at intervals not to exceed months. Valve OPERABILITY lshall.be '

F determined by verifying that when the measuued leakage rate is added to the leakage rates determined pursuant to Specification 4.6.1.2.d for all other Type B and C penetration, the combined leakage rate is.less than or, equal.to.0.60La..

rj However,' the leakage rate for the containment purge and' vent isolation valves shall be compared to the previously measured leakage rate to detect excessive valve degradation.

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