ML20039H027

Draft Safety Evaluation of Containment Purging & Venting During Normal Operation.Debris Screens Should Be Provided for Purge Supply & Exhaust Sys.Tech Spec Changes Re Standby Gas Treatment Sys Also Required

ML20039H027
Person / Time
Site:	Brunswick
Issue date:	12/15/1981
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20039H020	List: ML20039H019 ML20039H027
References
NUDOCS 8201190439
Download: ML20039H027 (5)

Text

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DRAFT SAFETY EVALUATION REPORT FOR CONTAINMENT PURGING AND VENTING DURING NORMAL OPERATION OF THE BRUNSWICK STEAM ELECTRIC 'LANT, UNITS 1 AND 2 (Docket Nos. 50-325/50-324)

I.

INTRODUCTION A number of events have occurred over the past several years which directly re-late to the practice of containment purging and venting during normal plant op-eration. These events have raised concerns relative to potential failures af-fecting the purge penetrations which could lead to degradation in containment integrity, and, for PWRs, a degradation in ECCS performance. By letter dated November 28, 1978, the Commission (NRC) requested all licensees of operating reactors to respond to certain generic concerns about containment purging or venting during normal plant operation. The generic concerns were twofold:

(1) Events had occurred where licensees overrode or bypassed the safety ac-tuation isolation signals to the containment isolation valves. These events were determined to be abnormal occurrences and wcra so character-ized in our report to Congress in January 1979.

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

The NRC position of the November 1978 letter requested licensees to cease purg-ing (or venting) of containment or limit purging (or venting) to an absolute minimum. Licensees who elected to purge (or vent) the containment were re-quested to demonstrate that the containment purge (or vent) system design met j

the criteria outlined in the NRC Standard Review Plan (SRP) 6.2.4, Revision 1, and the associated Branch Technical Position (BTP) CSB 6-4 (Revision 1).

ENCLOSURE 3 8201190439 811215 PDR ADOCK 05000324 p

PDR II. DISCUSSION AND EVALUATION Purging at the Brunswick Steam Electric Plant, Units 1 and 2 (Brunswick 1 and 2)

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is performed through the Containment Atmospheric Contrp1 (CAC) System valves. The CAC system isolation valves are of various sizes, the largest of which are 18,

20, and 24-inch butterfly-type valves. The exhaust lines from the drywell and torus are connected to a common exhaust header which leads to the containment purge exhaust fan system and the Standby Gas Treatment (SBGT) system. Large isa-lation valves are provided to isolate these systems individually from the commo'1 exhaust header.

Two 18-inch butterfly isolation valves configured in series (one of which is by-passed by a 2-inch line containing an isolation valve) are provided to isolate the exhaust line from the drywell. Two 20-inch butterfly isolation valves con-figured in series (one of which is bypassed by a 2-inch line containing an iso-lation valve) are provided to isolate the exhaust line from the torus. The purge supply lines to the drywell and torus are connected to a common supply header which leads to the Reactor Building.

One 24-inch butterfly isolation valve is provided for the comon header. One 18-inch butterfly isolation valve (which is bypassed by a 1-inch line having an isolation valve) is provided to isolate the supply line to the drywell. 0.ae 20-inch butterfly isolation valve (which is bypassed by a 1-inch line having an isolation valve) is provided to isolate the supply line to the torus.

l The CAC system is primarily used in the de-inerted mode of operation.

We have l

reviewed the isolation provisions for all of the above small bypass lines and conclude that they comply with General Design Criteria 54 and GDC 56. Moreover, the concern over the ability of the valves to close during LOCA transients does not apply to these small valves.

In addition, the Brunswick plant is equipped 1

) with a SBGT system which is used for low pressure venting of the containment and is primarily designed for post-LOCA conditions.

The licensee responded to the NRC position letter of November 1978, by stating that their investigations have revealed no safety concerns over purging during normal operations and requested not to be limited to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year. The li-censee indicated that inerting and de-inerting operations are controlled by plant procedures and Technical Specifications. The drywell is required to be inerted within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after reaching 15% power and until 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to a scheduled reduction below 15% power.

The nitrogen makeup and " burping" (venting) operations occur much more frequently than inerting/de-inerting, but these operations utilize smaller valves. The li-censee indicated that, at present, inerting and venting operations average approxi-mately 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> per day. We have reviewed the licensee's justification for usage of the purge system and find it to be acceptable.

The licensee has conducted an analysis to provide the amount of steam released in the event of a LOCA during venting operations. Their analysis was based 'on the assumption that all of the large CAC containment isolation valves are fully open at time zero and that no credit was taken for reduced flow during valve closure.

The results of the analysis indicate that 6,051 pounds of steam is released. We i

have reviewed the licensee's assumptions and analysis and find the results accept-able.

The licensee has evaluated the impact of purging during operation on ECCS perform-ance and has concluded that should a LOCA occur during purging operations, the op-erations, the operation of the ECCS systems would not be affected. Based on our review of the licensee's evaluation, we find their conclusion to be acceptable.

. The licensee has not provided sufficient information concerning the provisions made to insure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.

The licensee indicated that the SBGi system would not withstand being subjected to direct LOCA conditions via the large butterfly valves normally used for low pressure venting of the containment. However, provisions have been made for venting of the primary containment through two one-half-inch valves (SGT-V8 and SGT-V9) which are provided to bypass the large butterfly isolation valves between the SBGT system and the common exhaust header.

We agree with the licensee that by utilizing only these valves for periodic containment venting, the post LOCA equipment (SBGT system) would be protected from damage in the event a LOCA oc-curred during venting operation.

III. CONCLUSIONS We have reviewed the Brunswick 1 and 2 purge system against the provisions of BTP CSB 6-4 (Revision 1), " Containment Purging During Normal Plant Operations."

The licensee has not provided sufficient information concerning the provisions made to insure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.

We recommend that debris screens be provided for the purge supply and exhaust sys-tems. The debris screens should be designed to seismic Category I criteria and installed about one-pipe-diameter away from tlie inner side of each inboard iso-lation valve.

The piping between the debris screen and the isolation valve should also be designed to seismic Category I criteria.

We recommend that the licensee propose a Technical Specification that would re-quire the SGTS be configured via the one-half-inch valves (SGT-V8 and SGT-V9) l

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, during operating modes 1 through 4 to prevent damage to the SBGT system should a LOCA occur during venting operation.s.,

In addition, as a result of numerous reports on the unsatisfactory performance of resilient seats in butterfly-type isolation valves due to seal deterioration, periodic leakage integrity tests of the 18, 20, and 24-inch butterfly isola-tion valves in the purge system are necessary. Therefore, the licensee should also propose a Technical Specification for testing the valves in accordance with the following testing frequency:

"The leakage integrity tests of the isolation valves in the containment purge / vent lines shall be conducted at least once every three months."

The purpose of the leakage integrity tests of the isolation valves in the con-tainment purge lines is to identify excessive degradation of the resilient seats for these valves. Therefore, they need not be conducted with the precision re-quired for the Type C isolation valve tests in 10 CFR Part 50, Appendix J.

These tests would be performed in addition to the 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.

Subject to successful implementation of the above recommended actions, we find the purge / vent system design and operating practices for Brunswick 1 and 2 to be acceptable.

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' Enclosure 4 CONTAINMENT SYSTEMS LIMITING CONDITION FOR OPERATION I

3.6.1.7 The containment purge supply.and exhaust iso'lation valves may be open for safety-related reasons [or shall be locked. closed). The.

containment vent line isolation valves may be. open for safety-related reasons [or shall be locked closed].

f APPLICABILITY:

MODES 1, 2, 3, and 4.

ACTIONi:

l (For plants with valves closed by technical specification).

With one containment purge supply and/or one exhaust isolation valve open, cl_ose the open valve (s) within one hour or be in at least HOT i

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 4

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) l 1.

With one containment purge supply and/or o.ne exhaust isolatitm or vent valve inoperable, close the associated OPERABLE valve and either restore l

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 OPERABLE valve closed.

2.

Operation ray then continue until performance.of the next required valve test provided that the OPERABLE valve is. verified to be locked closed at least onde per 31 days.

3.

Otherwise, be in at least HOT STANDBY within the next six hours and j

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 />.

1 The provisions of Specification 3.0.4 are not applicable.

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SURVEILLANCE RE0UIREMENTS 4.6.1.7.1 The

-inch containment purge supply and exhaust isolation valves

-incTvent line isolation valves sh~allfbe determined locked closed and the

'at least7nce per 31 days.

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

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CONTAINMENT SYSTEMS l

3/4 4.6.3 CONTAINMENT ISOLATION VALVES LIMITING CONDITION FOR OPERATION 3.6.3 The containment isolation valves specified 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.

4 4

ACTION:

4 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:

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 /> a.

or 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 l

l b.

one deactivated automatic valve secured in the isolation position, l

or 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 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 d.

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 REOUIREMENTS The isolation valves specified in Table 3.6-1 shall be demonstated 4.6.3.1 OPERABLE prior to returning the valve to service af ter maintenance, repair or replacement work is performed on the valve or its associated actuator, control i

or power circuit by performance of a cycling test, and verification of isola-tion time, i

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CONTAINMENT SYSTEMS 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:

Verifying that on a Phase A containment isolation test signal, each a.

Phase A isolation valve actuates to its i' solation position.

b.

Verifying that on a Phase B containment isolation test signal, 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 Specification 4.0.5.

4.6.3.4 The containment purge and vent isolation valves shall be demonstated OPERABLE at intervals not to exceed months.

Valve OPERABILITY shall be 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 l

C penetratibn, the combined leakage rate is less than or equal to 0.60La.

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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