ML20058F783

Draft Safety Evaluation for Containment Purging & Venting During Normal Operation.Addl Info Required Before Review of Purge/Vent Sys Can Be Completed

ML20058F783
Person / Time
Site:	Peach Bottom
Issue date:	07/07/1982
From:	NRC
To:
Shared Package
ML20058F776	List: ML20058F783
References
TASK-2.E.4.2, TASK-TM NUDOCS 8208020454
Download: ML20058F783 (5)

Text

o l.

Enclcsure 2 DRAFT SAFETY EVALUATION REPORT FOR CONTAINMENT PURGING AND VENTING DURING NORMAL OPERATION OF THE PEACH BOTTOM ATOMIC POWER STATION, UNITS 2 AND 3 (Docket Nos. 50-277 and 278)

I.

INTRODUCTION A number of events have occurred over the past several years which directly relate to the practice of containment purging and venting 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 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 gen,eric concerns were twofold:

(1)

Events had occurred where licensees overrode or bypassed the safety i

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.

(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 loads of a design basis loss of coolant accident (DBA-LOCA).

The NRC position of the November 1978 letter requested licensees to cease j

purging (or venting) of containment or limit purging (or venting) to an l

absolute minimum.

Licensees who elected to purge (or vent) the containment were requested to demonstrate that the containment purge (or vent) system I

8208020454 820707 l

PDR ADOCK 05000277 i

P pDR

. design met the criteria outlined in the NRC Standard Review Plan (SRP) 6.2.4, Revision 1, and the associated Branch Te::hnical Position (BTP)

~

CSB 6-4,,Revi sion 1.

II.

DISCUSSION AND EVALUATION The Containment Atmospheric Control System and Containment Atmospheric Dilution System are utilized to control the containment atmosphere during normal plant operations and post loss-of-coolant accident (LOCA), respec-tively.

The portion of these systems used for containment venting is j

i shared. All vent lines discharge to the Standby Gas Treatment System j

(SGTS).

The torus and drywell are each provided with two 18-inch-diameter penetra-l tions for de-inerting during shutdowns, ventilation during outages, and inerting during startups. These 18-inch penetrations are each provided with two system isolation valves.

The butterfly valves used in this service are designed to maintain a tight seal against post-LOCA contain-i ment pressures.

In addition to the above 18-inch penetrations, the torus and drywell are each provided with small lines for controlled purging / venting during plant operation and post-LOCA.

These small lines a're either one inch or two inches in diameter.

Each is provided with two system isolation yal.ves (either two globe valves or a globe and a check).

The valves used in this i

service are designed for very rapid closure and tight seal against post-LOCA containment pressures. We have reviewed the isolation provisions for these small lines and conclude that they comply with General Design Criteria 54 and 56.

Moreover, the concern over the ability of the valves to close during LOCA transients does not apply to these small valves.

I i

a

. The licensee responded to the NRC position letter of November 1978, by stating that they will limit purging to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year, and submitted (by letter dated July 31, 1979) a Technical Specification change request' that limits use of the purging system to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year during those periods when a LOCA is possible (e.g., when the reactor pressure is greater than 105 psig, with the reactor critical and the mode switch in the startup or run position).

i The licensee indicated (by letter dated March 3,1980) that provisions to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam are currently being developed by their valve manufacturer and Architect Engineer.

We recommend that debris screens be provided for the purge supply and ex-haust systems.

The debris screens should be seismic Category I design, installed about one-pipe-diameter away from the inner side of each inboard isolation valve.

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

I The licensee reported (by letter dated March 3,1980) that their Architect Engineer indicated that the SBGT system filters could be subjected to d.ifferential pressures in excess of design specifications if the 18-inch valves were in the open position, and that they are currently evaluating methods of preventing filter damage.

However, the licensee' has not provided an analysis which demonstrates the acceptability of the provisions made to protect other structures and safety-related equipment (e.g., fans, filters, and ductwork located beyond the purge system isolation valves) against loss of function from the environment created by the es'caping air and steam.

i

' t.

. III.

CONCLUSIONS We have reviewed the purge system for the Peach Bottom Atomic Power Station, Un'its 2 & 3, against the guidelines of BTP CSB 6-4 (Revision 1), " Containment Purging During Normal Plant Operations." We are unable to complete our review of the Peach Bottom containment purge / ventilation system design aspects i

because the licensee has not provided the following:

(1)

Information concerning the provisions made to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.

(2) An analysis which demonstrates the acceptability of the provisions made to protect structures and safety-related equipment located beyond the purge system isolation valves.

In addition, as a result of numerous reports on the unsatisfactory performance of resilient seats in butterfly-type isolation valves due to seal deteriora-tion, periodic leakage integrity tests of the 18-inch butterfly isolation 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:

i "The leakage integrity tests of the isol,ation 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 l

containment purge lines is to identify excessive degradation of the resilient, l

seats for these valves. Therefore, they need not be conducted with the pre-l cision required for the Type C isolation valve tests in 10 CFR Part 50, l

Appendix J.

These tests would be performed in addition to the quantitative l

l l

L

l

~

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

e I

1 t

l o

m e

CONTAINMENT SYSTEMS LIMITING CONDITION FOR OPERATION 3.6.1.7 The containment purge supply and exhaust isolation 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].

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

ACTION:

(For plants with valves closed by technical specification)

With one containment purge supply and/or one exhaust isolation valve open, close the open valve (s) within one hour 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 SHUTDOWN within the following 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) 1.

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

Operation cay then continue until performance of the next required 2.

valve test provided that the OPERABLE valve is verified to be locked closed at least once per 31 days.

3.

Othersise, be in at least HOT STANDBY within the next six hours 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 />.

The provisions of Specification 3.0.4 are not applicable.

4.

SURVEILLANCE REQUIREMENTS

-inch containment purge supply and exhaust isolation valves The 4.6.1.7.1

-incIi vent line isolation valves shall be 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.

3/4 6-10 01

\\ n,h 9 h110

'VL J c WG q^+'(y/

CONTAINMENT SYSTEMS 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.

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:

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 b.

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 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 af ter 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.

3/4 6-14

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 isolation 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 leaka!Ie 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.

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.

3/4 6-15

BTP CSB 6.4 Pesition B.4 amolification 1.

Purging / venting should be minimized during reactor operation because the pite; is inherently safir with closed purge / vent valves (containment) than with Open lines which require valve action to provide contair. ment.

(Sarious consideration is being given to ultimately requiring that future plants be designed such that

~

purging / venting is not required during operation).

2.

Some purging / venting on current plants will be permitted provided that:

a) purging is needed and justified for safety purposes, and b) valves are judged by the staff to be both operable and t

reliable, and c) the estimated amount of radioactivity released during the time required to close the valve (s) following a LOCA either i.

dces not cause the total dose to exceed 10 CFR Part 100 Guidelines; then a goal should be established which represents a 11mit on the annual hours of purging expected through each particular valve, or ii.

causes the total dose to exceed the guideline values; then purging / venting shall be limited to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> / year.

3.

Purging / venting should not be permitted when valves ar'e being

~

used that are known to be not operable or reliable under transient or accident conditions.

9 6