ML20059N225

Safety Evaluation Accepting Proposed Actions Re Potential Design Deficiency,Per LER 89-023

ML20059N225
Person / Time
Site:	Calvert Cliffs
Issue date:	10/01/1990
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20059N224	List: ML20059N223 ML20059N225
References
NUDOCS 9010110010
Download: ML20059N225 (4)

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ENCLOSURE 1 1 '

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION POTENTIAL-SEISMIC DESIGN DEFICIENCY IN THE SERVICE WATER SYSTEM

'CALVERT CLIFF _S. UNITS 1 AND 2-DOCKEi & 60-317 AND 50-318'- .I 1.0 INTRODUC7 ION -

In Calvert ',liffs'- LER 89-023' dated January 19, L1990, Baltimore Gas _ an'd Electric  !

Company .1censee) identified a' potential design deficiency. whereby a failure 1

'in the nonseismic portion'of _the, service water system-(SWS) could result ~in the J

• .;ning and consequent failure of both safety-related seismic Category I trains of the SWS.

The SWS at each of the Calvert Cliffs units (Units 1 and 2) is a closed loop-cooling water system which supplies cooling water to two safety-related  ;

. seismic Category I (safe shutdown earthquake) trains and a consnon =

nonsafety-related, seismic Category II'(operating basis earthquake) train. The-safety-related trains supply cooling water to the: spent fuel pool cooling heat- a exch:.nger, containment cooling units and the emergency ~ diesel generators. The _

e nonsafety-related train supplies cooling water to various turbine building components. The consnon nonsafety-related train is' fed by both safety-related trains via redundant air-operated automatic ~1 solation valves which close on a .

safety in,jection actuation signal (SIAS)_and fa11' closed on loss of air.

However, they do not. fail closed on loss of offsite power.. ' A pipe break in  !

the nonsafety portion of theisystem could cause rapid draining of_ the surge (head) tanks in both safety-related trains.with the potential loss of emergency diesel generators (EDG) due to a~ loss of cooling water. _ Hence', a loss of offsite power coupled with the ' pipe break could result'in aLloss of all AC power.

Supplement No. 1 to'LER 89-023 dated March 12,' 1990, provided the results of  ;

the licensee's followup and identified cor.ective actions.. . These corrective '

actions included a task force to determine. appropriate long-term actions plus interim compensatory. actions to be ' accomplished . prior to the startup of either.

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2.0 EVALUATION- a a

In Supplement No.1 to LER 89-023, the licensee has identified' interim.

compensatory actions that will be established prior to startup. These include j changing the alarm manual to include requiring the operator to insnediately isolate the turbine building header on large rupture indications, to assure i that the operators are informed of the required operator action, and increased l

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4 frequency of leak rate monitoring of the SWS prior to Unit 1.startup. The licensee also identified that a task force had been fonned to determine long.

term corrective actions. By letter dated August 24, 1990, the licensee provided a commitment that the long-term followup would include automatic isolation of the safety-related portion of the SWS from the nonsafety-related portion upon indication of a rupture of the nonsafety-related portion of the system. ,

l The interim measures provide adequate justification for continued operation -

because of the low probability of the combination of events that must occur.in order to make the loss of SWS at Calvert Cliffs a serious threat to plant i safety. A pipe rupture or break in the nonsafety-related portion of the i system, taken by itself as the initiating event, is not a significant contributor j to risk because the only risk-related components cooled by the SWS are the containment air coolers and the EDGs. The SWS itself is not necessary for safe plant shutdown following a rupture unless a loss-of-Coolant-Accident (LOCA) {

or loss of Offsite Power (LOOP) also occurs. Without a seismic event, the staff does j not postulate a complete rupture of this moderate energy system. For the more-likely small leakage cracks, operator action to isolate the leak can be relied ,

upon prior to draining the system. If a larger leak were to occur, that could l l

not be isolated prior to draining both trains of the system, the probability of i recovery is high because the plant can be shutdown and maintained in a safe shutdown condition without operation of the SWS.  ;

The long-term corrective action to provide automatic isolation of the  !

safety-related portion of the SWS from the nonsafety-related portion when pipe rupture indications in the nonsafety-related portion are detected, will make i the system capable of withstanding a pipe rupture due to seismic event (assuming a single active failure) without requiring. operator action.  !

These interim and long-term corrective actions provide' reasonable assurance-that the system design will meet the requirements of General Design Criterion.2,

" Design Basis for Protection Against Natural Phenomena," as they'specifically relate to earthquakes taken in combination with the effects of normal and

. accident conditions.

3.0- CONCLUSION  !

l Based on its evaluation of the licensee's interim actions and consnitinent to provide long-term corrective actions, the staff concludes that the licensee's  !

followup actions are acceptable and that continued operation' is ' justified. j These conclusions are based in part on the-licensee's consnitment to complete 1 the long-tenn modifications on Unit I during refueling outage No.10-(fall.

1991) and outage No. 9 (fall 1992) for Unit 2. i j

4 Dated: October 1, 1990 f

Principal Contributor: "

W. LeFaye  !

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ENCLOSURE 2-3 0,, UNITED STATES J

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l EVENT CLASSIFICATION ASSESSMENT j LER 89-023. SUPPLEMENT 1 I CALVERT-CLIFFS UNITS 1 AND 2 >

DOCKET NOS. 50-317 AND 50-318 -

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1.0 INTRODUCTION

j l I In Supplement No. l' to LER 89-023 dated March 12, 1990, the Baltimore Gas and Electric Company (licensee) concluded that the identified design deficienc outside the original-licensing design basis for the service water system (ySWS). was I at Calvert Cliffs, Units 1 and 2. The licensee's conclusion was based on.the ' '

fact that the specific scenario of concern (seismic event coupled with alloss of offsite power) was not identified in the staff's 1972 Safety Evaluation .

Report (SER).

2.0 ASSESSMENT Wedonotagreewiththelicer.see'sconclusionsrelatedtothedesihn' basis for the SWS. The licensee's reference only to tha staff's-1972 SER is inappropriate. The staff's'SER is not the sole licensing basis for a plant.

The staff's SERs do not describe all of the scenarios.that make up the design basis for any system. In the case of the Calvert Cliffs SWS, the SER described what was the worst case design basis. accident,1.e.,'a Loss-of--

Coolant-Accident (LOCA) with a simultaneous Loss of Offsite Power (LOOP).

This desigr tis worst case accident is presumed to place the most heat load demand:on ...s 2 5. The scenario of concern, a seismic event coupled with a y

L LOOP is not considered an " accident" and is, therefore, not. addressed as.a' Chapter 15'(Chapter 14 for Calvert Cliffs) event.- However, the overall response of a plant and its systems to a seismic event coupled with a single active failure is evaluated by the staff. This is generally done on a system '

by system evaluation. As part of this evaluation, it is assumed-that a LOOP occurs because the offsite power system is not designed to seismic Category If t

l requirements- In the case.of Calvert Cliffs, the. drawings in the Final Safety; l

Analysis Report (FSAR) indicate! that the' air-operated isolation- valves which isolate the nonseismic portion of the SWS are fail closed valves; . Therefore.

an assumption that these valves . fail closed on loss of air and/or power would (

have been made by the staff during its review. If in fact, they'.did fail '

L closed on a LOOP, the system would be able to perform its safety, function.

J (assuming an adequate closure time) following a combined seismic event LOOP, 7 and single active failure.

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l The staff's SER is based on the design details provided in the licensee's FSAR I which basically documents the licensing basis for the plant. .In Section 8.4.1.2 I of the licensee's FSAR, it is stated that "the emergency diesel generators and- I their auxiliaries are designed to withstand Seismic Catege'ry I accelerations {

and are installed in Category I structures." The staff's assessment of the onsite power system'is performed assuming the offsite power system is not available, the onsite power system including its auxiliary support systems are seismic Category I, and a single failure occurs. The statement in the FSAR Section 8.4.1.2 supports this staff assumption. Further the staff includes appropriate combinations of the effects of normal and accident conditions with the effects of natural phenomena- when reviewing systems important to safety, which includes the SWS.

3.0 CONCLUSION

We have concluded that the initial notification indicating that the event is .

reportable per 50.73(a)(2)(v) is appropriate and the subsequent reclassification was-incorrect. We based our conclusion on the review process and assumptions used  ;

during the licensing review for the Calvert Cliffs facility as discussed above.

Dated: October 1, 1990 -'

Principal Contributors:

W. Letave D. Mcdonald 1

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