ML20116E733
| ML20116E733 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/31/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20116D885 | List:
|
| References | |
| FOIA-96-237 NUDOCS 9608060104 | |
| Download: ML20116E733 (3) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PLANT SYSTEMS BRANCH POTENTIAL SEISMIC DESIGN DEFICIENCY,... THE SERVICE WATER SYSTEM CALVERT CLIFFS, UNITS 1 AND 2 DOCKET NO. 50-217 AND S0-218
1.0 INTRODUCTION
In Calvert Cliffs LER 89-023, the licensee identified a potential design deficiency whereby a failure in the nonseismic portion of the service water system (SWS) could result in the draining 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 comon nonsafety-related, seissiic Category 2 (operating basis earthquake) train. The safety-related trains supply cooling water to the spent fuel pool cooling heat exchanger, containment cooling units and the emergency diesel generators. The nonsafety-related train supplies cooling water to various turbine building components. The common nonsafety-related train is fed by both safety-related trains via redundant air-operated automatic isolation valves which close on a safety injection actuation signal (SIAS) and fail closed on loss of air.
However, they do not fail closed on loss of offsite power. A pipe break in the nonsafety portion of the system 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 a loss of all AC power.
Supplement No. I to LER 89-023 dated March 12, 1990 provided the results of the licensee's followup and identified corrective 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 unit.
2.0 EVALUATION In Supplement No. I to LER 89-023, the licensa has identified interim compensatory actions that will be established prior to startup. These include changing the alarm manual to include requiring the operator to isinediately isolate the turbine building header on large rupture indications, to assure that the operaturs are informed of the required operator action, and increased frequency of leak rate monitoring of the SWS prior to Unit 1 startup. The licensee also identified that a task force had been formed to detennine long term corrective actions. By letter dated August 24, 1990, the licensee i
provided a comitment that the long term followup would include automatic 1
9608060104 960731 p$IcoW6-237 PDR j
' isolation of the safety-relateo portion of the SWS from the nonsafety-related portion upon indication of a rupture of the nonsafety-related portion of the sy stem.
The interim measures provide adequate justification for continued operation because of the low probability of the combination of events that noust occur 10 order to make the loss of SWS at Calvert Cliffs a serious threat to plant safety.. A pipe rupture or break in the nonsafety-related portion of the system, taken by itself as the initiating event, is not a significant contributor 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 LOCA or LOOP also occurs. Without a seisinic event, the staff does 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 not be isolated prior to draining both trains of the system, the probability of recovery is high because the plant can be shutdown and maintained in a safe i
shutocwn condition without operation of the SWS.
The icng term corrective action to provide automatic isolation of the f
safety-related pcrtion of the SWS from the nonsafety-related portion when pipe rupture ir.dications in the nonsafety-related portion are detected will make 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 f or Protection Against Natural Phenomena," as they specifically relate to earthquakes taken in combination with the effects of normal ano accident conditions.
3.0 CONCLUSION
Based on its evaluation of the licensee's interim actions and comitment to provide long term corrective actions, the staff concludes that the licensee's followup actions are acceptable and that continued operation is justified.
These conclusions are based in part on the licensee's comitment to complete the long-term modifications on Unit I during refueline outage No. 10 (fall 1991) and outage No. 9 (fall 1992) for Unit 2.
Principal Contributor W. LeFaye
[CALVERT TACS 77301/2]
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SPLB SALP INPUT Plant Name:
.Calvert Cliffs, Units 1 and 2 l
Subject:
Potential Seismic Deficiency in the Service Water System (SWS)
TAC No.:
77301 and 77302 Summary of Review / Inspection Activities The staff reviewed the licensee's interim actions and long term corrective actions to address a potential seismic design deficiency in the SWS. A scismic event could disable both trains of the SWS which is used to cool the crergency diesel generators (EDG) and the containment coolers (used in LOCA analysis). Therefore, the system design, hence the plant could not withstand an SSE coupled with a loss of offsite power. Additionally, LOCA responst j
systems were not designed to seismic Category I requirements.
Interim actions w2re procedur41 to isolate the nonseismic portion of the system and in the l
1:ng term connitments were made to make this isolation automatic.
Narrative Discussion of Licensee Performance - Functional Area l
The licensee's followup to this initial discovery did not reflect a good l
understanding of the safety implications of this event or the licensing basis for his plant. The licensee appeared to be more concerned with trying to show how the design was in accordance with NRC requirements and in accordance with the staff's 1972 SER. The only licensing basis the licensee considered were tords in the staff's SER and cuncluded that because the scenario was not specifically described in the SER that it was outside the design basis. No discussion of GDCs or the FSAR was made with respect to the systems licensing basis. We had to request the licensee to make a commitment for long term corrective actions.
Author:
W. LeFave Date: August 29, 1990 l
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