ML13333B765

Forwards Case Study Rept Containing Detailed Description, Findings,Conclusions & Recommendations Re 800310 Loss of Salt Water Cooling Event

ML13333B765
Person / Time
Site:	San Onofre
Issue date:	08/12/1982
From:	Michelson C NRC Office for Analysis & Evaluation of Operational Data (AEOD)
To:	Deyoung R, Harold Denton, Minogue R NRC/IE, Office of Nuclear Reactor Regulation, Office of Nuclear Regulatory Research
Shared Package
ML13333A766	List: ML13333B765 ML13333B766 ML13333B767 ML13333B768
References
TAC-65149 NUDOCS 8208270684
Download: ML13333B765 (3)

Text

AUG 1 2 1982 MEMORANDUM FOR:

Harold R. Denton, Director Office of Nuclear Reactor Regulation Richard C. DeYoung, Director Office of Inspection and Enforcement Robert 8. Minogue, Director Office of Nuclear Regulatory Research FRON:

Carlyle Michelson, Director Office for Analysis and Evaluation of Operational Data

SUBJECT:

CASE STUDY REPORT O SAN OAOFRE UNIT 1 LOSS OF SALT WATER COOLING EVENT OF MARCH 10, 1980

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2-a7 697 On March 10, 1980, while operating at 100% power, Sari Onofre Unit 1 experienced a complete loss of the salt water cooling system. The event involved an unlikely triple failure which resulted in operations exceeding the plant's limiting conditions for operation. The event was later determined to be an abnormal occurrence. Enclosed for your information and appropriate action is the AEOD case study of the event.

The report contains a detailed description of what occurred along with our findings, conclusions, and recommendations.

The report recommendations concern:

a) single failure vulnerability of the salt water cooling system; b) contamination of plant air systems; c) in-service testing programs; and d) plant technical specifications With regard to the single failure vulnerability of San Onofre 1's salt water cooling system, we note that on May 13, 1982, while the plant was in cold shutdown, maintenance activities were performed which caused two more complete losses of the salt water cooling system.

These occurred as follows:

8208270684 820812 PDR ADOCK 05000206 P

PDR OFFICE SURNAMEr..................

DATE NRC FORM 318 (10-80) NRCM 0240 OFFICIAL RECORD COPY USGPO: 1981-335-960

Harold R. Denton 2

While the plant staff was removing the internals of one salt water cooling pump for preventive maintenance operations, the Pacific Ocean flooded the pump bay.

The flooding took place because an error was made in calculating the tide elevation.

Subsequently, the operating salt water cooling pump was secured to prevent it from being damaged.

The auxiliary salt water cooling pump was inoperable due to the on going maintenance activities.

About an hour after resuming salt water cooling pump operations, the discharge valve on the north salt water cooling pump failed closed causing another interruption of the salt water cooling system. The flooding is suspected as the cause of this failure (residual moisture in the pressure switch and melted insulation in an associated time delay relay).

During both of these interruptions of cooling the screen wash pumps (which are of a lower capacity and are not "safety-related")

were used to supply salt water cooling. Since the unit had been in cold shutdown at the time, there were no adverse effects to the plant or the public.

As shown in the case study report (Section 3.1), a complete loss of the salt water cooling system during the early stages of RHR operation could lead to damage to safety-related equipment within a few minutes.

Fortunately, the March 10, 1980 and the May 13, 1982 events did not occur while the plant was in the early stages of RHR operation.

In NRR's peer review comments (memorandum from H. Denton to C. Michelson, June 7, 1982),

NRR agreed that the salt water cooling system is critical during RHR operation, and that special attention should be focused on such single failure vulnerability.

Furthermore, NRR stated that SEP Topic 1X-3, Station Service and Cooling Water Systems, will include a single failure analysis of the cooling water systems.

We note that the May 13, 1982 failures have provided additional failure modes for consideration in the SEP study.

This office would like to be kept informed as to how the aforementioned recommendations are being addressed and/or will be addressed by future actions.

OFFICE SURNAME I)

DATE)

I--CR CP NRC FORM 318 (10-80) NRCM 0240 OFFIC IAL REC DC YUSGPO:

1981-335-960

Harold R. Denton 3

If you have any questions regarding this matter, please contact either myself or Harold Ornstein of my staff.

Original Signed by Carlyle Michelson Carlyle Michelson, Director Office for Analysis and Evaluation of Operational Data

Enclosure:

As Stated cc w/enclosure:

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