ML18141A061
| ML18141A061 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 06/13/1983 |
| From: | Zukor D NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML18141A060 | List: |
| References | |
| TASK-AE, TASK-T318 AEOD-T318, NUDOCS 8307290307 | |
| Download: ML18141A061 (3) | |
Text
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- ttEOD Technical Review Report e UNIT:
Surry Units 1 and 2 DOCKET No.:
280 and 281 LICENSEE:
Virginia Electric and Power Co.
NSSS/AE:
Westinghouse/Stone & Webster TR REPORT NO.: AEOD/T318 DATE: June 13, 1983 EVALUATOR/CONTACT:
D. Zukor
SUBJECT:
FAILURE OF RECIRCULATION SPRAY SERVICE WATER MOY-s EVENT DATE:
February 9, 1983
SUMMARY
During testing seven out of eight recirculation spray service water valves failed to open-on demand from the control room.
Inspection of the valves revealed corrosion of some of the valves and valve operators. This system provides one of the interfaces with the ultimate heat sink of the plant; its failure during a LOCA could ultimately result in serious core damage.
This event has been suggested to the Data Management Section as an Abnormal Occurrence since it represents a major degradation of safety related equipment.
DISCUSSION The Recirculation Spray Subsystem is one of the systems available to cool and depressurize the containment following an accident (See Figure 1). It also ensures subatmospheric pressure within 20 minutes for a prolonged time period following a design-basis accident. During the recirculation phase of a LOCA it provides the only pathway to remove heat from the core.
There are four 50% design capacity recirculation spray pumps.
Two are located inside of containment and two are located outside. They pump water from the containment sump, through the recirculation spray heat exchangers, to the recirculation spray headers.
When a LOCA occurs, four 24 11 Henry Pratt butterfly valves open to admit service water to the recirculation spray heat exchangers.
In Figure 1 these are valves MOV-SW-103A, MOV-SW-1038, MOV-SW-103C. and MOV-SW-103D.
On February 9, 1983, all four of these valves failed to open on unit 1 and three failed to open on u~it 2.
One failure to open (MOV-SW-1038) was attributed to torque switch corrosion; two of the other failures were due to motor corrosion (MOV-SW-103C and 203C).
The cause for the other failures was not known.
In Unit 1, valves 103A, B, C, D were lifted manually to get the butterfly disc off of the seat. Valves 103A and 103D were then operated successfully from the control room.
Valves 1038 and 103C would still not operate electrically and had to be manually opened.
In Unit 2, valves 203A and D required a small increase of the torque setting to cycle the valves. The motor of valve 203C was corroded and was replaced.
A similar event occu*rred at Surry 2 during a functi ona 1 periodic test on November 8, 1981 (LER 81-076). Valve 203C failed in an intermediate position.
No cause of failure could be identified at that time.
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Numerous similar events involving corrosion in the service water system or its equivalent exist at other plants. The generic implication of the Surry failures have not yet been evaluated.
FINDINGS The valves which failed at Surry are located in pits. It is possi~le, though not c~rtain, that these valves and/or valve operators have been submerged at one time. A similar problem was found at Surry concerning the valves which.
control service water to the component cooling heat exchangers (AE0D/E303).
Modifications in terms of dikes and level alarms have been installed to pre-vent future flooding. This is an area which requires further evaluation.
In addition, c_orrosion due ;to brackish water needs to be evaluated.
The licensees modifications to prevent filling the sumps and a schedule of more-frequent testing (from 18 months to quarterly) may eliminate some failures but does not solve the problem.
CONCLUSIONS
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Corrosion in service water systems is present in many plants where brackish water is used in that system. Corrosion due to brackish water or flooding
- indicate a potential for common mode failure of both containment spray systems.
Although these two containment spray system provide redundancy to reduce containment pressure, the safety analysis does not assume that the entire recirculation spray system is inoperable due to a pre-existing failure.
An engineering evaluation wi.11 be performed to further analyze and evaluate
. the Surry event.
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