ML15239A253
| ML15239A253 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 06/17/1986 |
| From: | Freeman R NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Rubin S NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| Shared Package | |
| ML15239A254 | List: |
| References | |
| REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR AEOD-T605, NUDOCS 8607230052 | |
| Download: ML15239A253 (2) | |
Text
a JUN 17 1986 MEMORANDUM FOR:
Stuart Rubin, Acting Chief AEOD/T605 Reactor Operations Analysis Branch Office for Analysis and Evaluation of Operational Data THRU:
Peter Lam, Chief Reactor Systems Section 2 Reactor Operations Analysis Branch Office for Analysis and Evaluation of Operational Data FROM:
Robert Freeman, Engineer Incident Investigation Staff Office for Analysis and Evaluation of Operational Data
SUBJECT:
TECHNICAL REVIEW REPORT:
FAILURE OF MAIN STEAM SAFETY VALVES (MSSVs) TO PROPERLY RESEAT Enclosed is AEOD Technical Review report entitled "Failure of Main Steam Safety Valves (MSSVs) to Properly Reseat" for your consideration. On July 11, 1985 with Oconee Unit 2 at 94% power, while troubleshooting the electro hydraulic control (EHC) system, a spurious signal was generated causing steam isolation to the turbine and resulting in a reactor trip.
Following the reactor trip, two main steam safety valves (MSSVs) that actuated to reduce main steam pressure failed to fully reseat at their proper setpoint. To reseat the MSSVs, main steam pressure was reduced to approximately 990 psig by use of the turbine bypass valves (TBVs).
The spurious signal generation was caused primarily by inadequate procedures on the use of EHC test points.
A contributing factor to the spurious signal generation was the inherent sensitivity of the EHC system to electrical noise. The failure of the MSSVs to reseat was caused by improper blowdown ring settings.
The results of this investigation indicate that the safety implications of the Oconee event were minimal because no reactor coolant system overcooling occurred. Furthermore, even though the Oconee event and other operating experience shows that the potential for MSSVs failing to reseat and initiating an overcooling transient is higher for Babcock and Wilcox (B&W) designed plants 8607230052 86o617 PDR ADOCK 05000270 S
-2 than for other pressurized water reactors, the likelihood of such an overcooling to challenge the structural integrity of the pressure vessel is small.
The corrective actions taken by the licensee were judged to be appro priate and no further action by this office is deemed necessary.
Robert Freeman, Engineer Incident Investigation Staff Office for Analysis and Evaluation of Operational Data
Enclosure:
As Stated cc w/enclosure:
R. Dennig, AEOD J. Bryant, Region II V. Brownlee, Region II M. Wegner, IE DISTRIBUTION:
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