ML20156A129
| ML20156A129 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-069-00 | |
| Download: ML20156A129 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
160497 Date:
October 20, 1980
Title:
Inadvertent Opening of Safety Relief Valve at Pilgrim 1 The failure sequence was:
- 1. Operating pressure in the nitrogen supply line to the solenoid valve that operates the safety relief valve was in excess of the design specifications for the solenoid valve, resulting in leakage through the solenoid valve seat into the diaphragm of the safety relief valve.
- 2.
The reactor was operating at steady state at 95% power.
At the associated high reactor pressure, the leakage through the valve seat was enough to lift the relief valve.
- 3.
The reactor was manually scrammed.
- 4.
Attempts were made to close the relief valve, per operating procedures, which entailed switching the valve to the open position (which opens the nitrogen supply valve) and then to the closed position.
- 5.
The high nitrogen pressure (160 psi) delivered when the nitrogen supply valve opened, was above the set point (135 psi) at which the solenoid valve could respond to a "close" signal when the reactor is pressurized.
- 6.
The relief valve remained open until the reactor depressurized.
- 7.
The unit was successfully taken to cold shutdown.
Corrective action:
- 1. Operation at reduced nitrogen supply pressure (110 psi) was to be implemented.
- 2.
Station procedures were to be revised to require an operator verification check of nitrogen pressure once per shift.
Design purpose of failed system or component:
The nitrogen system provides control gas to actuate the opening and closing of reactor relief valves upon automatic control demands as well as manual demands.
The reactor relief system provides overpressure protection for the RCS.
Reactor operating Safety relief valve Reactor is Procedure followed at full power opens due to N2 system manually to close the valve pressure exceeding tripped results in valve design specs for stuck open relief valve operators Potential Severe Core Damage No -
reactor success-fully shut down No No - auto scram and safety injection available No NSIC 160497 - Actual Occurrence for Inadvertent Opening of Safety Relief Valve at Pilgrim 1
Small Reactor Standby High Automatic LPCI Long Loss of Scram Liquid Pressure Depressuri-or CS Term Coolant Control Cooling zation
Response
Core Accident Initiated Provided System Adequate Cooling j
Operates Potential Sequence Severe No.
Core Damage No Yes No 1
2 3
4 5
Yes Yes Yes 6
No 7
Yes Yes Yes 8
9 10 NSIC 160497 -
Sequence of Interest for Inadvertent Opening of Relief Valve at Pilgrim 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
160497 LER NO.:
80-069 DATE OF LER:
October 20, 1980 DATE OF EVENT:
October 7, 1980 SYSTEM INVOLVED:
Pressure relief system COMPONENT INVOLVED:
Relief valve CAUSE:
Excessive nitrogen pressure to valve operator SEQUENCE OF INTEREST:
Main steam line break ACTUAL OCCURRENCE:
Stuck open relief valve REACTOR NAME:
Pilgrim 1 DOCKET NUMBER:
50-293 REACTOR TYPE:
BWR DESIGN ELECTRICAL RATING:
655 MWe REACTOR AGE:
8.3 years VENDOR:
General Electric ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Boston Edison Co.
LOCATION:
4 miles SE of Plymouth, Massachusetts DURATION:
N/A PLANT OPERATING CONDITION:
Full power TYPE OF FAILURE:
Design basis event DISCOVERY METHOD:
Operational event COMMENT:
All safety systems were available.
See Accession No.
160559 for a similar event at Pilgrim 1 (50-293, LER 80-080, Nov.
14, 1980) but with a different cause.