ML20156A201
| ML20156A201 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-005-00 | |
| Download: ML20156A201 (5) | |
Text
C Accession Number: 164149 e: February 12, 1981 Isolable Small Break LOCA at Robinson 2 failure sequence was:
With the plant at 100%, the "A" electrohydraulic control oil pump developed a seal leak and a plant shutdown was begun. The "B" EHC pump was already out of service because of vibration problems.
The "B" feedwater and condensate pumps were stopped due to erratic feedwater pump behavior.
immediately following the opening of the generator output breakers (6% power), the turbine governor valve spiked open (apparently due to the electrohydraulic problems) and generated a momentary high steam flow signal. This, in combination with an existing low T signal resulted in train B safequards initiation. (Train A did not initiate nor did the MSIVs close, apparently because of the short duration of the high steam flow signal). The SI signal tripped the reactor.
The "A" SI train was manually actuated and the MSIVs were closed.
The "A" containment fire alarm was received shortly after the SI actuation.
During the automatic isolation of the letdown line on safety injection, relief valve CVC-RV-203 bellows ruptured, either because of the relatively slower closure of valves upstream of the relief valve compared with those downstream of it, or because of leakage past the upstream valves. In addition, a pressure surge due to the isolation valves closing caused a drain cap on a partially open drain valve to be blown off.
Having determined that a spurious SI had occurred and unaware of the above failure, the operators reset SI and feedwater isolation and restored letdown.
Containment pressure and dewpoint increased and RCS pressure de-creased. Letdown was secured approximately 15 min later. A con-tainment entry was made in an attempt to determine the leakage path. Approximately 3000 gallons of water were in the containment sump at that time.
After letdown was isolated, pressurizer pressure continued to de-crease. A second safety injection occurred on low pressure. Both trains of safeguards equipment actuated.
Four hours after the first containment entry a second entry was made and the leaking drain line identified. The two upstream level control valves were leaking at approximately 5-7 gpm. The drain valve was closed.
demand in lieu of stem position, which delayed identification of the cause of the depressurization.)
The leak rate could not be accurately determined but it was estimated to have been approximately 100 gpm while letdown was unisolated. A total of about 4500 to 6000 gallons of water was leaked to the containment sump during the event.
rective action:
The leaking drain valve was closed and a new pipe cap installed.
All other similar valve/pipe cap combinations were verified closed.
Corrective action concerning the failed relief valve was not identified.
ign purpose of failed system or component:
The reactor coolant system transfers heat generated in the core to steam generators. The letdown line provides a means of removing ctor coolant from the RCS for boron concentration changes and for ification.
jection slow valve letdown to unisolated continues to failed relief valve RCS pressure spray valve Core tiated closures restored CVCS leakage decrease due and open drain line due in part to identified Damage d MSIVs result in paths (-3000 to leakage identified; drain leaking pres- by stopping osed CVCS relief gal in 15 flow through line closed; addi- surizer spray RC pumps B valve bellows min) closed CVCS tional letdown valve and C failure and valves, second isolation valve drain valve safety injec- closed pipe cap tion failure No No - charging flow available for makeup No No - charging flow available for makeup No No - charging flow available for makeup No No - SI available No No - charging flow available for makeup No No NSIC 164149 - Actual Occurrence for Isolable Small Break LOCA at Robinson 2
No 1 Yes 2 Yes 3 No 4 Yes 5 Yes 6 Yes 7 NSIC 164149 - Sequence of Interest for Isolable Small Break LOCA at Robinson 2
- auto isolation on safety injection closure of upstream valves
C ACCESSION NUMBER: 164149 NO.: 81-005 E OF LER: February 12, 1981 E OF EVENT: January 29, 1981 TEM INVOLVED: Containment chemical volume control system PONENT INVOLVED: Relief valve, drain valve, pipe cap, pressurizer spray valve SE: Bellows rupture, drain valve vibrated open, pipe cap blew off, leaking spray valve UENCE OF INTEREST: Small break LOCA UAL OCCURRENCE: Small break LOCA CTOR NAME: H. B. Robinson 2 KET NUMBER: 50-261 CTOR TYPE: PWR IGN ELECTRICAL RATING: 700 MWe CTOR AGE: 10.4 years DOR: Westinghouse CHITECT-ENGINEERS: Ebasco RATORS: Carolina Power & Light ATION: 5 miles NW of Hartsville, South Carolina ATION: N/A NT OPERATING CONDITION: 100% power (6% at time of trip)
E OF FAILURE: Small LOCA COVERY METHOD: Operational event MENT: Additional information: "Engineering Evaluation of the H. B.
Robinson Reactor Coolant System leak on January 29, 1981,"
Office for Analysis and Evaluation of Operational Data, March 23, 1981.