ML20156A245
| ML20156A245 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-056-00 | |
| Download: ML20156A245 (4) | |
Text
Accession Number: 172198
- January 18, 1982 Inadvertent MSIV Closure and Inadvertent Safety Valve Lifts at St. Lucie I failure sequence was:
At 4:14 a.m. on December 19, 1981, a combination of low instrument air pressure to the MSIVs and a slightly higher than normal steam flow resulted in the inadvertent closure of both MSIVs.
The reactor pressure increased to 2410 psig (normal lift pressure is 2500 psig), causing a reactor trip on high pressurizer pressure and opening the PORVs. Pressurizer code safety valve V1200 apparently also opened, but this was not realized at the time.
The quench tank rupture disk ruptured because of the relief valve discharge.
Pressurizer safety valve V1200 disk and seat were probably damaged during the lift due to the improper installation of an adjusting ring set screw, but this was not known at the time.
The reactor was restarted and held below the power range during repair of the rupture disk and MSIV trouble shooting.
At 1:45 p.m. with the RCS at normal operating pressure, valve V1200 again spuriously opened and was verified open by acoustic flow monitor indication. A high blowdown (34% in lieu of the specified 4%) occurred due to a maladjusted nozzle ring.
RCS pressure decreased to 1670 psig and the reactor tripped on thermal margin/low pressure. A reactor cooldown was begun to replace V1200.
On December 23, 1981, after replacement of valve V1200, a turbine/reactor trip occurred during startup. The reactor was again started up and power operation was commencing when the "B" steam generator pressure relief valves started lifting. It was suspected that the "B" MSIV was closed even though it indicated open.
A shutdown and cooldown was initiated. The "B" MSIV was found to have one bent and one broken actuator connecting pin. The "A' MSIV was found to have two slightly bent connecting pins.
rective action:
Pressurizer safety valve V1200 was replaced. The MSIVs were ired.
gn purpose of failed system or component:
The code safety valves provide relief protection to prevent vessel/
piping overpressure during transient events.
The main steam isolation valves provide for steam generator isolation during steam line break events as well as providing for containment isolation.
er Reactor trip on Reactor restarted Pressurizer code RCS pressure Cooldown to Turbine/reactor trip Potential high pressurizer and held below power safety V1200 lifts decrease, trip replace V1200 during next startup; Severe pressure. Quench range for rupture spriously; high on thermal reactor restarted, Core ru- tank rupture Disk disk repairs and blowdown due to margin/Low power operation Damage re ruptured because MSIV troubleshooting maladjusted nozzle pressure commencing when gh of relief valve ring steam generator B discharge. Pres- saftey valve, started surizer code safety lifting due to closed V1200 apparently MSIV B (valve was lifts (lift is indicating open) undetected), disk/
seat damage results from improper set screw installation No No No No No NSIC 172198 - Actual Occurrence Tree for Inadvertent MSIV Closure and Inadvertent Safety Valve Lifts at St. Lucie 1
Small Reactor Auxiliary High Low Pressure Potential Sequence LOCA Trip Feedwater and Pressure Recirculation Severe No.
Secondary Injection and LPR/HPI Core Heat Removal Cross-Connect Damage No Yes 2 Yes 3 No 4 Yes Yes 6 Yes 7 NSIC 172198 - Sequence of Interest for Inadvertent Pressurizer Code Safety Valve Opening at St. Lucie 1
- reseating of safety valve V1200 would provide mitigation
C ACCESSION NUMBER: 172198 NO.: 81-056 E OF LER: January 18, 1982 E OF EVENT: December 19, 1981 TEM INVOLVED: Main steam and pressurizer pressure relief PONENT INVOLVED: MSIV, pressurizer code safety SE: MSIVs (spurious); PSRV (assembly error)
UENCE OF INTEREST: LOFW UAL OCCURRENCE: LOFW CTOR NAME: St. Lucie 1 KET NUMBER: 50-335 CTOR TYPE: PWR IGN ELECTRICAL RATING: 802 MWe CTOR AGE: 5.7 years DOR: Combustion Engineering HITECT-ENGINEERS: Ebasco RATORS: Florida Power and Light Company ATION: 12 miles SE of Ft. Pierce, Florida ATION: N/A NT OPERATING CONDITION: 98%
E OF FAILURE: Inadequate performance OVERY METHOD:
MENT: