ML20168A720
| ML20168A720 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 06/16/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1976-015-00 | |
| Download: ML20168A720 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
120995 Date: November 11, 1976
Title:
Suction Valves to Decay Heat Pumps Fail to Open at Rancho Seco The failure sequence was:
- 1. During testing, neither sumnp isolation was applied.
valve opened when an open signal
.Corrective action;
- 1. The valves were moved manually and then cycled electrically.. The bypass switches for the valve torque switches-was-adjusted to permit more motor turns before the bypass switches difopped. out.
Design purpose of failed system or component:
- 1. The valves provide for fluid flow from the sump to the low pressure and high pressure recirculation systems and the building spray system (while in the recirculation mode) following a LOCA.
Unavailability of system per WASH 1400:
- low pressure recirc:
1.3 x 10-2 /D high pressure recirc:
9 X 10-3/D Unavailability of component per WASH 1400:
- motor operated valve, failure to operate.
1 x 10-3/D UnavailabilitieQ are in units of per demand D-1.
Failure rates are in units of per hour HR-T
Potential Severe core Damage No No No -
No LOCA and unit in shutdown.
NSIC 120995 -
Actual Occurrence for Failure of Both Suction Valves to Decay Heat Pumps from Emergency Sump at Rancho Seco
Small Reactor Auxiliary
]High Low Pressure LOCA Trip Feedwater and
- Pressure, Recirculation Secondary jInjection and LPR/HPI Heat Removal Cross-Connect Potential Severe Core Damage Sequence No.
2 3
4 5
6 7
NSIC 120995 -
Sequence of Interest for Both Sump Suction Valves to Decay Heat Pumps Fail to Open at Rancho Seco
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER-120995 DATE OF LER:
November 22, 1976 DATE OF EVENT:
November 11, '1976 SYSTEM INVOLVED:
Decay heat COMPONENT INVOLVED:
Pumps CAUSE:
Switch setting incorrect.
SEQUENCE OF INTEREST:
LOCA ACTUAL OCCURRENCE:
Valves fail to open for decay heat system.
REACTOR NAME: Rancho Seco DOCKET NUMBER:
50-312 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
918 MWe REACTOR AGE:
2.1 yr VENDOR:
B&W ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Sacramento Municipal Utility District LOCATION:
.25 mi1les SE..of. Sacramento, CA DURATION:
360(a) hours PLANT OPERATING CONDITION:
Shut down.
SAFETY FEATURE TYPE OF FAILURE:
(a) inadequate performance; (b) failed to start; QDmade inoperable; (d)
DISCOVERY METHOD:
During test.
COMMENT:
Bypass switches for torque switches were dropping out before valve disc cleared seat resulting in torque switch stopping valve movement.