ML20156A194
| ML20156A194 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-039-00 | |
| Download: ML20156A194 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
168548 Date:
August 25, 1981
Title:
Switchyard Voltage Drops Below Low Limit at Rancho Seco The failure sequence was:
- 1. With the reactor in hot shutdown, excessive electrical demand resulted in a reduction in switchyard voltage to 206 kV.
This is below the minimum voltage (214 kV) assumed for analysis.
- 2.
The diesel generators were started and provided power to the safety-related buses.
Corrective action:
Direct switchyard voltage indications and alarms were to be installed to facilitate control room monitoring of switchyard voltages.
Design purpose of failed system or component:
Offsite power provides the preferred source of power to safety-related loads.
The vital buses have 2 power supplies, offsite and emergency diesel generators.
Reactor in hot shutdown Diesel generators and excessive load demand supply safety-related results in reduction of loads switchyard voltage to below 214-kV minimum voltage Potential Severe Core Damage V--
No Possible -
(Use of turbine-driven AFW train for natural circulation cooling may provide adequate core cooling)
NSIC 168548 - Actual Occurrence for Effective LOOP at Rancho Seco
Loss of Turbine Emer-Auxiliary PORV PORV or High Long Offsite Generator gency Feedwater and Demanded PORV Isola-Pressure Term Power Runs Back Power Secondary tion Valve Injection Core and Assumes Heat Removal Closure Cooling House Loads Potential Severe Core Damage Sequence No.
No I
No 2
No 3
4 Yes Yes 5
No 6
No 7
Yes 8
Yes 9
No 10 Yes 11 No 12 Yes 13 NSIC 168548 -
Sequence of Interest for Effective LOOP at Rancho Seco
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
168548 LER NO.:
81-039 DATE OF LER:
August 25, 1981 DATE OF EVENT:
August 7, 1981 SYSTEM INVOLVED:
Offsite power COMPONENT INVOLVED:
Switchyard CAUSE:
Low switchyard voltages due to excessive load demand SEQUENCE OF INTEREST:
LOOP ACTUAL OCCURRENCE:
Effective LOOP REACTOR NAME:
Rancho Seco DOCKET NUMBER:
50-312 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
918 MWe REACTOR AGE:
6.9 years VENDOR:
Babcock & Wilcox ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Sacramento Municipal Utility District LOCATION:
25 miles SE of Sacramento, California DURATION:
N/A PLANT OPERATING CONDITION:
Shutdown TYPE OF FAILURE:
Inadequate performance; made inoperable DISCOVERY METHOD:
Operational event COMMENT:
The safety feature equipment called upon was the DGs.
They performed as designed and powered the vital buses.
They did not experience inadequate performance or inoperability.
Also see Accession 167117 (Rancho Seco, 50-312, LER 81-034, July 7, 1981).