ML20156A150
| ML20156A150 | |
| 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 1981-034-00 | |
| Download: ML20156A150 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
167117 Date:
July 7, 1981
Title:
Switchyard Voltage Drops Below Low Limit at Rancho Seco The failure sequence was:
- 1. With the reactor in a heatup mode coming from cold shut down, excessive electrical demand resulted in a reduction in switchyard voltage to 207 kV.
This is below the minimum voltage (214 kV) assumed for analysis.
- 2.
The reactor coolant pumps were tripped to avoid excessive tempera-tures.
- 3.
Two failures in the electrohydraulic control system for the turbine generator occurred.
- 4.
The diesel generators were started and provided power to the safety-related buses.
- 5.
The reactor was operated in the decay heat mode.
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 power and emergency diesel generators.
The unit generator cannot directly power these buses.
Reactor shutdown Reactor coolant Diesel Reactor heat and excessive pumps tripped generators removal via grid demand supply safety-decay heat results in low related loads removal switchyard system voltage Potential Severe Core Damage No Possible -
RCS heatup and use of turbine-driven AFW train for natural circulation cooling may provide adequate core cooling Possible -
RCS heatup and use of turbine-driven AFW train for natural circulation cooling may provide adequate core cooling No Possible RCS heatup and use of turbine-driven AFW train for natural circulation cooling may provide adequate core cooling Possible -
RCS heatup and use of turbine-driven AFW train for natural circulation cooling may provide adequate core cooling NSIC 167117 - 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 1
No No Yes 4
Yes 5
No 6
No 7
8 Yes Yes 9
NO 10 Yes 10 No 12 Yes 13 NSIC 167117 -
Sequence of Interest for Effective LOOP at Rancho Seco
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
167117 LER NO.:
81-034 DATE OF LER:
July 7, 1981 DATE OF EVENT:
June 19, 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:
6.8 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:
Cold shutdown TYPE OF FAILURE:
Inadequate performance; made inoperable DISCOVERY METHOD:
Operational event COMMENT:
The safety features equipment called upon were the DGs.
They performed as designed and powered the vital buses.
They did not experience inadequate performance or inoperability.
Also see Accession 168548, Rancho Seco, 50-312, LER 81-039, Aug.
25, 1981.