ML20168A575
| ML20168A575 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/16/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1976-049-00 | |
| Download: ML20168A575 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
117944 Date:
September 3, 1976
Title:
Offsite Power Lost at Millstone 2 The failure sequence was:
- 1. During a hurricane, severe salt contamination caused several switchyard failures, resulting in a loss of offsite power and a reactor trip from 100% power.
- 2. The diesel generators, which had been running prior to the trip, provided power to safety related loads.
Corrective action; Switchyard equipment and insulators were washed down, damaged circuit breakers were repaired, and the offsite transmission lines returned to service.
Design purpose of failed system or component:
Offsite power provides the preferred source of power to safety related loads when the unit generator is not available.
Unavailability of system per WASH 1409:
- off-site power:
2 x lO-5Ihr Unavailability of component per WASHi 1400:*
Unavailabilities are in units of per demand D-1.
Failure rates are in units of per hour HR-1.
Reactor at Diesel genera-Severe salt spray Diesel generators 100% power tors running
-causes switchyard assume safety during equipment failures related loads hurricane and loss of offaite power and conse-quent reactor trip Potential Severe Core Damage No No -
steam driven AFW pump available for RX cooling No No No -
steam driven AFW pump available for Rx cooling No NSIC 117944 -
Actual Occurrence for Offsite Power Lost at Millstone 2
Loss of Turbine Offsite Generator Power Runs Back and Assumes House Loads Emer-gency Power Auxiliary PORV Feedwater and Demanded Secondary Heat Removal PORV or PORV Isola-tion Valve Closure High Long Pressure Term Injection Core Cooling Potential Severe Core Damage I
Sequence No.
2 3
4 5
6 7
8 9
10 11 12 13 NSIC 117944 -
Sequence of Interest for Offsite Power Lost at Millstone 2
- diesel generators running but not loaded
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NULMBER:
117944 DATE OF LER:
September 3, 1976 DATE OF EVENT:
August 10, 1976 SYSTE[ INVOLVED: offsite power COMPONENT INVOLVED:
switchyard insulators and equipment CAUSE:
severe salt spray wetting during hurricane SEQUENCE OF INTEREST:
loss of off site power ACTUAL OCCURRENCE:
reactor trip with loss of offsite power and diesel generators previously started and running REACTOR NAMtE.
M~illstone 2 DOCKET NUMBER:
50-336 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
830 MWe REACTOR AGE:
.8 yr VENDOR:
Combustion Engineering ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Northeast Nuclear Energy Co.
LOCATION:
5 miles SW of.New London, Conn.
DURATION:
N/A PLANT OPERATING CONDITION:
100% powet SAFETY FEATURE TYPE OF FAILURE:
(a) inadequate performance; (b) failed to start; r(O made inoperable; (d)__________
DISCOVERY MET1EOD:
during operation COMMENT:
-