ML20168A550
| ML20168A550 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 06/16/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1976-014-00 | |
| Download: ML20168A550 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
115875 Date:
July 9, 1976
Title:
Total Loss of 115 KV Station Service Power Occurs at Connecticut Yankee The failure sequence was:
- 1. During refueling~maintenance was being performed on one of the two incoming 115 KV station service lines.
- 2. While switching to restore this line to service, protective relays sensed a spurious 115 KV fault signal (due to improperly located backup relaying potential sensing circuits) and tripped the automatic circuit breaker on the station service transformer associated with the operating 115 KV line, resulting in a loss of offsite power (3 times).
- 3. The diesel generators started and locled safety related loads.
Corrective action:
- 1. The position of the applicable backup relaying potential sensing circuits were changed.
Design purpose of failed system or component:
Offsite power provides power to safety-related plant loads when the unit generator is not operating.
Unavailability of system per WASH 1400:
- Offsite power:
2 x 105 /hr.
Unavailability of component per WASH 1400:
- Unavailabilities are in units of per demand D Failure rates are in unit§ of per hour HRC'.
Reactor in Maintenance in During switching to Diesel generators refueling progress on one restore line to service, start and assume shutdown of two incoming improperly placed backup safety related loads 115kv station relaying potential sensing service lines circuits sense a spurious 115kv fault and trip a circuit breaker associated with the operating 115kv line Potential Severe Core Damage k11 NO
.1
,Possible if offsite power is not restored in a reasonable period of tine N n No NSIC 115875 -
Actual Occurrence for Total Loss of 115kv Station Power Occurs, at Connecticut Yankee
Loss of Offsite Power Turbine Generator Runs Back and Assumes House Loads Emer-gency Power Auxiliary Feedwater and Secondary Heat Removal PORV PORV or Demanded PORV Isola-tion Valve C lo sure High ( Long
- Potential Pressure Term Severe Injection Core Core Cooling Damage Sequence No.
L 1
No No Yes Yes No 2
3 4
5 6
7 8
9 10 11 No Yes No Yes 12 13 NSIC 115875 -
Sequence of Interest for Total Loss of 115kv Station Power Occurs at Connecticut Yankee not part of mitigation procedure
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
115875 DATE OF' LER:
July 9, 1976 DATE OF EVENT:
June 26, 1976 SYSTEM INVOLVED:
offsite power COMIPONENT INVOLVED:
backup relaying potential sensing circuits CAUSE:
improper placement of sensing circuits SEQUENCE OF INTEREST:
loss of offsite power ACTUAL OCCURRENCE:
loss of offsite power during refueling.
REACTOR NAME:
Haddam Neck DOCKET NUMBER:
50-213 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
575 MWe REACTOR AGE:
9 yr VENDOR:
Westinghouse ARCHITECT-ENGINEERS:
Stone & Webster OPERATORS:.
Connecticut Yankee Atomic Power Co.
LOCATION:
13 mi. East of Meridan, Conn.
DURATION:
N/A PLANT OPERATING COND)IT ION:
refueling SAFETY FEATURE TYPE OF FAILURE:
(a) inadequate performance; (b) failed to start; Omade inoperable; (d)
DISCOVERY METHOD:
operational event COMMENT: