ML20147A338
| ML20147A338 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 07/14/1980 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-018-00 | |
| Download: ML20147A338 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
158279 Date:
July 14, 1980
Title:
Degraded Emergency Feedwater System During a Loss of Offsite Power at Arkansas Unit 2 The failure sequence was:
- 1. With the reactor at full power with atmospheric dump valves isolated due to vibration and failure to close problems, tornado activity resulted in the sequential loss of four of five offsite power lines.
Protective relaying disconnected the remaining offsite power line from the bus tie autotransformer.
(Offsite power was available through manual connection from the 161 kV transmission system.)
- 2.
Both diesel generators started and powered safety-related loads.
- 3.
Natural circulation was established with both emergency feedwater (EFW) pumps using a common suction from the condensate storage tanks and the startup and blowdown demineralizer effluent.
- 4.
Approximately 15 min after the LOOP, emergency feedwater flow became erratic with flow rate oscillating between 80% and 100% of rated flow due to cavitation.
This was caused by flashing of the startup and blowdown demineralizer effluent.
- 5.
The startup and blowdown demineralizer effluent was isolated from the EFW pump suction and both EFW pumps were alternately
- stopped, vented, and restarted.
- 6.
The process-computer was unavailable during the event.
This is be-lieved to have been caused by protective trips from low voltage.
Corrective action:
Offsite power was restored via startup transformers ST-2 and ST-3.
The EFW system operating procedures were revised to require isolation of the startup and blowdown effluent prior to exceeding 5% power.
Design purpose of failed system or component:
Offsite power provides the preferred source of power to safety-re-lated loads when the unit generator is not available.
The EFW system provides water to the steam generators for RCS when the main feedwater system is unavailable.
Loss of Diesel Emergency feed-Emergency feedwater Demineralizer offsite generators water provided pumps cavitate due effluent power supply power to steam to mixing of hot isolated and to safety-generators startup and blow-EFW pumps related down demineralizer vented loads effluent with CST flow Potential Severe Core Damage Possible -
- however, bleed & feed could provide core cooling No Possible -
- however, bleed & feed could provide core cooling No
-Possible -
- however, bleed & feed could provide core cooling NSIC 158279 - Actual Occurrence for Degraded Emergency Feedwater System During a Loss of Offsite Power at Arkansas Unit 2
Loss of Turbine Emer-Auxiliary PORV J
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 No No Yes Yes I
2 3
4 5
6 7
8 No No Yes Yes No Yes 9
10 11 12 13 No Yes NSIC 158279 -
Sequence of Interest for Degraded Emergency Feedwater System During a Loss of Offsite Power at Arkansas Unit 2
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
158279 LER NO.:
80-018 DATE OF LER:
July 14, 1980 DATE OF EVENT:
April 7, 1980 SYSTEM INVOLVEDz Offsite power, emergency feedwater system COMPONENT INVOLVED:
Transmission lines, both EFW pumps CAUSE:
Tornado damage and failure of operating procedures to require isolation of the startup and blowdown effluent thereby allowing flashing to occur in EFW pump suction lines.
SEQUENCE OF INTEREST:
LOOP ACTUAL OCCURRENCE:
LOOP and FW pump cavitation from hot demineralizer effluent causing flashing.
REACTOR NAME:
Arkansas Nuclear Unit 2 DOCKET NUMBER:
50-368 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
912 MWe REACTOR AGE:
1.3 years VENDOR:
Combustion Engineering ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Arkansas Power and Light LOCATION:
6 miles NW of Russelville, Arkansas DURATION:
N/A PLANT OPERATING CONDITION:
100% rate power TYPE OF FAILURE:
Inadequate performance; made inoperable DISCOVERY METHOD:
Operational event COMMENT: