ML20147A482
| ML20147A482 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Reactor Regulation |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-027-00 | |
| Download: ML20147A482 (5) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
158650 Date:
June 3, 1980
Title:
Failure of Service Water System Plus Subsequent Auxiliary Feedwater System Unavailability at Calvert Cliffs I The failure sequence was:
- 1. With the plant at 100% power, the No.
12 service water subsystem was removed from service for heat exchanger saltwater side cleaning.
The heat exchanger service water side outlet valve was closed.
- 2.
A complete failure occurred in one of the No.
11 instrument air compressor aftercooler tubes.
The air compressor after cooler is cooled by a common portion of the service water system (during safeguards actuation, the common portion of the service water system is isolated from the two redundant safety-related portions).
- 3.
The tube leak allowed compressed air to enter the service water system.
The constant vent valves on the operating header were designed to maintain the service water system free of air.
However, air accumulated in the idled heat exchanger because the rate of leakage exceeded the capacity of that of the two constant vent valves.
- 4.
When the idled heat exchanger was returned to service, the air bubble was released and, since the service water systems are not independent in the turbine building.
Both No.
11 and No.
12 service water pumps lost suction.
- 5.
The operator received low pressure alarms on both service water subsystems and verified that valve lineups were correct.
- 6.
The reactor was manually tripped due to high main turbine bearing temperatures.
All reactor coolant pumps, auxiliary feedwater pumps and the main condenser remained operable and were utilized to remove decay heat.
- 7.
During the shutdown, No.
12 condensate storage tank (CST) was used to supply AFW to the steam generators.
- 8.
When low level was indicated in No.
12 CST, flow was switched to No.
11 CST and No.
12 CST was isolated.
- 9.
Later, the main feed system was restored to operation on auxiliary steam and the AFW system was shut down.
The control room operator incorrectly designated the CST valves to be realigned.
- 10. Due to the valve realignment error, No.
11 and 12 CSTs were both isolated, rendering the auxiliary feedwater system unavailable.
Corrective action:
- 1. Service water was isolated from the affected compressor; the system was vented, and normal flow was restored.
- 2.
The No.
12 CST was properly aligned for service 3 h after the operator error was made.
- 3.
A design change was made to increase the capacity of the continuous vents at high places in the system.
- 4.
Operating procedures were modified to eliminate unisolated dead legs during maintenance and to require venting prior to returning subsystems to service.
Design purpose of failed system or component:
The service water system provides cooling water for turbine-side components as well as the diesel generators, containment coolers, and spent fuel pool coolers.
The auxiliary feedwater system provides water for steam generator cooling in the event the main feedwater system is unavailable.
Unit at Air compressor Air bubble Loss of Manual reactor Condensate full power aftercooler air travels to suction trip due to storage and service leak results in both ser-pressure to high main tur-tank valves water heat accumulation of vice water service bine bearing incorrectly exchanger air in isolated subtrains water pumps temperatures.
realigned maintenance heat exchanger when heat and loss of Auxiliary when AFW in progress exchanger service feedwater flow is returned to water system pro-terminated service cooling vides SG and MFW cooling system started for SG cooling Potential Severe Core Damage No No NSIC 158650 - Actual Occurrence for Failure of Service Water System and Subsequent Auxiliary Feedwater Unavailability at Calvert Cliffs 1
Loss of Turbine Emer-Auxiliary PORV PORV or High Long Offsite Generator gency Feedwater and Demanded PORV Isola-Pressure Term lPower 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 I
2 3
4 Yes Yes 5
No No 6
7 Yes Yes 8
9 No Yes 10 11 12 13 No Yes NSIC 158650 -
Sequence of Interest for Failure of Service Water System and Subsequent Auxiliary Feedwater Unavailability at Calvert Cliffs 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
158650 LER NO.:
80-027 DATE OF LER:
June 3, 1980 DATE OF EVENT:
May 20, 1980 SYSTEM INVOLVED:
Service water system, auxiliary feedwater system COMPONENT INVOLVED:
Air compressor aftercooler, condensate storage tank CAUSE:
Air leakage to service water system due to aftercooler tube failure, operator error in realigning valves when switching from one CST to another SEQUENCE OF INTEREST:
LOOP ACTUAL OCCURRENCE:
Loss of service water and subsequent unavailability of auxiliary feedwater REACTOR NAME:
Calvert Cliffs Unit 1 DOCKET NUMBER:
50-317 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
845 MWe REACTOR AGE:
5.6 years VENDOR:
Combustion Engineering ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Baltimore Gas Electric LOCATION:
40 miles south of Annapolis, Maryland DURATION:
3 h PLANT OPERATING CONDITION:
100% power TYPE OF FAILURE:
Made inoperable DISCOVERY METHOD:
Operational event and operator inspection COMMENT:
See also NSIC 157124 (for Arkansas Nuclear One, 50-368, April 24, 1979).