ML20168A737
| ML20168A737 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 06/16/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1978-LTR-00 | |
| Download: ML20168A737 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
141097 Date:
March 29, 1978
Title:
Safety Injection Occurs at TMI-2 The failure sequence was:
- 1. Alternate power source feeder breakers to vital bus 2-IV (120 V a-c) were tripped for test.
- 2. Frequency control module failed resulting in blown fuses in the DC input to invertor.
- 3. Vital bus 2-IV tripped on invertor failure, resulting in the PORV failing open.
- 4. Because of the reactor coolant pump configuration at the tine, a reactor trip also occurred.
- 5. The operators did not realize the relief valve had failed open because of lack of PORV position indication.
- 6. ECCS was initiated at 1650 psig.
- 7. Four minutes into the transient, vital bus 2-IV was re-energized, which closed the relief valve and terminated the transient.
Corrective action; 1.. A design change was initiated to change the failure position of the relief valve upon loss of power to closed in lieu of open.
- 2. Relief valve position indication was provided in the control room.
Design-purpose of failed system or component:
- 1. Provide 120 V a-c power for loads which require uninterrupted power.
- 2. The pilot operated relief valve provides overpressure protection for the RCS.
Unavailability of system per WASH 1400:
- N/A Unavailability of component per WASH 1400: *solid state device, high power application:
3 x 10-6 /hr.
Unavailabilities are in units of per demand D-1. Failure rates are in units of per hour HR-1.
Testing with Invertor Pressure switch Pressure indi-Operator Vital bus reactor at failure &
failed closed cation powered intervention 2-IV zero power vital bus opening relief from vital bus successful reenergized 2-IV trip valve 2-IV available closing
& reactor to operator relief valve trip
& terminating CS blowdown Potential Severe Core Damage No No No No -reactor at power No No NSIC 141097 -
Actual Occurrence for Loss of Vital Bus and Relief Valve Opening at Three Mile Island 2
Small Reactor Aukiliary High Low Pressure LOCA Trip Feedwater and Pressure Recirculation Secondary jInjection and LPR/HPI Heat Removal Cross-connect Potential Severe Core Damage Sequence No.
2 3
4 5
6 7
NSIC 141097 -
Sequence of Interest for Safety Injection Occurs at Three Mile Island 2
- failure requires operator error of failing to close the PORV isolation valve.
CATEGORIZAtTION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
141097 DATE OF~ LER:
June 27, 1978 DATE OF EVENT:
March 29, 19,78 SYSTEM INVOLVED:
120 V a-c vital power, ACS COMPONENT INVOLVED:
Vital bus invertor CAUSE:
Blown fuse, faulty invertor control module SEQUENCE OF INTEREST:
small LOCA -
stuck open PORV ACTUAL OCCURRENCE:
stuck open PORV REACTOR NAME:
Three Mile Island 2 DOCKET NUMBER:
50-320 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
906 MWe REACTOR AGE:
0.0+
yr VENDOR:
Babcock & Wilcox ARCHITECT-ENGINEERS:
Burns & Roe OPERATORS:
Metropolitan Edison Co.
LOCATION: 10 miles SE of Harrisburg, PA DURATION:
N/A PLANT OPERATING CONDITION:
Zero power physics testing SAFETY FEATURE TYPE OF FAILURE:
(a) inadequate performance; (b) failed to start; (c) made inoperable; G~)ailed inunafe position DISCOVERY METHOD:
incident during physics testing COMMENT:
Vital bus tripped because of invertor failure while alternate power source was removed for testing.