ML20149K496
| ML20149K496 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-024-00 | |
| Download: ML20149K496 (4) | |
Text
B- 18 PRECURSOR DESCRIPTION SHEET LER No.: 255/87-024
- Event
Description:
Loss-of-offsite power for 7.5 h Date of Event: 7/14/87 Plant: Palisades EVENT DESCRIPTION Sequence While at 91% power, technicians were working to correct an alarm problem on the main transformer deluge system. The system air pressure for the main transformer and the startup transformer deluge systems are cross connected. After calibration of the main transformer pressure switch, the system air pressure was increased and then decreased to balance the system. The deluge system actuates on differential pressure across a diaphragm. One side of the diaphragm has system air pressure and the other side has heat actuated device (HAD) air pressure. Under normal circumstances the air pressure is the same on both sides of the diaphragm with a compensating vent maintaining this equilibrium. If a sudden imbalance occurs, the device will actuate.
When the air pressure was inadvertantly reduced too quickly, it resulted in deluge system actuation. Contaminants in the water per-mitted a flashover arc that jumped from the "Y" phase insulator bushing cap to the transformer case of the 1-2 startup transformer. This caused a ground fault to occur on the "Y" phase. Relays tripped on the 345-kV switchyard "R" bus air blast breakers. The normal fast transfer to the startup transformer was blocked due to the faults resulting from the flashover arc. A LOOP occurred, and the plant tripped. The DGs started and loaded onto their buses as required. All systems responded as designed except the atmospheric steam dump and turbine bypass valves, which did not open as quickly as expected. They did open at 18 and 31 s after plant trip. The LOOP lasted for 7.5 h. During the restoration of offsite power, several procedural deficiencies in resetting relays were discovered.
Corrective Action The deluge system will be flushed more often to prevent contaminant/corrosion buildup. The procedures were revised. The quick-opening dump valves were repaired.
Plant/Event Data Systems Involved:
Main electrical Components and Failure Modes Involved:
Transformer fails in operation Event Identifier: 255/87-024
B- 19 Component Unavailability Duration: N/A Plant Operating Mode: 1 (91%)
Discovery Method: Operational event Reactor Age: 16.1 y Plant Type: PWR Comments None.
MODELING CONSIDERATION AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP No recovery Branches Impacted and Branch Nonrecovery Estimate None Plant Models Utilized PWR plant Class G Event Identifier: 255/87-024
B-20 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 255/87-024 Event
Description:
Seven and one-half hour loss of offsite power Event Date: 07/14/87 Plant: Palisades INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 4.3E-04 Total 4.3E-04 CV LOOP 1.1E-05 Total 1.1E-05 ATWS LOOP 0.OE+00 Total 0.0E+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec*
217 LOOP -rt/loop emerg.power ep.rec CD 3.9E-04 1.4E-O0 216 LOOP -rt/loop emerg.power -ep.rec afw/emerg.power CD 3.2E-05 2.3E-01 215 LOOP -rt/loop emerg.power -ep.rec -afw/emerg.power -porv.or.srv CV 9.1E-06 2.2E-01
.chall ss.releas.term 209 LOOP -rt/loop -emerg.power -afw -porv.or.srv.chall ss.releas.te CV 1.2E-06 2.9E-01 rm hpi 213 LOOP -rt/loop emerg.power -ep.rec -afw/emerg.power porv.or.srv CV 3.7E-07 2.2E-01
.chall -porv.or.srv.reseat/emerg.power ss.releas.term
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
209 LOOP -rt/loop -emerg.power -afw -porv.or.srv.chall ss.releas.te CV 1.2E-06 2.9E-01 rm hpi 213 LOOP -rt/loop emerg.power -ep.rec -afw/emerg.power porv.or.srv CV 3.7E-07 2.2E-01
.chall -porv.or.srv.reseat/emerg.power ss.releas.term 215 LOOP -rt/loop emerg.power -ep.rec -afw/emerg.power -porv.or.srv CV 9.1E-06 2.2E-01
.chall ss.releas.term 216 LOOP -rt/loop emerg.power -ep.rec afw/emerg.power CD 3.2E-05 2.3E-01 217 LOOP -rt/loop emerg.power ep.rec CD 3.9E-04 1.4E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\newmodel\pwrgnew.cmp BRANCH MODEL: c:\asp\newmodel\palis.new PROBABILITY FILE: c:\asp\newmodel\pwrbnew.pro Tvent Identifier: 255/87-024
B-21.
No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 4.eE-04 1.OE+00 LOOP 4.6E-06 > 4.6E-06 3.9E-01 > 1.0E+00 Branch Model: INITOR Initiator Freq: 4.6E-06 loca 2.4E-06 4.3E-01 rt 2.8E-04 1.2E-01 rt/loop O.OE+00 1.OE+00 emerg.power 2.9E-03 8.OE-Oi ep.rec 1.OE+O0 1.7E-01 afw 1.3E-03 2.6E-01 afw/emerg.power 5.OE-02 3.4E-01 mfw 2.OE-01 3.4E-01 porv.or.srv.chall 4.OE-02 1.0E+00 porv.or.srv.reseat 2.OE-02 1.1E-02 porv.or.srv.reseat/emerg.power 2.OE-02 1.oE+00 ss.releas.term 1.5E-02 3.4E-01 ss.depress 3.6E-02 I.OE+O0 cond/mfw 1.0E+00 3.4E-01 1.OE-02 hpi 3.OE-04 8.4E-01 hpi(f/b) 3.OE-04 8.4E-01 l.OE-02 porv.open 1.OE-02 1.0E+00 4.OE-04 hpr/-hpi 1.5E-04 I.OE+00 I.OE-03 csr 2.OE-03 3.4E-01
- branch model file
- forced Minarick 05-16-1989 06:51:45 Event Identifier: 255/87-024