ML20147A548
| ML20147A548 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 07/14/1984 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-028-00 | |
| Download: ML20147A548 (6) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.:
331/84-028 Event
Description:
LOOP and HPCI Trip Date of Event:
July 14, 1984 Plant:
Duane Arnold EVENT DESCRIPTION Sequence on July 14, 1984 at 1524 h, with the reactor at 0% thermal power, in the startup mode at 176 psig, the essential buses were automatically transferred from offsite to onsite power because of degraded offsite grid voltage.
As per design, the reactor protection system was de-energized, resulting in a scram.
The two essential and two nonessential 4160-ky buses were receiving offsite power via the startup transformer when the essential bus's undervoltage protection instrumentation sensed grid voltage <92.3% of nominal for +8 s.
Consequently, the essential bus breakers tripped, as per design.
The nonessential buses remained energized, and no load shedding occurred because grid voltage did not drop below 65%
of nominal.
Both DGs auto started upon loss of power to the essential buses and within 10 s had assumed the essential busts loads.
The degraded voltage was caused by the accidental motoring of a 650-MW(e) generator for over 20 s at the Louisa Generating Station.
The HPCI inboard steam supply valve (BJ-ISV-2238) closed following the scram.
Although this was not per design, if necessary the valve could have been opened within a short time by manual operation after re-setting the HPCI logic.
This was done later at 1810 h after Operations personnel had returned other systems to normal.
The false isolation signal due to the power loss was received from the SLDS.
The isolation may have been due to a spurious signal from one or both SLDS temperature switches.
The reactor scram was reset at 1556 h, following the restarting of the reactor protection system M-G sets.
All required systems were returned to normal by 1600 h. At 1620 h after the Iowa Electric system control center had advised the plant that recurrence of the grid voltage excursion was unlikely, the essential buses were transferred back to the startup transformer, and both diesels were unloaded.
The diesels were secured at 1642 h.
After a postevent review determined the operability of all safety-related systems and concluded that there had been no ef-fect upon safe plant operation, startup of the reactor was commenced at 1901 h.
Event Identifier:
331/84-028 D-143
Corrective Action
ý..IIiýý on October 15, 1984, a special test procedure was run on the "A" logic of the HPCI SLDS.
The reactor was in the shutdown mode for a planned maintenance outage, with RV pressure below that at which Tech-nical Specifications requires HPCI to be operable.
A review of the isolation logic for the HPCI inboard steam supply valve indicated that the spurious isolation of this valve following the LOOP. on July 14, 1984, most likely originated in the HPCI SLDS isolati on logic (temper-ature switches).
Three trials of the test procedure were performed.
On the first and third trials, the suspected temperature switches (TS-2261A and TDS-2260A) closed and quickly reopened upon restoration of p.ower.
The result was an isolation signal of short duration that -was sealed into the HPCI isolation logic.
The second test produced no isolation sig-nal.
Test results proved that a random signal could be expected from the two suspect instruments upon reenergizing after LOOP.
After review, a minor design change was instituted to eliminate the random HPCI[ ac power dependency that results from powering up the HPCI SLDS logic.
The design change implemented in both the "A" and "B" logic trains was to introduce a short time delay of -1 s on restoration of ac power.
Plant/Event Data Systems Involved:
RPCI and electrical power Components and Failure Modes Involved:
HPCI isolation valve -
spurious operation Essential buses -
transferred to onsite power Component Unavailability Duration:
NA Plant Operating Mode:
2 (0% power)
Discovery Method:
Operational event Reactor Age:
10.3 years Plant Type:
BWR Comments The assumption for this analysis is that the Louisa station generator motoring, which initiated the event, could have occurred while Duane Arnold was at power.
Event Identifier:
331/84-028 D-144
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 0.34 Potential grid recovery considered possible within 30 min Branches Impacted and Branch Non-Recovery Estimate HPCI 0.12 Recovery possible from control room after HPCI logic reset Plant Models Utilized BWR plant Class C Event Identifier:
33 1/84-028 D-145
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 331/84-028 Event Desription: LOOP and HPCI Trip Event Date:
7/14/84 Plant:
Duane Arnold INITIATING EVENT NON-ECOVERABLE INITIATING EVENT PROBABILITIES 1LOOP SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 3.4E-01 Probability CV, LOOP Total 5.9E-07 5.SE-07 CD LOOP Total 7.3E-05 7.3E-05 ATW'S LOOP Total
- 7. IE-06 7.1E-06 DOMINANT SEQUENCES End State: CV Conditional Probability:
5.7E-07 226 LOOP -EMERG.POWER SCRAM -SLC.OR.RODS HPCI RCIC/TRANS.OR.LOOP -SRV.AIJS -LPCS -RHR(SDC)
End State: CD Conditional Probability:
5.OE-05 215 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM SRV.CLOSE HPCI RCIC/LOCA SRV.ADS End State: ATWS Conditional Probability:
6.9E-06 Event Identifier: 331/84-028 D-146
2-40 LOOP -EMERS.POWERi SCRAM SLC.OR.RODS SEQUENCE CONDITIONAL PROBABILITIES Sequence N'Re'c**
End State CD Prob 201 LOOP -EMER6.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM -SRY.CLOSE -HP CI RHR(SDC) RHR(SPCOOL)/-LPCI.RHR(SDC) C..AND.V/RHR(SD C)
.RHR(SPCOOL) 202 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM -SRV.CLOSE HP CI -RCIC/TRANS.OR.LOOP RHR(SDC) RHR(SPCOOL)/-LPCI.RHR(SO C) C.I.AND.Y/RHR(SDC).R'H(SPCOOL) 208 LOOP -EMERG.POWER -SCRAM SRY.CHALL/LOOP.-SCRAM -SRV.CLOSE HP CI RCIC/TRANS.OR.LOOP CR0 SRV.ADS 215 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LGOP.-SCRAM SRV.CLOSE HP C1 RCIC/LOCA SRV.ADS 226 LOOP -EMERI3.POWER SCRAM -SLC.OR.RODS HPCI RCIC/TRANS.OR.LOO P -SRV.ADS -LPCS -RHR(SDC) 240 LOOP -EMERG.POWER SCRAM SLC.OR.RODS 243 LOOP EMERB.POWER -SCRAM SRY.CHALL/LOOP.-SCRAM -SRY.CLOSE HP CI RCIC/TRANS.OR.LOOP 246 LOOP EMERS.POWER -SCRAM S1RV
.CHALL/LOOP.-SCRAM SRV.CLOSE HP CI RCIC/LOCA CD CD CD CV 1.4E-05 3.5E-02 1.8E-06 4.6E-03 3.5E-06 2.3E-'02 5.6E-05
- 4.1&-02 5.7E-07 * '2.3E-02 6.9E-06
- 3.4kiO 2.2E-06
.1.2E-02 1.6E-06 2.IE-02 ATWS CD CD
- dominant sequence for end state 4*non-recovery credit for' edited case MODEL:
DATA :
b :\\BWRCTREE.CMP b :\\ARNOLPRO. CMP No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System TRANS LOOP LOCA SCRAM SLC.OR.RODS PCS/ TRANS PCS/LOCA SRV.CHALL/TRANS.-SCRAM SRY.CHALL/TRANS..SCRAM SRV.CHALL/LOOP'.-SCRAM SRV.CHALL/LOOP.SCRAM SRV.CLOSE EMERS.POWER Event Identifier: 331/84-028 1
.lE-03 1
.3E-05 3.3E-06
- 4.
1E-04 1.OE-02 1.7E-01 1.GE+00 1.OE+O0 1.OE+00 I ' E+0O 1.OE+00
-6bE-02 2.9E-03 Non-Recov 1.0E+00 3.4E-01 3.4E-01 1.0E+00 1.0E+00 1.0E+06 1
.OE+00 1.0E+00 1
.0E+00 1AO+00 1.0E+00 I.0E+00 5.1E-01 Opr Fail 4.OE-02 D-147
FW/PCS.TRANS FW/PCS.LJCA HPCI Branch Model: 1.OF.1 Train 1 Cond Prob:
RC IC/TRANS.OR.LOOP RCIC/LOCA CRD SRV SADS COND/FW.PCS LPCS LPCI(RHR)/LPCS RHRSW/LPCS.LPCI.TRANS RHRSN/LPCS.LPCI SLOOP RHRSW/LCS.LPCI SLOCA RHR(SDC)
RHR(SDC) /-LPCI RHR(SDC) /LPCI RHR(SPCOOL)/-LPCI.RHR(SDC)
C.!.AND.V/RHR(SDC).RHR(SPCOOL) 2.9E-01 4
.OE-02 1.OE-O1 > 1.OE+OO 1.OE-O1 > Failed 6.7E-02 1.0E400 1
.OE-02 6.7E-03 1
.OE+OO 3
.OE-03 4
.OE-04 5
.OE-O1 5.OE-O1 5
.OE-01 2.OE-02 2.OE-02 1.OE+00 2.GE-02 5.41-01 1
.OE+00 3A.E-01 3A.E-01 5.7E-01 > 1.2E-01 I.7OE-00 1.OE+00 1.OE+00 3A.E-01 3.4E-01 3.4E-01 1.OE+00 I.OE+0O 3A.E-01 3A.E-01 I.OE+00 1 AO+00
- 1. OE+00 3A.E-01 4
.OE-02 4 OE-02 4 OE-02 4
.E-02 4 OE-02 4** forced Minarick 04-12-1987 16:32:12 Event Identifier: 331/84-028 D-148