ML20147A547
| ML20147A547 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 06/07/1984 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-001-00 | |
| Download: ML20147A547 (7) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.:
331/84-001 Event
Description:
LOFW and SRV Opens Briefly Date of Event:
.June 7, 1984 Plant:
Duane Arnold EVENT DESCRIPTION Sequence At 08:08:26 (T =
0), while the reactor was at 99.8.% -power, feed-water recirculation valve B (SJ-FCV-1611) failed open because of a brokei-~air supply line fitting.
As a result,, a portion of "B" reactor feedwater flow was returned to the condenser, and the. vessel level
- imeiatlybegan to drop.
While operators were diagnosing and compen7-sating for the decrease in vessel level, a technician's error caused the "B" feedwater pump to trip on low suction pressure and one of two SRVs (S]3-RV-4401) utilizing low-low set logic to cycle open at T + 43 s.
After the RV opened, a momentary upswing in vessel level was ex-
.perienced, followed by a rapid decrease in level to the low-level trip
-set point (170 in.) and an automatic scram initiation at T + 44 s. At
.T + 57 s, the "B" f eedwater pump breaker was reset.'
At T + 66 s, both
- feedwater pumps tripped on low suction pressure (due to condensate pumps being unable to match RFP flow with the high vessel demand and return flow to the condenser).
During this time, the vessel level was continu-ing to fall until the low-low level HPCI/RCIC initiation set point of 119.5 in. was reached at T +
73 s.
At this point, HPCI and RCIC initiated per design, and the level began to rise.
As the vessel level momentarily fell to the low-low level set point, HPCI initiated but did not inject at any time in the event.
HPCI control logic requires low-low level signal to remain present for the duration of the IV initiating timne (-15 s) to have HPCT actually inject.
At T + 112 s, the "B" reac-tor feedwater pump breaker was again closed to provide additional make-up, and it remained closed with no further tripýs.
After operator ac-tion, the open SRV was reseated at T + 118 s* and remained closed; As RCIC was injecting and the "B" feedwater pump was' functioning, the level quickly recovered to normal operating level (maximum level reached was 204.4 in. at T + 4 min and 30 s).
After the level had recovered, RCIC secured at T + 3 min 50 s, and HPCI was secured at T + 4 min and 30 s.
At this point, the vessel level and pressure were stable at 194 in. and 810 psig, respectively.
All systems necessary for remaining in a safe shutdown condition were operable, and no further system perturbations were experienced.
Event Identifier:
331/84-001 D-136
Main steam SRV valve (SB-RV-4401) is one of two non-ADS SRVs that are utilized in the low-low set logic.
Following an event that has opened one of the six SRVs, the low-low set logic established a lower opening pressure (lifting pressure:
1020 to 1025 psig, reseating pres-sure:
900 to 905 psig, respectively)..Investigation revealed that the lifting of the SRV was totally unrelated to the-.failure of the feedwater recirculation valve.
Prior to the recirculation valve failure, a low-low set instrument functional test had commenced. While performing the routine surveillance procedure, the instrument technician erroneously placed an ohmmeter across the high-pressure switch contacts too early in the procedure.
As a result, the SRV actuation solenoid relay was falsely energized with a high-pressure test signal that, in conjunction with the procedure, step to. push the test button, caused the valve to cycle open (-40-.s. after the recirculation valve failure).. Approximately 75 s after the,.SRV had opened, the operators reset the low-low SRV logic, thereby disarming the solenoid and cycling the valve closed.-, It was later theorized that the relatively low internal impedance of, the ohmmeter caused,the meter to act as a jumper and to bypass the con-tacts.
It is noteworthy that prompt identification of the cause of the SRV actuation was greatly aided by the technician volunteering that he had indeed committed an error.
This theory was confirmed prior, to startup af ter a special test procedure was run.
This procedure re-created the applicable sequence of test steps leading up to the opening of the SRV and. revealed that the connection of an ohmmeter across,the contacts, in conjunction with.pressing the test *button, does in 'f act energize the SRV solenoid.
Corrective Action-.
The following causes and determinations can be made as to the exact component failures and related events leading up to, and aft er.,, the scram.
The feedwater recirculation valve (SJ-FCV-1611) is an air-actuated, fail-open control valve, Control.,Components model No. PDA964-96BW.
In-vestigation revealed that a flexible air-supply line fitting broke due to fatigue. When, the, air supply-was lost.,, the valve cycled open. Prior to startup, the broken, air line on the "B" recirculation valve was re-paired.
As an additional precaution,' the identical airline on the "A" recirculation valve. (SJ-FCV-1569) was inspected and found satisfactory.
As' a long-term corrective action, a maintenance action request has been generated to replace the.~fittings subject to fatigue with higher
.strength fittings.,
Event Identifier:
331/84-001 D-137
To preclude recurrence of similar SRV opening' sttuaktions, All in-strument technicians were assembled and shown the exact cause of the event during a step-by-step reconstruction..
The.'...fmý,ori't.aftce. of pro-cedural compliance without deviating from the prescribed testing sequence was impressed upon them.
To reduce' the margin for personnel error, the surveillance test procedure has been revised to utilize a volt meter in lieu of an ohmmeter.
This revision',wii~l,..,elimiiiate, the possibility of the meter acting as a jumper in a circuit under test, regardless of when it is inserted.
As a long-term corrective action, selected surveillance test procedures are continuing to be revised to simplify and clarify the testing sequence, t~hereby reducing the pos-sibility of personnel error.
In addition to this, a joint management and union task force is being formed to determine; anrd.i imlement methods of maintaining a heightened awareness of the importance of minimizing personnel errors.
Prior to startup, all systems initiated during the scram and sub-sequent evolutions were reviewed to determine whether they had func-tioned per design and Technical Specifications.
At the 170-in, reactor water level, the reactor scrammed; valve groups 2, 3, 4, and 5 isolated; and both trains of the standby gas treatment system initiated per design.
At the 119.5 in. reactor water level valve group 8 isolated, LPCI logic tripped both recirculation pumps, loop-select logic initiated and performed its function, and HPCI/RCIC initiated per design.
During and after the transient, the operators observed a normal SRV tail-pipe temperature response.
As an additional precaution, a walkdown was per-formed on the tailpipe of the opened SRV.
The piping and restraints were inspected and found satisfactory.
Plant/Event Data Systems Involved:
Steam relief Components and Failure Modes Involved:
MFW -
failed in operation Steam RVs -
failed to close in operation Component Unavailability Duration:
NA Plant Operating Mode:
1 (100% power)
Discovery Method:
Operational event Reactor Age:
9.8 years Plant Type:
BWR Comments None Event Identifier:
331/84-001 D-138
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Small-break LOCA 0.34 Base case nonrecovery Branches Impacted and Branch Nonrecovery Estimate PCs 1.0 Unavailable MFW 0.12 Failed but recoverable Plant Models Utilized BWR plant Class C Event Identifier:
331/84-001 D-1 39
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 331/84-001 Event
Description:
LOFW and SRV Opens Briefly Event Date:
6/7/84 Plant:
Duane Arnold INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOCA SEQUENCE CONDITIONAL PROBABILITY SUNMS End State/Initiator 3.4E-01 Probability CV LOCA Total 8.6E-07 8
.6E-07 CD LOCA Total 1.2E-04 1.2E-04 ATWS LOCA Total 6.9E-06 6.9E-06 DOM INANT SEQUENCES End State:
CV Conditional Probability:
5.7E-07 314 LOCA SCRAM -SLC.OR.RODS PCS/LOCA FW/PCS.LOCA HPCI -SRV.ADS -COND/FW.PCS -RHR(SDC)
End State: CD Conditional Probability:
1.1E-04 310 LOCA -SCRAM PCS/LOCA FW/PCS.LOCA HPCI RCIC/LOCA SRV.ADS End State: ATWS Conditional Probability:
6.9E-06 Event Identifier: 331/84-001 D-140
332 LOCA SCRAM :,SLCý.OR.RODS SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec**
302 LOCA -SCRAM PCS/LOCA -FW/PCS.LOCA RHR (SDC) RHR (SPCOOL) /-LPC I
.RHR(SDC) C.I.AND.Y/RHR(SDC).RHR(SPCOOL) 310 LOCA -SCRAM PCS/LOCA FW/PCS.LOCA HPCI RCIC/LOCA SRV.ADS 314 LOCA SCRAM -SLC.OR.RODS PCS/LOCA FW/PCS.LOCA HPCI -SRV.ADS
-COND/FW.PCS -RHR (SDC) 318 LOCA SCRAM -SLC.OR.RODS PCS/LOCA FW/PCS.LOCA HPCI -SRV.ADS COND/FW.PCS -LPCS -RHR(SDC) 332 LOCA SCRAM SLC.OR.RODS CD CD CV CV 1.4E-05 3.5E-02 1.1E-04
- 2.3E-02 5.7E-07
- 1.5E-02 2.9E-07 7.9E-03 6.9E-06
- 3.4E-01 ATWS
- dominant sequence for end state
- non-recovery credit-.for edited case MODEL:
DATA:
b :\\BWRCTREE.CMP b-\\ARNOLPRO.CMP No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP LOCA SCRAM SLC.OR.RODS PCS/TRANS Branch Model: 1.OF.1 Train 1 Cond Prob:
PCS/LOCA SRV.CHALL/TRANS.-SCRAM SRV SCHALL/TRANS.SCRAM SRV.CHALL/LDOP.-SCRAM SRV.CHALL/LOOP.SCRAM SRV.CLOSE EMERS.POWER FW/PCS.TRANS Branch Model: 1.OF.1 Train 1 Cond Prob:
FW/PCS.LOCA Branch Model: 1.OF.1 Train 1 Cond Prob:
HPCI Event Identifier: 331/84-001 1.1E-03 1
.3E-05 3.3E-06
- 4.
1 E-04 1
.OE-02 1.7E-01 > 1.0E+00 1.7E-01 >i Unavailable 1
.0E+00 1
.0E+00 1.0E+00 1.0E+00 1
.0E+00 2.6E-02 2
.9E-03 2.9E-01 > 1.0E+00
'?.9E-01 >Unavailable 4.OE-02 > 1.OE+00 4.OE-02 >,
Failed 1
.OE-01 1.0E+00 3.4E-01 3.4E-01 I.OE+00 1.OE+00 1.OE+00 1
.OE+00 1.0E+00 1.OE+00 I.OE+00 I
.0E+00
- 1. OE+00 5.1E-01 3.4E-01 > 1.2E-01 3.E-01 > 1.2E-01 5.7E-031 4.OE-02 D-14 1
RCIC/TRANS.DR.LOOP RCIC/LOCA CR13 SRV.ADS COND/FW.PCS LPCS LPCI(RHR)/LPCS RHRSW/LPCS.LPCI.TRANS RHRSW/LPCS.LPCI.LDDP RH1RSW/LPCS.LPCI.LOCA RHR (SDC)
RHR(SDC) /-LPCI RHR(SDC)/LPCI RHR(SPCOOL) /-LPCI.RHR(SDC)
- forced flinarick 04-12-1987 16-.28:08 Event Identifier: 331/84-001 6.E-02 I.OE+00 1.OE-02 M.E-03 1.OE+00 3.OE-03
- 4.
OE-04 5.OE-01 5.OE-01 5.OE-01 2
.OE-02 2.OE-02 1.OE+00 2
.OE-02 5.2E-01 1
.OE+00 5.7E-01 1
.OE+00 I.OE+00 I.OE+00 M.E-01 3.E-01 3.E-01 1.OE+00 1.(E+00 1
.OE+00 3.E-01 3.E-01 1.OE+00 1
.OE+00 I.OE+00 M.E-01
- 4.
OE-02 4 OE-02 4.E-02 4.OE-02 4.E-02 D-142