ML20147A546
| ML20147A546 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-017-00, LER 1983-018-00 | |
| Download: ML20147A546 (6) | |
Text
B.33-1 B.33 LER No. 331/83-017 and -018 Event
Description:
HPCI and RHRSW Loop B Inoperable Date of Event:
May 23, 1983 Plant:
Duane Arnold B.33.1 Summary During normal operation on May 23, 1983, the pressure differential across the residual heat removal service water (RHRSW) system strainer 1 S-90B increased. The strainer jammed with river water debris, causing the drive motor coupling shear pins to shear. On the same day, during routine surveillance testing, the high-pressure coolant injection (HPCI) pump did not meet Technical Specification output pressure flow requirements. Investigation revealed that the HPCI speed indication circuit for the turbine was out of calibration. The estimated increase in core damage probability, or importance, over the duration of the event is 1.7 x 10'. The base-case core damage probability (CDP) over the duration of the event is 1.0 x 10-7, resulting in an estimated conditional core damage probability (CCDP) of 1.7 x 10V.
B.33.2 Event Description During normal operation on May 23, 1983, the pressure differential across the residual heat removal service water system strainer I S-90B increased. The strainer jammed with river water debris, causing the drive motor coupling shear pins to shear as per design. The B loop of RHRSW was declared inoperable, and the redundant loop was satisfactorily tested. The strainers were cleaned and the shear pins were replaced. On the same day, during routine surveillance testing, the HPCI pump did not meet Technical Specification output pressure flow requirements. Technical Specifications require an output pressure of 1,050 psig at 3,700 RPM and 3000 gpm.
The test measured an output pressure of 780 psig. Investigation revealed that the HPCI speed indication circuit for the turbine was out of calibration. The turbine speed was actually lower than indicated. The speed circuit was recalibrated and the pump tested satisfactorily.
B.33.3 Additional Event-Related Information The RHRSW system provides cooling water to the residual heat removal (RHR) system heat exchangers. The RHR system provides three functions: suppression pool cooling, containment spray, and shutdown cooling.
Suppression pool cooling is used to remove heat from the suppression pool whenever the water temperature exceeds 95°F. Containment spray is used in the event of a nuclear system break within the primary containment to prevent excessive containment pressure and temperature by condensing steam and cooling noncondensable gases. Shutdown cooling can be used during normal shutdown and cooldown to remove decay heat, once the reactor coolant temperature is low enough that the steam supply pressure is not sufficient to maintain turbine shaft gland seals or vacuum in the main condenser. RHR requires the use of at least one heat exchanger (and thus RHRSW) for all three modes.
LER No. 331/83-017 and -018
B.33-2 RHRSW is a two-loop system (A and B). Each loop has two pumps (1 P22A and I P22C, and I P22B and 1 P22D, respectively) and one heat exchanger (1 E201 A and I E201 B). Each pair of pump discharge lines connects to a common line which flows through a self-cleaning strainer and then to an RHR heat exchanger.
If the strainers become clogged, flow to the RHR heat exchangers is degraded. One pump supplying one heat exchanger is sufficient to cool all RHR.
RHRSW also has a crosstie which enables the RHRSW pumps to provide coolant to the RHR system for use as an alternative injection system. Flow from the RHRSW common lines proceeds through the strainers to the crosstie line. The crosstie line contains two motor-operated valves in series, which must be opened for injection. One pump is sufficient to provide the alternative injection source for RHR.
B.33.4 Modeling Assumptions HPCI was assumed to be inoperable for half its surveillance period, 360 hours0.00417 days <br />0.1 hours <br />5.952381e-4 weeks <br />1.3698e-4 months <br />. Since HPCI did not pass Technical Specification requirements due to a miscalibrated turbine speed indication circuit, the HPCI pump was assumed to be failed and nonrecoverable. The clogged strainers were assumed to lead to degraded RHR.
Since the RHR system model is composed of four pump trains and two of the four trains flow through one heat exchanger which is cooled by RHRSW, two of the four trains were assumed to be failed. Since it is likely that the RHRSW loop A strainer could also get clogged with river debris, the first two trains of RHR and RHR (SPCOOL) were set to failed to reflect the potential for a common cause failure due to river debris in loop A.
The probability of RHRSW injection failure was also revised to reflect the potential failure of both RHRSW loops. The potential for common cause failure exists, even when a component is failed. Therefore, the conditional probability of a common cause failure was included in the analysis for those components that were assumed to have been failed as part of the postulated event. It is unlikely that clogged strainers would go unnoticed for more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, so this event was modeled as the unavailability of HPCI, two RHR pump trains, and degraded RHRSW injection for a period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The nonrecovery probability for RHR was revised to 0.054 to reflect the RHRSW failures (see Appendix A). For sequences involving potential RHR or power conversion system (PCS) recovery, the nonrecovery estimates were revised to 0.054 x 0.52 (PCS nonrecovery), or 0.028.
B.33.5 Analysis Results The estimated increase in core damage probability over the duration of this event is 1.7 x 10'. The base-case CDP (not shown in calculation) is 1.0 x 10-7, resulting in an estimated CCDP of 1.7 x 105. The dominant sequence is a postulated transient with a successful reactor shutdown, failure of PCS, successful feedwater, and failure of RHR, and is shown in Figure B.33.1.
LER No. 331/83-017 and -018
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Figure B.33.1 Dominant core damage sequence for LER 331/83-017 and -018 LER No. 331/83-017 and -018
B.33-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
Event
Description:
Event Date:
Plant:
331/83-017 HPCI and RHRSW loop B inop May 23, 1983 Duane Arnold UNAVAILABILITY.
DURATION= 24 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS LOOP LOCA SEQUENCE CONDITIONAL PROBABILITY SUMS 2.3E-02 1.4E-04 5.3E-05 End State/Initiator Probability CD TRANS LOOP LOCA Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) 1.6E-05 1.2E-06 7.3E-08 1.7E-05 Sequence End State Prob N Rec**
103 trans -rx.shutdown pcs srv.ftc.<2 -mfw RHR.AND.PCS.NREC CD 107 trans -rx.shutdown pcs srv.ftc.<2 mfw HPCI -rcic RHR.AND.PC CD S.NREC 204 loop -rx.shutdown -ep srv.ftc.<2 HPCI -rcic RHR CD 1.4E-05 2.6E-02 1.5E-06 9.4E-03 1.1E-06 1.9E-02
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
103 trans -rx.shutdown pcs srv.ftc.<2 -mfw RHR.AND.PCS.NREC 107 trans -rx.shutdown pcs srv.ftc.<2 mfw HPCI -rcic RHR.AND.PC S.NREC 204 loop -rx.shutdown -ep srv.ftc.<2 HPCI -rcic RHR CD CD CD 1.4E-05 2.6E-02 1.5E-06 9.4E-03 1.1E-06 1.9E-02
- non-recovery credit for edited case Note:
For unavailabilities, conditional probability values are differential values which reflect the added risk due to failures associated with an event.
Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
SEQUENCE MODEL:
d:\\asp\\models\\bwrcB283.cmp LER No. 331/83-017 and -018
B.33-5 BRANCH MODEL:
PROBABILITY FILE:
d:\\asp\\models\\duarnold.82 d:\\asp\\models\\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans loop loca rx. shutdown pcs srv.ftc.<2 srv.ftc.2 srv.ftc.>2 mfw HPCI Branch Model:
1.OF.1 Train 1 Cond Prob:
rcic srv.ads crd(inj) cond 1
pcs 1
pci RHRSW( INJ)
Branch Model:
1.OF.l+opr Train 1 Cond Prob:
RHR Branch Model : 1.OF.4+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
RHR.AND.PCS.NREC Branch Model:
1.OF.4+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
RHR/-LPCI Branch Model:
1.OF.l+opr Train 1 Cond Prob:
rhr/lpci RHR(SPCOOL)
Branch Model:
1.OF.4+ser+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
Serial Component Prob:
rhr(spcool )/-lpci ep ep. rec 9.5E-04 1.6E-05 3.3E-06 3.SE-04 1.7E-01 1.OE+O0 1.3E-03 2.2E-04 2.9E-01 2.9E-02 > 1.OE+00 2.9E-02 > 1.OE+O0 6.OE-02 3.7E-03 1.OE-02 1.0E+O0 2.OE-03 1.1E-03 2.OE-02 > 0.012 2.OE-02 > 0.012 1.5E-04 > 1.5E-01 **
1.OE-02 1,0E-01 3.OE-01 5.OE-01 1.5E-04 > 1.5E-01 **
1.OE-02 1i0E-01 3.OE-01 5.OE-01 O.OE+O0 > 1.5E-01 **
O.OE+O0 1.OE+O0 2.1E-03 > 1.5E-01 **
1.0E-02 1.0E-Ol 3.OE-01 5.OE-01 2.OE-03 2.OE-03 2.9E-03 6.6E-02 1.OE+O0 3.6E-01 6.7E-01 1i0E-01 1.OE+O0 1.OE+O0 1.OE+O0 1.OE+O0 3.4E-01 7.OE-01 > 1.OE+O0 7.OE-01 7.OE-01 1.OE+0O 3.4E-01 1.OE+0O 1.OE+00 1.0E+O0 1.6E-02 > 5.4E-02 8.3E-03 > 2.8E-02 1.OE+0O > 5.4E-02 1.OE+00 1.OE+0O > 5.4E-02 1.OE+O0 8.7E-01 1.0E+O0 1.OE-02 1.OE-02 1.OE-03 1.OE-02 1.OE-05 1.OE-05 1.OE-05 1.OE-05 1.OE-03 1.OE-03 LER No. 331/83-017 and -018
B.33-6 rpt 1.9E-02 1.OE+O0 sIcs 2.OE-03 1.OE+O0 1.OE-02 ads.inhibit O.OE+O0 1.OE+O0 1.OE-02 man.depress 3.7E-03 1.OE+O0 1.OE-02 branch model file
- forced LER No. 331/83-017 and -018