ML20140A230
| ML20140A230 | |
| Person / Time | |
|---|---|
| Issue date: | 05/19/2020 |
| From: | NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1994-002-00 | |
| Download: ML20140A230 (7) | |
Text
Appendix C Appenix CLER No. 304/94-002 C.7 LER No. 304/94-002 Event
Description:
Unavailability of Turbine-Driven Auxiliary Feedwater Pump and Emergency Diesel Generator Date of Event: March 7, 1994 Plant: Zion Unit 2 C.7.1 Summary During a refueling outage, with Unit 2 in hot shutdown, operators were performing a surveillance test on the turbine-driven auxiliary feedwater (TDAFW) pump and an endurance test on the 2B emergency diesel generator (EDG).
During the tests, the TDAFW pump tripped on "overspeed," and the EDG experienced. frequency swings and was manually tripped. An operator also observed an increase in lube oil and jacket water cooler temperatures for the EDG before it was manually tripped. The cause of the TDAFW pump trip could not be determined. The EDG frequency swings were caused by a blown fuse, and the elevated lube oil and jacket water cooler temperatures were caused by zebra mussel shells in the lube oil and jacket water coolers for EDG 2B. The conditional core damage probability estimated for this event is 2.3 x 10-.
C.7.2 Event Description Zion Unit 2 was performing several tests required to conclude a refueling outage. During a surveillance test on the TDAFW pump, the pump tripped at 053 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> on March 7, 1994. The cause of the TDAFW piump trip could not be determined. An endurance test of the 2B EDG was also being performed. During the endurance test, the EDG experienced frequency swings, and lube oil and jacket water cooler temperatures increased. The EDG was manually tripped at 0618 hours0.00715 days <br />0.172 hours <br />0.00102 weeks <br />2.35149e-4 months <br /> on March 7, 1994. It was later determined that the frequency swings were caused by a blown fuse, and the increased coolant temperatures were caused by zebra-mussel shells in the lube oil andjacket water coolers. The zebra mussels were from the fire protection header that was used to supply EDG cooling during a dual-unit service water outage.
The zebra-mussel shells were cleaned from EDG 213, and the blown fuse was replaced. The coolers for the 0 EDG and the 2A EDG were inspected and few or no shells were found. The IA and lB EDGs were not inspected, but testing was performed to verify that the EDGs were operable.
C.7.3 Additional Event-Related Information The auxiliary feedwater (AFW) system consists of two 200% capacity subsystems. One subsystem utilizes two 100%
capacity motor-driven pumps that are powered from separate engineered safety features (ESF) buses. Each motor-driven pump supplies a header, which in turn supplies all four of the steam generators (SGs). The TDAFW pump supplies all four of the SGs. Steam to drive the TDAFW pump is supplied from either SG 2A or SG 2D.
There are three safety-related buses for each unit. There are three sources of power for each bus-a normal feed from the respective unit's transformers, a cross-tie to the opposite unit, and an emergency diesel generator. There are five diesel generators-two for Unit 1, two for Unit 2, and one common diesel that can serve one bus on both units. If a safety injection signal is present, the common diesel generator will align to the unit with the safety injection signal. If a safety injection signal is absent, the common diesel generator is capable of supplying power to the associated electrical bus of each unit simultaneously.
C.7-1 NURIEG/CR-4674, Vol. 21
LER No. 304/94-002 Apni Appendix C C.7.4 Modeling Assumptions Although this event occurred during a refueling outage, it was modeled assuming it could have occurred with the plant at power. The fuse failure that rendered the EDG inoperable could have occurred at any time. The failure mechanism for the TDAFW pump could not be determined, but is was assumed that the failure could also have occurred at any time. The zebra mussel shells could have been introduced during a short outage, and the plant could have been returned to a power condition prior to performing an endurance run ofthe EDG. Therefore, this event was modeled as if it occurred during power operation.
It was assumed that the EDG 2B was inoperable for one-half of its 30-day surveillance period. It was assumed that the EDG surveillance tests performed every 30 days would have run the EDG long enough to detect the degraded cooling condition. It was also assumed that the TDAFW pump would have tripped on "overspeed" during this period. The equipment powered by the 2B EDG would be unavailable during a LOOP event prior to restoration of offsite power.
This event was modeled as an unavailability of the 2B EDG and the TDAFW pump for a period of 15 days (360 h). The TDAFW pump failure to start and run probability (AFW-TDP-FC-1 C) was set to 1.0 (TRUE) to reflect its condition, and the operator nonrecovery probability was set to 0.04 because recovery was considered to be proceduralized and could have been performed from the control room. Note, this value is the default value and is nearly identical to the probability used for the failure of auxiliary feedwater. The 2B EDG failure probability (EPS-DGN-FC-lB) was set to 1.0 (TRUE). The emergency power system was treated as a three-train system because of the common diesel.
Common-cause failure probabilities are estimated using the MGL model. In this model, the nominal common-cause basic event for a three-train system is Q x P3 xy. If one train suffers a random failure and the other trains are exposed to this failure mechanism, then the common-cause basic event becomes J3 x y. Therefore, the common-cause failure probability becomes 2.7 x 10- (0.1 x 0.27). The initiating event frequency for all initiators was calculated for a 360-h period.
C.7.5 Analysis Results The conditional core damage probability estimated for this event is 2.3 x 10-5. The dominant sequence highlighted on the event tree in Figure C.7.1 involves apostulated LOOP, a successful reactortrip, failure of emergency power, aPORV lift and successful reseat, recovery of AFW, and failure to recover offsite power prior to core uncovery following a reactor coolant pump seal LOCA. If the zebra mussels were judged not to be a common cause failure, then the CCDP would be 7x 10-6.
Definitions and probabilities for selected basic events are shown in Table C.7.l1. The conditional probabilities associated with the highest probability sequences are shown in Table C.7.2. Table C.7.3 lists the sequence logic associated with the sequences listed in Table C.7.2. Table C.7.4 describes the system names associated with the dominant sequences.
Cutsets associated with each sequence are shown in Table C.7.5.
C.7.6 Reference
- 1.
LER 304/94-002, Revision 1, "Exceeded Limiting Condition for Operation 3.7.2 Action e for Placing Unit in Mode 4 with a Turbine-Driven and Motor-Driven AFW Pump Inoperable," July 25, 1994.
NUREGICR-4674, VoL 21 C.7-2 NUREG/CR-4674, VoL 21 r.7-2
Appendix C Appenix CLER No. 304/94-002 Figure C.7. 1. Dominant core damage sequence for LER 304/94-002.
C.7-3 C.7-3NIJREGICR-4674, Vol. 21
LER No. 304/94-002 Appendix C Table C.7.1.
Definitions and probabilities for selected basic events for LER 304/94-002 Base Current Modified Event name Description probability probability Type for this event AFW-TDP-FC-lC AFW Turbine Driven Pump Fails 3.9E-002 1.OE-+OOO TRUE Y
AFW-XIHE-NOREC-EP Operator Fails to Recover AFW A-0 4.102Y During Station Blackout 3.EO1 4O-0 AFW-XIHE-NOREC-L Operator Fails to Recover AFW 2.E01 4O02 System During LOOP2.EOl 4E-0Y EPS-DGN-CF-ALL Common Cause Failure of Diesel LE03 37-0 EPS-DGN-CF-ALL Generators1.O-0 3.E03Y EPS-DGN-FC-10 Diesel Generator 0 Fails 3.7E-002 3.7E-002 N
EPS-DGN-FC-IA Diesel Generator IA Fails 3.7E-002 3.7E-002 N
EPS-DGN-FC-IB Diesel Generator lB Fails 3.8E-002 l.OE+000 TRUE Y
EPS-XIHE-NOREC Operator Fails to Recover 8.OE-0Ol 8.OE-00l N
Emergency Power HPI-MOV-00-RWST HPI RWST Isolation MOV Fails 3.OE-003 3.OE-003 N
I-IPR-MOV-CC-RHRB RHR Train B Discharge MOV Fails 3.OE-003 3.OE-003 N
HPR-MOV-CC-SMPB Failure of Sump MOV SI-881 lB 3.OE-003 3.OE-003 N
HPR-X21-I-NOREC-L Operator Fails to Recover H-PR l.OE+000 l.OE+000 N
System During LOOP LE-LOOP Loss-of-Offsite Power Initiating 8.6E-006
- 3. E-003 Y
Event LE-SGTR Steam Generator Tube Rupture 1.6E-006 5.9E-004 Y
Initiating Event IE-SLOCA Small Loss of Coolant Accident 1 OE-006 3.6E-004 Y
Initiating Event IE-TRANS Transient Imitiating Event 5.3E-004 1.7E-001 Y
OEP-XI-IE-NOREC-BD Operator Fails to recover offsite
- 3. lE-002
- 3. E-002 N
power before battery depletion OEP-XI-IE-NOREC-SL Operator Fails to Recover Offisite 5.7E-001 5.7E-001 N
Power (Seal LOCA)
PPR-SRV-00-1 PORV 1 Fails to Reclose After 3.OE-002 3.OE-002 N
Opening PPR-SRV-00-2 PORV 2 Fails to Reclose After 3.OE-002 3.OE-002 N
Opening RCS-MDP-LK-SEALS RCP Seals Fail Without Cooling 2.7E-001 2.7E-001 N
and Injection RHR-MDP-FC-IB RITR Train B Fails 4.OE-003 4.OE-003 N
RHR-MOV-CF-RWST Common Cause Failure of 2.6E-004 2.6E-004 N
RLHRIRWST MOVs NUREG/CR-4674, Vol. 21C7-C.74
Appendix C LER No. 304/94-002 Appendix C LER No. 304/94-002 Table C.7.1.
Definitions and probabilities for selected basic events for LER 304/94-002 (cont.)
Base Current Modified Event name Description probability probability Type for this event RHR-MOV-00-RWSTA RI-RIRWST Isolation MOV 3.OE-003 3.OE-003 N
8812A Fails to Close RHIR-MOV-00-RWSTB RFIRIRWST Isolation MOV 3.OE-003 3.OE-003 N
8812B Fails to Close RIIR-X1HE-NOREC Operator Fails to Recover the REIR 1.OE+O0O 1 OE+000 N
system RHR-XIHE-NOREC-L Operator Fails to Recover the RHR1l 1.OE+000 1.OE+O00 N
System During LOOP Table C.7.2.
Sequence conditional probabilities for LER 304/94-002 Conditional core Core damage moane
/
Event tree name Sequence name damage probability (CCporacDP
%0otibto probability (CDP)
(CPCP (CCDP)
LOOP 37 1.OE-005 1.2E-006 9.6E-006 46.2 LOOP 38 4.2E-006 1.7E-007 4.OE-006 18.0 LOOP 39 2.8E-006 1.8E-007 2.6E-006 12.0 LOOP 30 2.1E-006 5.lE-008 2.1E-006 9.3 LOOP 05 1.7E-006 1.7E-007 1.5E-006 7.4 Total (all sequences) 2.3E-005 2.4E-006
- 2. 1E-005 Table C.7.3.
Sequence logic for LER 304/94-002 Event tree Sequence name Logic name LOOP
- 37.
/RT-L, EP, /AFW-L-EP, PORV-L, /PORV-EP, SEALLOCA, OP-SL LOOP 38
/RT-L, EP, /AFW-L-EP, PORV-L, PORV-EP LOOP 39 IRT-L, EP, AFW-L-EP LOOP 30
/RT-L, EP, /AFW-L-EP, PORV-L, /PORV-EP, /SEALLOCA, OP-BD1 LOO 05
/RT-L, /EP; I AFW-L, PORV-L, PRVL-RES, /OP-2H, /lIII-L, LOOP 05
/COOLDOWN, RHR-L, I-PR-L C.7-5 NURE G/CR-4674, Vol. 21
LER No. 304/94-002 Appendix C Table C.7.4.
System names for LER 304/94-002 System name Description AFW-L No or Insufficient AFW Flow During LOOP AFW-L-EP No or Insufficient AFW Flow During Station Blackout COOLDOWN RC S CoolDown to RJIR Pressure Using TBVs, etc.
EP Failure of Both Trains of Emergency Power H-PI-L No or Insufficient Flow From HPI System During LOOP HPR-L No or Insufficient HlPR Flow During LOOP OP-2H-Operator Fails to Recover Offsite Power Within 2 lIrs OP-BD Operator Fails to Recover Offisite Power Before Battery Depletion OP-SL Operator Fails to Recover Offisite Power (Seal LOCA)
PORV-EP PORVs Fail to Reclose (No Electric Power)
PORV-L PORVs Open During LOOP PRVL-RES PORVs and Block Valves Fail to Reclose (EP Succeeds)
RHR-L No or Insufficient Flow From RI{R System During LOOP RT-L Reactor Fails to Trip During LOOP ISEALLOCA IRCP Seals Fail During LOOP Table C.7.5.
Conditional cut sets for higher probability sequences for LER 304/94-002 Cut set
%FreunyCtst No.
Contribution reucyCtss LOOP Seq: 37
- 1. IE-005 1 949 LO-005 EPS-DGN-CF-ALL, EPS-XHE-NOREC,,OEP-XIHE-NOREC-SL, 1 94.
1.O-005 RCS-MDP-LK-SEALS 2 5.
5AE007 EPS-DGN-FC-lA, EPS-XIHE-NOREC, OEP-XI-E-NOREC-SL, 2 5.
5.4-007 RCS-MDP-LK-SEALS, EPS-DGN-FC-10 LOOP Seq: 38 4.2E-006 1~.
47.4.............
DG..F........ENO EC PP -S V-O 2
47.4 2.OE-006 EPS-DGN-CF-ALL, EPS-XIHE-NOREC, PPR-SRV-00-2 2
947.9 2.lE-006 EPS-DGN-CF-ALL, EPS-XIHE-NOREC, PEPR-SRV-00-1 B
.E....S-DG....N........-
.IA E...X......EC
.EP........-B 2..5.0....................F....
NUREGICR-4674, Vol 21 C.7-6 NUREG/CR-4674, Vol. 21 C.7-6
Appendix C LER No. 304/94-002 Table C.7.5.
Conditional cut sets for higher probability sequences for LER 304/94-002 (cont.)
Cut set FreunyCtss N. Contribution eunyCtst LOOP Seq: 05 1.8E-006...................
1 20.
3.6-007
/EPS-DGN-FC-1A, IHPR-XIHE-NOREC-L, PPR-SRV-OO-2, 1 20.
3.6-007 RJHR-MDP-FC-IB, RflR-XIHE-NOREC-L 2 15.
2.7-007
/EPS-DGN-FC-1A, HPR-XIHE-NOREC-L, PPR-SRV-OO-2, 2I53 27-0 RHR-XIHE-NOREC-L, HPR-MOV-CC-RHRB 3 1.3
.7E007
/EPS-DGN-FC-LA, HIPR-XHE-NOREC-L, PPR-SRV-OO-2, 3 15.
2.7-007 RHR-XIHE-NOREC-L, RHR.-MOV-00-RWSTA 4 15.
2.7E007 EPS-DGN-FC-1A, HPR-XIHE-NOREC-L, PPR-SRV-OO-2, 4 15.
2.7-007 RIIR-XI-IE-NOREC-L, HPI-MOV-00-RWST 5
15.3 2.7E-007 IEPS-DGN-FC-LA, HIPR-XIHE-NOREC-L, PPR-SRV-OO-2, RHR-XIHE-NOREC-L, HPR-MOV-CC-SM4PB Total (all sequences)
I2.3E-005 C.7-7 C.7-7 NLREGICR-4674, Vol. 21