ML20161A182
| ML20161A182 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-007-00 | |
| Download: ML20161A182 (7) | |
Text
B.19-1 B.19 LER No. 304/83-007 Event
Description:
Postulated Grid/Weather-Related LOOP with 2 EDGs Inoperable Date of Event:
January 31, 1983 Plant:
Zion 2 B.19.1 Summary On January 31, 1983, during normal operations, the 0 diesel generator failed to accept a load greater than 50%
during an operability check for taking residual heat removal (RHR) 2A pump out for servicing. The 2B diesel generator was also declared inoperable due to an oil leak. Rampdown of the unit was started. The estimated increase in core damage probability, or importance, over the duration of this event is 4.8 x 10'. The base-case core damage probability (CDP) over the duration of the event is 1.9 x 10', resulting in an estimated conditional core damage probability (CCDP) of 5.0 x 10'.
B.19.2 Event Description On January 31, during normal operations, the 0 diesel generator failed to accept a load greater than 50% during an operability check for taking RHR 2A pump out for servicing. The 2B diesel generator was also declared inoperable due to an oil leak. These failures resulted in two Technical Specification violations (3.15.2.C and 3.15.2.H).
Investigation of the 0 diesel generator revealed that the 0 diesel generator turbo charger ET-18EK9V had seized, thus reducing capacity to 50%. The turbo charger was replaced along with the 2B diesel generator oil filter gasket.
B.19.3 Additional Event-Related Information Zion 2 has three emergency diesel generators, each rated at 4,000 kW and cooled by service water. Two diesel generators are specifically dedicated to Zion 2. Diesel generator 2A feeds 4-kV bus 248, and diesel generator 2B feeds 4-kV bus 249. One diesel generator (diesel generator 0) is connected to both Zion I bus 147 and Zion 2 bus 247. The buses are electrically interlocked to prevent the diesel from supplying both buses at the same time. All diesel generators have a 50,000-gallon storage tank which is sufficient for seven days of operation as well as a 600-gallon day tank equipped with automatic level controls. The diesels start automatically upon receipt of an automatic or manually initiated safety injection signal, loss of power to any two of four 4-kV non-engineered safety feature (ESF) buses, and an undervoltage on the 4-kV bus served by the diesel generator. Diesel generator 2B bus 249 supplies power to auxiliary feedwater pump IC, RHR pump A, and charging pump A. Diesel generator 0 bus 247 supplies power to safety injection pump A and charging pump B. In addition to the diesel generators, power from the Unit I station auxiliary transformer (SAT) can be manually aligned to supply power to Unit 2.
LER No. 304/83-007
B.19-2 B.19.4 Modeling Assumptions Since auxiliary power can be supplied from Unit 1, plant-centered losses of offsite power (LOOPs) would not be of particular importance in this event. LOOPs which affected both units (i.e., when Unit 1 could not provide auxiliary power to Unit 2), such as grid-related and weather-related LOOPs, would be of importance given both dedicated emergency diesel generators (EDGs) were inoperable. Thus, this event was modeled as a postulated grid-related/weather related LOOP with two EDGs inoperable. The LOOP frequency, the offsite power recovery probabilities, and the probability of seal loss-of-coolant accident (LOCA) were modified as shown in Table B.23.1 to reflect those values associated with grid-related and weather-related LOOPs (see ORNL/NRC/LTR 89/11, Revised LOOP Recovery and PWR Seal LOCA Models, August 1989). The first train of emergency power was set to failed to reflect the failed EDG since it was assumed that the fault discovered in EDG 0 could also have occurred in the other EDGs. 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 a part of the postulated event. The second train of emergency power was set to failed to reflect the assumption that the oil leak in EDG 2B was severe enough to prevent the EDG from operating if needed. The corresponding system trains which rely on these diesels for power given the loss of offsite power were also modified to reflect their unavailability.
Since the length of time in which both faults were present is unknown, a duration of half the surveillance period on the diesels was chosen (15 days or 360 hours0.00417 days <br />0.1 hours <br />5.952381e-4 weeks <br />1.3698e-4 months <br />).
Table B. 19.1 Revised LOOP Probabilities Event T
Default Probability Revised Probability LOOP frequency 1.6E-5 2.8E-6 LOOP short-term nonrecovery 0.53 0.66 Seal LOCA probability 0.27 0.42 Offsite power recovery prior to battery depletion given no seal 0.031 0.14 LOCA Offsite power recovery prior to battery depletion given seal 0.57 0.77 LOCA Offsite power recovery within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> (OFFSITE.PWR.REC/-
0.22 0.52 EP.AND.-AFW)
Offsite power recovery within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (OFFSITE.PWR.REC/-
LER No. 304/83-007
B.19-3 B.19.5 Analysis Results The estimated increase in core damage probability over the duration of this event is 4.8 x 10'. The base-case CDP (not shown in calculation) is 1.3 x 10'6, resulting in an estimated CCDP of 5.0 x 10-'. The dominant sequence highlighted on the event tree in Figure B. 19.1 involved a postulated LOOP with emergency power failure (station blackout), an RCP seal LOCA, and failure to recover offsite power before core uncovery.
LER No. 304/83-007
B.19-4 S I I
.OFSITE RECOV RCSI RPOV POR POWER F
EED
[SR_
LOOP SEA(.
O RECOV HPI BLEED SIDE (OOLDOWI N
A
-L
,N E ES END SEQ STATE NO OK OK OK CD OK CD CD OK CD CD OK OK OK CD CD OK OK CD CD OK OK CD OK CD CD CD OK CD CD OK OK CD OK CD CD CD OK CD CD CD 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 Figure B.19.1 Dominant core damage sequence for LER 304/83-007 LER No. 304/83-007
B.19-5 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
Event
Description:
Event Date:
Plant:
304/83-007 Postulated grid/weather related LOOP with 2 EDGs inop.
January 31. 1983 Zion 2 UNAVAILABILITY, DURATION= 360 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP SEQUENCE CONDITIONAL PROBABILITY SUMS 6.7E-04 End State/Initiator Probability CD LOOP Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) 4.8E-05 4.8E-05 Sequence End State Prob N Rec**
226 LOOP -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep SEAL
.LOCA OFFSITE.PWR.REC/SEAL.LOCA 228 LOOP -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep -SEAL
.LOCA OFFSITE.PWR.REC/-SEAL.LOCA 229 LOOP -rt(loop)
EP -afw/ep porv.chall/sbo porv.reseat/ep 239 LOOP -rt(loop)
EP afw/ep CD CD CD CD 3.5E-05 58BE-01 8.8E-06 5.8E-01 2.2E-06 5.8E-01 1.9E-06 2.OE-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
226 LOOP -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep SEAL
.LOCA OFFSITE.PWR.REC/SEAL.LOCA 228 LOOP -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep -SEAL
.LOCA OFFSITE.PWR.REC/-SEALLOCA 229 LOOP -rt(loop)
EP -afw/ep porv.chall/sbo porv.reseat/ep 239 LOOP -rt(loop)
EP afw/ep CD CD CO CO 3.5E-05 5.8E-01 8.8E-06 5.8E-01 2.2E-06 5.8E-01 1.9E-06 2.OE-O1
- 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.
LER No. 304/83-007
B.19-6 SEQUENCE MODEL:
BRANCH MODEL:
PROBABILITY FILE:
c:\\aspcode\\models\\pwrb8283.cmp c:\\aspcode\\models\\zion2.82 c:\\aspcode\\models\\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans LOOP Branch Model :
INITOR Initiator Freq:
loca sgtr rt rt(loop)
AFW Branch Model:
1.OF.3+ser Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
AFW/ATWS Branch Model:
I.OF.1 Train 1 Cond Prob:
afw/ep mfw porv.chall porv.chall/afw porv.chall/loop porv.chall/sbo porv.reseat porv. reseat/ep srv.reseat(atws)
HPI Branch Model:
1.OF.3 Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
FEED.BLEED Branch Model:
1.OF.3+ser+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
emrg.boration recov.sec. cool recov.sec.cool/offsite.pwr rcs.cool down RHR Branch Model:
1.OF.2+ser+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Serial Component Prob:
1.5E-03 1.6E-05 > 2.8E-06 1.6E-05 > 2.8E-06 2.4E-06 1.6E-06 2.8E-04 O.OE+O0 3.8E-04 > 1.3E-03 2.OE-02 i.0E-01 > Unavailable 5.GE-02 2.8E-04 4.3E-03 > 7.OE-02
-4.3E-03 > 7.OE-02 5.OE-02 2.OE-01 4,OE-02 1.OE+O0 1.OE-01 1.OE+O0 2.0E-02 2.OE-02 1.0E-01 1.OE-05 > 1.OE-02 1.OE-02 1.0E-01 > Unavailable 1.OE-02 > Unavailable 2.OE-02 > 3.OE-02 1.OE-02 1.0E-01 > Unavailable 1.OE-02 > Unavailable 2.0E-02 O.OE+O0 2.OE-01 3.4E-01 3.OE-03 2.2E-02 > 4.OE-02 2.OE-02 1.0E-01 > Unavailable 2.OE-02 1.0E+O0 5.3E-01 > 6.6E-01 5.4E-01 1.OE+O0 1.0E-01 1.OE+O0 4.5E-01 1.OE+O0 3.4E-01 3.4E-01
- 1.
OE+00 1.0 E-'-O
- 1.
OE+00
- 1.
OE+00
- 1.
- 1.
OE+00 1.0 E+00 8.9E- 01
- 1.
OE+00
- 1.
OE+00
- 1.
OE+00 1.0 E+0O
- 1.
OE+00
- 7.
OE -02 1.OE-03 1.GE-Q2 1.OE-02 1.OE-03 1.OE-03 LER No. 304/83-007
B.19-7 RHR.AND.HPR Branch Model:
1.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
HPR Branch Model:
1.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
EP Branch Model:
1.OF.3 Train I Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
SEALLOCA Branch Model:
1.OF.1 Train 1 Cond Prob:
OFFSITE.PWR.REC/-EP.AND.-AFW Branch Model:
1.OF.1 Train 1 Cond Prob:
OFFSITE.PWR.REC/-EP.AND.AFW Branch Model:
1.OF.1 Train 1 Cond Prob:
OFFSITE.PWR.REC/SEAL.LOCA Branch Model:
1.OF.1 Train 1 Cond Prob:
OFFSITE.PWR.REC/-SEAL.LOCA Branch Model:
1.OF.1 Train 1 Cond Prob:
sg.iso.and rcs.cooldown rcs.cool.below.rhr prim.press.limited 1.OE-03 > 1.OE-02 1.OE-02 1.0E-01 > Unavailable 4.OE-03 > 4.OE-02 4.OE-02 1.0E-01 > Unavailable 5.4E-04 > 1.9E-01 5.OE-02 > Failed 5.7E-02 > Failed 1.9E-01 2.7E-01 > 4.2E-01 2.7E-01 > 4.2E-01 2.2E-01 > 5.2E-01 2.2E-01 > 5.2E-01 6.7E-02 > 3.2E-01 6.7E-02 > 3.2E-01 5.7E-01 > 7.7E-01 5.7E-01 > 7.7E-01 3.1E-02 > 1.4E-01 3.1E-02 > 1.4E-01 1.OE-02 3.OE-03 8.8E-03
- 1.
OE+OO 1.OE+OO 8.9E-01
- 1.
OE+OO
- 1.
OE+OO 1.OE+OO
- 1.
OE+OO
- 1. Es-DO iDE-01
- 1. Es-DO 1.DEs-DO 1.OE-03 1.OE-03 3.0E-03 branch model file
- forced LER No. 304/83-007