ML20140A214
| ML20140A214 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 05/19/2020 |
| From: | NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1993-002-00 | |
| Download: ML20140A214 (5) | |
Text
A.3-1 A. 3 LER No. 289/93-002 Event
Description:
Both Residual Heat Removal-Heat Exchangers Unavailable Date of Event: January 29, 1993 Plant:
Three Mile Island I A.3. 1 Summary Three Mile Island 1 (TMI-1) was operating at 100% power on January 29, 1993, when an operator aligned river water system valves to bypass both decay heat service (DHS) coolers. The coolers remained unavailable for about 3 h. With the DHS coolers unavailable, it would not have been possible to remove heat from several safety-related systems had they been demanded. The conditional core damage probability estimated for this event is 3. 1 x 10-6. The relative significance of this event compared to other postulated events at Three Mile Island 1 is shown in Fig. A. 3. 1.
LER 289/93-002 1 E-7 I E-6 I E-5 1 E-4 I E-3 I E-2 I
L360 h EP 8,-- -
Precursor Cutoff L30hAWLLO TRIP LOFW &1 MVTR AFW Fig. A.3.1I Relative event significance of LER 289/93-002 compared with other potential events at Three Mile Island 1 A. 3.2 Event Description During execution of a surveillance instruction involving operation of decay heat river water (DHRW) pumps, an auxiliary operator simultaneously bypassed DHS coolers DC-C-2A and DC-C-2B3. The DHS coolers serve as the heat sink for the decay heat closed cooling water (DCCW) system. Loads on the DCCW system include decay heat removal (DHR) coolers, DHR pump motor and bearing coolers, DCCW pump bearing coolers, reactor building spray (BS) pump motor and bearing coolers, and two of three makeup
[charging/high-pressure injection (HPI)] pump motor, bearing, and gear reducer coolers.
After -2.5 h, a control room operator discovered the error while evaluating the steps taken for the surveillance instruction. The DHS coolers were returned to service -0. 5 h later.
In the LER, the licensee discussed the potential plant response to a large-break loss-of-coolant accident (LOCA) with the DHS coolers isolated. They concluded that core and containment response would be unaffected before sump recirculation. Following initiation of sump recirculation, DHR would be provided by the reactor building emergency cooling fan coolers in conjunction with the recirculation flow from the low-pressure injection (LPI) and reactor BS pumps. They also concluded, based on the licensee's engineering judgement, that at least 30 min was available to restore cooling to the LPJ and spray pumps. The impact of the isolated DHS coolers on sump recirculation following a small-break LOCA was not discussed in the LER.
LER No. 289/93-002
A.3-2 A. 3.3 Modeling Assumptions In the sump-recirculation phase following a small-break LOCA, flow from the discharge of the DHR coolers is directed to the suction of the makeup HPI pumps to provide adequate net positive suction head for HPI pump operation. This water is cooled to prevent damaging the makeup pumps (the TMI-1 final safety analysis report indicates that the design temperature of the makeup pumps is 200'F). With the DHS coolers isolated, makeup and LPI pump cooling water temperatures would exceed design temperatures during sump recirculation following a small-break LOCA, resulting in failure of high-pressure recirculation (HPR). The time to pump failure cannot be accurately estimated based on available data, although it may be as long as several hours.
The event was modeled as a 3-h unavailability of HPR. Because of the uncertainty in the available time before pump damage and the potential radiological conditions at the closed valves following initiation of HPR, recovery of the isolated DHS coolers (through operation of the two 18-in, manual valves in each train) was assumed not to be possible in the analysis. The low temperature of the borated water storage tank (B3WST) fluid before sump recirculation was assumed not to impact HPI pump operation in the injection phase.
A. 3.4 Analysis Results 6
The conditional core damage probability estimated for this event is 3. 1 x 10-. The dominant sequence, highlighted on the event tree in Fig. A. 3.3, involves a postulated small-break LOCA, success of reactor trip, auxiliary feedwater, and HPI functions followed by failure of HPR.
The core damage probability estimated for this event is strongly influenced by the probability of not recovering the DHR service coolers used in the analysis. For example, if a nonrecovery probability of 0.34 (ASP Recovery Class R2, the failure appeared recoverable in the required period at the failed equipment, and the equipment was accessible; recovery from the central room did not appear possible) is assumed, the conditional core damage, probabilIity is reduced to 1. 1 x 10-6.
LER No. 289/93-002
A.3-3 LOCA RT AFW MFW I HPI HPR PORVON SEQ END NO STATE OK 71 CD 72 CD 73 74 OK CD CD OK 75 CD 76 CD 77 CD 78 ATWNS Fig. A. 3.2 Dominant core damage sequence for LER 289/93-002 LER No. 289/93-002
A.3-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
289/93-002 Event
Description:
Both RHR heat exchangers unavailable Event Date:
January 29, 1993 Plant:
Three Mile island 1 UNAVAILABILITY, DURATION= 3 NONRECOVERABLE INITIATING EVENT PROBABILITIES TRANS LOOP LOCA SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 3.9E-04 2.6E-05
- 3. 1 E-06
- 0. OE+OO
- 0. OE+OO
- 0. OE+OO
- 0. OE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 71 Loca -rt -afw -hpi HPR/-HPI 16 trans -rt afw mfw -hpi(flb)
HPR/-HPI 44 Loop -rt/loop -emerg.power afw -hpi(f/b) HPR/-HPI 11 trans -rt -afw porv.or.srv.chatl porv.or.srv.reseat -hpi HPR/ -HP I 73 Loca -rt afw -mfw -hpi HPR/-HPI 51 Loop -rt/Loop emerg.power -afw/emerg.power -porv.or.s rv.chatt seaL.Loca -ep.rec(st) -hpi HPR/-HPI 41 loop -rt/Loop -emerg.power -afw porv.or.srv.chaLL porv.or.srv.reseat -hpi HPR/-HPI 76 Loca -rt afw mfw -hpi HPR/-HPI 46 Loop -rt/Loop einerg.power -afw/emerg.power power.or.srv.chaLL porv.or.srv.reseat/emerg.power seat.Loca -ep.rec(sL) -hpi HPR/ -HPI 13 trans -rt afw -mfw porv.or.srv.chatt porv.or.srv. reseat-hpi HPR/-HPI End State Prob CD CD CD CD CD CD CD CD CD
- 3. 1 E -06 1.5E-08 1.5E-08 3.4E-09 1.7E-09 1.1 E-09 2.3E-10 N Rec**
- 4. 3E-01
- 8. 8E-02 1.4E-01 1.1 E -02 1.1E-01 4.2E-01 5.8E-03 1.2E-10 3.8E-02 9.1E-11 4.2E-01 1.9E-12 2.7E-03 CD SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
11 trans -rt -afw porv.or.srv.chatt porv.or.srv.reseat -hpi HPR/ CD
- HP I 13 trans -rt afw -mfw porv.or.srv.chatt porv.or.srv.reseat -hpi CD HPR/-HPI 16 trans -rt afw mfw -hpi(f/b) HPR/-HPI CD 41 Loop -rt/Loop -emerg.power -afw porv.or.srv.chatL porv.or.srv. CD reseat -hpi HPR/-HPI 44 loop -rt/toop -emerg.power afw -hpi(f/b) HPR/-HPI CD 46 loop -rt/Loop emerg.power -afw/emerg.power porv.or.srv.chatt -
CD porv.or.srv.reseat/emerg.power seat.loca -ep.rec(sL) -hpi HPR/
- HP I 51 Loop -rt/Loop emerg.power -afw/emerg.power -porv.or.srv.chal L CD seaL.Loca -ep.rec(st) -hpi HPR/-HPI 71 Loca -rt -afw -hpi HPR/-HPI CD 73 Loca -rt afw -mfw -hpi HPR/-HPI CD 3.4E-09 1.1E-02 1.9E-12 2.7E-03 1.5E-08 8.8E-02 2.3E-10 5.8E-03 1.5E-08 1.4E-01 9.1E-11 4.2E-01 1.1E-09 4.2E-01 3.1E-06 4.3E-01 1.7E-09 1.1E-01 LER No. 289/93-002
A.3-5 76 Loca -rt afw mfw -hpi HPR/-HPI CD 1.2E-10 3.8E-02
- nonrecovery 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:
BRANCH MODEL:
PROBABILITY FILE:
No Recovery Limit s :\\asp\\prog\\mode Is\\pwrdseaI. cmp s:\\asp\\prog\\models\\tmil.st1 s :\\asp\\prog\\modetLs\\pwr bst11. pro BRANCH FREQUENCIES/PROBABILITIES Branch trans loop loca rt rt/loop emerg.power afw afw/emerg.power mfw porv.or.srv.chaL I porv.or.srv. reseat porv.or.srv. reseat/emerg.power seat. Loca ep.rec(sl) ep. rec hpi hpi(f/b)
HPR/-HPI Branch Model:
1.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
- branch model file
- forced System 1.3E-04 1.6E-05 2.4E-06 2.8E-04
- 0.
OE+OO 2.9E-03 2.3E-03 5.OE-02 2.OE-01 8.OE-02 1.OE-02 1.OE-02 4.6E-02
- 5.
7E-01 1.6E-01 1.OE-03 1.OE-03 1.5E-04 > 1.OE+OO
- 1.OE-02 1.5E-02 Nonrecov 1.OE+OO 5.3E-01 4.3E-01 1.2E-01 1.OE+OO 8.OE-01 2.6E-01 3.4E-01 3.4E-01 1.OE+OO 1.1 E-02 1.OE+OO 1.OE+OO 1.OE2+00 1.OE+OO 8.4E-01 8A.E -01 1.OE+OO Opr FailI 1
.OE-02 1
.OE-03 LER No. 289/93-002