ML20147A351
| ML20147A351 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 08/14/1984 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-032-00 | |
| Download: ML20147A351 (6) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 259/84-032 Event
Description:
Inadvertent Overpressurization and Leakage from LPCS:
Date of Event:- August 14, 1984 Plant: Browns Ferry 1 EVENT DESCRIPTION Sequence While at full power, the LPCS's normally closed, motor-operated*
isolation valve was undergoing a surveillance test. The normal interý-.
lock preventing opening the valves simultaneously at power was by-passed.* By error, 8 months previously, the testable isolation check valve's air operator had been installed backwards, thereby causing the valve to actually be open while the indicator showed closed. By a.
second operator error, the power to the closed motor-operated valve was not locked out during the surveillance test. The normally open motor-7 operated isolation valve remained open. While applying the open signal in the test, the operator caused the normally closed motor isolation valve to cycle open. The LPCS overpressurized, and the line RV dis-charged *steam and water into the pump room. The overpressure alarm failed to sound, and the operator did not observe the change in system pressure. The pipe heated to 400'F. The seal there leaked due to back-f low from the common drain that serves the seal leak line,- and the clean radwaste line for the A train pump ruptured. The event lasted 13 mmn before the line was isolated. The workers responding to the event had their clothing contaminated by the leaking water.
Corrective Action CS loop I was isolated and tagged, which placed the unit in a 7-d limiting condition of operation. Meanwhile, the plant manager ordered an investigation of the event. Site engineering and maintenance staffs inspected all affected components and found no damage. The extent of the pipe heating was determined by examination of paint damage on the piping. The maximum temperature experienced was estimated to be (400*F. Paint damage extended from the injection valves down to the system RV. Tennessee Valley Authority's Office of Engineering Design analyzed the system piping and supports for the transient and found that integrity for continued use was ensured. The pump A seal was removed, and no damage was observed. Also, there was no evidence that hot water entered the pump area piping, which indicates that the pump discharge check valve was holding.
Event Identifier: 259/84-032.,
D-51
Plant/Event Data Systems Involved:
LPCS Components and Failure Modes Involved:
LPCS isolation valves - inadvertently open Component Unavailability Duration: 8 months Plant Operating Mode: 1 (100% full power)
Discovery Method: During testing Reactor Age: 11 years Plant Type: BWR Comments Development of probability estimates related to this and other overpressurization events is addressed. in An Evaluation of BWR Over-Pressure Incidents in. Low Pressure Systems, J. D. Harris and J. W.
Minarick, May 1985 (internal accident sequence percursor report). Based on the impact of the event on Browns Ferry Unit -1.(one train of LPCI and one train of LPCS impacted), the following modifications to probability values used in that document are required to estimate' the conditional probability for the event:
p (core damage/pipe rupture and RCS depressurization) =2E-12 p (core damage/small-break LOCA) = 1'.1E-4 In addition, the probability of pipe rupture given overpressurization has been assumed to be I1E71 (see the above document). These estimates result in an event tree/probability model for core damage associated with the events shown in the figure below. The attached calculations address sequences 15 and 17. The overall core damage likelihood is estimated using the model in the figure to be 6E-6. See also Abnormal Occurrence Reports to Congress, NUREG,-O0990,-7(3) foir additional inf or-mation on this event.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOCA 0.12 Recoverable locally at valves Branches Impacted and Branch Nonrecovery Estimate LPCS Base case LPCI/RHR Base case Event Identifier: 259/84-032 D-52
Plant Models Utilized BWR plant Class C CHECK PIPE OPEN MOV PLANT RELIEF FLOOD CORE END STATE SEQUENCE VALVE RUPTURE CHECK CLOSED DELIBER- VALVE PATHWAYS COOLING AND MOV OCCURS VALVE ATELY CLOSES EXIST PROVIDED OPENED CLOSES DEPRES-SURIZED OK 1 CD 2 OK 3 OK 4 CD OK OK CO OK 9 CD 10 OK 11 OK 12 OK 13 OK 14 CD 15 OK 16 CD 17
- 1. 1E-4 P(CORE DAMAGE) - 6E-6 Core damage model for LER 259/84-032.
Event Identifier: 259/84-032 D-53
CONDITIONAL CORE DAM'AE PROBABILITY CALCLLATIONS Event Identifier: 259/84-032 Event
Description:
Inadvertant Overpressurization and Leakage f rom LPCS Event Date: 8/14/84 Plant: Browns Ferry 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOCA 1.2E-01 SEQ(NCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV LOCA 8 .6E-07 Total 8 .6E-07 CD LOCA 1IE-04 Total 1.E-04 ATWS LOCA 2.*4E-06 Total 2.4E-06 DOMINANT SE91JENCES End State: CV Conditional Probability: 5.7E-07 314 LOCA SCRAM1 -SLC.OR.RODS PCS/LOCA FWIPCS.LOCA HPCI -SRV.ADS -COND/FW.PCS _R-RR(SDC)
End State: CD Conditional. Probability: l.1E-04 310 LOCA -SCRAM PCS/LOCA FW/PCS.LOCA HPCI RCIC/LOCA SRV.ADS End State: ATWS Conditional Probability: 2.4E-06 Event Identifier: 259/84-032 D-54
332 LOCA SCRAM SLC.OR.RODS SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec**
302 LOCA -SCRAM PCS/LOCA -FW/PCS.LOCA RHR(SDC) RHR(SPCOOL)/-LPC CD 3.7E-06 9.2E-03 I .RHR(SDC) C.! .AND.V/RHR(SDC) .RHR(SPCO0L-)
310 LOCA -SCRAM PCS/LOCA FW/PCS.LOCA HPCI RCIC/LOCA SRV.ADS CD 1.1E-04 * :2.3E-02 314 LOCA SCRAM -SLC.OR.RODS PUS/LOCA FW/PCS.LOCA HPCI -SRV.ADS CV 5.7E-07
- 1.5E-02
-COND/FW .PCS -RHR (500 318 LOCA SCRAM -SLC.OR.RODS PCS/LOCA FW/PCS.LOCA HPCI -SRV.ADS Cv 2.9E-07 7.8E-03 COND/FW .PCS -LPCS -RHR (500) 332 LOCA SCRAM SLC.OR.RODS ATWS 2.4E-06
- 1.2E-01
- dominant sequence for end state
- non-recovery credit for edited case MODEL. b:\bwrctree.cmp DATA: b :\bfprob .cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr FailI TRANS 1.1E-03 1.OE+00 LOOP 1.3E-05 3.4E-01 LOCA 3.3E-06 > 3.3E-06 3.4E-01 > 1.2E-01 Branch Model- INITOR Initiator Freq: 3 .3E-06 SCRAM 4. IE-04 1.0E+00
¶.C .OR .RODS 1.OE-02 1.0E+00 4.OE-02 PCS/TRANS 1.7E-01 1.0E+00 PCS/LOCA 1.0E+00 1.0E+00)
SRV.CHALL/TRANS.-SCRAM 1.0E+00 1.0E+00 SRV.CHALL/TRANS.SCRAM 1.0E+00 1.0E+00 BRY .CHALL/LOOP .- SCRAM 1.0E+00 1.0E+00 SRV.CHALL/L0OP .SCRAM I.OE+0O 1.0E+00 SRV .CLOSE 3.6E-02 1.0E+00 EMERG.POWER 5.4E-04' 5.1E-01 FW/PCS .TRANS 4.6E-01 3.4E-01 FW/PCS .LOCA 1.0E+00 3.4E-01 HPCI 1.OE-01 5.7E-01 RCIC/TRANS .OR.LOOP 6.7E702 5.7E-01 RCIC/LOCA 1.0E+00 I.0E+00 CR0 1.OE-02 1.0E+00 4.OE-02 SRV.ADS 6.7E-03 1.0E+00 4.OE-02 Event Identifier: 259/84-032 D- 55
COND/FW .PCS 1.OE+00 3.4E-01 LPCS 3.OE-03 ) 3.OE-02 3.4E-01 Branch Model. 1.01'.2 Train 1 Cond Prob: 3.OE-02 Train 2 Cond Prob: 1.OE-01 > Failed LPCI (RHR) /LPCS 4.OE-04 ) 4C0E-03 3.4E-01 Branch Model: 1.0F.2 Train I Cond Prob: 4.OE-03 Train 2 Cond Prob: 1.OE-01 > Failed RHRSW/LPCS .LPCI .TRANS 5.OE-01 1.OE+00 4 .OE-02 RHRSW/LPCS .LPCI .LOOP 5.OE-01 I .OE400 4.OE-02 RHRSW/LPCS .LPCI .LOCA 5.OE-01 1.OE+OO 4.OE-02 RHR(SDC) 2.OE-02 3A.E-01 RHR(SDC) /-LPCI 2.OE-02 3.4E-01 RHR(SDC)/LPEI 1.OE+00 1.OE+O0 RHR (SPCOOL) /-LPCI .RHR (SBC) 2.OE-02 1.OE+O0 RHR(SPCOOL) /LPCI .RHR(SDC) 5.2E-01 1.OE+00 C.I.AND .V/RHR (SDC) .RHR (SPCOOL) 1.OE+00 3.4E-01
- forced Minarick 04-11-1987 13:56:22 Event Identifier: 259/84-032 D-56