ML20149K470
| ML20149K470 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-012-00 | |
| Download: ML20149K470 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 336/84-012 Event
Description:
Trip, LOFW, and AFW Degraded Date of Event: November 28, 1984 Plant: Millstone 2 EVENT DESCRIPTION Sequence The unit had been operating at 100% power whenla tube leak was de-tected in feedwater heater 5A. An orderly shutdown~of/the.'unit had been under way for some time when a steady rise in the level in the feedwater heater 5A was noted. The reactor was then tripped to protect the tur-bine from water intrusion. At the time of the trip, the unit was, oper-ating at 62% power.
Following the ,trip, standard posttrip actions were-<carried out. In addition, trip recovery procedures were also followed. When the "B" steam generator feed pump was taken to minimum speed, the level in both SGs. started decreasing. The "B" .SG feed pump was secured due to low discharge pressure, and AFW flow was initiated. The level in the SG 1 increased while the level in SG 2 continued to decrease. AFW flow to SG 2 was increased with no effect on the level decrease in SG 2. Opera-tions personnel noted steam escaping from the "B" SG feed pump. It was theorized that the MFW check valve to the SG 2 (2-FW-5B) failed to seat, thus resulting in a backflow of AFW to the "B" SG feed pump. At this time, the feed-regulating valves, the feed-regulating block valves, and the SG feed pump discharge valves were shut. Level in SG 2 was brought on scale and returned to normal.
The unit was placed in hot standby (mode 3). The tubes in the
.feedwater heater.5A were inspected and plugged as required. An inspec-tion of the malfunctioning check valve, 2-FW-5B, determined that the valve stem had bound up slightly, not, allowing the valve to seat. Ad-justments were made to the valve, and its operability was evaluated through in-service test T84-36. The valve was deemed operable before the unit was returned to 100% power operation.
Corrective Action Check valves 2-FW-5A and 2-FW-5B were inspected and reworked during the 1985 refueling outage. The rework consisted of machining a spacer ring internal to the valves to eliminate binding. The valve vendor con-curred with this modification.
Event Identifier: 336/84-012 D-164
Plant/Event Data Systems Involved:
AFW, MFW Components and Failure Modes Involved:
MFW check valve - failed in operation MFW pump - failed in operation AFW train flow - degraded Component Unavailability Duration: NA Plant Operating Mode: 1 (62% power)
Discovery Method,: Operational event Reactor Age: 9.1 years Plant Type: PWR Comments For information concerning a similar event, see: J. W. Minarick and J. D. Harris, Analysis of the November 21, 1985, San Onofre 1 Transient from the Standpoint of Potential Severe Core Damage, ORNL Letter Report from J. R. Buchanan to F. J. Hebdon, Office for Analysis and Evaluation of Operational Data, U.S. Nuclear Regulatory Commission, January 17, 1986.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1 .0 No recovery (manual trip)
Branches Impacted and Branch Nonrecovery Estimate AFW Base case Degraded flow, one train failed MFW 1 .0 No recovery assumed Plant Models Utilized PWR plant Class G Event Identifier: 336/84-012 D-1 65
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 336/84-012 Event
Description:
Trip With LOFW and AFW Degraded Event Date: 11/28/84 Plant: Millstone 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00, SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 5.3E-05 Total 5.3E-05 CD TRANS 3.OE-05 Total 3.OE ATWS TRANS 3.QE-05 Total 3.OE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 4.1lE-05 118 TRANS -RT AFW MFW HPI (F/B) -SS.DEPRESS -COND/MFW End State: CD Conditional Probability: 2.1E-05 119 TRANS -RT AFW MFWHPI(F/B) -SS.DEPRESS COND/MFW End State: ATWS Conditional Probability: 3.OE-05 Event Identifier: 336/84-012 D-166
121 TRANS RT SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec**
112 TRANS -RT AFW MFW -HPI(E/B) ý-HPR/-HPI PORV.OPEN -SS.DEPRESS CV 9.7E-06 I.BE-01
-CO ND/MFW 113 TRANS -RT AFW MFW -HPI(F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CD 5.OE-06 9.2E-02 COND/MFW 118 TRANS -RT AFW MFWHPI(F/B) -SS.OEPRESS -COND/MEW CV 4.1E-05
- 1.2E-01
- dominant sequence for end state
- non-recovery credit for edited case MODEL: b:\PWRSTREE .CMP DATA: b:\M'ILL2PRO.CMP No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.OE-03 l.OE+00 LOOP 2.3E-05 3.4E-01 LOCA 4.2E-06 3.4E-01 RT 2.5E-04 1.2E-01 RT/LOOP 0.OE+00 1.OE+00 EMERS .POWER 5.4E-04 5.1E-01 AFW 1.OE-03 > 5.9E-03 2.7E-01 Branch Model: I.OF..3+ser Train 1 Cond Prob: 2.OE-02 > Failed Train 2 Cond Prob: I.0E-O1 Train 3 Cond Prob: 5.OE-02 Serial Component Prob: 9.2E-04 AFW/EMERS .POWER 5 .OE-02 3.4E-01 MFW 2.OE-01 > 1.OE+00 3.4E-01 > 1.0E+00 Branch Model: 1.0F.1 Train 1 Cond Prob: 2.OE-01 > Failed PORY .OR .SRV .CHALL 2.OE-02 1.0E+00 PORV.OR.SR V.RESEAT 1.OE-02 1.2E-01 PIJRV.OR .SRV .RESEAT/EMERG .POWER 1.OE-02 1.2E-01 SS .RELEAS .TERM 1.5E-02 3.4E-01 SS.RELEAS .TERN/-NFW 1.5E-02 3.4E-01 55 .DEPRESS 3.6E-02 1.0E+00 Event Identifier: 336/84-012 1)--167
COND/NFW 1.OE+OO 3.E-O1 HPI 3.OE-04 5.2E-01 HP! (F/B) 3,OE-04 5.2E-01 4.()E-02 PORV.PEN 1.OE-02 1.OE+t)O HPR/-HPI 1.OE-03 1.OE+OO CSR 2.OE-03 3.E-01
- forced tiinarick 04-12-1987 16:23:05 Event Identifier: 336/84-012 D-1 68