ML20161A172
| ML20161A172 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-016-01 | |
| Download: ML20161A172 (5) | |
Text
3-35 2 Accident Sequence Precursor Program Event Analysis LER No:
424/88-016 Ri Event
Description:
Water leakage into control room causes spurious PORV Date of Event:
Plant:
Si f t June 3, 1988 Vogtle 1 Summnary Water from a leak-off valve associated with a spuriously activated fire header flowed through unsealed control room penetrations and dripped on control room cabinets, resulting in a spurious PORV lift.
The core damage probability estimated for the event is 8.0 x 0-5.
The relative significance of this event compared with other potential events at Vogtle 1 is shown below.
I E-8 1 E-7 LER 424/88-0 16 R I
-\\
E4 1E-6 I E 1 E-3 I E-2 Trip Trip w/1 AEW Train Unavail j L EP Unavail AEW Unavail (360 hrs)
(360 hrs)
LOOP Event Description During the course of air balancing, an outside air damper was opened.
It is believed that the cooler outside activated a thermostatically controlled heater.
The initial burnoff of accumulated dust and debris from the heater generated enough smoke to activate the area smoke detectors and charge the sprinkler system headers.
Although the sprinklers did not actuate, water collected on the floor via leakage through 3/8-in. leakoff valves located immediately downstream of the deluge valves.
A high point in the hall floor caused water to flow into the upper cable spreading room instead of the area floor drain.
The water subsequently flowed around unsealed cable penetrations in the floor and seeped through the ceiling of the control room, where it
B3-353 dripped into various process panel cabinets.
About 25 min af ter the smoke alarms were received, the control room received a pressurizer high-level deviation alarm, and the pressurizer backup heaters began to cycle. Operators responded by placing the pressurizer backup heaters in manual control.
Nineteen minutes later, a power-operated relief valve spuriously opened for 5 s until it was manually closed.
Operators sub-sequently closed the corresponding PORV block valve and declared the PORV inoperable.
About an hour after the smoke alarms were received, operators recognized that water was leaking into the process panels and directed technicians to cover the panels with plastic and dry the affected areas.
The event was caused by -1/2 to 1 gal of water leaking under embedded angles and past the foam in penetrations in the ceiling of the control room.
Silicon sealant was placed to block the seepage path.
Event-Related Plant Design Information The as-built floor design assumed that embedded steel angles would main-tain a watertight seal with the concrete floor slab after being seal-welded to the penetration's upper angle iron assembly.
A series of tests was performed to determine the effectiveness of the newly sealed penetrations.
Even after sealing, some leakage (several drops per minute) was still observed through the inside of the cable bundle.
ASP Modeling Assumptions and Approach This event has been modeled as a loss of coolant accident initiated by the spurious PORV lift.
The likelihood of nonrecovery was assumed to be 0.04.
If the PORVs had not been quickly closed, a plant trip and safety injection would have been expected to occur.
Analysis Results The conditional probability of core damage is estimated to be 8.0 -
10-'.
Two sequences, involving the potential loss of high-pressure injection and recirculation, contribute to this event.
In thE first sequence (highlighted on the following event tree), the open PORV is not closed and results in a small-break LOCA requiring mitigation (p =
0.04).
Following this, high-pressure recirculation fails (p =
1.5 x 10-4) following successful high-pressure injection.
The second sequence is similar but involves failure of high-pressure injection (p = 8.4 10-4).
[It should be noted that Georgia Power Co.
experienced a similar problem at its Hatch 1 facility (see LER 321/85-018).]
8-354 LOCA I RT I AFW I MPW IHPI IHPR OPORV SEQ END NO STATE 71 72 OK CD CD OK 73 00 74 00 OK 75 CD 76 CO 77 C0 78 ATWS Dominant Core Damage Sequence for LER 424/88-016
B-355 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
424/88-016 Event
Description:
Water leakage into control room causes PORV lift Event Gate:
06/03/88 Plant:
Vogtle 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOCA SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator
- 8. CE-05
- 8. CE-OS
- 1. 3E-06 1.3E-06 tOGA Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 71 LOCA -rt -afw -hpi hpr/-hpi 72 LOCA -rt -afw hpi 78 LOCA rt.
-- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 71 LOCA -rt -afw -hpi hpr/-hpi 72 LOCA -rt -afw hpi 78 tOGA rt
-* non-recovery credit for edited case SEQUENCE MODEL:
c:\\asp\\sealmod\\pwrbseal.cmp BRANCH MODIft:
c:\\asp\\sealmod\\vogtle.sll PROBABILITY FILE:
c:\\asp\\sealmod\\pwr~bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System trans 1.8E-03 loop 1.6E-05 LOCA 2.4E-06 > 2.4E-06 End State CO CO ATNS End State CO CO ATWS Non-Recov 1. OE-400
- 3. 4E-05
- 1. 3E-06 P rob 4. GE-OS 3.4E-05
- 1. 3E-06 N Rec**
4.OE-02
- 3. 4E-02 4.8E-03 N Rec.*
4. OE-02
- 3. 4E-02 4.8E-03 Branch Model:
INITON Initiator Freg:
rt rt/loop eme rg.power a fw afw/emerg.p~ower mfw Event Identifier: 424/88-016 2.4E-06 2. BE-04
- 0. OE+OO 2. 9E-03
- 3. 8E-04 5.0 OE-02 1.OE+OO Opr Fail 1.OE-03
B-356 porv.or.srv.chall 4.OE-02 1.OE+O0 porv.or.srv.reseat 2.OE-02 1.1E-02 porv.or.srv. reseatlenierg.power 2.OE-02
- 1. OE+00 seal.Jloca 2.7E-01 1.OE+00 ep.rec(sl) 5.7E-01 1.OE+400 ep.rec 3.7E-02 1.OE+00 hpi 1.OE-03 8.4E-01 hpi(f/b) l.OE-03 8.4E-01 1.OE-02 hpr/-hpi 1.5E-04 1.OE+00 1.OE-03 porv.open 1.OE-02 1.OE+00 4.OE-04
- branch model file
- forced Minarick 11-09-1989 12 :04 :4 3 Evenmt Identifier:
424/88-016