ML20149K476
| ML20149K476 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 338-87-017 | |
| Download: ML20149K476 (4) | |
Text
B-84 PRECURSOR DESCRIPTION SHEET LER No.: 338/87-017 Ri Event
Description:
Steam generator tube rupture and plant trip Date of Event: 7/15/87 Plant: North Anna 1 EVENT DESCRIPTION Sequence At 0630 h during operation, a high radiation alarm was received from the SC C main steam line. Simultaneously, pressurizer pressure and level began to rapidly decrease.
At 0635 h the pressurizer, level had fallen to 45% and pressure had fallen to 2100 psig from 2235 psig. The operators manually tripped the plant, and 20 s later the safety injection system automatically actuated on low-low pressurizer pressure (less than 1765 psig on two of three channels). Based on SG indications, by 0648 h the operators had deter-mined that a SC tube had ruptured in SG C, and they isolated the SC.
An orderly plant shutdown was begun at 0718 h to bring the plant to cold shutdown conditions.
Prior to the event the condenser air ejector radiation monitor had been declared inoperable due to erratic operation, but all other safety systems were operable. This monitor would divert air release from the environment to the containment on detecting high radiation. Because of the radiation monitor's inoperability, a potential radiological release path to the environment existed until the operators manually realigned the system.
The C SC steam supply to the TDAFW pump turbine was isolated. Two relief valves, one on the MFWP B suction line and the other on the 2A feedwater heater tube side, lifted and failed to reseat. They were manually closed 30 min into the event. Data analysis indicated 1.59 x 10-1 Ci were released, mostly as gases.
Corrective Action An investigation into the cause of the tube rupture was begun.
Plant/Event Data Systems Involved:
Steam generator Main feedwater Components and Failure Modes Involved:
SC tube ruptures in operation Two MFW relief valves stick open Event Identifier: 338/87-017 R1
B-85 Component Unavailability Duration: N/A Plant Operating Mode: 1 (100%)
Discovery Method: Operational event Reactor Age: 9.3 y Plant Type: PWR Comments None.
MODELING CONSIDERATION AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate SC tube rupture 1.0 No recovery rupture Branches Impacted and Branch Nonrecovery Estimate None Plant Models Utilized PWR plant Class A Event Identifier: 338/87-017 RI
B-86 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 338/87-017RI Event
Description:
Steam generator tube rupture and plant trip Event Date: 07/15/87 Plant: PWR STGR INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES SGTR 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD SGTR 7. 7E-04 Total 7.7E-04 ATWS SGTR 3.4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
102 sgtr -rt -afw -hpi rcs.depr<sg.rv.setpoint CD 4. 1E-04 1.OE+00 103 sgtr -rt -afw hpi CD 2. 5E-04 B.4E-01 101 sgtr -rt -afw -hpi -rcs.depr<sg.rv.setpoint ruptured.sg.isol r CD 1.OE-04 1.OE+O0 cs.cold.prior.to.rwst.depl 108 sgtr rt ATWS 3.4E-05 1.2E-OI
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
101 sgtr -rt -afw -hpi -rcs.depr<sg.rv.setpoint ruptured.sg.isol r CD 1.OE-04 1.OE+00 cs.cold.prior.to.rwst.depl 102 sgtr -rt -afw -hpi rcs.depr<sg.rv.setpoint CD 4.1E-04 1.OE+O0 103 sgtr -rt -afw hpi CD 2. 5E-04 S. 4E-01 108 sgtr rt ATWS 3. 4E-05 1.2E-OI
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\newmodel\pwrsgtr.cmp BRANCH MODEL: c:\asp\newmodel\pwrsgtr.new PROBABILITY FILE: c:\asp\newmodel\pwr-bnew.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Rec .ov Opr Fail sgtr 5.0E-03 1.0E+OC rt 2.BE-04 1.2E-01 afw 3.BE-04 2.6E-01 mfw 2.OE-Ol 3.4E-01 hpi 3.OE-04 8.4E-01 ruptured.sg.isol 1.0E-02 1.OE+O0 rcs.depr<sg.rv.setpoint 1.0E-05 l.0E+00 4.0E-04 Event Identifier: 338/87-017Rl
B-87 rcs.cold.prior.to.rwst.depl 1.OE-02 1.OE+00 4.OE-04
- branch model file
- forced Minarick 05-16-1989 07:04:31 Event Identifier: 338/87-017RI