ML20149K479
| ML20149K479 | |
| 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 1981-076-00 | |
| Download: ML20149K479 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
171939 Date:
October 28, 1981
Title:
Inadvertent Steam Dump Valve Opening and Safety Injection at North Anna 2 The failure sequence was:
- 1.
With the reactor at 100% power, a turbine trip and reactor trip oc-curred as a result of a failure in an electrohydraulic control line to No.
4 governor valve.
- 2.
Three and one-half hours later, with the reactor at 2% power, it was observed that the steam dumps were in the T mode in lieu of the steam pressure mode of operation.
- 3.
The operator switched to the steam pressure mode of operation and shifted the steam dump controller to auto.
All eight steam dumps opened.
- 4.
The operator immediately shifted to manual on the controller and to the Ta position on the steam dump selector switch.
- 5.
Either lhis action or the low-low T interlock closed the dump avg valves but not before safety injection was initiated.
- 6.
All safety injection equipment operated as required, except the pressurizer liquid space inside isolation valve failed to close.
- 7.
The specific cause for the high controller output was not determined, and an investigation of equipment failure and human error revealed no discrepancies.
Corrective action:
The event was reviewed for equipment failure and human error and no cause could be determined.
Design purpose of failed system or component:
The steam dump valves provide for steam generator pressure control following plant trip by venting steam to the condenser.
Turbine/previous Operator observes Operator switches Inadvertent Operator Safety Dump valves reactor trip due steam dump selec-to steam pressure opening of immediately injection closed due to to ERC line tot in Tavg mode mode and shifted all 8 atmos-switches to initiated either the failure to #4 in lieu of steam the steam dump pheric dump manual on operator's governor valve pressure mode controller to valves controller actions or to (reactor at 2%
auto (cause not and to Tavg iow-low Tavg power) determined) on steam interlock dump selec-tor switch Potential Severe Core Damage No No -
safety injection provides core protect'on No No - safety injection available for core protection if required No No No NSIC 171939 -
Actual Occurrence for Inadvertent Steam Dump Valve Opening and Safety Injection at North Anna 2
Steam Reactor Required Auxiliary High Required PORV PORV Long Potential Sequence Line Scram Steam Feedwater Pressure Concentrated Opened Closure Term Severe No.
Break Generator Injection Boric Acid Due To Cooling Core Isolation (HPI)
Addition Continued Damage Effected HPI No 1
No 2
Yes 3
No 4
No S
No 6
Yes 7
Yes 8
No 9
No 10 Yes 11 No 12 Yes 13 Yes 14 No 15 Yes 16 Yes 17 Yes 18 Yes 19 NSIC 171939 -
Sequence of Interest for Inadvertent Steam Dump Valve Opening and Safety Injection at North Anna 2
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
171939 LER NO.:
81-076 DATE OF LER:
October 28, 1981 DATE OF EVENT:
October 3, 1981 SYSTEM INVOLVED:
Steam dump to condenser COMPONENT INVOLVED:
Dump valves CAUSE:
Inadvertent opening SEQUENCE OF INTEREST:
Main steam line break ACTUAL OCCURRENCE:
Eight opened dump valves REACTOR NAME:
North Anna 2 DOCKET NUMBER:
50-339 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
907 MWe (net)
REACTOR AGE:
1.3 years VENDOR:
Westinghouse ARCHITECT-ENGINEERS:
Stone and Webster OPERATORS:
Virginia Electric & Power Co.
LOCATION:
40 miles NW of Richmond, Virginia DURATION:
N/A PLANT OPERATING CONDITION:
2% power following a trip TYPE OF FAILURE:
Inadequate performance DISCOVERY METHOD:
Operational event COMMENT: