ML20156A201
| ML20156A201 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-005-00 | |
| Download: ML20156A201 (5) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
164149 Date:
February 12, 1981
Title:
Isolable Small Break LOCA at Robinson 2 The failure sequence was:
- 1. With the plant at 100%,
the "A" electrohydraulic control oil pump developed a seal leak and a plant shutdown was begun.
The "B"
EHC pump was already out of service because of vibration problems.
- 2.
The "B" feedwater and condensate pumps were stopped due to erratic feedwater pump behavior.
- 3.
immediately following the opening of the generator output breakers (6% power), the turbine governor valve spiked open (apparently due to the electrohydraulic problems) and generated a momentary high steam flow signal.
- This, in combination with an existing low T signal resulted in train B safequards initiation.
(Train A did not initiate nor did the MSIVs close, apparently because of the short duration of the high steam flow signal).
The SI signal tripped the reactor.
- 4.
The "A" SI train was manually actuated and the MSIVs were closed.
- 5.
The "A" containment fire alarm was received shortly after the SI actuation.
- 6.
During the automatic isolation of the letdown line on safety injection, relief valve CVC-RV-203 bellows ruptured, either because of the relatively slower closure of valves upstream of the relief valve compared with those downstream of it, or because of leakage past the upstream valves.
In addition, a pressure surge due to the isolation valves closing caused a drain cap on a partially open drain valve to be blown off.
- 7.
Having determined that a spurious SI had occurred and unaware of the above failure, the operators reset SI and feedwater isolation and restored letdown.
- 8.
Containment pressure and dewpoint increased and RCS pressure de-creased.
Letdown was secured approximately 15 min later.
A con-tainment entry was made in an attempt to determine the leakage path.
Approximately 3000 gallons of water were in the containment sump at that time.
- 9.
After letdown was isolated, pressurizer pressure continued to de-crease.
A second safety injection occurred on low pressure.
Both trains of safeguards equipment actuated.
- 10.
Four hours after the first containment entry a second entry was made and the leaking drain line identified.
The two upstream level control valves were leaking at approximately 5-7 gpm.
The drain valve was closed.
- 11.
After the drain valve was closed RCS pressure still continued to decrease in part as a result of a partially opened pressurizer spray valve.
(The pressurizer spray valve position is indicated by demand in lieu of stem position, which delayed identification of the cause of the depressurization.)
- 12.
The leak rate could not be accurately determined but it was estimated to have been approximately 100 gpm while letdown was unisolated.
A total of about 4500 to 6000 gallons of water was leaked to the containment sump during the event.
Corrective action:
- 1. The leaking drain valve was closed and a new pipe cap installed.
All other similar valve/pipe cap combinations were verified closed.
- 2.
Corrective action concerning the failed relief valve was not identified.
Design purpose of failed system or component:
The reactor coolant system transfers heat generated in the core to the steam generators.
The letdown line provides a means of removing reactor coolant from the RCS for boron concentration changes and for purification.
Reactor at Train A CVCS pressure SI reset RCS pressure Letdown Pressurizer Second containment Continued Leaking 100% power safety surges and and decrease due isolated pressure entry made and reduction in pressurizer and second-injection slow valve letdown to unisolated continues to failed relief valve RCS pressure spray valve ary side initiated closures restored CVCS leakage decrease due and open drain line due in part to identified problems and MSIVs result in paths (-3000 to leakage identified; drain leaking pres-by stopping result in closed CVCS relief gal in 15 flow through line closed; addi-surizer spray RC pumps B train B SI valve bellows min) closed CVCS tional letdown valve and C signal and failure and
- valves, second isolation valve reactor drain valve safety injec-closed trip pipe cap tion failure Potential Severe Core Damage No No - charging flow available for makeup No No -
charging flow available for makeup No No -
charging flow available for makeup No No -
SI available No No -
charging flow available for makeup No No NSIC 164149 -
Actual Occurrence for Isolable Small Break LOCA at Robinson 2
Small Reactor Auxiliary High Low Pressure Potential Sequence LOCA Trip Feedwater and Pressure Recirculation Severe No.
Secondary Injection and LPR/HPI Core Heat Removal Cross-Connect Damage No 1
Yes 2
Yes 3
No 4
Yes 5
Yes 6
Yes 7
NSIC 164149 -
Sequence of Interest for Isolable Small Break LOCA at Robinson 2
- auto isolation on safety injection closure of upstream valves
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
164149 LER NO.:
81-005 DATE OF LER:
February 12, 1981 DATE OF EVENT:
January 29, 1981 SYSTEM INVOLVED:
Containment chemical volume control system COMPONENT INVOLVED:
Relief valve, drain valve, pipe cap, pressurizer spray valve CAUSE:
Bellows rupture, drain valve vibrated open, pipe cap blew off, leaking spray valve SEQUENCE OF INTEREST:
Small break LOCA ACTUAL OCCURRENCE:
Small break LOCA REACTOR NAME:
H.
B.
Robinson 2 DOCKET NUMBER:
50-261 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
700 MWe REACTOR AGE: 10.4 years VENDOR:
Westinghouse ARCHITECT-ENGINEERS:
Ebasco OPERATORS:
Carolina Power & Light LOCATION:
5 miles NW of Hartsville, South Carolina DURATION:
N/A PLANT OPERATING CONDITION:
100% power (6% at time of trip)
TYPE OF FAILURE:
Small LOCA DISCOVERY METHOD:
Operational event COMMENT:
Additional information: "Engineering Evaluation of the H.
B.
Robinson Reactor Coolant System leak on January 29, 1981,"
Office for Analysis and Evaluation of Operational Data, March 23, 1981.