ML20168A458
| ML20168A458 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/16/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1970-LTR-00 | |
| Download: ML20168A458 (4) | |
Text
PRECURSOR DESCRIPTTON AND DATA NSIC Accession Number:
44751 Date:
April 27, 1970
Title:
Failure of Three of Four Safety System Sensors for Primary Drum Low Level Scram at Dresden 1 The failure sequence was:
During a routine test, three of four primary drum low level scram system sensors were found failed due to crud build-up in the switches.
These failures would cause a failure to scram on low drum level if that were required.
Corrective action:
The switches were flushed and their proper operation was demonstrated.
The switches were to be replaced with differential-type switches at the up-coming refueling, Design purpose of failed system or component:
The switches provide trip input to the scram system for primary drum low level.
Unavailability of system per WASH 1400:
- Unavailability of component per WASH 1400:
- float switches not considered in WASH-14 00 Unavailabilities are in units of per demand D-1.
Failure rates are in units of per hour HR'1
(Reactor condition IThree of four primary Potential unknown) testing drum low level scram Severe in progress jswitches found failed Core Damage No -
scram on primary drum low level not required No NSIC 44751 -
Actual Occurrence for Failure of Three of Four Safety System Sensors for Primary Drum Level Scram at Dresden 1
Loss of feedwater due Reactor scram Operator detects Emergency to inadvertent valve on low primary low primary drum condenser closure, etc. (feed drum level level and manually provides system still pressurized scrams reactor (or core cooling normal loss of feedwater initiates secondary1 trip unavailable) shutdown system)
Potential Severe Core Damage I
No LII Yes No Yes Yes NSIC 44751 -
Sequence of Interest for Failure of Three of Four Safety System Sensors for Primary Drum Level Scram at Dresden 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
44751 DATE OF LER:
April 27, 1970 DATE OF EVENT:
unknown SYSTEM INVOLVED:
Reactor Protection System COMPONENT INVOLVED:
Primary Drum Level Float Switches CAUSE:
Crud buildup in the float chambers SEQUENCE OF INTEREST:
Loss of Main Feedwater ACTUAL OCCURRENCE:
Switch failure during testing REACTOR NAME:
Dresden 1 DOCKET NUMBER:
50-10 REACTOR TYPE:
BWR DESIGN ELECTRICAL RATING:
200 MWe REACTOR AGE:
10.5 yr VENDOR:
GE ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Commonwealth Edison Co.
LOCATION:
Nine miles E of Morris, Ill.
DURATION:
360 (a) hours PLANT OPERATING CONDITION:
unknown SAFETY FEATURE TYPE OF FAILURE:
(a) inadequate performance; (b) failed to start; QDmade inoperable; (d)
DISCOVERY METHOD:
during testing COMMENT:
only abstract available