ML20168A459
| ML20168A459 | |
| 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: ML20168A459 (4) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
47814 Date:
June 5, 1970 -
Title:
Depressurization Incident at Dresden 2 The failure sequence was:
- 1. A spurious-signal in. the reactor pressure control system occurred causing the turbine control valve to open from 75% to 80% and turbine bypass valve to open 100%.
- 2. The reactor scrammed and the water level began to drop.
The pen in the water level stuck on the low water level mark.
Due to this incorrec-t signal the operator took manual control of the feedwater system and began to increase flow to the reactor.
- 3. After no change in water level indication the operator realized the pen was stuck.
He tapped the pen, however water was already blowing through the relief valves.
- 4. The feedwater flow was throttled back.
Corrective action:
The plant was shutdown for an extended period for repair of and inspection.
minor damage Design purpose of failed system or component:
The reactor water level instrumentation indicates the water level in the reactor vessel.
Unavailability of system per WASH 1400:
Unavailability of component per WASH 1400:
Unavailabilities are In units of per demand D-1.
Failure rates are in units of per hour HR-1.
A Spurious Signal The Reactor Tripped Due to an Erroneous Signal Feedwater Was Throttled Potential Initiates a Feed-the Operator Took Control Back and the Reactor Severe Water Transient of the Feedwater Controls Placed in Cold Shutdown Core
____and Overfilled the Vessel Damage No MSLB initiator No ATWS NSIC 47814 -
Actual Occurrence of the Depressurization Incident at Dresden 2
Excessive Coolant Inventory Reactor Scram Reactor Vessel Or Turbine Isolate Reactor Coolant Overflows Into Steam Lines, Is Dis-charged Through Relief Valves, Which Stick Open Steam Line Break Due To Turbine Missiles, etc.
Long Term Core Cooling Success Potential Severe Core Damage o
Small LOCA Initiator I
No r~No I
e5l'71YWý0%%
-Yes y R A I
No Yes NSIC 47814 -
Sequence of Interest for-the Depressurization Incident at Dresden 2
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER: 47814 DATE OF LER:
July 6, 1970 DATE OF EVENT:
June 5, 1970 SYSTEM4 INVOLVED:
Feedwater COMPONENT INVOLVED:
Reactor Water Level Indicator.
CAUSE: Component failure SEQUENCE OF INTEREST:
Excessive Coolant Inventory ACTUAL OCCURRENCE:
Depressurization Incident REACTOR NAME:
Dresden 2 DOCKET NU~!BER: 50-237 REACTOR TYPE:
BWR DESIGN ELECTRICAL RATING:
794 MJ e REACTOR AGE:
0.4 yr VENDOR: General Electric ARCHITECT-ENGINEERS:
Sargents and Lundy OPERATORS:
Commonwealth Edison LOCATION:- Nine miles from Morris, Ill.
DURATION:
N/A PLANT OPERATING CONDITION:
75%
SAFETY FEATURE TYPE OF FAILURE:
(ainadequate performance; (b) failed to start; PC) made inoperable; (d)____________
DISCOVERY METHOD: operational event COMM*ENT: