ML20147A359
| ML20147A359 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-032-00 | |
| Download: ML20147A359 (5) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
166072 Date:
May 19, 1981
Title:
Damaged RHR Heat Exchangers at Brunswick 1 The failure sequence was:
- 1. Oyster shells growing in the service water (SW) piping dislodged and accumulated in the tubing of the B RHR heat exchanger (HX).
The shell buildup resulted from the service water chlorination system being out of service for an extended period of time.
- 2.
The blockage in the MX tubes created a high pressure drop which ultimately displaced the baffle plate normally separating the SW inlet and outlet.
The displacement allowed the service water to bypass the HX tubes, rendering the heat removal capability unavailable.
This was discovered during a special inspection conducted during a cold shutdown April 19, 1981.
- 3.
The 1B RX was removed from service for repair while the 1A RHR HX maintained the cold shutdown condition until April 25, 1981, when the second service water pump for the 1A RHR HX was started.
- 4.
The increased flow caused the 1A HX baffle to displace in the same manner as the 1B HX, resulting in a loss of cooling.
Shell buildup in the 1A RX was also responsible for the high pressure drop condi-tions leading to the baffle displacement.
- 5.
Both RHR HXs for Brunswick 1 were unavailable for heat removal.
Corrective action:
- 1.
An alternate shutdown cooling lineup was established using fuel pool coolers, the condensate storage tank, and the core spray system.
- 2.
Temporary repairs were performed on the 1A heat exchanger and it was returned to service while permanent repairs were still in progress on the 1B heat exchanger.
Permanent repairs for the 1A HX were to follow return to service of the 1B HX.
- 3.
Programs were being pursued to monitor safety-related HX perfor-mance, clean the HX tubes and SW piping, and resume the SW chlorination operation.
- 4.
Plant procedures were to be revised to vent the RHR service water system regularly.
Design purpose of failed system or component:
The RHR system provides long-term core cooling for normal shutdown, maintenance of cold shutdown, and heat removal capability for emergency shutdown modes.
Loss of RHR-lB IX Loss of RHR-IA HX on Alternate RHR from damage due to startup of second service path success blockage by oyster water pump due to excessive shells pressure drop caused by oyster shells Potential Severe Core Damage I
No Possible -
however, plant in cold shutdown No NSIC 166072 - Actual Occurrence for Loss of RHR Heat Exchangers at Brunswick 1
Potential Severe Core Damage Sequence No.
No Yes No Yes Yes Yes No Yes Yes Yes NSIC 166072 -
Sequence of Interest for Loss of RHR at Brunswick 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
166072 LER NO.:
81-032 DATE OF LER:
May 19, 1981 DATE OF EVENT:
April 19, 1981 SYSTEMS INVOLVED:
Residual heat removal COMPONENT INVOLVED:
RHR heat exchanger CAUSE:
Excessive pressure drop from aquatic growth SEQUENCE OF INTEREST:
LOCA ACTUAL OCCURRENCE:
none REACTOR NAME:
Brunswick Unit 1 DOCKET NUMBER:
50-325 REACTOR TYPE:
BWR DESIGN ELECTRICAL RATING:
821 MWe REACTOR AGE:
4.5 years VENDOR:
General Electric ARCHITECT-ENGINEERS:
United Engineers & Constructors OPERATORS:
Carolina Power & Light LOCATION:
3 miles north of Southport, North Carolina DURATION:
512 h (estimated).
This includes half the test interval (360 h) plus the period between the two failure discoveries (144 h) plus 8 additional hours to make the temporary repairs and return the 1A heat exchanger to service.
PLANT OPERATING CONDITION:
Cold shutdown TYPE OF FAILURE:
Inadequate performance; made inoperable DISCOVERY METHOD:
Special inspection
COMMENT:
Further information:
NSIC 166019 (Brunswick 1, 50-325, LER 81-0005, April 30, 1981).
Feed and bleed using the main feedwater and main steam systems could potentially be an alternative for RHR cooling but may be difficult to implement due to the potential radioactive environment of the containment following a LOCA.