ML20147A355
| ML20147A355 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-024-01 | |
| Download: ML20147A355 (6) | |
Text
IC Accession Number: 163405 te: July 28, 1980 tle: Failure of 76 Control Rods to Insert at Browns Ferry 3 e failure sequence was:
. The reactor was being shut down for maintenance on the feedwater system following steady state operation at 400 MWe (37% power).
Power was reduced to 390 MWe by decreasing recirculation flow and inserting 10 control rods.
Normal operating procedures at Browns Ferry involve scramming the reactor from about 30% power, so the operator initiated a manual scram.
All the west bank rods scrammed full-in except rod 30-23 which set-tled at position "02."
However, due to excess water in the east bank scram discharge headers, 75 out of 88 east bank withdrawn rods failed to fully in-sert, coming to rest at various positions from 46 to 02.
This first scram was sufficient to reduce the reactor power from 36% to less than 2%, but not to subcriticality. Water level was maintained by the feedwater control system.
The scram discharge volume was drained for periods of 93 and 53 s respectively and the reactor was manually scrammed two additional times. On each occasion additional rod insertion occurred.
The scram discharge volume was allowed to drain again for 160 s.
Finally the reactor auto scrammed on high drain volume when the auto scram bypass was removed. The remaining withdrawn control rods then inserted at normal speed to the fully inserted position.
The total time that elapsed between the initial scram and final in-sertion of all the control rods was 14 min.
rrective action
. The operator manually scrammed all rods. Scram discharge volumes were drained and the bypass was removed from the high-level-drain scram interlock.
An investigation was initiated to identify the problem. No problems were identified with the electrical/control system, hydraulic control unit valve lineup, vent and drain piping (i.e.,
no line blockage found), or seal inleakage to the SDV. The cause for the excess water in the east SDV was not identified.
The following measures were to be incorporated promptly to ensure adequate drainage of the scram volume headers:
- b. Increase the test frequency of the scram discharge volume level switches to once per month.
- c. Develop procedures to verify that the scram discharge volume is free of residual water following each scram and before startup.
- e. Verify daily the normal position indication of SDV vent valves and drain valves.
- f. Additional requirements of IE 80-17 will be implemented in accordance with that document.
esign purpose of failed system or component:
The scram system is designed to rapidly insert control rods for rompt reduction of the reactor power.
er was a manual scram after to insert completely the scram system resumed and all Severe allow reducing the core after receiving scram and initiated two control rods then Core ce power to 36% signals due to water more scrams, but inserted upon Damage ater in the east scram not all rods auto scram (the discharge volume fully inserted fourth scram)
No No - no requirement for scram, secondary side systems available to remove core heat No - no requirement for scram, secondary side systems available to remove core heat No No 3405 - Actual Occurrence of Failure of 76 Control Rods to Insert at Browns Ferry 3
Damage Initiated Cooling No 1 Yes 2 No 3 Yes 4 Yes S Yes 6 No 7 Yes 8 Yes 9
Yes 10 NSIC 163405 - Sequence of Interest for Failure of 76 Control Rods to Insert at Browns Ferry 3
C ACCESSION NUMBER: 163405 R NO.: 80-024 Rev. 1 E OF LER: July 28, 1980 E OF EVENT: June 28, 1980 TEM INVOLVED: Reactivity control MPONENT INVOLVED: Scram discharge volume USE: Insufficient drainage from east SDV UENCE OF INTEREST: Control rods fail to insert UAL OCCURRENCE: Failure of 76 control rods to insert CTOR NAME: Browns Ferry 3 CKET NUMBER: 50-296 ACTOR TYPE: BWR SIGN ELECTRICAL RATING: 1065 MWe CTOR AGE: 3.9 years DOR: General Electric CHITECT-ENGINEERS: Tennessee Valley Authority RATORS: Tennessee Valley Authority CATION: 10 miles NW of Decatur, Alabama RATION: 1/2 of interval from last scram, 240 h (estimated)
NT OPERATING CONDITION: 37% power E OF FAILURE: Inadequate performance COVERY METHOD: Operational event
power, the maximum power after the scram would have been 345 MW(t) [see Nuclear Safety, 23(5), September-October 1982].
The after-scram power level would likely have been even higher if scram had been demanded at 100% power because some or all of the east side control rods (5) that were manually inserted as part of the power reduction procedure could have also failed to fully insert.