ML19319E547
| ML19319E547 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 12/30/1975 |
| From: | Rueter D ARKANSAS POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML19319E544 | List: |
| References | |
| NUDOCS 8004110808 | |
| Download: ML19319E547 (4) | |
Text
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1.
Abnornni Occurrence Report No.
50-313/75-l'0 2.
Report Date:
12/30/75 3.
Occurrence Date:
12/20/75 4.
Facilityi Arkansas Nuclear One-Unit 1 Russellville, Arkansas 5.
Identification of Occurrence:
Loss of reauired overlap between operating control rod groups.
6.
Conditions Prior to Occurrence:
Steady-State Power X
Reactor Powcr 1600 b!Wth ilot Standby Net Output 500 Mwe Cold Shutdown Porcent of Full Power 62 t
Refueling Shutdown Load Changes During Routino T
Power Operation Routine Startup Operation Routine Shutdown Operation Other (specify.)
5 i-7.
Description of Occurrence:
A ratchet trip of group 6 control rods occur'ed at 2040 hours0.0236 days <br />0.567 hours <br />0.00337 weeks <br />7.7622e-4 months <br /> on December 20, r
1975, causing an apparent violation of Tech Spec 3.5.2.5, group overlap requirement of 25 + 5% between two sequential groups. At the time of this
^
occurrence, it appeared a runback was initiated due to an asymmetric rod i
and' group 6 was subsequently re-aligned to its appropriate position. Sub-
. sequent investigation following a second drop of group 6 on December 21, 1975, at 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> indicates the December 20, 1975, drop was due to a ratchet trip. The drop on December 21, 1975, was followed immediately by, a manually initiated reactor trip.
O O
bbrch 4, 1975 NSP-10, Rev. 2
' Page 2 of 4
s m
C k
Abnormal Occurrence Rcport No.
50-313/75-10 e
8.
Desip. nation of Apparent Cause of Occurrence:
Design
, Procedure htinufacturc Unusual Service Condition Including Unvironmental Installation /
Construction Component Failure y
Operator Other (specify)
Cause is apparent group 6 power supply failure.
9.
Analysis of Occurrence:
There is no core safety significance associated with the minimum. overlap requirement, rather the concern is for an overlap greater than 30 percent.
Following the group 6 drop, the overlap became O percent until the 5
required overlap was re-established with 5 minutes on~the December 20, 1975, drop. On the December 21, 1975, drop the reactor was manually i,
tripped. This reduction in overlap did not create any adverse conditions, and no' core protection limits were approached. This incident did not offect the health and safety of the public.'
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f a
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\\s March 4, 1975 NSP-10, Rev. 2 Pa ge 3 Of 4 s
.O e.,.
Abnormal Occurrence Report No.
50-313/75-10 i
a
- 10. Corrective Action:
The 25 1 5 percent overlap was immediately re-established by realigning groups.5 and 6 to appropriate positions. An investigation into the cause of the event is underway.
j 4
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11.
Failure Data:
No previous failures of this type.
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I March.4, 1975 NSP-10, Rev. 2 Page a of.t l.
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