ML19317F384
| ML19317F384 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/07/1977 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317F380 | List: |
| References | |
| RO-270-77-04, RO-270-77-4, NUDOCS 8001140637 | |
| Download: ML19317F384 (2) | |
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' DUKE' POWER COMPANYT f
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'OCONEE UNIT 2-i:
.c _. Report No.': '_RO-270/ 7 7-4 -~
' Report Date:{A'pril.7, 1977-
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~ 0ccurrence Date: ' March 24,.'1977 Facility: Oconee Unite 2, Seneca, South' Carolina-u Identification ~of> Occurrence: Rod overlap-in excess of Technical Specification
-limit due to a dropped control. rod group; i'
Conditions Prior'to Occurrence: ~Uniti at 78 percent full power
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. Description'of Occurrence:
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p a On March 24,z1977, group 6 control rods dropped into the core from a 67%
. withdrawn position reducing the reactor. power level to'44 percent" full power.
A condition'of 5% control _ rod: overlap between rod group 5 and 6 resulted.
Oconee Technical Specification 3.5.2.5 specifies an overlap of 25 1 5%
between.two adjacent operating control rod groups.
The Integrated Control. System-Immediately-relatched the group 6 rods and
. began withdrawing =the rods in order;to maintain the power level a.t 78%.
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-Rod 3 in group 6.did not relatch and this asymmetric. rod' caused power to.
be limited'to 55.. percent;-full-power. The power supply.for rod 3 was de--
energized by removing the fuses. No problems were found so the fuses were reinstalled and~ rod 3 was relatched and realigned with'the. rest of group.6.
L Control rod. group 6 ;was'then placed on auxiliary power and reactor power escalation commenced. : Repairs to control rod group 6 power supply'were completed.within four hours and the-group was returned to its normal power I
- supply.
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Apparent Cause-of Occurrence:
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h This occurrence resulted from the failure of the gate drive of phase "CC"~
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ine the '?B'? power supply..Normally, the "A" power supply would have held.
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.the rods.in position', however,.the "A".. power supply to the "CC" p'ase
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f uiomentarily - failed.. Investigation of the."A": power supply revealed no pro-1 blems. It isipostulated that l prolonged energization of Lone magnetic: phase
-in"the,"A"; power / supply resulted'in tso opposing phases being simultaneously n
nenergized, therefore canceling each other and result'ing in the drop and
.'immediate-relatch of the rods.
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' Analysis of-Occurrence:
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- ThisLincidentirssulted!inl control rodjgroup;6~ dropping Into the core and.a
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fcondition of:;approximately Supercentjcontrol rod overlap existing until group.
C6 control fods'.wereire -positioned.and the required overlap was re-established.
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.Thisfreductionin control" rod' overlap'did not' affect the: safe operation of I
lthe reactor andinojcore protectionflimit'sEwere approached.
It'is'therefore
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Jconcluded that thisLoccurrence did.notJ. affect:the health 2and. safety of thec
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C yrective Action:
d on rod 3 of group
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l With four hours following the incident fuses were rep ac ice and.
1 verified operable.-
drive stator power In addition, a modification to improve the control rodimplemented on each unit supply. reliability has been initiated and will be during.:its respective refueling outage.
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