ML17345B267
| ML17345B267 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 07/27/1983 |
| From: | Ashe F NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML17345B266 | List: |
| References | |
| TASK-AE, TASK-T324 AEOD-T324, NUDOCS 8309230280 | |
| Download: ML17345B267 (8) | |
Text
AEOD TECHNICAL REVIEW, REPORT*
TR REPORT NO. T324 DATE:
July 27, 1983 EVALUATOR/CONTACT:
F. Ashe
.UNIT:
Turkey Point Unit 3 DOCYET No..:
50-250 LICENSEE:
Florida Power
&.Light Company NSSS/AE:
Westinghouse/Bechtel
SUBJECT:
EVENTS INVOLVING TWO OR MORE SIMULTANEOUSLY DROPPED ROD CONTROL
- CLUSTER ASSEMBLIES EVENT DATE:
March 9, 1983
SUMMARY
This technical review report provides information concerning seven events involving dropping'of two or more rod control cluster assemblies (RCCA's).
An event which
. occurred. at Turkey Point Unit 3. oo" March 9, 1983 was identified by our.LER review process and as a result of this event report a search of the RECON data base system was conducted.'his search covered the approximate seven year period from.1976.to the present and resulted in,the identification of six additional events involving dropping of multiple rod control cluster assemblies.
As a result of our. review of, these operational experience
- events, we believe that
,the safety.implication for.such. events are minor'since.the rate of these events are infrequent (approximately one/year based.
on the data base set of events) and the consequences are as exp'ected.
The fuel. design limits were not exceeded in any. of the events.
This conclusion is in accordance with an analysis performed by NRR for. Westinghouse Plants with negative flux rate trips and is provided in a memorandum from L. S. Rubenstein, DSI, to. F. J.. Miraglia,.DL,."Review of:"the Westinghouse Report Dropped Rod Methodology for.Negative Flux Rate Trip Plants",
March=2, 1983.
It is noted.that the Combustion Engineering. Plants'.and some of the Westinghouse Plants (Haddam Neck, Indian.Point 2 and 3, Rober t.E. Ginna,.
Robinson 2,
San Onofre 1, Surry, 1'E 2, Turkey Point 3 and 4, and.Yankee.Rowe) do not incorporate a negative flux rate trip in their scram systems.
However, in these
- cases, core analyses indicate that DNBR limits may be exceeded for a short period of time (approximately one to two,minutes or.less) with no resulting significant fuel damage.
This analysis assumes no.automatic, turbine runback or other power reduction, actions.
In view of. the above,.we conclude that such events require no further review or actions at this time.
However, since the operating.procedures at Turkey Point Unit Number 3 Station.(and possibly some of the other. plants identified.above) did not explicitly address the multiple dropped rod incident, it may be appropriate to include this event in Power Reactor Events to make licensees aware of such procedures.
- This document. supports ongoing AEOD and NRC activities and does not represent the position or requirements of the responsible NRC,program office.
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DISCUSSION LER 250/83-005/01T-O dated March 23, 1983 provides a.description of a multiple dropped rod control.cluster assembly event which occurred at Turkey Point Unit 3 on March 9, 1983.
As. described while Unit 3 was operating at one-hundred percent power, rod control cluster assemblies D8. and M8 of control bank D simul:taneously dropped.
The applicable technical specifications section 3.2.4.a requires that sustained power operation of the unit shall not be permitted with more than one inoperable control rod.
The Nuclear Instrument System and:the Rod Position.."
Indication dropped rod circuitry caused an automatic turbine 'runback to seviiity percent power.
According to plant procedures, power reduction to hot shutdown was initiated..
Within approximately fifteen minutes after the shutdown
- began, the two dropped rods were retrieved and were verified to be back in the correct position by.a flux map.
Immediate inspection of.the control rod power cabinet revealed that water was dripping on the cabinet and seeping inside.
It appears that the water inside the cabinet resulted. in a momentary short in the lead to the D8 and M8 control rod stationary coils.
The cabinet was dried and the water leakage was stopped at the source.
.The unit was subsequently returned to full power.
Westinghouse was;consulted and it was determined that no.safety limits.
were encroached
- upon, due to the short duration of the incident and the subsequent operability of the two rod control cluster assemblies.
Because the simultaneous dropping of two control rods was considered,to be a rare
- event, Turkey Point Unit 3 did not have explicit plant procedures addressing it.
The plant procedures at tbis station mainly addressed operator..action in the case of one dropped rod.
However, the.occurrence on March 9, 1983 has made plant personnel aware of the need to address the multiple-dropped-rod incident in the operating.procedures.
'For this acti.vity Westinghouse will be consulted for guidance. in writing the new imnediate,.actions.for the. multiple-dropped-rod incident.
As awesult of.the Turkey Point licensee.event report,. the Plant Systems'nit initi~ted a search of the RECON data.base. system for., events involving multiple dropped rod control'luster assemblies.
The search which covered the period from 1976 to the present, identified. a.total of six additional events involving two or-:more simultaneously dropped rod. control cluster. assemblies.
One of these.six events. occurred at. the.St.-Lucie"Unit.l Station and was reported by LER 335/80-050/03L-0.
'As'described,. while changing the 15Y power. supp'ly'for Control Element.Assembly (CEA),42,. CEA 44.dropped,.possibly due to a'voltage spike.
Due to a failure of the Public Address
- System, maintenance personnel were not notified that CEA 44 dropped'and they continued removing the power supply'for CEA 42 which led to.the dual rod drop.
Action in accordance with technical specification was taken and the reactor was manually tripped.
No abnormal sub-sequent actions or occurrences were identified.
Another one of these events occurred at the Calvert Cliffs Unit 2 Station and reported by LER 318/82-018/03L-O.
Durinj..normal operation CEA 21 dropped into the core after electricians inadver-tently'isconnected power from it.
Approximately three minutes later CEA 20 dropped. into the core for the. same reason at which point the reactor was manually tripped.
The cause of this event was attributed to personnel error.
To preclude recurrence, the lead person on the job was interviewed by supervision and instructed in proper means of determining job scope.
A revision to an administrative instruc-tion was also made.
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Another one of the.six-events occurred at A'rkansas Nuclear One Unit 2 and was
'eponted by LER 360/78-023/03L-0.
During low,power physics testing in mode 2
operation CEAs 26, 1,.48, 46, 57, and 52 dropped and CEAs 22, 27,.and'9 slipped while moving for positioning.
The individual CEA misalignments caused no con-sequences as the reactor power was less.than one percent The dropping or j
slipping of CEAs'6, 1, 48, 46, 57, 22 and 52 were attributed to timer card failures whereas. the slipping of CEA 27 and 29 was attribu'ted to sequencer card failure.
Subsequent to the'se occurrences repairs were.mme and operations,c'op-tinued.,
The remaining three. events occurred at the Robert E. Ginna.station and were reported as Reportable Occurrences 76-21; 76-18 and 76-13.
Reportable Occurrence 76-21 provides.a description of an event involving two dropped rods'hich occurred on August 4, 1976.
As descr'ibed, during steady load, turbine runback occurred when "D" bank group 2 rod control cluster assemblies G-3 and G-11 partially dropped into the core.
Although the cause of the two dropped rod control cluster assemblies was not explicitly -identified, it was believed to be associated with
,the 2BD power cabinet which provides power to these two rod control assemblies.
Reportable Occurrence 76-18 provides a description of a similar event which occurred on July 4, 1976.
During steady load, turbine runback occurred when "B" bank group 2
rod control cluster assemblies G-5 and G-9 dropped.
The.exact cause for these rods
'ropping was not ideitified, however on two previous occasions dropping of these two, rod assemblies were associated with water leaks over.the attendant power cabinet.
An alarm card indicated stationary coil'A" regula'tion failure.
Following this occurrence and based on a Westinghouse
.recommendation, fuses and current sensing resistors were replaced. in the stationary coil circuitry.
Reportable Occurrence 76-13/3L.describes an event which occurred on June 16, 1976 involving the dropping of "B".bank group 2 control rod cluster assemblies G-5 and G-9.
For this event, the. alarm card detector lamp indicated four printed. circuit.cards as the.poss'ible
- cause, however no explicit cause was identified.
No abnormal system behavior or
. unexpected actions were identified during or following any of these events.
FINDINGS The search of the RECON data base. system which was conducted for two or more
.dropped rod control cluster assembly. events resulted in the identification 'of six additional events which occurred during the. period from 1976 to the present.
The.cause of each of these events appears to.be the direct result of either main-tenance personnel errors and/or disturbances in the.attendant'rod*control cluster assembly power supply circuitry.
The safety implications of the identified multiple rod droo events are minor since the rate of these events are infrequent (approximately one/year. based on the data base set of events)
.and the consequences are as expected.
The fuel design limits are not exceeded in any of the events.
This conclusion is. in accordance'with
.an analysis performed by NRR.for Westinghouse'lants with negative flux rate trips and is provided in a memorandum from L. S.
Rubenstein, DSI, to F. J. Miraglia,.DL, "Review of the Westinghouse Report Dropped Rod Methodology for Negative Flux Rate Trip Plants",
March 2, 1983.
It is noted that the Combustion Engineering Plants and some of the Westinghouse Plants (Haddam Neck, Indian Point 2 and 3, Robert E. Ginna, 'Robinson 2,
San Onofre 1, Surry 1
E 2, Turkey Point.3 and 4, and Yankee Rowe) do not incorporate a negative flux rate trip in their scram systems.
However, in these cases.,
core analyses indicate that DNBR limits may be exceeded for a short.period of time (approximately one to two'minutes or less)'with no resulting significant fuel damage assuming no automatic turbine runback or power reduction actions.
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0 CONCLUSION For the reason provided in.the above findings, we believe that the safet'y implications for the identified multiple rod drop events are minor and. as such require no further review or. actions at this time.
.However, since the operating procedures at the Turkey Point Number 3 Station (and possibly some of the other plants identified in the above findings) did not explicit1y address the multiple dropped rod incident, it may be appropriate to include this event in Power Reactor Events to.make licensees aware of 'such procedures.".~
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