ML20023D706
| ML20023D706 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 05/25/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20023D702 | List: |
| References | |
| NUDOCS 8306020511 | |
| Download: ML20023D706 (3) | |
Text
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UNITED STATES g
NUCLEAR REGULATORY COMMISSION
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.E WASHINGTON, D. C. 20555 E
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Safety Evaluation Maine Yankee Atomic Power Company Maine Yankee Docket No. 50-309 Maine Yankee was requested to submit a letter relative to their intentions on the issue of thermal shield integrity in the light of the damage that had occurred at St. Lucie which was discussed in a meeting on April 12, 1983.
The licensee's response dated April 14, 1983 stated that they would:
Follow closely the progress of the investigation of the thermal o
shield situation at St. Lucie, and reflect the knowledge gained in assessments of the implications of the St. Lucie problem for the Maine Yankee plant.
Review the conclusions concerning Maine Yankee's thermal shield o
presented in the report of February 18, 1983 in light of the information obtained from St. Lucie.
- o Maintain the loose parts monitoring system (LPMS) operable.
Review LPMS indications from past operations.
o Reflect knowledge gained from the above as appropriate in plans for o
internal.s inspection at the next refueling outage.
Consider the feasibility of additional monitoring of reactor internals o
performance, especially focused on characterizing internals motions through neutron noise analysis and characterization of hydraulic forcing functions acting on internals.
Additionally, Maine Yankee concurs with the Combustion Engineering position that reactor shutdown is not warranted, advanced at the April 12 meeting.
Their concurrence is based on:
the detailed knowledge of the conditions of the thermal shield support system and internals gained in the -recent 10 year insetvice inspection, conducted with the internals removed; on the knowledge that core flow cessation would not occur even if the thermal shield were to drop because motion would be arrested by either the barrel snubbers or core stops; and on the evidence that thermal shield support system distress might start early but progresses gradually over a period of years rather than suddenly or as a result of a single plant event, thus allowing periodic assessment based on refueling interval, inspections.
' Maine Yankee had previously committed to a limited visual inspection of
'the thermal shield pins at the next refueling outage.
A representative sample of thermal shield positioning pins and~ support lugs can be viewed without removal of the core support barrel from the reactor vessel.
This
~is accomplished by lowering a television camera down through the sur-veillance capsule access ~ holes in the core support barrel upper flange.
The. circumference of the thermal shield visible through the surveillance i
8306020511 830525 PDR ADOCK 05000309
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capsule access holes is indicated by the cross hatchec =':7F t'
- n i attacned figure.
The representative inspection of the thermal sniele 1
support systeT. through the core support barrel upper flange would not guarantee that there are no icose or missing positioning pins as four of the remaining upper positioning pins cannot be seen with this pro-cedure, but it would show any wear on the thermal shield supports resulting from excessive motion of the thermal shield relative to the core support barrel.
The reactor vessel bottom head can also be inspected, partially, through the four television access holes in the lower support structure plates.
The television access holes will pro-vide a view of up to fifty percent of the reactor vessel bottom head.
The areas of the reactor vessel bottom head exterior to the flow skirt accessible for inspe-tion are shown in the attached figure.
Based on a review of the above, the staff concludes that continued operation of Maine Yankee is justified based on their ability to perform loose parts monitoring and the potential for performing neutron noise analysis.
Further justification is prcvided by the commitment to perform the limited visual inspection at the next refueling outage.
Date:
Principal Contributor:
C. D. Sellers, MTEB f
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