ML19312E143
| ML19312E143 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 05/27/1980 |
| From: | Andognini G BOSTON EDISON CO. |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| 80-94, NUDOCS 8006030345 | |
| Download: ML19312E143 (3) | |
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I BOSTON EDISON COMPANY a Ncmat arriers eco savtstow sTascT B o s rcN. MAS $4CNUSETTS Q2199 G. Cast ANoceNiNs SUPERINTENO(NT NUCLEAR OPCMaflONS DEPan?NENT May 27, 1980 BEco Ltr. #80-94 Mr. Thomas A.
Ippolito, Chief Operating Reactors Branch #3 Division of Operating Reacters Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D. C.
20555 License No. DPR-35 Docket No. 50-293 Supplemental Response to Containment Purge and Vent System Mechanical Review Questions l
Ref. (a) BECo Letter #80-22, G. C. Andognini to T. A.
Ippolito " Additional Information for Contain-ment Purge and Vent System" January 30, 1980 (b) USNRC Letter to Boston Edison Co. ' Mechanical Review Qt'estions Concerning Containment Purge and Vent System" November 28, 1980
Dear Sir:
The enclosed information is provided to you to supplenent our initial response.
Reference (a), to your request for information concerning containment purginr.
and ventins, Reference (b), which would enable you to complete your review of this subject in the mechanical area.
We trust that this information is responsive to your needs. If we can be of any further_ assistance, please contact us.
Very truly yours, gy Enclosure
/O f
8006030J 6
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ENCLOSURE In Ref. (a) we provided the results of the preliminary engineering analysia which was performed in response to Item 1.b of Ref. (b).
This analysis addressed the acceptability of the provisions made to protect the structures and safety related equipment located beyond the purge system 20" isolation valves against loss of function from the environment created by escaping air and steam. A subsequent Services, was scheduled for completion on March 1,1980. detailed analysis, performe Demands placed on our engineering staff by the refueling cutage prevented their full time support of the Teledyne analysis and subsequently the completion date was delayed until April, 1980.
The Teledyne analysis substantiated the results of the preliminary analysis.
Should a design base LOCA occur while the 20" purge valves are open, the fans, filters and ductwork, located beyond the valves, may suffer a loss of function.
The 20" contain=ent purge and vent isolation valves are maintained in the open position only during the containment inerting and deinerting processes.
Technical Specifications 3.7.A.S.b permits deinerting twenty-four hours prior to shutdown and allows a twenty-four hour period before inerting following a plant startup.
The Basis for the Technical Specifications allows limited plant operation with open purge and vent valves and presents the rationale for this operation.
benefit Th e derived from permitting access to the containment for leak inspection at operating temperature and pressure is increased plant safety. This keys upon the relatively low probability of an accident occuring during these limited periods of plant operation.
The recently identified potential for loss of function of the SBGT System prompted a reevaluation of the basis which justifies the twenty-four hour inspection windows.
Pilgrim Station and other facilities benefit greatly from performing containment entries at operating temperature and pressure following a prolonged shutdown.
These inspections preclude the possibilities of starting up and operating with significant leaks in the primary system which in all probability would necessitate a subsequent plant shutdown to remedy.
Pilgrim's record of detecting leaks and other conditions during the inspections and the corresponding low number of shutdowns required to investigate unidentified leakage in containment substantiate the above propositions.
Prohibiting leak inspections during plant startup may unnecessarily subject the plant to additional cycling and expose it to potentially undesirable transients-i and challenges to safety systems.
This is a position which is to be avoided.
Boston Edison has initiated actions to reduce the likelihood of a design base LOCA during plant operation with the 20" purge valves open. These steps maximize plant safety.both f rom an accident consequence position and situation dete: tion perspective.
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4 The twenty-four hour deinerting period prior to shutdown, which is presently allowed by Technical Specification 3.7.A.5.b, will be procedurally reduced to i-as short as practicable. Deinerting will not commence until the plant is subcritical.
The twenty-four period allowed after startup prior to inerting will be procedurally reduced to as short as practicable. PNPS operations personnel will receive training and the applicable procedures will be revised to emphasize the importance of minimizing operating time with the 20" purge valves open and to provide the rationale for this constraint. Modifications are being developed which will, upon implementation, protect the fans, filters and ductwork located beyond the purge system isolation valves against potential loss of function due to LOCA environ-These modifications will be implemented upon the completion of the design ment.
analyses.
Item 1.(c) of Ref. (b) stated:
"For the containment purge isolation valves, specify the differential pressure across the valves for which the maximum leak rate occurs. Provide test results (e.g. from a vendor test of leak rate vs. differential pressure) which support your conclusion."
Our response, provided in Ref. (a), informed you of our intention to perform tests during our scheduled refueling outage.
This test would obtain data to support our expectations that the leakage is approximately directly proportional j
to the differential pressure and that the maximum leakage would therefore occur at the maximum differential pressure. Also noted in Ref. (a) Rockwell Company no longer manufactures butterfly "alves and we have been unable to obtain any of the vendor's test data.
Testing was performed during the refueling outage. The test consisted of j
pressurizing al sample set of the 20" containment purge and vent valves from a.
test connection between the valves.
The valves selected were A0-5036 A and B.
The test pressure ranged from 23 to 45 psig.
The data obtained during the test
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supported the original conclusion that the maximum leakage occurs at the maxiuum differential pressure.
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