ML20084U499

Describes Significance of Failure of Containment Isolation Valves in Traversing Incore Probe Sys to Close & Plan to Prevent Similar Occurrences

ML20084U499
Person / Time
Site:	Browns Ferry
Issue date:	08/10/1973
From:	Hinds J GENERAL ELECTRIC CO.
To:	Knuth D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084U431	List: ML20084U446 ML20084U462 ML20084U499 ML20084U519 ML20084U551 ML20084U609 ML20084U662 ML20084U689 ML20084U853 ML20084U869
References
NUDOCS 8306290087
Download: ML20084U499 (2)

Text

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. NUCLEAR ENERGY GENERAL .

ELECTRIC oivisioN GENERAL ELECTRIC COMPANY,175 CURTNER AVENUE, SAN JOSE,' CALIFORNIA 95114

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Phone (408) 297-3000, TWX NO. 910-338-0116 DEPARTMENT August 10, 1973 cc: G. J. Stathakis i

1 Dr. D. F. Knuth Deputy Director for Field Operations Directorate of Regulatory Operations United States Atomic Energy Commission Washington, D. C. 20545

Dear Sir:

Your letter to Mr. G. J. Stathakis dated July 12, 1973 cited two cases at the Browns Ferry 1 reactor facility in which the containment isolation valves in the traversing in-core probe (TIP) system failed to close. You also requested a list of i

operating boiling water reactors which had the potential for similar failures along with our plans and schedule for affect-ing the necessary corrective action.

The purpose of this letter is to describe the significance of the events that occurred at Browns Ferry 1 and the action plan that GE is pursuing to prevent similar occurrences. The TIP system is essentially the same on all GE BWRs from Oyster Creek forward so your questions and our reply is generically applicable.

The Browns Ferry events resulted from the failure of one step in the normal sequence of TIP withdrawal and isolation when the containment was pressurized. Specifically, when a TIP is with-drawn out of the containment, there is an actuator rod which normally drops down to actuate the isolation valve. In the Browns Ferry case, containment pressure testing at 62 psig was in progress; the TIP guide tube was therefore pressurized and this was sufficient to keep the actuator rod up. Thus, the isolation valve could not close.

If a TIP were in the reactor at the time of a Loss-of-Coolant Accident, it is also possible that the events described above could occur. It should be noted, however, that the highest containment pressure of any significant time duration during an LOCA would be about-half that experienced in the Browns Ferry event, in which case the isolation valves would operate normally, d v}-

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, ~3 GENER AL (h ELECTRIC ATOMIC POWER EQUIPMENT DEPARTMENT San Jose, California Dr. D. F. Knuth August 10, 1973 Page Two This is not a safety problem because of the available backup procedure, which is described in the FSAR's on all plants, to insure TIP isolation. If the above described sequence of events were to occur and the automatic isolation valve failed to close, this would be indicated in the control room. The operator can then immediately actuate the backup manual shear valve, control of which is also located in the control room, thus ensuring containment isolation. Of course, this is not necessary for safety purposes during containment pressure testing prior to plant operation, such as was the case at Browns Ferry.

Because of GE's interest in improving the overall mechanical performance of the TIP system, a development program was launched early this year, and one of the items in the program is to provide a different isolation valve actuating system.

The objective is to ensure that the automatic isolation valve will be actuated under any possible containment pressurization conditions. This change is expected to be available to all plants by the first quarter of 1974.

Communications have been sent to all GE BWR owners with operating plants in order to advise them of the above-described possible sequence of events. It also describes to them a procedure for manually closing the automatic isolation valve from the control room as a further back-up to the procedure for closing the manual shear valve, which is already established.

Sincer ,

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ohn A. Hin s, Manager Safety and Licensing jgj l

NUCLEAR ENERGY G E N ER AOM E LECTRIC O oivismN 1

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GENERAL ELECTRIC COMPANY,175 CURTNER AVENUE, SAN JOSE.. CALIFORNIA 95114 Phone (408) 257-3000. TWX NO. 910-338-0116 DEPARTMENT, August 10, 1973 cc: G. J. Stathakis Dr. D. F. Knuth l Deputy Director for Field Operations Directorate of Regulatory Operations United States Atomic Energy Commission Washington, D. C. 20545

Dear Sir:

I Your letter to Mr. G. J. Stathakis dated July 12, 1973 cited two cases at the Browns Ferry 1 reactor facility in which the containment isolation valves in the traversing in-core probe (TIP) system failed to close. You also requested a list of operating boiling water reactors which had the potential for similar failures along with our plans and schedule for affect-ing the necessary corrective action.

The purpose of this letter is to describe the significance of the events that occurred at Browns Ferry 1 and the action plan

'that GE is pursuing to prevent similar occurrences. The TIP system is essentially the same on all GE BWRs from Oyster Creek forward so your questions and our reply is generically applicable.

The Browns Ferry events resulted from the failure of one step in the normal sequence of TIP withdrawal and isolation when the containment was pressurized. Specifically, when a TIP is with-drawn out of the containment, there is an actuator rod which normally drops down to actuate-the isolation valve. In the Browns Ferry case, containment pressure testing at 62 psig was in progress;,the TIP guide tube was therefore pressurized and this was sufficient to keep the actuator rod up. Thus, the isolation valve could not close.

l -

If a TIP were in the reactor at the time of a Loss-of-Coolant Accident, it is also possible that the events described above could occur. It should be noted, however, that the h.ighest containment pressure of any significant time duration during an LOCA would be about half that experienced in the Browns Ferry event, in which case the isolation valves would operate normally. .

\ .

GENER AL @ ELECTbC ATOMIC POWER EQUIPMENT DEPARTMENT O

l S,an Jose, California '

Dr. D. F. Knuth -

August 10, 1973 Page Two ,

This is not a safety problem because o'f the available backup procedure, which is described in the FSAR's on all plants, to s insure TIP isolation. .

If the above deceribed sequence of events were to occur and the automatic isolation valve failed to close, this would be indicated in the control room. The operator can then immediately actuate the backup manual shear valve, control of which is also located in the control room, thus ensuring containment isolation. Of course, this is not necessary for safety purposes during containment pressure testing prior to plant operation, such as was the case at Browns Ferry.

Because of GE's interest in improving the overall mechanical performance of the TIP system, a development program was launched early this year, and one of the items in the program i is to provide a: dif f er'ent isolation valve actuating system.

The objective is to ensure that the. automatic isolation valve will be actuated under any possible containment' pressurization conditions. This change is expected to be available to all plants by the first quarter of 1974.

Communications have been sent to all GE BWR owners witli operating

. planta in order to advise them o f t tle above-d'escribed possible sequence of events. It also describ'es to them a procedure for manually closing the automatic isolation valve from the control room as a further back-up to the procedure for closing the manual shear valve, which is already established.

Sincer ,

/

NS7 ,b ohn A.

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• Hinds, Manager Safety and Licensing j8j