ML20216J078

Forwards AEOD, Partial Failures of Control Rod Sys to Scram, Engineering Evaluation Rept,In Response to 841120 Request for Listing & Analysis of Failures Since Feb 1983 Salem 1 Events.Concerns Re 13 Events Discussed

ML20216J078
Person / Time
Site:	Salem
Issue date:	03/11/1985
From:	Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To:	Zech NRC COMMISSION (OCM)
Shared Package
ML20216J082	List: ML20216J078 ML20216J100
References
NUDOCS 9709170151
Download: ML20216J078 (2)

Text

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UNITED STATES NUCLEAR REGULATORY COMMISSION

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3/n/ts MEMORANDUM FOR: Commissioner Zech FROM:

William J. Di cks PU9tfC 3900 MENT R$$M Executive Director for, Operatiorys, .

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SUBJECT:

PARTIAL FAILURES OF b i k. b D S b S TO SCRAM '

por t re t m 3 During the semiannual briefing to the Commissioners by the Office for Analysis and Evaluation of Operational Data (AEOD) on November 20, 1984, you had requested a listing and analysis of events that have occurred since the Salem 1 ATVS, events in February 1983 involving failures of control rods to perform their scram function properly. The enclosed AEOD study report is in response to that request.

During the appi.oximately two year period covered in this study, a total of 13 events were found where there was a failure of from one to six control rods to properly perfonn their reactor scram function. The 13 events are listed in Appendix A of the report. In six of these events, the failures occurred during an actual scram demand, and in the renaining seven events the failures sore discovered during surveillance testing activities.

In all cases, the plant was safely shut down by the proper functioning of the remaining operable control rods. , ,

There are two real concerns associated with such failures. One is the potential for common-cause failure, e.g., an inability to insert sufficient centrol rods to assure reactor shutdown due to a single type or cause of failure. The second is generic implications, e.g., other reactors may 'be susceptible to the same type of failures. Even though the design and manufacture of control rod systems are certainly mature, it is of concern and significance that those 13 events over a two year period involved four N potential common-cause failure mechanisms, three of which have generic implications for similar, reactors.

The potentia'i common-cause events are: *

1. November 1983 ovent at Peach Bottom 3 where two control rods had excessive scram times because of foreign material (l.octite) in the scram solenoid valves.

2. October 1984 event at Susquehanna 1 where four control rods failed to

, scram due to sticking of the disc holder subassembly in the scram pilot solenoid valves. '

3. The event at Ko-Ri 5 in Korea where a rod assembly guide screw had fallen ,

out'and prevented rod movement. U.S. reactors having the same type of f-mechanism include Catawba 1 and 2. McGuire 2. Watts Bar 1 and'2, and  !

Seabrook 1 and 2. '

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[. June 1984 event at fort St. Vrain where six out of 37 rod pairs' failed

, to scram during a reactor trip.

• s The first three potential common-cause events noted above p'1so have potential generic concerns for other facilities. Only the last eveni be unique and therefore applicable to only Fort St. Vrain.,t is considered ,to ,

i for the three events that involved potential common-cause failure mechanismsj

. which' had generic implications, adequate corrective actions and ' actions to gr  !

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alert other utilities have been taken. In the case of Fort St. Vrain, the v unit has remained shut down since the event and will be started up.only after' ..

i all_ corrective actions have been completed and approved by the NRC. ,  ?

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! The remaining nine events were caused by^ apparently random failures eciddo.

not appear to have common-cause failure or generic implications. .

Concerns regarding inadequacies in post-trip review, post-maintenance testing and identification of root cause of failure are evident in some of r the 13 events. Lessons learned from past experience have still not resulted

-in complete correction of the problems identified. These concerns should be alleviated when the actions discussed in the staff's Generic Letter 83-28, . .

" Required Actions Based on Generic Implications of Salem ANS Events," are established and fully implemented.

Please contact me if you require any further infonnation on this subject.

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. William J. Dircks , ..

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Executive Director for Operations .

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