ML20128C349

Discusses Proposal of New Generic Issue, Multiple SG Tube Leakage, as Resolution to DPO Received Addressing Operation of SGs W/Microscopic Tube Wall Cracks.Dpo Encl

ML20128C349
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	06/16/1992
From:	Beckjord E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:	Murley T Office of Nuclear Reactor Regulation
Shared Package
ML18153D185	List: ML20128C314 ML20128C320 ML20128C349
References
NUDOCS 9212040356
Download: ML20128C349 (3)

Text

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o,4 JUN I 6 19T MEMORANDUM FOR: Thomas E. Murley, Director Office of Nuclear Reacto' Regulation FROM: Eric S. Beckjord, Director Office of Nuclear Regulatory Research

SUBJECT:

A NEW GENERIC ISSUE: MULTIPLE S' TEAM GENERATOR TUBE LEAKAGE A Differing Professional Opinion (DPO) was recent1/9318I i th g5 S"OfYice of Research regarding steam generator tube integrity during a postulated main steam line break (MSLB). The DP0 specifically addressed the operation of steam generators with microscopic tube wall cracks. This concern deals with the possibility of having multiple steam generator tube leaks during a MSLB that can ; Se isolated. This sequence could lead to core melt resulting from the loss oi all primary system coolant and safety injection fluid in the refueling water storage tank. The DP0 recommended that plants operating under these conditions have additional sources of borated water readily available to replenish the refueling water storage tank. It was agreed to resolve the DP0 that this concern would be proposed as a new generic issue. This new generic issue is entitled, " Multiple Steam Generator Tube Leaktge," the details of which are enclosed. Since your staff is currently evaluating the issue of microscopic cracks in , team generator tubes, we ars 7bmitting this information to you for your review. This is also in accordance with RES Office Letter No.1, Revision 3, " Procedure for Identification, Prioritization, and Tracking of the Resolution of Generic Issues," page 3, second paragraph, which states:

"After their acceptance, generic issues that originate from outside NRR or from an individual within NRR (i.e., not sent through NRR management) will be transmitted by RES to NRR/PMAS for an immediate action determination and screening for identification of overlap or duplication with already imposed or completed Multi-Plant Actions (MPAs). If NRR cannot complete this immediate action determination and MPA screening within 15 days, RES should be informed when the NRR review will be completed."

We will also keep you informed of our progress in resolving this issue.

ORIGINAL SIGNE BT 14 LO .M Eric S. Beckjord, Director Office of Nuclear Regulatory Research

Enclosure:

As stated cc: F. Gillespie J. Richardson A. Thadani CONCURRENCE: SEE PREVIOUS CONCURRENC_fg/ "

// uf 0FFICE:RES:DSIR RES:DSIR RESjGS(R DD/RES DD/RES D/l NAME: G.MARIN0* T. KING * (.HINNERS T.SPEIS C.HELTEMES E .1 _ ORD DATE: 6/11/92 6/11/92 6/tf/92 6/ /92 6/ /92 6/y92 l

9212040356 921124 PDR ADOCK 05000344 P PDR i

h DISTRIBUTI@ Copies w/o enc.

OSIR c/f T. King RES Circ./Chron R.Emrit Beckjoru < J.Hopenfeld Finners < P.Norian Marino / K.Kniel Marino c/f-Heltemes s

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DIFFERING PROFESSIONAL OPINION

'92 NOV 25 M1:32 Recent experience at the Trojan plant indicates tnat present inspection techniques are not sufficiently sensitive to detect steam generator tube degradation. The problem is inherent in the eddy current probe design and its use. It is essentially impossib;e to detect tight through the wall cracks, especially at the tube support plate regions.

' he plants were not designed to operate continuously with a large number of tubes containing through the wall cracks.

My concern is that a Main Steam Line Break (MSLB) outside containment could trigger a multiple steam generator tube failure whic would than result in a core melt because of depletion in coolant inventory.

NRC is currently addressing the uncertainties in the in service inspection procedures by considering the possibility of allowing affected utilities to operate with tube imperfections beyond the 40% tech specs through the wall plugging limit.

While the above action is useful for the long term, I believe it is not focused on the main issue. The main issue is whether the core can be maintained intact and -

radioactivity release prevented with a MSLB outside containment and multiple steam generator tube rupture. While considerable research will be required to define a new plugging limit and change the SRP, the result will not increase plant safety. The basic problem is with the NDE procedures and their inability to predict tube degradation and leakage.

Rather than concentrating efforts on alternate plugging limits, the NRC should request all affected licensees to provide warranties that they have the capability to keep the core intact and prevent allowable dose releases with a MSLB and a multiple tube rupture of no less than 80% of all tubes.

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