ML20148H099

Responds to 770722 Inquiry Re Recent Shutdown of Facility. Util Elected to Shut Down on 770609 Far Earlier than Scheduled Refueling,Eccs Mods & Other Maint.Early Shutdown Promoted by 770607 Discovery of Oversight in ECCS Analysis

ML20148H099
Person / Time
Site:	Yankee Rowe
Issue date:	08/22/1977
From:	Case E Office of Nuclear Reactor Regulation
To:	Weiss E MASSACHUSETTS, COMMONWEALTH OF
Shared Package
ML20148H104	List: ML20148H099 ML20148H113
References
NUDOCS 8011170177
Download: ML20148H099 (3)

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Docket No'. 50-29 , ]

t'.s. Ellyn R. Weiss Assistant Attorney General Envirornental Protection Division pg3 T' ~T T COMTMS One Ashburton Place,19th Floor 4 POOn, e 11f MGES 1 Boston, fiassachusetts 02108 ,

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Dear Hs. Weiss:

I am pleased to repicy tt your letter dated July 22, 1977, in which you inquired about the recent shutdown of the Yankee Nuclear Power .

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Station (Yankee-Rowe).

Yankee Atomic Electric Company ithe licensee), elected to shutdown Yankee-Rowe on June 9,1977, for earlier than scheduled refueling, Er.ergency Core Cooling System (ECCS) modifications and other maintenance.

This early shutdown was prompted by the licensee's discovery on June 7,1977, of'an oversight in the emergency core cooling system (ECCS) analysis for the next core reload (Core XIII). Specifically, during the review of the small break analysis, the licensee identifiec a specific location in a short pipe section in the safety injection lines, for which an assumed worst case (conplete severance and separatien) i type break could result in higher calculated fuel cladding tcmperature - t than previously calculated for another location which had been considered to be the post limiting small pipe break location. -

The written naterial including tw ainutes of a recent necting with tbc licensee, has been sent to tir. Ancrew t.ipton, c member of your staff, with our letter dated July 26, 1977. This material provides a more detailed account of the circumstances related to the recent shutdown of Yankee-Rowe. A copy cf thht letter is enclosed.

Our responses to your specific requests for clarification are provicea below in the order that those requests appear in your letter.

, 1. The situation that led to the shutdown of Yenkee-Rowe involved an l error in the ECCS performance analysis which has permitted operation of Yankee-Rowe prior to the June 9,1977 shutdown, in a r,anner less conservative than assumed in the analysis.

Discovery of this error is reportable as renvired in the facility  ;

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by promptly reporting this discovery to the NRC. In addition, ,

the licensee on its own initia+.ive, took aporopriate conservative action by shutting cown the facility pending further evaluation and resolution of the matter with the NRC. So far as we know at this time,'there was no violation of NRC requirenents, since the licensee has stated that the analytical error discovered on June 7,1977, had not been known previously. It could probably have been established that Yankee-Rowe had been operated with the previous Core XII in a manner which would have resulted in exceeding HRC limits for s pipe break in a certain location, if the consequences were calculated according to the very conservative calculational methods specified by UP.C regulations.

However, a "best estimate" calculation perfonned by the licensee after shutdown has indicated that limits would not have Deen exceeded for this specific break. For continued operation we will, of course, require conservative, rather than "best estimate" calculational methods. For consideration of the period prior  ?:

to shutdown before the existence of the calculational error was '~

known, it should be noted that the probability of a pipe break occurring precisely in the specific location identified is extrer.ely low and thus, did not contribute significantly to the '

overall risk.

'2. The error in the analysis was discovered at this time, because the significant changes to the ECCS subsysten, involving the addition of a safety injection delay feature during the present refueling cutage, required a complete ECCS reanalysis for operation with the new Core XIll.

3. To recedy the situation, the licensee is ncdifying the sefety injection piping and is adding valves which are throttled to achieve acceptable flow resistance. The added resistance in the safety injection lines will provide the necessary ECCS injection characteristics. The nagnitude of the flow resistances in the nodified ECCS piping will be verified by flow testing to be performed during this refueling outage. The licensee will  :

suomit to the !JRC an entirely revised ECCS analysis, to demonstrate  !

by approved analysis Pethods that the calcul1ted perfornance of the modified ECCS neets the !;RC acceptance criteria. l S

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4. ifhile it is true that Yankee-Rowe could have continuca to operate at a reduced power level consistent with acceptat,le consequences based on conservative calculational methods, the pertonrance of such calculations would have involved a r' us analysis which itself would have been time consuming an' insive. Because of -

significant time and expense required to 'm such calculattons and the recognized need to simultaneousi m. such c iculations .

on the nodified facility to justify retui rull power operation,  !

the licensee elected to shutdown Yankec-Ros _ for its refuelin, ,

outage somewhat earlier than originally scheduled. "

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5. As discussed elsewhere in this letter, the licensee is making ...

corrective modifications to the ECCS and is perfoming a ccrnplete ,

ECCS reanalysis for the modified ECCS configuration to support operation at full licensed power. NRC is reviewing these revisions to detemine acceptability. Before returning to power,, the licensee will require a license amendment from the NRC. ,

6. In response 3. above, we indicated the corrective actions being .

taken by the licensee during the present refueling catage. The ECCS piping modification introduces additional flow resistance g~ ,

in the ECCS injection flow paths; calculations will be perfomed based on design values of the flow resistances as modified. Thi s .

will demonstrate that the design of the taoified ECCS is within r acceptable limits; flow testing will verify that the expected i resistances have been achieved. If not, appropriate adjustncnts of resistance will be aade curing the course of the test to echieve acceptable results.

I trust that our reply is responsive to your recuest for clarification of certain aspects relating to the recent shutcorn of Yankec-P. owe.

Sincerely, j Odginal Signed By

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E. G. Case

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Eason G. Case, Acting Director Office of Nucicer Reactor Regulatien , ,

Enclosure:

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Docket h'o$0 29 July 26, 1977 Mr. Andrew Lipton Departnent of the Attorney General of the Commonwealth of Massachusetts Environmental Protection Division 1 Ashburton Place Boston, Massachusetts 02108

Dear Mr. Lipton:

It has been brought to my attention that during a recent telephone conversation with a member of my staff, you inquired about the reasons for the earlier than anticipated shutdown of the Yankee-Rowe Nuclear Power Station.

To supplement the information given you during the telephone conversation, we enclose a copy of our letter dated July 20, 1977, to the Secretary of the Alternative Energy Coalition of Greenfield. That letter, with its enclosures, provides a more detailed account on the recent shutdown of iankee-Rowe and identifies the actions required of the licensee to obtain NRC approval to operate Yankee-Rowe with the new core loading.

We trust that the enclosed documents provide all the information you need in this matter.

Sincerely, ,

,y ^1 L'hW p[ Karl R. Goller, Assistant Director

/ for Operating Reactors L) Division .of Operating Reactors

Enclosures:

1. NRC Letter dated July 20, 1977

2. LER dated June " 1977

3. Minutes of Meet. 3 dated June 22, 1977 i

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