ML17037C350

Letter Authorizing the Return to Operation of Unit 1 in Accordance with Your Documented Program and Subject to Conditions Defined and Enclosing an ACRS Report Dated June 16, 1970

ML17037C350
Person / Time
Site:	Nine Mile Point
Issue date:	06/19/1970
From:	Morris P A US Atomic Energy Commission (AEC)
To:	Pratt M H Niagara Mohawk Power Corp
References
Download: ML17037C350 (12)

Text

0 JUN 3,9 1970 Docket Mo.50-220 Attention:

le.Knot H.Pratt Vice President and Executive Engineer h EIIy letter dated March 13, 1970, requested appropriate xcpoxtimg of your xcpair plans and thc significant results of your investigation and evaluation of thc furnace-sensitized atcinleas steel safe ends prior tq the rezmption of h"'P reactor operations.

You have sub>>mitted this information along with your plane for future surveillance and tha, resumption of operations in the following documents:

1.Reactor Primary System Investigation at Nine IQ.lc Point.Nuclear Station" dated Hay 1, 1970.DISTRIBUTION Dooly DR R., Engelken, CO (2)H.Shapar, OGC (2)N.Dube~DRL (5)J.R.Buchanan, ORNL T.W Laughlin, DTXE, W.D.Gilbert, GE Document Room v5ocket File DR Reading DRL Reading Niagara Mohawk Pc~rex Corporation Branch Rading 300 Erie Boulevard West D.Thompson, DRL'yracuse, Ncv York 13202 D.J.Skuvholt, DRL R.H.Vollmex, DRL D.L.Ziemann, DRL C.J.DeBevec,, DRL R.M.Diggs, DRL ACRS (3)Gentlemen:, F.Schroeder, DRL R.Boyd R.DeYoung This lottcr authoxi"cs the return to operation of the Nine IiXXe Point Nuclear Station (KP)in accordance with your documented pxogxau for restoration to service and subject to other conditions which axc defined herein.2.'Reactor Pximry System Xnvcstigati.on, at Nina Nile Point Nuclear Station-Report No.2" dated ofay ll, 1970.U 3."'Pxogram for Restoration to Service Based on Reports of Pximaxy System Investigation

-Nine.Hale Point Nuclear Station" dated kwy ll, 1970, We have xcvicved these reportsincluding the results of the inves-tigative program and the evaluation of the metallurgical pxoblem, and have concluded.

that your plans for repair of the safe ends and for resumption of operations are acceptable as oct forth in your report (Item 3 above).In this regard, Me note that a reinspection of furnace=

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The Advt.sory Committee on Reactor Safeguards (ACRS)revieved this matter at its 122nd meeting held June ll-'l3, 1970.A copy of the report of the ACRS, dated June 16, 1970, is enclosed.In its report, the ACRS made recommendatfons, concerning

'resumption and futux'e opera-tion of the facilftyi These items include: 1, At least one leak-detection system in addition to'he proposed sump accumulatfon"rate and dev point systems should be installed vithin a fev months.2.Assurance should be provfded that'the biological shield suxroundfng the reactor vessel can withstand the pxessure that could be developed by loss of integrfty of a safe end or nozzle, or that failure of the shield vould have no intolerable consequences.

Please inform us expeditiously of your plans regarding implementation of item 1.Pith, regard to item 2, ve request that you submit an analysis of shield integrity and consequences of failure under the prescribed conditions.

Please advise us of your planned schedule for submittag.

In addition, a program for surveillance of the sensitized matex'ial ovex'he long term should be developed.

Since determination of the appropriate extent of such a program vill depend upon the results of the surveillance perfoxmed during the forthcoming year, ve request that, in your report of this surveillance effort, you include your plans for further surveillance of this material.Sub)ect to the above considerations, ve have concluded that resumption of operations of the Nine Mile Point reactor will not endanger the health and, safety of the public.Sincerely, Peter A, Morris,'ixector Division of Reactor licensing RS Report-6 OFFICE>c SURNAME>Arvin E.U......I.eBoeuf

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Subject:

REPORT ON NINE MILE POINT NUCLEAR STATION

Dear Dr.Seaborg:

At its 122nd meeting, June 11-13, 1970, the Advisory Committee.

on Reactor Safeguards reviewed the program proposed by the Niagara Mohawk Power Corporation for restoration to service of the Nine Mile Point Station following the discovery during March, 1970, of cracks and leakage in a"safe end" (stainless steel extension of the reactor vessel nozzle).The program was also considered at Subcommittee meetings on May 5, 1970, and June 1 and 2, 1970.During its review, the Committee had the benefit of discussions with representatives of the applicant, the General Electric Company, the AEC Regulatory Staff, and their consultants, and of the documents listed.The Committee previously reported to;you on this pro)ect on April 17;, 1969.\Normal procedures for most reactor pressure vessels have been to join the austenitic stainless steel safe ends to the nozzles prior to, the stress relieving heat treatment.

This heat treat-ment'sensitizes the safe ends, which makes the steel less resistant to certain types of corrosion.

Sensitized austenitic stainless steels in this condition have given reasonably satis-factory service over many reactor years of operation.

The applicant and the General Electric Company have conducted an extensive investigation of the cracking and its causes, An independent stress analysis of the as-built piping has revealed that stresses in the cracked safe end, and one other safe end, were excessive.

It is believed that this excessive stress, possibly in combination with a high concentration of

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C Hon.Glenn T.Seaborg'r~, oxygen in the non-flowing fluid in the pipe concerned, caused the intergranular cracking of the furnace-sensitized stainless steel safe end.Both, of the overstressed safe ends have been removed and replaced with new ones made of unsensitized material.The thermal sleeves have been slotted to avoid the possibility of gas bubbles at the high points.The piping supports have been rearranged, and the entire primary system re-analyzed, for both hot and cold conditions, to give assurance that stresses will remain within allowable limits.One other safe end made of sensitized material has been removed and examined, found not to contain cracks, and has been replaced with a new one of unsensitized material.All other safe ends made of sensitized material have been non-destructively tested.The minor defects found will be ground out before the reactor is operated again.The applicant stated that expansions of primary piping will be measured during a hot functional test to be conducted prior to restarting the reactor, to check the pipe supports and the seismic restraints.

The applicant has proposed an augmented surveillance program for the sensitized safe ends remaining in the primary system,',.including non-destructive testing at least once a year and re-checking piping expansions for several full thermal cycles.The Regulatory Staff should assure itself that the details of the proposed program are appropriate.

The applicant is studying improved leak-detection methods.The Committee believes that detection and location of small leaks is an essential part of the surveillance program.The applicant should expeditiously install such leak-detection devices as seem likely to give improved sensitivity or speed'I" of leak detection.

The Committee recommends that at least one leak-detection system in addition to the proposed sump accumu-lation rate and dew point systems be installed within a few months and wishes to be kept informed of progress, in this regard.

'IV v+8 s r+JI 1fonorabl(.

Glenn T.S>>aborg Jun(2', 1970 Thc Cnmmitte(.

believ>>s that thc Regulatory Staff should assur>>its(.lf: L'haL the bjological shield surrounding the reactor v>>ss(1 can wi thsL'and~th(.pressur>>thaL could be developed by loss of integrity of a safe cnd or nozzle, or that failure of the shield would have no intolerable con-s Q(fu('nc>>s e Th(, hCi>gard is given to the'r(.commendations above and,in its pr>>vious report Lo you of April 17, 1969, there is xeaso>>abl<<.

aSsur(mcc that the Nin>>Hile Point Nucl>>ar Station can be oper iL(.'(1 at power lev(:ls up to 1>38 MM(t)withouL'ndue risk to the health<<nd safety of.the public.Sincerely yours, Joseph H.liendrie Chaix'man Refer>>n'ces l.Niagara Hohawk Power Corporation Investigation at Nine Nile Poiht ,2.Niagara Hohawk Power Corporation InvestigaL'ion at Niiae Hilc Point daLed Hay 11, 1970.,report,"Reactor Primary System Nuclear Station," dated Hay 1, 1970.report,"Reactor Primary System Nuclear Station, Report No.2," I 3.'iag na Mohawk Power Corporation repox't,"Program for Restoration L'o S<<rvice Based on Repox ts of Primary System Investigation Nine , Nile I'oint Nuclear Station," dated May 11, 1970.

WC'P AD L 04 Hon.Glenn T.Seaborg%3 0~e Committee believes that the Regulatory Staff should assure elf that the biological shield surrounding the reactor ves el can withstand the pressure that could be developed by loss f integrity of a safe end or nozzle, or that failure of the sP eld would have no intolerable consequences.

The ACRS lieves that, if due regard is given to the recommendat'ons above and in its previous report to you of April 17, 19 , there is reasonable assurance that the Nine Mile Point Nuc ear Station can be operated at power levels up to 1538 MN(t)without undue risk to the health and safety of the public., Sincerely yours, Joseph M.endrie Chairman References 1~Niagara Mohawk Power Corporatio report, NEDM-10159,-"Preliminary Report, Core Spray N zle Safe End, Nine Mile Point Power Station", dat d March 27, 1970'.Niagara Mohawk Power Corporation repor ,"Reactor Primary System Investigation at Nine Mi Point Nuclear Station, Report No.2", dated May ll, 19~3.Niagara Mohawk Power Corporation report,"Pr gram for Restoration to Service Based on Reports of Pr ary System Investigation

'Nine Mile Point Nuclear S tion", dated May ll, 1970,

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