ML20062H359

Discusses Pipe Leak at Tvo 1,in Finland,Due to Faulty Fabrication Process of Components Mfg in France & Significance to Us Plants

ML20062H359
Person / Time
Site:	Prairie Island
Issue date:	10/24/1979
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Gilinsky V, Hendrie J, Kennedy R NRC COMMISSION (OCM)
Shared Package
ML20062H358	List: ML20062H356 ML20062H359
References
NUDOCS 7912210013
Download: ML20062H359 (14)

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Harold R. Denton, Director, Office of Muc1 car P.cactor ite;ulatien p

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Lee V. Gossick', Executive Director for C;: ration p

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L/6CE PIPE LEAX AT TV3 I, OLKILUOTO, FIMLAND TVO! is a 660 P.ic BC supplied by the Swedish Corpany Asen-Aten.

It first went critical in July,1970, and o::erated at full power since Anucry,1979. At 9:35 p.a. August 29,1979, a 1arte leak occurred in a G-inch diameter stainless steel pipe in the reactor uatcr cleanup system. Tnis syster, unlike cor ; arable systccs in U.S. C'J's, operates at the full prir.ary systcr cressure of 1232 PSI.

ine f siled section of ;;i;;e was up:trcam cf the filter;, so th* ust:r that leaked b

out was the same as in the reacter vessel.

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The plant protection systems were actuated by hign rec-tar.:erature, an: by water level switches en the ficer. The prctection systa: s ict:0 to cause reactor trip, closing the centcin.-ent isolation valves of the auxiliary systats, anc sritening.

the resctor buildin9 ventilation from norral to filtered rcce.

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r Tha f ailed pi;:e section was isolated by cicsing canually o;; crated isolation 3= ;=

valves at 11:00 p.m., when it was detemined that the radiation level in the area was not too high. Reacter pressure reduction 5:as st:.rted at 12:45 a.m.,

E the residual heat re : oval system was started at 3:00 c.c.

The plant was in cold

[rv shut down at 10:20 a.m.

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The total amount of water leaked was esti=ated to be about 1300 gallons, with a total ra:ioactivity of 10Ct:Ci. Tlie dose rate in the room was 10 m rem /hr.

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The fciled pi;:s secticn was at and downstrea:, of a T connection where a cy-pass a heat exchan;ct c:nnected to :he ipe dischar-ing frc-the heat 2x-I"'

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A: a r 's.1: Of :.r o; crt:icnti errer, 52 rr ::: v:.iic was po:iti:r.ed

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2-f a0:ition, there ua: a s : aller throtegh-wall crack criente. circu.:fcrcn:icil;.

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• ftar 5 cticnin?. it could be seen that ther2 u*.ra rany cr:cus en the ir:1,. c surf ace in c " crc:c-cracking" p:ttern, typiccl cf thar- :.1 f atigue f:1}ur::. '

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i:cre detailed cctallograchic and fractegrc:: hic analysis confirecd th:t tne jj i

cr:ck: were ccusec by f atic;ue. Fig; 2 shows the craze cracking. on the in:trie tN,

urfa~t of the pipe, as delineated by dyc pencerant. Frc:tographic evidence of Is:

fatigue on the fracture surface is shown in Fig. 3.

The parallel lines running m.;

horizontally in the photo are typical fatigue " striations," showing the pro-4' gression of the crack each stress cycle.

.:4,.T n It was concluded that the failure was caused by the ra:id therr.al fluctuation created by the mixing of hot and cold water. The piping was r:placed, and no furtner probicas are antici;:ated with the by-pass valve ;rcrerly closed.

Sirnificance To U.S. Plants A very similar failure occurred in lef2 h the Vallecites C'.T:.

Cold fec:: water i.

entering reactcr recirculating water through c T :ennectica ccused similar

.y cra:a. cracking and a leck. E/;Rs in this country have ha0 cracking on the inside radiu: of feedwater noz:les caused by leakage of ccid feedwater around the ther=al sleeve. The recently discoverec cracking in the PJA feecwater p

pi;:in: near the staan generator nez:le: 1: now believed : :2 primarily caused i.

r by cold feedwater atxing with hot water from the insice of the steam generater.

l Staff Actions (6.

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00R is prepcring an information letter to 055 cescribing this occurconce, and p

i recc=ending that they be on the alert for similar configurations in new plants.

l-A letter will be sent to licensees of all oxrating plants asking them to check their syste s for locations where hot and colc water are nixed, eitNr un:cr nor=al conditions or could nix if valves are :et incorrectly.

i CRAC!*.S CAUSED BY FAUL.TY FAE?.! CATION PROCESS If; F;10:CE p

Me have had several reports of cracking in stca-cencrator tube sheets and f

reactor vessel nozzle forgings in components manufactured in Franca. Althcugh s;:ecific technical details are not yet available to us, it apocars that the problem is caused by a carginal w21d cladding process used to clad the cocpon-41 cnts with corrosion resistant weld depotit.

In the case of the stean generator b

tube sheets, Inconel COO is weld ceposited on the prir.ary sidc, as i: cone en r

plants in this country. Cracks in soce of the French cc p:nents have been E

f run.: bene nh the cladding, in the base :: :1 fer:ing. 5:ue of the:e crechs r

cr, nn. rt:0 to oc c: :: 1/2 inct w.: (10 n '..

In the casa f th: tt tir,1ce:

st:01 01 : re:ct:r v : sci no::10., ne cracht ar:

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cut 5:n are c :: 1/4 inen ce:. All c-::%s :r: r:1 tively thcrt, t::t 1/?

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7.c :ce.:t c:as: cf the ers:': int is still sc e f.n o::scurc. i.tcut 10 y nr: c,

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'ft; i" M -.rin int 1rci. cl.'.. in? C rtti!",.*.~. 6 :s' it;.1 IJr;in ; f

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i susceptible (hir.h alloy) cecposition. The probler was first discovered in Ger=cny, and it appeared that forginas made in Europe ucre socewhat e:.re C

susceptible then those of United 5t:tes canufac:;re. This pr:blem was re-

'1 solved by codifying the weld deposition procedure, and in sene cases by

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modifying the chemical composition of the ferging.

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M The French habe stated that the current cracking proble: has a different EE..

Although it is still related to f abrication crocasses, and also ire cause.

' [R3 appears to be related to forging base metal cocpesitten, the cracks appear to be much deeper than those of 10 years ago. Although we have not yet been ik given enough technical detail, the French have said that the process sequence iL causing the cracking consists.of a first weld deposit pass with the usual pre-

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heat or post-heat, but the succeeding pass or passes arc ocnc without pre-heat i r..;

or post-heat. Further, they feel that the cracking is " cold cracking," and t

related to hydrogen cither in the forging or adccc in the wcid cladding oper-

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ation. It could also be that not all the cracking found is due to the same

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cause.

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Slenificance To U.S. Plants

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E At present there appears to be no reason for concern that similar cracks are present in cocponents of U.S. plants, because the wcld deposition processes have been carefully checked out as a result of the problem 10 years ago. The mr only U.S. plants with reacter vessels canuf actured in France (Creusot-Loire)

i are Prairie Island Units 1 and 2.

According to Westinghousr these were clad FE e

using Westinghouse approved procedures that required pre-hea: and post-heat i:A Fi

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for all weld passes.

taff actions

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The Frrnch have promised that full technical details will be made available EE to us early in !ovember, when several tepresentatives will be visiting NRC for

[i the Research Information Meetings. Appro;n-iate members of the staff will meet E5 with them to discuss the problem and the technical details, p~5

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Northern States Pcwer has been infomed of the French problem, and that it is E-l possible, althouch unlikely, that their reactor vessels could be affected. If E

af ter full details are available it appears prudent to inspect the Prairie EEi Island no::les, the staff will require inspection of at least the two most'..

E=E accessible no::les. If further information leads to the conclusion that other" F

plants could be affected, the staff will take statever action is appropriate.

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SUBJECT 3.@ CATALOC

INSPECT (UT) TIF4E MOZZLES FROM OPS / OQS P.EACTOR YESSELS

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TASK COMPLETED P.EPAIFJ3LE INDICATIONS IN ALL THREE N0ZZLES PER FR/MTOME CRITERIA FOUR BOAT S# PLES TO BE RDOYED FROM THE THREE N0ZZLES FIRST BOAT SAMPLE TO ARRIVE 11/18/79 FIRST B0

$#FLE EYALUATION 11/20/79 REQUESTED THAT ONE OUTLET N0ZZLE (OPS) AND ONE INLET N0ZZLE BE SENT TO WESTINGHOUSE a

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d It' SERVICE INSPECTION DEVELOPPINT SCHEDULE FOR DEVELOPING ISI PROCEC"RE 1.

FABRICATE CALISPATION BLOCKS 12/7/79 2.

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