ML20052F757
| ML20052F757 | |
| Person / Time | |
|---|---|
| Site: | 05000000, 05000465 |
| Issue date: | 01/20/1982 |
| From: | Reisch F SWEDEN, GOVT. OF |
| To: | Lafleur J NRC OFFICE OF INTERNATIONAL PROGRAMS (OIP) |
| Shared Package | |
| ML20049H209 | List: |
| References | |
| FOIA-82-167, RTR-REGGD-01.121, RTR-REGGD-1.121 NUDOCS 8205130578 | |
| Download: ML20052F757 (6) | |
Text
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STATENS EXilNMR AFilNSPERTION
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swtorsH NUCLEAR POWER INSPECTORATE Stockholm Jen. 20, 1982 o
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w, R3 - B.S.4.2-1430/81 Dr Joseph D Lafleur Nuclear Regulatory Commission Washington D C 20555 USA
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Dear Dr Lafleur,
Subject:
Steam generator tube fretting in Ringhals 3 (f
For your information there is a PM attached here to present this inspectorate's position on the subject matter.
Beside the two reactors in Sweden there are six reactors in the US, six in Spain and one in Brazil equipped with the same type of steam generators.
t The utility - the Swedish State Power Board - has sent us last December a plugging application based on Reg. guide 1.121 (some material from that is attached here too). The app-lication has been rejected. No resumed operation request for Ringhals 3 or core loading request for Ringhals 4 has been received yet.
We,will send you later the information you asked for in your letter, dated December 17, 1981.
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-V Should you want some further explanation, or should you want additional information, please don't hesitate to contact us.
Q Yours sincerely, i
Fdga %51
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Frigyes Reisch Leif Ericsson, Swedish Embassy, Washington cc:
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.t Summary of the Swedish Nuclear Power Inspectorate's po-sition on the steam generator tube frettings in the Rinchals 3 plant.
- 1. The fretting in the Ringhals 3 steam generators (Westinghouse type "D3") is a new phenomenon, and is of a generic nature. The fretting eW31ves very fast. Leakage in Ringhals 3 occured after 3 000 EFPH, i.e. less than
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the usual interval between inspections.
- 2. The damages in the first rows in the steam generators are very extensive. Most of Yhe damages occour in the inlet part of the preheater section, (between baffle plates 4
5 and 6) but single cases of fretting can be seen also -
kJ higher up i.e. between baf fle plates 11 and 12.
- 3. The cause of the harmful fretting seems to be vibrations, but the exact nature of that has not been shown yet.
- 4. The problem is considered to be a safety problem. All available safety studies indicate that small primary leaks increase the risk for large accidents. There is also a risk for simultanious multiple tube leakages in one or more steam generators. The tubes are the only barrier for release to atmosphere in certain operating conditions with leaked fuel.
- 5. The problem can most probably be solved but no plan for modification has been presented yet. Operation at reduced r
power with a damaged steam generator like Ringhals 3 is
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probably possible. It remains to be shown however that such operation can bee made without significant further fretting.
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- 6. Plugging criteria in accordance with Reg. guide 1.121 g,f is not sufficient as that guide was developed to take care of other phenomenas. This regulatory guide is suffi-cient to assure initial tube integrity, but special analysis are required for the effect of increased gap between tube and baffle plates.
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- 7. Full scale model tests are very important, j
to the scale tests performed by Westinghouse. The Ringhals 3 owner utility, the Swedish State Power Board, is at present conducting such tests in X1vkarleby, Sweden. There an 1:1 scale model of the preheater inlet section - between baffle plates 5 and 6 - is in operation now. The model l
will be extended further to contain 8 full length tubes.
Computer models have however failed to predict this phenomena.
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- 8. In May, 1981, eddy current testing was performed by 2etec on 14 tubes in row 49 after a water harner incident.
No dents were found on the preheater tubes, but "it was suggested that several tubes exhibited signals which should be monitored at a future inspection" SKI was however not informed of this recommendation nor was obviously NRC.
The tube which was showen in May, to suffer substantial wall thinning was the one which then leaked in October.
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$fATINS KKRH KRAFTINSPEKTION 1(3)
SwtDISM NUCL$AR POW 12 BNSPECTORATE Offics of Inspecticn 1982-01-20 Per Anders Siljestrom SHORT
SUMMARY
OF STEAM GENERATOR PROBLEMS AT RINGHALS UNIT 2 SWEDEN Ringhals Unit 2, Data I
NSSS Westinghouse SG number 3
SG model No 51 c Tubing material Inconel 600 Start-Up-date 5/75 Secondary Water Chemical to sept -74 PO Control
, fromOct-74Ad Waterhammer x
Denting x
SCC Initiated from ID IN U-Bends x
No.'.of leaking tubes to date 5.
No. and 4 of tubes plugged to 300 tubes; 2,95%
date
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Primary to secondary leakage 3
rate limit per steam generator 1,88 m /d I
1976 Water hammer On January 13, 1976, a water hammer occured in feed-water line No. 1 of the Ringhals 2 Nuclear Plant. The incident re:ulted in Stretching the bolts of the feed-water check valve,in line No. 1, producing a feedwater leakage. The plant wa.,
operating at 50% power. Following a reactor trip from 50% power originated by a fault in the exciter of the turbo-generator in operation, there was a start at first of the motor-driven auxiliary
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feed-pump. This combined with a low low level led to j
a waterhammer in steam generator 1. After the line in-spection, it was found that the bolts on the main check i
valve outside containment had been stretched and there-l fore a leakage occured. Further damages were a broken f
clamp on a vertical pipe support and a crack in the cast' iron casement of the isolation valve motordrive unit.
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1977-79 Denting, preventive plugginq InJune 1977 it was discovered that a denting problem had occured in all three steam generators at Ringhals-Unit 2. Measurement showed that the decrease in dia-meter was rather small and Westinghouse made the judgement that the denting was moderate. For preventive purpose, a tota 1 amount of approximatly 220 tubes were plugged.
In each steam generator, 72 tubes out of 94 in row 1 were plugged. Row 1 has the smallest bending radius and is the most sensitive row for SCC (stress corrosion-cracking).
At the annual revision in 1978 it was found that the denting problem still was in progress but not in an alarming extent. No plugging was made during this revision.
In 1979 the rest of the unplugged tubes in row 1 in all 3 steam generators were plugged. This increased the plugging rate to 2,954. The total number of plugged tubes are approximatly 300.
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1980 Tube leak above tube plate A minor leak has occured justabove the tube plate in one tube. The end of the tube is tucked in 2 "to the 21" thick tube flabe and just above the tube plabe there are some minor cracks discovered. They are located in a longitu-dinal direction. This part is send to England for exa-mination.
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3(3) t 1979 Leakins plugs In April.1979, there was a leaking plug which lead to an earlier start of the refueling period. Today, there are.a certain aucunt of leaking plugs estimated to 1-24
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