ML20148J386

Ro:On 721103,following Routine Insp of s-18 Shim Rod,Efforts to Reinsert S-18 in JK-45 Core Position Unsuccessful.Insp of Shim Rod Revealed Abnormal Wear Nine Inches Below Normal Block Wear

ML20148J386
Person / Time
Site:	Yankee Rowe
Issue date:	12/12/1972
From:	Autio H YANKEE ATOMIC ELECTRIC CO.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20148J385	List: ML20148J383 ML20148J386
References
NUDOCS 8011210758
Download: ML20148J386 (3)

Text

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YAhMEE ROWE, MASSACHUSETTS 01367 i Y

December 12, 1972 United States Atomic Energy Commission Washington, D. C. 20545 '

Attention: Directorate of Regulatory Operations s.:

Reference:

License No. DPR-3 (Docket No. 50-29)

Dear Sirs:

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Relative to the reporting requirements specified in 10 CFR 20 Part )

20.403 (b) (4), Yankee Atomic Electric Company - Rowe reported on November 13, 1972 that two control rod shroud tubes were displaced. s The following written report is submitted in accordance with 10 CFR _

20.405 (a) (2).

Following a routine inspection of shim rod S-18 on November 3, 1972, .;

cfferts to reinsert S-18 in core position JK-45 were unsuccessful. Furthe.

periscope inspection of the shim rod revealed abnormal wear approxicately mine inches below the normal guide block wear. 1; Following this evaluation of the problem, the decision was made to h

.pp receve the four fuel assemblies adjacent to JK-45 to permit inspection of the di shic rod slot irf the lower core support plate. An underwater television in- g pection revealed the following: T M

1. A cap screw with locking cup intact was lying East and l:#

West in the cruciform formed by guide blocks for the lI%

lower core support plate at core position HJ-45. Th1s  %

bolt and locking cup assembly was later proven to be a ' 'f shroud tube mounting bolt. The bolt was not obstruct- '

ing the shim rod hole. S ub s equen tly, this bolt was re- .w trieved from the lower core support plate. f!.

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2. Inspections through nozzle holes surrounding S-18 reveal- :p ed crescent shapes through two nozzle holes to the East of the shim rod. Indications were that the shroud tube fk f had shifted to the East.

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3. Inspections through shim rod slots of the lower core sup- je; g port plate revealed slots of North and South vanes nearly closed. j@r 801121,0 T V COPY CZNT HGION.._g c a

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paited Statn3 Atomic Energy' Commission atory Opsrations

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{J ctmber 12, 1972 7

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4 Upon discovery of the misaligned shroud tub.e and a shroud tube bolt, k!

the decision was made to remove

all fuel from the reactor and inspect the low- $ l l er reactor internals. T l i During the core unloading,' control rod A-101 (rod,#19) which had dis- i

- played erratic behavior during plant operation was removed from core position (1  ;

JK-67 for routine inspection. Later, an attempt to reinsert control rod 19  ?

was. unsuccessful. The problem was believed to have been caused by substantial l bowing of the control rod noted during the inspection. To substantiate this (i premise, a new control rod was inserted'into core position JK-67; it also [. l failed to insert beyond the guide block area of the lower core support plate, g l Subsequent television inspection of this core position revealed a second cap t screw and. locking -cup wedged between the guide blocks at the extreme southern f, end of the South vane. 4 4 i During removal of the core components a binocular inspection of the $;

lower core support plate was performed. This inspection revealed a third cap screw and locking cup resting on the Northeast guide block of nozzle G-4. f f

7 Following removal of all fuel elements, shim rods and control rods on November 13, 1972, a thorough television inspection was commenced of the @

lower core support plate to shroud tube bolting. The results were as follows:

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1. Core position JK- 4, bolt missing, cup in place.  %

2. Core position J-45, bolt missing, cup in place. T

3. Core position K-45, bolt and locking cup missing.

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4. Core position JK- 5, bolt missing, locking cup in place. @

5. Core position GH- 2, bolt and locking cup missing. )

6. Core position G-23, bolt and locking cup missing. 7

7. Cors position H-23, bolt and locking cup missing. te r

A binocular in'spection of the bottom of the reactor vessel revealed .

four shroud tube bolts, two with their locking cups. {s On November 15, 1972, the reactor vendor representatives arrived on ki site and commenced a television inspection of lower core internals. Their  %

findings were consistent with those of Yankee with the exception of a possibic k loose shroud bolt at core position G-12. h The vendor inspections resulted in the recommendation to remove the y lower core support barrel to pemit a more detailed inspection of the shroud g tube structure. The barrel was removed on November 16, 1972 and the follow- g ing additional abnormalities were observed. .

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1. A sheared shroud tube tie bar between shroud tubes No. 24 and No. 25. Binocular inspection of shroud R No. 25 on the Northwest side revealed a vertical h, scar one to two feet long on the outside lower g quarter of the shroud tube, t

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Unitrd*Stetrs Ato ic Ernr y Commission ~3- '

atory Operntions mber 12, 1972

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2. One bolt was found missing and one partially with-8, d

drawn at the bot'tbm tie plate on shroud tube No. 26. p

- e The problem described in (1) above appears to be related to an k occurrence early ir. plant life concerning dislodged speciv.cn holders; no l -

([,c relationship has been developed relative to the currently observed shroud '

E tube problem.

h The reactor vendor is presently studying a repair which is expect-  ?

H ed to result in a new unitized shroud structure replacing the old bolted shroud structure.

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Very truly yours, W"';

YANKEE ATOMIC ELECTRIC CO. - ROWE i

fan'u-<Y hY bcd$f Herbert A. Autio . l [i Plant Superintendent g

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