ML19210B269

Deficiency Rept Re Bent Vent Valve Thermocouple Guide Tubes & Bent Thermocouple Nozzles on Reactor Vessel Closure Head. Caused by Misalignment of Nozzles on Head to Guide Tubes on Plenum.Corrected by Partial Removal of Nozzles

ML19210B269
Person / Time
Site:	Three Mile Island
Issue date:	12/20/1973
From:	John Miller GENERAL PUBLIC UTILITIES CORP.
To:
Shared Package
ML19210B268	List: ML19210B269
References
NUDOCS 7911050499
Download: ML19210B269 (2)

Text

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q MO Cherry Hill Acad Parsippany, New Jersey 07054/201-539-6111 December 20, 1973 Dr. D. R. Knuth, Director ' " "

Directorate of Regulatory Operations United States Atomic Energy Commission Washington, D. C. 20545 Subj ect: Three Mile Island Unit 1 Docket No. 50-289 Bent Vent Valve Thermocouple Guide Tubes

Dear Dr. Knuth:

You were notified on November 26, 1973, of a situation which may be considered reportable under 10CFR50.55(e), " Conditions of Construction".

This situation related to bent vent valve thermocouple guide tubes.

DESCRIPTION OF INCIDENT On November 22, 1973, the Three Mile Island Unit i reactor vessel closure head was removed for inspection of the 0-rings. At this time it was discovered that seven of the eight vent valve thermocouple nozzles on the reactor vessel closure head were distort 3d. In addition, the corresponding thermocouple guide tubes on the plenum assembly were also distorted. Of the seven damaged thermocouple nozzles on the closure head, two were significantly bent out of shape while damage tc the other five consisted primarily of raised metal.

Of the corresponding thermocouple guide tubes on the plenum assembly, two were bent approximately 10 from the vertical while damage to the other five was limited to raised metal and so=e damage to the tube ends.

CORRECTIVE ACTION The vent valve thermocouples were originally included in the design because it was felt that they might be required for licensing. However, subse-quent to including the guide tubes in the fabrication, additional calculations and discussions with the AEC Staff by the NSSS supplier determined that these would not be required for the Three Mile Island Unit 1 power level.

The apparent cause of the bent tubes was misalignment of the nozzles on the head to the guide tubes on the plenum. Since the vent valve thermocouples are not required for operation of Three Mile Island Unit 1, it was decided to partially remove the nozzles. Otherwise, critical tolerances would need to be re-established and maintained to preclude future occurrences of this nature.

As a result of this corrective action, the situation at Three Mile Island Unit 1 with regard to the vent valve thermocouple guide tubes duplicates the situation at Oconee I.

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. -*w Dr. D. R. Knuth, Dire 3r December 20, 1973 Directorate of Regulatory Operations Jnitc1 States Atomic Energy Commission Washington, D. C. 20545 The corrective action was taken with technical direction from the

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NSSS contractor and consisted of the following:

A. The thermocouple nozzles were cut off approximately six inches below the inside surface of the reactor vessel closure head.

B. The thermocouple nozzle to the reactor vessel closure head welds were visually inspected and dye checked for

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defects and were found to be satisfactory.

C. All raised metal on the thermocouple guide, tubes (plenum assembly) was removed and blended.

D. The upper thermocouple guide tube reducer to guide tube weld and the guide tube to plenum upper weld were visually inspected with SX magnification for defects. None were found.

Very truly yours,

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.. m ,M m 7 J. G. Miller Vice President brh cc: Messrs. H. M. Dieckamp J. P. O'Reilly W. A. Verrochi 1585 130