ML20084M296

Suppl to AO 3-73-1:on 730106,reactor Coolant Leaked Into Reactor Containment from Differential Pressure Cell.Caused by Flange Bolt Failure.Bolts Replaced

ML20084M296
Person / Time
Site:	Turkey Point
Issue date:	03/15/1974
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084M298	List: ML20084M296 ML20084M319
References
AO-3-73-1, NUDOCS 8306020091
Download: ML20084M296 (2)

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Dear Mr. O' Leary:

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%.0 M DOCKET NO. 50-250 SUPPLEMENTAL REPORT ON ABNORMAL OCCURRENCE NO. 3-73-1 LEAKAGE OF REACTOR COOLANT INTO THE REACTOR CONTAINMENT FROT! A DIFFERENTIAL PRESSURE CELL I. INTRODUCTION On January 15, 1973, Abnormal Occurrence Report No. 3-73-1 concerning. leakage from a reactor co-olant D/P cell was submitted in accordance with Section 6.6.2a of the Technical Specifications.

This report presents the results of subsequent extensive investigation into the incident to determine the cause, and describes the corrective action taken to prevent occurrence of similar incidents in the future.

II. INVESTIGATIVE ACTION Inspection of the D/P cell revealed that two of the flange bolts had failed. Consultation with the D/P cell vendor and the Nuclear Steam System Supplier resulted in their recommendation to replace the or-iginal bolts (Silver-cadmium electroplated AISI 4037, stec1) with 17-4 Pil stainless steel bolts. In order to define the cause of the bolt failure, a detailed metallurgical examination of the D/P cell bolts wasconductedbytheNuc1carSteamSystehSupplier.

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Mr. John F. O' Leary Page 2 March 15, 1974 .-

The Nuclear Steam System Supplier metallurgical eval-uation concluded that:

a) The cause of the bolt failure was hydrogen stress cracking, b) Maintaining stress levels below a threshold level can prevent hydrogen stress cracking, and c) Tempering the AISI-4037 steel bolts at slightly elevated heat treating temperatures will improve their resistance to hydrogen-stress cracking. '

In light of the cause of the bolt failure, the Nuclear Steam System Supplier also confirmed that the use of the initially recommended 17-4 PH stainless steel bolts was acceptabic. However, the Nuclear Steam System Supplier cautioned that the 17-4 PH bolts must be of the 1025F heat treat grade. s III. CORRECTIVE ACTION Replacement bolts of 17-4 PH stainless steel have been installed in all similar D/P cells with AISI-4037 steel bolts located in high pressure safety related systems. The 17-4 PH stainless steel bolts were cer-tified to be the required 1025F heat treat grade.

IV. CONCLUSION The cause of the bolt failure has been determined and satisfactory action has been carried out to prevent similar occurrences in the future.

Very truly yours,

/A//Y" A. D. Schmidt Director of Power Resources HNP/kmw cc: Mr. Jack R. Newman Mr. Norman C. Moreley i