ML19309A909

LER 80-035/99X-0:on 800313,Westinghouse Informed Util of Potential for Supplied Control Rod Guide Tube Support Pins to Break Due to Stress Corrosion Cracking.Caused by Low Solution Heat Treatment Temp

ML19309A909
Person / Time
Site:	North Anna
Issue date:	03/27/1980
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19309A908	List: ML19309A907 ML19309A909
References
LER-80-035-99X, LER-80-35-99X, NUDOCS 8004010505
Download: ML19309A909 (2)

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h g l Certain support pins are susceptible to stress corrosion cracking due to their low I

,  ; solution heat treatment temperature. Corrective actions to be taken are nending the I

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Virginia Elsctric and Power Compcny North Anna Power Station, Unit #1

Attachment:

Page 1 of 1 Docket No. 50-338 Report No. LER 80-35/099X-0 Description of Event l

Recent support pin inspections at a foreign plant revealed stress corro-  !

sion cracking in Westinghouse supplied control rod guide tube support pins I which had been solution heat treated at 1625'F. The potential cracking of the control rod guide tube support pins is considered a generic problem and ,

is being reported for information purposes.

I Probable Consequences of Occurrence l The purpose of the support pins is to prevent lateral movement of the guide tubes. If a guide tube support pin should break, misalignment of-the guide tube could result, which, in turn, could restrict the movement i of the associated control rod. Because the safety evaluation performed by Westinghouse concluded that control rod operation is not jeopardized by a broken pin for non-Upper Head Injection plants (i.e. North Anna Power Station) due to the small gap clearance between the non-URI guide tube and the core plate, the health and safety of the general public are not affected. The support pin cracking problem is generic to Unit 2. As a preventive measure, the support pins in Unit 2 are being replaced with pinn having higher solution heat treat temperatures prior to the installation of the upper internals in the reactor vessel.

Cause of Event f

Certain guide tube support pins are susceptible to stress corrosion cracking because the temperatures at which they were solution heat treated were too low.

Immediate Corrective Action Extensive accelerated corrosion testing has been conducted at Westinghouse R&D Center as a part of the investigation into the support pin cracking problem. This testing has shown that the susceptibility of the support pie to stress corrosion cracking decreases with increasing solution heat treatment temperature and that support pins solution heat treated in the range of 1950*F to 2000*F have little, if any, potential for stress corrosion cracking even under the accelerated testing conditions.

Scheduled Corrective Action In the near future, Westinghouse will conduct ultrasonic inspections at two operat .ng domestic plants of guide tube support pins having solution heat treatment temperatures less than 1800*F. The results of this support pin inspection program as well as the on-going materials test program will determine what further corrective actions, if any, are required.

Actions Taken to Prevent Recurrence No further actior.s are required.

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