ML19309G083

Significant Deficiency Rept SD 369-370/80-03 Re Control Rod Guide Tube Support Pins Potential for Cracking.Caused by Increasing Solution Heat Treatment Temp.Pins Will Be Replaced W/New Pins Solution Heat Treated at 2,000 F

ML19309G083
Person / Time
Site:	Mcguire, McGuire
Issue date:	04/24/1980
From:	DUKE POWER CO.
To:
Shared Package
ML19309G081	List: ML19309G080 ML19309G083
References
NUDOCS 8005020331
Download: ML19309G083 (2)

Text

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s 80C5020 N MCGUIRE NUCLEAR STATION

-n' Report Namber: SD 369-370/80-03 ,

Report Date: April 24, 1980 Facility: McGuire Nuclear Station - Units 1 and 2 Description of Deficiency:

On March 25, 1980, Mr. J. R. Wells, Mr. J. K, Berry, Mr. V. H. Shellhorse, Mr. P. R. Herran, and Mr. L. C. Johnson advised Mr. Milt Hunt, NRC/0IE, of the potential for cracking in the McGuire control rod guide tube support pins.

In late 1978, cracked control rod guide tube support pins were found in PWR plants operating in a foreign country. Investigations at that time concluded that there was no safety issue for domestic operating planta because only one heat treatment lot of foreign manufactured support pins appeared to be affected.

No cracks were found in Westinghouse supplied support pins in the foreign plants nor had Westinghouse ever experienced support pin cracking in any plant.

Recent support pin inspections at a foreign plant revealed stress corrosion cracking in Westinghouse supplied support pins. Laboratory testing, conducted as part of the investigation into the support pin cracking problem, indicates that susceptibility to stress corrosion cracking decreases with increasing solution heat treatment temperature. These tests have established that Westing-house current manufacturing process, which utilizes a solution heat treatment at 20000F results in support pins which are highly resistant to stress corrosion cracking. The majority of support pins previously supplied by Westinghouse have had solution heat treatment at less than 20000F.

Specifically, all pin cracking was found in pins having solution heat treat-ment at temperatures less than 1800 F. The pins used on McGuire (1 & 2) were solution heat treated at less than 18000F.

Analysis of Safety Implications:

The Westinghouse Water Reactor Divisions Safety Review Committee concluded, on March 11, 1980, that the potential for broken guide tube support pins, due to stress corrosion cracking, is reportable to the NRC, under title 10CFR Part

21, (reference Westinghouse letter NS-TMA-2214 dated March 14, 1980 to Victor Stello) for the following reasons:

For Upper Head Injection (UHI) Plants: If a guide tube support pin should bre4 alignment of the guide tube may not be maintained. Guide tube mist gnment could jeopardize the operation of the associated control rod.

For UHI and Non-UHI Plants: In the unlikely event of a broken pin leaf, there may be some small potential for a loose part to adversely affect associated control rod operation. However, based on }[ operating experience and routine refueling inspections,1[ has never seen any evidence of broken pins in domestic plants. This includes some of the earliest Westinghouse l

plants to go into operation which are also known to include guide tube pins manufactured at the lower, suspect solution heat treatment temperature.

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Corrective Action:

- Westinghouse's reconmended action is to replace the pins on McGuire (1 & 2).

sestinghouse has proposed work to begin after McGuire Unit I hot functional and work will be completed on both units prior to fuel load. Westinghouse is to replace the pins with new pins solution heat treated at'a temperature of 20000F.

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