B10753, Final Deficiency Rept SD-6 Re Cracking of Control Rod Guide Tube Support Pins.Initially Reported on 800415.Pins Replaced W/Pins of New Design Providing Addl Margin Against Stress Corrosion Cracking

Final Deficiency Rept SD-6 Re Cracking of Control Rod Guide Tube Support Pins.Initially Reported on 800415.Pins Replaced W/Pins of New Design Providing Addl Margin Against Stress Corrosion Cracking

ML20073E230
Person / Time
Site:	Millstone
Issue date:	04/08/1983
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	Allan J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
10CFR-050.55E, 10CFR-50.55E, AEC-MP3-310, B10753, SD-6, NUDOCS 8304140388
Download: ML20073E230 (2)

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April 8,1983 Docket No. 50-423 AEC-MP3-310 B10753 Mr. James M. Allan Deputy Regional Administrator Region 1 Of fice of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406

References:

(1) W. G. Counsil letter to USNRC, Millstone Nuclear Power Station, Unit No. 3, Reporting of Potential Significant Deficiencies in Design and Construction, dated April 15, 1980.

(2) W. G. Counsil letter to R. C. Haynes, Millstone Nuclear Power Station, Unit No. 3, Reporting of Potential Significant Deficiencies in Design and Construction: Cracking of Control Rod Guide Tube Support Pins (SD-6), dated September 3,1982.

(3) W. G. Counsil letter to R. C. Haynes, Millstone Nuclear Power Station, Unit No. 3, Reporting of Potential Significant Deficiencies in Design and Construction: Cracking of Control Rod Guide Tube Support Pins (SD-6), dated October 12,1982.

Millstone Nuclear Power Station, Unit No. 3 Reporting of Potential Significant Deficiencies in Design and Construction: Final Report, Cracking of Control Rod Guide Tube Support Pins (SD-6)

Gentlemen:

In Reference (1) Northeast Nuclear Energy Company (NNECO) reported a potential significant deficiency concerning cracking of control rod guide tube support pins as required by Title 10, Code of Federal Regulations Part 50, Paragraph 55(e). In that letter, we also committed to inform you at a later date of what corrective and preventive actions were being taken. Reference (2) provided you with an update and a commitment to provide further information.

Reference (3) provided an update and a f urther commitment for an update.

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PDR ADOCK 05000423 S PDR

e Westinghouse has completed a detailed engineering evaluation of control and guide tube support pin failures, including metallurgical analyses of pins removed i from North Anna 1. This evaluation has verified that the ,nins cracked due to stress corrosion. Westinghouse has concluded that cracked or broken guide tube support pins do not constitute a safety concern. However, because of the potential for loose parts impacting other components (e.g. steam generator tube sheets), Westinghouse has recommended that the support pins in Millstone Unit No. 3 be replaced with a later design before plant startup.

Following Westinghouse's recommendation, NNECO has replaced all of the control rod guide tube support pins with pins of the new design. The upgraded pins utilize material heat-treated at 20000F, which has been fomd to provide additional margin against stress corrosion cracking. Several design modifications have been incorporated to reduce the potential for stresses.

By incorporating this new pin design, Northeast Nuclear Energy Company considers the reported significant deficiency to be resolved.

This letter constitutes our final report closing out all items related to SD-6. We trust the above information satisfactorily responds to your concerns.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY o

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, W. G. Counsil Senior Vice President i

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