ML19351E630

Final Deficiency Rept Re Broken Spring in Pressurizer Safety Valve,Initially Reported 801029.Part 21 Is Also Applicable. Failure Apparently Caused by Quench Cracks in Spring Matl. Replaced W/Crosby Valve & Gauge Co Spring

ML19351E630
Person / Time
Site:	Sequoyah
Issue date:	11/26/1980
From:	Mills L TENNESSEE VALLEY AUTHORITY
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8012100548
Download: ML19351E630 (2)

Text

' . l TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 374ot 400 Chestnut Street Tower II f 1

November 26, 1980! . ~{,..g i

90-06 0 - a3L Mr. James P. O'Reilly, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Region II - Suite 3100 101 Marietta Street Atlanta, Georgia 30303

Dear Mr. O'Reilly:

l SEQUOYAH NUCLEAR DLANT UNIT 2 - BROKEN SPRING IN PRESSURIZER SAFETY VALVE -

NCR 2397,- FINAL REPORT The subject deficiency was initially reported to NRC-0IE Inspector R. W. Wright on October 29, 1980, in accordance with 10 CFR 50.55(e).

Enclosed is our final report. We consider 10 CFR Part 21 to be applic-able to this deficiency.

If you have any questions, please get. in touch with D. L. Lambert at FTS 857-2581.

Very truly yours, TENNESSEE VALLEY AUTHORITY

. N

(. M. Mills, Manager Nuclear Regulation and Safety Enclosure cc: Mr. Victor Stello, Director (Enclosure)

Office of Inspection and Enforcement U.S. Nuclear Regulatory Comissica Washington, DC 20555 30/7 S

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%cqO Gpy An Ecual Cocortunity Employer Foitoon577 ,

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/, p ENCLOSURE SEQUOYAH NUCLEAR PLANT UNIT 2 j

BROKEN SPRING IN PRESSURIZER SAFETY VALVE NCR 2397 10 CFR 50.55(e)

FINAL REPORT Description of Deficiency A test was performed cm unit 2 pressurizer safety valve (2-RV-68-565) before installation. During the test, relief pressure appeared very erratic. The valve was disassembled and a broken spring was dis-covered. The valve (and its spring) was supplied by Crosby Valve and Gage Company.

Safety Implications Had the broken spring escaped detection, the pressurizer safety valve could not have functioned properly. The valve was designed to fail in the closed position. The valve spring's failure could have resulted in a blowdown of the RCS. Although this occurrence is wituin the design basis event para-

=eters, the integrity of the pressurizer must be maintained in order for the plant to operate safely.

Corrective Action The broken spring was taken out of the valve and replaced with one supplied by Crosby Valve and Gage Company. The broken spring was inspected; the failure was apparently caused by quench cracks in the spring material.

There is every indication that the broken spring was an occurrence of low probability. Crosby asserts that 300 nuclear and hundreds of thousands of nonnuclear valve springs (in noncorrosive environments) have no other reported history of failure. A TVA-sponsored Licensing Information Service search revealed only one failure in a 3/4-inch crosby relief valve. There were no known spring failures. Six domestic PWR's have a total of 33 '

Crosby relief. valves which were bought in the same lot as Sequoyah; none of these has experienced spring failure or displayed quench cracking. Unit 2 valve springs are being inspected and preliminary results indicate no aberrations.

The mishandling of the metallurgical process which formed the faulty spring could recur; however, examination and testing procedures have proven suf-ficient to reveal a deficiency of this nature.

TVA will continue to monitor and test valves in the preoperational phase of construction at Sequoyah Nuclear Plant (SNP) unit 2. As in this case, any defective or unsatisfactory valves or components will be documented and l dealt with as such.

TVA expects to complete inspection and preoperational testing of all similar valve springs at Sequoyah unit 2 by March 1, 1981.

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