ML20084L718

AO 50-237/1974-32,33 & 34:on 740724 & 29,primary Containment Failed Due to Leakage Through AO-2-1601-21 & 22 & Crack in Line 2-8503-8-LX.Caused by Liquid Nitrogen Reaching Both Valves.Valves & Line Repaired

ML20084L718
Person / Time
Site:	Dresden
Issue date:	08/02/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084L723	List: ML20084L718 ML20084L726 ML20084L729
References
554-74, NUDOCS 8305230653
Download: ML20084L718 (30)

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SUBJECT:

REPORT OF ARNOT!AL OCCURRENCE PER SECTIO!; 6.6.B.1.a CF THE TECR!i1 C SPECIFI CATIONS. AND CRACK IN FIFE

[ CRACK IN SEATS 07 AO-2-1601-21 AND AO-2-1601-22 ASSCCIATED WITH THESE VALVES.

References:

1) Regulatory Guide 1.16 Rev.1 Appendix A 2)' Hotification of Region III of AEC Regulatory Operations Telephone: Mr. F. Itaura,1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on July 26, 1974 Mr. F. Maura, 0815 hours0.00943 days <br />0.226 hours <br />0.00135 weeks <br />3.101075e-4 months <br /> on July 29, 1974 Telegram: Ur. J.' Keppler,1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> on July 26, 1974 iA. J. L.;.;.lcr, 1633 h~"= w Yuly 29. 1974

3) Drawi:tg Number: H-25 Report Mumber: 50-237/1974-32,33,6 34 Report Date: Augus~t 2,1974 Occurrence Date: July 24,.19.74 and July 29, 1974' Facility: Drcsden Nuclear rever Station, Morris, Illinois

'.IllCNTIFTCATION 0F OCCURREUCE - .

Failure - of prbary containment due tolleakage ' through ~AO-2-1601-21 2-1604-18-LX.

6 22 and crack in~ 1ine 2-8503-B-LX 'where it connects with line

" CONDITIONS PRIOR TO OCCitRRENCE-Prior...to the occurrcnce, tho' unit. was in' the - run mode and opersting at :an electrical 1 Icc.d of about '725 megauntts; Thermal power at the the of

' Local leak rate testing of the rubber..

~ discovery was about 2258 regavatts. j' 2 ecated vent;valvas wac in progress..

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DESCRIPTION OP OCCURRPNCE In the morning of July 24, 1974, preparations were being made for the routine quarterly leck rate test of the rubber scated primary containment valves. A perfunctory inspection of the valves was gado prior to the actual running of the leak test. It was at this tice that cracks in the seat of 2-1601-22 were discovered. A leak rate test was attecpted on this valve. As the pressure was increased to 48 psig (lcak test pressure), a loud noise was heard and the pressure quickly dissipated (42 psig to O psig in about 5 acc.).

It was observed that pieces of the valve scar. frca 1601-22 had dislodged from the valve. This fact then required that the valve be removed from place and a blank flange installed.

After 2-1601-22 was removed, observation of 2-1601-21 revealed that about 40% of its seat was missing. Since it was plainly evidant that another attcapt at a Icak test would be futile (even with 2-1601-22 blank flanged) an orderly shutdown was commenced.

During the outage for valve repair, an entry was made into the drywell for snubber inspection. In the course of this inspection, the missing valve seat pieces were discovered in the drywell near penetration X-126.

Af ter valve 2-1601-21 was repaired and installed, another leak test was conducted with 2-1601-22 blank finnged. This leak test failed. It was then discovered that a hair line crack existed cu the bottom of line 2-6503-6-LX oud umnad L..;,it .ii..all/ at :t an inch int? ! ! "

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2-8503-8-LX is the line used for nitrogen purge of the dryvell and the torus.

DESIGFATION OF APPARENT CAUSE OF OCCURRENCE It is believed that the cause of the occurrence was due to liquid nitrogen reaching both valves. Discussions with the valve nanufacturer revealed that the cracked valve seata exhibited the sace characteristics as ofmilar valve cents removed by the vendor. In order to remove chece seats, the manufacturer has dipped the valves into a vat of liquid nitregen. It is surmised that liquid nitrogen also caused the line crack.

ATALYSIS OF OCCURRENC;F During the occurrence, the safety of the plant and public was not compromiced. Although primary containment integrity had been lost, secondary containment was functional and the standby gas system was operational at the tice of the occurrence. Calculations show that leakage from the primary containment would have been approximately 230,000 scfh.

CORRECTIVE ACTION The i m diate currective cction ms to ini.t tate en crderlf p h r.t 1 shutdown. Uccessary repairs

• are trade c,a tha valves and cucked im. iciw;N approved procedures. Followins repairs, the piping section was leak tested l l

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U August 2, 1974 and found to be within limits. To prevent this type of an occurrence in the future, the nitrogen system is being studied to determine a ceans of preventing liquid nitrogen f rom reaching thece valves. In the cecn time, the low toep-erature alarm in this volur,e has been calibratcd and function tested. Also responsible people have been reminded of the ccaning of and immediate action required upon receiving this alarm. In view of cuculative experience, the corrective action taken was satisfactory.

FAILUltE DATA Concurrently with the Unit #2 occurrence, a similar problem arose

, on the Unit #3 valves 3-1601-21 & 22. It la felt that liquid nitrogen came in contact with these valves also. This is the first occurrence where it is felt that liquid nitrogen damaged these valves.

Sincerely, J

D. B. Stephenson Superintendent E30:1111: do

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