ML20084R853

AO 50-249/74-34:on 741109,while Placing Offgas Recombiner 3A in Svc,Air Ejector Rupture Disc 3A Failed.Caused by Detonation of Offgas Which Occurred When Recombiner Outlet Valve 3A Was Opened.Steam Jet Air Ejectors Changed

ML20084R853
Person / Time
Site:	Dresden
Issue date:	11/19/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084R855	List: ML20084R853 ML20084R858
References
830-74, AO-50-249-74-34, NUDOCS 8306150629
Download: ML20084R853 (2)

Text

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$?.3 Ltr.gc 3-74 Drceden Nuclear Power Station R. R. #1 -

k rris, Illinois 60450 Nove ber 19, 1974 . ,N y-

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Mr. James G. Keppler, Regicnal Director

• fe, Directorate of Regulatory Operations-Region III , , 'JJ U. S. Atc=ic Energy Cc:rission r 799 Roosevelt Road Glen Ellp, Illinois 60137

SUBJECT:

RFFORT OP EM01"tL OCCURRE:CE PER SIETION 6.6. A OP THE TECRNICAL SFECIFICA?!C::S UNIT 3 A AIR EJECTOR RUP!"JRE DISC FAILURE

References:

1) Regulatory Guide 1.16 Rev.1 Appendix A

2) Notification of Regica III of AEC Regulatory Operations Telephone: It. P. Johnson, 0345 hours0.00399 days <br />0.0958 hours <br />5.704365e-4 weeks <br />1.312725e-4 months <br /> on November 11, 1974 Telegram: 16. J. Keppler, 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br /> on November 11, 1974

3) Drawing Nu=bert M-371 Report Nu=ber: 50-249/1974-34 Report Date November 19, 1974 Occurrence Date: Novc=ber 9, 1974 Facility: Dresden Nucicar Power Station, Morris, Illinois IDE7PIFICATION OF OCCURRE CE Failure of Unit 3 "A" air ejector rupT,ure disc.

1 i CONDITIONS FRIOR TO CCCURRE:CE i

Prior to the failure, the 3A off gas recombiner was being placed in service.

The unit was in the run =oce. At the time of the occurrence, the unit was at an electrical load of 190 megawatts, and thercal power was approximately 600 megawatts.

DESCRIPTION OP OCCURREJCE At approxir.ately 0720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> on November 9,1974, the 3A off gas recombiner was being placed in service. 'ahile the reco=biner was being valved in a 6D*h -

8306150629 741119 PDR ADOCK 05000249

[#P 11323 g PDR COPY SENT REGION h

=co G. Ecp r Novc=ter 19, 1974 I

noise rece-bline a ;.ter P cr or a detenaticn was heard. Shortly after -

this incidcnt occurred, at i.c i:,a activity started to increase, and vacuum began to drop. Nring the investicaticn of the increase in stack gas activity, stcar:2 Jet air ejector 5 Las placed in service and steam jet air ejector 3A was valved out. After the steam jet air ejectors were changed, vacuum con-tinucd to decrease t.na :.t toca=c neccccary to ranually trip the turbine.

Follcwing the turbine trip, a reactor scra= occurred. The subsecuent investi-saticn revealed that the noise that was heard was not a water hr.:=er but a detenation in the off gas systc=. Upon further investigation it was found that the 3A off gas filter was da= aged, and the 3A air ejec+Ar rupture disc was blown.

DESIGNATICN OF APPARE.? CAUSE OF OCCU'E CE (Design Deficiency)

It is believed that the detonation of the off gas occurred when the 3A recom-biner outlet valve was opened. When the recombiner outlet valve ca=e off

. the closed coat, a spark may have occurred which caused the detonation.

AIU. LYSIS OF OCCL?E;CE During and after the explosion, the safety of the plant and public was not in jeopardy. At no ti=e during or after the off gas explosion was the Technical Specificaticn release li=it of 700,000 uOi/sec. exceeded. It was calculated that, for a two hour period, the release reached approx 1=ately 640,000 uCi/ cec. Alco, prelit-Hnary isotopic analysis results were perfor=ed on upwind, downwind, and soil and grass sa=ples which were collected on Novc=ber 10, 1974 The results indicate no radionuclide concentration attri-butable to this occurrence.

CCRRETIVE ACTICN The ir=cdiate corrective action taken was to change over steam jet air ejectors, and initiate an investigation into the probic:2. Following the reactor scram, the stec= Jet air ejector rupture dise was replaced and the 3A off gas filter was icolated.

PAILURE DATA In regards to off gas explosions, there were no previous failures in which the new off gas system has been involved. One previous failure on Unit 2 which occurred on March 27, 1973 was due to a detonation by welding oper-ations in the off gas filter area.

Sincerely, i

v b b l

N.B.Stephenson 0 Superintendent i BBS TEL:do )

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