ML20084D216

AO 50-237/75-35:on 750526,explosion Occurred in B Offgas Sys.Cause Not Determined.Load Drop to Minimize Releases Into Bldg Started

ML20084D216
Person / Time
Site:	Dresden
Issue date:	06/05/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
348-75, 6270, AO-50-237-75-35, NUDOCS 8304110003
Download: ML20084D216 (3)

Text

,-

C; nw alth Edis:n ,o ~

fy: .,

j g\,

.~ Nu.onal Ptua. Chicago. unno.s  ! <

• 4 ue >

Addr ep!y to. Post Oft:ce Box 767

/

]-((NO g/

c Chic,ago, lihno;s 50690

, y

. J.# ,

. .i w . L ,.  !

~Ncl/p;/ W q.Als J

s '

Ifra i BBS Ltr. #348-75 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 June 5, 1975 Mr. Ja=es G. Keppler, Regional Director Directorate of Re.;alatory Operatien-Region III U. S. Nuclear Regulatory Cc:=ission 799 Roosevelt Road Glen Ellyn, Illinois 60137 SU RA: REPCRT CP f??!0?2/AL OCCUF3F2:CE PER SECTION 6.6.A 0F THE TECP'!ICAL SPECIFIC /fiIC::3 UNIT-2 CFM13 EXPLOSICN

References:

1) Regulatory Guide 1.16 Rev. 1 Appendix A

2) Notification os Regien III of U. S. Nuclear Regulatory Cc::=ission Telephone: P. Johnson,1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> on Iby 27, 1975 Telegram J. Keppler, 0815 hours0.00943 days <br />0.226 hours <br />0.00135 weeks <br />3.101075e-4 months <br /> on May 27, 1975

3) Drawing Number Report Nu=ber: 50-237/1975-35 -

Report Date: June 5, 1975 Occurrence Date: May 26, 1975

'Pacility: Dresden Nuclear Power Station, Morris, Illinois 60450 IDDRIFICATION OF OCCURRD!CE <

At 1759 hours0.0204 days <br />0.489 hours <br />0.00291 weeks <br />6.692995e-4 months <br /> on May 26, 1975, an explosion occurred in the "B" off-gas system.

CONDITIONS FRIOR TO OCCURED!CE Prict to the occurrence Unit-2 was at a steady-state power level of 742 Wt and 206 We.

DESCRIPTION OF OCCURRD!CE I At the time of the occurrence, recombiner "A" was being cut in to the off-gas train. The aparging air comprecoor had operated since 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> with valve Ao 5430A open. Following procecuro, the operator cut in the steam supply on recombiner preheaters "A" & "B" and the "A" booster air e,jector and outlet l 8304110003 750605 g - 7']i i ~

PDR ADOCK 05000237 S PDR

r Mr. Jame] G. K d cr 2- p Juna 5, 1975 V

While atte=pting to apply the sparging air, the operstor discovered that the sparging air supply header was full of water. Js he was draining the header, the centrol rcen called, advising that the preheater inlet pressure stood at 15 psig. The operator then opened T,he reccmbiner outlet 5499-72A approximately SC5 as the procedure specified. Mien the control room notified him of a decrease in pressure, the operator returned control of the pressure to the sparging air flow controller. After roughly three minutes the explosion occurred. The following alams antunciated:

1. "B" off-gas system flow hi/lo slam

2. Off-gas filter hiAP 3 SJAE liquid drain hi level

4. Recocbiner-pressure drain tank hi-hi level The chimney gas activity conitors indicated an increase in activity while the off-gas flow monitors showed a decreased flow. Activity in the "B" SJAE room increased irclediately.

DESIGNATION OF APPAPR.'P CAUSE OF CCCURPS!CE No definitive cause of the explosion can be determined. A check of the recombiner system valving chowed that the preheater inlet and outlet manual drains on both trains were closed. These valves should have been open.

This blockage probably caused the 15 psig in the piping. All other valving was nomal. It appears unlikely that the recombiner system caused the explosion.

All filters in the off-gas train (including filter "A", which was in service when the explosion occurred) were securely grounded when they were installed.

ANALYSIS OF OCCURPS.'CE l

The safety of plant personnel and the public was not jeopardized as a result of this occurrence. Tne ntpture diaphraps relieved the pressure as designed.

All contamination was confined to the "B" SJAE room. A load drop was irrediately l

initiated to minimi ze any conh"inant releases. Damages were limited to the rupture diaphrag:n and the off-gas filter.

A subsequent DOP test on June 3 showed that the "A" off-gas filter did not pass the test and was probably damaged by the explosion.

1 i

' The estimated mimm off-gas activity during this. time was' about 1400-1500 pCi/sec. The off-gas spike lasted approximately one hour. The environmental contractor was requested to take soil and water samples in the surroundirJ3 area to verify that no outside contamination resulted from this explosion.

CORRECTIVE ACTION The imediate corrective action was to start a load drop to minimize any releases into the building. "A" SJAE was placed in service by 1805 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.868025e-4 months <br />.

-> Jun3 5, 1975 Mr. James G. Kcppler 0 0

• ' The lead drop was halted at 1820 houra r.t 115 Wo. At 1830 all valves that had been opened while cutting in "A" recombiner were closed. At 1900 the "B" off-gas filter was placed in service. At 1940 hours it was confimed The "A" recombiner was sub-that the "B" SJAE rupture discarasm was blown.

sequently cut in with no problems.

Evaluation of the incident by the station will continue. Should any new information develop indicating the cause of the incident or preventative action, a follow-up letter wa.11 be sutznitted.

FAILURE DATA The "A" off-gas filter is a grounded filter housing assembly, canufactured by the MSA Research Corporation. Si=ilar explosions resulting in filter failures occurred on Unit-2 March 27, 1973 and on Unit-3 February 20, 1974.

\

3d%%k.\

c- B. B. Stephenson" Superintendent BBStamp File /h'RC I

S 0 I

l l

-"' - . , _ , - , _ . . _ _