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1 FACIFIC GAS AND ELECTR.IC COMPANY FO'F3
-y-77 aEA.E 57REET. 31ST FLOOR. SAN FR AN CISCO. CALIFORNI A 94106 (415) 781 4211
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March 27, 1978 Mr. R. H. Engelken, Director Office of Inspection and Enforcement Region V U.S. Nuclear Regulatory Cc:=issica 1990 N. California seulevard
'rlalnut Creek, California 9h596 Re: Docket No. 50-133 License No. DPR-7
Dear Mr. Engelken:
In respcuse to your letter dated February 8,1978, which enclosed I.E. Bulletin No. 78-03 regarding pctential explosive gas =1,cture accu =ulaticas associated with MTR off gas system operaticns,,ve hereby infor= you of the results of our review and our plan of action.
1.
" Review the operatiens and =nintenance procedures related to the off gas system to assure proper cperatica in accordance with all desien parameters.
Include in this reviev measures you have taken or vill take to prevent inadvertent acticns (such as are strikes ) which ='.qM caus e isniticn of the mixture of gases centained in the off gas pipin.t".
The augnented off gas system (recc=biner and charcoal beds) is in the last stages of construction. Maintenance and operation procedures related to this sys tem have not yet been prepared by the p1snt staff.
The i
procedures will be prepared including the guidance of the I.E. Sulletin and will be available prior to operatica of.the system.
Procedures for the existing off gas holdup system are vritten to assure proper operaticn. There has neven been an off gas system explcsien in the operating history of the unit.
Our general velding centrol procedure centn N cautiens regarding centrol of potential explosive at=cspheres.
'N 8301100154 821207 l
l HIATT82-545 PDR l
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j Mr.'R. H. F.ngelken March 27, 1978 j
To ensure identification of areas. and systems which could contain an explosive atmosphere resulting from off gas system operation, a list of these areas and systems will be prepared and included in the appropriate procedure. With this change,.our procedures will be adequate to minimize the potential of inadvertent acticas which might cause ignition in the off gas syste=. Markings warning of an explosive mixture have existed since initial plant operation for the mad.n off gas holdup pipe. Additional signs or markings will be added where appropriate.
- 2.. " Review the adequacy of the ventilation of spaces and areas through which off gas system piping centaining exolesive ~4vtures of gases pass.
The review sbould ccnsider ventilation lesses and off-nor=al off gas system operatien, such as lack of dilution, steam, lest loop seals, blev rupture disks, bvuassing recombiners, and leakage of off gas into isolated portions of sys tems. "
The augmented off gas system described under Item 1 above will be reviewed for the adequacy of ventilatica and the need for monitoring equipment to warn i
of the accumulation of explosive gas mixtures. Any required modifications will be made prior to operation of the system.
3 "For those scaces and areas identified, describe what action you have taken or plan to take to assure that explosive mixtures cannot accu =ulate, that monitoring eculpment will warn of such an accumulatien, and that disposal of such mixtures will be centrolled without resulting in a damaging exclesion."
See Item 2 above.
4.
" Loop seals are cotential off gas leakage pa-ts following a cressure transient in the off gas system tiping.
Describe your design features to minimice and detect the less of licuid from loop seals 'and describe, e::egating procedures which assure prc=ot detection and re-seal of the bict lgep seals."
All loop seals in our off gas system are normally isolated or discharge to a drain trap during periods when significant H2 generation occurs. These crain traps discharge to the main ccadenser.
Thus, during normal operatien, there is no potential for leakage to atmosphere through icep seals and detectica of b1cwn loop seals is not required. During Unit startup, the loop seals are valved to discharge to the turbine building drain tank (TBDT). The TBDT is vented directly to the ventilaticn system; thus, as 1cng as the drain system to the TBDT is a closed line, there is no potential for leakage due to blown loop seals. The effected drain. line will be reviewed.
If any open drains are found, corrective actica will be taken to e1% ate the cenditica where equipment confi urations permit, or appropriate procedures will be developed 6
to reduce the probability of off gas related explcaiens.
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" Review coerating and e::.crgency procedures to assure that ycur coerating
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staff has adecuate cuidance to respend croperly to off gas system exclcsions."
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t Mr*.~ R.' H. E::gelken March 27, 1978 Procedure preparation for the augmented off gas system is described in Item 1 above. The procedures.will provide guidance for responding to off gas system explosions.
Very truly yours, Philip A. Crane, Jr.
cc:
ector, Office of Inspection. and Enforcement U.S. Nuclear Regulatory Com.issica Washin6 ten, D.C. 20555 b
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