ML19095A277

Response to Request for Additional Information on Fuel Handling Accident Inside Containment

ML19095A277
Person / Time
Site:	Surry
Issue date:	03/07/1978
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E, Schwencer A Office of Nuclear Reactor Regulation
References
Serial No. 059/012478
Download: ML19095A277 (7)

Text

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e e VIRGINIA RrcH~OND, VI1,'.GT~ I~ 23261 ffarch 7, 1978 Mr. Edson G. Case, Director Serial No. 059/012478 Nuclear Reactor Regulation PO&H/TAP:dgt U. S. Nuclear Regulatory Commission Docket Nos. 50-280 Washington, D, C. 20555 50-281 Attention: ~fr. Albert Schwencer, Chief License Nos. DPR-32 Operating Reactors Branch No. 1 DPR-37

Dear Hr. Case:

This letter is in response to your letter of January 24, 1978, regarding your continuing review of the consequences of a fuel handling accident inside the contaimnent. (FrL~IC)

We desire to be in compliance with your guidelines in that any systems required to keep the results of an accident within the guidelanes of 10CFRlOO should be Engineered Safeguards Features (ESF). We discussed with your staff that the electrical portion of the purge isolation circuit meets most of the current ESF design criteria, and that efforts have been made to upgrade it to full compliance, .However, we find this is not a beneficial venture in that any further modification to the electrical system will not significantly en-hance its reliability, but further modification would be required to ::ully comply. We have decided not to pursue this modification any further.

Our efforts will be directed toward upgrading the auxiliary building vent-ilation system and its associated filters, dampers and ducting. This will be of benefit to the station.

Our letter of July 5, 1977, shows that with the filters and not the purge isolation circuit, the consequences of the postulated Fuel Handling Accident in Containment is much less than 10CFRlOO. A preliminary system description and analysis of the modified ventilation system is attacned and further information will be made available as it is developed by our architect engineer.

Very truly yours,

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c_{~. .: ., ;. '?- *>_)i:U i{ ;,* c i:.:* _2,,..

t' C. H. Stallings Vice President-Power Supply and Production Operctions Attachment

• - PRELUfINARY e

CONTAINMENT PURGE i-\.;.\/D FILTER SYSTEM SURRY POWER STATION - lJNITS l & 2 VIRGINIA ELECTRIC AND PO,,/ER COMPANY DESCRIPTION The System The containment purge and filter subsystem, which is a part of the total auxiliary ventilation system, consists of a supply circuit and an exhaust circuit.

The supply circuit consists of two 50 percent capacity supply fans (F-4A and B),

powered off the normal station bus, which draw outdoor air through low efficiency roughing fi.lters and a heating coil, if required, and deliver the air to the con-tainment through ductwork and two isolation butterfly valves. The valves are seismic and powered off the normal station bus. The valves are norm.ally kept closed except during unit shutdo*,m when they are opened for ventilation, heating, and purging.

The exhaust circuit consists of ductwork and t*wo containment isolation butterfly valves connecting to the ESF filter trains through two isolation trip dampers in series. The butterfly valves are seismic and powered off the normal station bus.

The manipulator crane monitor and the containment gas and particulate.monitor are wired to close the butterfly valves on a high radiation signal.

The ESF filter train system to which the purge exhaust circuit connects, consists of two 36,000 cfm trains, each train consisting of roughing filters, HEPA filters, charcoal adsorbors, and a fan (F-58) which discharges through a stack in the wake of Unit 2 containment. The design flow condition for the filter trains is a LOCA when the exhaust from the safeguards building of the unit with the LOCA and the exhaust from the cubicles of three charging pumps are drm,m through the filter for treatment of ECCS leakage. The fans, filters, ducts, and isolation dampers are seismic. The fans are powered off the emergency buses; one fan off Unit l orange bus, the other fan off Unit 2 orange bus. (orange= H Bus/purple - J Bus)

The two isolation trip dampers in series connecting the purge exhaust circuit to the ESF filter inlet header are air operated (AOD), designed to fail ~n the closed position on loss of air.

Compressed air is supplied to the AOD's either from the station compressed air system (QA Category II) or through redundant QA Category I compressed air accumu-lators sized to store sufficient air to keep the dampers open for two hours.

Compressed air is supplied to each A.OD through two 3-wey solenoid-operated valves (SOV) piped in series. The power supplies to the two SOV's of the orange AOD are from Unit l orange and Unit 2 orange buses. The power supplies to the two SOV's of the purple AOD are from Unit l purple and Unit 2 purple buses. De-energized SOV' s direct compressed air to the AOD to open. Errergized SOV' s ven*t compressed air *from the AOD to close.

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• - 2 e

The fuel building exhaust circuit is connected to the ESF filter L71let header throug:-,

two isolation trip dampers in a manner identical to the purge.

Operation

1. Normal ?o"'er Generation 2.ncl Clean Fuel Building_

buring ~or2al Station Ooeration The containment purge system (RC) is not in operation, and the fuel buil~ing (F) .is exhausted 2.t 35,000 cfm by the nom,al exhaust fans (F-7A and .B) bypass-i~g the filters. The isolation trip daQpers of both the ~C and F streams are kept closed by energized SOVs.

2. Nor~al Power Generation and Conta~inated Fuel Building I£ radioactivity levels within the fuel building require th_e filtratior. of the F stream, the SOVs ot the isolation trip dam~ers of the F stream are de-energiz2d by a hand selector switch (HSS). This supplies conpressed air to the AODs which open. The F stre.ar:i is drawn through the filters :>y the filtered exhaust fans.

A LOCA signal in unit 1 (or Unit 2) will override the iiSS and eri..ergize the SOVs which vent the compressed air- f:::'om the AODs. The AODs fail closed and allow the filters to treat the air exhausted from ECCS equipment areas. If one AOD does not close, the other one in series will. If a Unit l (or Unit 2) orange SOV does not vent the orange AOD, the Unit l (or Unit 2) purple SOV will vent and close the purple AOD.

3. Unit l Purging Prior to Refueling - Unit 2 On-Line During the shutdo,;m of Unit 1 and prior to refueling, the purge air exhaust strea~ (RC) is routed through the filters. The S0Vs of the isolation trip dampers of the F.C stream are de-energized by an HSS. This supplies compressed air to the AODs which open. The RC stream is dr~m at 30,000 cfn through the filters by the filtered exh2.ust fans.

A LOCA signal in Unit 2 will override the HSS and energi~e the S0Vs which vent the compressed air from the AODs. The AODs fail closed and allow the filters to treat the air exhausted from ECCS equipraent areas.

If one AOD does not close, the other one in series will. If the Unit 2 orange SOV docs not vent the orange AOD, then Unit 2 purple. SO\' will vent and close the purple AOD.

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3 4, Unit 1 Refueli~g - Unit 2 On-Line Before starting Unit 1 refueling, both the RC and F strear.1s are aligned through the two filters. The S0Vs of tht::! isolation trip da::ipers of both the RC and F streams are de-energized by HSSs. Then, power to the SOVs is rer::oved from the control roo;r... 'I'he de-energized SOVs supply compressed air to the AODs which open, Iloth the RC and F streaus are drawn through both filtE!rs by the two filtered exhaust fans.

The *capacity of the filtered e:(haust fans l-VS-F-58A and B is auto;;,atically controlled by pneu7,tatically oper2.t<2d inlet vanes to draw the desig:i flow rates. The fatl inlet vanes are arranged to fail in the wide O?en ?OSition on loss of compressed air.

A refueling accident inside the containment or the fuel builcing will leave the system alignment unchanged, allowing filtration of the exhaust of both buildings through the two filter trains. Loss of station compressed air will not terwinate filtration of the refueling accident puff release, since the compressed air accumulators are sized to keep the isolation trip dampers open for two hours. Loss of station compressed air will reselt in loss of fan capacity control, .With inlet vanes wide open, the fans will draw the F and RC strear;1s at a higher rate than tC'.eir respective d2.sign rates but no higher than filter design capacity.

No single active failure can close the isolation trip d2s,pe::::s since there is no required mechanical move..'Tient of a component.

No passive failure in the short ter-m (two hours) is postulated to close the isolation t~ip da~pers.

No spurious signal can close the isolation trip dampers since the S0Vs are de-energized and electrically disconnected from the control room.

Failure of an emergency bus cannot close the isolation trip dampers since the SOV~ are already de-energized, Loss of a filter train (whet~,er <lL1e to loss of an emergency ous, fari, or fan back~draft damper) will trip the fans (F-4, F-6, and F-39) of the venti-lation supply air systems of both the containment and the fuel building.

This will leave one filter train to exhaust and treat the air from both buildings at a lower rate than design. It will also prevent overpres-surization of the two buildings,

e Compliance with FSAR Criteria for Engineered Safetv Features The engineered safety features of the ventilation system, modified as described above, for mitigating the consequences of a refueling accident meet and exceed all the safety criteria established in the FSAR.

Compliance with NUREG-75/087 Criteria for Engineered Safety Features The engineered safety features of the ventilation system, modified as described above, for mitigating the consequences of a refueling accider_t meet all the safety criteria of the NRC Standard Review Pla:i. NUREG-75/087, except.Regulatory Guide 1.52, referenced in Standard Review Plan 6.5.l as listed below.

LIST OF NONCONFORl-L~..1\TCES TO THE POSITIONS OF REGULATORY GUIDE 1.52, REVISION 1

1. C. 2 .a ..: The filter trains do not include (a) demisters, (b) HEPA filters after-absorber banks, and (c) heaters.

2. C.2.b - The filter trains are not protected from missiles generated by natural phenomenon (tornado).

3. C.2.f - Each filter train is 36,000 cfm. However, the fil.ter banks are 3 HEPA filters high.

L~. C. 2. i - The filter trains are not designed for replacement 2.s an intact unit or in a minimum numb.er of .segmented sections without removal of individual components.

5. C.2.k - Filter ductwork was designed to exhibit on test a leakage rate of approximately one percent of system flow.

6. C.3.c - Prefilters neither meet the UL Class 1 requirements nor have a minimum efficiency of 40 percent dust spot.

7. C.4.c - No space is provided between upstream HEPA filter and adsorber mounting frames for personnel access.

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s. c.5.c The station technical specifications require in-place DOP tests on HEPA filter banks to have 99.0 percent efficiency.

9. C.5.d The ste.tion techr1ical specifications require in-place halogen tests on adsorber banks to have a 99,0 percent etr1c1ency.

10. C.6.a,J - The station technical specifications require laboratory testing of sainples of used activated carbon to have methyl iodide removal efficie-ncy of 95,0 percent at 25 C and 85 percent relative humidity, REASONS 1.IHY IT IS NOT ::ECESSt,r.Y TO RECTIFY I,ONCOUFOR:1A1:TCES LISTED ,\BOVE Item l(a) - There is no potential for entrained water droplet*in exhaust air

• • str_eams durin.g a .. refueling* accident.,.

Item l(b) - The release of radioactively contaminated carbon fines from the adsorbers to the en~ironment is not a station design assuDption, Omission of dmmstream HEPA filters is, therefore, not an unreviewe.d safety question.

Item l(c) - Control of relative. huii!idity is not required for the low (less than 70 percent) ~ethly iodide removal efficiencies used in the refueling accident analysis.

Item 2 The filters and ventilation systec citigate the consequences of refueling accidents in two hours before long-te.rra natural phenom2non, such as tornadoes, could take place.

Item 3 This nonconforru.ance does not affect system safety functiort, Cutting the ESF filter system into segments without removal of indi-

• ~vidual components exposes the local environment and the personnel

\.;orking in it to unnecessary co;1ta~ir..atio11~  ;,J}1en components are individually removed for packagin8, shieldb.g, and shipment, operator exposure is minimized. After all components are removed and the hous-ing has been 'dashed dowa, it is then determin:2d whether the housing has been satisfactorily deconta~inated for reuse or whether cutting for shipment and burial off site is required,

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6 Item 5 Since leak.age is into cluct_,.r'iork., contamination of personnel is not a proble,n.

Item 6 The combustible material containe~ in the prefilters is insignificant

'(less than 10 percent) in. cor:rparison ,;;ith the ch;:ircoal in the adsor':)e.rs.

The lo~.J efficiency prcfilter-s m2~2ly shorten the life of the l-1...EPA fi.lters; they do not affect system safety function.

lter.l 7 The lack of access space between the HEPA filter and adsorber-rnounting frames makes in-place testing less conv2nient. It does not affect the system safety function.

Item 8 Since dose calculations take credit for 70 percent in particuL1te removal efficiency, in-place DOP testing to 99.0 percent represents a factor of safety of 30.

Items 9 The in-place halogen test of 99 percent efficiency coobined with the and 10 laboratory analysis of charcoal sa~ples at 95 percent methyl iodide removal efficiency, at 85 percent relative humidity, provides sufficient conservatism in fuel-handling accident dose calculation ~hich takes credit. for 70 percent methyl iodide re::',oval efficiency with no restrictions o:i rel2.tive hunidity,