ML20104A850

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Sys 80+ Design Certification PRA Flood Protection Assessment
ML20104A850
Person / Time
Site: 05200002
Issue date: 09/02/1992
From:
ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML20104A838 List:
References
NUDOCS 9209140189
Download: ML20104A850 (6)
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ABB COMBUSTION ENGINEERING NUCLEAR POWER COMBUSTION ENGINEERING.1NC.

U. S. DEPARTMENT OF ENERGY ADVANCED LIGHT WATER REACTOR CERTIFICATION PROJECT SYSTEM 80I" DESIGN CERTIFICATION PRA FLOUD PROTECTION ASSESSMENT t

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e i PRA FLOOD PROTECTION ASSESSMENT

The System 80+" btandard Plant includes a number of design features which provide flood protection to safety-related structures, systems, and components. These flood protection measures are designed in accordance with Regulatory Guide 1.102, " Flood i Protection for Nuclear Power Plants."

The System 80+" design emphasizes the elimination and minimization of potential flood sources within safety-related areas as a means of flood protection. For example, s*ation service water and component cooling water heat exchangers are located outside the Nuclear Annex, Water-cooled components within the Nuclear Annex are cooled by Component Cooling Water with the exception of HVAC

equipment which is cooled by chilled water syr e 's. These cooling water systems are closed systems !th a defi rolume of water.

Component Cooling Water, Emergency Feedwate sential Chilled

water, etc. are fully separated by division . .h no-open cross connections, thus eliminating the possibility of a single pipe 4 break from flooding one division and the other division being lost due to loss of pressure boundary integrity. Condenser circulating water is also located outside of the Nuclear Annex. These features reduce in-plant cooling water to a limited volume which can be easily accommodated to limit the extent'of flooding.

i The System 80+" control complex is protected from flooding in that no water lines are routed above or through the control room or computer room. Water lines routed to HVAC air-handling units, etc., around the-control room are contained in rooms with curbs which prevent any potential water leakage from entering the control room or computer room.

Protection from external flooding-is provided by elevated building entrances. Secondary flooding sources located in the Turbine Building are confined to that building. Entrances from the Turbine Building ;' the Nuclear hnnex are sufficiently elevated to allow operator uction to isolate a break in the Condenser Circulating

' Water System before the water level from the Turbine Building flood reaches the Nuclear Annex entrance.

Lengths of high energy and moderate- energy piping have been minimized by equipment location. Equipment is located in quadrants around the spherical containment to minimize the lengths of piping runs. The subsphere_provides further close proximity of equipment to reduce piping runs from containment.

Flood barriers have been integrated into the design to provide further flood protection while minimizing the impact on maintenance accessibility. The primary means of flood control in the Nuclear Annex is provided by the structural wall which serves as a barrier-between redundant divisions of safe shutdown systems and Page 1 of 3

i components. At the lowest elevation, this structural wall contains no doors or passages, and the limited penetrations through the wall-are sealed. This design confines floodwater to one division up to elevation 70+0. Migration of- floodwater to the _other division would begin only after the water level in the flooded o vision reaches elevation-70+0. Preliminary determination of major flood volumes such as the Component Cooling Water and Emergency Feedwater-Systems show that the volume of water contained in one division of these systems would not rise above elevation 70+0 should a large uncontrollable break occur. Thuc, the other division is unaffected.

Each half of the subsphere is compartmentalized to separate

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redundant safe shutdown components to the extent practical, while maintaining accessibility requirements. The subsphere, which houses the front line safety systems is' compartmentalized into quadrants,.with two. quadrants on either side ot the - divisional structural wall. Flood barriers provide separation between the quadrants, _wnile maintaining equipment removal- capability.

Emergency Feedwater pumps are located in separate compartments-within the quadrants with each compartment protected by flood-

'd barriers also provide ~ separation between

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barriers.

electrical equn. tent and_ fluid mechanical systems at the lowest elevation within the Nuclear Annex. Elevated equipment pads prevent equipment from being inundated-in the event of flooding.

Flood protection is also integrated into the floor drainage systems. The floor drainage systems are-separated by division and Safety Class 3, Seismic Category I valves prevent backflow of water to areas containing safe 2y-related . equipment . Each subsphere quadrant contains its own separate sump equipped - with : redundant safety Class 3, Seismic Category- I: sump - pumps and associated.

instrumentation. These pumps are _ also powered u 3 the diesel-generator in the event of loss- of offsite power._ The Nuclear- Annex also has -its own divisionally separated = floor drainage ' system, having no common drain lines between divisions. Floors are gently =

sloped to allow good drainage to ; the; divisional . sumps . Floor drains are routed to the lowest elevation to prevent flooding of the upper elevations. The lower elevation in each division has -

adequate volume t.o collect water from a break in any ' system withoutL

-flooding the other division. In addition, potential discharge'of fixed fire suppression systems and fire. hoses is_ considered'in-the

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sizing of floor drains to preclude flooding of. areas should the fire protection systems be-initiated.

The Diesel Generator Building floor drain sump pumps and associated- -

instrumentation are-Safety Class 3, Seismic Category-I'to prevent flooding of the diesel generators. _These pumps are.also powered from the diesel generators to: accommodate-a loss'of offsite power.

Flood protection is also incorporated into.the Component _ Cooling-Page 2 of 3 l

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Water Heat. Exchanger Building and Station Service Water' Structure.

i These structures are divisionally' separated by walls such that'a

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- flood in one division cannot flood the other division.

! In addition to the -- above design features, the_Nuc' lear Annex-and l Reactor Building are designed to ' maintain a dry environment during-F all floodc by inccrporuting the following safeguards into their- ,

i construction:

i A. No exterior access openings will be lower than 9" above

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plant grade elevation.

j B. The finished yard grade _ adjacent to the safety-related"

structures will be maintained at least 9" below the_

l- ground floor elevation.

1 i C. Waterstops are used in all horizontal and vertical

construction joints in all exterior walls up to flood 4 level elevation. -
4. .

t e D. Water seals are provided .for all penetrations in exterior.

walls up to flood level elevation.

l E. Waterproofing of walls subject to flooding is provided.

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