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(Note)

Approximate use changes depending on site conditions, such as plant power, climate conditions, and system capacity of radioactive waste treatment systems, in addition to the plant operating status and season.

  1. Design philosophy

  1. Air supply starts from clean areas. The pressure of clean areas is kept higher than contaminated (or possibly contaminated) areas. The exhaust air is discharged from contaminated areas.

  2. The exhaust air from contaminated areas is discharged from a stack after passing through the filter.

  3. The equipment which must be stopped for maintenance should have standby units.

  4. The temperature of such areas as the main control room where operators stay is controlled

to maintain a pleasant environmental condition for operators’ comfort. The temperatures of other areas are maintained to operate equipment normally. Hie cooling water and heating water are supplied to control temperature.

  1. Ventilation rate is defined according to the environmental condition of the working areas. These areas can be divided into the rooms where the operators stay for a long time, the areas to be accessed frequently, and other areas.

  1. Key equipment

NSRA, Japan

2-114

Chapter 2 Systems of BWR Nuclear Power Plants

Figure 2.11.3 Outline of house boiler system (example of heavy oil boiler)

primary containment vessel (PCV)

Figure 2.11.4 Outline of the compressed air supply system

2 115

NSRA, Japan

Table 2.11.3 Examples of compressed air uses or users

Item

Approximate use (NmVmin)

Main uses or users

Remarks

IA

5-8

•Air operated control valves

•Air operated instrumentation equipment

•Air operated piston valves

• Amount of use is almost constant

SA

10-20

■SLC tank mixing

•Back wash of filter demineralizers in the condensate water, CUW, and FPC systems

  • Condensate demineralizer resin mixing

  • Off-gas system off-gas ejector operation •Equipment purge and air line mask

  • Changes in amount of use are large because of the intermittent use

  • Constant use is relatively small (about 5 Nm3/min)

(Note)

Approximate use changes depending on site conditions, such as plant power and system capacity of uses or users.

  1. Reactor building HVAC system

The reactor building HVAC system mainly consists of the inlet fans, exhaust fans and filters. An outline of the system is shown in Figure 2.11.5.

The contaminated areas are kept at a more negative pressure than clean areas. The inlet air in the building is discharged to the atmosphere from the stack after passing through the filters. The supply and exhaust ducts have isolation valves. When a high radiation dose is detected in the exhaust duct, each isolation valve is shut automatically and the standby gas treatment system starts operation to prevent radioactive gas discharge. The ECCS pump room is cooled by the air cooling system supplied from the emergency power supply to be operated at the time of power loss.

  1. Turbine building HVAC system

The turbine building HVAC mainly consists of

the inlet fans, exhaust fans and filters. An outline of the system is shown in Figure 2.11.6. The contaminated areas are kept at a more negative pressure than clean areas. The inlet air in the building is discharged to the atmosphere from the stack after passing through the filters,

  1. Main control room HVAC system

The main control room HVAC system mainly consists of the air conditioning unit, recirculation fans, charcoal filters and exhaust fans. An outline of the system is shown in Figure 2.11.7. The main control room HVAC provides recirculation and conditioning of air by taking in outside air partially during normal plant operation. During an accident, the outside air is stopped by closing the isolation valves, and the room air is circulated through the charcoal filter. The power supply of this system is changed to the emergency power supply at a loss of the station power supply.

NSRA, Japan

2~ 116