Reactor Cavity

Decontamination Pi t

Spent Fuel Trailer

Plan

Reactor Containment

Fuel Handling Building Crane

Manipulator Crane

GL

Section

Spent Fuel Pi I

Crane

Containment Polar Crane

T

Manipulator Crane

Fuel Transfe Machine

Isolation Valve

Fuel Transfer Tube

Blind Cap

Figure 3.2.6 Fuel handling facilities

4 Loop Plant

2 Loop Plant

3 Loop Plant

Figure 3.2.7 Buildings configurationn of nuclear power plants in japan

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Figure 3.2.8 Variation in buildings arrangement with basic module of reactor building

components during the plant construction, operation and maintenance activities and economy. There may be some contradictions between requirements, as often seen when trying to establish consistency between the operability/ maintainability and the economy of a plant Such contradictions or frictions should be resolved by a synthetic approach harmonizing different requirements. Only a few out of about 600 components of the primary systems are arranged almost automatically; most of them are arranged based on the synthetic design approach to balance design requirements for each component and those for the whole plant, often contradictory to the operability/maintainability.

ii) Detailed requirements of plant layout design

1. Earthquake-resistant building configuration

Hie stability of the buildings should be assured and the floating motion of the buildings should be minimized (the adhesion to the ground should be increased to the given level), even when the buildings are subjected to postulated strong

seismic forces. In configuring the design of buildings, the following requirements should be considered.

(D Lower the gravity centers of buildings, including moving heavy components onhigh elevation floors to lower floors and reducing the thicknesses of concrete of floors at high elevations.

® Enlarge the basements of buildings.

3. Make the shape of basements of buildings as square as possible.

4. Ensure the dimensions of the basements of buildings satisfy their adhesion criteria under severe seismic conditions. In recent plant designs, the reactor building and the annex buildings often have common bases to increase the dimensions of basements.

The trends of earthquake-resistant building configuration designs are shown in Figure 3.2.9.

2. Physical separation

Redundant safety systems should be physically separated to maintain independence between

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shaft is perpendicular to the reactor building, may be selected instead of “T-type“ layout as comparatively shown in Figure 3.2.10.

2. Separation isolation) to minimize the effects of piping breaks

High energy system piping including the main steam and feed water pipings is isolated from other areas by partition walls, and features to relieve pressure in the isolated areas should be considered in the plant design.

@ Separation for radiation protection

The plant areas are categorized into two groups, radiation controlled areas and non­controlled areas, and areas of each group should be separated from other group areas by walls. The highly radioactive components should be contained in rooms with radiation shielding walls. Those areas, where radioactive fluid leakages are anticipated under postulated accident conditions, such as the annulus space and the residual heat removal pump rooms, are isolated from other areas to facilitate effective filtration of the inside air.

5. Protection against flooding

The rooms housing large volume tanks are separated from other rooms with water-tight partitions to protect safety systems located on the lower floors against potential flooding caused by water spilling out of tanks due to their failures caused by earthquakes. In recent plant designs, not only individual systems or components are separated, but also the whole building is divided

Expanding of Foundation Joining of

DG

AB

Expanding of *

Foundation [ Joining of ]

Foundation ’

FHB

RB •

■ DG

Foundation

RB ■ Reactor Building AB : Auxiliary Building FHB: Fuel Handling Building IB : Intermediate Building DG : Diesel Building

-RB‘-

l f

'The Sun Flag” Type

(Medium)

'The Sun Flag” Type

(Large)

Figure 3.2.9 Variation of earthquake-resistant configuration

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into several blocks, and such comprehensive separation of building areas is considered as an effective approach to improve the safety of NPPs. A typical divided block arrangement is shown in Figure 3.2.11.

3. Radiation exposure reduction

To reduce the radiation exposure of plant workers, the following approaches are practiced. (D To minimize the radiation exposure of plant operators during field operation and patrolling.

© To minimize the radiation exposure of workers involved in the assembling or disassembling of equipment during inspection and maintenance work.

In the detailed layout design, the following measures to reduce radiation exposures are implemented along with the above approaches.

(D To provide appropriate access routes.

2. To provide sufficient working spaces, and to install monorails for maintenance work, when necessary.

Trains separated within common blocks

Figure 3.2.11 Divided block arrangement

@ To enhance radiation shielding by laying out each component in a separate room, by providing separate valve rooms, by adding partial shielding walls and by using a labyrinth design for room entrances.

© To clearly identify the radiation controlled areas from the non-controlled areas and to locate non-radioactive components outside the radiation controlled areas.

In a PWR power plant, the most radiation exposure of workers occurs during inspections of steam generator tubes and seal assemblies of reactor coolant pumps. The following provisions are made in the layout design of the latest plants to reduce these radiation exposures.

(D Sufficient spaces are provided to conduct the automatic eddy current testing of steam generator (SG) tubes and dedicated platforms and stairs are provided for this purpose.

(2) Devices are provided to remove the manhole covers of SGs.

© Permanent ventilating equipment are provided around the manholes of SGs.

2. Piping around reactor coolant pumps (RCPs) is properly arranged to provide sufficient spaces for the maintenance and inspection operations of RCPs.

3. Dedicated access routes are provided to allow accesses to the reactor coolant pump areas for pump maintenance.

4. Protection against invaders

(D The outside walls of the buildings up to 2.5 m in height are of concrete.

(2) The number of entrances of the buildings is reduced to the extent possible and solid access doors are installed at those entrances.

©Safety-important areas such as the main control room are designed in a way that they cannot be easily reached by unauthorized individuals.

5. Emergency evacuation provisions

(D Emergency evacuation routes are clearly indicated with proper signs and signals.

(2) Emergency stairs are provided.

© Emergency escape exits to the outside of the buildings are provided.

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