2. Plant Layout

1. Plot Plan

A plot plan is the overall arrangement of power plant facilities including main building, intake and discharge structures, exhaust stacks, harbor facilities, station roads, piping conduits, electric cable conduits, and construction facilities, to be in the most functional manner.

The plot plan aims to achieve the most economic arrangement of the plant while satisfying the required functions consistent with the site conditions including its natural conditions such as geographical structure, general environment, shoreline, and meteologic and hydrographic conditions. The major items of concern are listed below. It must be noted that all Japanese NPPs are located on a seashore and the discussions that follow are based on this condition.

1. Grade level planning

The NPP site must be at a distance from populated areas and because of a need for a plentiful supply of cooling water, near the sea. The leveling of the site for the in-plant facilities requires investigation. Based on the geology and geomorphology, as well as the ground surface and seabed contour map of the site, locations of the main buildings are determined with considerations for oceanographic conditions (such as wave height and tide level) and depth and distribution of the bedrock foundation. Future expansion plans are also considered in determining the layout of the main building. The grade level is determined by considering the balance between the areas to be leveled (including the area used during construction), the amount of hill excavation, the amount of excavation for the main building embedments, and the amount of land fill necessary within the site. Depending on the site conditions, either a uniform single level ground or a multi level ground is adopted.

2. Configuration of the buildings

The final building configuration is determined based on the plant capacity, type of reactor, component layout inside the buildings and their seismic considerations together with functional requirements of yard facilities. In determining the

final building configuration, it is also important to optimize the entrance for large equipment, grade level, bedrock level and the foundation depth in relation to the seawater inlet and outlet levels. It is also generally advisable to design the buildings to be symmetrical with a simple outline vertically and horizontally so that the buildings will be stable seismically and structurally.

3. Road planning

In addition to normal access road to the site, it is necessary to plan roads from a harbor (usually exclusive to the nuclear power plant but sometimes the nearest conventional harbor facilities) for the transfer of large heavy equipment during the construction, including reactor pressure vessel, steam turbine, generator, main transformer, and later, spent fuel casks during the refueling outage. Access roads to main buildings and local roads around them are also planned. When the site has a multi level ground, considerations should be paid to secure appropriate slopes and areas for transporter and roller transfers as well as for anchor block positioning.

4. Pipe conduits and electric cable conduits planning

The NPP needs a huge amount of circulating water as a condenser coolant which passes through a piping system with a diameter of 3-4 m and the routing of such a large piping system needs careful planning from the early stage of the plant layout planning. Since the building air ventilation system needs a large diameter duct, its routing and the location of the exhaust stack must also be considered. For those piping systems that are seismically important, such as the reactor auxiliary system cooling sea water piping, diesel fuel oil piping, and emergency gas treatment system piping, their support foundations may have to be located directly on the bedrock and their routing in relation with the main building will have to be considered. An oil filled cable between the main transformers and the high voltage switchyard is contained in a square concrete duct of 3 to 4 m in cross section and its routing must be the shortest route considering the relative location of the main buildings, the main transformers, and the switchyard as well as the

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NSRA, Japan