Figure 3.4 shows the procedure followed in BWR core design. The fundamental specifications of a power plant such as reactor thermal power and operating pressure, and the main specifications of the core design such as shapes and numbers of fuel assemblies are established in the first step of the core design (Table 3.5). Next, the fuel rod design for a reactor operating period and a target fuel burnup is performed regarding fuel rod size and fuel enrichment, and the scheme of excess reactivity control is specified. The detailed design of fuel assemblies is determined based on the fuel rod design and the excess reactivity control scheme. Then, the fuel loading and refueling pattern is treated consid­ering power and burnup distributions, and an outline of the control rod insertion and withdrawal pattern during reactor operation is framed for reactivity and power distribution control. Core characteristics are evaluated for the reactor core, fuel assembly, and operating scheme mentioned above by using various nuclear and thermal-hydraulic coupled core analyses. This sequence of steps is repeated to determine core specifications which meet the core design criteria and target.

Table 3.5 Main design specifications of BWR (1,350 MWe-class ABWR)

Reactor thermal power Reactor pressure (at RPV dome)

Steam flow rate

Steam pressure

Steam temperature

Core Active height

Equivalent diameter Core flow rate Core inlet subcooling Core outlet average steam mass Core power density Fuel Specific power

Fuel loading amount No. of fuel assemblies