The main targets of the reactor core design are to reduce electricity generation costs and secure reactor safety. Core performance targets are established to realize the main targets. Improvement in power density and fuel burnup, reduction in necessary uranium resources, and extension of continuous operat­ing period are all related to the reduction in electricity generation costs. Security of negative power coefficient and reactor shutdown capability, and prevention of fuel failure are required from the viewpoint of reactor safety. Table 3.4 introduces the basic criteria [4, 5] to be considered in the BWR core design based on its features.

Table 3.4 Main criteria of BWR core design [4, 5]

Design criteria

Self — Designed to assure the inherent negative reactivity

controllability feedback characteristics (negative power coefficients) in the power operating range Reactor Designed to assure the complete core shutdown

shutdown capability even with the most reactive rod

stuck in the fully withdrawn position Designed with appropriate limits of any single­control rod worth and of the control rod speed to secure the core safety against accidental withdrawal of control rods

Fuel failure Designed to assure that at least 99.9 % of the fuel

prevention rods in the core would not be expected to

experience boiling transition Designed to assure that the plastic circumferential deformation of fuel rod cladding due to pellet cladding interaction (PCI) would not be expected to exceed 1 %

Stability Designed to secure the stability without the flow-

induced vibration (thermal-hydraulic stability of channel)

Designed to secure the stability without the power oscillation. (core stability and regional stability)

Designed to secure the stability with enough plant controllability (plant stability)

Designed to secure the stability without the spatial oscillation of power distribution due to Xe accumulation (Xe stability)