Reactor operation method

Purpose: To reduce construction cost and improve reliability of the operation of the spectral shift reactor. Method: The fuel assembly is composed of ring fuel rods, and both inside and outside of the fuel rods are the primary coolant flow paths. During its lifetime from the early stage to the middle, the flow rate at the inside path is regulated, the inlet temperature is set high and the coolant in the inside path is vaporized. During its lifetime from the middle to the end, the inlet temperature of the coolant is set lower than the previous one, the coolant in the inside path is changed to water and the water-to-fuel volume ratio is changed during its lifetime period to give the spectral shift effect. Since this effect can be achieved by decreasing the coolant temperature by about 10 - 20 deg C and any mechanical equipments or chemical processing facilities are not required, this method is of high reliability and enables cost reduction. The reactor core's effective multification factor or its reactivity increases for various kinds of burnup, which contributes to fuel cycle cost reduction. (Kamimura, M.)