Fuel assemblies

Purpose: To improve reactor safety by disposing a guide box with a gap above an upper tie plate and higher than a channel box to thereby increase the flow amount of spray water upon reactor accident and increase the cooling rate for the fuel assemblies. Constitution: A guide box is provided by way of a spacer to the inside of a channel box and above an upper tie plate. The guide box is fabricated from a thin plate about 1 mm thick and disposed higher than the channel box so as to separate spray water from blowing-up steam flow. Upon loss of coolant accident, most of the spray water enter the gap outside of the channel box and arrive at the upper end face of the box in a short time, pass through the gap between the guide box and the channel box and flow into the upper surface of the upper tie plate to effectively cool the peripheral portion of the fuel assemblies. This can increase the cooling effect for the entire fuel assemblies, as well as suppress the temperature rise in the fuel rods. (Seki, T.)