FUEL ASSEMBLY, CORE, AND OPERATING PROCESS OF WATER-COOLED NUCLEAR REACTOR Russian patent published in 2003 - IPC

FIELD: nuclear power engineering. SUBSTANCE: proposed invention relates to water-cooled reactor cores, their fuel assemblies incorporating fissionable fuel, and their operating process. Fuel assemblies are built of fuel rods; at least one fuel assembly is meant for raising water-to-uranium ratio by end of nuclear fuel life period by minimum 2%. Width of gap between fuel rods is between 2.0 and 2.75 mm. Relative pitch of their spacer grids (ratio of distance between fuel-rod centers to their outer diameter) is 1.1 1.5. Fuel assembly also has absorbing rods or displacers that can be extracted or their volume or sectional area can be changed by end of fuel life period. Washers fitted between fuel pellets are made of material whose volumetric swelling is greater than that of main nuclear fuel. In the course of operation of core built of fuel assemblies neutron spectrum is varied by varying composition or thermal characteristics of coolant. Content of heavy water and/or soluble compounds absorbing material neutrons is reduced by raising coolant temperature at core outlet and/or reactor power in beginning of reactor lifetime and as fuel burns out. Coolant temperature at core outlet is reduced to minimal admissible value at fuel burnout rate. EFFECT: enhanced fuel burnout, reduced probability of fuel-rod unsealing under normal and abnormal conditions of reactor. 12 cl