NON-CRITICALITY MEASURING SYSTEM FOR SPENT FUEL ASSEMBLY AND NON-CRITICALITY MEASUREMENT

摘要

PURPOSE:To measure non-criticality even if burnup degree eye are unknown by setting a spent fuel assembly in a water tight container in gas environment and providing a neutron absorbing body on the outer periphery of the container. CONSTITUTION:By using a neutron source intensity measuring device 1 soaked in water, first axial direction specified position neutron counting rate Co is measured in fuel assembly 3 by means of a neutron detector 5. As the inside of a container is set in gas environment and a neutron absorbing body 2 is provided along the circumference, a thermal neutron in a fuel part is eliminated, main system aggregate neutron effective multiplication constant and detector detection efficiency become roughly constant values, and assembly neutron source intensity So and the counting rate Co come to be in proportional relation, and it is possible to easily compute 6 the intensity So. In a non-criticality measuring device 11, as inside neutron source distribution and fission neutron distribution become identical to each other, the detection efficient of the detector following variation of burnup degree comes to be roughly constant value, and it is possible to compute 16 assembly neutron effective multiplication constant in accordance with a second axial direction specified position neutron counting rate measured 15 by the counting rate Co and the device 11.