Fuel reprocessing facility

A fuel containing vessel is disposed in a cell partitioned by radiation shielding walls, and neutron detectors are disposed toward the inside of the radiation shielding wall or the side of the fuel containing vessel, such that they protrude from the radiation shielding wall. Then, neutron absorbers are disposed to the inner surface of the shielding wall in front of the neutron detectors except for a predetermined range corresponding to a portion of the fuel containing vessel to be measured. With such a constitution, neutrons emitted from the fuel containing vessel and an artificial neutron source to all directions are neither scattered nor reflected by the radiation shielding wall, not to form high neutron background, but they are absorbed by the neutron absorbers disposed at the inner surface of the radiation shielding walls. Therefore, the background is greatly reduced, thereby enabling to accurately measure the neutrons emitted from the portion to be measured. (T.M.)