TOTAL ROOM HOLDUP OF PLUTONIUM MEASURED WITH A LARGE-AREA NEUTRON DETECTOR

The use of a large-area neutron detector for measuring plutonium holdup in process equipment has been investigated both in the laboratory and in an industrial plutonium facility. Results indicate that holdup measurements made with an array of five moderated ^He tubes suspended from the center of a room can achieve an accuracy comparable to much more time consuming Nal(TZ) detector gamma-ray measurements. To determine the holdup using this technique, the fissile material must be reasonably uniformly distributed, the room must be shielded from external sources, and the specific activity of the material must be known. Both experimental and calculational calibrations have been used.