Operational Characteristics of a Fission Gas Detector

Introduction: One of the major problems associated with the operation of nuclear reactors is the radioactivity hazard caused by the release of fission products from the fuel. In a solid-fuel reactor, the uranium is usually present in an allow or in the form of UO₂, either in the pure state or mixed with other oxides which improve the thermal and mechanical properties of the material. As the fuel material undergoes fission in the reactor, radioactive fission products are produced. If they were not prevented from doing so, these fission products would diffuse out of the fuel material, enter the reactor coolant as it flows past the fuel, and be carried from the reactor. The magnitude of the hazard thus created depends on the type of reactor, the reactor power, shielding of the coolant lines, and other factors. In a reactor where the coolant makes only a single pass through the system, such as the air-cooled the graphite reactors, the fission products are discharged into the atmosphere or into some coolant sink. This situation is usually unacceptable from a health standpoint. If the coolant flows in a closed loop, as in most present day water-cooled reactors, the fission products build up in the coolant, producing a radiation hazard in the coolant loop.