Measurement of occluded gases released from uranium-plutonium mixed carbide and uranium carbide fuels.

Abstract

The release of the occluded gases in uranium-plutonium mixed carbide and uranium carbide pellets for irradiation tests were measured successfully using a multipurpose high temperature apparatus. A new type of gas line filter was set up in the gas exhausting line, where the filter could be exchanged easily without plutonium contamination and degassed by heating. The release of the occluded gases in the carbide fuels was measured at 1,473, 1,673 and 1,873 K. At 1,473 K, most of the gases evolved was H2 gas and above this temperature, the oxygen contained in the fuel was released continuously in the form of CO gas. It was shown that the H2 gas was generated by the reaction of the fuel with moisture adsorbed at the fuel surface during storage and the CO gas was released in proportion to its equilibrium pressure of the oxycarbide solid solution. The release of the gases from the fuels scarcely affects the increase of the inner gas pressure of fuel pins since the amount of H2 gas is small, about 100 μl·atm/g-fuel corrected at 273 K and CO gas pressure equilibrated with carbided fuel is only several hundred Pascal.