Fission Gas Release from Irradiated Uranium-Plutonium Nitride Fuel

The results of an investigation of fission gas release from mixed nitride fuel after irradiation to maximum burnup 7.5% h. a. in 10 experimental FA in BN-600 are reported. It is shown that gas release commences at burnup >2% h.a. and increases with increasing burnup. The burnup dependence of gas release for mixed and uranium nitride fuel coincide quite well. The fission gas beneath the fuel-rod cladding consists of three basic components: xenon, helium, and krypton. The content of the remaining gases (N-2, Ar, O-2, CO2) does not exceed tenths of a percent. Xenon has the highest specific release, followed by helium and krypton. Helium has the highest relative release (>40%). Xenon and krypton have almost identical release not exceeding 20% for most of the investigated fuel rods. A higher release of fission gas is associated with either an increase of the fuel temperature (>1500 degrees C) or features of fuel microstructure.