Closing the nuclear fuel cycle: Potential of the gas cooled fast reactor

The fuel composition of the Generation IV 600 MWth 'efficient' Gas Cooled Fast Reactor (GCFR) that realizes zero breeding gain without using fertile blankets is determined. The analysis includes all the stages of the nuclear fuel cycle, including irradiation, reprocessing and fuel fabrication. The time-dependent multiplication factor, reactor safety parameters, and decay heat production for different fuel compositions are simulated using the deterministic SCALE 4.4 code. The depletion equation and the 1-D transport equation are solved for multiple timesteps during reactor irradiation. It is seen that adding a small percentage of minor actinides (MA) to a mixture of uranium- and plutonium carbide favors the creation of a closed fuel cycle with zero breeding gain. Furthermore, addition of MA increases the burnup potential of the fuel, extending its feasible irradiation time from 40 to 90 MWd / kg, due to the transmutation of Np-237 to fissionable Pu-238 and Am-241 to fissionable Am-242. Mixing MA negatively affects safety parameters by decreasing the delayed neutron fraction, decreasing the negative Doppler feedback and increasing the positive reactivity introduced when the reactor is depressurized. However, the magnitude of the delayed neutron fraction is comparable to existing fast reactors. Worths of individual isotopes are introduced as a value of their contribution to the core reactivity. Throughout the fuel cycle, the time-dependence of the isotopic and total worth of the fuel is determined. Zero breeding gain is achieved when the initial total worth of the fuel stays constant for multiple cycle burnup. The effect of different reprocessing strategies on the closed fuel cycle is shown. Research confirms that when there are no reprocessing losses, depleted uranium can be used during the recycling step to replace fission products and obtain a new critical fuel composition.Radiation, Science and TechnologyApplied Science