Design concepts of small CANDLE reactor with melt-refining process

Abstract

The CANDLE (Constant Axial shape of Neutron flux, nuclide densities and power shape During Life of Energy producing reactor) burnup strategy has been successfully applied to both fast and thermal reactors. In particular, fast CANDLE reactor has been found to offer many advantages. However, maintaining the material integrity of the fuel rods up to high burnup is a problem that requires particular attention. For presently available structural materials compatible with liquid metal coolants, the acceptable limit for radiation damage is 200 dpa. In order to overcome the material integrity issue while obtaining larger fuel burnup it is necessary to recondition the fuel by recycling and re-cladding. For the sake of keeping the fuel cycle as proliferation resistant as possible, which excludes actinide separation, the melt-refining process has been developed for metallic fuel in the Experimental Breeder Reactor II project. The objective of the present study is to show design concepts of small CANDLE reactor with the melt-refining process. A 300 MWt LBE cooled reactor is designed. The reactor uses metallic (90 wt. % U-10 wt. % Zr) natural uranium as fresh fuel and 12Cr ferritic ODS steel as cladding material. Neutronic analyses are performed to compare the burnup performance of reactors with and without the melt-refining process. Three bounding scenarios are considered: all actinides are recovered during the melt-refining process (scenario 1), 5 % (scenario 2) and respectively 10 % (scenario 3) of all actinides are unrecovered during the melt-refining process. The radioactive decay of the fission products during cooling time intervals is taken in consideration during the melt-refining process. Thermal-hydraulic analyses are conducted in steady state regime to make sure that the core design obeys a number of constraints: fixed core inlet and outlet temperatures, core pressure drop, maximal core coolant velocity, peak cladding temperature and peak fuel temperature. However, these analyses have no ambition at assessing the global performance of the cooling systems. In particular, once equilibrium has been reached, the hottest sub-channel, located in the core center, is selected for the thermal-hydraulic analysis. The results of the simulations show that the burnup performance of the small CANDLE reactor is remarkably increased in the scenario where all actinides are recovered during the melt-refining process. Its increase can be maximized by optimizing the melt refining regions in the core and by adjusting core design parameters, such as the radius of the active core, the thickness of the reflector and the fuel pin pitch. The analysis results show that the application of the melt-refining process makes it possible to reduce the radius of the active core zone from 130 cm to 100 cm, the fuel pin pitch being increased from 1.08 cm to 1.175 cm. The average discharged burnup is increased by 20.8 % in comparison with that of the reference small CANDLE reactor. Uranium consumption in each fuel cycle is reduced by 50.0 % in comparis...

Feasibility of Sodium-Cooled Breed-and-Burn Reactor with Rotational Fuel Shuffling

“…Once applying the control assemblies for the reactor, it would have an effect on the criticality of the cores with a rotationalfuel-shuffling scheme. However, it was mentioned in the previous studies [19][20][21] that the excess reactivity would be increased by applying the melt-refining process because of FP removal during the reprocessing. Therefore, it was expected that criticality would be ensured throughout the cycle for the melt-refining core designed with the control systems.…”

“…To reduce the maximum dpa value, the fuel cycle length of operation should be decreased or fuel reprocessing, such as the melt-refining process, should be applied. [19][20][21] These changes would result in an altered equilibrium state. Therefore, further analyses and optimizations for a practical reactor design must be performed in a future work.…”