Comparison of open and closed U–Pu equilibrium fuel cycles for Generation-IV fast reactors with the EQL3D procedure

Abstract

The advanced fast reactors of the fourth generation should enable an indirect burning of poorly fissile 238U through 239Pu breeding and recycling of the actinides from their own spent fuel. The recycling or actually the fuel cycle closure can significantly reduce the amount of long-lived radioactive waste and the 238U burning can multiply the sustainability of the uranium fueled reactors. Regular periodic operation with the fuel recycling converges to an equilibrium cycle. To enable its simulation a numerical tool named equilibrium fuel cycle procedure for fast reactors (EQL3D) was developed in the FAST group of LRS at Paul Scherrer Institut. The procedure is based on the ERANOS code and can be used to yield the description of two basic situations: the equilibrium of an open fuel cycle and the equilibrium of a closed fuel cycle. The goals of the present study are (i) to apply EQL3D to the Gas-cooled Fast Reactor (GFR), Sodium-cooled Fast Reactor (SFR), and Lead-cooled Fast Reactor (LFR), (ii) to simulate and confirm the GFR, SFR, and LFR neutronics capability for closed fuel cycle, and (iii) to evaluate and compare the equilibrium cycle safety and performance parameters. The EQL3D capability enables to characterize the equilibrium cycle for complex reloading patterns within a multi-batch scheme. Therefore, a specific ring-wise reloading pattern within a multi-batch cycle was developed for each core. The convergence path to equilibrium differs between the cores. It is determined mainly by the initial fuel composition. However, the capability for closed fuel cycle was proved for all three systems. It was also found that the equilibrium 239Pu/238U mass ratio, even though it depends on the feed and spectrum, is similar for all compared fast reactors. In spite of this similarity, the equilibrium safety-related parameters differ between the cores. Nevertheless, the degradation caused by the fuel cycle closure is comparable with the degradation between initial core state and open cycle equilibrium. From neutronics point of view all three cores could serve after prospective optimization as a sustainable and clean energy source.