Study of fissile fuel breeding concept for the force-free helical reactor

The force-free helical reactor (FFHR) is a demo relevant helical-type D–T fusion reactor based on the large helical device (LHD). In this study, the possibilities of fissile fuel breeding (FFB) and incineration of curium oxide discharged from spent fuel of pressured water reactor (PWR) have been investigated in the FFHR. For this purpose, FFB zone containing mixed fuel has been located in the blanket of the FFHR by using two different design shapes (models 1 and 2). Four different mixtures, namely, 244CmO2–UC, 244CmO2–UO2, 244CmO2–UN and 244CmO2–U3Si2, have been used as fuel. The mixed fuels have been spherically prepared, and cladded with SiC to prevent fission products from contaminating coolant and fuel–coolant contact. The prepared fuel spheres have been replaced in the FFB zone as ten rows in radial direction, and two different coolants, helium (for models 1a and 2a) and flibe (for models 1b and 2b), have been selected for the nuclear heat transfer in the FFB zone. Calculations of neutronic data per DT fusion neutron have been performed individually for each of 16 different cases created by using four different mixed fuels in each of four different models. In the models 1 and 2, the case of helium coolant has higher M (the blanket energy multiplication ratio), which is one of main parameters in a fusion–fission hybrid reactor than the case of flibe coolant. M is quite high, and varies in the ranges of 4.747–5.895 and 2.453–2.784 in the models 1 and 2, respectively, depending on the fuel and coolant types. The fissile fuel breeding ratio (FFBRs) are also quite high in the model 1a with respect to model 1b, although coolant type does not change the FFBRs substantially in the model 2. Total FFBR (239Pu+245Cm breeding ratio) varies from 0.551 to 0.650 and from 0.170 to 0.184, in the models 1 and 2, respectively, depending on the fuel and coolant types. Values of tritium breeding ratio (TBR), which is another important parameter in a fusion–fission hybrid reactor, are about 1.2 for all investigated cases so that tritium self-sufficiency is maintained for (D,T) fusion driver. Values of peak-to-average fission power density ratio, Γ are in the range of 1.108–1.249 in all investigated cases, depending on the fuel and coolant types. Furthermore, values of neutron leakage out of the blanket for all models are quite low due to B4C shielding. Consequently, for all cases, the investigated reactor has high neutronic performance and can produce substantial electricity in situ, fissile fuel and tritium required for (D,T) fusion reaction.