Fusion-fission Hybrid Energy Blanket For Neutron Science Concept

There are two big challenges in the sustainable development of nuclear energy, one is to make best use of uranium resources and the other is to dramatically increase the ratio of nuclear power in the total energy supply. Fusion-fission hybrid is a possible solution. Hybrid can be cataloged into reactors for breeding and transmutation, the former is vulnerable to nuclear proliferation or accompanied by huge fusion driving power, the latter usually needs tens of tons fissile material. Both of them can not play an important role in power supply in the near future. It is of big significance to conduct hybrid research on power supply and overcome the difficulties facing above.A promising blanket concept, which takes the fusion core parameters of the International Thermal Experimental Reactor (ITER) as reference, is given in this paper by blanket neutronics study. It uses natural uranium or spent fuel of Pressure Water Reactor as fuel, light water as coolant and Li4SiO4 as tritium breeder. Uranium is made into alloy with zirconium and dry reprocessing without separation of uranium and plutonium is preferred so as to improve economic performance and be proliferation resistant. This design can achieve relatively high energy multiplication (M) so as to lower fusion power and fusion gain (Q).It is also of great advantage to improve share of nuclear power when natural uranium is used, since no fissile material accumulation is needed.A linkage code between MCNP and ORIGENS is developed and named MCORGS. It is suitable to burnup calculation of systems with complex geometry and neutron spectrum. It can compute nuclide inventory, radioactivity, decay heat, and give neutron balance analysis. MCNP is in charge of transport computation and provides transition cross section of important nuclides for ORIGENS, and ORIGENS is used to deal with burnup computation. Total macro cross section is used to determine whether the specified nuclides will be considered in MCNP and to judge which kinds of transition cross section are to be updated in ORIGENS. Several burnup benchmark problems for PWR, VVER and ADS are used to validate MCORGS and the results are satisfactory.Neutronics conceptual study of blanket is conducted using MCORGS. A conceptual model, which takes natural uranium as fuel and 100 percent coverage ration, is first given by neutron balance analysis. Both the volume ratio (VR) of uranium to water and the fuel zone thickness play important role in blanket design, and their influences to neutronics are investigated. Several reprocessing scenario are simulated so as to find whether it is possible to make full use of uranium resources by adding depleted uranium to spent fuel of the hybrid. The radioactivity and decay heat variation with time are also computed. A homogenization model which blends uranium and water is then given based on the conceptual model, and the coverage ration of 85% is used. The nuclide inventory along radial and poloidal are computed as a function of time. As far as blanket which takes spent fuel from PWR is concerned, the VR of uranium to water and its influence to neutronics are investigated. It also discusses the possible way to use thorium in the blanket in a preliminary way. Finally, different kinds of fusion, such as laser ICF and Z-Pinch ICF as well as MCF, and their influence on blanket are briefly compared.It is found that the VR of uranium to water has a significance influence on the fissile material generation rate(F),burnup rate(B),energy multiplication factor(M) and tritium breeding ratio(TBR).As the VR increases, F/B increases while the sum of F,B and TBR decrease; and vice the versa. On the one hand, the value of F/B at the beginning of the core will determine the variation trend of M and TBR. On the other hand, F and TBR will compete for neutrons, and it is necessary to balance the VR and total fuel zone thickness so as to maintain tritium self sufficiency.According to research results in this paper, if nature uranium is used, the VR of 2:1 is preferred. At the beginning of core, M is about 5-10, TBR is near to 1.15, F/B equals to 2.72; It is possible to sustain more than 100 years without changing the fuel zone. When VR is smaller than 2:1, M will increase while tritium can't be self-sufficiency at beginning of the core. If spent fuel from PWR is used, there is more room for VR. If VR is 2:1, Mis about 16, TBR is greater than 1.32 and F/B equals to 1.7, it is also possible to sustain more than 100 years. If VR is 1:1, F/B is near to 1.0 and it can sustain 5 years with M and TBR greater than 29 and 1.15 separately. If VR is 2:3, F/B is 0.75 and it can sustain 5 years with M and TBR greater than 50 and 1.31 separately. However, in the last two cases, there are no fissile material breeding.It is possible to reload the fuel zone every five years and reuse the spent fuel in the next cycle by adding another 5 tons of depleted uranium or thorium. It is also possible to mix the spent fuel with same quantity of depleted uranium so as to supply fuel for two equal scale hybrids. The radioactivity and decay heat of HR is comparable to PWR with the same power, and there is no difficulty in decay heat removal. However, it should pay more attention to radioactivity during the fuel storage and manufacture since the fuel will be reused many times.