Conceptual Design of a Hybrid Fusion–Fission Power Reactor with a Tokamak and a Depleted Uranium Blanket

Abstract

We assess the viability of energy generation with depleted uranium irradiated with fast neutrons from the reaction of DT fusion driven by a tokamak reactor. Since existing nuclear power plants employ uranium fuel enriched to 4.5% 235U, over 90% of natural uranium currently goes to nuclear waste and is no longer used for power generation. The amount of depleted uranium with the 235U content of 0.2–0.3% accumulated in the world exceeds 1 500 000 t and is continually increasing owing to the operation of thermal neutron power plants. Industrial fast neutron power plants using depleted uranium as nuclear fuel are still at the development stage. Therefore, alternative approaches to utilizing depleted uranium for power generation should be considered. Compared to fast reactors with a closed cycle utilizing plutonium, the proposed facility involves less radiation hazard since the irradiated fuel has to be reprocessed and reloaded less frequently. Apart from that, the proposed hybrid power reactor operates in the deeply subcritical regime, which provides a high level of nuclear safety. A tokamak reactor similar to that of the ITER project is selected as a source of a high-power flux of fusion neutrons whereby a reactor blanket of depleted uranium is irradiated. The heat will be removed with a liquid metal coolant rather than with water as in the ITER reactor. This will help maintain the hardness of the neutron spectrum, thereby maximizing the rate of 238U fission. With such a neutron source and a blanket of natural uranium with an optimized thickness of ~20 cm, each fission of uranium (with an energy release of 200 MeV) is estimated to finally produce four 239Pu atoms in the blanket (see the 2009 proceedings of the ROSATOM commission on optimizing the development of power generation with tokamaks). This estimate equally applies to a reactor blanket of depleted uranium. According to estimates, an “ideal” reactor with a blanket of depleted uranium operating in a stationary mode with a capacity factor of 70% would generate nearly 1.5 GW of electric power. However, only an estimated one-third of the total power can actually be delivered to the electrical network since the rest is required for breeding tritium and powering the facility itself. Toward maximizing the capacity factor, the first wall of the fusion reactor will be coated with lithium for protection against plasma-induced erosion.