Nuclear Reactors 751 - Russian Scientists Are Working On A Hybrid Fusion-Fission Reactor Design That Uses Thorium As A Fuel.
A collaboration of Russian scientists at Tomsk Polytechnic University, All-Russian Scientific Research Institute of Technical Physics (VNIITF), and Budker Institute of Nuclear Physics of SB RAS has just published a report on a new type of nuclear reactor. The reactor is what is being called a “hybrid” reactor. It utilizes both nuclear fusion and nuclear fission to generate power. Most of the fuel for this new reactor is thorium. Computer simulations of the new design have been run. They show that an “energy-generating blanket” would be able to produce high power in a small footprint and it would not generate much radioactive waste.
This new reactor design offers middle-ground solutions with respect to fuel, reactor design and safety. Thorium is one of the most abundant elements of its kind. It is more abundant that tin which is very common and accessible. On the other hand, uranium which is the primary nuclear fuel today is not rare but it is also not readily and easily available.
The hybrid thorium reactor uses thorium-plutonium pellets in a high-temperature, gas cooled reactor. The published report about the new design does not say which specific gas is used for cooling but both carbon dioxide and helium gases have been used in other reactor designs for cooling. Gas cooled reactors offer a way in which unenriched uranium can be used to generate power. This makes such reactors more accessible and affordable to many countries that do not have the capacity to enrich uranium. This new thorium reactor design could offer the same benefits.
Experts say that a subcritical reactor is safer than a critical reactor because it requires less containment and safeguards. Thorium is way less reactive and explosive than uranium or plutonium.
The reactor is relatively small when compared to conventional light water nuclear power reactors. The plasma chamber is only about forty feet long. Combining a fusion reaction with a fission reaction maximized the efficiency of the reactor. It will be much simpler to develop this technology than a tokamak pure fusion reactor.
There will be less time necessary to reach full operation and it will be less volatile once in operation.
Andrei Arzhannikov is a chief researcher of Budker Institute of Nuclear Physics of SB RAS. He said “At the initial stage, we get relatively cold plasma using special plasma guns. We retain the amount by deuterium gas injection. The injected neutral beams with particle energy of 100 keV into this plasma generate the high-energy deuterium and tritium ions and maintain the required temperature. Colliding with each other, deuterium and tritium ions are combined into a helium nucleus so high-energy neutrons are released. These neutrons can freely pass through the walls of the vacuum chamber, where the plasma is held by a magnetic field, and entering the area with nuclear fuel. After slowing down, they support the fission of heavy nuclei, which serves as the main source of energy released in the hybrid reactor.”
Igor Shamanin is the head of the TPU Division of Natural Sciences and the TPU Isotope Analysis and Technology Laboratory. He said, "The hybrid reactor consists of two elements. The main part is the energy-generating blanket as the active zone of a nuclear reactor. It distributes nuclear fissile material that is part of nuclear fuel. Due to this, a fission chain reaction of heavy nuclei is possible. The second part is placed inside the blanket to generate neutrons that fall into the energy-generating blanket. The thermonuclear fusion reactions are generated inside this part filled with deterium plasma, releasing the neutrons. A feature of the hybrid reactor is that the operating blanket, where the fission reactions take place, is in the subcritical state (near-critical). Operating at a constant power level, a conventional reactor is in a critical condition, supported by a control and safety system.”