Viable clean nuclear energy by fusion-fission combined power
Physicists at The University of Texas, Austin, have designed a new system that would use fusion to eliminate most of the transuranic waste produced by nuclear fission plants. The invention would combat global warming by turning nuclear power mostly clean and thus a more viable replacement of carbon-heavy energy sources, such as oil or gas.
“We have created a way to use fusion to relatively inexpensively destroy the waste from nuclear fission,” says Mike Kotschenreuther, senior research scientist with the Institute for Fusion Studies (IFS) and Department of Physics. “Our waste destruction system, we believe, will allow nuclear power-a low carbon source of energy-to take its place in helping us combat global warming.”
The scientists propose destroying the waste using a fusion-fission hybrid reactor, the centerpiece of which is a high power Compact Fusion Neutron Source (CFNS) made possible by a crucial invention.
The CFNS would provide abundant neutrons through fusion to a surrounding fission blanket that uses transuranic waste as nuclear fuel. The fusion-produced neutrons augment the fission reaction, imparting efficiency and stability to the waste incineration process.
The scientists’ waste destruction system would work in two major steps. First, 75 percent of the original reactor waste is destroyed in the standard relatively inexpensive fission reactors (LWRs). This step produces energy, but it does not destroy highly radiotoxic, transuranic, long-lived waste, what the scientists call “sludge.”
In the second step, the sludge would be destroyed in a CFNS-based fusion-fission hybrid. The hybrid’s potential lies in its ability to burn this hazardous sludge, which cannot be stably burnt in conventional systems.
The process would ultimately reduce the transuranic waste from the original fission reactors by up to 99 percent. Burning that waste also produces energy.
The CFNS is designed to be no larger than a small room, and much fewer of the devices would be needed compared to other schemes that are being investigated for similar processes. In combination with the substantial decrease in the need for geological storage, the CFNS-enabled waste-destruction system would be much cheaper and faster than other routes, say the scientists.
The CFNS is based on a tokamak, which is a machine with a “magnetic bottle” that is highly successful in confining high temperature (more than 100 million degrees Celsius) fusion plasmas for sufficiently long times.
The crucial invention that would pave the way for a CFNS is called the Super X Divertor. The Super X Divertor is designed to handle the enormous heat and particle fluxes peculiar to compact devices; it would enable the CFNS to safely produce large amounts of neutrons without destroying the system.
In moving their hybrid from concept into production, the scientists hope to make nuclear energy a more viable alternative to coal and oil while waiting for renewables like solar and pure fusion to ramp up.
“The hybrid we designed should be viewed as a bridge technology,” say scientists. “Through the hybrid, we can bring fusion to the service of the energy sector today. We can hopefully make a major contribution to the carbon-free mix dictated by the 2050 time scale set by global warming scientists.”
The scientists say their Super X Divertor invention has already gained acceptance in the fusion community. Several groups are considering implemented the Super X Divertor on their machines, including the MAST tokamak in the United Kingdom, and the DIIID (General Atomics) and NSTX (Princeton University) in the U.S. Next steps will include performing extended simulations, transforming the concept into an engineering project, and seeking funding for building a prototype.