August 03, 2015

China plans to build a hybrid fusion fission reactor by 2030 but no real technical details

The South China Morning Post and Chinese media are reporting that China will build a new hybrid reactor that can burn nuclear waste via a combined fusion-fission method by 2030.

The proposed hybrid reactor will use nuclear fusion to burn u-238 and could in theory recycle the waste from traditional reactors into new fuel.

The project is being developed at the Chinese Academy of Engineering Physics in Sichuan, a top secret military research facility where China's nuclear weapons are developed.

The scheme was first reported by the Science and Technology Daily, a newspaper run by the official Ministry of Science and Technology.

At the core of the proposed hybrid plant is a fusion reactor which is powered by electric currents as strong as 60 trillion amps. The reactor will be blanketed by a fission shell stuffed with uranium-238.

Such a design has numerous advantages. The high-speed neutrons generated by fusion could split apart the u-238 atoms to generate fission, and the fission could generate lots of energy to help maintain the fusion, thus significantly reducing the amount of external energy input, and achieve the complete burning of nuclear fuel to avoid radioactive waste.

Professor Wang Hongwen, deputy director of the hybrid reactor project, said that the key components will be built and tested around 2020, with an experimental reactor due to be finished by 2030.

The papers seem to assume that the fusion system would some version of a Tokamak fusion reactor.

There have been dozens if not hundreds of proposed fusion fission hybrid systems.

The Fusion system would generate neutrons which would help the fissioning of all of the uranium 238.

The concept dates to the 1950s, and was strongly advocated by Hans Bethe during the 1970s. At that time the first powerful fusion reactors were being built, but it would still be many years before they could be economically competitive. Hybrids were proposed as a way of greatly accelerating their market introduction, producing energy even before the fusion systems reached break-even. However, detailed studies of the economics of the systems suggested they could not compete with existing fission reactors. The idea was abandoned and lay dormant until the 2000s, when the continued delays in reaching break-even led to a brief revival around 2009, notably as the basis of the LIFE program.

LIFE, short for Laser Inertial Fusion Energy, was a fusion energy effort run at Lawrence Livermore National Laboratory (LLNL) between 2008 and 2013. LIFE aimed to develop the technologies necessary to convert the laser-driven inertial confinement fusion (ICF) concept being developed in the National Ignition Facility (NIF) into a practical commercial power plant, a concept known generally as inertial fusion energy (IFE). LIFE used the same basic concepts as NIF, but aimed to lower costs using mass-produced fuel elements, simplified maintenance, and diode lasers with higher electrical efficiency. The failure of NIF to achieve ignition in 2012 led to the LIFE project being cancelled in 2013.

There was a molten salt variant of the LIFE hybrid system

Molten salt with dissolved uranium is being considered for the Laser Inertial Confinement Fusion Fission Energy (LIFE) fission blanket as a backup in case a solid-fuel version cannot meet the performance objectives, for example because of radiation damage of the solid materials. Molten salt is not damaged by radiation and therefore could likely achieve the desired high burnup (over 99%) of heavy atoms of 238U. A perceived disadvantage is the possibility that the circulating molten salt could lend itself to misuse (proliferation) by making separation of fissile material easier than for the solid-fuel case.

There was a 244 page review from a 2009 hybrid fusion fission conference.

Any fusion (laser, magnetic, dense plasma focus etc...) can be made into a hybrid

Without a lot of technical details we have no idea what China is planning to do

Neutron economy

A key issue for the fusion-fission concept is the number and lifetime of the neutrons in the various processes, the so-called neutron economy.

In a pure fusion design, the neutrons are used for breeding tritium in a lithium blanket. Natural lithium consists of about 92% Li-7 and the rest is mostly Li-6. Li-7 requires neutron energies even higher than those released by fission, around 5 MeV, well within the range of energies provided by fusion. This reaction produces T, Helium-3, and another slow neutron. Li-6 can react with high or low energy neutrons, including those released by the Li-7 reaction. This means that a single fusion reaction can produce several tritiums, which is a requirement if the reactor is going to make up for natural decay and losses in the fusion processes.

When the lithium blanket is replaced, or supplanted, by fission fuel in the hybrid design, neutrons that do react with the fissile material are no longer available for tritium breeding. The new neutrons released from the fission reactions can be used for this purpose, but only in Li-6. One could process the lithium to increase the amount of Li-6 in the blanket, making up for these losses, but the downside to this process is that the Li-6 reaction only produces one tritium atom. Only the high-energy reaction between the fusion neutron and Li-7 can create more than one tritium, and this is essential for keeping the reactor running.

To address this issue, at least some of the fission neutrons must also be used for tritium breeding in Li-6. Every one that does is no longer available for fission, reducing the reactor output. This requires a very careful balance if one wants the reactor to be able to produce enough tritium to keep itself running, while also producing enough fission events to keep the fission side energy positive. If these cannot be accomplished simultaneously, there is no reason to build a hybrid. Even if this balance can be maintained, it might only occur at a level that is economically infeasible

Форма для связи


Email *

Message *