DT fusion releases 80% of its energy into 14 MeV neutrons and 20% into charged particles. The uncharged neutrons, unlike the charged particles, cannot be contained by a magnetic field and cannot therefore be used to convert electric energy into it. To drive a turbo-generator, neutrons must be slow down in a medium and heated to less than 103K. The conversion of nuclear energy into electricity has a Carnot efficiency around 30%. The efficiency of DT fusion, where 80% of fusion energy is released into neutrons is no higher than 24% (maximum – probably much lower than that in real first-generation fusion power stations). This low conversion efficiency can’t be overcome with magnetic confinement, but it can be overcome using inertial confinement, which surrounds the target with a thick layer of liquid hydrogen, and an outer layer of boron to create a hot plasma fireball. It is important that the hydrogen layer be thick enough to allow neutrons to heat it to 100,000K. A pulsed magnetohydrodynamic generator can be driven by fusion that has been fully ionized and is rapidly expanding. This generator achieves almost 100% Carnot efficiency.
(Further information can be found in the following paper by Friedwardt Winterberg, fusion visionary).
Initial production of electricity by nuclear fusion power plants may be difficult. However, the first use of fusion energy might actually be
1) Using neutrons from Fusion to burn high-level nuclear waste from the current fission Light Water Reactors
2) Using fusion neutrons to breed medical isotopes in order to cure and diagnose cancer
For the rest of the century, fission reactors may have a greater chance to produce nuclear heat reliably than fusion reactors. The vast majority of the energy from fission is converted to heat (kinetic energy in fission product). It will likely be cheaper and easier to use fission for reliable nuclear electricity in the next 100 years than first-generation fusion reactors. First Generation MCF Fusion reactors such as stellarators and tokamaks will likely be complex and large, and they will have serious reliability issues. MCF fusion experiments have not produced power for more than 5 seconds. Commercial fusion systems will be far better, but first generation reactors will likely have a lower capacity factor than current and future fission nuclear reactors for at least a few decades.
Inertial Confinement Fusion reactors that produce fusion in a series of small fusion bursts have the potential to be more reliable than MCF Fusion and could offer reliability comparable with fission as a source for nuclear electricity.
Fission can aid fusion in maintaining stable grids, load following unreliable sources of energy (renewables or potentially first generation MCF Fusion).
Fusion reactors are “neutron-rich” and produce a lot of neutrons at a low cost relative to fission reactors. Fast neutrons account for more than 80% of DT fusion’s energy. The first use of fusion reactors will be applications that require neutrons. These applications include
1) Breeding fissilefuel to create new fission reactors using fertile fuel (this includes breedingU233 of Thorium).
2) Rapidly burning Light Water Reactor Sent Nuclear Fuel – especially long half life Minor Actinides with Fusion neutrons
DT and DD Fusion fuel are approximately 4 times more energy dense that fission fuels by mass.
DT fusion produces 24 times more neutrons per unit of fuel than fission, even though they consume the same mass of fuel.
DD fusion is a mixture of protons and neutrons. It generates about 66% of its energy from neutrons, which is still quite impressive. Each fusion neutron can be used to create nuclear applications such as waste burning and fissile fuel generation. The Fission reaction can only be propagated by neutrons. This means that a substantial portion of the neutrons from fission must be dedicated to maintaining the fission reaction.
Fusion can be used to economically manage rapidly burning Minor Actinide nuclei nuclear waste fission reactor Spent Nuclear Fuel. Nearly mono-energetic, fusion neutrons can be used to create efficient Minor Actinide burning blankets that consume the most problematic elements of spent fission fuel.
First generation fusion reactors will likely use either DT or DD fusion, which produces large quantities of neutrons. Future generations of fusion reactors might use aneutronic fusionfuels that directly produce charged particles such as protons. The fusion reactions p-B11, He3-He3 and He3-He3 directly release their fusion energy and protons can be collected and used to make electricity at extremely high efficiency.