Just over a hundred years ago, Albert Einstein came up with the notion that mass and energy are equivalent in his theory of Special Relativity. About twenty years later the idea that the sun was a nuclear reactor and provided near endless energy was first mooted. In fact one of the initial problems seen with Darwin’s concept of Evolution was that there was not enough time in the life of the sun for evolution to occur. It is now known that the sun is about 4.6 billion years old, providing plenty of time for the evolution of life to occur.
The sun is powered by Nuclear Fusion where light elements are fused to become heavier elements and release enormous amounts of energy in doing so. Back in the discussion of Nuclear Fission it was shown how the Binding energy curve gave energy from fusion of light elements or fission of heavy elements with a lot more energy per atom coming from the fusion of Hydrogen than from any fission reaction.
In the 1930s the concept of a nuclear chain reaction was proposed. Adelaide’s own Mark Oliphant has been credited with showing that nuclear fusion works. By the mid 1940s, the first nuclear fission bombs were detonated. About ten years later the first fusion bombs, or thermonuclear devices where a fission bomb was used to detonate a fusion reaction, were tested. In 1957 the International Atomic Energy Commission was established leading to commercial energy from Nuclear fission reactors. The nuclear powered submarine, USS Nautilus was launched a few years earlier.
So it was about fifty years from the concept of near unlimited energy from nuclear reactions to the first commercial production. In the early 1950s the concept of a contained nuclear fusion reaction was also proposed. The biggest problem was achieving the very high temperatures required for nuclear fusion and then containing the reaction. Russian scientists back in the early fifties proposed the container to be a magnetic bottle. Two types were proposed, the Tokamak (Russian) and the Stellarator (US).
Current day – Public money
Both were conceptualised to be donut shaped where one magnetic field holds the shape of the donut (or toroid) and a second magnetic field follows the high temperature material contained. Both designs are still in use and look like our best chance to achieve contained Nuclear Fusion energy. Both have had significant problems with their manufacture. The Stellarator was a more difficult concept to build and had fewer supporters. Germany has just commissioned the largest of these built and Australia has a smaller version.
The largest Tokamak built to date (1980s) is the Joint European Torus (JET). A fusion reactor ten times the size is being built in France and is called ITER (International Thermonuclear Experimental Reactor) It is expected to be operational and producing commercial power by 2035. Germany’s Stellarator called Wendelstein 7-X is also hoping to achieve commercial generation by about the same time. Australia also has just signed a deal with China to develop it’s stellerator.
All of these have been developed with public funding, US and Russia to begin with and then Europe and Britain. Brexit is likely to create problems on funding for JET vs ITER with the former currently funded until 2018.
In recent years private enterprise has stepped in, believing that they can commercialise fusion energy quicker and cheaper than the public enterprises. Tokamak Energy has built its first plant and has achieved a run time of plasma creation of 29 hours, out doing the European efforts. They have recently announced a plan to build a commercial tokomak by 2025 and have commercial power by 2030!
Tokamak Energy was initially fronted by UK billionaire David Harding, who made a fortune on share market trading using high powered statistical data. There are now many other billionaires jumping on the band wagon, hoping to develop the first commercial fusion power station. They are all after funding and we are now seeing Elon Musk type promotional tactics.
Is it safe?
As far as we know fusion energy is only available by producing temperatures akin to those within the sun. Tokomak Energy are working to build hotter reactors, leading to a commercial process. These reactors produce a state of matter called plasma (other states are solid, liquid and gas). The plasma needs to be contained in a magnetic field (any physical material will combust at these temperature) and the be surrounded by a physical blanket.
The first safety issue then is the release of an enormous amount of energy if anything goes wrong with the containment.
There are charlatans in the business (as in any new startups) who will push the boundaries of promotion. Cold fusion is one of these. That is fusion energy created without needing immense amounts of heat. It may be possible but all scientific tests to date have shown it does not work (yet). So we are currently stuck with the dangerous high energy containment.
There are a number of different types of radiation, and a number of ways it can be created.
Alpha (α) – high energy Helium nucleus ( 2 protons and 2 neutrons). Easily shielded, so only a problem if ingested.
Beta (ß) – high energy electron. Can penetrate skin but most problems from ingestion
Gamma (Ɣ) – high energy photon beam. Needs lead shielding.
X Ray – similar to Gamma radiation but lower energy (longer wave length)
Neutron Radiation – high energy neutron. When these hit other particles they are absorbed and make the particle unstable producing any of the above radiation. Hard to stop.
Nuclear fission is a process by which heavy elements slowly break down to more stable ones giving off radiation energy in the process. A lot of these “fission products” are deadly and have long half-lives.
The fusion process tends to create about 80% high energy neutrons and 20% alpha radiation. It is also likely to produce radioactive Tritium.
Fusion materials and products
Fusion is about creating heavier elements from lighter ones and thereby producing energy. Elements are listed by the number of protons in their nucleus. The periodic table is a list in order from the lightest element, Hydrogen (H). The next lightest is Helium (He) having 2 protons then Lithium (Li) with 3. Then Boron (B) has 4 and Beryllium (Be) 5. These elements are the most likely to be used in fusion reactions.
The elements can also be supplied as chemically combined molecules. Hydrogen gas is two hydrogen atoms combined to form the stable H2 for example. It may also be combined with oxygen to form water (H2O).
Elemental hydrogen has 1 proton in its nucleus with 1 electron in its shell. If it loses the electron it is ionised and becomes H+. It can also occur with a neutron in its nucleus. This is called Deuterium and is an isotope of hydrogen. If it combines with oxygen it produces heavy water. A second isotope of hydrogen called Tritium contains 2 neutrons in its nucleus. When combined with oxygen it also produces heavy water. Whereas deuterium is relatively stable, Tritium is radioactive with a half-life of 12.3 years. It emits Beta radiation only and is most problematic when ingested as heavy water.
High energy neutrons are required to get the chain reaction fusion process going. They are also what heat up (get faster) and provide the released energy. These are absorbed by the blanket material. Any material with high activation potential will absorb the neutrons and begin to decay, emitting radiation (of any or all kinds) in the process.
Deuterium and Tritium are likely to be used to supply these neutrons, and may be created as waste. High energy neutrons can also be supplied by an accompanying fission reaction.
High energy neutrons will make the blanket material brittle as well as radioactive. Low activation steels (ferritic- martensic) are being developed as a blanket material. Other options include Vanadium or Tungsten. Currently though, these blankets need to be replaced regularly and stored as nuclear waste probably for a few hundred years.
Will it work?
We are probably now at a stage where nuclear fusion will be commercially available in the next 20 years or less. Many billions of dollars have already been spent on development and many more billions will be spent over the next few years. It is highly unlikely that fusion energy will be cheap, at least in our lifetimes.
It will likely be more expensive than nuclear fission and will still have a waste problem (unless the technology improves). This means it is really only an option for the developed countries. Australia has not seen the need to build a commercial fission reactor to date! Can’t see us building a commercial fusion reactor for at least 20 years.
Fusion reactors will still need to be isolated for safety and will therefore have problems getting the local neighbourhood on side (as with fission).
Over time it may be the best energy source we have, as we will not run out of fuel (it essentially runs on water). In the meantime there is an argument that it is not as cost or environmentally effective as our big fusion reactor in the sky.
Time will tell.