European Union member states have agreed the additional funds needed to construct Iter (the International Thermonuclear Experimental Reactor).

The French-based machine will prove the concept of harvesting energy from the fusion of hydrogen nuclei – the same process at the heart of the Sun.

Iter has seen its baseline price tag rise dramatically since a consortium of nations green lit the project in 2006.

The extra 1.4bn euros will cover a shortfall in building costs in 2012-13.

After months of protracted negotiations, the monies were finally sanctioned at an Agriculture and Fish Council meeting on 12 July.

“The neutrons produced in the fusion reaction will be emitted essentially isotropically in all directions around the fusion zone. These neutrons must somehow be convinced to escape without further interactions through the first wall surrounding the few 1000 m3 plasma zone. Next, the neutrons have to interact with a “neutron multiplier” material like beryllium in such a manner that the neutron flux is increased without transferring too much energy to the remaining nucleons. The neutrons then must transfer their energy without being absorbed (e.g. by elastic scattering) to some kind of gas or liquid, like high pressure helium gas, within the lithium blanket. This heated gas has to be collected somehow from the gigantic blanket volume and must flow to the outside. This heat can be used as in any existing power plant to power a generator turbine. This liquid should be as hot as possible, in order to achieve reasonable efficiency for electricity production. However, it is known that the lithium blanket temperature cannot be too high. This limits the efficiency to values well below those from today’s nuclear fission reactors, which also do not have a very high efficiency.

Once the heat is extracted and the neutrons are slowed sufficiently, they must make the inelastic interaction with the Li6 isotope, which makes up about 7.5% of the natural lithium. The minimal thickness of the lithium blanket that surrounds the entire plasma zone has been estimated to be at least 1 meter. Unfortunately, lithium like hydrogen (tritium atoms are chemically identical to hydrogen) in its pure form is chemically highly reactive. If used in a chemical bound state with oxygen, for example, the oxygen itself could interact and absorb neutrons, something that must be avoided. In addition, lithium and the produced tritium will react chemically -which is certainly not included in any present computer modeling- and some tritium atoms will be blocked within the blanket. Unfortunately, additional neutron and tritium losses cannot be allowed, as will be described in more detail in Section 5.2.

Next, an efficient way has to be found to extract the tritium quickly, and without loss, from this lithium blanket before it decays. We are talking about a huge blanket here, one that surrounds the few 1000 m3 plasma volume. Extracting and collecting the tritium from this huge lithium blanket will be very tricky indeed, since tritium penetrates thin walls relatively easily, and since accumulations of tritium are highly explosive. An interesting description of some of these difficulties that have already been encountered in a small-scale experiment can be found in reference [38].

Finally assuming we get that far, the extracted and collected tritium and deuterium, which both need to be extremely clean, need to be transported, without losses, back to the reactor zone.

Each of the unsolved problems described above is by itself serious enough to raise doubts about the success of commercial fusion reactors.”

Tokamak-style fusion is predicted to become practical in a few decades. But by then, we may near to past the world peak in helium. Helium demand will soar and helium price will soar, too, but it will be too late. Perhaps it really is true that fusion is the power source of the future, and it always will be, as the joke goes.

Will these materials become horribly radioactive?