Assessing Nuclear Fusion
The temperature in fusion plasma is approximately ten times higher than that at the heart of the Sun. This heat allows the fusing of two nuclei, deuterium and tritium. Tritium, also known as hydrogen-3, is a radioactive isotope of hydrogen. While deuterium is stable, tritium is not and requires high levels of caution. Fusion experts have planned to build a storage area for tritium, right next to the fusion experiment. But – can fusion be a hazard to people’s health? In particular, the beta particles of hydrogen-3, are unable to penetrate the skin. They can be dangerous when inhaled or ingested via food or water. Additionally, tritium only has a half-live time of about twelve-years.
The biggest radiation issue we have come across is related to one of the reaction products: fast neutrons. The neutron, which carries 80 percent of the energy produced in the fusion reaction, is not confined within the plasma. It escapes and penetrates into the components surrounding the plasma chamber, mainly the blanket. Here the neutrons release their energy which is then used to produce electricity. But a side effect is that the materials near the plasma can become radioactive and must be treated accordingly when the fusion device is being decomissioned.
The blanket inside a fusion reactor should not only be there to absorb the energy in order to produce electricity. It should also ensure that the energy of the neutron is used to “breed” tritium since it occurs somewhat rarely on Earth. Tritium, generated by the neutrons in the blanket, can be removed from the blanket and sent back into the plasma as fuel. Among others, the scientists of EUROfusion are currently investigating such solutions.
The basic challenge, as physicists first learned in the 1950s and 60s, is that fusion plasmas—free-flowing soups of protons and electrons in which atomic nuclei collide and release energy—do not like to be contained. They want to splatter everywhere, and yet, we need to contain them, at high enough pressures and for long enough time intervals that we can produce more energy than we put in.