Tritium ordinary hydrogen, but they do fuse the small minority of deuterium nuclei. Like the other isotopes of hydrogen, tritium is difficult to confine. Rubber, plastic, and some kinds of steel are all somewhat permeable. This has raised concerns that if tritium were used in large quantities, in particular for fusion reactors, it may contribute to radioactive contamination, although its short half-life should prevent significant long-term accumulation in the atmosphere. The high levels of atmospheric nuclear weapons testing that took place prior to the enactment of the Partial Test Ban Treaty proved to be unexpectedly useful to oceanographers. The high levels
Tritium in small quantities by some nuclear power plants. In January 2014 it was made public that a total of 875 TBq (2.45 g) of tritium are on the site of Fukushima Daiichi, and the amount of tritium contained in the contaminated water is increasing by approximately 230 TBq (0.64 g) per year. According to a report by Tepco ""Tritium could be separated theoretically, but there is no practical separation technology on an industrial scale"." Tritium's decay product helium-3 has a very large cross section for reacting with thermal neutrons, expelling a proton, hence it is rapidly converted back to tritium