Can the JT-60SA plant leak radiation?

JT-60SA uses either hydrogen or deuterium fuel. Hydrogen does not undergo nuclear reactions under these conditions. Deuterium-deuterium reactions are about 100 times less likely to occur than deuterium-tritium reactions, as used in ITER. Thus the fuel only represents a minor chemical explosion risk, which is easily avoided or contained.

One branch of the deuterium-deuterium reaction produces tritium. However, plasma exhaust in JT-60SA can be vented to the atmosphere without cleanup, because the rate of tritium production is ~100Curie/100s pulse. The maximum additional dose to the most exposed individual at the site boundary due to potential tritium releases is <1% of natural background radiation.

There can be local problems with all the energy concentrating on certain surfaces, causing melting and damaging the investment. Certain accidents can release water coolant into the reaction chamber. If there are hot surfaces nearby these can dissociate water into hydrogen and oxygen, and explosive mixtures can result if care is not taken. Again, the energies are enough to damage the investment, but not to cause sufficient damage to affect the general public. There is not enough energy in the plant, nor sufficiciently radioactive material generated in the course of operation, to produce contamination outside the plant in the case of any accident.