while water-insoluble forms of plutonium such as plutonium dioxide are very harmful to the lungs, this toxicity is not relevant during a loss of coolant accident (loca) because plutonium is very involatile and unlikely to leave the reactor in large amounts. plutonium dioxide has a very high boiling point. the toxic effect of the plutonium to the public under these conditions is much less than that of iodine-131 and caesium. during a loss of cooling accident, the fuel is not subject to such intense mechanical stresses, so the release of radioactivity is controlled by the boiling point of the different elements present.