For many objects, usefulness ends with failure as when milk goes bad or a light bulb burns out. The simple act of refrigerating a carton of milk postpones, but does not prevent, entry into Region C. Conversely, leaving the carton on the kitchen counter hastens the arrival of Region C and spoilage. In today's nuclear plants and in those proposed to be fueled by MOX, power is created by the splitting, or fissioning, of uranium and plutonium atoms. The splitting of plutonium atoms releases more neutrons at higher energy levels than the splitting of uranium atoms. More neutrons traveling at greater speeds may increase the number that strike the metal reactor vessel containing the reactor core.
Neutrons weaken metal by making it more brittle.
A hot, brittle reactor vessel might shatter like hot glass when placed into cold water. The reactor vessel metal can reach nearly 550 F when the plant is running. In case of a small problem, the plant's emergency systems may automatically start sending 40 F water to the reactor vessel. If the reactor vessel has become too brittle and shatters, all the King's men and all the King's horses would be no more successful putting it back together than they were with Humpty Dumpty. A shattered reactor vessel makes it virtually impossible to cool the reactor core, resulting in a reactor accident significantly worse than at Three Mile Island.