ABSTRACT
The release of radionuclides, especially while fuel degrades within the reactor coolant system, has been the focus of much attention in severe reactor accident analyses. A bounding analysis of radionuclide behavior was done by neglecting any retention of radionuclides during transport through the reactor coolant system. Release of radionuclides during a reactor accident begins with the so-called “gap release” of vapors and some small amount of particulate material when the fuel cladding ruptures. By far the greatest amount of study of radionuclide release processes has been devoted to the release from intact fuel rods. As melting, especially of the fuel, progresses, radionuclides in metallic form can partition from the fuel into the metallic melt. Little work has been done on release from rubble beds. Little work has been done on release from molten fuel pools within the reactor coolant system. For many accidents, significant fractions of released radionuclides are predicted to be retained in the coolant system.
