Experimental Studies of Fission Product Release from Commercial Light Water Reactor Fuel Under Accident Conditions

Fission product release from fully irradiated light water reactor fuel under accident conditions and the chemical forms and behavior of the released material have been studied at high temperatures. This work has emphasized release from commercial fuels, but tracer-level tests using specific fission product species have been used in efforts to clarify chemical behavior. The specimens were heated in an induction furnace in flowing steam at temperatures of 1700 to 2300 K. The fractional releases of krypton, iodine, and cesium increased with temperature, reaching maxima of nearly 60% in 20 min. The release of tellurium varied strongly with the extent of cladding oxidation and approached that of cesium for completely oxidized cladding. In addition to some structural material, the major chemical forms in the furnace effluent appeared to include CsI, CsOH, silver, antimony, and tellurides of cesium and tin. The fractional releases of the volatile fission products correlated with the amount of fuel porosity, and the masses of aerosol collected increased with test temperature and oxidation. Comparison of our results with several fission product release models showed agreement ranging from good to poor.