FISSION-PRODUCT RELEASE DURING ACCIDENTS - AN ACCIDENT MANAGEMENT PERSPECTIVE

One of the aims when managing a reactor accident is to minimize the re lease of radioactive fission products. Release is dependent not only o n the temperature, but also on the partial pressure of oxygen. Strongl y oxidizing atmospheres, such as those that occurred during the Cherno byl accident, released semi-volatile elements such as ruthenium which has volatile oxides. At low temperatures, UO2 oxidization to U3O8 can result in extensive breakup of the fuel, resulting in the release of n on-volatile fission products as aerosols. Under less oxidizing conditi ons, when hydrogen accumulates from the zirconium-water reaction, the resulting low oxygen partial pressure can reduce these reactions signi ficantly. At Three Mile Island (TMI-2), only the noble gases and volat ile fission products were released in significant quantities. A knowle dge of the effect of atmosphere as well as temperature on the release of fission products from damaged reactor cores is therefore a useful, if not necessary, component of information required for accident manag ement.