Fission product release from overheated uranium--a laboratory study.

Abstract

The nature and amount of radioactive material released during a reactor accident are of importance to reactor hazards evaluations, design of containment facilities and establishment of operating criteria. A laboratory study is currently underway at Hanford to provide experimental data which will be pertinent to analyses of accidental release under a wide range of reactor conditions. The investigation is designed to determine the effects of temperature, time of heating, atmosphere in which heated, irradiation level and specimen size on release of eight key fission-product elements from irradiated normal uranium. Preliminary tests investigated the oxidation and ignition behaviour of unirradiated uranium in air and steam. Small uranium cylinders were then irradiated to 2 × 1014 nut and heated out-of reactor under carefully controlled conditions and the fractions of the fission product isotopes leaving the specimen were determined. Temperatures up to 14400C for as long as 4 hr in atmospheres of air, steam and helium were measured; release in air was from two to ten times greater than in steam, while in helium the release was very low. Iodine, tellurium and xenon were released in proportion to the amount of uranium oxidized. Cesium and ruthenium were found to be semi-volatile. The release of strontium, barium and zirconium was found to be less than 0.2 per cent under all conditions tested. Efficiencies of several filter media in retaining volatilized fission products were measured. Tests are currently being performed to determine the influence of high irradiation level and specimen size on the fraction of fission products released from heated uranium.