Determination of Gases in Low Enriched Coated Oxide Particles

The gas content of single irradiated and unirradiated low enriched UO₂ coated particles has been investigated in a crushing unit developed by SGAE, Seibersdorf by means of a mass spectrometer. Whereas the content of fission gas has been determined at room temperature only, the CO content has been measured in addition at elevated temperatures. It was found that the internal fission gas release followed a 1/T relation at low burn-ups of 1. 3% FIMA, At a burn-up of 4.5% FIMA the internal fractional fission gas release reached 70-80% even at medium temperatures,. The measurements of the CO gas at elevated temperatures showed a dependence of the CO content in unirradiated and irradiated particles on the heating time before crushing. A strong temperature dependence of the CO content has been found for unirradiated and irradiated CD-1032; the CO content increased nearly one order of magnitude after a burn-up of 6% FIMA. The CO contents of unirradiated particles from the more recent LE series have been lower compared to the corresponding values of CD-1032 and their temperature dependence up to 1600°C was less pronounced. In the LE series no significant increase of the internal CO pressure up to a burn-up of 5% has been observed. Finally a conversion of the CO content into CO pressure is discussed making simplified assumptions about the free volume in the particles.