Distribution of Cesium Isotopes in UO2 Reactor Fuel

Abstract

The absolute abundances of several isotopes of cesium and uranium in an enriched uranium oxide fuel rod have been measured with a mass spectrometer, using the isotope dilution technique. Samples taken from the inside and edge of the rod have shorn that the cesium abundances, particularly Cs134, near the centre are much less than expected, whereas at the edge, the abundances are as expected. An explanation for this distribution and for the unexpected Cs134 behaviour lias been put forward, along with a new value for the effective capture cross section of U235. A suggestion as to the mechanism of the movement of uranium oxide has been made, to account for the cylindrical hole found in the centre of the non-stoichiometric fuel rods.