X-ray Photoelectron Spectroscopic Study of U- and Sr-Containing Hot Particles Prepared under Laboratory Conditions, Accounting for Parameters of U5f Electron Lines

Abstract

Physicochemical processes of hot particle formation during an NPP accident were simulated. Samples of fuel-containing masses and hot particles yielded by heating the model fuel containing 10 and 5 wt % Sr relative to U at 2300°C for 6 min in an argon atmosphere were obtained. The elemental and ionic composition of these samples was analyzed by X-ray photoelectron spectroscopy. Under such fuel heating conditions, strontium is emitted much more actively than uranium, and hot particles consist predominantly of strontium atoms. The relative concentrations of strontium and uranium in the hot particles were estimated at 82 and 18 at. % and up to 71 and 29 at. %, respectively, for the samples collected after heating the fuel containing 10 and 5 wt % Sr relative to U, respectively. The samples comprise metal carbonates and hydroxides which in the case of hot particles can be found not only on the surface but also in the bulk. Uranium occurs in the samples both as complex oxides UO_x x (2 <x ≤ 3) and as uranyl compounds SrUO₄, SrUO₆, and SrU₃O₂CO₃(OH)₂. After heating, the fuel-containing mass can include uranium ions in an oxidation state lower than U(IV), which is in agreement with the data for fuel-containing masses from the Fourth Block of the Chernobyl NPP.