The Composition of NO_x Generated in the Dissolution of Uranium Dioxide

The composition of NO_x generated in the dissolution of UO₂ has been described in different ways by earlier authors. Finding a way to determine the NO_x composition in the dissolution included experiments concerning the reactions of NO and NO₂ with 3 to 6 M HNO₃. The following conclusions have been obtained for the dissolution: (a) of the NO_x, NO is the direct product of the dissolution [3UO₂ + 8HNO₃ → 3UO₂(NO₃)₂ + 2NO + 4H₂O]; (b) part of the NO is converted quickly to NO₂ by the second reaction, i.e., NO + 2HNO₃→ 3NO₂ + H₂O (the equilibrium constant of this reaction determines the NO_x composition); (c) the dissolution is therefore expressible as 3UO₂ + 4(2 + x)HNO₃→3UO₂(NO₃)₂ + 2(1 — x)NO + 6xNO₂ + 2(2 + x)H₂O, (0 < × < 1) (some values of the × were obtained); (d) the amount of NO₂ in the NO_x is considerably smaller than that reported by earlier authors, e.g., 25% for 6.7 MHNO₃ at 101°C; (e) UO₂(NO₃)₂ coexisting in the solution tends to increase the NO component in the NO_x.