The Composition of NOx Generated in the Dissolution of Uranium Dioxide

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Abstract
The composition of NOx generated in the dissolution of UO2 has been described in different ways by earlier authors. Finding a way to determine the NOx 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 NOx, 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 NOx 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 NOx 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 NOx.

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