Water in Molybdate Melts and Reactions with its Participation

Abstract

It is confirmed experimentally that water is soluble in sodium molybdate metal, and the solubility at 800°C is 0.018 wt.%. On the basis of this phenomenon, a technology is proposed for dewatering zirconium articles, which are subjected to heating in sodium molybdate, by introducing 1‐4 wt.% NiMoO 4 . As a result, the hydrogen content in the article decreases from 10 ‐2 to 0.4·10 ‐3 %. It is confirmed experimentally that metallic nickel, with which dissolved water reacts with hydrogen being released, introduced into the melt reduces U 3 O 8 to UO 2 in sodium molybdate melt. Pyrochemical methods using salt melts are one direction for reprocessing spent nuclear fuel. The presence of certain impurities in melts can considerably affect the quality of regenerated fuel. One such impurity is water dissolved in melt; its effect on processes occurring in melts has not been given adequate attention. The present article examines the processes occurring in molybdate melts with the participation of traces of water. Investigations of the crystallization of uranium dioxide and molybdate from molybdate melts in metallic nickel containers have revealed large prismatic MoO 2 crystals and metallic nickel in the form of dendritic crystals. The amount of crystals increased with increasing interaction time of the components of the system MoO 3 ‐Na 2 MoO 4 ‐Ni. It followed from observations that a reducing agent not introduced initially into the system is present in the melt. It was asserted that traces of water were present in the melt. In this case, reactions explaining the appearance of the products named occur: