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Sue, Kasumi*; Hirasawa, Izumi*; Miyazaki, Yasunori; Takeuchi, Masayuki
no journal, ,
In the dissolving process of spent nuclear fuel, poor water soluble substances precipitate and accumulate, which lead to lower heat transfer efficiency and pipe blockage. The major substance is known as zirconium molybdate dihydrate (ZMH). ZMH has characteristic properties; for example, water solubility decreases and adhesibility increases as the reaction temperature raises. This study revealed that encrustation of the metal wall vessel was prevented by adding ZMH crystal when compared to the case without ZMH addition. As the ZMH crystal was added, the reaction between Zr and Mo was accelerated that inhibits nucleation in the reaction solution.
Kamoi, Kensuke*; Hirasawa, Izumi*; Miyazaki, Yasunori; Takeuchi, Masayuki
no journal, ,
In spent nuclear fuel reprocessing, one of the unsettled issues is an undissolved fuel component that generates various kinds of sludge. A typical example is Zirconium Molybdate Dihydrate (ZMH). Because of its poor water solubility and strong adsorbability at high reaction temperature, ZMH is easily encrusted to the wall of reprocessing equipment, which leads to critical problems such as pipe blockage and degradated heat transfer performance. Therefore, a practical method is required to suppress the encrustation of ZMH. In this study, the crystal state of ZMH was elucidated to find out a dominant factor that promoted accumulation and resulting encrustation on the surface. The ZMH crystal changed from elliptic to cubic as the reaction progressed while the crystal habit unaffected the crystal state. The following three steps were taken place in the ZMH encrustation process. (1) Small particles which are precursors of ZMH and which the ratio of Zr:Mo is 1:1, encrustate to the pipe, (2) Small particles are connected to form a layered amorphous, and (3) ZMH single crystals and aggregates encrustate on the layered amorphous.