Preparation of ammonium diuranate particles by external gelation process of uranium in INET

In order to satisfy the mass spherical fuel elements (SFE) requirements for the High Temperature gas-cooled Reactor (HTR)–Pebble bed Module (HTR-PM), a modified and optimized fabrication of dense uranium dioxide (UO2) kernel via an acid-deficiency uranium nitrate (ADUN) solution was researched and developed in the institute of nuclear and new energy technology (INET). In this study, external gelation process of uranium (EGU) based on the total gelation of uranium (TGU) in the period of 10 MW HTR (HTR-10) was used to prepare the ammonium diuranate (ADU) compound particles, an intermediate for UO2 kernel. The scale of batch production was improved from 500 g U/batch at that time to current 3 kg U/batch. Improvements in many aspects such as large scale preparation of ADUN, multiple-nozzle casting system and new aging, washing and drying (AWD) system without isopropanol were also presented. Under strict controls and measures, ADU particles with good sphericity and uniform diameter were acquired to ensure the subsequent preparation of dense UO2 kernels for HTR-PM.

► External gelation of uranium was developed to prepare ammonium diuranate (ADU).
► Requirements of acid-deficiency uranyl nitrate were discussed and analyzed.
► Multiple-nozzle casting system was applied to ensure batch production of ADU.
► New aging, washing and drying system without isopropanol have been developed.
► ADU particles with uniform diameter and good sphericity were prepared.