Spherical UO2 kernel Particle Preparation for HTGR fuel in Korea

A VHTR(Very High Temperature Reactor) is an important reactor concept for a near-term deployment under the nuclear R and D program of the Ministry of Education and Science Technology in Korea. The proposed nuclear fuel for the preliminary reactor concept is a TRISO(Tri-Isotropic or multi-layered structure) coated particle prepared by pyro-carbon and silicone coatings on a spherical UO2 kernel surface as a fissile material. Generally, the HTGR nuclear fuel production processes have been classified as five categories of research and development; - Spherical UO2 kernel preparation - Pyro-carbon(PyC) and silicon carbide(SiC) coatings - Pebble or Prismatic block preparation by using graphite matrix powder - Fuel performance including a fission products release - Advanced and improved fuel development Several proven fuel production processes are currently available for a spherical UO2 kernel production. The typical processes are an internal gelation process and an external gelation process. The well-known GSP(gel supported precipitation) process is one of the modified process for an external gelation method NUKEM of Germany. As developed above mentioned, both processes are based on the reaction of UN(Uranyl Nitrate, UO2(NO3)2)) and ammonia. The fundamental difference between the internal and external processes is in method of an ammonia supply to a liquid medium. The ammonia is supplied from an ammonium hydroxide solution within a gelation column in the external gelation process, whereas, in the internal gelation process, the ammonia is supplied from a thermal decomposition of an ammonia precursor solution which is included the HMTA(Hexa-Methylene Tetra Amine, C6H12N4) chemical. Here, the HMTA chemical contains the ammonia functional group at a low temperature condition. In this study, spherical ADU gel and UO3 particles via an UN solution as a raw material were prepared with the GSP process. And the spherical UO2 particles were obtained by a conversion of UO3 in a sintering furnace. The characteristics of the ADU gel, UO3, and UO2 particles were analyzed by a Streoscope, FT-IR, TG/DTA, and X-ray