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Iwasa, Toma; Arima, Tatsumi*
JAEA-Technology 2021-036, 23 Pages, 2022/03
JAEA-Technology-2021-036.pdf:1.35MB
Knowledge on the liquefaction (thermal decomposition and melting) temperatures of MA-bearing nitride fuels for transmutation by accelerator-driven system is essential for elucidation of the fuel behaviors under abnormal condition and for the safety analysis. A melting temperature measurement system for refractory materials was developed based on a laser spot heating method, which is expected to measure in a very short time with a small amount of sample, and demonstration tests using refractory metals and zirconium nitride were performed. As the results, it was found that this melting temperature measurement system can be applicable up to the temperatures around 3000 K which is close to the thermal decomposition temperature of nitride fuels and we confirmed the technical feasibility of this system for future application to small specimens of transuranium nitrides.
Iwasa, Toma; Takano, Masahide
JAEA-Technology 2020-024, 29 Pages, 2021/03
JAEA-Technology-2020-024.pdf:2.33MB
Partitioning and transmutation of minor actinides (MA) is an important issue to reduce volume and radio-toxicity of high-level radioactive wastes. In Nuclear Science Research Institute, we have been carrying out R&D on MA-bearing nitride fuel for accelerator driven system. In the actual nitride fuel fabrication process, a special nitrogen gas highly enriched with 
N is required to avoid 
C production from N by (n,p) reaction in the fuel. For the economical use of such expensive gas, we need a nitrogen circulation refining system that can remove carbon monoxide (CO) evolved by carbothermic nitridation of oxides and can use the nitrogen gas in the closed system without loss. To develop the system, at first we listed up the performance requirements, and then designed and assembled a prototype system for laboratory-scale demonstration. The system consists of CO removal unit and circulation unit that can automatically keep the system pressure and the gas flow rate constant. As a result of demonstration on the nitridation of oxide, both units completely satisfy the requirements. We confirmed that the concept can be applied to the actual fuel fabrication with further additional function such as automatic hydrogen feed for the control of decarburization.
Iwasa, Toma
no journal, ,
Minor actinide (MA) transmutation by ADS (accelerator driven system) is studied for volume and radioactivity reduction of high-level radioactive waste. Candidate of the MA transmutation fuel is nitride, and it is important to acquire physical properties of the MA-bearing nitride fuel. Melting point is one of the crucial thermophysical properties, however measuring melting point of nitride fuel is difficult because of its high melting point and high radioactivity. So, this study focus on measuring melting point by combination of laser local heating and measuring spectral emissivity that is able to measure without contact and container. Considering scalability, the measuring system with spectrometer have been constructed. Samples are ZrN as the inert matrix and (Er,Zr)N solid solution as surrogate fuel material. High pressure vessel filled with pure nitrogen gas and preheating by CW laser enabls to measure with minimal oxidation and cracking by thermal shock. Measuring by spectrometer enabls to obtain thermal emission spectrum and calculate spectral radiance of sample.
Iwasa, Toma; Takano, Masahide
no journal, ,
R&D on the application of Sol-Gel method and the economical use of nitrogen-15 enriched gas has been carried out as elemental technologies for MA-bearing nitride fuel fabrication in engineering scale. High purity nitride sphere particles could be successfully fabricated by carbothermic reduction of mixed particles of rare-earth oxide and carbon prepared through external gelation technique. Very high efficiency in the particle nitridation was demonstrated. The lab-scale prototype model of nitrogen circulation refining system that can remove CO gas evolved from nitridation reaction and automatically supply nitrogen gas of the consumed amount is demonstrated. As a result, the system shows the satisfactory performance. An additional function needed for the practical application is considered.
Iwasa, Toma; Takano, Masahide
no journal, ,
For the analysis of nitride fuel behavior for minor actinide transmutation under abnormal conditions, it is important to know the liquefaction temperatures (thermal decomposition and melting). The measurement system for refractory materials based on laser spot heating was developed and demonstrated for future application to small specimens of transuranium nitrides. Measurement in the temperature range around 3000K was enabled by high melting temperature metals as references. We measured surrogate nitride fuel samples and found the decrease in liquefaction temperature with increasing Er content.