Sintering and characterization of ZrN and (Dy,Zr)N as surrogate materials for fast reactor nitride fuel

高速炉用窒化物燃料を模擬したZrN及び(Dy,Zr)Nの焼結と性状分析

Pukari, M.*; 高野 公秀 

Pukari, M.*; Takano, Masahide

不純物炭素及び酸素の起源と影響評価を目的として、不活性母材のZrNと窒化物燃料を模擬した(Dy,Zr)Nペレットを調製した。1.2wt%までの酸素を意図的に加え、焼結体密度を酸素濃度、焼結温度、粉末比表面積をパラメータとして調べた結果、ZrNに比べて(Dy,Zr)Nの方が酸素固溶による密度増大効果が大きいことを明らかにした。ZrNの組織には酸化物相析出が見られ、窒素雰囲気下では酸素固溶量が少ないことが示唆された。ペレット調製の各工程で酸素,窒素,炭素の分析を詳細に行うことで、工程毎の不純物濃度増大の程度を定量的に評価した。

Pellets of inert matrix material ZrN, and surrogate nitride fuel material (DyZr)N, are fabricated for the purpose of investigating the origin and the effect of carbon and oxygen impurity concentrations. Oxygen concentrations of up to 1.2 wt% are deliberately introduced into the materials with two separate methods. The achievable pellet densities of these materials, as a function of O content, sintering temperature and dimensional powder properties are determined. O dissolved into (Dy,Zr)N increases the achievable densities to a larger extent than if dissolved into ZrN. The segregation of O-rich phases in ZrN indicates a low O solubility in the material. Oxygen pick-up during the fabrication of the product as well as its exposure to air is demonstrated. The quality of the materials is monitored by the systematic analysis of O, N and C contents throughout the fabrication and sintering processes, supported by XRD and SEM analyses.