Measurements on crystal lattice strain and crystallite size in irradiated UO pellet by X-ray diffractometry

X線回折による照射されたUOペレットの結晶格子歪と結晶子径の測定

天谷 政樹  ; 中村 仁一 ; 更田 豊志

Amaya, Masaki; Nakamura, Jinichi; Fuketa, Toyoshi

高燃焼度ペレット(燃焼度41-61GWd/t)のX線回折で、結晶格子歪,結晶子径及び結晶粒間に生じる不均一歪みを測定することにより、燃焼に伴うペレット内部の結晶状態を調査し、組織変化に及ぼす照射の影響を調べた。格子定数は、燃焼度とともに単調に増加して約70GWd/tでピークを示し、それ以上の燃焼度領域では若干減少する傾向を示した。また、回折ピークの広がり具合いから求めた結晶子径は、100-200nmでありリム組織で観察される再結晶粒の大きさに近かった。格子定数と不均一歪から求めた弾性歪エネルギー密度は燃焼度とともに増加し、約50GWd/tと70GWd/tでプラトーを示した。

Lattice parameters, crystallite sizes and non-uniform strains of high burnup UO fuel samples were measured using micro-X-ray diffractometry in order to investigate the so-called rim structure formation, in UO pellets. The pellet-averaged burnups of the samples were in the range 41 to 61GWd/t. While the lattice parameters of the samples increased linearly in the burnup region up to approximately 70GWd/t, the lattice parameters quickly decreased and tended to level off above 70 GWd/t. Measured crystallite sizes were in the range 100 to 200 nm and these were nearly the same size as the "recrystalized grains" in the rim structure. Elastic strain energy densities, which were evaluated from the lattice parameters and non-uniform strains, tended to increase with burnup and show two plateaus at burnups of approximately 50 and 70 GWd/t, respectively.