Relationship between changes in the crystal lattice strain and thermal conductivity of high burnup UO pellets

高燃焼度UOペレットの結晶格子歪み変化と熱伝導率変化との関係

天谷 政樹  ; 中村 仁一 ; 更田 豊志; 高阪 裕二*

Amaya, Masaki; Nakamura, Jinichi; Fuketa, Toyoshi; Kosaka, Yuji*

2種類のディスク状UO試料を試験炉にてそれぞれ60及び130GWd/tまで照射した。試料の微細組織を光学顕微鏡観察,SEM/EPMA及び微小X線回折法により調べた。試料の熱拡散率を測定し、熱伝導率を評価した。熱伝導率測定結果から、試料に蓄積された照射欠陥の量が各試料の照射条件に依存することが示唆される。熱拡散率測定前後での格子定数,歪みエネルギー密度の比較から、1200から1500Kの温度領域で見られる熱伝導率の回復は転位の移動に関係していると考えられる。

Two kinds of disk-shaped UO samples were irradiated in a test reactor up to about 60 and 130 GWd/t, respectively. The microstructures of the samples were investigated by means of optical microscopy, SEM/EPMA and micro-X-ray diffractometry. Thermal diffusivities of the irradiated samples were also measured and their thermal conductivities were evaluated. The thermal conductivity measurement results suggest that the amount of accumulated irradiation-induced defects depends on the irradiation condition of each sample. From the comparison of the changes in the lattice parameter and strain energy density before and after the thermal diffusivity measurements, it is likely that the thermal conductivity recovery in the temperature region from 1200 to 1500 K is related to the migration of dislocation.