報告書番号

T97083

タイトル（和文）

高燃焼酸化ウラン燃料のリム組織形成と試験方法に関する調査

タイトル（英文）

A SURVEY OF MICROSTRUCTURAL EVOLUTION IN HIGH BURNUP FUELS FOR LIGHT WATER REACTOR -IMPLANTATION OF HIGH ENERGY PARTICLES IN ACCELERATOR-

概要 （図表や脚注は「報告書全文」に掲載しております）

本調査報告では軽水炉燃料挙動について低燃焼時から高燃焼時に到るまでの知見を集約・整理し，リム組織形成機構について現在提唱されているモデルと，現時点で未解明な事項を明らかにした。具体的には，リム組織形成機構モデルとして１）粒内気■による細分化，再結晶，２）ポリゴニゼーションによる細粒化，３）欠陥蓄積による再結晶粒の核形成及び成長による再粒化，が提唱され，それらの起点形成機構は内部エネルギーのａ）均質な蓄積，とｂ）不均質な蓄積・放出，に大別される事を理解した。また，加速器を用いた模擬照射実験が燃料中で同時発生している損傷挙動を分離・抽出出来ることが理解され，リム組織形成機構解明および新型燃料開発の為には蛍石型結晶構造を持つ一般セラミックスから高燃焼度ＵＯ２まで加速器を用いた模擬照射実験を進める事が有効である事が解った。

概要 （英文）

IN RECENT YEARS, THE BURNUP OF LWR UO2 FUEL HAS FREQUENTLY BEEN INCREASED BY STEPS FROM 33 TO 55 GWD/TU ASSEMBLY AVERAGE HAVE BEEN REACHED. AT BURNUPS ABOVE ABOUT 45 GWD/TU OF THE PELLETAVERAGE, A POROUS OUTER RING (THE SO-CALLED RIM STRUCTURE ) IS FORMEDWITH A TYPICAL THICKNESS OF 100 TO 200MU M. THIS REGION EXHIBITS SEVERAL CHANGES OF MATERIAL PROPERTIES, SUCH AS DEGRADATION OF THERMAL CONDUCTIVITY AND SWELLING WITH HIGH POROSITY. IN ORDER TO DEVELOP FUELS FOR HIGH BURNUP USAGE, UNDERSTANDING OF THE FORMATION PROCESS OF THE RIM STRUCTURE IS ESSENTIAL. THIS SURVEY SUMMARIZES THE PREVIOUS MODELS FOR THE FORMATION MECHANISM OF RIM STRUCTURE, AND CLARIFIES THE RELATIONSHIP BETWEEN THE RIM STRUCTURE AND THE ACCUMULATION PROCESS OF DEFECTS AND PRECIPITATES UNDER HIGH BURNUP IRRADIATION. THE FORMATION MECHANISM OF RIM STRUCTURE IS SUMMARIZED AS (1)FRACTURE OF GRAINS DUE TO INTRAGRANULAR PORES AND RECRYSTALLIZATION, (2) POLYGONIZATION, AND (3) RECRYSTALLIZATION AFTER DEFECT ACCUMULATION. THE MECHANISM (1) OCCURS IN THE HETEROGENEOUS PHASE AND (2) AND (3) TO HOMOGENEOUS PHASE IN THE NUCLEATION OF RECRYSTALLIZED GRAINS. IN ORDER TO STUDY VARIOUS EFFECTS SEPARATELY TO INVESTIGATE THE FORMATION AND RECOVERY OF RADIATION DAMAGE AS WELLAS THE BEHAVIOR (LATTICE LOCATION, DIFFUSION, DISLOCATION, BUBBLES, PRECIPITATION, ETC.) OF THE FISSION PRODUCTS, HIGH ENERGY PARTICLES (ELECTRON, GAMMA, KR, XE, CS AND ETC.) IRRADIATION IN ACCELERATORS IS EFFECTIVE IN CLARIFYING THE FORMATION PROCESS OF RIM STRUCTURE. THIS SURVEY SUMMARIZES THE ADVANTAGES AND POSSIBILITIES OF HIGH ENERGY PARTICLES IRRADIATION EXPERIMENTS. FINALLY, THE EFFECTIVE EXPERIMENTS FOR UNDERSTANDING OF THE FORMATION MECHANISM OF THE RIM STRUCTURE ARE PROPOSED

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