報告書番号

N10039

タイトル（和文）

有限要素法による余裕深度用処分容器（蓋ボルト締結タイプ）の構造健全性評価

タイトル（英文）

Evaluation on the structural soundness of the package with the lid bolted for subsurface disposal by finite element method

概要 （図表や脚注は「報告書全文」に掲載しております）

余裕深度処分施設に埋設される低レベル放射性廃棄物廃棄体（蓋ボルト締結タイプ）に対し設計時において要求される条件および落下などの事故時条件ついて構造健全性を評価した。有限要素法汎用解析コード ABAQUSを用いて廃棄体の吊り上げ時、積重ね時、ピット内部充てん時に対する解析を行い、いずれのケースにおいても発生する応力は当該材料降伏応力に比較して十分小さく容器が健全であることを確認した。
また、落下事故として発電所での8ｍ高さからのコンクリート床板への落下に対し有限要素法衝撃解析コード LSDYNAによる解析を行った。解析結果によれば廃棄体の衝突部で圧潰が生じるとともに蓋締め付けボルトに塑性ひずみが発生し、蓋が僅かであるが開口した状態となることがわかった。さらに、廃棄体に4MPaの外圧が作用した場合を想定してABAQUSコードによる解析を実施し容器が破損しないことを確認した。

概要 （英文）

The structural analysis of the disposal package for low-level radioactive wastes with relatively high activities (called L1 waste in Japan) were performed against normal and hypothetical conditions. As a normal condition the external load due to lifting, stacking of the package and filling the space of disposal pit with mortar or something were considered. Drop incident during handling and pressure due to some external force were taken up as hypothetical conditions.
Using finite element code ABAQUS and three dimensional finite element model, structural analyses were carried out for the normal conditions. The results show that the maximum stresses occurred at the package due to the loads above mentioned were far less than the yield strength for all conditions. Therefore, it is confirmed that the disposal package keeps its integrity against the normal conditions.
Analyses for load cases of 8m drop onto the reinforced concrete slab were performed by using finite element code LS-DYNA. The results show that the strains at the impact zone of the package exceeded the fracture strain of the material and the opening of the lid at the vicinity on the impact zone was observed but the damaged area was limited in the vicinity of impact zone.
As a maximum external pressure, 4MPa was applied to the surface of the packages which were piled up in four layered in the disposal tunnel. According to the results of analyses by ABAQUS code the maximum strain occurred at the contact surfaces between lid and body of the top package. However, the package stays in sound because the plastic zone was so small and the value of the maximum strain was less than the fracture strain of the materials.

報告者

キーワード