低レベル放射性廃棄物トレンチ処分施設の遮水層の検討状況

Status of design for the impermeable layer installed the trench disposal facility for low level radioactive waste

坂井 章浩 

Sakai, Akihiro

研究施設等廃棄物における安定五品目以外の廃棄物をトレンチ処分するため、国内及び海外における遮水層の構造を参考にトレンチ処分に設置する遮水層の設計を行った。遮水シートの材質の検討では、遮水シートの長期間に相当する耐候性試験を実施し、高弾性タイプのHDPEは引張強度及び伸び率の基準を満足したが、中弾性タイプのMEPEは引張強度について基準を満足しない結果が得られた。遮水層モデルについて、米国で開発されたHELPコードを用いて浸出水量の比較計算を行ったところ、2重の遮水シートの上部に排水層及び遮水シート間に低透水性シートを設置する構造が浸出水の抑制に十分な効果を期待できる結果が得られた。

The impermeable layer installed in trench disposal facility was designed in order to dispose of radioactive waste other than concrete and metal waste generated from research facilities, etc. In study of material of impermeable liners, weathering test in equivalent to long time was done. The test results showed that the tensile strength and the elongation percentage of HDPE that is a high elasticity type liner met standard values. However, the tensile strength of MEPE that is a medium elasticity type liner did not meet the standard value. The seepage water through several models of impermeable layers were calculated by use of the HELP code developed in U.S. The results showed that the structure that was composed of double impermeable liners, a drainage layer on the upper liner, and an impermeable sheet between the liners can be expected to have the enough performance to restrict seepage water.