Suitability Of LBP Clay As Backfill Material For LILW Disposal

Along with the continuous development of nuclear energy and nuclear technology, a considerable amount of radioactive wastes has been produced since 1940s, in which most part is low and intermediate-level radioactive wastes (LILW). For low and intermediate-level radioactive wastes, near surface disposal mode is used most widely all around the world. In multiple barrier system of near surface disposal mode, backfill materials are used as engineering barrier for blocking radioactive wastes migration, such as clay, cement, concrete, asphalt and mix materials etc. The clay is considered to be a better backfill material among them.Because of a low and intermediate-level radioactive wastes disposal site was suggested, this thesis chose the clay near disposal site as the research object. Systematic researches on the physical properties, water properties, chemical properties, and the mechanics properties of the clay were done through outdoor investigations and indoor experiments. On this basis, through the radionuclide migration simulation research of this material, a positive answer of the suitability of this clay material as backfill material for low and intermediate-level radioactive wastes disposal was given. The main research contents and achievements are as follows.(1) Field investigations shows that the resource of clay has some advantages, such as wide distribution, abundant storage, conducive to exploitation and transportation, which provides conditions to meet the requirement of disposal engineering.(2) Laboratory tests were conducted to study the physical properties, water properties, chemical properties, and the mechanics properties of the LBP clay. Compared with a backfill material used in a low and intermediate-level radioactive wastes disposal site, the preliminary research suggests that LBP clay is feasible when used as backfill material in low and intermediate-level radioactive wastes disposal.(3) The research of engineering characteristic on LBP clay is carried out. The results show this clay has an extremely low permeability coefficient, appropriate expansion rate and expansion force, high mechanical strength, low shrinkage and compressibility after compaction, which can satisfy the most requirement of backfill material.(4) This thesis makes a radionuclide migration simulation of137 Cs and239 Pu in compaction clay, the simulative results suggests after a reasonable backfilling design, the clay can effectively block radionuclide migration for low and intermediate-level radioactive wastes disposal in 300～500a.