Change in Bioavailability of Nutrients (Organic Matter) Associated with Clay-Based Buffer Materials as a Result of Heat and Radiation Treatment

摘要

AECL has developed a concept for the permanent disposal of nuclear fuel waste inplutonic rock of the Canadian Shield (AECL 1994). The concept involves the disposal of nuclear fuel wastes in an engineered excavation (vault), at a depth of 500 to 1000 m in plutonic rock. Fuel wastes would be isolated in corrosion-resistant metal (Ti or Cu) containers and emplaced in disposal rooms, surrounded by a highly-compacted clay-based buffer materail (consisting of 50 wt. percent Na-bentonite and 50 wt. percent silica sand). The rooms would be backfilled with a backfill material consisting of 75 wt. percent crushed and graded host rock and 25 wt. percent glacial lake clay. Clays naturally contain small quantities of organic matter that may be resistant to bacterial degradation. The containers with highly radiactive material would subject the surrounding compacted buffer material to both heat (max. 95 degres C) and radiation (max. 52 Gy/h) (Stroes-Gascoyne and West 1994). Both could potentially break down complex organic material to smaller, more bioavailable compounds. This could stimulate microbial growth which then could affect processes such as gas production, microbially-influenced corrosion and radionuclide migration in a vault environment. The objective of this study was to quantify the effects of heat and radiation on the bioavailablity of natural organics in buffer clay.