Sorption Properties of Rocks as a Potential Component for Backfill of High-Level Waste Underground Repository

High-level nuclear waste containing long-lived radionuclides must be reliably contained in a deep underground storage facility. Its safety will be ensured by a system of artificial engineered barriers and the surrounding geological environment. Backfill is one of the least studied barriers, and it is often considered in conjunction with a bentonite buffer. However, it has its own tasks: fixing the position of the buffer and waste container, stabilizing tunnels and galleries, decreasing their permeability and thermal conductivity, maintaining groundwater Eh and pH to reduce the solubility and enhance the sorption of radionuclides, and preventing their migration as colloids on bentonite particles derived from the buffer erosion. Clays, bentonite, zeolites, cement, and a mixture of bentonite and crushed rock were proposed previously as potential backfill materials. One of the requirements to the backfill is its compatibility with the geological environment, which is met by the crushed rocks around the repository. High sorption properties of such rocks for radionuclides significantly reduce the radionuclide washout by water from the repository into the biosphere.