In the framework of the HotBENT international field experiment on nuclear waste management, geologists from the Lawrence National Laboratory at Berkeley, Sandia National Laboratory and Los Alamos National Laboratory are conducting modeling and laboratory studies to evaluate the behavior of bentonite as an impermeable backfill material for radioactive waste geological repositories.
Bentonite is a natural clay-based material with very low water permeability that swells on contact with moisture. Therefore, it is a material suitable for filling cavities around waste containers and tunnels in geological repositories. It can be used to protect radioactive materials from contact with water. It forms the third barrier in the multi-barrier approach, where high-level radioactive waste is immobilized in an insoluble matrix (first barrier) and placed inside sealed corrosion-resistant containers (the second barrier).
The aim of the HotBENT project (Impact of High Temperatures on Bentonite Buffers), led by the Swiss National Cooperative for Radioactive Waste Disposal (Nagra), is to assess how well a natural clay-based material (bentonite) placed around high-level waste disposal containers retains its protective functions during simulation of long-term heating.
The possibility of using bentonite in the nuclear waste management started to be tested in September 2021 at the Grimzel Test Site (GTS) in Switzerland, the data obtained will be supplemented by information from studies by US National Laboratories.
Geoscientists from the Lawrence Berkeley National Laboratory simulated the field test in a scaled-down laboratory set-up to look at changes in the materials over a year and a half, compared with five- and 15- to 20-year periods in the field, with a focus on understanding possible losses in bentonite’s ability to swell
Teams at Sandia will analyze bentonite samples sent from the Berkeley experiment and unheated samples from the Swiss test site to investigate heat-induced changes to the material’s mineralogy and its ability to swell.
At Los Alamos, studies are focusing on how a mixture of bentonite and other engineered barrier materials respond to heating, as well as testing the host rock the canisters will be buried within to clarify how the overall combination of materials responds at temperature increase up to 300°C.
According to World Nuclear News