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Partners (Detailed Design Phase and partially full project):

Nagra, CH


Obayashi, JP

HotBENT Aims & Objectives

HotBENT will provide information and data for repository optimisation with respect to design, space, emplacement strategies and costs. The experiment aims to evaluate current accepted safety functions by investigating the effects of high temperatures on bentonite-based barriers and their safety functions.
The performance of bentonite barriers in the < 100 °C temperature range is underpinned by a broad knowledge base built on laboratory and large-scale in-situ experiments. Bentonite parameter characterization above 100 °C is sparser (especially for pelletized materials), although up to about 150 °C no significant changes in safety-relevant properties are indicated. That information is desirable for repository optimization with respect to design, space and costs (e.g. footprint, layout) and to enable more options with respect to the required interim storage time periods. HotBENT corresponds to the initial highest thermal-output period of geological disposal, the data can be used to evaluate strategies for the performance confirmation period.

The results from HotBENT are not associated with a particular disposal concept.
Specific aims:
  • Increase data base on buffer/host-rock performance under higher T-conditions (optional up to 200°C heater surface temperatures) and at realistic scales
  • Upscaling/changing of boundary conditions of bentonite buffers of laboratory and modelling knowledge to large, 1:1 scale with its inherited and commonly observed gradients
Secondary objectives:
  • Compare different materials, concepts/designs, boundary conditions (e.g. different types of bentonite and canister materials, water chemistries, temperatures, …)
  • Evaluation of microbial activities / corrosion / gases (e.g. buffer/canister)
  • Integrating of modelling (e.g. THMC) and lab activities (e.g. mock-up experiments), also via the EU funded EJP HITEC program
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HotBENT location

HotBENT has been emplaced in the well characterized former FEBEX gallery comprising a granitic hostrock.

The current HotBENT set-up (March 2020) including the currently forseen instrumentation sections

The current HotBENT set-up (in discussion – May 2019)
Current activities provisional timeplan

Following an intensive planning stage (till January 2020) and gallery preparation works including the construction of a cavern and gallery surrounding boreholes, the actual HotBENT experiment since September 2020. It consists of 4 heater modules, which were placed on compacted bentonite blocks, surrounded by granular bentonite material (GBM). The wo bentonites used were Wyoming type bentonite and BCV (Czech) bentonite.  Emplacement of the GBM was performed by an auger-machine achieving densities of higher around 1.40 g/cm3 dry density.

The completion of the construction is anticipated for August 2021 with the construction of a second sandwich plug and coeval start of the temperature ramping up of the heaters.

For more information about this project, or to get in touch, please use our contact page.