Over the last decade, SCK CEN obtained a large set of diffusion coefficients for different gases in different Members of the Boom Clay. These diffusion experiments were performed in the lab on Boom Clay samples with diameter 80 mm and length 30 mm. When performing safety calculations, diffusion of gas is assumed to take place within an approximate domain over 100’s of meters. This led to the question: is the lab-scale diffusion coefficient also valid on a larger (meter) scale In the past, a similar question was raised for more classical tracers such as HTO and iodide, and several in situ diffusion experiments lead to the confirmation of lab results. Hence, SCK CEN, ESV Euridice and ONDRAF/NIRAS will perform a new in situ diffusion experiment with dissolved neon in the HADES URL with as main objective to confirm/improve the current knowledge on diffusion of dissolved gas at a large scale.
The experiment preferably takes place under conditions that are relevant for the Boom Clay, thus not in an excavation damaged zone. Therefore, it was our aim to re-use an existing setup. All setups in HADES were screened against a list of criteria, and the MEGAS setup (drilled in 1992) was considered the best option.
Experiments with hydrogen are often complicated by the microbial conversion of hydrogen into methane, and therefore neon, considered to be the best proxy for hydrogen, will be used.
The experiment will consist of one injection circuit and three monitoring vessels. Dissolved neon will diffuse from the injection circuit/filter, through the clay, in the monitoring filters/vessels. The monitoring vessels are connected to a gas analyser which performs on line analysis of the neon concentration. By monitoring the concentration increase of neon in time in the monitoring vessels, the diffusion parameters can be determined.
This report describes both the technical aspects of the experiment, and the protocol to be followed.
|Number of pages||36|
|State||Published - 28 May 2020|
|Publisher||Belgian Nuclear Research Center|