Gas-Permeable Seal Test - Introduction

 Current partners
alt  National Radioactive Waste Management Agency (ANDRA), France
alt  National Cooperative for the Disposal of Radioactive Waste (Nagra), Switzerland
alt  Korea Radioactive Waste Agewncy (KORAD), South Korea
alt  Nuclear Waste Management Organization (NWMO), Canada

The degradation of organic substances and metals leads to gas production and accumulation in the emplacement caverns of radioactive-waste repositories. A concept for gas-permeable plugs and seals was developed in the framework of phase 1 of the Swiss sectoral plan process for deep geological repositories. The main aim of these plugs and seals is to increase the gas transport capacity of the backfilled underground structures without compromising the radionuclide retention capacity of the engineered barrier system. The design option is called "engineered gas transport system" (EGTS) and involves specially designed backfill and sealing materials e.g. seals made of sand/bentonite (S/B) mixtures which are part of the L/ILW repository concept.

Fig 3.3 2 SMA english

Figure 1: Concept of the designed gas path (red arrows) for the L/ILW repository with inlay showing the detailed design drawing of repository seal mod. V4 (after Nagra, 2008).

The GAST experiment is a large-scale demonstration and validation experiment which focuses on the specific issue of S/B seal behavior during saturation, and the gas transport capacity in the later gas invasion phase. The consolidation behavior and the gas transport capacity of the EDZ and the intact host rock formation are disregarded intentionally. They are investigated in the HG-A experiment performed in the Mont Terri rock laboratory. The GAST experiment demonstrates the efficiency of the gas permeable seal and enables providing high-quality datasets at realistic scale to validate and, if necessary, improve the existing models in order to make reliable long-term predictions of the EGTS behavior.

alt
Figure 2: Schematic layout of the GAST experiment

Previous experimental studies confirmed the high gas transport capacity of the S/B mixtures. These experiments have shown as well the ability to design S/B mixtures with specific target permeabilities for water and gas flow. First in-situ experiences were gained through the Gas Migration Test (GMT) at Grimsel Test Site (GTS), but with in-silo emplacement.A comprehensive laboratory program on combined gas/water transport in S/B mixtures has been conducted as part of the EU project FORGE.

For more information please contact: Thomas Spillmann, This email address is being protected from spambots. You need JavaScript enabled to view it.

Gas-Permeable Seal Test (GAST)

The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.