GAST Gas Flow Test Data Report

The Gas-Permeable Seal Test (GAST) at the Grimsel Test Site (GTS) is a field experiment to demonstrate the gas permeability of the 80/20% sand/bentonite (S/B) mixture under realistic scale and boundary conditions. After an extended period of system saturation and characterisation, multiple gas injection and gas flow experiments were performed.

This report describes operational activities and the data recorded during the performance of the gas flow test (GFT) and covers the reporting period from 01 January 2022 to 31 December 2023. It is part of the scientific documentation of the GAST project, which is briefly outlined in Sections 2.1 and 2.2. This report provides essential background information and details about the GFT performance to facilitate understanding and interpretation of the recorded data. Nagra (2025) present further analyses and preliminary interpretations of the recorded data and observations.