State of the engineered barrier system and host rock of the HE-E experiment after 12 years of heating

Abstract

This paper presents the status of the HE-E heater experiment, which is currently running at the Mont Terri Underground Research Laboratory (URL) in Switzerland. The experiment is located in a 10 m-long section of a micro-tunnel in the shaly facies of the Opalinus Clay and includes two 4 m-long heater sections isolated by plugs. Heater 1 is located in a sand/bentonite (65/35) buffer section and Heater 2 is located in a granular bentonite buffer section. Heating started on 28 th June 2011, and this paper reports results up to 30 th June 2023. During the 12 years of heating the system has otherwise been left undisturbed with ongoing but very slow resaturation from the Opalinus Clay. The observed response to heating is considered in two phases 1) the initial transient period of about 500 days when heater temperatures rose to the target 140°C and 2) the subsequent evolution. Recently a novel telescoped drilling procedure has been performed to recover and characterize material from the bentonite buffer without interruption of the heating. This paper describes the experimental long-term evolution and status prior to this disturbance, together with expectations regarding the current state of the buffer. Thematic collection: This article is part of the Sustainable geological disposal and containment of radioactive waste collection available at: https://www.lyellcollection.org/topic/collections/radioactive Supplementary material: https://doi.org/10.6084/m9.figshare.c.7186450