51316-7458-Anoxic Corrosion of Carbon Steel in Bentonite in Relation to the Swiss Deep Geological Repository

Available for download

Product Number: 51316-7458-SG

ISBN: 7458 2016 CP

Author: Nikitas Diomidis

Publication Date: 2016

Member Price: $0.00

Non Member Price: $20.00

Price: $20.00

Qty:

The concept for the Swiss national program for the disposal of spent fuel and high level radioactive waste consists of a deep geological repository at a depth of 650-900m in Opalinus Clay host rock. The repository will be based on a series of excavated tunnels within which disposal canisters containing spent fuel assemblies or vitrified high level waste will be set on pedestals made from compacted bentonite blocks. After emplacement of the canisters the tunnel will be backfilled with granular bentonite and sealed. According to the current reference canister design concept the canisters will be cylindrical with flat ends that incorporate a handling feature and made from forged low carbon steel. After closure of the repository ingress of porewater from the host rock will eventually saturate the bentonite while oxygen will gradually be consumed. Saturated and anoxic conditions are expected to remain indefinitely and will therefore be present for the vast majority of the lifetime of the disposal canisters.The corrosion rate of carbon steel embedded in saturated bentonite under anoxic conditions was measured using barometric gas cells. The evolution of the corrosion rate was monitored for over four years during which quasi steady-state conditions have been reached. The measured corrosion rates are in agreement with weight loss measurements and with previous tests under similar conditions.Dismantling one of the gas cells and characterisation of the surface of the corrosion coupons and the steel/bentonite interface provided an insight into the prevailing mechanisms under relevant repository conditions. The main corrosion product was identified as being magnetite while there were also indications of other iron oxy-hydroxides. The thickness of the corrosion product layer characterized by FIB and metallographic cross-sections is in agreement with the corrosion rate results. Surface microstructural analysis and profilometry indicated that some roughening of the surface and localised phenomena had occurred.