Near-field chemistry of a HLW/SF repository in Boom Clay - scoping calculations relevant to the supercontainer design

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Abstract

This report presents results of computer simulations to assess the time dependent evolution of near-field chemistry from a cementitious repository in Boom Clay. Because of large quantity of concrete used in the repository design and the very slow ingress of Boom Clay pore water by diffusion, an alkaline condition with a high pH > 12 is expected to sustain for at least 80,000 years based on model calculations assuming chemical equilibrium and diffusion transport in concrete. As a result of Boom Clay pore water and concrete interactions, three types of concrete pore fluids are derived as concrete degradation proceeds: a young concrete fluid with pH > 13 at the beginning stage (hundreds of years), an evolved concrete fluid with pH 12.5 for more than 80,000 years, and a calcium-silicate-hydrates (CSH) fluid. Redox condition within the near-field will likely be very reducing before the complete depletion of the metallic barriers due to corrosion. Afterwards, the redox will be governed mainly by the in- diffusing pore water from Boom Clay. Key factors influencing model simulation are porosity change of concrete and its influence on transport, boundary conditions, and diffusion coefficient in concrete
Original languageEnglish
PublisherSCK CEN
Number of pages53
Volume1
Edition0
StatePublished - Dec 2009

Publication series

NameSCK•CEN Reports
PublisherStudiecentrum voor Kernenergie
No.ER-17

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