[1C13-18] Bentonite chemistry

5:15 PM - 5:30 PM JST(8:15 AM - 8:30 AM UTC)

[1C17] Evaluation of Alteration Behavior at the OPC Paste/Bentonite Interface and Applicability Assessment of Reactive Transport Modeling Based on 3.5 Year Long-Term Tests

*Sho Nagai¹, Ayaka Koike¹, Sohtaro Anraku², Ryohei Kawakita² (1. NUMO, 2. JAEA)

Keywords:

Cement-bentonite interaction,reactive transport modeling,geological disposal

In geological disposal, bentonite buffers are emplaced near cementitious materials, raising concerns about alteration due to alkaline porewater. This study evaluates alteration at the cement–bentonite interface and the applicability of a reactive transport by comparing analyses of specimens reacted for about 3.5 years at 50°C with results obtained using the reactive transport model used in the NUMO Safety Case. The experiments showed Si depletion and Ca enrichment in bentonite near the interface, together with C–S–H precipitation and porosity reduction. The model reproduced these trends qualitatively but overestimated Si depletion. This discrepancy is attributed to limited representation of transport restriction by pore clogging and uncertainties in C–S–H formation and cement dissolution at elevated temperature.