Evaluation of the characteristic properties of grouts made with high volume of supplementary cementitious materials

Building on international experience in decommissioning experimental reactors through <i>in-situ</i> decommissioning (ISD) techniques, two Canadian experimental reactors that have been in storage with surveillance mode for the past three decades, Nuclear Power Demonstration (NPD) and the Whiteshell Reactor No. 1 (WR-1) are proposed to be decommissioned <i>in situ</i> resulting in two disposal facilities. The approach proposed by the applicant is to encase the below-grade structures in two specially-formulated grouts, with the above-grade structures dismantled and either removed or grouted below grade. Finally, a concrete cap and a low permeability engineered cover would be installed to achieve closure.<br>One area of interest for both ISD projects is that the grouted structures would be below the water table. The long-term behaviour of the specially-formulated grouts and existing structures with regards to groundwater flow and solute transport therefore needs to be adequately assessed and understood from long-term human health and ecological risk assessment perspectives.<br>The Canadian Nuclear Safety Commission (CNSC) has initiated a research project aimed to characterize some properties of the grouts that Canadian Nuclear Laboratories (CNL) has indicated that it intends to use for the NPD and WR-1 ISD projects. This research aims to support CNSC staff in their regulatory assessment of the validity of the assumptions made in CNL’s safety analysis reports and, more generally, of the adequacy of the proposed grouts to fulfil their functions in the ISD projects.<br>The paper presents the details of the ongoing experimental research project conducted by the CNSC. In particular, in addition to characterizing some of the usual properties of the grouts (such as workability, air content, temperature, unconfined compressive strength, etc.), the experimental program will characterize the grouts’ bleeding, static segregation, adiabatic behaviour, pH, Young’s modulus, tensile strength as well as density, absorption and leaching properties. The shrinkage will also be assessed, with a particular focus on the early-age strain behaviour of both mixes. Finally, the (relatively) long-term behaviour of the grouts will be assessed through a characterization of their hydraulic conductivity at different ages and under different crack opening conditions.