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

Building on international experience in decommissioning experimental reactors through in-situ 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 in situ 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.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.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.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.依托国际上利用原位退役（in-situ decommissioning, ISD）技术开展实验堆退役的既有经验，两座已以监控储存模式封存三十年的加拿大实验堆——核电示范堆（Nuclear Power Demonstration, NPD）与怀特谢尔1号堆（Whiteshell Reactor No.1, WR-1）——拟采用原位退役方案，由此形成两座放射性废物处置设施。申请者提出的技术路线为：将地下结构采用两种特制灌浆料进行包覆，地上结构则予以拆除，或移除至地下后再进行灌浆包覆。最终将铺设混凝土盖板与低渗透性工程覆盖层，完成退役闭合流程。两项原位退役项目均关注的核心问题之一为：灌浆包覆后的结构将处于地下水位以下。因此，需从长期人类健康与生态风险评估的视角出发，对特制灌浆料与既有结构在地下水渗流与溶质运移过程中的长期性能开展充分评估与研究。加拿大核安全委员会（Canadian Nuclear Safety Commission, CNSC）已启动一项研究项目，旨在对加拿大核实验室（Canadian Nuclear Laboratories, CNL）拟用于NPD与WR-1原位退役项目的灌浆料部分性能进行表征分析。本研究旨在为CNSC工作人员提供技术支撑，以协助其开展两项监管评估工作：一是验证CNL安全分析报告中所采用假设的合理性，二是从更广泛的层面评估拟用灌浆料在原位退役项目中履行其功能的充分性。本论文详述了CNSC正在推进的实验研究项目细节。具体而言，除了对灌浆料的常规性能（如工作性、含气量、温度、无侧限抗压强度等）进行表征外，本实验方案还将对灌浆料的泌水性、静态离析性、绝热性能、pH值、杨氏模量、抗拉强度，以及密度、吸水率与浸出特性开展表征分析。同时还将对灌浆料的收缩性能进行评估，重点关注两种灌浆料的早期应变行为。最终，将通过测定不同龄期、不同开裂开度条件下灌浆料的水力传导系数，对其相对长期性能进行评估。