Confirmation of the applicability of low alkaline cement-based material in the Horonobe Underground Research Laboratory

Abstract

In Japan, high-level radioactive waste repository will be constructed in a stable host rock formation more than 300m underground. Tunnel support is used for safety during the construction and operation, so, shotcrete and concrete lining are used as the tunnel support. Concrete is a composite material comprised of aggregate, cement, water and various additives. Low alkaline cement has been developed for the long term stability of the barrier systems whose performance could be negatively affected by highly alkaline conditions arising due to cement used in a repository. Japan Atomic Energy Agency (JAEA) has developed the low alkaline cement, named as HFSC (Highly fly-ash contained silicafume cement), containing over 60wt% of silicafume (SF) and Fly-ash (FA).JAEA is presently constructing the underground research laboratory (URL) at Horonobe for research and development in the geosciences and repository engineering technology.HFSC was used experimentally as the shotcrete material in construction of part of the 350m deep gallery in the Horonobe URL in 2013.The objective of this experiment was to assess the performance of HFSC shotcrete in terms of mechanics, workability, durability, and so on. HFSC used in this experiment is composed of 40wt% OPC (Ordinary Portland Cement), 20wt% SF, and 40wt% FA. This composition was determined based on mechanical testing of various mixes of the above components. Because of the low OPC content, the strength of HFSC tends to be lower than that of OPC in normal concrete. The total length of tunnel constructed using HFSC shotcrete is about 112m at 350m deep drift. The workability of HFSC shotcrete was confirmed by this experimental construction. In this report, we present detailed results of the in-situ construction test.

Changes of Temperature and Moisture Distribution over Time by Thermo-Hydro-Chemical (T-H-C)-Coupled Analysis in Buffer Material Focusing on Montmorillonite Content

“…The validation of the proposed model is performed by comparison with the results of in situ tests conducted by JAEA at Horonobe, Hokkaido, Japan [17,18]. The data used are for approximately 1200 days from 00:00 on 2015/1/16 (water injection start date).…”

“…The analytical conditions are summarized in the following Table 4. Under the experimental conditions, a play of a width of 2 cm is provided between the overpack and the buffer material [17]. This play will disappear due to the swelling of the buffer material.…”

“…In addition to simulations, in situ tests have been conducted at underground research facilities in Japan and overseas to understand coupled T-H-C phenomena. In Japan, in situ tests of engineered barriers have been conducted at the Horonobe Underground Research Center (JAEA), and measurement data such as the buffer material's saturation and temperature distribution have been obtained [17,18].…”

Evaluation of temporal changes in fracture transmissivity in an excavation damaged zone after backfilling a gallery excavated in mudstone

“…After the experimental setup was completed in January 2015, the modelled overpack was heated at 100°C to simulate the heat from radioactive waste. Groundwater was injected into the buffer blocks and back lling material at a rate of 300-400 mL/min from January 2015 to October 2016, and thereafter at 1.0 L/min (Nakayama et al 2016).…”