Study of measuring bentonite density with active heating and OFDR measurement (Measurement of bentonite’s heat conduction with heated fiber-optic cable)

Abstract

In the concept of the disposal of High Level radioactive Waste (HLW) in Japan, bentonite material such as the engineered barrier system is planned to backfill around over-pack in the disposal tunnel. For the barrier with sufficient performance, this bentonite density in this tunnel is very important factor to control the quality of the performance. In this study, the mixture of the technology between an actively heated system and a Distributed Temperature Sensing (DTS) using fiber-optic cable was applied with the aim to measure the density of the bentonite as this performance in order to take advantage of the character such as each density of bentonite under same water content has different heat conductivity. Specifically, to define the density of bentonite, the heat conductivity in an unsteady state continuously was measured. Moreover, we performed to measure a density using Optic-fiber cable to improve the measurement performance instead of the existing measurement sensor. 1) High resolution measuring a temperature system which has multi-point measurement 2) The usage of reference box which have some fixed density of bentonite in the container beforehand and connect them on the measurement same line of fiber-optic cable. Before the In-situ performance, we conducted this system at our laboratory in order to check the handling of a measurement procedure and improve the evaluation method about the temperature data.