In a high-level radioactive waste disposal, it is important to understand the temporal change in transmissivity of the excavation damaged zone (EDZ) induced around the gallery because the EDZ could potentially serve as a potential migration pathway for radionuclides after the emplacement of radioactive wastes. The transmissivity of EDZ decreases by self-sealing due to saturation of EDZ and/or increase in external stress as shown by previous studies for sedimentary rock with high swelling potential of clay minerals. However, it is difficult to distinguish the quantitative contribution of each of them. Then, we have investigated temporal change in transmissivity of the EDZ in sedimentary rock with poor swelling potential by hydraulic tests performed in the gallery at 350 m depth of Horonobe Underground Research Center to understand its primary control. As a result, transmissivity of the EDZ under unsaturated condition has not been significantly changed for about 5 years. The transmissivity under saturated condition, where the gallery has been backfilled, has also not significantly changed over the past 4 years. In conclusion, self-sealing of the EDZ would not be expected in sedimentary rock with poor swelling potential.

This study aims to clarify the thermal piercing behavior of carbon fiber reinforced thermoplastics (CFRTP) using near-infrared heating. The objective of the proposed thermal piercing method is to suppress stress concentration and strength reduction around the hole compared with conventional mechanical drilling. The materials used for the experiments were carbon fiber reinforced polypropylene (CF/PP) and carbon fiber reinforced polyether ether ketone (CF/PEEK) laminates. Firstly, heating experiments of the laminates were conducted using near-infrared heating and high-frequency induction heating in order to investigate suitable heating methods for thermal piercing. A ring shaped near-infrared heater was used for infrared heating, and a pancake-shaped coil with 2 MHz high-frequency power source was used for induction heating. The results showed that near-infrared heating enabled uniform heating regardless of the stacking sequence of the laminates. Based on these results, thermal piercing machine consisting of near-infrared ring heater, puncture pin, and servo press unit capable of precisely controlling load and displacement was developed. Various experiments revealed the thermal piercing behavior of each laminate and the associated process issues. Furthermore, the damage behavior around the pierced area was evaluated by double-lap tensile shear tests. It was found that the maximum load and toughness of the thermally pierced specimens were improved compared with those of mechanically drilled specimens.