In situ experiments on the performance of near-field for nuclear waste repository at KURT

To obtain the information on the design and performance assessment of a geological repository for nuclear waste, several in situ experiments on the performance of the near-field have been conducted for 5 years in the small-scale underground research laboratory, KURT. This paper summarizes the results from the in situ experiments. In the borehole heater test, the rock temperature at 0.3 m distance from the heater hole with 90 °C showed a 40 °C increase over initial temperature. After heating with 120 °C, the rock temperature at 0.3 m distance from the heater hole increased up to 50 °C over initial temperature. The EDZ size measured from the in situ test was in the range of 0.6–1.8 m, and was higher than that from the laboratory tests, which was estimated to be around 1.1–1.5 m. The maximum errors in estimating the location of acoustic emission source were 1.0 m in EDZ and 0.6 m in an intact rock zone, respectively. The damping ratios of the EDZ and intact rock were 0.091 and 0.005, respectively. The permeability of rock increased with decreasing distance from the tunnel wall because of the EDZ. The permeability in the EDZ seems to be increased up to 2 orders compared with that in the intact rock.

► Results of in situ experiments on the near-field of a repository are summarized.
► In BHT, the rock temperatures at 0.3 m from heater showed 40–50 °C increase.
► EDZ size measured from the in situ test was in the range of 0.6–1.8 m.
► Maximum errors in estimating the location of AE source were 0.6–1.0 m.
► Permeability in the EDZ increased up to 2 orders compared with the intact rock.