This paper reports the results of a survey of regulatory documents to clarify the concepts of ALARA and BAT in UK radioactive waste management and disposal. The results of this survey indicated that ALARA concept has been included in the BAT decision-making process as an indicator to evaluate the reduction of exposure doses. It also indicated that when applying the BAT concept to the selection of options for facility components, it is important to aim for a systematic and balanced selection of options with a view to the facility as a whole, rather than selecting options that can minimize emissions to the environment and exposure doses. It was also shown that long-term uncertainty can be an important indicator when applying the BAT concept to the selection of facility design options for a radioactive waste disposal.

  Groundwater flow analysis is used to evaluate groundwater travel times and pathways over several kilometers to several tens of kilometers, covering the entire groundwater recharge and discharge areas, during preliminary investigations for a potential repository for high-level radioactive waste. A rock's hydraulic effective porosity (kinematic porosity) is a sensitive parameter while analytically determining the travel time of groundwater in the fractured rock. However, the concept of kinematic porosity in fractured sedimentary rock is unclear. For example, the permeability of fractures obtained from in-situ hydraulic packer tests in borehole investigations is treated as the permeability of the rock, while the porosity of the intact rock obtained from other tests is treated as the kinematic porosity. In this study, we examined the method to estimate the kinematic porosity of fractured sedimentary rock by comparing the travel time using the kinematic porosity estimated based on the fracture aperture and intact rock’s porosity with the observation results, using the Koetoi Formation and Wakkanai Formation (shallower part), which are sedimentary rocks with fracture development in low-permeability rock matrix, as an example. The travel time was consistent with the observations when the kinematic porosity was estimated based on the fracture aperture; the kinematic porosity was one to three orders of magnitude smaller than the porosity in the intact rock. In the case of sedimentary rocks with a water-conducting-fracture network in low-permeability rock matrix, it was shown that estimating the kinematic porosity based on the fracture aperture width is effective.

  Geological disposal of high-level radioactive waste requires not only selecting sites appropriate for the waste repository, where its isolation ability would not be damaged by natural phenomena for several tens of thousands of years, but also rationally constructing the disposal system depending on site-specific geological environments and their anticipated long-term variability. Recently, elemental/isotopic compositions of underground fluids (deep groundwaters, hot/cold spring waters, brines associated with oil and natural gas reservoirs, and so on) in Japan have been studied for evaluating the long-term stability of the geological environments of this country. Iodine and its radioactive isotope ¹²⁹I (half-life = 15.7 million years) are included in the subjects of the study. The current review paper provides overviews of (i) the iodine content and iodine-129/127 ratio (¹²⁹I/¹²⁷I ratio) of various materials in Earth's surface layers, (ii) relevant sample pretreatments and measurements, and (iii) ¹²⁹I/¹²⁷I data of the underground fluids in Japan, then gives (iv) some interpretations of the fluid ¹²⁹I/¹²⁷I data, along with their problems and uncertainties, and (v) some implications towards evaluating the long-term stability of geological environments.