Quality review of transmissivity data from Olkiluoto site: Drillholes OL-KR1 - KR57

This report presents a quality evaluation of transmissivity data measured with the PFL tool, the HTU tool and the data obtained in connection with long-term pumping campaigns until the end of 2010. The magnitude and the distribution of transmissivity data form an essential part of the performance assessment and safety analysis of the disposal repository of spent nuclear fuel. The only possible way for radionuclides to reach the biosphere is to migrate in the groundwater flow and the character of the flow depends on the amount and hydraulic properties of transmissive fractures driven by a pressure field in the bedrock. The performance of technical barriers is also dependent on the character and magnitude of groundwater flow. For this reason, it is necessary to create a site-specific model that reliably describes the distribution of transmissivities. Furthermore, as the construction of the final repository for spent nuclear fuel progresses, it is vital to evaluate and understand the undisturbed baseline conditions prior to construction. A reliable database is a pre-requisite for fulfilling the requirements set for the geohydrological description and model of the site. Transmissivity is measured with the PFL tool by guiding, without pumping, the water flowing into the drillhole or out of the drillhole into the bedrock, and after several days of pumping, the water flowing from the bedrock into the drillhole through the flow sensor of the tool. A corresponding value is determined with the HTU tool by injecting water at constant overpressure from the double-packer section into the bedrock. In the evaluation of transmissivity values, the main focus was on finding out the most representative values among the data set, which in some cases was disturbed by groutings in ONKALO or by ongoing activities in the nearby drillhole(s). The increased yield caused by a hydraulic connection into nearby open drillhole(s) was also taken into account in the evaluation of the data. Transmissivity has been determined for a total of 3833 fractures in different campaigns between the years 1990 and 2012. The main corrections made in the measured values were an assessment of the friction loss of the tool for high flows and an assessment of the effect of hydraulic connections to adjacent drillhole(s). Statistically these corrections compensate each other, which means that the basic statistics remained fairly unchanged.