Comparing the effects of two ONKALO access ramp alternatives with numerical and analytical modeling

The spent fuel from the Finnish nuclear power reactors will be disposed of in the deep bedrock of Olkiluoto. The site investigations for the high level nuclear waste disposal will culminate in the excavation of an underground rock characterization facility, the ONKALO, from mid-2004 until 2010. Investigations in the ONKALO aim at confirming earlier characterization results in the conditions representing the actual deep rock environment. This report, which supports a siting plan for the access ramp, compares the hydrogeologic impact of two access ramp alternatives with numerical and analytical modeling means before the closure of the tunnels. One of the cases depicts the access tunnel in the vicinity of borehole KR8 while in the other one has it located in the vicinity of borehole KR9. According to results the ONKALO and the related access tunnel may affect the groundwater flow in their vicinity quite strongly but the siting of the access ramp is not significant factor for deep groundwater flow conditions under the influence of the ONKALO. (orig.)