Geochemical groundwater investigations. Final disposal of spent fuel

Teollisuuden Voima Oy (Industrial Power Company Ltd) will prepare itself for the final disposal of spent nuclear fuel into the Finnish crystalline bedrock. The final disposal has been planned to start in 2020. During the winter of 1984 a testhole will be drilled for gaining more experience and testing equipment and methods. This report has been written to support making the program for groundwater sampling and analysis for the testhole. The knowledge of groundwater chemistry is very important when evaluating the safety in the final disposal. Corrosion of capsule material, dissolution of uranium dioxide, diffusion and valency of leached radionuclides are all dependant on the redoxpotential and pH of groundwater. Sweden, Canada and Great Britain are among those countries that perform investigations for the final disposal of spent fuel into crystalline bedrock. Therefore this report is concentrated more on the methods and equipment of those countries, because that knowledge and experience may perhaps be applied to the Finnish bedrock. Some groundwater chemistry parameters ought to be analysed without any delay as an in situ-measurement in the borehole or as a surface field-measurement. Sweden seems to be the leading country in this field. Different isotopes and dissolved gases are recommended to be analysed for the estimation of the origin and age of groundwater