Questions on geology in connection with final radioactive waste disposal in the Fennoscandian Shield

The use of nuclear power involves handling and disposal of radioactive waste. A number of methods for disposal have been proposed, one of which is the construction of repositories in crystalline bedrock of old continental crust. This possibility is usually considered reliable because of the relative stability of such bedrock. The Fennoscandian area has repeatedly been glaciated during the past 3 mission years. The last glacial event terminated some 10 000 years ago. This glacial ''massage'' has maintained a dense network of fractures and faults open for circulating water and ascending gas. Blocks of relatively unfractured bedrock have been proposed as suitable sites for the disposal of nuclear waste. Such questions concern neotectonic activity, the movement, salt content and amount of water at a few hundred metres depth, the mobility of elements in the bedrock as well as the geological processes which might be active beneath any future ice cap. Deep groundwaters, dating of young fracture minerals and neotectonic movements have been studied during 1985 - 1989 in a Nordic reserach program sponsored by NKA, the Nordic Liaison Committee for Atomic Energy. Deep saline groundwaters may have a negative effect on repositories of nuclear waste and the knowledge of the location of such waters may also give a hint as to the pattern of water movement in the bedrock. Therefore the composition, origin and location of deep groundwaters were studied. The development of faults in the bedrock through a site of waste disposal before the radioactivity in the waste has decayed to a safe level is considered a serious risk factor. Neotectonic movements have mostly followed old faults and fracture zones in the bedrock, which repeatedly have been reactivated during geological time, leaving blocks between the faults tectonically undisturbed. (CLS) 80 refs