Learning from the past, looking to the future
Years of research on the glaciers of Greenland have come to their conclusion. Posiva now has more detailed information of the conditions that prevail during and after an ice age. This means another step in the right direction in the process of assessing the long-term safety of the final disposal of spent nuclear fuel.
Posiva specialists have gained new insight into the impact of ice age conditions on the final depository. In recent years, the designers of the final repository have been working in Greenland to gather new information about the glaciation phase, the coldest period of an ice age, and the subsequent melting phase.
The research location in western Greenland, close to the settlement of Kangerlussuaq, exhibits bedrock and fracturing conditions that share many characteristics with the final disposal location in Olkiluoto. The area is therefore analogous to future conditions in Finland.
“The results of our research in Greenland will add more detail to the model created to depict future conditions in Olkiluoto. We have been able to confirm many of our earlier assumptions of the effect of an ice age”, says hydrogeologist Anne Lehtinen from Posiva.
Field testing showed, among other things, that the estimated impact of the ice load on the hydrological pressure used in earlier models was close to the actual conditions.
“The estimate had been considered rather conservative, but the actual conditions were in fact found to be very close to it”, Lehtinen says.
The research conducted in Greenland also offered valuable insights into the salinity and oxygen content of the water that drains down to the disposal depth.
Practical research concluded
Posiva has been carrying out research into the impact of glaciers in Greenland since 2009 together with SKB from Sweden and the Canadian NWMO. All three organisations will process the results together and participate in final reporting. According to Lehtinen, the final report will be completed in spring 2015.
“The main part of the research effort in Greenland has now been completed. We may take new monitoring samples from deep boreholes eventually.”
During the latest research expedition, Lehtinen worked together with chemist Tiina Lamminmäki, also from Posiva, and a microbiologist from VTT Technical Research Centre of Finland to gather water samples from and around deep boreholes, and microbiological and chemical samples from the boreholes. Lehtinen has visited Greenland every year since 2008.
Research into conditions during and after an ice age
When assessing the long-term safety of final disposal, detailed information of the conditions during and after an ice age is essential. The ice mass may be up to several kilometres thick, and will inflict great pressure on the repository.
When the ice finally melts, the melting water will drain away along any available route. It is necessary to estimate whether the water will be able to penetrate the cracks in the bedrock, and how deep it will flow. Melting water may also change the chemical properties of groundwater. Another factor to account for is the movement of bedrock as the Earth's crust begins to return to its former position during the melting phase.
Posiva participated in a wide variety of research projects in Greenland between 2009 and 2014. A deep-look radar was used to measure the thickness of the ice and the shape of the ground beneath it. GPS data provided information on the movement of the glacier and any changes in its thickness. Weather stations monitored the temperature, wind conditions, radiation from the sun and evaporation of water.
Holes were bored into the glacier and bare ground. Based on the data gathered from the boreholes, the depth of permafrost in the area was estimated at 350 metres.