THE ÄSPÖ HARD ROCK LABORATORY

THE ÄSPÖ HARD ROCK LABORATORY

A dress rehearsal for the construction of a final repository for spent nuclear fuel is currently being held deep down in the Swedish bedrock in the Äspö Hard Rock Laboratory (HRL). At a depth of nearly 500 metres, scientists and engineers are conducting field tests and developing technical solutions that will make the final repository safe for both man and the environment. The Äspö HRL resembles the future final repository in many respects. Most elements are already in place: canisters, clay, machines, tunnels and deposition holes. But the facilities differ in one essential respect: there is no spent nuclear fuel in the Äspö HRL. Come down and have a look!

Dress rehearsal and research resource The Äspö HRL outside Oskarshamn is a unique facility. SKB is conducting full-scale research and development here in preparation for the construction of a final repository for spent nuclear fuel. At the Äspö HRL outside Oskarshamn, a dress rehearsal is being held for construction of a final repository for spent nuclear fuel. The picture on the left shows the research village. The underground part of the laboratory consists of a tunnel that reaches down to a depth of 460 metres (see illustration at right). Understanding the long-term changes in a final repository for spent nuclear fuel requires research, both in the laboratory and in the field. The Äspö HRL is SKB s unique facility for such research. We are conducting a variety of tests and experiments involving both Swedish and international experts in this underground hard rock laboratory at a depth of nearly 500 metres. PRACTICE MAKES PERFECT The purpose is to find out how the final repository s barriers (copper canister, bentonite buffer and rock) prevent radioactive substances in the spent fuel from reaching the ground surface. The laboratory is continuing the work previously conducted in the Stripa mine. However, most of the activities being conducted in the Äspö HRL have to do with development of technology. A dress rehearsal is being held here of various work operations in the final repository. We are practicing depositing canisters, backfilling and plugging tunnels, and retrieving previously deposited fuel. Another important task is testing different machines that will be used in the final repository.

4 The various tests and experiments are being conducted in branches and niches in the tunnel. Some have been concluded, but most are still in progress. Horizontal Deposition RNR Experiment True Block Scale Demo Test Backfill and Plug Test Alternative Buffer Material Pillar Stability Experiment Minican Project Prototype Repository Zedex Experiment Lot Test Canister Retrieval Test RNR Experiment TBT Test Microbe Project Lasgit Test Two-Phase Flow Experiment LTDE Experiment Matrix Fluid Chemistry Experiment Rex Project Colloid Project True-1 Experiment SPIRAL-SHAPED TUNNEL The underground part of the Äspö HRL takes the form of a tunnel running from the Simpevarp Peninsula, where the Oskarshamn nuclear power plant is located, to the southern part of the island of Äspö. On Äspö the main tunnel descends in two spiral turns to a depth of 460 metres. The various tests are being performed in branches and niches in the tunnel. The laboratory s surface facility is located on Äspö. There the tunnel is connected to elevator and ventilation shafts. On the surface is a research village with offices, storerooms, etc. METHODS AND MODELS The facility began to be built in 1990 and was finished in 1995. We used the time before and during construction to test different methods for conducting site investigations (thorough investigations of the bedrock). The methods were refined, along with the models used to describe the properties of the rock. Above all we wanted to ensure that the boreholes that had been drilled from the surface provided sufficient information on the rock. Once under ground, we were able to study the rock in detail from the laboratory s tunnels and shaft.

More than 10,000 persons visit the Äspö HRL every year. The spent nuclear fuel will be deposited at a depth of about 500 metres. The barriers in the final repository canister, buffer and rock prevent the radionuclides from being transported to the ground surface. It s important to test all work operations and machines in a realistic environment. International cooperation Many different countries are participating in the experiments being conducted in the Äspö HRL. SKB is collaborating today with a number of countries and organizations that work with nuclear waste issues. In different forms and project groups we are working with sister organizations, research institutes and universities in Canada, the Czech Republic, Finland, France, Germany, Japan, Switzerland and Spain. The international contacts are important for being able to compare different methods for calculations and analyses, as well as for a thorough discussion and evaluation of the results. Cooperation also means our resources can be better utilized. It also gives us an opportunity to engage the foremost experts in different fields. However, this international cooperation is not about Sweden s agreeing to receive nuclear waste from other countries. MANY VISITORS The Äspö HRL is a popular destination to visit. Every year the Äspö HRL receives more than 10,000 visitors from both Sweden and abroad. We are more than happy to show the facility to anyone who is interested and explain what we do there. Free guided tours are given all year long. The lower age limit is seven years. Go to www.skb.se for more information.

6 Testing theory in practice We know what the final repository for spent nuclear fuel will look like in theory. The dress rehearsal of the practical parts is in full swing in the Äspö HRL. Here we are testing both machines and methods. The deposition machine that will be used in the final repository must be tested under realistic conditions. REALISTIC CONDITIONS A final repository for spent nuclear fuel must meet very stringent standards on radiation protection and reliability. Testing different machines and methods in a realistic environment is therefore becoming increasingly important as we approach the start of construction of the final repository. A number of tests and experiments are being conducted in the Äspö HRL to develop the final repository barriers and the deposition technology. Some, though far from all, are described on these two pages. The final repository method is based on SKB s proceeding in steps. At first only a small amount of the total quantity of spent nuclear fuel will be deposited. The results of this trial operation will then be evaluated, and if the results are negative in any respect we must be prepared to extract and retrieve the canisters from the deposition holes again. This is what we are testing in the Canister Retrieval Test. DEPOSITION MACHINE In a nearby tunnel we are conducting the Demo Test to determine the best way to place the 25-tonne copper canisters with spent fuel and the surrounding bentonite clay in the deposition holes. We have developed a remotecontrolled and radiation-shielded deposition machine for this test. SKB is also testing technology for backfilling and plugging tunnels. In the Äspö HRL we have backfilled and plugged a 30-metre long test area in a drill-and-blast tunnel. We are monitoring the sealing capacity of the backfill and the plug continuously with approximately 200 different measurement instruments. The results of the measurements will tell us whether the technology works and how well the calculation models we have been using agree with reality.

7 In the Prototype Repository we have built a copy of a part of the final repository. The picture shows one of the six canisters being deposited. A variety of instruments must be installed for the tests. Here cables are being run between different locations. DIFFERENT CLAYS The canisters with the spent nuclear fuel will be embedded in a buffer of bentonite clay. So far we have concentrated on investigating an American bentonite of defined composition. Now we will also test whether other bentonite clays from India and Greece work equally well or perhaps even better. The tests are being performed in the so called Apse tunnel, where we have previously made measurements of stresses in the rock. To demonstrate how a final repository works we have built the Prototype Repository a deposition tunnel with six full-scale canisters. No spent nuclear fuel is being used in the test. The heat output from the fuel is instead generated by electric heaters. Measurement instruments in the boreholes, the clay, the canisters, the bentonite, the backfill and the surrounding rock record what is happening. HORIZONTAL CANISTERS The canisters with spent nuclear fuel can be deposited in either an upright (vertical) or a reclining (horizontal) position. When the canisters are deposited horizontally, specially designed equipment is required for boring of the deposition holes and emplacement of the canister. We are testing this equipment at the 220-metre level in the Äspö tunnel.

At the cutting edge of research SKB s research is largely concerned with what happens in the long term in the final repository with the canister, the buffer and the rock. At the Äspö HRL we can conduct field tests and experiments to make our picture of the repository as complete as possible. It is important to find out how the water flows in the rock in order to determine whether the final repository is safe. LONG-TERM SAFETY Even though most of the tests currently being conducted are concerned with technology and methods, a number of experiments are also being carried out having to do with the final repository s long-term safety. The goal is to understand all the changes that occur in the repository and how they affect the repository s ability to isolate the spent nuclear fuel. If for some reason a canister is damaged, water can enter and cause corrosion of the cast iron insert. In the Minican Project we are investigating how corrosion occurs in the gap between the insert and the copper shell. Five miniature canisters are lowered into boreholes and monitored. On all the canisters the shell is perforated with small holes. The Lasgit (Large Scale Gas Injection Test) Test is also related to what happens if the canister is damaged. When the iron in the insert rusts, hydrogen gas is formed. The pressure in the canister then rises and the gas is forced out through the surrounding bentonite. This could theoretically lead to the formation of channels in the clay. In the Lasgit Test we are pressurizing a canister with gas to make sure this doesn t actually happen. LIFE UNDER GROUND One of the most interesting projects in the Äspö HRL is the Microbe Project, in which experiments are being conducted with underground bacteria. One of the goals of the Microbe Project is to find out whether bacteria that produce sulphide ions can survive in the

Sampling of microbes. Underground microbes can protect the canister against corrosion. Investigations in boreholes drilled in the rock wall provide knowledge of how radionuclides find their way into fractures and pores in the rock. layer of bentonite clay that surrounds each canister in the final repository. Sulphide ions could be a threat to the canisters, since they can cause corrosion. But the microbes could also counteract corrosion by consuming oxygen, which can otherwise react with the copper. The Microbe Project will study to what extent microbes can keep the repository free from oxygen. PARCELS IN THE FLOOR The purpose of the Lot (Long Term Test of Buffer Material) Test is to study how the bentonite clay changes with time both in an environment similar to that in the future repository and in an even more aggressive environment. Parcels consisting of copper tubes and bentonite have been placed in holes bored in the tunnel floor. After the parcels have been heated for a number of years, we remove them and investigate how the properties of the clay have changed and how radioactive tracers have moved in the clay. In order to study how bentonite clay is affected by heat we have lowered parcels consisting of copper tubes and clay into the tunnel floor. The parcels are heated by electric heaters.

10 You have to go deep to build a safe final repository. ROCK RETARDS The purpose of the LTDE Experiment (Long Term Diffusion Experiment) is to investigate to what extent radionuclides penetrate into pores and fractures in the rock. This phenomenon is called diffusion and is important for the rock s ability to retard radionuclide transport. We also want to obtain data on the sorption properties of different radionuclides. Sorption is the process by means of which a substance in solution adheres to a solid phase. TINY SUSPENDED PARTICLES Can colloids transport radionuclides? This question has long been on the agenda and is now being investigated in the Colloid Project. Colloids are particles that are so small that they remain suspended in a solution without sedimenting. Their size usually varies between a thousandth and a millionth of a millimetre. They are naturally present in the groundwater, and in later phases of the evolution of the repository flowing groundwater can erode the bentonite clay in the buffer so that colloidal particles are formed in this way as well.

11 This brochure provides only a cursory sampling of the activities in the Äspö Hard Rock Laboratory. You can read more about the experiments in the publication Experiments at the Äspö Hard Rock Laboratory. Download it or order it from SKB s website at www.skb.se. The website also has more information on our activities, our facilities and our plans for the future. Don t hesitate to contact us if you have any questions or wish to visit our facilities.

12 Äspö HRL Oskarshamn Recitera/Edita 2006-09 Swedish Nuclear Fuel and Waste Management Co Box 5864, SE-102 40 Stockholm, Sweden Phone +46 8 459 84 00, www.skb.se