The Nuclear industry’s KBS method
The main idea of this method, proposed by the Swedish power industry’s nuclear waste company SKB, is to dispose of the spent nuclear fuel in mined tunnels at depths of around 500 meters below the surface. The most important barrier in safety case is considered to be man-made barriers, that is to say a copper canister with a buffer of bentonite clay. The theory of KBS is that while covered in clay, the copper will not corrode. And if the copper will not corrode, the hazardous waste will be contained safely inside the canister.
A site for building such a repository, if the application for a license is approved by the Government, has been chosen to be near the existing nuclear power plant in Forsmark.
Possible benefits:
- Mature state; cost-efficient completion of concept if potential issues are ignored/deemed erroneous
- Completion of project will take advantage of sunken costs
- The community of Forsmark has a high acceptance for a repository
Possible issues:
- In contrast to studies presented by the power industry’s nuclear waste company SKB, independent scientific studies in Sweden and Finland has shown that the copper canister may in fact corrode long before the canister has fulfilled its purpose, which in turn would mean a failure of the main barrier while the waste is still hazardous
- At the relatively shallow depth of 500 meters, the ground water flows rapidly, which means that any leakage of a failed barrier will reach the surface/biosphere in a relatively short time
- The chosen site is on the, which means an even quicker route to the biosphere (50-100 years) due to an increased flow of ground water
- Repository may not be able to withstand an ice-age due to the shallow placement, as permafrost, earthquakes as well as rock and stress movement at the proposed depth may compromise the integrity of the man-made barriers, resulting in the hazardous waste reaching the surface when ice recedes
- Relatively easy to access by humans, by mistake or otherwise
- Expensive; cost of a KBS-type repository in Forsmark is estimated to hit 42 billion SEK by SKB
Our conclusion is therefore that, as of now, the problems with the method far outweigh the benefits, making the method highly questionable for a viable final repository for spent nuclear fuel. In other words, the KBS method does not appear to meet the high demands for long-term safety that is expected of a final repository for spent nuclear fuel.
The Alternative Deep Borehole Disposal (DBD)
The main concept behind this method is to dispose of the spent nuclear fuel in drilled holes at a depth of between three to five kilometers. In contrast to the KBS method, stagnant groundwater, sheer depth, and very tight bedrock are considered to be the main barrier.
Possible benefits:
- Strong safety case as the spent nuclear fuel will be totally isolated from the biosphere, if the natural conditions at these depths remain unaffected by the repository
- Main barrier of stagnant groundwater not affected by ice age
- Low risk for human intrusion, either intentional or unintentional
- When sealed, the surface may be put back into pristine condition which means that the environmental impact on the surface level is down to a minimum
- Considerably less expensive than the 42-billion SEK KBS method
Possible issues:
- Are we capable of creating these holes?
- Critical moment of lowering the canister down the hole, and of retrieving it mid operation if necessary
So, are we capable of creating these holes? The answer is: “yes”. Since drilling for oil and gas is constantly pushing the envelope for what is possible in terms of deep drilling, drilling at these depths with the necessary diameter/width is possible today.
As noted, concerns have been raised regarding the critical moment of lowering the spent nuclear fuel down the hole, and subsequently retrieving the canisters mid operation if necessary. However, recent reports state that we are in fact capable of designing canisters that are unlikely to get stuck. It is also worth pointing out that at the slow rate of lowering the canister down the hole, it is very unlikely that it will get stuck regardless of shape. And even if a canister does get stuck, we are capable of retrieving the canister without damaging its content at over one kilometers depth. Having said that, we are quite capable of designing metal canisters that will not only remain intact if stuck, but will also withstand corrosion for at least 1000 years.
Either way of looking at it, a stuck and broken canister at great depth is a preferable scenario to a leaking canister in a KBS repository at mere 500 meters.
As the sheer depth of disposal on its own seems capable of preventing and/or containing any leakage for millions of years, the potential problems addressed (which all have feasible solutions if not already solved) do not outweigh the possible benefits. The only reasonable conclusion is that, at the present time and with present knowledge, the DBD method appears to be a superior solution to the KBS method, and should therefore be investigated further.
