Conference Keynote: Digitalization and Decommissioning Technologies
Stefan Thierfeldt on radiological characterization
Radiological characterization is actually the essential basis for the further execution of all work - be it release of radioactive waste, decontamination and so on. In fact, the procedures still have a high degree of conservatism. This must be reduced in order to achieve the necessary throughput that release procedures simply must have today in order to provide the necessary inputs to the KONRAD procedures for the radioactive waste - which also does not arise until the dismantling as a whole is carried out. On the other hand, also to keep the dismantling period within a tolerable framework.
The activities in individual wastes that span as wide a range as possible, think for example of absorber rods in the core, think of structural material that are activated over a wider range over several orders of magnitude, or even residual materials with varying levels of contamination that you bring together from a wide range of wastes from a repository. Of course, you can pack them separately, the low activity wastes in the simple containers, the high activity ones in the complex ones with high shielding, etc. to keep all the characteristics and requirements for the waste packages. However, it is better to mix them appropriately to take advantage of self-shielding as well, thereby reducing the total number of containers and making the process more effective overall and the cost of the container lower.
Thomas XU explains the challenges of radioactive waste.
Actually, we have two challenges in decommissioning. These would be, first, how to achieve very good efficiency, while minimizing secondary waste, and still get a type of waste that is very easy to treat. This includes solid waste in particular, as it is much easier to handle and landfill than liquid or other types of waste.
Thus, we reduce the amount of waste volume below that of the initial product used at the beginning. As I mentioned before, we have a decontamination factor between 17 and 25, so on average we have a value of 20, so we reduce the radioactive dose by 20 times the original dose. And I think it would also be important to mention that the final waste is actually 100% mineral in nature, so there is no organic component in the final waste. The decontamination is now in the dried gel. This is a very important fact because if you have 100% mineral content, no organic, there is no risk that hydrogen could be present. So the waste is safe if you have to store it for a long time.
Tim Thomas points out how imaging technologies help with hotspot detection
In Germany, we have the special case that we do the dismantling for all nuclear power plants more or less at the same time. That is, we do industrial dismantling. This is exactly what the system is designed for, because we have the problem that we have to create a throughput and we have to do it with know-how that brings radiation protection into it.
A release is usually achieved by a decision measurement. And this is done by a direct measurement, a gamma spectroscopy, by the germanium detector or by the free measurement facility. The free-measurement facility is the one that controls the most mass flux. This is exactly where we want to show the quantum leap for clearance for nuclear decommissioning.
We've looked at where we can find a model that has exactly this hotspot detection in some form. We found it in medical physics, where imaging technologies are used. We have taken exactly this model of evaluation and adapted it to the nuclear requirements, as the DIN ISO 11929. For this we have the advantage that we do not initiate anything, because at worst we have activity in the waste. With this technique, we can now determine hotspots to a certainty of 95%, which is essentially only a computationally intensive task.
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