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discovered_02_2015 - Near and far

WWW.HZDR.DE discovered 02.15 TITLE // Barriers, transport, and containment – how fundamental research is contributing to the safe storage of high-level radioactive waste. _TEXT . Christine Bohnet NEAR AND FAR In principle, waste and the pollutants it contains should not be allowed to leak out of a waste disposal site and into the environment, and thus the biosphere. It is for this very reason that Germany has a waste disposal site regulation that specifies a multibarrier concept. It applies to household and industrial waste, but also dictates that multiple barriers must ensure that highly radioactive waste stays safely contained for several hundred thousand years. The "Repository Search Law" adopted in 2013 even requires proof that it will be safely stored away for one million years. "From a historical perspective we are not capable of thinking so far into the future for such a long period of time, but if you base it all on geological processes, it would seem possible that the nuclear waste would remain safely contained for a million years," says Thorsten Stumpf, institute director at the Dresden Helmholtz center. All European countries faced with the task of disposing of waste from nuclear power plants rely on the safety of such a geological storage facility deep underground. Stumpf: "The repository must be capable of surviving multiple ice ages. This places very high demands on construction." Technical barriers may start to break down after just a few thousand years. This is the case with containers made of steel, for example, which could be encased in cast iron or graphite. These containers, together with the surrounding fill material made of concrete, bentonite, or salt grit, count as part of the immediate environment. Repository experts consider the surrounding host rock, however, to be part of the distant environment and this must be composed of geologically stable rock layers in order to ensure the safety of the repository for as long as possible - even if water seeps in that could possibly transport the radioactive heavy metals such as actinides and other waste materials into the environment. Repository research at the Helmholtz Association "Here at the Helmholtz Association we have divided the work between Jülich Research Center, the Karlsruhe Institute of Technology, and the HZDR in order to find solutions for the most important aspects of a future repository that are as stringent as possible," explains Stumpf, who worked as a radiochemist at the Karlsruhe Institute of Technology (KIT) before being called to work as the director of the Institute of Resource Ecology at the HZDR. This way, the research program known as "NUSAFE" covers a broad spectrum of issues, with the focus being on the behavior of radionuclides in repositories. But there are also other topics of concern when it comes to the disposal of radioactive waste. "All of our work ultimately revolves around the aspects of migration and retardation," Stumpf explains. "The mobilization of radioactive substances can be prevented using intelligent barriers, but also through processes that occur without our intervention." This could be chemical bonds between molecules and complexes, or electrostatic processes involving the exchange of ions on surfaces. A bond is always considered to be especially stable if the actinides are firmly incorporated into the mineral. Today repository research is investigating these processes on the molecular level. "It used to be that in the lab you would mix a solution, shake it for a while, and then figure out the distribution curve," Stumpf explains. This was used to estimate the dispersion of individual materials. If, however, a single parameter such as temperature changes, then the result would be invalid. "In the past we have generated some relevant examples that weren't included in the dispersion calculations." It is for this reason that Thorsten Stumpf is convinced that reliable conclusions can only be drawn by understanding the system as a whole. The findings on nuclear repositories from the research of the Helmholtz Association are made available to scientists around the world as well as government agencies and future repository operators in freely accessible databanks. CONTACT _Institute of Resource Ecology at HZDR Prof. Thorsten Stumpf INSTITUTE DIRECTOR: Thorsten Stumpf. Photo: AVANGA