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Opalinuston as host rock for radioactive waste investigated

Mainz nuclear chemists study the spread of radioactive
elements such as plutonium in natural clay

More than four years have investigated Mainz scientists natural clay in the laboratory to determine how the radioactive elements plutonium and neptunium in the rock act. The study was conducted as part of a Federal Ministry of Economics and Technology (BMWi) funded, nationwide project to Disposal of radioactive waste. As host rock for a repository that are in principle nuclear non-salt domes and granite formations and shales in question. As the analysis of nuclear chemists at the Univ. Dr. Tobias Reich confirm, has favorable properties of natural clay, to counter the spread of radioactive substances. "The tone seems to be suitable as a host rock, and even long-term safety assessments are needed," says Reich, Executive Director of the Institute of Nuclear Chemistry at the Johannes Gutenberg University (JGU), the results together. The

used for the investigations of the Mainz nuclear chemist cylinder of clay have a long way: from the Mont Terri in the Swiss Jura Mountains core samples are taken with Opalinuston - a rock formation that was deposited about 180 million years ago. Opalinuston in Switzerland as a possible host rock for a nuclear waste repository in the discussion. The cores used for the production of small, eleven millimeters thick, round slices first to Karlsruhe in the Institute for Nuclear Waste Management. At the Institute of Nuclear Chemistry in Mainz this clay disks are then packed in diffusion cells and placed in contact with pore water that contains radioactive neptunium or plutonium. Other clay samples in turn are used in test tubes, suspended shaken, centrifuged and then analyzed with highly sensitive mass spectrometers to study the sorption properties of clay. And they are to the particle accelerators to Grenoble, Karlsruhe and the Swiss Villigen (PSI), where 0.0015 mm dissect the fine synchrotron radiation with radio-elements shifted tone. "This means we get very high-resolution information on the distribution of elements and see where and how they are attached," says Reich.

shows the batch experiments, that in case of radioactive plutonium oxidation state of the four are almost 100 percent adsorption on the Opalinuston, while virtually no plutonium still remains in the solution. When neptunium the oxidation level five, the ratio of 60 to 40 But such as neptunium is reduced by ferrous minerals in the clay to neptunium four, also an almost complete binding to clay. Diffusion experiments with "radioactive" water show that water diffuses in one week by the 1.1-cm-thick clay cylinders. Neptunium is however much progress and is still after a month almost on top of the path found.

mm fine cuts of the small clay disks also show the chemical behavior of radioactive elements on their way through the rock: Hexavalent plutonium is reduced on the way through the clay cylinder and emerges as a tetravalent plutonium in appearance. ". This is advantageous because tetravalent plutonium remains seated in the place" Rich and his team have also identified who is responsible for the binding of radioactive substances, namely mainly the clay minerals and to a small extent, iron minerals, for the reduction have responsibility.

Opalinuston, as occurs not only in Switzerland but also in southern Germany seems so for further studies on the propagation behavior of long-lived radionuclides - for Neptunium the half-life is 2.14 million years - to be suitable. Similar findings were obtained earlier studies of the Mainz nuclear chemist with kaolinite clay minerals from the United States. "We now have the tools developed and established the key processes," Reich describes the work completed on Opalinuston. Next, his group in the next three years, the properties of clay is explored with higher salt contents.

The studies are part of investigations for site selection for a nuclear disposal facility, who started the BMWi 1995th The project "Migration and transport of actinides in natural argillaceous rock considering humic substances and Tonorganika" are a total of eight research institutions involved in order to determine the suitability of Opalinuston as host rock for disposal to investigate high-level radioactive waste. The Institute of Nuclear Chemistry at the Johannes Gutenberg University of Mainz in 1972 went forth from the Institute of Inorganic Chemistry and Nuclear Chemistry and currently employs around 100 staff. It operates one of the three research reactors in Germany.

publication:
T. Wu, S. Amayri, J. Drebert, LR Van Loon, T. Reich
Neptunium (V) sorption and diffusion in clay Opalinus
Environ. Sci. Technol. 49 (2009) 6567

DR Frohlich, S. Amayri, J. Drebert, T. Reich
sorption of neptunium (V) on clay Opalinus under aerobic / anaerobic conditions
Radiochim. Acta 1999 (2011) 71

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