Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Opalinus Clay as a potential host rock for nuclear waste repositories

08.03.2011
Nuclear chemists at Johannes Gutenberg University Mainz, Germany, are investigating the interaction between radioactive elements such as plutonium and clay stones

Scientists at Johannes Gutenberg University Mainz (JGU), Germany, have studied natural claystone in the laboratory for more than four years in order to determine how the radioactive elements plutonium and neptunium react with this rock.

The experiments have been performed as part of a Germany-wide project sponsored by the Federal Ministry of Economics and Technology (BMWi) to find a suitable geological repository for radioactive waste. Geological configurations that could play a role for the permanent disposal of nuclear waste include not only salt and granite formations, but also claystone. The results obtained by the team of nuclear chemists under the supervision of Professor Tobias Reich confirm that natural clay has certain useful properties that counteract the migration of radioactive materials. Professor Reich, director of the Institute of Nuclear Chemistry at Mainz University, summarizes the results obtained so far as follows: „It does seem that clay could be suitable as host rock, although we still need to wait for the outcome of long-term investigations.“

The cylinders of clay used by the Mainz team of nuclear chemists have come a long way: Cores of Opalinus Clay were obtained by drilling in the Underground Rock Laboratory Mont Terri in the Swiss Jura mountains. This clay formation was deposited some 180 million years ago. In Switzerland, Opalinus Clay is being considered as a rock formation for the storage of radioactive waste. The bore cores were first transferred to the Institute for Nuclear Waste Disposal (INE) in Karlsruhe, Germany, where they were cut in small round disks with a thickness of 11 millimeters. At the Institute of Nuclear Chemistry in Mainz, these clay disks were packed in diffusion cells and contacted with pore water containing radioactive neptunium or plutonium. Other samples of clay were transferred to test tubes where a suspension of this material with pore water and the radioactive elements was agitated and centrifuged and then analyzed by highly sensitive mass spectrometers in order to determine the sorption characteristics of the clay material. Afterwards, the samples were transported to the particle accelerators in Grenoble, Karlsruhe, and at the Paul Scherrer Institute in Switzerland, where they were investigated by beams of synchrotron radiation with a width of only 0.0015 millimeters. “This provides us with detailed information on the distribution of the elements, and where and how the elements are sorbed on the clay material,” explains Reich.

The batch experiments show that radioactive plutonium in the oxidation state IV is nearly totally sorbed on Opalinus Clay, leaving almost no plutonium in the aqueous solution. In the case of neptunium(V), the corresponding ratio is 60:40. However, if neptunium is reduced to neptunium(IV) by iron minerals present in the clay, a near 100 percent sorption of neptunium on the clay is observed. The diffusion experiments using “radioactive” water have demonstrated that water passes through a clay cylinder with a thickness of 1.1 centimeters within a week. Neptunium, on the other hand, hardly diffuses through the clay, and even after a month it is still almost where it started.

Thin, millimeter-wide sections of the clay disks also show which chemical reactions of the radioactive elements occur as they pass through the clay material: Plutonium(VI) is reduced during its passage through the clay cylinder and is recovered as plutonium(IV). “This is a great advantage, as plutonium(IV) stays where it is put.” Professor Reich and his research team also discovered what is responsible for the sorption of the radioactive substances: It is predominantly the clay minerals, while the iron minerals responsible for the reduction process are only of minor importance in this connection.

Opalinus Clay, which occurs not only in Switzerland but also in Southern Germany, thus appears to be an excellent candidate for further investigation on the migration of long-lived radionuclides – neptunium, for example, has a half-life of 2.14 million years. The Mainz team of nuclear chemists had previously reported similar results using the clay mineral kaolinite from the United States of America. “In the meantime we have developed the necessary equipments and have defined the experimental processes required,” Reich summarizes the outcome of the experiments with Opalinus Clay. Over the coming three years, he and his team plan to investigate the behavior of clay in the presence of higher salt concentrations.

The studies are being conducted as part of a project initiated by the German Federal Ministry of Economics and Technology in 1995 to find a suitable location for a nuclear waste repository. Eight research institutions are participating in the joint project entitled “Interaction and transport of actinides in natural claystone, under consideration of humic substances and organic clay materials” to investigate to what extent Opalinus Clay could be a suitable host rock for the permanent disposal of highly radioactive waste.

The Institute of Nuclear Chemistry at Johannes Gutenberg University Mainz came out in 1972 from the Institute of Inorganic Chemistry and Nuclear Chemistry. It currently employs some 100 personnel. The institute operates one of three research reactors in Germany.

PUBLICATIONS:

T. Wu, S. Amayri, J. Drebert, L.R. Van Loon, T. Reich
Neptunium(V) sorption and diffusion in Opalinus Clay
Environ. Sci. Technol. 49 (2009) 6567
D.R. Fröhlich, S. Amayri, J. Drebert, T. Reich
Sorption of neptunium(V) on Opalinus Clay under aerobic/anaerobic conditions
Radiochim. Acta 99 (2011) 71

Petra Giegerich | idw
Further information:
http://www.uni-mainz.de/eng/14054.php

More articles from Life Sciences:

nachricht Cells communicate in a dynamic code
19.02.2018 | California Institute of Technology

nachricht Studying mitosis' structure to understand the inside of cancer cells
19.02.2018 | Biophysical Society

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Japanese researchers develop ultrathin, highly elastic skin display

19.02.2018 | Information Technology

Dispersal of Fish Eggs by Water Birds – Just a Myth?

19.02.2018 | Ecology, The Environment and Conservation

Studying mitosis' structure to understand the inside of cancer cells

19.02.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>