READS: Database of Promising Adsorbents for Decontamination of Radioactive Substances

Japanese

A large amount of radioactive substances was discharged from the Fukushima Daiichi Nuclear Power Plant following the Tohoku Earthquake and Tsunami, and made severe damages around the plants. The discharged radionuclides were ¹³¹I (half-life: ca. 8 days), ¹³⁷Cs (half-life: ca. 30 years), ⁹⁰Sr (half-life: ca. 29 years), ⁸⁹Sr (half-life: ca 50 days) and so on. Contamination resulting from the release of radioactive substances affects a wide range of environments. The assumed objects range from contaminated water including seawater which was used to tool the reactor core and accumulated at the power plant site, contaminated soil in the immediate vicinity of the plant and in the larger region around the plant (rice paddies, fields, orchards, etc.), woods and forests, water, buildings, roadways, and others. The distribution of contaminated water was also extremely diverse, encompassing seawater, river water, ponds and lakes, pools, agricultural water, etc. Because it was necessary to remove radioactive substances from this diverse range of sites, NIMS performed experiments and collecting data on many types of adsorbents under a wide variety of conditions.

In reality, even natural minerals having the same group name possess different adsorption capacities, depending on the chemical composition and original region where the substance was produced. Performance also varies greatly depending on use conditions, such as the concentration of radioactive substances, acidity of the use environment, and the like. In other words, because the most effective adsorbent will vary depending on the use environment, it is necessary to select the optimum adsorbent for the conditions at each site. However, comprehensive data showing the adsorption capacities of the large number of promising materials did not exist anywhere in the world, highlighting the urgent need to create a database for use when selecting adsorbents. The National Institute for Materials Science (NIMS) collected basic data on natural minerals produced in various regions and inorganic materials with different chemical compositions as a tool for selecting suitable materials. The objects are adsorbents for cesium, strontium, and iodine. For the adsorbents under study, NIMS collected nearly 800 basic data items for 60 species of materials from various localities and with various chemical compositions.

The basic data for adsorption capacities were collected in the following Figure (Experimental Procedures). The adsorption experiments were carried out for the promising materials with distilled water containing different amount of cesium chloride, strontium chloride and iodine. The mixture of adsorbent with appropriate amount of cesium chloride, strontium chloride or iodine aqueous solution was prepared at the fixed solid/solution ratio (e.g. 0.1g of adsorbent with 10 mL solution), and then shaken at room temperature (23°C) for 24 hours. After solid/liquid separation, the amount of Cs, Sr or I were determined by ICP method, etc. The experiments were performed at a limited condition. Therefore the collected data do not discuss the merits of the desired adsorbent. The appropriate adsorbent should be selected according to the conditions and processes. Please use the database by your responsibility.

Database construction was carried out by a total of 7 universities, 4 Independent Administrative Institutions (IAIs), and 1 foundation under National Institute for Materials Science. In addition to NIMS, the participating organizations are Hokkaido University, Iwate University, Tokyo Institute of Technology, Shimane University, the University of Miyazaki, Tokyo Metropolitan University, Kanazawa Institute of Technology, the Japan International Research Center for Agricultural Sciences (JIRCAS), the National Institute of Advanced Industrial Science and Technology (AIST), the Japan Atomic Energy Agency (JAEA), and the Central Research Institute of the Electric Power Industry (CRIEPI). These research teams are also key members of the Clay Science Society of Japan.

This research and development project was implemented mainly with support from the FY2011 Strategic Funds for Promotion of Science and Technology, "Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT).