Article pubs.acs.org/est
Dealing with the Aftermath of Fukushima Daiichi Nuclear Accident: Decontamination of Radioactive Cesium Enriched Ash Durga Parajuli,† Hisashi Tanaka,† Yukiya Hakuta,† Kimitaka Minami,† Shigeharu Fukuda,‡ Kuniyoshi Umeoka,‡ Ryuichi Kamimura,‡ Yukie Hayashi,§ Masatoshi Ouchi,§ and Tohru Kawamoto*,† †
Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 305-8565, Japan ‡ Tokyo Electric Power Environmental Engineering Co. Inc., 4-6-14 Shibaura, Tokyo, 108-8537, Japan § Koriyama Chip Industry Co. Ltd., 1-71-2 Tsuchiuri, Koriyama, 963-0204, Japan S Supporting Information *
ABSTRACT: Environmental radioactivity, mainly in the Tohoku and Kanto areas, due to the long living radioisotopes of cesium is an obstacle to speedy recovery from the impacts of the Fukushima Daiichi Nuclear Power Plant accident. Although incineration of the contaminated wastes is encouraged, safe disposal of the Cs enriched ash is the big challenge. To address this issue, safe incineration of contaminated wastes while restricting the release of volatile Cs to the atmosphere was studied. Detailed study on effective removal of Cs from ash samples generated from wood bark, household garbage, and municipal sewage sludge was performed. For wood ash and garbage ash, washing only with water at ambient conditions removed radioactivity due to 134Cs and 137Cs, retaining most of the components other than the alkali metals with the residue. However, removing Cs from sludge ash needed acid treatment at high temperature. This difference in Cs solubility is due to the presence of soil particle originated clay minerals in the sludge ash. Because only removing the contaminated vegetation is found to sharply decrease the environmental radioactivity, volume reduction of contaminated biomass by incineration makes great sense. In addition, need for a long-term leachate monitoring system in the landfill can be avoided by washing the ash with water. Once the Cs in solids is extracted to the solution, it can be loaded to Cs selective adsorbents such as Prussian blue and safely stored in a small volume.
■
INTRODUCTION The Great East Japan Disaster of March 11, 2011 crippled the Fukushima Daiichi Nuclear Power Plant (NPP) leading to a long-term radiation contamination issue. The radioisotopes released, on the order of 630 000−770 000 TBq (terabecquerel), left the region with contaminated soil, air, and water.1−3 As a consequence, thousands of people fled their home and are hesitating to or even prohibited from returning home, while life in the less affected areas is also facing unprecedented impacts. One year after the disaster, the main problem is potential exposure to the radioactivity due to the long living radioisotopes of cesium distributed widely in the disaster affected areas, 134Cs (approximately 1.8 × 1016 Bq) and 137Cs (approximately 1.5 × 1016 Bq), mentioned hereafter as Cs-r.4 Among the huge volume of contaminated materials of various categories, including soil, vehicles, buildings, roads, plants, cleaning wastes, etc., millions of tons need urgent disposal. Because a designated disposal system is required for such wastes, emphasis is given to volume reduction, which includes mainly compaction and incineration methods for the solid wastes.5−7 Also, when the wastes comprise high percentage organics, incineration is preferred as it reduces volume on the order of tens of folds. A post Fukushima NPP © 2013 American Chemical Society
accident study by Koarashi et al. demonstrating the distribution of Cs-r in crop land, grass land, and forest shows the highest percent of Cs-r aboveground in the litter layer of forest sites.8 In addition, study by Shibata et al. found that the permeable wastes, such as woody materials and soil, show higher radiation levels in comparison to the impermeable wastes like concrete, etc.9 Therefore, collecting the litter for initial few years is expected to decrease the surface activity along with controlling the entry of Cs-r to the food chain via rainwater. As Fukushima prefecture alone covers 70% forest area, collection of litter is certainly highly effective in controlling the continuous dispersion of Cs-r, though safe disposal of litters from a huge area, conversely, is a big issue. According to the IAEA guidelines thermal treatment is the most suitable option for the volume reduction, especially of the organics-rich waste.6 However, enrichment of the contaminants is the limiting factor. In other words, the incineration products of wastes showing activities in hundreds order would enrich to Received: Revised: Accepted: Published: 3800
August 27, 2012 January 29, 2013 March 13, 2013 March 13, 2013 dx.doi.org/10.1021/es303467n | Environ. Sci. Technol. 2013, 47, 3800−3806
Environmental Science & Technology
Article
Figure 1. Modified hot air furnace incineration facility for the safe burning of Cs-r contaminated debris. (1) Dust collector, (2) feeder, (3) cyclone, (4) air heating furnace, (5) bottom ash, (6) fly ash-1, (7) cooling system, (8) bag filter, (9) fly ash-2, (10) HEPA filter, (11) chimney. Temperatures at different points of the system as recorded in midwinter: (a) furnace 815−830 °C, (b) furnace-out 510−525 °C, (c) bag filter-in
