Cesium transfer to Gramineae biofuel crops grown in a field polluted by radioactive fallout and efficiency of trapping the cesium stable isotope in a small-scale model system for biomass gasification

The accident at the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Company, Inc.) caused by the Great East Japan Earthquake of 11 March 2011 resulted in radioactive fallout that caused heavy damage to agricultural production over a wide area of eastern Japan. Production of biofuel crops and their conversion to energy may be one way to resume agricultural production at an early date and to put renewable energy to practical use. This study addressed two concerns relevant to this scenario: (i) the degree of transfer of radioactive cesium from the soil to biofuel crops; and (ii) evaluation of gasification technology from the standpoint of removal of cesium contained in the biomass. Sixteen lines of Gramineae crops grown in an experimental field 112 km from the nuclear power plant contained 143.4–600.4 Bq kg−1 dry matter (DM) of radioactive cesium, the arithmetic average being 285.9 Bq kg−1 DM. The crops included, inter alia, Erianthus arundinaceus (Retz.) Jesw., Miscanthus spp., maize (Zea mays L.) and sorghum (Sorghum bicolor Moench), all of which were cultivated without tillage in 2011. A comparison of Miscanthus spp. that overwintered between 2011 and 2012 revealed that radioactivity decreased from 146.1 to 229.3 Bq kg−1 DM (arithmetic average: 193.3 Bq kg−1 DM) to 53.0–81.0 Bq kg−1 DM (arithmetic average: 66.0 Bq kg−1 DM). A simplified laboratory-scale experiment revealed that the stable isotope of cesium attached to pulverized biomass of Japanese cedar (Cryptomeria japonica D. Don) and E. arundinaceus was completely trapped in gasification system and gas purification system. This result indicates that cesium was not transferred to the gas that was produced for fuel. Gasification using polluted biomass will be practical after further studies have addressed problems related to issues such as scale-up, troubleshooting continuous runs and disposal of radioactive wastes.