Analysis of the behavior of radioactive cesium in incinerators during garbage - 5010

Approximately 4.7 and 0.3 kg of Cs¹³⁷ and Cs¹³⁴, respectively, were released to the atmosphere in Fukushima Prefecture because of the accident at the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant after the March 11, 2011 Great Earthquake in East Japan. In the general incineration system, which is owned by the local government, garbage to which radioactive cesium (Cs) had adhered (with radioactivity levels of less than 8000 Bq/kg) was incinerated for the usual time. Before incinerating the radioactive Cs-bearing garbage, we conducted preliminary testing. If a very special case is removed, it is confirmed by measurement that radioactive Cs is not released from the exhaust stack of a general incineration system. The purpose of this study was the elucidation of the mechanism by which radioactive Cs contained in garbage is re-released to the atmosphere with combustion gas. We focus on the agglomeration of Cs molecules and deposition of radioactive Cs particles on ash particles that occurs during refuse incineration. We formulated a simulation model to analyze this phenomenon. It is assumed from the analytical results that radioactive Cs is not re-released for the following reasons. First, radioactive cesium hydroxide (Cs(OH)) adhering to garbage changes to radioactive cesium oxide (CsO₂) during the incineration process, and subsequently to radioactive cesium chloride (CsCl). CsCl and Cs(OH) molecules are deposited on the surrounding incineration ash (i.e., main and fly ash), and thus agglomerations are formed. For fly ash, agglomeration and deposition occur from the combustion chamber to the bag filter via the flue and the temperature reducing tower. During the incineration process, all radioactive Cs is deposited on fly ash and main ash particles. Therefore, radioactive Cs is not re-released to the atmosphere with combustion gas. (author)