Soil Washing Experiment for Decontamination of Contaminated NPP Soil

The preliminary experiment was performed to obtain the operating conditions of soil washing decontamination process such as decontamination agent, decontamination temperature, decontamination time and ratio of soil and decontamination agent. To estimate decontamination efficiency, particle size of soil was classified into three categories; ≥ 2.0 mm, 2.0 ∼ 0.21 mm and ≤ 0.21 mm. Major target of this experiment was decontamination of Cs-137. The difference of decontamination efficiency using water and neutral salts as decontamination agent is not high. It is concluded that the best temperature of decontamination agent is normal temperature and the best decontamination time was about 60 minutes. And the best ratio of soil and decontamination agent is 1:10. In case of Cs decontamination for fine soils, the decontamination results using neutral salts such as Na2CO3 and Na3PO4 shows some limits while using strong acid such as sulfuric acid or hydrochloric acid shows high decontamination efficiency (≥90%). But we conclude that decontamination using strong acid is also inappropriate because of the insufficiency of decontamination efficiency for highly radioactive fine soils and the difficulty for treatment of secondary liquid waste. It is estimated that the best decontamination process is to use water as decontamination agent for particles which can be decontaminated to clearance level, after particle size separation. (authors)