Supercritical water pretreatment method for analysis of strontium and uranium in soil (Andosols)

Nagaoka, Mika  ; Fujita, Hiroki; Aida, Taku*; Guo, H.*; Smith, R. L. Jr.*

The radioactivities in the environmental samples are analyzed to monitor the nuclear power facilities. The pretreatment of radioactive nuclides of alpha and beta emitters in the environmental samples is performed with acid to decompose organic matter and extract object nuclide such as Sr, U and Pu. However, the pretreatment methods are time-consuming and used many concentrated acid solutions that are unsafe and hazardous. Therefore, we develop to the new pretreatment method using supercritical water instead of acid. Hydrothermal pretreatment of soils (Andosols) from Ibaraki prefecture (Japan) was used to improve methods for monitoring radioactive Sr and U. Calcined samples were pretreated with subcritical or supercritical water (SCW) followed by extraction with 0.5 M HNO solutions. With SCW pretreatment, recoveries of Sr and U were 70% and 40%, respectively. Experimental recoveries obtained can be described by a linear relationship in water density. The proposed method is robust and can lower environmental burden of routine analytical protocols.