For the radiochemical analysis of low-level radioactive wastes, a relatively large quantity of sample solutions must be prepared. In order to dissolve incinerated ash (fly ash and bottom ash) of radioactive combustible wastes and cement-solidified products of radioactive liquid wastes, a dissolution method using microwave heating devices was developed. In the present method, most metal elements in samples were extracted with HCl and HNO3 to the sample solution and a precipitate with silica as the main ingredient was decomposed with HF and HNO3. As a result, the fluoride residue was sufficiently reduced and more than 99% of the radionuclides were recovered to the sample solution. The ash and cement-solidified product samples were successfully dissolved in a shorter time compared with that of a conventional method by external heating, because HClO4 with a high boiling point and having much time for heating to dryness was not used.
