An effective method to dry the sludge produced in a reaction between the evaporator concentrates of a pressurized water reactor (PWR) and calcium oxide (CaO) has been sought. The optimum reaction condition in this study for avoiding the adhesion of dried products to the heating wall of a dryer and for preventing the agglomeration of dried products was found to be about 0.75 mol ratio of CaO/boric acid (H³BO³). In this condition the dried products were porous spheres, and their true density was 2.04 × 10³ kg/m³.

In the immersion test of the solidified forms with unsaturated polyester in deionized water for 520 days, the weight change of the solidified forms was not more than 1%, and their volume change was negligible. The specific gravity of the solidified form containing 40% by weight of dried products was 1.45 and increased to 1.55 with an increase of the dried products to 50% by weight. The compressive strength of a solidified form in the above range was increased from 139.3 to 162.8 MPa. The effective diffusion coefficients in the 18-month leaching test for Cs-137 and Co-60 were 2.08 × 10^-15 m²/s and 3.30 × 10^-19 -2.26 × 10^-18 m²/s, respectively.