With regard to the cementation of the evaporator concentrate from pressurized water reactors, this study identifies the operating conditions giving properly coherent waste forms of a high volume reduction factor, high compressive strength, and good workability without the development of freestanding water. Simulated waste specimens prepared by varying the mixing ratios of simulated borate waste [boric acid (H3BO3) 12% by weight, pH 9], Portland cement, and slaked lime were tested. The results appear in a three-phase diagram depicting the proper blending necessary to yield final products possessing a compressive strength of over 15 MPa and a volume reduction factor above 0.65.
The solubility of sodium borate is higher than that of H3BO3, and cementation of a concentrated borate solution (24 wt% H3BO3, pH 9) was therefore also tested. The region of over 15 MPa of compressive strength with a volume reduction factor of over 0.6 based on the waste volume was identified. By increasing the H3BO3 concentration in the waste from 12 to 24 wt%, the actual volume was reduced by an additional factor of about two.