The Optimization of Immobilization for the Low-Activity Waste of theEvaporation Product with Cement

The experimental investigation of immobilization the low active wasteconcentration containing 2.44x10-3 μCi/cc a great deal of NaNO3 withcement was done. The immobilization process was carried out by mixing cement,water, concentrate, and Ca-bentonite with a given ratio within a glassbeaker. The mixture was then stirred with an electrical hand mixer untilhomogeneous. The studied immobilization condition were the influences of theweight ratio water to cement, the weight ratio of concentrate to cement withwhich the concentrate pH was varied, and the influence of the addition ofCa-bentonite (% in weight) with the optimum pH of concentrate. The sample inthe container with the size of 2.54 cm in diameter and 3.0 cm in height wasmade of polyethylene and was covered by a tight lid and was cured for 28days. After the sample was cured for 28 days and then it was taken out of thecontainer. This sample quality was ready for being tested. The quality ofcementation product tested compressive strength, density, chemical stability,irradiation stability and thermal stability. The optimum results ofinvestigation were the weight ratio of water to cement = 0.30, thecompressive strength of 30.37 N/mm2. For the immobilization of the waste andcement with the optimum pH being used, yielded in the compressive strength of28.07 N/mm2. Further more from the condition of waste and cement at theoptimum pH which was added by the optimum Ca-bentonite gained the compressivestrength of 33.64 N/mm2 before irradiation, where as after irradiation thecompressive strength was 32.41 N/mm2. The optimum thermal test resultachieved was 250 oC with the compressive strength of 44.10 N/mm2. For theleaching test results after being cured for 91 days in the distilled watermedia was 0.47x10-4 gcm-2day-1, while in the sea water was 0.66x10-4gcm-2day-1. Water medium activity until 91 days = 3.1x10-7 μCi/cc,MPC from ICRP = 8.1x10-7 μCi/cc. The experimental investigation ofcemented waste monolith block resulted like : 68.63% cement; 20.60% water;7.86% concentrate; and 2.91 % Ca-bentonite. (author)