Implications of Analcime Hydrothermally Formed from Na‐alumino‐borosilicate Glasses Containing Cs and Sr for the Stability of High‐level Radioactive Waste Form

Abstract

Abstract:In order to know the behaviors of radioactive elements such as cesium and strontium during a hydrothermal alteration of borosilicate glass of radioactive waste, some alumino-borosilicate glasses belonging to the systems Na 2 O-Al 2 O 3 -B 2 O 3 -SiO 2 -SrO, Na 2 O-Al 2 O 3 -B 2 O 3 -SiO 2 -Cs 2 O and Na 2 O-Al 2 O 3 -B 2 O 3 -SiO 2 -SrO-Cs 2 O have been treated hydrothermally at 200°C under a vapor pressure of 1.54 MPa. The result shows that all glasses are changed into crystalline phases with running time up to 60 days, and that analcime-type zeolite is formed as a major product. The formed zeolite is shown to contain cesium and/or strontium. Considering the fact that natural zeolite occurs in wide physicochemical conditions including hydrothermal one, the analcime-type zeolite is expected to fix stably the radioactive elements in the disposal site. Since aluminum is necessary for the formation of the analcime-type zeolite, the waste glass should have aluminum as one of major components.Keywords: radioactive waste, borosilicate glass, alteration, analcime-type zeolite, cesium, strontium Experimental Starting materialsAluminum is added as a major component to the sodium-borosilicate glass compositions examined before by Sohn et al. (2001). Since lithium is difficult to analyze and its content in actual radioactive waste glass is low, lithium was excluded in the present study.Before the main experiment, a preliminary experiment was carried out to examine the influence of addition of aluminum to glass component. The glass compositions of the preliminary experiment are based on the radioactive waste glass proposed in Japan (IAEA, 1979) except minor components. Since analcime-type zeolite was formed as a major product in the preliminary experiment, the chemical formula of analcime-type zeolite was selected as the chemical compositions of the starting glasses: Si/(Al+B) = 2 and (Al+B)/(Na+Cs+2Sr) = 1 in the main experiment.Each starting material tested in the preliminary and main experiments belongs to one of systems Na 2 OAl 2 O 3 -B 2 O 3 -SiO 2 -SrO (System NABS-Sr), Na 2 OAl 2 O 3 -B 2 O 3 -SiO 2 -Cs 2 O (System NABS-Cs) and Na 2 OAl 2 O 3 -B 2 O 3 -SiO 2 -SrO-Cs 2 O (System NABS-SrCs). Each glass was prepared by the following procedure: 1) reagent-grade B 2 O 3 , Al 2 O 3 and SiO 2 were dried at about 1200°C for over 20 minutes; 2) reagent-grade Na 2 CO 3 , Cs 2 CO 3 and SrCO 3 were dried, and decarbonated at about 850°C for over 30 minutes; 3) these reagents were weighted in appropriate proportions in accordance with each starting composition, and mixed for 20 minutes; 4) each oxide mixture was melted in a platinum crucible at about 1200°C for about one hour; 5) after melting, the melt was quenched; 6) the obtained glass was crushed, and ground to grain size of about 50 µm; and 7) this melting and grinding process was carried out two times in total.In each system, three different glass compositions were prepared (Table 1): one for the preliminary experiment, the other two for the main experiment as s...

Review on Selection and Experiment Method of Commonly Studied Simulated Radionuclides in Researches of Nuclear Waste Solidification

“…It can be seen that the high-temperature calcination process (1100∼1350°C) is an essential process for glass preparation. In the typical preparation process of borosilicate glass, Cs e high temperature may inevitably cause some volatilization loss of Cs 2 O in the glass [77], and this can lead to numerical deviations in the quantitative analysis of Cs + . us, the residual Cs + content in the prepared glass samples needs to be determined in some quantitative studies, such as the leaching test of the glass solidified body.…”

“…Sr 2+ is the main simulant of 90 Sr in present studies of 90 Sr immobilization [32,33,62]. In some of the studies mentioned above [10,62,77], 90 Sr was studied simultaneously with 137 Cs in the same solidified bodies in which Sr(NO 3 ) 2 , SrCO 3 , and SrCl 2 •6H 2 O were used as the simulants of 90 Sr.…”