Joint Vitrification of Various Mixed Wastes
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Mat. Res. Soc. Symp. Proc. Vol. 608 © 2000 Materials Research Society
cation of CRT glass as a glass forming agent in the vitrification of Nuclear Power Plant (NPP) wastes. EXPERIMENTAL Typical institutional and NPP LILW compositions are shown in Table I. In all the wastes, sodium and nitrate ions are predominant. NPP wastes from VVER type reactors (Russian analog of PWR) also contain potassium and boron. Occasionally, rather high amounts of iron, sulfate and chloride ions also may be present. The major radioactive constituent is '"Cs. Volume activities of 13 4Cs and corrosion products are lower by 1-2 orders of magnitude. Minor actinides are also present. Table I. LILW compositions Institutional NPP wastes from RBMK waste Leningrad Kursk Chernobyl
Parameters Ions Na' 6b K+ NINH 4
50-150 1-10 n.m.*
71.0 3.1 2.1
82.0 2.4 -
15.0 1.5 n.m.
5-20 1-10
10 (1250) 5.1 13.7 8.6 90 10 8.7(1250) 7.7 20.1 12.4 85 15
and CRT glass Glass Leach rate, densit•', g/(cm 2.day) g/cm Na÷ Pb + I 10"2.10-6 2.74 2.73 2.67 2.59 2.47 2.75 2.75
2.6.10-5 4.10-6 6.10.6
1.10-6
3,10-6 6.10-6
10"8
9.10-6
10-
10-7
7
10-7 7
10-
R-3
20
80
15.9
23.1
7.2
5.7(1250)
2.75
1.3.10-5
2.10'6
R-4 R-5
25 30
75 70
19.1 22.1
23.1 31.9
4.0 9.8
4.2 (1250) 3.7(1250)
2.76 2.77
2.8-10-5 5.2.10.5
2.10-6 3.10-6
more sulfate ions than VVER waste glasses and elevated sodium leaching occurs from the sodium-sulfate-rich constituent, whereas Pb2÷ ions incorporated in the glass network are leached significantly more slowly. Most of the glass melts produced from NPP waste surrogates and CRT glass have a viscosity suitable for electric melting both in a Joule heated ceramic melter and a cold crucible. Bench-scale tests on joint vitrification of surrogate NPP wastes and CRT glass Tests on joint vitrification of VVER surrogate waste and CRT glass were performed using the bench-scale cold crucible system. The cold crucible (inside diameter 135 mm, surrounded by a copper inductor with an internal diameter of 195 mm) was placed in a process box. The unit was energized from a high frequency generator with 60 kW and an operating frequency of 1.76 MHz. In the first test, the crucible was filled with CRT glass breakage and silicon carbide rods inserted to heat the glass and initiate melting. To reduce the melting temperature and electric resistivity, VVER waste surrogate was admixed in portions until homogeneous melt formation was achieved; this was followed by removal of the rods and continuous batch feeding. The calculated glass composition was as follows: waste oxide - 25 wt.%, CRT glass - 75 wt.%. Melt separation, a major problem, occurred because of the difference between the specific gravity of the surrogate waste salts and that of the CRT glass breakage used. To eliminate this effect, several methods of batch preparation such as moisturizing, compaction of the mixture of salts and finely ground CRT breakage, and calcination were tested. The best results were achieved using a calcined batch. No melt separation was observed. The average spec
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