Characterization of Composite Ceramic High Level Waste Forms
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Mat. Res. Soc. Symp. Proc. Vol. 481 ©1998 Materials Research Society
approximately 8 wt% surrogate fission products, and dried zeolite are then hot mixed at approximately 775K at which time the surrogate fission products in the salt are occluded into the zeolite structure. HIPing time at maximum temperature and pressure is approximately 100 minutes. For zeolite 5A, the salt loading is 21 wt% of the salt/zeolite mixture which is equivalent to 7.5 Cl/unit cell (uc) in the zeolite structure. For zeolite 4A an equivalent of 3.2 Cl/uc (10 wt% salt loading) is obtained. The salt occluded zeolite is then mixed with the glass binder. The mixture is then poured into an 11.4 cm diameter by 22.9 cm high stainless steel can through a pour tube and settled using a vibratory compactor. All preparations, prior to HIPing, are performed in a dry, argon atmosphere. The hot isostatic press operates at a pressure of approximately 170 MPa and a temperature of 900K for formation of the zeolite waste form and 1173K for the in-situ converted sodalite ceramic waste form. The major elemental composition (wt%) and the surrogate fission product concentrations (ppm) of the two salt occluded zeolites and final ceramic waste forms (1:1 zeolite/glass mixture) are shown in Table I. Table I. Major elemental composition for the surrogate, salt-loaded zeolite and the HIPed ceramic waste forms (1:1 zeolite/glass mixture) in weigh percent (wt%). Matrix Flement-.
Li
Na
K
Silt COrrluded Zeolite 4A
0.8
14-8
1.9
Zeolite 4A Waste Form SAit Oer-lided Zenlife SA Zeolite 5A Was•te Form
0-4 0-9 0-4
10-1 4-6 5-0
12 1.9 1.2
Ca 7-6 3.8
RF
Al
3-0 3-0
Si
0
CI
17.1
17-9
40-_5
6 5
10-4 15 4 9.5_
24.4 16.0 _23.5
47-1 3•6-6 45-?
3 ? 1-. I 6-6
Table I continued. Surrogate fission product elemental composition for the salt occluded zeolite and the HIPed ceramic waste form in parts-er-million (ppm). F.P. Salt Elements
Br
Cs
Rb
Sr
Y
Ba
La
Ce
Pr
Nd
Sm
Eu
Salt Occluded Zeolite 4A 50 Sodalite Waste Form 25
13 7
810 405
90 45
230 115
120 60
300 150
270 135
1930 965
260 130
860 430
150 75
11 6
Salt Occluded Zeolite 5A 100
26
1620 180
460
240
600
540
386
520
1720 300
22
13
810
230
120
300
270
193
260
860
11
Zeolite Waste Form
I
50
90
150
CERAMIC WASTE FORM CHARACTERIZATION Powder x-ray diffraction (XRD) was performed on the pre-HIPed materials after each processing step. After formation of the ceramic waste form by hot isostatic pressing, the compressed HIP can was cut into four radial sections using a high speed saw with a diamond blade and water lubricant. Core sections, 1 cm in diameter, were also obtained from numerous locations within each cut section. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were performed on polished ceramic monoliths or on powdered waste form samples. Density measurements of ceramic waste form monoliths were performed by gas displacement pycnometry and water immersion. Product durability testing of the ceramic waste form was determined both
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