-OttCLAMKR. 7 s V VITRIFICATION OF HIGH-LEVEL ALUMINA NUCLEAR WASTE J. R. Brotzman Exxon Nuclear Idaho Company, Inc. P. 0. Box 800 Idaho Falls, ID 840 ABSTRACT Borophosphate glass compositions have been developed for the vitrification of a high-alumina calcined defense waste. The effect of substituting SiO^, POC and CuO for BO on the viscosity and leach resistance was measured/ The effect of the alkali to boxate ratio and the Li0:Na0 ratio on the melt viscosity and - :! leach resistance was also measured. i * INTRODUCTION I o i Vitrification of high-level nuclear wsste is one of the waste management alternatives being investigated at the Idaho Chemical Processing Plant (ICPP). Currently the nuclear waste solutions are calcined to a mixture of granules and powder by a fluidizedbed calcination process. The calcined waste has been produced since 96 and is currently stored in near-surface stainless steel bins within concrete vaults. The two most abundant wastes produced are zirconia calcine,consisting of approximately 4% ZrO» 5Z AIO, and 5.?Z CaF, and alumina calcine consisting of approximately 90% AIO, % Na0, Z O, 0.5Z fission products, and.5 miscellaneous. Glass compositions have been developed for the zirconia calcine. The flux developed for the zirconia waste does not readily vitrify the alumina calcine, nor does it : vitrify mixtures of the two wastes lil in alumina calcine. Because of this, formulation's to vitrify the alumina calcine were developed. Although both borophosphate and borosilicate frits were evaluated, only the borophosphate frits reported on here resulted in practical alumina waste glasses. r.!!.- _.: i *
i -i. i * iii* tii -i Wrtdtrf lit-' I *- ' i-itm J4j«vfci*tai'i. : V -^,' 'MiitT,^ *SK< i.'f!4bvt. *»««;. i.. s: o... '- ' '.' : Each of the glass compositions were evaluated on the. basis of nelt viscosity and leach resistance. These two criteria were used because glasses with melt viscosities of 50-00 poise at temperatures of lt)50-00 C are desired for proposed nuclear waste vitrification processes of in-can melting or joule heated melting»" and glasses with high leach resistance are desired for environmental safety. -._... EXPERIMENTAL METHOD J Glass Preparation =- ;.- Experimental glasses were melted at 00 C in either 00 ml - ±- platinum or high-fired alumina crucibles. Glasses were made -. using reagent grade oxides and carbonates, and a simulated alumina : -~ calcine. 5 A G-4 h fining period was used after the charging -=?- of the glass additives was completed. The glass samples were ~~ poured into graphite molds, cooled, and then ground to a -6+0 ^-- mesh size for leach testing. ; :v.i Upon pouring, each glass was judged on a relative scale - - - ±~ r for viscosity ranging from -5^75-poise, *75-50, -50-00, if-'y ^SOO-SOO, and 5»not pourable, as estimated from standard -; -. ~- viscosity fluids. The actual viscosity of selected melts was ^-t- measured with a' Brookf ield viscome'ter. ' -:. ' -ri '' T. ' ' ''. """" ~ ~ ~ t * ". * - ' ir-t- Numerous compositions developed a meltable borophosphate -': T - glass containing molz calcine which was then used as a base glass. i~- for further study (Table ). The glass was evaluated in the -; -^=- four leach solutions shown in Table. The solutions were '-. zf- designed to evaluate the glass over a wide range of pll conditions. z - The soxhlet test was used because it measured the corrosion rates -^j of the glasses in a neutral ph region at a elevated temperature. : -fv Preliminary experiments showed that the borophosphate glasses ~- ^~ varied most In the Soxhlet leach test and had good leach resistance - if^r In the other leach solutions. Thus, the Soxhlet leach test was "- r^- used to compare the modifications made to the Base borophosphate fr- glass. The modified glasses were checked periodically for both. ; [ fy acid and Soxhlet leach resistance....-.-.. : ri~ Leach Tests ' '-'. - ' - " ", 7~T I Experimental procedures previously used at the IGPP Z were If followed in leaching the glasses. Four grams of the ground-glass T~ sample was weighed and placed in. either a 00 ml leachant solution TT (Table ) at 5 C or in a Sdxhlet apparatus at 95 C. After 9 T:^r hours on a magnetic stirrer or 7 hours in the Soxhlet apparatus, t~ Che sample was removed, dried, and then weighed. The gross weight
weight percent lost was then calculated. All leach rates referred to in this report are expressed as weight percent lost in either a 9 hour or 7 hour period. Table. Types of Leaching Solutions and Conditions Solution ph Temperature, C Time, h Description A.6-.8 5 9 " Uf acetic acid, buffered 7 95 7 distilled water, Soxhlet test C 9" " 5 9 M NHi^OH, buffered D 7.5 5 9 WIPP brine water, 06 g/l dissolved solids Table. Base Borophosphate Glass Composition and Properties Composition, in'oiz' ] ^ SiO BO PO5 LigO Na 0 CuO Al?0^ Calcine 78 4 40 0 0 0 Properties at 00 C 5-75 (poise) Acid Leach, wtz lost/ * * 0.5 9 h (5 C). ' Soxhlet Leach, wt% $ lost/7 h C95 C) BOROPHOSPHATE GLASS DEVELOPMENT Single Substitutions of SiO? or PO5 for B?Oq 4 The base borophosphate glass (No. 78) has a high Soxhlet :.' leach rate and a low melt viscosity. Individual substitutions of S0 and PO5 were made for BO in this base glass (Table ) to improve the Soxhlet leach rate. The substitution of SiO (8-0 moix) decreased the Soxhlet leach rate to only.5 wtz while only moderately increasing the melt viscosity. The substitution of (5 mol%) PO5 also lowered'the Soxhlet leach rate without
Table. Substitution of SiO or P 0 5 for BP A. Substitution of SiO? MolZ 87 78 88 0-44 4-40 8-6 - 6-8 7 8-6 7 0-4 B. Substitution of P?Os Mol% 76 78 86 85. 9. 9 94 0-50 0-40.5-7.5 5-5 7.5-.5 0-0 7.5-.5 A. Substitution of SiO? MolZ 85 _. 4 7 74 4-5.. 6-8- 0-9 -7 4-5 6- Base Glass 78. - 4 5 Base Glass 85.., i i ' Soxhlet Leach Rate; wtz lost/7 h - 6.5 6.0 5...5.4.. wtz' lost/7. h 7 6 * 6. 8 not reproducible wtz lost/7 h.0 -.4.0.6.0..4
«significantly raising the melt viscosity. At levels above 5 molz PO5, the glasses become very viscous, melted with heavy'surface scums, and had a high Soxhlet leach rate. Having observed a useful range of 0-5 molx PO5 * n t^e base glass, it was decided to substitute SiO for B 0 in glass 85 which contained 5 mol% PO5 (Table ). Substitutions of 4-4 molz S0 had little effect on the Soxhlet leach rate, and only moderately Increased the melt viscosity. X.t was not until substitutions of 4-6 molz SIO were made that the leach rate decreased and increased the viscosity to 75-50 poise. The Li0 to Na0 ratio, alkali.to borate ratio, and CuO content was then varied In the selected glasses (Table 4) to improve the melt viscosity and s oxhlet leach resistance. Table 4. Selected Low and High Silica Borophosphate Glasses r SiO? B?Oq Composition, raolz P?0$ Na?0 Li?O CuO Al?Oq Calcine 78 4.40 *P 0 0 85 4 5 5 0 0 7 8 6-0 0 0 7 0 4 0 0 0 74 6 5 0 0 Variation of the Alkali Ratio The alkali ratio was varied In a low silica glass (No. 78) and a high silica glass (No. 7). The effect of variation in the alkali ratio on the viscosity and Soxhlet leach rate of glass 78 was markedly different from that of glass 7 (Tables 4 and 5). All of the low silica glasses with a Li0:Na0 ratio of : or greater had leach Vates of 6-9 wtz while glasses with less LIO present had leach rates of 5-0 wtz. The variation of the Li0:Na<) ratio had no effect on melt viscosity. This glass was not Improved By changing the alkali ratio. All of the high silica mixed alkali glasses (Table 5) had leach rates between - wtz but the viscosity of the glasses decreased with increasing Li0 content. As an example, glass 0, which contains only LJJLO had the lowest viscosity (50 poise) and leach rate ( wt%). j
Table 5. Effect of Variation of Alkali' Ratio on and Leach Rate MolZ Li?0-Na?0 Glass 78 wtz lost/7 h 0-0 7. 5-5 9.4 78 0-0 6.0 4 5-5 5.6 5 0-0. Mol% Li?O-Lia?O Glass 7 wtz lost/7 h 0 0-0.0 0 5-*5 -: 7 0-0.4 0 5-5.0 04 0-0.5 Variation of the Alkali to Borate Ratio The alkali to borate ratio was varied in two low silica glasses (No.'s 78 and 85) and two high silica glassies (No.'s 7.. and 74) (Table 6). It was observed that the viscosity of the glasses decreased as the alkali content increased, and that the effect became more pronounced as the SiC> and PO5 content in the glass increased. For example, the most significant decrease in viscosity occurred in glass 74, a high SiC>, high P 5 glass. The low silica glass 78 had acid leach rates of 5 to 40 wtz when the alkali content was other than 0 molz (alkali:borate-:). The low PO5 and S0 contents of the glass are the cause for the high leach rates. The other glasses showed no major changes in leach rate if the alkali content was between 8-4 molz. Thus, improvements of the glasses (other than 78) can be made by increasing the alkali to borate ratio of the glass.
Table 6. Effect of Variation of Alkali to Borate Ratio on and Leach Rates 48 49 78 50 5 67 68 85 69 70 7 05 06 8 8 74 8 84 Substitutions Base Glass 78 MolZ Alkali-B^O* 6-44 8-4 0-40 -8 4-6 Base ' Mol% Alkali-B?0, 6-9 8-7 0-5. - 0- Base Mol% Alkali-BoO, 0-4 - 4-0 Base Mol% Alkall-BjO, 6-7 8-5 0- - 4-9 of CuO for BjO-^ ; Glass 85. Glass 7 Glass 74 ' -: ' wt* lost/7 h 4,.6 6.0.0 8.9 vtz lost/7 h 8-.7...0 ".8.0 - wtz lost/7 h..4 \.4 wtz lost/7 h 4.7...85.8 * Substitutions of CuO for JBO were made in a low silica glass (78) and a high silica glass (7) (Table 7). Both glasses were affected by CuO in a similar manner. Glass 78 without CuO did not dissolve the AIO calcine. The glasse with and 5 molz
I CuO produced good melts and had leach rates of 6-7 wt%. The viscosity of the glasses slightly decreased as the CuO content increased. Glass 7 without CuO melted well and had a Soxhlet leach rate similar to the glasses with and 5 mol% CuO (.5 wt%). The viscosity decreased as the CuO content decreased, but all were still within the viscosity range of 75-50'poise. Thus, the low silica and high silica glass were improved by substitutions of CuO for BO. ' " ' Table 7. Effect of Substituting CuO for BO on and Leach Rate 09 78 07 7 08 0 CuO-B^O, 0-4 -40 5-8 Mol%. 0-7 -4 5- Base Glass 78. Base Glass 7 Soxhlet' Leach Rate, wtz lost/7 h '- 6.0 7. wtz lost/7 h..4.4 Brookfield Measurements Actual 000-00 C viscosities, as measured by a Brookfield viscometer were determined for four glasses containing 0% PO5 and 0% alkali and for two glasses containing 5 PO5 and 0% alkali. In addition, the reduction in viscosity achieved in these glasses by Increasing the.alkali to borate ratio and the LiQ to Na 0 ratio was measured (Table 8]. Glasses with leach rates of about.5 wt% (glasses 7, 7, and 74 and wt% (glasses 85 and ) were measured for viscosity. All of the 0% PO5 glasses have better viscosity ranges than the - corresponding 5 PO5 glasses. The former glasses appear more suitable for calcipe vitrification.. '. "., Reductions of 0-50 poise were achieved by increasing the alkali to borate ratio of the glasses. A similar reduction in viscosity (about 0 poise) occurred when Li0 was replaced for ;_ N«0 in the glass. As stated earlier, it appears that high alkali, high Li0 glasses are improvements over the base compositions.
Table 8. The -Temperature Profile of Borophosphate Glasses Selected Condition Comparison of 0Z, 5% P 0 5 Glasses 000 C 85 75 0 7 74 75 580 Glass 050 C 05. 60 50 50 (poise) 00 C 0 40. 90 0 Alkali to Borate Ratio 7 06 74 8 75 0 580 80 50 0 50 00 90 70 0 70 Use of LIO 7 0 0 60 0 90 80 50 SUMMARY AND RECOMMENDATIONS. Substitutions of SiO and PO5 for BO were made using a base borophosphate (0 mol%. PO5) composition. Both of the additives increased the melt viscosity and decreased the Soxhlet leach rate. Substitutions of 4-5 molz S0 in a 5 mol% PO5 base glass also lowered the leach rate and increased the viscosity, but these glasses are more viscous when compared at equal leach rates. The viscosity of the low silica glasses, such as No. f s 78 and 85, Is slightly decreased by Increasing the alkali to borate ratio and by the substitution of CuO for BO. These modifications produced variable effect on the leach rates. The viscosity of the high silica glasses, such as No.'s 7 and 74, is decreased by. v increasing the alkali to borate ratio, increasing the HO to Na ratio, and by substituting, CuO for BO. These modifications cause only slight changes in the Soxhlet leach rate. The acid leach rates of these high and low silica glass «re quite low (0.5 wtz). Based on Soxhlet leach rate, melt viscosity, and glass meltability, there are a number of borophosphate glasses suitable for vitrification of the alumina calcine. High silica glasses with 0-5 molz PO5 and 0-4 molzjalkali (with a Li 0 to Na 0 ratio.
of : or greater) have soxhlet leach rates approxiraately one half that of the low silica glasses. All glasses meet the viscosity requirements of joule heated melting or "in-can" melting. These experiments demonstrate that leach resistant glasses containing alumina calcine can be made at temperatures compatible to the proposed vitrification processes. REFERENCES. G. F. Offutt and B. R. Wheeler, First Zirconium Alloyed Fuel Reprocesssing Campaign Using Soluble Nuclear Poison, AEC-IN-09 (March 968).. D. Gpmbert, H. S. Cole, J. R. Berreth, Vitrification of High Level ICP? Calcined Wastes, DOE-ICP-77 (February 979)... H. T. Blair, Vitrification of Nuclear Waste Calcines by In-Can Melting, DOE-BNWL-06 (May 976). 4. J. H. Valentine, B. J. Newby, et al., Calcination Flowsheet Development, DOE-ICP-6 (October 978). 5. S. A. Birrer, Pilot Plant Development of a Rover Waste Calcination Flowsheet, DOE-ICP-48 (April 978).