This paper describes the off-gas analysis of samples collected during the radioactive vitrification experiments. Production and characterization of the Hanford waste-containing LAW and HAW glasses are presented in related reports from this conference

Bibler, N.E.

Choi, A.S.

Crawford, C.L.

Ferrara, D.M.

Ha, B.C.

UNT Digital Library

WSRC-MS-98-00038 CeoF- Qg0705 = Off -Gas Analysis During the Vitrification of Hanford Radioactive Waste Samples by B. C. Ha Westinghouse Savannah River Company Savannah River Site Aiken, South Carolina 29808 D. M. Ferrara c. L. crawford A. S. Choi N. E. Bibler A document prepared for SPECTRUM '98, NUCLEAR AND HAZARDOUS WASTE MANAGEMENT INTERNATIONAL TOPICAL MEETING at Denver, CO, USA from 9/13/98 - 9/18/98. DOE Contract No. DE-AC09-96SR18500 This paper was prepared in connection with work done under the above contract number with (he U. S. Department of Energy. By acceptance of this paper, the publisher andor recipient acknowledges the U. S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper, along with the right to reproduce and to aufhorize others to reproduce all or part of the copyrighted paper. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or nyresents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Govemment or any agency thereof. This report has been reproduced directly from the best available copy. Available to DOE and DOE contractors from the Office of Scientific and Technical Infoxmation, P.O. Box 62, Oak Ridge, TN 37831; prices available from (615) 576-8401. Available to the public from the National Technical Information Service, U.S. Department of Commerceq 5285 Port Royal Road, Springfield, VA 22161. DISCLAIMER Portions of this document may be illegible eiectronic image products. Images are produced from tbe best available original document. WSRC-MS-98-00038 x OFF-GAS ANALYSIS DURING THE VITRIFICATION OF HANJ7ORD RADIOACTIVE WASTE SAMPLES B. C. Ha, D. M. Ferrara, C. L. Crawford, A. S. Choi and N. E. Bibler Savannah River Technology Center Westinghouse Savannah River Company Aiken, South Carolina 29808 Extended Summary of a Paper Proposed for Presentation at "Spectrum '98," Nuclear and Hazardous Waste Management International Topical Meeting, September 13-1 8, 1998, Denver, CO, and for Publication in the Proceedings. This paper was prepared in connection with work done under Contract No. DE-AC09- 89SR18035 with the U. S. Department of Energy. By acceptance of this paper, the publisher and/or recipient acknowledges the U. S. Government's right to retain a nonexclusive, royalty-fi-ee license in and to any copyright covering this paper, along with the right to reproduce and to authorize others to reproduce all or part of the copyrighted paper. OFF-GAS ANALYSIS DURING THE VITRIFICATION OF HANFORD RADIOACTIVE WASTE SAMPLES by B. C. Ha, D. M. Ferrara, C. L. Crawford, A. S. Choi and N. E. Bibler Westinghouse Savannah River Company, Aiken, South Carolina 29808 INTRODUCTION As part of the Tank Waste Remediation System (TWRS), the United States Department of Energy (DOE) issued a Request for Proposal (RFP)' to vendors interested in building and operating a privatized facility for immobilizing radioactive waste currently being stored in tanks at the DOE site in Hanford, Washington. British Nuclear Fuels Limited (BNFL), responded to the RFP and was awarded a contract' to perform the initial phase of this work. BNFL has teamed with SAIC, Bechtel National Inc., GTS Duratek and the Vitreous State Laboratory (VSL) at Catholic University to develop and demonstrate technology needed to meet the terms outlined in the TWRS RFP. In collaboration with the BNFL team, the Savannah River Technology Center (SRTC) was asked to perform radioactive demonstrations with four samples of the actual radioactive waste from Hanford. SRTC has produced and characterized three Low-Activity (LAW) glasses and a single High-Level Waste (HLW) glass from actual radioactive Hanford waste samples. This paper describes the off-gas analysis of samples collected during the radioactive vitrification experiments. Production and characterization of the Hanford waste-containing LAW and HAW glasses are presented in related reports from this conference. WORK DESCRIPTION The radioactive demonstration was performed remotely in the SRTC Shielded Cells. Vitrification of the Hanford LAW and HLW samples was performed in three steps. First, water was evaporated from the sample and collected in one of the off-gas system traps. Then, the mixture was calcined. This removed the semi-volatile species that were in the waste form, e.g. nitrate and nitrite. Finally, the material was brought to the melt temperature and held there before the resulting glass waste form was taken from the furnace and sampled. 1 WESTINGHOUSE SAVANNAH RIVER COMPANY SAVANNAH RIVER TECHNOLOGY CENTER At the start of the experiment, the glass-forming chemicals and waste streams were mixed. Then, the off-gas system was set up. The off-gas system included a condenser, a dry-ice trap, charcoal filters, and a vacuum pump. The off- gas system was developed to keep hazardous species fiom the shielded cells environment. The crucible was put in the furnace, and the off-gas system was connected. The temperature of the furnace was then slowly increased 10 "C every 30 minutes, from the initial 50 "C, until water was collected below the condenser. When water started to accumulate in the condenser trap, the temperature was held constant until the condensation stopped. Then, the temperature was increased at the same rate until water started condensing again. This was continued until the h a c e  reached 200 "C. Page 2 of 4 Next, the furnace temperature was increased to 900 "C (at a nominal rate of 100 "C per hour) during which time the volatile species, e.g. nitrate and nitrite, were driven fiom the mixture. The temperature was increased slowly to avoid foaming or "splattering" of the material in the crucible. During this temperature ramp, brown vapor (NOa) was typically seen in the off-gas system. Once the furnace reached 900 "C, it was held at this temperature for thirty minutes. The off-gas system was disconnected. Material was finally brought to the melt temperature of between 1120 "C and 1150 "C and held there for 2 hours. The resulting glass waste form was taken from the firmace, quenched and sampled. The condensate trap and the cold trap were sampled after the experiment and the mass of the charcoal filters was measured to determine whether anything was adsorbed on the filters. The mass of the filters increased from 8 1 grams at the start of the tests to 86 grams after vitrifying the last glass indicating that 5 grams of material (organic carbon and perhaps some moisture) had been adsorbed on the activated charcoal. Off-gas samples were transfened to Analytical Development Section (ADS) for analysis by gamma PHA, ICP-ES and mass spectroscopy to determine what was volatilized from the mixture during vitrification. ANALYSIS OF THE OFF-GAS SAMPLES Analysis of samples taken from the condenser and the cold trap indicated that very little other than water was collected in the condenser or cold trap. The charcoal filters were not analyzed. WESTINGHOUSE SAVANNAH RIVER COMPANY SAVANNAH RIVER TECHNOLOGY CENTER Page 3 of 4 Table 1 gives the radionuclide composition of the condensates from the LAW vitrifications. Although very little of the radionuclides appear to have volatilized, a larger than expected fraction of the volatile Cs passed through the condenser into the dry-ice cold trap before.it was condensed and collected. Sr/Y-90 could not be determined for the cold trap samples because of limited sample volumes. Table 1. Radionuclide Composition (pCi/mL) of Off-Gas Samples Collected during Vitrification of Envelope A, B, and C LAW Waste Streams Table 2 gives the radionculide composition of the condensate and cold trap samples collected during the HLW vitrification demonstrations. Although the Cs-137 and Tc-99 concentrations were between two and three orders of magnitude greater in the samples than in the LAW samples, they were two to three orders of magnitude lower than the concentrations in the HLW glass. Sr-90 was not detected in these samples. Concentrations of Cs-137 and Tc- 99 were much higher in the dry-ice cold traps than initially expected. Table 2. Radionuclide Composition (pCi/g) of Off-Gas Collected during Vitrification of HLW Samples Radionuclide Envelope D Condensate Cold-Trap Condensate Cold-Trap CS-137 3.89 1.38 6.38 0.82 Tc-99 2.88 x10-~ 5.86 x10” 5.56 x104 4.5 xlo-s A comparison can be made of the major Cs-137 and Sr-90 radionuclides detected in the glass to the amounts of these species added in the HLW glass formulation. Table 3 shows the results of such a comparison. Cs-137 was added predominately from the treated supernate stream and the HLW filtered sludge solids. A total of approximately 1.4 x105 pCi of Cs-137 was present in the feed streams used to produce the 60 grams of HLW glass. The concentration of Cs-137 in the HLW glass was in the range of (1.9 to 2.1) x103 pCi/g of glass. Therefore, a total of 60 grams of glass contained (1.1 to 1.3) xlOs pCi of (3-137. Relatively low levels of 0-137  were detected in the HLW glass off-gas condensate and cold-trap samples. A total of only about 300 pCi of Cs- 137 is estimated from c WESTINGHOUSE SAVANNAH RIVER COMPANY SAVANNAH RIVER TECHNOLOGY CENTER Page 4 of 4 analyses of the off-gas samples. Thus, the calculated amounts of Cs-137 in the feed streams is close to the amount found in the HLW glass. Table 3. Comparison of Radionuclides in the Feed Streams to Radionuclides in the HLW Glass and Off-Gas Samples Table 3 also shows the results of a comparison for Sr-90. Sr-90 was added predominately fi-om the treated supernate stream from Envelope C pretreatment and the HLW filtered sludge solids. A total of approximately 5.5 x104 pCi of Sr-90 was present in the HLW feed streams. Of this Sr-90 source, about 1.3 x104 pCi was in the TRU/Sr/Fe solids and about 4.2 x104 pCi was in the HLW filtered sludge solids. The concentration of Sr-90 in the HLW glass was (1 .1 to 1.2) x 1 O3 pCi/g of glass. Therefore, a total of 60 grams of glass had (6.6 to 7.2) x 1 O4 yCi of Sr-90. Sr-90 was not detected in the HLW glass off-gas condensate or cold-trap samples. Therefore, the amount of Sr-90 measured in the feed streams was within 20% of the Sr-90 detected in the product HLW glass. REFERENCES 1. United States Department of Energy, “TWRS Privatization Request for Proposals,” DE-RP006-96RL13308, February 1996. 2. British Nuclear Fuels Limited, Incorporated, “Tank Waste Remediation System Privatization Technology Development and Demonstration Program,” August 1995. 

Off-Gas Analysis During the Vitrification of Hanford Radioactive Waste Samples

https://digital.library.unt.edu/ark:/67531/metadc692991/m2/1/high_res_d/639514.pdf

Off-Gas Analysis During the Vitrification of Hanford Radioactive Waste Samples

Abstract

Similar works

Full text

Available Versions

UNT Digital Library