Final Report - High Level Waste Vitrification System Improvements, VSL-07R1010-1, Rev 0, dated 04/16/07 [report]

Albert A. Kruger, H. Gan, I. L. Pegg, W. Gong, C. C. Champman, I. Joseph, K. S. Matlack
2013 unpublished
11 Al, Th, Bi, etc. in the waste and their tendency to form crystalline phases. While the presence of crystalline phases rarely affects the quality of the glass product, it can present a significant processing concern since such phases can settle and accumulate in the melter, ultimately reducing the life of the melter. For this reason, HLW glasses (e.g., DWPF and WVDP) have traditionally been designed to have a liquidus temperature that is lower than the nominal processing temperature by some
more » ... rget value. Since the basic practical issue is crystal settling and accumulation, depending upon the crystal size and density, non-zero amounts of near-liquidus phases can often be maintained in suspension and, therefore, tolerated in bubbled melters. These considerations have led Duratek/VSL to develop and implement an "operational liquidus" constraint in which a non-zero fraction of crystals is tolerated at a given temperature. Glasses designed for DuraMelter vitrification systems have employed a limit of <1 vol. % crystals at a reference temperature (typically 950°C) below the operating temperature. Based on this experience and recommendation, this constraint has now been formally adopted for use at the Hanford WTP in place of the traditional, much more conservative, liquidus-temperature constraint. Additional increases in the amount of crystals allowable in the glass would further increase waste loadings and therefore further reduce waste treatment costs. However, at present, although it is expected that the actively mixed DuraMelter systems should be able to tolerate a larger amount of crystals than is the case for conventional melters, the maximum concentration of crystals such melter systems can tolerate is not yet known. For the current work, glass formulations with modestly higher amounts of crystals (i.e., closer to the 1 vol% limit than is typical of the current WTP baseline glasses) were considered for melter testing, if it resulted in higher waste loading. The maximum amount of crystals in the glass formulations selected for melter testing was decided on a case-by-case basis, in consultation with ORP, and was based on the specific glass formulation and the composition and characteristics of the crystal phase. Previous DM10 work demonstrated successful processing of high-iron wastes with glasses formulated with up to ~3 vol% crystals at 950P o Under a separate contract to support the WTP, the VSL is developing and testing glass formulations for WTP HLW waste compositions to provide data to meet the WTP contract requirements and to support system design activities [4][5][6]. That work is based upon small-scale batch melts ("crucible melts") using waste simulants. Selected formulations have also been tested in small-scale, continuously fed, joule-heated melters (DM100) [7-10] and, ultimately, in the HLW DM1200 Pilot Melter [9][10][11][12][13][14][15][16][17]. Such melter tests provide information on key process factors such as feed processing behavior, dynamic effects during processing, secondary phase formation, processing rates, off-gas amounts and compositions, foaming control, etc., that cannot be reliably obtained from crucible melts. This sequential scale-up approach in the vitrification testing program ensures that maximum benefit is obtained from the more costly melter tests and that the most effective use is made of those resources. The glass formulation and melter testing work described in this report is aimed at identifying glass compositions that maximize waste loadings for the four waste streams specified by ORP. This information provides ORP with a basis for projection of the amount of Immobilized High Level Waste (IHLW) to be produced at Hanford, and evaluation of the likely potential for future enhancements of the WTP over and above the present well-developed baseline. It should be noted that the compositions of the four specified waste streams differ significantly from those of the feed tanks (AZ-101, AZ-102, C-16/AY-102, and C-104/AY-101) ORP-56297 Rev. 0 The Catholic University of America High Level Waste Vitrification System Improvements Vitreous State Laboratory Final Report, VSL-07R1010-1, Rev. 0 P and a variable glass inventory of between 110 kg, when only the bottom pair of electrodes is used, and about 170 kg when both pairs of electrodes are used, which was the case in the present tests. Off-Gas System For operational simplicity, the DM100-BL is equipped with a dry off-gas treatment system involving gas filtration operations only. Exhaust gases leave the melter plenum through a film cooler device that minimizes the formation of solid deposits. The film-cooler air has constant flow rate and its temperature is thermostatically controlled. Consequently, under steady-state operating conditions, the exhaust gases passing through the transition line (between the melter and the first filtration device) can be sampled at constant temperature and airflow rate. The geometry of the transition line conforms to the requirements of the 40-CFR-60 air sampling techniques. Immediately downstream of the transition line are cyclonic filters followed by conventional pre-filters and HEPA filters. The temperature of the cyclonic filters is maintained above 150°C while the temperatures in the HEPAs are kept sufficiently high to prevent moisture condensation. The entire train of gas filtration operations is duplicated and each train is used alternately. An induced draft fan completes the system.
doi:10.2172/1105982 fatcat:z2eqrzi6bvcbjorkolper3qlbe