IMPACT OF REDUCING THE 100 C LIQUIDUS TEMPERATURE OFFSET ON WASTE LOADING TARGETS
The objective of this report is to assess the potential impact of reducing conservatism in the implementation of the current liquidus temperature (TL) model in the Product Composition Control System (PCCS) on the ability to target higher waste loadings (WLs) for future sludge batches. No changes to the TL model or the associated uncertainties (model or measurement) are proposed, rather only changes in the magnitude of the offset used between the nominal melt pool temperature (1150 C) and the Property Acceptance Region (PAR) value (1050 C). This strategy is consistent with that outlined and initially assessed by Brown et al. (2001). In that report, the authors stated even a fairly conservative change in this safety factor could have a significant impact on waste loading. The results of this study clearly indicate that the implementation of an 1100 C TL PAR criterion (which translates into a reduction in the TL offset from 100 C to 50 C) can have significantly positive impacts on the ability to gain access to WLs exceeding 45%. This is especially true for those frit and sludge systems that are TL limited using the current 1050 C TL criterion, and are not limited by a second constraint (such as viscosity, nepheline, or durability) until much higher WLs. Examples of various glass forming systems are provided that are currently limited to maximum WLs in the mid-40s, but could be processed in the lower 50s through implementation of this new strategy. One example is in the Sludge Batch 10 (SB10) system, where for a specific glass forming system the projected operating window of 38-41% WL (using the current constraints) became 38-52% WL with the use of an 1100 C TL PAR value. This change both provided access to significantly higher WLs, and transitioned a once infeasible flowsheet to a system that could potentially be processed in the Defense Waste Processing Facility (DWPF). This potential change in the TL constraint also provides access to frit compositions (or glass forming regions) that are not accessible under the current limitations. These new composition regions not only provide access to higher WLs, but may also allow frit development efforts to target other specific properties to support enhanced melter operations. It should be noted that under certain flowsheet conditions, the implementation of the 1100 C TL PAR must be accompanied by a shifting categorization of what is deemed an acceptable operating window for DWPF operation. For example, the use of a 50 C offset may not be effective if access to WLs < 30% are still required. Assuming the intent of implementing the 1100 C PAR criterion is to gain access to higher WLs (> 45%), the need to identify frit and sludge systems that are predicted to form acceptable glasses at these lower WLs (< 30%) should no longer be of concern. Although this strategy could have a significant impact on DWPF's ability to target higher WLs (> 45%), its implementation is not risk free. The reduction in the TL offset does reduce the conservatism currently implemented, which is aimed at minimizing or eliminating the potential for massive devitrification within the melt pool. Prior to implementation of this alternative strategy, DWPF should perform a risk-based assessment or review of this alternative approach to ensure it aligns with needs and processing strategies.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-08SR22470
- OSTI ID:
- 993935
- Report Number(s):
- SRNL-STI-2010-00528; TRN: US1100068
- Country of Publication:
- United States
- Language:
- English
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