The model-based assessments of nominal Sludge Batch 4 (SB4) compositions suggest that a viable frit candidate does not appear to be a limiting factor as the Closure Business Unit (CBU) considers various tank blending options and/or washing strategies. This statement is based solely on the projected operating windows derived from model predictions and does not include assessments of SO{sub 4} solubility or melt rate issues. The viable frit candidates covered a range of Na{sub 2}O concentrations (from 8% to 13%--including Frit 418 and Frit 320) using a ''sliding Na{sub 2}O scale'' concept (i.e., 1% increase in Na{sub 2}O being balanced by a 1% reduction in SiO{sub 2}) which effectively balances the alkali content of the incoming sludge with that in the frit to maintain and/or increase the projected operating window size while potentially leading to improved melt rate and/or waste loadings. This strategy or approach allows alternative tank blending strategies and/or different washing scenarios to be considered and accounted for in an effective manner without wholesale changes to the frit composition. In terms of projected operating windows, in general, the sludge/frit systems evaluated resulted in waste loading intervals from 25 to the mid-40%'s or even the mid-50%'s. The results suggest …

The model-based assessments of nominal Sludge Batch 4 (SB4) compositions suggest that a viable frit candidate does not appear to be a limiting factor as the Closure Business Unit (CBU) considers various tank blending options for SB4 with or without the Actinide Removal Process (ARP) streams. This statement is based solely on the projected operating windows derived from model predictions and does not include experimental assessments of SO{sub 4} solubility or melt rate issues. To assess the impact of the various ARP options on the projected operating windows, the 1100 canister SB4 baseline options served as the technical baseline or reference point for the comparisons. With respect to the various ARP options being considered, the impacts to the projected operating windows were relatively consistent with the impacts being dependent upon the property limiting access to higher WLs. More specifically, for those 1100 canister SB4 systems (without ARP) which were T{sub L}-limited, the general impact was an increase in the upper WL which was classified as acceptable resulting in an overall increase in the operating window size. The anticipated negative impact of TiO{sub 2} (due to an assumed increase in T{sub L} which would further reduce the size of the operating …

This report documents parallel scaling characteristics of NERSC user project codes between Fiscal Year 2003 and the first half of Fiscal Year 2004 (Oct 2002-March 2004). The codes analyzed cover 60% of all the CPU hours delivered during that time frame on seaborg, a 6080 CPU IBM SP and the largest parallel computer at NERSC. The scale in terms of concurrency and problem size of the workload is analyzed. Drawing on batch queue logs, performance data and feedback from researchers we detail the motivations, benefits, and challenges of implementing highly parallel scientific codes on current NERSC High Performance Computing systems. An evaluation and outlook of the NERSC workload for Allocation Year 2005 is presented.