Demonstration of Defense Waste Processing Facility (DWPF) Higher Fissile Content Glass

Abstract

The Accelerated Basin De-inventory (ABD) Program has been proposed as an alternative for future spent nuclear fuel (SNF) and nuclear material processing at the Savannah River Site (SRS). This approach would change the baseline H-Canyon (HCAN), Concentrate, Storage, and Transfer Facility (CSTF), and Defense Waste Processing Facility (DWPF) operations. The ABD Program would require that all domestic and foreign research reactor SNF currently at SRS be dissolved, stored, and then transferred to CSTF without the recovery of uranium. Preliminary assessments in the ABD Program plan have shown that ~5000 extra SRS high-level waste (HLW) canisters would be produced if the fissile mass loading remains at the current 897 g/m 3 limit; however, increasing the limit to 2500 g/m 3 would result in ~520 extra canisters. Thus, the ABD Program plan requires an increase of the DWPF fissile mass loading limit to 2500 g/m 3 to minimize canister production.The Department of Energy (DOE) Office of Environmental Management (EM) authorized a phased approach to increase the fissile mass loading of vitrified HLW at DWPF to 2500 g/m 3 . Phase 1 begins with testing actual radioactive waste samples to determine if the DWPF glass will meet relevant requirements. Additionally, Savannah River Remediation (SRR) has performed a Nuclear Criticality Safety Evaluation (NCSE) for the increased fissile mass loading limit. The Savannah River Nuclear Solutions (SRNS) Materials Disposition Engineering group requested that the Savannah River National Laboratory (SRNL) demonstrate that increasing the fissile mass loading in vitrified HLW to 2500 g/m 3 will have no adverse effects on glass quality specifications. The objective of this task was to fabricate and characterize two radioactive glass samples prepared with actual radioactive SRS HLW samples. One glass was prepared with a fissile mass loading below the current 897 g/m 3 limit, and a second glass was prepared with a fissile mass loading bounding the 2500 g/m 3 concentration. Both glasses were evaluated for product consistency to confirm the Waste Acceptance Product Specifications (WAPS) acceptance criterion (section 1.3) can be met with the increased fissile mass loading. Glass product consistency was determined using the Product Consistency Test (PCT) per ASTM C1285-14. Complementary X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to compare phase homogeneity among both glass samples.Most of the fissile mass from the ABD Program will be attributed to U-235. DWPF has produced homogeneous HLW glasses with total U3O8 concentrations of 1.1-3.5 weight percent (wt.%) that meet the WAPS acceptance criterion for product consistency; however, these glasses have different fissile uranium isotope distributions than those expected for HLW glasses containing ABD material. Therefore, an additional goal of this study was to confirm that DWPF HLW glass durability remains predictable with the DWPF Product Composition Control System (PCCS) durability models when the percentage of U-235 is inc...

Technical Evaluation of Accelerated Basin De-Inventory Material Addition to Sludge Batch 11

“…TTR Task 2a is specific to gadolinium interactions with organics in the waste. TTR Task 2b requests an evaluation of the conclusions of the three previous SRNL reports [4][5][6] with regards to the new minimum mass ratio of gadolinium to equivalent uranium-235 in sludge. Since the three past SRNL reports on ABD, the minimum mass ratio of gadolinium to equivalent uranium-235 ( 235 U(eq SLU )) has been increased to 2.5:1.…”

“…Previous glass testing in 2021 to support the increase in fissile mass loading from 897 to 2,500 g fissile/m 3 glass was performed to demonstrate that a glass with a fissile mass loading of 2,500 g fissile/m 3 glass met the Waste Acceptance Product Specifications (WAPS) acceptance criterion for product consistency. 6,62 This study assumed a Gd to equivalent 235 U in the sludge mass ratio (Gd: 235 U(eq SLU )) of 0.55:1 since the actual ratio had not been determined by an NCSE. The 0.55:1 ratio resulted in a Gd 2 O 3 concentration in glass of 0.10 wt%.…”

“…The 0.55:1 ratio resulted in a Gd 2 O 3 concentration in glass of 0.10 wt%. 6 More recently, nuclear criticality safety analysts have completed initial model evaluations and have determined a minimum Gd: 235 U(eq) ratio of ~2.5:1. 63 To determine the projected Gd 2 O 3 concentration in SB11 glass, the SRMC System Planning group provided a SB11 Tank 40 blend projection, which represents a Gd: 235 U(eq SLU ) mass ratio of 2.73:1 in Tank 51 and SRNL-STI-2022-00502 Revision 0 includes conservatism relative to the ratio of ~2.5:1 proposed by nuclear criticality safety analysts.…”

“…the study of impacts of increasing the fissile mass loading in glass. 6 Based on the planned additions of ABD discards from H-Canyon to SB11, Savannah River Mission Completion (SRMC), the SRS LW contractor, issued a Technical Task Request (TTR) requesting that SRNL assess the technical gaps related to the following items: 7  increased gadolinium poisoning requirement  impacts of performing the LTAD process in Tank 51 with H-Canyon discards present.…”

Technical Evaluation of Accelerated Basin De-Inventory Material Addition to Sludge Batch 11 (Rev. 1)

“…The 0.55:1 ratio resulted in a Gd 2 O 3 concentration in glass of 0.10 wt%. 6 More recently, nuclear criticality safety analysts have completed initial model evaluations and have determined a minimum Gd: 235 U(eq) ratio of ~2.5:1. 63 To determine the projected Gd 2 O 3 concentration in SB11 glass, the SRMC System Planning group provided a SB11 Tank 40 blend projection, which represents a Gd: 235 U(eq SLU ) mass ratio of 2.73:1 in Tank 51 and includes conservatism relative to the ratio of ~2.5:1 proposed by nuclear criticality safety analysts.…”