Neutralization of Plutonium and Enriched Uranium Solutions Containing Gadolinium as a Neutron Poison

Bronikowski, M.G.

doi:10.2172/823030

Cited by 7 publications

(5 citation statements)

References 4 publications

(23 reference statements)

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“…Previous neutralization experiments showed that the Pu-Gd precipitate began to form at pH 3. 5 Solutions containing Pu, U, and Gd or U and Gd began to precipitate at pH 4.5, [8][9][10] consistent with the behavior of U solutions. 2 Although surprising, this observation can be explained by the termination of the Pu polymer chain by UO 2 2+ which keeps more Pu in solution at pH 3 and, at these U:Pu ratios, prevents precipitation until pH 4.5 when both U and Pu precipitate.…”

Section: Iiia Ph Testsmentioning

confidence: 58%

Caustic Precipitation of Plutonium and Uranium with Gadolinium as a Neutron Poison

2006

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The caustic precipitation of plutonium (Pu) and uranium (U) from Pu and Ucontaining waste solutions has been investigated to determine whether gadolinium (Gd) could be used as a neutron poison for precipitation with greater than a fissile mass containing both Pu and enriched U. Precipitation experiments were performed using both actual samples and simulant solutions with a range of 2.6-5.16 g/L U and 0-4.3:1 U:Pu.Analyses were performed on solutions at intermediate pH to determine the partitioning of elements for accident scenarios. When both Pu and U were present in the solution, precipitation began at pH 4.5 and by pH 7, 99% of Pu and U had precipitated. When complete neutralization was achieved at pH > 14 with 1.2 M excess OH -, greater than 99% of Pu, U, and Gd had precipitated. At pH > 14, the particles sizes were larger and the distribution was a single mode. The ratio of hydrogen:fissile atoms in the precipitate was determined after both settling and centrifuging and indicates that sufficient water was associated with the precipitates to provide the needed neutron moderation for Gd to prevent a criticality in solutions containing up to 4.3:1 U:Pu and up to 5.16 g/L U.2

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Section: Iiia Ph Testsmentioning

confidence: 58%

Caustic Precipitation of Plutonium and Uranium with Gadolinium as a Neutron Poison

2006

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“…In some cases, x-ray diffraction patterns identified crystalline uranium phases of Na 3 UO 4 and Na((UO 2 O(OH))), Gd(OH) 3 , and possibly a mixture of Pu(OH) 4 and Gd(OH) 3 or NaGdPuO x . [86][87] From this evidence, U apparently does not co-precipitate with Gd and only a poorly defined mixed phase of Gd and Pu has been reported. Thus, if a portion of the Gd(OH) 3 in the overall slurry is introduced via precipitation in the absence of U and Pu, it is expected to behave similarly to the Gd(OH) 3 that was precipitated in the presence of U and Pu.…”

Section: Abd Expectations During Aluminum Dissolutionmentioning

confidence: 75%

“…Previous studies indicated that the precipitated solids are small particles less than about 20 microns in size with the uranium, plutonium, and gadolinium intimately dispersed throughout the solids. [86][87] The bulk of the solids are amorphous hydroxides (e.g., Gd(OH) 3 , Pu(OH) 4 and UO 2 (OH) 2 ). In some cases, x-ray diffraction patterns identified crystalline uranium phases of Na 3 UO 4 and Na((UO 2 O(OH))), Gd(OH) 3 , and possibly a mixture of Pu(OH) 4 and Gd(OH) 3 or NaGdPuO x .…”

Section: Abd Expectations During Aluminum Dissolutionmentioning

confidence: 99%

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

MARTINO¹,

Johnson²,

Lambert³

et al. 2023

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The Accelerated Basin De-inventory (ABD) program involves discarding spent nuclear fuel that is currently stored in L-Basin to the Defense Waste Processing Facility (DWPF) for vitrification. The first ABD discards will occur during the preparation of Sludge Batch (SB) 11. Savannah River Mission Completion has requested that the Savannah River National Laboratory assess the technical gaps related to the increased gadolinium poisoning requirement and the impacts of performing the Low Temperature Aluminum Dissolution (LTAD) process in Tank 51 with H-Canyon discards present.The following summarizes the evaluation of the impacts of increasing the quantity of gadolinium (and related topics) from what was previously evaluated in the SRNL studies of gadolinium-poisoned ABD material solubility, the overall ABD flowsheet review, and increasing the fissile mass loading in glass: Based on literature surveys, there is no indication that organic interactions with gadolinium will be significant at the high pH (typically >13) conditions of the Concentration, Storage, and Transfer Facilities. Any interactions of gadolinium with organics in DWPF are not expected to adversely impact DWPF or downstream facilities. Thus, there is little-to-no residual risk from organic interactions with gadolinium. [Gap closed]  Increasing the gadolinium mass ratio to 3.0:1 Gd: 235 U(eq SLU ) should lead to the same or higher partitioning of gadolinium into the solid phase within the DWPF Chemical Process Cell, resulting in both liquid and solid phases with expected partitioning of Gd consistent with the prior solubility study. [Gap closed for SB11]  There are no expected impacts on DWPF melt temperature and melter operations due to the minimal ~0.2 weight percent (wt%) increase in Gd concentration relative to previous sludge batches.[Gap closed for SB11]  As observed previously, Gd is expected to enter the off-gas system via physical entrainment, but at a slightly higher concentration than what was observed for SB9 melter off-gas pluggage deposits (0.07 wt%). [Gap closed for SB11]  There are no expected impacts on DWPF recycle or the Recycle Collection Tank glycolate destruction process. [Gap closed for SB11]  Gd is projected to be a trace component in the SB11 glass (<0.5 wt%) and can be ignored for process control. Trace components do not significantly impact glass durability, thus the conclusions of the previous Product Consistency Test evaluation at a fissile mass loading of 2,500 g fissile/m 3 glass still applies to SB11. The ~0.1 wt% increase in Gd 2 O 3 concentration relative to the previous study will not impact the predictability of SB11 glass with the DWPF Product Composition Control System (PCCS) models for durability or the acceptability of glass according to the Waste Acceptance Product Specifications (WAPS) criterion for product consistency. [Gap closed for SB11]  No additional Toxicity Characteristic Leaching Procedure testing is necessary for SB11 and the hazardous waste specification of the SB11 DWPF waste form is unchanged a...

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“…These particle sizes are small enough that the Gd self-shielding should be minimized (general guideline is less than 100 µm to minimize self-shielding). 31 The Simulant #1 samples were observed to settle to a much more compact volume in comparison to the SRNL-STI-2022-00114 Revision 0 22 Simulant #2 samples. A photograph taken after several days of settling is shown in Figure 3-5.…”

Section: As-batchedmentioning

confidence: 92%

Flowsheet for the Neutralization of Accelerated Basin De-inventory (ABD) Material

None¹

2022

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Under the Accelerated Basin De-inventory (ABD) program H-Canyon will be dissolving aluminum spent nuclear fuel (ASNF) and then neutralizing that solution without performing head-end strike or uranium recovery operations. After dissolution in H-Canyon the material will be neutralized to a free hydroxide concentration of either 0.6 M or 1.2 M to meet the waste acceptance criteria for transfer to the SRS Concentration, Storage and Transfer Facility (CSTF). In order to ensure the material could be successfully neutralized and transferred, SRNL completed experiments with simulated H-Canyon dissolver solutions. Two bounding simulants were developed based on the expected compositions of ASNF to be dissolved, one containing only Gd as the neutron poison and one containing Fe as an additional poison.The first simulant represented a batch of dissolver solution from dissolution of HFIR fuel after isotopic adjustment to 3 wt% 235 U and poisoning with Gd at a ratio of 0.625:1 Gd: 235 U. The second simulant also represented a batch of dissolved HFIR fuel, adjusted to 3 wt% 235 U enrichment, with Gd added at a ratio of 0.625:1, but also included the addition of Fe as a neutron poison at a ratio of 160:1 Fe: 239 Pu equivalent. Analysis of samples taken throughout the neutralization indicated the lowest Gd: 235 U ratio was observed at about the mid-point of the neutralization where the ratio was 0.549 in the solids. This ratio is still well within the safety limits based on the Nuclear Criticality Safety Evaluation (NCSE) performed to calculate the minimum critically safe Gd: 235 U ratio in an infinite system. The evaluation found this ratio to be 0.025 Gd: 235 U for all credible hydrogen to fissile atom ratios. Similar results were obtained for the simulant also containing Fe, where the minimum Gd: 235 U ratio observed was 0.552 in the solids.Physical and rheological properties of the resulting neutralized simulants were also studied to provide the necessary data for performing flow calculations examining the transfer of neutralized slurry from H-Canyon to the CSTF. All endpoints had a final density above the 1.35 g/mL limit and therefore require further dilution at the end of the neutralization. For Simulant #1, the slurry can be successfully transferred after dilution to a density between 1.27 and 1.35 g/mL for both the 0.6 M and 1.2 M OHendpoints. To minimize water addition for Simulant #1, it is recommended to process at 1.35 g/mL. For Simulant #2, it was determined that flow will backup into the header if the pipe roughness is greater than 0.00015 ft for densities above 1.33 g/mL for the 0.6 M slurry. For Simulant #2 it is recommended to target final densities of 1.33 g/mL for the 0.6 M OHendpoint or 1.35 g/mL for the 1.2 M OHcase if the transfer is non-Newtonian. If simulant #2 is transferred as a Newtonian fluid, target 1.25 g/mL for either the 0.6 M or 1.2 M OHendpoints, given densities higher than 1.25 g/mL should be treated as non-Newtonian. At 1.21 g/mL for Simulant #2, the critical velocity needed to maintain the Na ...

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Neutralization of Plutonium and Enriched Uranium Solutions Containing Gadolinium as a Neutron Poison

Cited by 7 publications

References 4 publications

Caustic Precipitation of Plutonium and Uranium with Gadolinium as a Neutron Poison

Caustic Precipitation of Plutonium and Uranium with Gadolinium as a Neutron Poison

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

Flowsheet for the Neutralization of Accelerated Basin De-inventory (ABD) Material

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