skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: DISSOLUTION OF FISSILE MATERIALS CONTAINING TANTALUM METAL

Abstract

The dissolution of composite materials containing plutonium (Pu) and tantalum (Ta) metals is currently performed in Phase I of the HB-Line facility. The conditions for the present flowsheet are the dissolution of 500 g of Pu metal in the 15 L dissolver using a 4 M nitric acid (HNO{sub 3}) solution containing 0.2 M potassium fluoride (KF) at 95 C for 4-6 h.[1] The Ta metal, which is essentially insoluble in HNO{sub 3}/fluoride solutions, is rinsed with process water to remove residual acid, and then burned to destroy classified information. During the initial dissolution campaign, the total mass of Pu and Ta in the dissolver charge was limited to nominally 300 g. The reduced amount of Pu in the dissolver charge coupled with significant evaporation of solution during processing of several dissolver charges resulted in the precipitation of a fluoride salt contain Pu. Dissolution of the salt required the addition of aluminum nitrate (Al(NO{sub 3}){sub 3}) and a subsequent undesired 4 h heating cycle. As a result of this issue, HB-Line Engineering requested the Savannah River National Laboratory (SRNL) to optimize the dissolution flowsheet to reduce the cycle time, reduce the risk of precipitating solids, and obtain hydrogen (H{sub 2})more » generation data at lower fluoride concentrations.[2] Using samples of the Pu/Ta composite material, we performed three experiments to demonstrate the dissolution of the Pu metal using HNO{sub 3} solutions containing 0.15 and 0.175 M KF. When 0.15 M KF was used in the dissolving solution, 95.5% of the Pu in the sample dissolved in approximately 6 h. The undissolved material included a small amount of Pu metal and plutonium oxide (PuO{sub 2}) solids. Complete dissolution of the metal would have likely occurred if the dissolution time had been extended. This assumption is based on the steady increase in the Pu concentration observed during the last several hours of the experiment. We attribute the formation of PuO{sub 2} to the complexation of fluoride by the Pu. The fluoride became unavailable to catalyze the dissolution of PuO{sub 2} as it formed on the surface of the metal. The mass of Pu dissolved is equivalent to the dissolution of 343 g of Pu in the HB-Line dissolvers. In the initial experiment with 0.175 M KF in the solution, we achieved complete dissolution of the Pu in 6 h. The mass of Pu dissolved scales to the dissolution of 358 g of Pu in the HB-Line dissolvers. The second experiment using 0.175 M KF was terminated after approximately 6 h following the dissolution of 92.7% of the Pu in the sample; however, dissolution of additional Pu was severely limited due to the slow dissolution rate observed beyond approximately 4 h. A small amount of PuO{sub 2} was also produced in the solution. The slow rate of dissolution was attributed to the diminishing surface area of the Pu and a reduction in the fluoride activity due to complexation with Pu. Given time (>4 h), the Pu metal may have dissolved using the original solution or a significant portion may have oxidized to PuO{sub 2}. If the metal oxidized to PuO{sub 2}, we expect little of the material would have dissolved due to the fluoride complexation and the low HNO{sub 3} concentration. The mass of Pu dissolved in the second experiment scales to the dissolution of 309 g of Pu in the HB-Line dissolvers. Based on the data from the Pu/Ta dissolution experiments we recommend the use of 4 M HNO{sub 3} containing 0.175 M KF for the dissolution of 300 g of Pu metal in the 15 L HB-Line dissolver. A dissolution temperature of nominally 95 C should allow for essentially complete dissolution of the metal in 6 h. Although the H{sub 2} concentration in the offgas from the experiments was at or below the detection limit of the gas chromatograph (GC) used in these experiments, small concentrations (<3 vol %) of H{sub 2} are typically produced in the offgas during Pu metal dissolutions. Therefore, appropriate controls must be established to address the small H{sub 3} generation rates in accordance with this work and the earlier flowsheet demonstrated for Pu metal.[3]« less

Authors:
; ;
Publication Date:
Research Org.:
SRS
Sponsoring Org.:
USDOE
OSTI Identifier:
910168
Report Number(s):
WSRC-STI-2007-00285
TRN: US0704103
DOE Contract Number:
DE-AC09-96SR18500
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 36 MATERIALS SCIENCE; ALUMINIUM; CLASSIFIED INFORMATION; COMPOSITE MATERIALS; DISSOLUTION; DISSOLVERS; EVAPORATION; FISSILE MATERIALS; FLOWSHEETS; FLUORIDES; HEATING; HYDROGEN; NITRATES; NITRIC ACID; PLUTONIUM; PLUTONIUM OXIDES; POTASSIUM FLUORIDES; SENSITIVITY; SURFACE AREA; TANTALUM

Citation Formats

Rudisill, T, Mark Crowder, M, and Michael Bronikowski, M. DISSOLUTION OF FISSILE MATERIALS CONTAINING TANTALUM METAL. United States: N. p., 2007. Web. doi:10.2172/910168.
Rudisill, T, Mark Crowder, M, & Michael Bronikowski, M. DISSOLUTION OF FISSILE MATERIALS CONTAINING TANTALUM METAL. United States. doi:10.2172/910168.
Rudisill, T, Mark Crowder, M, and Michael Bronikowski, M. Tue . "DISSOLUTION OF FISSILE MATERIALS CONTAINING TANTALUM METAL". United States. doi:10.2172/910168. https://www.osti.gov/servlets/purl/910168.
@article{osti_910168,
title = {DISSOLUTION OF FISSILE MATERIALS CONTAINING TANTALUM METAL},
author = {Rudisill, T and Mark Crowder, M and Michael Bronikowski, M},
abstractNote = {The dissolution of composite materials containing plutonium (Pu) and tantalum (Ta) metals is currently performed in Phase I of the HB-Line facility. The conditions for the present flowsheet are the dissolution of 500 g of Pu metal in the 15 L dissolver using a 4 M nitric acid (HNO{sub 3}) solution containing 0.2 M potassium fluoride (KF) at 95 C for 4-6 h.[1] The Ta metal, which is essentially insoluble in HNO{sub 3}/fluoride solutions, is rinsed with process water to remove residual acid, and then burned to destroy classified information. During the initial dissolution campaign, the total mass of Pu and Ta in the dissolver charge was limited to nominally 300 g. The reduced amount of Pu in the dissolver charge coupled with significant evaporation of solution during processing of several dissolver charges resulted in the precipitation of a fluoride salt contain Pu. Dissolution of the salt required the addition of aluminum nitrate (Al(NO{sub 3}){sub 3}) and a subsequent undesired 4 h heating cycle. As a result of this issue, HB-Line Engineering requested the Savannah River National Laboratory (SRNL) to optimize the dissolution flowsheet to reduce the cycle time, reduce the risk of precipitating solids, and obtain hydrogen (H{sub 2}) generation data at lower fluoride concentrations.[2] Using samples of the Pu/Ta composite material, we performed three experiments to demonstrate the dissolution of the Pu metal using HNO{sub 3} solutions containing 0.15 and 0.175 M KF. When 0.15 M KF was used in the dissolving solution, 95.5% of the Pu in the sample dissolved in approximately 6 h. The undissolved material included a small amount of Pu metal and plutonium oxide (PuO{sub 2}) solids. Complete dissolution of the metal would have likely occurred if the dissolution time had been extended. This assumption is based on the steady increase in the Pu concentration observed during the last several hours of the experiment. We attribute the formation of PuO{sub 2} to the complexation of fluoride by the Pu. The fluoride became unavailable to catalyze the dissolution of PuO{sub 2} as it formed on the surface of the metal. The mass of Pu dissolved is equivalent to the dissolution of 343 g of Pu in the HB-Line dissolvers. In the initial experiment with 0.175 M KF in the solution, we achieved complete dissolution of the Pu in 6 h. The mass of Pu dissolved scales to the dissolution of 358 g of Pu in the HB-Line dissolvers. The second experiment using 0.175 M KF was terminated after approximately 6 h following the dissolution of 92.7% of the Pu in the sample; however, dissolution of additional Pu was severely limited due to the slow dissolution rate observed beyond approximately 4 h. A small amount of PuO{sub 2} was also produced in the solution. The slow rate of dissolution was attributed to the diminishing surface area of the Pu and a reduction in the fluoride activity due to complexation with Pu. Given time (>4 h), the Pu metal may have dissolved using the original solution or a significant portion may have oxidized to PuO{sub 2}. If the metal oxidized to PuO{sub 2}, we expect little of the material would have dissolved due to the fluoride complexation and the low HNO{sub 3} concentration. The mass of Pu dissolved in the second experiment scales to the dissolution of 309 g of Pu in the HB-Line dissolvers. Based on the data from the Pu/Ta dissolution experiments we recommend the use of 4 M HNO{sub 3} containing 0.175 M KF for the dissolution of 300 g of Pu metal in the 15 L HB-Line dissolver. A dissolution temperature of nominally 95 C should allow for essentially complete dissolution of the metal in 6 h. Although the H{sub 2} concentration in the offgas from the experiments was at or below the detection limit of the gas chromatograph (GC) used in these experiments, small concentrations (<3 vol %) of H{sub 2} are typically produced in the offgas during Pu metal dissolutions. Therefore, appropriate controls must be established to address the small H{sub 3} generation rates in accordance with this work and the earlier flowsheet demonstrated for Pu metal.[3]},
doi = {10.2172/910168},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 29 00:00:00 EDT 2007},
month = {Tue May 29 00:00:00 EDT 2007}
}

Technical Report:

Save / Share:
  • Scrap materials containing plutonium (Pu) metal are currently being transferred from the FB Line vault to HB Line for dissolution and subsequent disposition through the H-Canyon facility. Some of the items scheduled for dissolution contain both Pu and beryllium (Be) metal as a composite material. The Pu and Be metals were physically separated to minimize the amount of Be associated with the Pu; however, the dissolution flowsheet was required to dissolve small amounts of Be combined with the Pu metal using a dissolving solution containing nitric acid (HNO3) and potassium fluoride (KF). Since the dissolution of Pu metal in HNO3/fluoridemore » (F-) solutions is well understood, the primary focus of the experimental program was the dissolution of Be metal. Initially, small-scale experiments were used to measure the dissolution rate of Be metal foils using conditions effective for the dissolution of Pu metal. The experiments demonstrated that the dissolution rate was nearly independent of the HNO3 concentration over the limited range of investigation and only a moderate to weak function of the F- concentration. The effect of temperature was more pronounced, significantly increasing the dissolution rate between 40 and 105 degrees C. The offgas from three Be metal foil dissolutions was collected and characterized. The production of hydrogen (H2) was found to be sensitive to the HNO3 concentration, decreasing by a factor of approximately two when the HNO3 was increased from 4 to 8 M. This result is consistent with the dissolution mechanism shifting away from a typical metal/acid reaction toward increased production of nitrogen oxides by nitrate (NO3-) oxidation.« less
  • Scrap materials containing plutonium (Pu) metal from FB-Line vaults are currently being dissolved in HB-Line for subsequent disposition through the H-Canyon facility. However, milestone and schedule commitments may require the dissolution of material containing Pu and beryllium (Be) metals in H-Canyon. To support this option, a flowsheet for dissolving Pu and Be metals in H-Canyon was demonstrated using a 4 M nitric acid (HNO{sub 3}) solution containing 0.3 M fluoride (F{sup -}). The F{sup -} was added as calcium fluoride (CaF{sub 2}). The dissolving solution also contained 2.5 g/L boron (B), a nuclear safety contingency for the H-Canyon dissolver, andmore » 3.9 g/L iron (Fe) to represent the dissolution of carbon steel cans. The solution was heated to 90-95 C during the 8 h dissolution cycle. Dissolution of the Be metal appeared to begin as soon as the samples were added to the dissolver. Clear, colorless bubbles generated on the surface were observed and were attributed primarily to the generation of hydrogen (H{sub 2}) gas. The generation of nitrogen dioxide (NO{sub 2}) gas was also evident from the color of the solution. Essentially all of the Pu and Be dissolved during the first hour of the dissolution as the solution was heated to 90-95 C. The amount of residual solids collected following the dissolution was < 2% of the total metal charged to the dissolver. Examination of residual solids by scanning electron microscopy (SEM) showed that the largest dimension of the particles was less than 50 {micro}m with particles of smaller dimensions being more abundant. Energy dispersive spectra from spots on some of the particles showed the solids consisted of a small amount of undissolved material, corrosion products from the glassware, and dried salts from the dissolving solution.« less
  • This report summarizes and compares the Immobilized and Direct Beep Borehole Disposition Alternatives. The important design concepts, facility features and operational procedures are briefly described, and a discussion of the issues that affect the evaluation of each alternative against the programmatic assessment criteria that have been established for selecting the preferred alternatives for plutonium disposition.
  • The end of the cold war has resulted in excess PCMs from nuclear weapons and associated production facilities. Consequently, the US government has undertaken studies to determine how best to manage and dispose of this excess material. The issues include (a) ensurance of domestic health, environment, and safety in handling, storage, and disposition, (b) international arms control agreements with Russia and other countries, and (c) economics. One major set of options is to convert the PCMs into glass for storage or disposal. The chemically inert characteristics of glasses make them a desirable chemical form for storage or disposal of radioactivemore » materials. A glass may contain only plutonium, or it may contain plutonium along with other radioactive materials and nonradioactive materials. GMODS is a new process for the direct conversion of PCMs (i.e., plutonium metal, scrap, and residues) to glass. The plutonium content of these materials varies from a fraction of a percent to pure plutonium. GMODS has the capability to also convert other metals, ceramics, and amorphous solids to glass, destroy organics, and convert chloride-containing materials into a low-chloride glass and a secondary clean chloride salt strewn. This report is the initial study of GMODS for vitrification of PCMs as input to ongoing studies of plutonium management options. Several tasks were completed: initial analysis of process thermodynamics, initial flowsheet analysis, identification of equipment options, proof-of-principle experiments, and identification of uncertainties.« less