Dissolution of Plutonium Metal in HNO/sub 3/-N/sub 2/H/sub 4/-KF. PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Plutonium metal dissolves in HNO/sub 3/-N/sub 2/H/sub 4/. HNO/sub 3/-KF solution to yield a Pu/sup 3 +/ solution without an accompanying precipitation of plutonium oxide solids. The reaction evolves less than 0.2 mole of gas per mole of plutonium dissolved; the gas contains only 3% H/sub 2/. About 10/sup -3/ moles of HN/sub 3/ are produced per mole of plutonium dissolved. Optimum conditions for dissolving both alpha-phase and delta-phase plutonium metal were developed. Possible applications are to the recovery of plutonium metal or the processing of irradiated plutonium metal and alloys.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Plutonium metal dissolves in HNO/sub 3/-N/sub 2/H/sub 4/. HNO/sub 3/-KF solution to yield a Pu/sup 3 +/ solution without an accompanying precipitation of plutonium oxide solids. The reaction evolves less than 0.2 mole of gas per mole of plutonium dissolved; the gas contains only 3% H/sub 2/. About 10/sup -3/ moles of HN/sub 3/ are produced per mole of plutonium dissolved. Optimum conditions for dissolving both alpha-phase and delta-phase plutonium metal were developed. Possible applications are to the recovery of plutonium metal or the processing of irradiated plutonium metal and alloys.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The H-Canyon facility will be used to dissolve Pu metal for subsequent purification and conversion to plutonium dioxide (PuO2) using Phase II of HB-Line. To support the new mission, the development of a Pu metal dissolution flowsheet which utilizes concentrated (8-10 M) nitric acid (HNO3) solutions containing potassium fluoride (KF) is required. Dissolution of Pu metal in concentrated HNO3 is desired to eliminate the need to adjust the solution acidity prior to purification by anion exchange. The preferred flowsheet would use 8-10 M HNO3, 0.015-0.07 M KF, and 0.5-1.0 g/L Gd to dissolve the Pu up to 6.75 g/L. An alternate flowsheet would use 8-10 M HNO3, 0.1-0.2 M KF, and 1-2 g/L B to dissolve the Pu. The targeted average Pu metal dissolution rate is 20 mg/min-cm2, which is sufficient to dissolve a 'standard' 2250-g Pu metal button in 24 h. Plutonium metal dissolution rate measurements showed that if Gd is used as the nuclear poison, the optimum dissolution conditions occur in 10 M HNO3, 0.04-0.05 M KF, and 0.5-1.0 g/L Gd at 112 to 116 C (boiling). These conditions will result in an estimated Pu metal dissolution rate of ≈11-15 mg/min-cm2 and will result in dissolution times of 36-48 h for standard buttons. The recommended minimum and maximum KF concentrations are 0.03 M and 0.07 M, respectively. The maximum KF concentration is dictated by a potential room-temperature Pu-Gd-F precipitation issue at low Pu concentrations. The purpose of the experimental work described in this report was two-fold. Initially a series of screening experiments was performed to measure the dissolution rate of Pu metal as functions of the HNO3, KF, and Gd or B concentrations. The objective of the screening tests was to propose optimized conditions for subsequent flowsheet demonstration tests. Based on the rate measurements, this study found that optimal dissolution conditions in solutions containing 0.5-1.0 g/L Gd occurred in 8-10 M HNO3 with 0.04-0.05 M KF at 112 to 116 C (boiling). The testing also showed that solutions containing 8-10 M HNO3, 0.1-0.2 M KF, and 1-2 g/L B achieved acceptable dissolution rates in the same temperature range. To confirm that conditions identified by the dissolution rate measurements for solutions containing Gd or B can be used to dissolve Pu metal up to 6.75 g/L in the presence of Fe, demonstration experiments were performed using concentrations in the optimal ranges. In two of the demonstration experiments using Gd and in one experiment using B, the offgas generation during the dissolution was measured and samples were analyzed for H2. The experimental methods used to perform the dissolution rate measurements and flowsheet demonstrations and a discussion of the results are presented.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The deinventory and deactivation of the Savannah River Site's (SRS's) FB-Line facility required the disposition of approximately 2000 items from the facility's vaults. Plutonium (Pu) scraps and residues which do not meet criteria for conversion to a mixed oxide fuel will be dissolved and the solution stored for subsequent disposition. Some of the items scheduled for dissolution are composite materials containing Pu and tantalum (Ta) metals. The preferred approach for handling this material is to dissolve the Pu metal, rinse the Ta metal with water to remove residual acid, and burn the Ta metal. The use of a 4 M nitric acid (HNO3) solution containing 0.2 M potassium fluoride (KF) was initially recommended for the dissolution of approximately 500 g of Pu metal. However, prior to the use of the flowsheet in the SRS facility, a new processing plan was proposed in which the feed to the dissolver could contain up to 1250 g of Pu metal. To evaluate the use of a larger batch size and subsequent issues associated with the precipitation of plutonium-containing solids from the dissolving solution, scaled experiments were performed using Pu metal and samples of the composite material. In the initial experiment, incomplete dissolution of a Pu metal sample demonstrated that a 1250 g batch size was not feasible in the HB-Line dissolver. Approximately 45% of the Pu was solubilized in 4 h. The remaining Pu metal was converted to plutonium oxide (PuO2). Based on this work, the dissolution of 500 g of Pu metal using a 4-6 h cycle time was recommended for the HB-Line facility. Three dissolution experiments were subsequently performed using samples of the Pu/Ta composite material to demonstrate conditions which reduced the risk of precipitating a double fluoride salt containing Pu and K from the dissolving solution. In these experiments, the KF concentration was reduced from 0.2 M to either 0.15 or 0.175 M. With the use of 4 M HNO3 and a reduction in the KF concentration to 0.175 M, the dissolution of 300 g of Pu metal is expected to be essentially complete in 6 h. The dissolution of larger batch sizes would result in the formation of PuO2 solids. Incomplete dissolution of the PuO2 formed from the metal is not a solubility limitation, but can be attributed to a combination of reduced acidity and complexation of fluoride which slows the dissolution kinetics and effectively limits the mass of Pu dissolved.
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
Thermal stability tests were conducted with a nitric acid (HNO3)/hydroxylammonium nitrate (HAN)/potassium fluoride (KF) solution. The solution has great potential for use in plutonium dissolution because of the small quantity of hydrogen and other offgases produced. Tests were carried out in a Reactive Systems Screening Tool (RSST). The RSST is a calorimeter equipped with temperature and pressure probes as well as a heater that can heat a liquid sample at a programmed rate. In most cases, the calorimeter was pressurized with nitrogen to reduce evaporation of the liquid sample during heating. For the proposed solution, an autocatalytic reaction occurred between 113 and 131 degrees Celsius with 300 psig or 50 psig nitrogen inside the RSST vapor space. At ambient pressure, the solution boiled at about 110 degrees Celsius. After extensive boiling, the concentrations of HNO3 and HAN increased and the autocatalytic reaction occurred. Tests were also conducted with 1000 ppm Fe present in the solution. The range of the autocatalytic reaction initiation temperature was reduced to 105-120.5 degrees Celsius. With iron at ambient pressure, boiling still occurred above 100 degrees Celsius prior to the autocatalytic reaction, which occurred at 108-109 degrees Celsius. These results demonstrated the stability of the proposed HAN flowsheet, for which the planned dissolving temperature is 50-60 degrees Celsius. Additional tests were carried out with more concentrated solutions to further characterize the autocatalytic reaction initiation temperature. Increasing the nitric acid concentration to 3M decreased the reaction initiation temperature to 102-103 degrees Celsius. Increasing the HAN concentration increased the temperature rise of the reaction from 10-30 degrees Celsius to greater than 40 degrees Celsius. Increasing both reactants-to 3M nitric acid and 0.9M HAN-yielded a reaction initiation temperature of 91 degrees Celsius (with or without iron), the lowest observed in this study. This study was the first part of a larger flowsheet development / demonstration program for the plutonium metal dissolving process. The results of the study may be useful for similar flowsheets.
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
Several processing options for dissolving plutonium oxide (PuO[sub 2]) from high-fired materials have been studied. The scoping studies performed on these options were focused on PuO[sub 2] typically generated by burning plutonium metal and PuO[sub 2] produced during incineration of alpha contaminated waste. At least two processing options remain applicable for dissolving high-fired PuO[sub 2] in canyon dissolvers. The options involve solid solution formation of PuO[sub 2] With uranium oxide (UO[sub 2]) and alloying incinerator ash with aluminum. An oxidative dissolution process involving nitric acid solutions containing a strong oxidizing agent, such as cerium (IV), was neither proven nor rejected. This uncertainty was due to difficulty in regenerating cerium (IV) ions during dissolution. However, recent work on silver-catalyzed dissolution of PuO[sub 2] with persulfate has demonstrated that persulfate ions regenerate silver (II). Use of persulfate to regenerate cerium (IV) or bismuth (V) ions during dissolution of PuO[sub 2] materials may warrant further study.
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Author: David G. Karraker
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