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Title: Uranium-Molybdenum Dissolution Flowsheet Studies


No abstract provided.

  1. Savannah River Site (SRS), Aiken, SC (United States)
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Research Org.:
Savannah River Site (SRS), Aiken, SC (United States)
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DOE Contract Number:
Resource Type:
Technical Report
Country of Publication:
United States

Citation Formats

Pierce, R. A. Uranium-Molybdenum Dissolution Flowsheet Studies. United States: N. p., 2007. Web. doi:10.2172/1183716.
Pierce, R. A. Uranium-Molybdenum Dissolution Flowsheet Studies. United States. doi:10.2172/1183716.
Pierce, R. A. Thu . "Uranium-Molybdenum Dissolution Flowsheet Studies". United States. doi:10.2172/1183716.
title = {Uranium-Molybdenum Dissolution Flowsheet Studies},
author = {Pierce, R. A.},
abstractNote = {No abstract provided.},
doi = {10.2172/1183716},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}

Technical Report:

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  • The Super Kukla (SK) Prompt Burst Reactor operated at the Nevada Test Site from 1964 to 1978. The SK material is a uranium-molybdenum (U-Mo) alloy material of 90% U/10% Mo by weight at approximately 20% 235U enrichment. H-Canyon Engineering (HCE) requested that the Savannah River National Lab (SRNL) define a flowsheet for safely and efficiently dissolving the SK material. The objective is to dissolve the material in nitric acid (HNO3) in the H-Canyon dissolvers to a U concentration of 15-20 g/L (3-4 g/L 235U) without the formation of precipitates or the generation of a flammable gas mixture. Testing with SKmore » material validated the applicability of dissolution and solubility data reported in the literature for various U and U-Mo metals. Based on the data, the SK material can be dissolved in boiling 3.0-6.0 M HNO3 to a U concentration of 15-20 g/L and a corresponding Mo concentration of 1.7-2.2 g/L. The optimum flowsheet will use 4.0-5.0 M HNO3 for the starting acid. Any nickel (Ni) cladding associated with the material will dissolve readily. After dissolution is complete, traditional solvent extraction flowsheets can be used to recover and purify the U. Dissolution rates for the SK material are consistent with those reported in the literature and are adequate for H-Canyon processing. When the SK material dissolved at 70-100 o C in 1-6 M HNO3, the reaction bubbled vigorously and released nitrogen oxide (NO) and nitrogen dioxide (NO2) gas. Gas generation tests in 1 M and 2 M HNO3 at 100 o C generated less than 0.1 volume percent hydrogen (H2) gas. It is known that higher HNO3 concentrations are less favorable for H2 production. All tests at 70-100 o C produced sufficient gas to mix the solutions without external agitation. At room temperature in 5 M HNO3, the U-Mo dissolved slowly and the U-laden solution sank to the bottom of the dissolution vessel because of its greater density. The effect of the density difference insures that the SK material cannot dissolve and concentrate within the charge bundles. Solubility behavior of the SK material during dissolution at 70 o C reflected data reported in the literature for 100 o C. When solutions containing solids at 70 o C were heated to 105 o C, the solids dissolved. After 21 days, the samples that had been heated closely resembled the non-heated ones with respect to solids content. Super-saturated solutions of U-Mo have been produced which can be stable for more than 10 days, but these conditions are outside of the bounds of the recommended flowsheet. It is not known how the different dissolution pathways affect solution stability, but the results agree with the fact that solubility should not be affected by the dissolution pathway. Therefore, the literature data should be used as the bounding condition for solubility. Dissolution of the SK material consumed 2.8-8.0 moles of acid per mole of metal dissolved, which agrees with behavior reported elsewhere for U and U-Mo metals. The acid consumption values confirmed that a starting acid concentration in the dissolver of 4.0-5.0 M HNO3 will allow H-Canyon Operations to avoid adjusting the feed from the dissolver prior to solvent extraction while providing maximum operating margin for avoiding precipitate formation.« less
  • H-Canyon Engineering requested the Savannah River National Laboratory (SRNL) to perform two solvent extraction experiments using dissolved Super Kukla (SK) material. The SK material is an uranium (U)-molybdenum (Mo) alloy material of 90% U/10% Mo by weight with 20% 235U enrichment. The first series of solvent extraction tests involved a series of batch distribution coefficient measurements with 7.5 vol % tributylphosphate (TBP)/n-paraffin for extraction from 4-5 M nitric acid (HNO{sub 3}), using 4 M HNO{sub 3}-0.02 M ferrous sulfamate (Fe(SO3NH2)2) scrub, 0.01 M HNO3 strip steps with particular emphasis on the distribution of U and Mo in each step. Themore » second set of solvent extraction tests determined whether the 2.5 wt % sodium carbonate (Na2CO3) solvent wash change frequency would need to be modified for the processing of the SK material. The batch distribution coefficient measurements were performed using dissolved SK material diluted to 20 g/L (U + Mo) in 4 M HNO{sub 3} and 5 M HNO{sub 3}. In these experiments, U had a distribution coefficient greater than 2.5 while at least 99% of the nickel (Ni) and greater than 99.9% of the Mo remained in the aqueous phase. After extraction, scrub, and strip steps, the aqueous U product from the strip contains nominally 7.48 {micro}g Mo/g U, significantly less than the maximum allowable limit of 800 {micro}g Mo/g U. Solvent washing experiments were performed to expose a 2.5 wt % Na2CO3 solvent wash solution to the equivalent of 37 solvent wash cycles. The low Mo batch distribution coefficient in this solvent extraction system yields only 0.001-0.005 g/L Mo extracted to the organic. During the solvent washing experiments, the Mo appears to wash from the organic.« less
  • A dilute aqua regia flowsheet for the complete dissolution of solid uranium slugs in 7.5 hours is shown. Before the dissolver product solution can be further prooessed in stainiess steel equipment, the chloride must be removed. Two flowsheets for chloride removal are presented. In the first flowsheet, the chloride is removed by volatilization and in the second, by oxidation. The chloride removal need not be carried out in the dissolver vessel. The larger safe batch sizes of a homogeneous system may permit combining several batches from the heterogeneous dissolver system before chloride removal. Titanium, Haynes 25, and Hastelloy F aremore » possible materials of construction for the process equipment that is to contain both nitric and hydrochloric acids. (auth)« less
  • H-Canyon Engineering (HCE) is evaluating the feasibility of processing material from the Super Kukla Prompt Burst Reactor, which operated at the Nevada Test Site from 1964 to 1978. This material is comprised of 90 wt % uranium (U) (at approximately 20% 235U enrichment) alloyed with 10 wt % molybdenum (Mo). The objective is to dissolve the material in nitric acid (HNO{sub 3}) in the H-Canyon dissolvers and then to process the dissolved material through H-Canyon First and Second Cycle solvent extraction. The U product from Second Cycle will be sent to the highly enriched uranium (HEU) blend down program. Inmore » the blend down program, enriched U from the 1EU product stream will be blended with natural U at a ratio of 1 part enriched U per 3.5 parts natural U to meet a reactor fuel specification of 4.95% 235U before being shipped for use by the Tennessee Valley Authority (TVA) in its nuclear plants. The TVA specification calls for <200 mg Mo/g U (200 ppm). Since natural U has about 10 mg Mo/g U, the required purity of the 1EU product prior to blending is about 800 mg Mo/g U, allowing for uncertainties. HCE requested that the Savannah River National Laboratory (SRNL) define a flowsheet for the safe and efficient processing of the U-10Mo material. This report presents a computational model of the solvent extraction portion of the proposed flowsheet. The two main objectives of the computational model are to demonstrate that the Mo impurity requirement can be met and to show that the solvent feed rates in the proposed flowsheet, in particular to 1A and 1D Banks, are adequate to prevent refluxing of U and thereby ensure nuclear criticality safety. SASSE (Spreadsheet Algorithm for Stagewise Solvent Extraction), a Microsoft Excel spreadsheet that supports Argonne National Laboratory's proprietary AMUSE (Argonne Model for Universal Solvent Extraction) code, was selected to model the U/Mo separation flowsheet. SASSE spreadsheet models of H-Canyon First and Second Cycle solvent extraction show that a standard unirradiated fuel flowsheet is capable of separating U from Mo in dissolved solutions of a U/Mo alloy. The standard unirradiated fuel flowsheet is used, except for increases in solvent feed rates to prevent U refluxing and thereby ensure nuclear criticality safety and substitution of higher HNO{sub 3} concentrations for aluminum nitrate (Al(NO{sub 3})){sub 3} in the feed to 1A Bank. (Unlike Savanah River Site (SRS) fuels, the U/Mo material contains no aluminum (Al). As a result, higher HNO3 concentrations are required in the 1AF to provide the necessary salting.) The TVA limit for the final blended product is 200 {micro}g Mo/g U, which translates to approximately 800 mg Mo/g U for the Second Cycle product solution. SASSE calculations give a Mo impurity level of 4 {micro}g Mo/g U in the Second Cycle product solution, conservatively based on Mo organic-to-aqueous distributions measured during minibank testing for previous processing of Piqua reactor fuel. The calculated impurity level is slightly more than two orders of magnitude lower than the required level. The Piqua feed solution contained a significant concentration of Al(NO{sub 3}){sub 3}, which is not present in the feed solution for the proposed flowsheet. Measured distribution data indicate that, without Al(NO{sub 3}){sub 3} or other salting agents present, Mo extracts into the organic phase to a much lesser extent, so that the overall U/Mo separation is better and the Mo impurities in the Second Cycle product drop to negligible concentrations. The 1DF U concentration of 20 g/L specified by the proposed flowsheet requires an increased 1DX organic feed rate to satisfy H-Canyon Double Contingency Analysis (DCA) guidelines for the prevention of U refluxing. The ranges for the 1AX, 1BS, and 1DX organic flow rates in the proposed flowsheet are set so that the limiting ratios of organic/aqueous flow rates exactly meet the minimum values specified by the DCA.« less