Chemical Head-end Steps for Aqueous Reprocessing of Carbide Fuels

Abstract

The organic compounds formed during the dissolution of carbide fuels in nitric acid adversely affect the extraction of plutonium by tributyl phosphate. This work was undertaken as a preliminary study of the effect of refluxing the dissolver solutions obtained by dissolution of uranium carbide in 13 Μ nitric acid on the subsequent solvent extractions steps. The extraction of plutonium from carbide dissolver solutions by 30% TBP in ndodecane and the subsequent stripping and partitioning of Pu from the organic phase loaded with uranium and plutonium were studied. The results obtained were compared with those obtained with control solutions containing uranyl nitrate and plutonium(IV) nitrate with concentrations of uranium, plutonium and nitric acid similar to those of the dissolver solutions. The distribution ratios obtained with the dissolver solution and the control solution were comparable, indicating that the dissolver solution obtained after refluxing for 20h may give a feed solution suitable for PUREX process. Similarly, extraction and partitioning experiments were carried out with (U, Pu)C dissolver solutions and the results were similar to the results obtained with uranium carbide dissolver solutions.As an alternative chemical route for the destruction of carbonaceous materials in the UC dissolver solution, the effectiveness of sodium dichromate as an oxidizing agent was also investigated in terms of the percentage carbon remaining after treatment of the dissolver solution with sodium dichromate. The treatment resulted in destruction of nearly 97% of the initial carbon present in the carbide fuel.

Electrochemical behavior of UC in acidic media: Preliminary results

“…However, uranium oxidation was accompanied by the accumulation of undefined organic species in the electrolyte [3,4]. Photochemical [5] and electrochemical [6] techniques were applied to oxidize the organic species to CO 2 and to accelerate UC dissolution.…”

“…This preliminary study addresses UC electrochemical behavior in nitric acid media from 0.1 to 2 M. Because of the chemical and electrochemical inertness of ClO 4 − ions, perchloric acid solutions were also chosen as the working electrolytes for the present study. Linear voltammetry (LV) and multistep potential sweep coulometry (MPSC) were used as preliminary methods to determine the electrochemical properties of UC, and especially the potential boundaries characterizing the different rates of UC oxidation.…”

Impurity analysis and dissolution behaviour of plutonium bearing impure MOX scrap: an assessment of recycling feasibility

“…This further may render difficulties to deploy the solvent extraction based separation of actinides. However, the organics can be removed using ozone, perchloric acid, sodium dichromate, by photochemical destruction or using Ag(II) [42][43][44]. The purification by solvent extraction or ion exchange steps may then be subsequently followed by microwave co-denitration [14,16] or co-precipitation to deliver sinterable grade mixed powder.…”

UC oxidation with HNO2 in aqueous solutions of HNO3 and HClO4

“…The results of electrochemical measurements agree with the data of numerous dissolution studies of UC, U 2 C 3 and UC 2 in the presence of strong oxidizing agents. UC, U 2 C 3 and UC 2 dissolution in mixtures of 15 M HNO 3 -18 M H 2 SO 4 [4], 0.1-15 M HNO 3 [5][6][7][8][9] resulted in uranium oxidation to U(VI) with simultaneous accumulation of organic compounds of non-defined nature stemming from the carbon oxidation. The reported UC dissolution rate in HNO 3 > 4.0 M corresponds to quantitative dissolution of 0.5 g UC in 25 mL HNO 3 (> 4 M) during the time period less than 1 h. The dissolution kinetics was studied by direct measurements of the U(VI) concentration in the solution [6] and by analysis of evolving gas [7].…”

“…The authors assume the presence of carboxylic (HCOOH, CH 3 COOH, H 2 C 2 O 4 ) [6,7] and aromatic (benzoic, trimellitic and mellitic) acids [5,6,10] in the 4.0-8.0 M HNO 3 UC dissolver solutions. Even after 20 h reflux boiling of the 13 M HNO 3 UC dissolver solution, 18% of carbon introduced into the reaction as UC were still found in the solution [9], thus proving the extreme stability of organic compounds toward further oxidation. The organic compounds may exhibit an adverse effect on the uranium separation by liquid-liquid extraction because they can form stable complexes with U(VI) and they may participate in the possible formation of a so-called "third phase" during the extraction process [5,6].…”