IDAHO CHEMICAL PROCESSING PLANT TECHNICAL PROGRESS REPORT FOR JANUARY- MARCH 1960

Abstract

9 > ? ( ing schedule included MTR, ETR, and other aluminum-type fuels that were processed through the TBP headend at 75 to 100% of flowsheet rates and through the Hexone second and third cycle extraction system at up to l5O% of flowsheet values, achieving an over-all recovery of 99.60%. In carrying out basic studies on aqueous zirconium processing, results obtained during the potentiometric titration of zirconium-fluoride-nitric acid solutions with sodium hydroxide were explained by a mechanism in which the untitrated zirconium fluoride species is converted to a fluozirconate and further hydrolysis proceeds via a fluozirconate route. A modified Zirflex flowsheet for processing 2.5% U-Zr alloy fuels is proposed as a result of bench scale dissolution studies on unirradiated PWR plates that showed that dissolver solutions could be stabilized by adding aluminum nitrate and nitric acid. that higher ammonium fluoride concentrations increased the dissolution rate, that higher hydrogen peroxide concentrations lowered the dissolution rate and decreased solution stability, and that ammonia removal by boiling with or without air sparging had little effect on the reaction. Density curves for Zirflex solutions are reported. First tests of the pilot plant for continuous dissolution of zirconium-type elements have indicated that the dissolution rate is approximately four times as great as predicted on the basis of batch dissolution rates and comparison with the rate ratio for batch vs. continuous dissolution of aluminum, which was used to establish the dissolver size. The continuous dissolution rate for a 2% zirconium- 98% uranium element was approximately proportional to the acid feed rate and reached l9O kg/day at an acid feed rate of 36 l/hr (11M nitric acid, 0.30M hydrofluoric acid, and 0.35M aluminum nitrate). Development of new waste treatment methods is influenced by waste volumes and the associated storage costs involved. A survey of current and proposed zirconium fuel proc esses indicates highest waste volumes are generated by the Zirflex and the original STR processes, with moderate improvement for the currentiy modified STR process. In identification of ionic species present in process solutions, electrolytic conductance has been useful as an analytical tool: data obtained are of significance in application to process problems as well as instrumental analysis and control. The Onsager-Fuoss limiting law for electrical conductance of electrolyte mixtures has been tested by measurements of KCl-HCl mixtures at 25 deg C and, within experimental error, has been confirmed. Experiments on electrolytic dissolution of stairless steel in nitric acid, designed to study the quantity of anode sludge formed as the temperature was varied from 40 to 90 deg C, the current density from 0.4 to 1.2 amp/cm/sub 2/, and the acidity from 1 to 5M, disclosed that minimum sludge (0.2 to 0.5 g/100 g of metal dissolved) was formed at the lower temperature and under high-current density-high acidity or lowcurrent density-low acidity conditions. Other combinations of these variables gave l to 3 g of sludge per 100 g of metal dissolved. An extension of the ARCO process which employs molten lead chloride as a solvent for zirconiumuranium alloys followed by regeneration of lead chloride from the lead produced, utilizes direct chlorination in the dissolver vessel to rechlorinate lead as it is formed or to directly chlorinate (by addition of chlorine to the lead chloride bath) and rapidly dissolve a wide variety of metals including stainless steel, chromium, niobium, aluminum, and zirconium at rates of at least l5 to 30 mg/cm/sup 2//min. Relatively rapid attack eliminates many materials from consideration for dissolver construction, but an alumina ceramic appeared to withstand the dissolution medium. In continued studies of solvent stability in the TBP-HNO/sub 3/Zr system, it has been shown that the Zr-TBP reaction is first order with respect to zirconium concentration, the