Dissolution of Plutonium Scrub Alloy and Anode Heel Materials in H-Canyon

Abstract

SUMMARYH-Canyon has a "gap" in dissolver operations during the last three months of FY03 in which they can dissolve FBLine legacy residues. One group of material to be processed during the gap is pre-existing scrub alloy material received from the Rocky Flats Plant in the early 1980's. There are 14 cans of material containing approximately 3.8 kilograms of plutonium. Of the 14 cans, it was anticipated that four cans contain salts from the Molten Salt Extraction (MSE) process, two cans contain anode heel materials, and eight cans contain scrub alloy buttons.H-Canyon desires to process the materials using a flowsheet similar to the SS&C (sand, slag and crucible) dissolution flowsheet used in F-Canyon. The proposed flowsheet for this material will have a starting nitric acid (HNO 3 ) level of ~3M, an ending acid level of ~ 1.5M, 0.002M mercury, ~2 g/L boron, and 0.15M CaF 2 (calcium fluoride). The materials will be loaded into carbon steel cans and then placed into aluminum metal charging bundles.Samples of 13 items were sent to Savannah River Technology Center (SRTC) for characterization and flowsheet testing --four MSE salts, two anode heels, and seven scrub alloy buttons. SRTC dissolved and characterized each of the samples. Two of them, originally thought to be MSE salts, were found to be graphite mold materials and were unsuitable for processing in H-Canyon. Characterization studies confirmed that the identification of the remaining items as MSE salts, scrub alloy buttons, and anode heel materials was correct.The MSE salts and anode heels solids are comprised primarily of plutonium, potassium, sodium and chloride. The solids dissolve readily in 4M HNO 3 /0.3M HF (hydrofluoric acid) without any noticeable gas generation. Both the MSE salts and anode heels left behind small amounts of residual solids. The scrub alloy buttons are comprised primarily of plutonium and aluminum. The solids dissolve readily with light, effervescent gas generation at the material surface and only trace amounts of NOx generation. Of the seven button samples, four dissolved completely. Two button samples contained small amounts of tantalum that did not dissolve. The last of the seven scrub alloy samples left a trace amount of residual plutonium solids. It is anticipated that the presence of undissolved fissile material is a function of where the sample was located relative to the button surface.Process simulation experiments followed characterization studies. The baseline flowsheet (starting HNO 3 ~3.0M) was tested along with an increased-acid flowsheet (starting HNO 3 ~5.5M) at a 1:10,000 scale. Experiments show that both flowsheets are effective in dissolving the scrub alloy buttons, MSE salts, and anode heel samples. The vigor of the reaction of nitric acid with the items is characterized as a gentle "fizz" at the surface of the scrub alloy button samples with only trace amounts of NOx generation. As a result, the aggressiveness of overall process is determined by the dissolution of the steel cans and aluminum charge bundles. If a st...

Uranium Metal Dissolution in the Presence of Fluoride and Boron

“…The Pu-Al scrub alloy "solids dissolve readily with light, effervescent gas generation at the material surface." 7 This presumption turned out to be a reasonable assessment of reaction as can be readily seen from the pictures in Attachment 1.…”

“…Without fluoride, the oxide coating remains at the metal surface and impedes dissolution. 7 Boron is frequently added to Savannah River Site canyon dissolvers as a component of dissolution at 2 g/L to function as a neutron poison. It has the added effect of complexing some of the available fluoride.…”

Dissolution of Fb-Line Metal Residues Containing Beryllium in H-Canyon

“…To meet milestone and schedule commitments, material containing Pu and Be metals may be dissolved in H-Canyon. A dissolution flowsheet similar to the flowsheets used for the dissolution of scrub alloy in H-Canyon [1] and unirradiated Mark 42 targets in F-Canyon [2] has been proposed. In those flowsheets, high concentrations (0.2-0.3 M) of F¯ with (3 or 8 M) HNO 3 were required to catalyze the dissolution of Pu metal or oxide due to F¯ complexation with the boron (B).…”