Elizabeth A. Bluhm

Plutonium Oxide Polishing for MOX Fuel Production

Abstract: Los Alamos National Laboratory (LANL) has been tasked to produce 120 kg of plutonium as highly purified PuO2 for the European Mixed Oxide (MOX) Lead Test Assembly managed by Duke, COGEMA, Stone & Webster (DCS). To meet stringent and challenging technical requirements for PuO2 production, the LANL aqueous polishing team recently established consistency in generating quality material from weapons-grade PuO2. Polishing was required to remove undesirable quantities of trace-metal impurities, particularly gallium, and to produce a material with appropriate powder characteristics, such as particle size and surface area. The process flow sheet for PuO2 polishing was based on aqueous purification and included the unit operations of dissolution, ion exchange, oxalate precipitation, and calcination.

Removal of Actinides from Acidic Solution via Carrier‐Mediated Facilitated Transport Across Mesoporous Substrates with Nanoengineered Surfaces: Thiol Self‐Assembled Monolayers with D(tBu)ΦD(iBu)CMPO Ligands

Abstract: The surface engineering of polycarbonate track-etched (PCTE) membranes was performed to create a permselective membrane for the removal of trace levels of fission products and transuranic metals from acidic streams. Electroless gold deposition was used to place a gold coating on the PCTE substrates. The gold coating was subsequently functionalized through the formation of a self-assembled monolayer of dodecanethiol, which was further functionalized with di-(4-t-butylphenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide. Transport characteristics of metal ions, 137Cs, 85Sr, 241Am, and 239Pu, were obtained using a two-compartment diffusion apparatus. Transport studies showed that the functionalized membranes enhance the transport rates of 241 Am and 239Pu and inhibit the transport of 137Cs and 85Sr. Diffusion studies over an extended time revealed that the facilitated transport characteristics of 239Pu through the ligand-coated membranes are dependent on nitrate anion concentrations in the feed and sink cells.

Robust membrane systems for actinide separations

Our objective in this project is to develop very stable thin membrane structures containing ionic recognition sites that facilitate the selective transport of target metal ions, especially the actinides.

Purification of Plutonium Chloride Solutions via Precipitation and Washing

Abstract Pyrochemical operations at Los Alamos Plutonium Facility use high temperature melts of calcium, sodium, and potassium salts in the plutonium metal purification process. Aqueous chloride operations recover the remaining plutonium from the residue salts, generating copious quantities of corrosive aqueous waste while occupying a large area of the facility. To minimize these problems, an alternative flow sheet was tested in which dissolved salts were precipitated and washed to remove interstitial chloride before further processing in aqueous nitrate operations. Results of the tests will be discussed from the perspective of chloride removal, plutonium recovery, filterability, and waste minimization.

Purification of aqueous plutonium chloride solutions via precipitation and washing.

Pyrochemical operations at Los Alamos Plutonium Facility (TA-55) use high temperature melt s of calcium chloride for the reduction of plutonium oxide to plutonium metal and hi gh temperature combined melts of sodium chloride and potassium chloride mixtures for the electrorefining purification of plutonium metal . The remaining plutonium and americium are recovered from thes e salts by dissolution in concentrated hydrochloric acid followed by either solvent extraction or io n exchange for isolation and ultimately converted to oxide after precipitation with oxalic acid . Figur e 1 illustrates the current aqueous chloride flow sheet used for plutonium processing at TA-55 .

Aqueous Ion Transport Studies in Stainless Steel Membranes

Aqueous ion transport through unmodified, acid/base resistant, stainless steel membrane material was investigated to determine the feasibility of using the material as a basis for an actinide separation unit operation. The Mott Metal Corporation membrane material used for testing was a sintered 316L stainless steel membrane having a particle size cutoff rating of 0.5 μm and an average pore size of 2.2 ± 0.5 μm. Radiotracer transport experimentation was conducted with 45Ca, 137Cs, 241Am, 152Eu, and 239Pu cations at varying pH and at dilute cation concentrations. Infinite-dilution diffusion coefficients for the cations were measured and had the same order of magnitude (10-6 cm2 s-1). The infinite-dilution diffusivities compared well with values found in the cited literature. These results confirmed bulk diffusion as the controlling mechanism for cation transport through the water-saturated stainless steel membrane pores and support the hypothesis that the membrane, in the unmodified form, does not add any c...