Kevin B. Ramsey

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.

Development of Nonfertile and Evolutionary Mixed-Oxide Nuclear Fuels for Use in Existing Water Reactors

Abstract Investigations of an advanced fuel form are currently under way. This new fuel form, referred to as evolutionary mixed oxide (EMOX), is a slight perturbation on standard mixed-oxide (MOX) fuel, and analyses show that it can be an effective plutonium management tool in existing light water reactors. The addition of a small fraction of calcia-stabilized zirconia to the uranium-plutonium oxide matrix allows for greater plutonium conversion while also providing a licensing path forward toward eventual implementation of higher-plutonium-destruction fuels. These fuels, referred to as nonfertile (NF) fuels, achieve their high destruction rates through the absence of uranium, which breeds plutonium, in the fuel composition. Extensive calculations have been performed to assess the feasibility of incorporating the EMOX fuel form into existing pressurized water reactor systems, and the results are given in detail. Specifically, calculations have been made to determine the plutonium consumption achievable by the EMOX concept, and comparisons have been made of this performance to that of typical MOX and NF fuels. The results indicate that EMOX and NF fuels can provide flexibility with regard to controlling plutonium inventories in spent fuel. In addition, fabrication experiments have been conducted to determine the feasibility of fabricating suitable EMOX and NF fuels. NF and EMOX fuels have been fabricated using the solid-state reaction method. Precursor powders were successfully blended and milled using a combination of ball milling and high-energy vibratory milling. Sintering data for EMOX fuel indicated that significant densification occurred at a temperature of 1700°C.

Recycle of scrap plutonium-238 oxide fuel to support future radioisotope applications

The Nuclear Materials Technology (NMT) Division of Los Alamos National Laboratory has initiated a development program to recover & purify plutonium-238 oxide from impure feed sources in a glove box environment. A glove box line has been designed and a chemistry flowsheet developed to perform this recovery task at large scale. The initial demonstration effort focused on purification of 238PuO2 fuel by HNO3/HF dissolution, followed by plutonium(III) oxalate precipitation and calcination to an oxide. Decontamination factors for most impurities of concern in the fuel were very good, producing 238PuO2 fuel significantly better in purity than specified by General Purpose Heat Source (GPHS) fuel powder specifications. A sufficient quantity of purified 238PuO2 fuel was recovered from the process to allow fabrication of a GPHS unit for testing. The results are encouraging for recycle of relatively impure plutonium-238 oxide and scrap residue items into fuel for useful applications. The high specific activity of pl...

Nitrate anion exchange in 238Pu aqueous scrap recovery operations

Strong base, nitrate anion exchange (IX) is crucial to the purification of 238Pu solution feedstocks with gross levels of impurities. This paper discusses the work involved in bench scale experiments to optimize the nitrate anion exchange process. In particular, results are presented of experiments conducted to a) demonstrate that high levels of impurities can be separated from 238Pu solutions via nitrate anion exchange and, b) work out chemical pretreatment methodology to adjust and maintain 238Pu in the IV oxidation state to optimize the Pu(IV)-hexanitrato anionic complex sorption to Reillex-HPQ resin. Additional experiments performed to determine the best chemical treatment methodology to enhance recovery of sorbed Pu from the resin and VIS-NIR absorption studies to determine the steady state equilibrium of Pu(IV), Pu(III), and Pu(VI) in nitric acid are discussed.

Development program for 238Pu aqueous recovery process

Aqueous processing is necessary for the removal of impurities from 238Pu dioxide (238PuO2) scrap due to unacceptable levels of 234U and other non-actinide impurities. 238PuO2 is used to supply the thermal energy in General Purpose Heat Sources (GPHS). Impurities at levels above GPHS fuel specifications may impair the performance of the heat source. Efforts at Los Alamos have focused on developing the bench scale methodology for the aqueous process steps which include comminution, dissolution, ion exchange, precipitation, and calcination. Recently, work has been performed to qualify the bench scale methodology, to show that the developed process produces 238PuO2 that meets GPHS fuel specifications. This work has also enabled us to determine how liquid waste may be minimized during fullscale processing. Results of process qualification for the bench scale aqueous recovery operation and waste minimization efforts will be presented.

Removal of Pu-238 from aqueous process streams using a polymer filtration process

A glovebox facility is under construction at Los Alamos that will recover a significant quantity of the impure Pu-238 that exists in scrap and residues from past production operations. The general flowsheet consists of milling, acid dissolution, ion exchange, precipitation, calcination, oxygen isotope exchange, and waste treatment operations. As part of the waste treatment operations we are using polymer filtration to remove Pu-238 to meet facility discharge limits. Polymer filtration (PF) technology uses water-soluble polymers prepared with selective receptor sites to sequester metal ions, organic molecules, and other species from dilute aqueous solutions. The water-soluble polymers have a sufficiently large molecular size that they can be separated and concentrated using ultrafiltration (UF) methods. Water and small, unbound components of the solution pass freely through the UF membrane while the polymer concentrates in the retentate. The permeate stream is “cleaned” of the components bound to the polym...

238Pu recovery and salt disposition from the molten salt oxidation process

We have begun designing and optimizing our recovery and recycling processes by experimenting with samples of “spent salt” produced by MSO treatment of surrogate waste in the reaction vessel at the Naval Surface Warfare Center-Indian Head. One salt was produced by treating surrogate waste containing pyrolysis ash spiked with cerium. The other salt contains residues from MSO treatment of materials similar to those used in 238Pu processing, e.g., Tygon tubing, PVC bagout bags, HDPE bottles. Using these two salt samples, we will present results from our investigations.

Process parameters optimization in ion exchange 238Pu aqueous processing

This paper describes bench-scale efforts (5–7 grams of 238Pu) to optimize the ion exchange process for 234U separation with minimal 238Pu losses to the effluent and wash liquids. The bench-scale experiments also determine the methodology to be used for the full-scale process: 5 kg238Pu annual throughput. Heat transfer calculations used to determine the thermal gradients expected during ion exchange processing are also described. The calculations were performed in collaboration with Westinghouse Savannah River Technology Center (WSRTC) and provide information for the design of the full-scale ion exchange equipment.

Materials compatibility for 238Pu-HNO3/HF solution containment: 238Pu aqueous processing

The Power Source Technologies Group at Los Alamos National Laboratory is building a 238Pu Aqueous Scrap Recovery Line at the Plutonium Facility. The process line incorporates several unit operations including dissolution, filtration, ion exchange, and precipitation. During 1997–1999, studies were carried out to determine the chemistry used in the full-scale process. Other studies focussed on the engineering design of the operation. Part of the engineering design was to determine, in compatibility studies, the materials for reaction and storage vessels which will contain corrosive 238Pu−HNO3/HF solutions. The full-scale line is to be operational by the end of year 2000.

Stabilization of 238Pu-contaminated combustible waste by molten salt oxidation

Surrogate studies were conducted using the molten salt oxidation system at the Naval Surface Warfare Center-Indian Head Division. This system uses a rotary feed system and an alumina molten salt oxidation vessel. The combustible materials were tested individually and together in a homogenized mixture. A slurry containing pyrolyzed cheesecloth ash spiked with cerium oxide, which is used as a surrogate for plutonium, and ethylene glycol were also treated in the molten salt oxidation vessel.