Comparison of silver(II), cobalt(III), and cerium(IV) as electron transfer mediators in the MEO mixed waste treatment process

Mediated electrochemical oxidation (MEO) has been developed as a method to treat mixed hazardous waste. The technology has for the most part been targeted toward wastes generated by the nuclear industry, consisting of a hazardous or non-hazardous organic material contaminated by a radioactive substance. The MEO process consists of the electrochemical generation of a powerful oxidizing agent, which serves as an electron transfer mediator to bring about the oxidation of the organic component. Numerous studies on a variety of organic substrates have demonstrated complete oxidation to carbon dioxide can be realized under the proper reaction conditions, with water serving as the source of oxygen. The radioactive component, usually an actinide element or heavy metal isotope, can then be recovered from the resulting organic free aqueous solution by standard methods such as ion exchange or solvent extraction. In addition to the variety of organic compounds tested, investigators have also looked at a number of process parameters including choice of mediator, temperature, concentration of mediator, current density, anode material, acid concentration, and cell separator material. From these studies it would appear that for a given organic substrate, the two most important process parameters are choice of mediator and temperature. The purpose of this work is to evaluate these two parameters for a given organic material, holding all other parameters constant. The organic material chosen for this study is the industry standard sulfonated styrene-divinyl benzene based cation exchange resin. This material is ubiquitous throughout the nuclear complex as a process residue, and is very resistant to chemical attack making it an ideal substrate to evaluate MEO capability. A high acid concentration is necessary to solubilize the mediator in its higher oxidation state, 6 M nitric acid was chosen since it is compatible with existing subsequent actinide element recovery processes

The Kane fracture zone in the Central Atlantic Ocean

The Kane fracture zone has been traced as a distinct topographic trough from the Mid-Atlantic Ridge near 24°N to the 80-m.y. B.P. isochron (magnetic anomaly 34) on either side of the ridge axis for a total of approximately 2800 km. Major changes in trend of the fracture zone occur at approximately 72 m.y. B.P. (anomaly 31 time) and approximately 53–63 m.y. B.P. (anomaly 21–25 time) which are the result of major reorientations in spreading directions in the central Atlantic Ocean

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 and 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 {sup 238}PuO{sub 2} fuel by HNO{sub 3}/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 {sup 238}PuO{sub 2} fuel significantly better in purity than specified by General Purpose Heat Source (GPHS) fuel powder specifications. The results are encouraging for recycle of relatively impure plutonium-238 oxide and scrap residue items into fuel for useful applications. A sufficient quantity of purified {sup 238}PuO{sub 2} fuel was recovered from the process to allow fabrication of a GPHS unit for testing. The high specific activity of plutonium-238 magnifies the consequences and concerns of radioactive waste generation. This work places an emphasis on development of waste minimization technologies to complement the aqueous processing operation. Results from experiments allowing more time for neutralized solutions of plutonium-238 to precipitate resulted in decontamination to about 1 millicurie/L. Combining ultrafiltration treatment with addition of a water-soluble polymer designed to coordinate Pu, allowed solutions to be decontaminated to about 1 microcurie/L. Efforts continue to develop a capability for efficient, safe, cost-effective, and environmentally acceptable methods to recover and purify {sup 238}PuO{sub 2} fuel