Dennis Padilla

Hydrothermal oxidation of radioactive combustible waste

Abstract A hydrothermal processing system was designed, built and tested for treatment of transuranic combustible material. The operation is performed in a plutonium glovebox. Presented in this paper are results from the study of the hydrothermal oxidation of plutonium and americium contaminated organic wastes. The use of thermal liquefaction, via pyrolysis, to prepare solid materials for hydrothermal processing was tested and compared to the pumping of slurries of small particle sized solids (ion exchange resin). Experiments show that the hydrothermal process converts greater than 99.9% of the organic component to CO 2 and H 2 O, with 30 wt% H 2 O 2 as an oxidant, at 540°C and 46.2 MPa. The majority of the actinide component forms insoluble products that are easily separated by filtration. A titanium liner in the reactor and heat exchanger provides corrosion resistance for the oxidation of chlorinated organics.

PARTICULATE CAPTURE OF PLUTONIUM BY HIGH GRADIENT MAGNETIC SEPARATION WITH ADVANCED MATRICES

A high performance superconducting magnetic separator is being developed for near single particle retrieval from low concentration field collected samples. Results show that maximum separation is obtained when the effective matrix element diameter approaches the diameter of the particles to be captured. Experimentally, we were able to capture very dilute levels of 0.2 to 0.8 μm PuO2 particles with dodecane as a carrier fluid. The development of new matrix materials is being pursued through the deposition of nickel dendrites on an existing stainless steel matrix material. The new materials are promising for the submicron collection of paramagnetic particles. Results indicate that these new matrices contain a high number of capture sites for the paramagnetic particles. We have also derived a force-balance model that uses empirically determined capture cross section values. The model can be used to optimize the capture cross section and thus increase the capture efficiency. This enables the prediction of high gradient magnetic separator performance for a variety of materials and applications.

Magnetic separation for environmental remediation

Magnetic separation is a physical separation process that segregates materials in a mixture on the basis of magnetic susceptibility. Because all actinides and their compounds and fission products are paramagnetic, and most host materials such as water, graphite, soil, and sand are diamagnetic, magnetic separation methods can be used to extract the actinides from these hosts, concentrating the toxic materials into a low volume waste stream. The technology relies only on physical properties, and therefore separations can be achieved while producing little or no secondary waste.

CAPTURE AND RETRIEVAL OF PLUTONIUM OXIDE PARTICLES AT ULTRA-LOW CONCENTRATIONS USING HIGH-GRADIENT MAGNETIC SEPARATION

A high-gradient magnetic separation system has been developed for capture and retrieval of ultra-low plutonium oxide concentrations. The application of advanced matrix materials and improved methodology has demonstrated the effective collection and recovery of submicron paramagnetic actinide particles with particle concentrations as low as 10−23 M. Incorporation of multiple passes during recovery of magnetically captured particles improves the system mass balance. Activity balances for plutonium were verified with stringent sampling protocols. Collection and recovery values demonstrate that 99% of the submicron plutonium oxide particles can be accounted for when recycle loops are incorporated into capture and recovery circuits, magnetically captured particles are released by sonication, carrier fluids are organically based, and longer matrix lengths are utilized.

Magnetic Separation for Nuclear Material Surveillance

A high performance superconducting magnet is being developed for particle retrieval from field collected samples. Results show that the ratio of matrix fiber diameter to the diameter of the captured particles is an important parameter. The development of new matrix materials is being pursued through the controlled corrosion of stainless steel wool, or the deposition of nickel dendrites on the existing stainless steel matrix material. We have also derived a model from a continuity equation that uses empirically determined capture cross section values. This enables the prediction of high gradient magnetic separator performance for a variety of materials and applications. The model can be used to optimize the capture cross section and thus increase the capture efficiency.

Surveillance of sealed containers with plutonium oxide materials (ms163)

DOE is embarking upon a program to store large quantities of plutonium-bearing materials for up to fifty years. Materials destined for long-term storage include metals and oxides that are stabilized and packaged according to the DOE storage standard, where the packaging consists of two nested, welded, stainless steel containers. We have designed instrumented storage containers that mimic the inner storage can specified in the 3013 standard at both full- and small-scale capacities (2.4 liter and 0.005 liter, respectively), Figures 1 and 2. The containers are designed to maintain the volume to material mass ratio while allowing the gas composition and pressure to be monitored over time.

Destruction of halogenated organics with hydrothermal processing

Chemical reactions in high temperature water (hydrothermal processing) allow new avenues for effective waste treatment and radionuclide separation. Successful implementation of hydrothermal technologies offers the potential to effectively treat many types of radioactive waste and reduce the storage hazards and the disposal costs, while minimizing the generation of hazardous secondary waste streams.1–5 Halogenated hazardous organic liquids containing actinides are a difficult to treat category of TRU radioactive wastes. These liquids are typically used for degreasing operations or density measurements and can include trichlorethylene and bromobenzene. Experiments have demonstrated that hydrothermal processes can eliminate hazardous halogenated organics generated by the nuclear industry by the complete oxidation of the organic components to CO2 and H2O.