F. Coyne Prenger

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.

Performance Limits of Gravity-Assist Heat Pipes with Simple Wick Structures

Experiments using gravity-assist heat pipes with simple wick structures were used to establish performance limits due to entrainment of the liquid by the counter-flowing vapor. A physical model is postulated which leads to a single correlation predicting entrainment limits for all data investigated. The characteristic length in the entrainment parameter is the depth of the wick structure and the model infers an upper bound on this parameter.

High-Gradient Magnetic Field Split-Flow Thin Channel (HGMF-SPLITT) Fractionation of Nanoscale Paramagnetic Particles

ABSTRACT High-gradient magnetic field (HGMF) split-flow thin channel (SPLITT) fractionation (HGMF-SPLITT) is a newly developed magnetic fractionation technique for separating submicron and/or nanoscale paramagnetic particulate species in a continuously flowing separator. Incorporation of high-gradient magnetic fields, into the split-flow-fractionation separator geometry, increases the magnetic force experienced by a paramagnetic submicron particle relative to current magnetic field-flow-fractionation devices. The application of HGMF-SPLITT fractionation, for selective separation of paramagnetic submicron particulates, was experimentally investigated.

A Novel Magnetic Separation Technique: Selective Separation of Ultrafine Particles by Magnetophoresis

ABSTRACT The selective and specific extraction of species of interest from local environmental and other sample sources are important for scientific research, industrial processes, and environmental applications. A novel process for selective separation of magnetic particles using magnetophoresis is investigated. The principle of this process is that the direction and velocity of particle movement in a magnetic field gradient are determined by magnetic, gravitational, and drag forces. By selectively controlling these forces, it is possible to control the mobility of the different species and, therefore, magnetically fractionate mixtures of them into discrete groups. This study demonstrated the selective separation of various species, such as iron (III) oxide and cupric (II) oxide. Experimental results showed that around 70–80% of iron was selectively collected in the upper part of the separation media and around 90% of copper was concentrated in the lower part of the media. A magnetophoresis model was developed in this work to provide a theoretical understanding of this phenomenon and to assist in the design of magnetophoresis experiments.

Effect of the expansion associated with the plutonium α–β–γ phase transitions on storage can integrity

Abstract The effects of the volume expansion of plutonium metal through the α–β and β–γ phase transitions on a stainless steel storage container were examined. A cylindrical plutonium ingot was placed in the axial center of an annealed stainless steel cylinder and thermally cycled until a steady state in the strain response of the cylinder was reached. The average plastic hoop strain was 1.47% and 1.55% after six and four cycles through the α–β and α–β–γ phase transitions, respectively. Elastic strain was ∼0.2%, indicating a 8.96 MPa back pressure on the Pu ingot. This is an order of magnitude less than the compressive yield strength of α- and β-Pu at the transition temperature. Metallographic analyses indicate that anisotropic expansion of the Pu ingot is due to preferentially oriented grain growth of the β-Pu along the axial direction due to stress applied by the steel cylinder during the α–β phase transition.

Apparatus for Testing Rotating Heat Pipes

*† ‡ A test apparatus, that will be used to study the heat transfer performance of rotating heat pipes, has been designed and built. The apparatus allows for simultaneous testing of a pair of crank-shaped rotating heat pipes operating near room temperature. The test rig is designed to support heat pipes with an on-axis rotating condenser section, an off-axis eccentrically rotating evaporator section, and a curved adiabatic section. Due to the length of the heat pipes (55”), the distance from the axis of rotation to the off-axis evaporator section (9.5”), and the maximum rotation speed (5500 rpm), care had to be taken in the design of a substantial support structure for the heat pipes, the selection of a drive system, and the design of the mounting frame. These design issues, as well as safety considerations associated with the test apparatus, are discussed here. Preliminary test data for stationary and low-speed tests are also presented.

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.

Performance Predictions and Measurements for Space Power System Heat Pipes

High temperature liquid metal heat pipes designed for space power systems have been analyzed and tested. Three wick designs are discussed and a design rationale for the heat pipe is provided. Test results on a molybdenum, annular wick heat pipe are presented. Performance limitations due to boiling and capillary limits are presented. There is evidence that the vapor flow in the adiabatic section is turbulent and that the transition Reynolds number is 4000.

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.