Stephen J. Tobin

Bio: Stephen J. Tobin is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Spent nuclear fuel & Burnup. The author has an hindex of 7, co-authored 62 publications receiving 346 citations. Previous affiliations of Stephen J. Tobin include Swedish Nuclear Fuel and Waste Management Company & Uppsala University.

Formation and steady-state maintenance of field reversed configuration using rotating magnetic field current drive

Abstract: Rotating magnetic fields (RMF) have been used to both form and maintain field reversed configurations (FRC) in quasisteady state. These experiments differ from steady-state rotamaks in that the FRCs are similar to those formed in theta-pinch devices, that is elongated and confined inside a flux conserver. The RMF creates an FRC by driving an azimuthal current which reverses an initial positive bias field. The FRC then expands radially, compressing the initial axial bias flux and raising the plasma density, until a balance is reached between the RMF drive force and the electron–ion friction. This generally results in a very high ratio of separatrix to flux conserver radius. The achievable final conditions are compared with simple analytic models to estimate the effective plasma resistivity. The RMF torque on the electrons is quickly transferred to the ions, but ion spin-up is limited in these low density experiments, presumably by ion-neutral friction, and does not influence the basic current drive process. However, the ion rotation can result in a rotating n=2 distortion if the separatrix radius is too far removed from the plasma tube wall.

The TCS Rotating Magnetic Field FRC Current-Drive Experiment

Abstract: Field-reversed configurations (FRCs) have extremely attractive reactor attributes because of their singly connected geometry. They have been created in theta-pinch devices, but being compact toroids and lacking a center hole, their toroidal current cannot be sustained by transformer action as in other toroidal configurations. A new device, the Translation, Confinement, and Sustainment (TCS) facility has been constructed to use rotating magnetic fields (RMFs) to build up and sustain the flux of hot FRCs formed by the normal theta-pinch method. RMF formation and sustainment of similar, but cold, pure poloidal field configurations have been demonstrated in devices called rotamaks, and RMF formation, but not sustainment, has been achieved in a smaller FRC facility called the Star Thrust Experiment (STX). Initial formation and sustainment have now been achieved in TCS, albeit still with cold (T{sub e} {approx} 50 eV) plasmas. Both the formation and final steady-state conditions are found to agree with newly developed analytic and numerical models for RMF flux buildup and sustainment inside a standard cylindrical flux conserver. The required plasma conditions (mainly resistivity but also density) can now be determined for the planned hot FRC, RMF flux buildup experiments and for eventual reactor conditions.

PWR and BWR spent fuel assembly gamma spectra measurements

Abstract: A project to research the application of nondestructive assay (NDA) to spent fuel assemblies is underway. The research team comprises the European Atomic Energy Community (EURATOM), embodied by the European Commission, DG Energy, Directorate EURATOM Safeguards; the Swedish Nuclear Fuel and Waste Management Company (SKB); two universities; and several United States national laboratories. The Next Generation of Safeguards Initiative–Spent Fuel project team is working to achieve the following technical goals more easily and efficiently than in the past using nondestructive assay measurements of spent fuel assemblies: (1) verify the initial enrichment, burnup, and cooling time of facility declaration; (2) detect the diversion or replacement of pins, (3) estimate the plutonium mass, (4) estimate the decay heat, and (5) determine the reactivity of spent fuel assemblies. This study focuses on spectrally resolved gamma-ray measurements performed on a diverse set of 50 assemblies [25 pressurized water reactor (PWR) assemblies and 25 boiling water reactor (BWR) assemblies]; these same 50 assemblies will be measured with neutron-based NDA instruments and a full-length calorimeter. Given that encapsulation/repository and dry storage safeguards are the primarily intended applications, the analysis focused on the dominant gamma-ray lines of 137 Cs, 154 Eu, and 134 Cs because these isotopes will be the primary gamma-ray emitters during the time frames of interest to these applications. This study addresses the impact on the measured passive gamma-ray signals due to the following factors: burnup, initial enrichment, cooling time, assembly type (eight different PWR and six different BWR fuel designs), presence of gadolinium rods, and anomalies in operating history. To compare the measured results with theory, a limited number of ORIGEN-ARP simulations were performed.

Determining plutonium in spent fuel with nondestructive assay techniques

Abstract: There are a variety of motivations for quantifying plutonium in used (spent) fuel assemblies by means of nondestructive assay including the following: shipper/receiver difference, input accountability at reprocessing facilities and burnup credit at repositories or fuel storage facilities. Twelve NDA techniques were identified that provide information about the composition of an assembly. Unfortunately, none of these techniques is capable of determining the Pu mass in an assembly on its own. However, it is expected that the Pu mass can be quantified by combining a few of the techniques. Determining which techniques to combine and estimating the expected performance of such a system is the purpose of the research effort recently begun. The research presented here is a complimentarily experimental effort. This paper will focus on experimental results of one of the twelve non-destructive assay techniques - passive neutron albedo reactivity. The passive neutron albedo reactivity techniques work by changing the multiplication the pin experiences between two separate measurements. Since a single spent fuel pin has very little multiplication, this is a challenging measurement situation for the technique. Singles and Doubles neutron count rate were measured at Oak Ridge National Laboratory for three different burnup pins to test the capability ofmore » the passive neutron albedo reactivity technique.« less

Nondestructive Assay Options for Spent Fuel Encapsulation

Abstract: This report describes the role that nondestructive assay (NDA) techniques and systems of NDA techniques may have in the context of an encapsulation and deep geological repository. The potential NDA ...

Review of field-reversed configurations

Abstract: This review addresses field-reversed configurations (FRCs), which are compact-toroidal magnetic systems with little or no toroidal field and very high β (ratio of plasma pressure to magnetic pressure). Although enthusiasm for the FRC has primarily been driven by its potential for an attractive fusion reactor, this review focuses on the physics rather than on technological or engineering aspects. Major advances in both theory and experiment have taken place since the previous comprehensive FRC review in 1988. Even so many questions remain. In particular, even though FRC experiments have exhibited remarkable stability, how well this extrapolates to larger systems remains unresolved. The review considers FRCs under familiar topical categories: equilibrium, global stability, self-organization, transport, formation, and sustainment.

Formation and steady-state maintenance of field reversed configuration using rotating magnetic field current drive

Abstract: Rotating magnetic fields (RMF) have been used to both form and maintain field reversed configurations (FRC) in quasisteady state. These experiments differ from steady-state rotamaks in that the FRCs are similar to those formed in theta-pinch devices, that is elongated and confined inside a flux conserver. The RMF creates an FRC by driving an azimuthal current which reverses an initial positive bias field. The FRC then expands radially, compressing the initial axial bias flux and raising the plasma density, until a balance is reached between the RMF drive force and the electron–ion friction. This generally results in a very high ratio of separatrix to flux conserver radius. The achievable final conditions are compared with simple analytic models to estimate the effective plasma resistivity. The RMF torque on the electrons is quickly transferred to the ions, but ion spin-up is limited in these low density experiments, presumably by ion-neutral friction, and does not influence the basic current drive process. However, the ion rotation can result in a rotating n=2 distortion if the separatrix radius is too far removed from the plasma tube wall.

Flux conversion and evidence of relaxation in a high-β plasma formed by high-speed injection into a mirror confinement structure

Abstract: High-$\ensuremath{\beta}$ plasmoids can survive the violent dynamics of supersonic reflection off mirror structures, producing a stable high-$\ensuremath{\beta}$ field-reversed configuration (FRC). This shows both the robustness of FRCs and their tendency to assume a preferred plasma state, possibly conforming to a relaxation principle. The key observations are (1) approximate preservation of the magnetic helicity, (2) substantial conversion from toroidal to poloidal magnetic flux, (3) substantial toroidal flow, and (4) a high-$\ensuremath{\beta}$ quiescent final state. These results are from the Translation, Confinement, and Sustainment experiment where a disorganized plasmoid is injected at super-Alfvenic speed into a confinement chamber. After successive reflections from end mirrors, the plasmoid settled into a near-FRC state with high $\ensuremath{\beta}$ and low toroidal magnetic field. The flux conversion and helicity preservation are inferred by an interpretive model.

The TCS Rotating Magnetic Field FRC Current-Drive Experiment

Abstract: Field-reversed configurations (FRCs) have extremely attractive reactor attributes because of their singly connected geometry. They have been created in theta-pinch devices, but being compact toroids and lacking a center hole, their toroidal current cannot be sustained by transformer action as in other toroidal configurations. A new device, the Translation, Confinement, and Sustainment (TCS) facility has been constructed to use rotating magnetic fields (RMFs) to build up and sustain the flux of hot FRCs formed by the normal theta-pinch method. RMF formation and sustainment of similar, but cold, pure poloidal field configurations have been demonstrated in devices called rotamaks, and RMF formation, but not sustainment, has been achieved in a smaller FRC facility called the Star Thrust Experiment (STX). Initial formation and sustainment have now been achieved in TCS, albeit still with cold (T{sub e} {approx} 50 eV) plasmas. Both the formation and final steady-state conditions are found to agree with newly developed analytic and numerical models for RMF flux buildup and sustainment inside a standard cylindrical flux conserver. The required plasma conditions (mainly resistivity but also density) can now be determined for the planned hot FRC, RMF flux buildup experiments and for eventual reactor conditions.