Ronald James Ellis

The Development of the Material Plasma Exposure Experiment

The availability of future fusion devices, such as a fusion nuclear science facility or demonstration fusion power station, greatly depends on long operating lifetimes of plasma facing components in their divertors. ORNL is designing the Material Plasma Exposure eXperiment (MPEX), a superconducting magnet, steady-state device to address the plasma material interactions of fusion reactors. MPEX will utilize a new highintensity plasma source concept based on RF technology. This source concept will allow the experiment to cover the entire expected plasma conditions in the divertor of a future fusion reactor. It will be able to study erosion and redeposition for relevant geometries with relevant electric and magnetic fields in-front of the target. MPEX is being designed to allow for the exposure of a priori neutron-irradiated samples. The target exchange chamber has been designed to undock from the linear plasma generator such that it can be transferred to diagnostics stations for more detailed surface analysis. MPEX is being developed in a staged approach with successively increased capabilities. After the initial development step of the helicon source and electron cyclotron heating system, the source concept is being tested in the Proto-MPEX device. Proto-MPEX has achieved electron densities of more than 4×1019 m-3 with a large diameter (13 cm) helicon antenna at 100 kW power. First heating with microwaves resulted in a higher ionization represented by higher electron densities on axis, when compared with the helicon plasma only without microwave heating.

Assumptions and Criteria for Performing a Feasability Study of the Conversion of the High Flux Isotope Reactor Core to Use Low-Enriched Uranium Fuel

A computational study will be initiated during fiscal year 2006 to examine the feasibility of converting the High Flux Isotope Reactor from highly enriched uranium fuel to low-enriched uranium. The study will be limited to steady-state, nominal operation, reactor physics and thermal-hydraulic analyses of a uranium-molybdenum alloy that would be substituted for the current fuel powder--U{sub 3}O{sub 8} mixed with aluminum. The purposes of this document are to (1) define the scope of studies to be conducted, (2) define the methodologies to be used to conduct the studies, (3) define the assumptions that serve as input to the methodologies, (4) provide an efficient means for communication with the Department of Energy and American research reactor operators, and (5) expedite review and commentary by those parties.

Plutonium management in the medium term

Abstract For many years various countries with access to commercial reprocessing services have been routinely recycling plutonium as UO2/PuO2 mixed oxide (MOX) fuel in light water reactors (LWRs). This LWR MOX recycle strategy is still widely regarded as an interim step leading to the eventual establishment of sustainable fast reactor fuel cycles. The OECD/NEA Working Party on the Physics of Plutonium Fuels and Innovative Fuel Cycles (WPPR) has recently completed a review of the technical options for plutonium management in what it refers to as the “medium term.” For the purpose of the review, the WPPR considers the medium term to cover the period from now up to the point at which fast reactor fuel cycles are established on a commercial scale. The review identified a number of different designs of innovative plutonium fuel assemblies intended to be used in current LWR cores, in LWRs with significantly different moderation properties, as well as in high-temperature gas reactors. The full review report describes these various options and highlights their respective advantages and disadvantages. This paper briefly summarizes the main findings of the review.

The Material Plasma Exposure eXperiment MPEX: Pre-design, development and testing of source concept

The availability of future fusion devices such as a Fusion Nuclear Science Facility (FNSF) or DEMO greatly depends on long operating lifetimes of plasma facing components in their divertors. ORNL is designing the Material-Plasma Exposure eXperiment (MPEX), a superconducting magnet, steady-state device to address the plasma material interactions of fusion reactors. MPEX will utilize a new high-intensity plasma source concept based on RF technology. This source concept will allow the experiment to cover the entire expected plasma conditions in the divertor of a future fusion reactor. It will be able to study erosion and re-deposition for relevant geometries with relevant electric and magnetic fields in-front of the target. MPEX is being designed to allow for the exposure of a-priori neutron-irradiated samples. The target transfer cask has been designed to undock from the linear plasma generator such that it can be transferred to diagnostics stations for more detailed surface analysis. MPEX is being developed in a staged approach with successively increased capabilities. After the initial development step of the helicon source and ECH system the source concept is being tested in the Proto-MPEX device (100 kW helicon, 200 kW EBW, 30 kW ICRH). Proto-MPEX has achieved electron densities of more than 4×1019m-3 with a large diameter (13cm) helicon antenna at 100 kW power. First heating with microwaves resulted in a higher ionization represented by higher electron densities on axis, when compared to the helicon plasma only without microwave heating.

Experimental and Computational Forensics Characterization of Weapons-Grade Plutonium Produced in a Fast Reactor Neutron Environment

A terrorist attack using an improvised nuclear device is one of the most serious dangers facing the United States. The work presented here is part of an effort to improve nuclear deterrence by developing a methodology to attribute weapons-grade plutonium to a source reactor by measuring the intrinsic physical characteristics of the interdicted plutonium. In order to demonstrate the developed methodology, plutonium samples were produced from depleted uranium dioxide (DUO2) surrogates irradiated in a fast-neutron environment. In order to replicate the neutron flux in a fast-neutron-spectrum reactor and obtain experimental samples emulating weapons-grade plutonium produced in the blanket of a fast breeder reactor, DUO2 samples were placed in a gadolinium sheath and irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Previous computational work on this topic identified several fission products that could be used to distinguish between reactor types (fast and thermal reactors), specifically: 137Cs, 134Cs, 154Eu, 125Sb, 144Ce, 85Rb, 147Pm, and 150Sm along with the plutonium isotopes. Simulations of the fast neutron irradiation of the DUO2 fuel surrogates in the HFIR were carried out using the Monte Carlo radiation transport code MCNPX 2.7. Comparisons of the predicted values of plutonium and fission product concentrations to destructive and nondestructive assay measurements of neutron-irradiated DUO2 surrogates are presented here. The agreement between the predictions and gamma spectroscopic measurements in general were within 10% for 134Cs, 137Cs, 154Eu, and 144Ce. Additional experimental results (mass spectroscopy) agreed to within 5% for the following isotopes: 85Rb, 147Pm, 150Sm, 154Eu, 148Nd, 144Ce, and 239Pu. Two indicator isotopes previously suggested to differentiate between the reactor types were ruled out for use in the attribution methodology; 125Sb was ruled out due to the difficulty in accurately predicting its concentration, and 242Pu was ruled out because of its low content in weapons-grade plutonium.

Generation of a Broad-Group HTGR Library for Use with SCALE

With current and ongoing interest in high temperature gas reactors (HTGRs), the U.S. Nuclear Regulatory Commission (NRC) anticipates the need for nuclear data libraries appropriate for use in applications for modeling, assessing, and analyzing HTGR reactor physics and operating behavior. The objective of this work was to develop a broad-group library suitable for production analyses with SCALE for HTGR applications. Several interim libraries were generated from SCALE fine-group 238- and 999-group libraries, and the final broad-group library was created from Evaluated Nuclear Data File/B Version ENDF/B-VII Release 0 cross-section evaluations using new ORNL methodologies with AMPX, SCALE, and other codes. Furthermore, intermediate resonance (IR) methods were applied to the HTGR broadgroup library, and lambda factors and f-factors were incorporated into the library s nuclear data files. A new version of the SCALE BONAMI module named BONAMI-IR was developed to process the IR data in the new library and, thus, eliminate the need for the CENTRM/PMC modules for resonance selfshielding. This report documents the development of the HTGR broad-group nuclear data library and the results of test and benchmark calculations using the new library with SCALE. The 81-group library is shown to model HTGR cases with similar accuracy to the SCALE 238-group library but with significantly faster computational times due to the reduced number of energy groups and the use of BONAMI-IR instead of BONAMI/CENTRM/PMC for resonance self-shielding calculations.

Neutron-Irradiated Samples as Test Materials for MPEX

Abstract Plasma-material interaction is a major concern in fusion reactor design and analysis. The Material Plasma Exposure eXperiment (MPEX) will explore plasma-material interaction under fusion reactor plasma conditions. Samples with accumulated displacement damage (characterized by displacements per atom) produced by fast neutron irradiations in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory will be studied in the MPEX facility. This paper presents assessments of the calculated induced radioactivity and resulting radiation dose rates of a variety of potential fusion reactor plasma-facing materials, e.g., tungsten. The scientific code packages Monte Carlo N-Particle (MCNP) and Standardized Computer Analyses for Licensing Evaluation (SCALE) were used to simulate irradiation of the samples in HFIR. This included the generation and depletion of nuclides in the material and the subsequent composition, activity levels, gamma radiation fields, and resultant dose rates as a function of cooling time. A challenge of the MPEX project is to minimize the radioactive inventory in the preparation of the samples and the sample dose rates for inclusion in the MPEX facility.

An Analysis of the Nuclear Data Libraries’ Impact on the Criticality Computations Performed using Monte Carlo Codes

The major aim of this work is a sensitivity analysis related to the influence of the different nuclear data libraries on the k‐infinity values and on the void coefficient estimations performed for various CANDU fuel projects, and on the simulations related to the replacement of the original stainless steel adjuster rods by cobalt assemblies in the CANDU reactor core. The computations are performed using the Monte Carlo transport codes MCNP5 and MONTEBURNS 1.0 for the actual, detailed geometry and material composition of the fuel bundles and reactivity devices. Some comparisons with deterministic and probabilistic codes involving the WIMS library are also presented.