Lynne Ecker

Design of radiation resistant metallic multilayers for advanced nuclear systems

Helium implantation from transmutation reactions is a major cause of embrittlement and dimensional instability of structural components in nuclear energy systems. Development of novel materials with improved radiation resistance, which is of the utmost importance for progress in nuclear energy, requires guidelines to arrive at favorable parameters more efficiently. Here, we present a methodology that can be used for the design of radiation tolerant materials. We used synchrotron X-ray reflectivity to nondestructively study radiation effects at buried interfaces and measure swelling induced by He implantation in Cu/Nb multilayers. The results, supported by transmission electron microscopy, show a direct correlation between reduced swelling in nanoscale multilayers and increased interface area per unit volume, consistent with helium storage in Cu/Nb interfaces in forms that minimize dimensional changes. In addition, for Cu/Nb layers, a linear relationship is demonstrated between the measured depth-dependent swelling and implanted He density from simulations, making the reflectivity technique a powerful tool for heuristic material design.

Understanding the Adsorption Mechanism of Xe and Kr in a Metal-Organic Framework from X-ray Structural Analysis and First-Principles Calculations.

Enhancement of adsorption capacity and separation of radioactive Xe/Kr at room temperature and above is a challenging problem. Here, we report a detailed structural refinement and analysis of the synchrotron X-ray powder diffraction data of Ni-DODBC metal organic framework with in situ Xe and Kr adsorption at room temperature and above. Our results reveal that Xe and Kr adsorb at the open metal sites, with adsorption geometries well reproduced by DFT calculations. The measured temperature-dependent adsorption capacity of Xe is substantially larger than that for Kr, indicating the selectivity of Xe over Kr and is consistent with the more negative adsorption energy (dominated by van der Waals dispersion interactions) predicted from DFT. Our results reveal critical structural and energetic information about host-guest interactions that dictate the selective adsorption mechanism of these two inert gases, providing guidance for the design and synthesis of new MOF materials for the separation of environmentally hazardous gases from nuclear reprocessing applications.

An Integrated Analysis of a NERVA Based Nuclear Thermal Propulsion System

This paper presents results and conclusions derived from an integrated analysis of a NERVA based Nuclear Thermal Propulsion (NTP) system. The NTP system is sized to generate a thrust of 70,000 N (15,000 lbf), and have a specific impulse (Isp) of 860 s. This implies a reactor that operates at 350 MWth and has a mixed mean propellant outlet temperature of 2760 K. The integrated analysis will require that self‐consistent neutronic/thermal‐hydraulic/stress analyses be carried out. The major code packages used in this analysis are MCNP, RELAP, and ANSYS. Results from this analysis indicate that nuclear data will have to be re‐generated to cover the wide temperature range, zone loading will be necessary to avoid entering the liquidus region for the fuel, and the effectiveness of the ZrC insulator will have implications for bi‐modal applications. These results suggest a path forward in the development of a viable NTP system based on a NERVA reactor should initially concentrate on fuel and structural materials and associated coating development. A series of safety related criticality determinations were carried out addressing water immersion following a launch incident.

Sample environment for in situ synchrotron corrosion studies of materials in extreme environments

A new in situ sample environment has been designed and developed to study the interfacial interactions of nuclear cladding alloys with high temperature steam. The sample environment is particularly optimized for synchrotron X-ray diffraction studies for in situ structural analysis. The sample environment is highly corrosion resistant and can be readily adapted for steam environments. The in situ sample environment design complies with G2 ASTM standards for studying corrosion in zirconium and its alloys and offers remote temperature and pressure monitoring during the in situ data collection. The use of the in situ sample environment is exemplified by monitoring the oxidation of metallic zirconium during exposure to steam at 350 °C. The in situ sample environment provides a powerful tool for fundamental understanding of corrosion mechanisms by elucidating the substoichiometric oxide phases formed during the early stages of corrosion, which can provide a better understanding of the oxidation process.

Automated X-ray diffraction of irradiated materials

Synchrotron-based X-ray diffraction (XRD) and small-angle Xray scattering (SAXS) characterization techniques used on unirradiated and irradiated reactor pressure vessel steels yield large amounts of data. Machine learning techniques, including PCA, offer a novel method of analyzing and visualizing these large data sets in order to determine the effects of chemistry and irradiation conditions on the formation of radiation induced precipitates. In order to run analysis on these data sets, preprocessing must be carried out to convert the data to a usable format and mask the 2-D detector images to account for experimental variations. Once the data has been preprocessed, it can be organized and visualized using principal component analysis (PCA), multi-dimensional scaling, and k-means clustering. From these techniques, it is shown that sample chemistry has a notable effect on the formation of the radiation induced precipitates in reactor pressure vessel steels.

High Temperature Mechanical Properties, Fractography and Synchrotron Studies of ATF clad materials from the UCSB-NSUF Irradiations.

A variety of tensile samples of Ferritic and Oxide Dispersion Strengthened (ODS or nanostructured ferritic) steels were placed the ATR reactor over 2 years achieving doses of roughly 4-6 dpa at temperatures of roughly 290°C. Samples were shipped to Wing 9 in the CMR facility at Los Alamos National Laboratory and imaged then tested in tension. This report summarizes the room temperature tensile tests, the elevated temperature tensile tests (300°C) and fractography and reduction of area calculations on those samples. Additionally small samples were cut from the undeformed grip section of these tensile samples and sent to the NSLS synchrotron for high energy X-ray analysis, initial results will be described here.

Automated Synchrotron X-Ray Diffraction of Irradiated Reactor Pressure Vessel Steels

In this work, we outline the development of an automated, high-throughput robotic system designed for the structural characterization of radioactive samples at the X-ray Powder Diffraction beamline of the National Synchrotron Light Source-II (NSLS II).Copyright

Engineering Report on the Fission Gas Getter Concept

In 2010, the Department of Energy (DOE) requested that a Brookhaven National Laboratory (BNL)-led team research the possibility of using a getter material to reduce the pressure in the plenum region of a light water reactor fuel rod. During the first two years of the project, several candidate materials were identified and tested using a variety of experimental techniques, most with xenon as a simulant for fission products. Earlier promising results for candidate getter materials were found to be incorrect, caused by poor experimental techniques. In May 2012, it had become clear that none of the initial materials had demonstrated the ability to adsorb xenon in the quantities and under the conditions needed. Moreover, the proposed corrective action plan could not meet the schedule needed by the project manager. BNL initiated an internal project review which examined three questions: 1. Which materials, based on accepted materials models, might be capable of absorbing xenon? 2. Which experimental techniques are capable of not only detecting if xenon has been absorbed but also determine by what mechanism and the resulting molecular structure? 3. Are the results from the previous techniques useable now and in the future? As part of the second question, the project review team evaluated the previous experimental technique to determine why incorrect results were reported in early 2012. This engineering report is a summary of the current status of the project review, description of newly recommended experiments and results from feasibility studies at the National Synchrotron Light Source (NSLS).

An Infiltration Manufacturing Process for Nuclear Fuels

The Infiltrated Kernel Nuclear Fuel (IKNF) process deposits nuclear fuel into the naturally occurring porosity in graphite. IKNF consists of infiltrating uranyl nitrate dissolved in an organic solvent into the graphite and then heat-treating the sample at low (<300°C) temperatures to remove the solvent and convert the uranyl nitrate to UO2 . Complete conversion to UC2 can then be accomplished by heating to temperatures higher than 3000°C. IKNF is extremely flexible: it is appropriate for very high temperature applications and heating the infiltrated product to intermediate temperatures (higher than 900°C) produces nuclear fuel with a range of chemistries in the U-C-O system (similar to the current US TRISO fuel). It is probable that the process can also be used to produce fuel containing transuranics. It is believed that IKNF will be less expensive, more robust and more suitable for on-line quality monitoring than current fuel fabrication method. Graphite infiltration involves a few, easily measurable and controllable variables. It is reproducible and predictable.Copyright