Nuclear Science User Facilities

The presence of a metal oxide surface can significantly alter the product yield distribution during the radiolysis of water with some metal oxides such as ZrO 2 or CeO 2, increasing the yield of H 2 during the irradiation of water adsorbed on the oxide as compared to liquid water, while other oxides such as PuO 2 decrease H 2 yields. In this study, the γ-ray radiolysis of the ZnO/H 2 O system was investigated. Surprisingly, both O 2 and H 2 were produced in similar quantities. The production of O 2 is unexpected as no, or negligible, amounts of O 2 have been observed for the radiolysis of water adsorbed on other oxides. Molecular oxygen production is observed during the radiolysis of both wet and dry ZnO, indicating that the source of at least some of the O 2 is the bulk oxide. The production of H 2 due to the radiolysis of water adsorbed on ZnO is an order of magnitude greater than for pure water. This increase is likely due to an energy-transfer process from the oxide to the adsorbed water molecules. However, the radiolysis of aqueous suspensions of ZnO resulted in lower radiolytic H 2 yields than for pure water.

Room temperature post-irradiation measurements of diffuse reflectance and electron paramagnetic resonance spectroscopies were made to characterize the long-lived radiation-induced species formed from the gamma irradiation of solid KCl, MgCl2, and ZnCl2 salts up to 100 kGy. The method used showed results consistent with those reported for electron and gamma irradiation of KCl in single crystals. Thermal bleaching of irradiated KCl demonstrated accelerated disaggregation of defect clusters above 400 K, due to decomposition of Cl3-. The defects formed in irradiated MgCl2 comprised a mixture of Cl3-, F-centers, and Mg+ associated as M-centers. Further, Mg metal cluster formation was also observed at 100 kGy, in addition to accelerated destruction of F-centers above 20 kGy. Irradiated ZnCl2 afforded the formation of Cl2- due to its high ionization potential and crystalline structure, which decreases recombination. The presence of aggregates in all cases indicates the high diffusion of radicals and the predominance of secondary processes at 295 K. Thermal bleaching studies showed that chloride aggregates' stability increases with the ionization potential of the cation present. The characterization of long-lived radiolytic transients of pure salts provides important information for the understanding of complex salt mixtures under the action of gamma radiation.

A thermoacoustic engine is operated within the core of a nuclear reactor to acoustically telemeter coolant temperature (frequency-encoded) and reactor power level (amplitude-encoded) outside the reactor, thus providing the values of these important parameters without external electrical power or wiring. We present data from two hydrophones in the coolant (far from the core) and an accelerometer attached to a structure outside the reactor. These signals have been detected even in the presence of substantial background noise generated by the reactor's fluid pumps.

The generation of sound by heat has been documented as an acoustical curiosity since 1568 when a Buddhist monk reported in his diary the loud tone generated by a ceremonial rice cooker. Over the last four decades, significant progress has been made in understanding thermoacoustic processes, enabling the design of thermoacoustic engines and refrigerators. Motivated by the Fukushima nuclear reactor disaster, we have developed and tested a thermoacoustic engine that exploits the energy-rich conditions in the core of a nuclear reactor to provide core condition information to the operators without a need for external electrical power. The heat engine is self-powered and can wirelessly transmit the temperature and reactor power level by generation of a pure tone that can be detected outside the reactor. We report here the first use of a fission-powered thermoacoustic engine capable of serving as a performance and safety sensor in the core of a research reactor and present data from the hydrophones in the coolant (far from the core) and an accelerometer attached to a structure outside the reactor. These measurements confirmed that the frequency of the sound produced indicates the reactor's coolant temperature and that the amplitude (above an onset threshold) is related to the reactor's operating power level. These signals can be detected even in the presence of substantial background noise generated by the reactor's fluid pumps.

The generation of sound by heat has been documented as an “acoustical curiosity” since a Buddhist monk reported the loud tone generated by a ceremonial rice-cooker in 1568. Over the last four decades, significant progress has been made in understanding “thermoacoustic processes,” enabling the design of thermoacoustic engines and refrigerators. We have developed and tested a thermoacoustic engine that exploits the energy-rich conditions in the core of a nuclear reactor. The heat engine is self-powered and can wirelessly transmit the temperature and reactor power by generation of a pure tone which can be detected outside the reactor. We report here the first use of a fission-powered thermoacoustic engine capable of serving as a performance and safety sensor in the core of a research reactor and present data from two hydrophones in the coolant (far from the core) and an accelerometer attached to a structure outside the reactor. These measurements confirmed that the frequency of the sound produced indicates the reactor’s coolant temperature and that the amplitude (above an onset threshold) is related to the reactor’s operating power level. These signals can be detected even in the presence of substantial background noise generated by the reactor’s fluid pumps. [Work supported by Idaho National Laboratory and Westinghouse Electric Co.]

A computational Monte Carlo simulation approach for modeling the thermalization of low-energy electrons is presented. The simulation methods rely on, and use, experimentally based cross sections for elastic and inelastic collisions. To demonstrate the different simulation options, average numbers of interactions and the range of low-energy electrons with initial energies ranging from 1 to 20 eV are calculated for density normalized gaseous water. Experimental gas-phase cross sections for (subexcitation) electrons of energies in the range of 1-20 eV were taken from the compilation of Hayashi. The ballistic collision-by-collision simulations provide information on the intricacies of the thermalization processes not available experimentally. © 2018 Wiley Periodicals, Inc.

Over 60 samples of plutonium dioxide (PuO2) powders of varying provenance have been exposed to humid atmospheres and the hydrogen (H2) generation rates measured by gas chromatography. The effects of relative humidity (RH), specific surface area (SSA), plutonium isotopic composition (absorbed dose), and overlying atmosphere have been investigated for ‘as received’ PuO2 powders from the United Kingdom’s Thorp and Magnox reprocessing plants, high surface area powder produced in the laboratory and Magnox PuO2 that was recalcined at 800, 900 or 950°C. Hydrogen generation was shown to be susceptible to subtle influences with the most consistent results observed at 95% RH. However, it was shown that the measured (net) hydrogen decreases with decreasing RH and with atmosphere in the order: Air > argon > nitrogen. There was no clear effect of SSA, apart from with the highest SSA samples (∼40 m2.g−1) but these powders also have very different morphology, porosity, and carbon content to the rest. The results presented substantially enhance the growing body of literature on the factors that determine hydrogen and gas generation from PuO2 that has significant implications for long term safe storage of plutonium globally.

It is essential for the U.S. nuclear energy community to have access to world-leading equipment suitable for conducting research on both nuclear fuels and structural materials, including neutron irradiated?and therefore activated?materials. To address future research infrastructure requirements to support the DOE-NE mission, the Office of Reactor Fleet and Advanced Reactor Deployment established an ad hoc committee to gather information on potential capability gaps for radioactive materials and radiation effects research. This document summarizes the discussions of the committee addressing the high-level challenges in irradiated and radioactive materials research and the capabilities needed to address these challenges. After considering the various needs, the committee agreed on the four top-level targets and priority capability gaps.

As a first step toward full scale utilization of the Advanced Test Reactor (ATR) and associated post irradiation examination (PIE) equipment at INL, the NRC and INL staffs have formulated a test program that is designed to help to establish INL and the Nuclear Science User Facilities (NSUF) as a viable destination for irradiation and PIE of reactor structural materials. This initial research program utilized two materials (304 Stainless Steel weld Heat Affected Zone (HAZ) and sensitized 304L stainless steel) that have previously been irradiated at the Halden reactor in Norway and tested at Argonne National Laboratory (ANL) so that test results may be compared, thereby establishing a measure of comparability between Halden and ATR irradiations. A secondary objective of this test program was to characterize the quality of data produced using INL’s newly constructed irradiation assisted stress corrosion cracking (IASCC) test cells. The specimens were be tested in typical boiling water reactor (BWR) conditions to measure stress corrosion cracking (SCC) and fracture toughness of un-irradiated specimens and then IASCC and fracture toughness of specimens irradiated to a fluence equal to approximately 1.0 X 1021 n/cm2 (E > 1 MeV).

A standing-wave thermoacoustic engine with dimensions identical to an ordinary fuel rod was designed to be placed in the core of the Breazeale Nuclear Reactor on Penn State’s campus. The heat necessary to produce thermoacoustics oscillations was provided by two 10 mm long by 5 mm diameter, 7.5% enriched, 235U fuel pellets. Those pellets were contained within a stainless-steel finned heat exchanger that was fabricated by additive manufacturing (3-D printing). The (mass-controlled) resonator was suspended in the surrogate fuel rod using two six-armed leaf springs (spiders) that centered the resonator in the “slotted tube” and allowed longitudinal vibrations of the entire resonator that coupled the oscillatory momentum of the gas within the resonator to the surrounding light-water reactor coolant. A 2.0 MPa mixture of 25% argon and 75% helium provided a trade-off between dipole radiation efficiency, resonator length, and low onset temperature differential, to produce a frequency that was high enough to be above the dominant noise produced by coolant and 16N diffusion pumps. These trade-offs were optimized using the Los Alamos DELTAEC software. [Work supported by Idaho National Laboratory and Westinghouse Electric Co. Fabrication and fueling was completed in collaboration with IST-Mirion.]