A Research Program on Very High Temperature Reactors

Track I: Power GenerationIncludes audio file (27 min.)Prismatic and pebble bed very high-temperature reactors (VHTRs) are very attractive both from a thermodynamic efficiency viewpoint and hydrogen-production capability. This project addresses numerous challenges associated with the fuel cycle, materials, and complex fluid dynamics and heat transfer. The objectives of the project are to: i. Conduct physical experiments for fission product transport phenomena in the overcoating and compact structural graphite and transport through TRISO coating layers; ii. Develop improved sorption measurement techniques to measure the accumulation of condensable radionuclides (“plateout”) in the VHTR primary coolant circuit and obtain representative data; iii. Develop advanced computations of charged, radioactive dust (aerosol) transport in the VHTR coolant circuit and confinement by exploring direct simulation Monte Carlo (DSMC) techniques for deposition and resuspension and conduct experiments to verify computational predictions; iv. Develop a program to measure emissivity for various VHTR component materials, both bare and oxidized, and obtain extensive data; v. Develop an experimental program to characterize gas, fission product, and particle flows in the complex geometries of pebble bed modular reactors (PBMRs) and help improve computational approaches and computer programs through experimental understandings. This project is leading to research training of about a dozen Ph D students at the participating universities. Upon graduation, these students will be able to contribute even more effectively to the future challenges in the global deployment of nuclear power generation and hydrogen technologies. We will discuss the VHTR technology and research challenges. We also describe progress on the project by the three Consortium participants

The impact of pay-for-percentile incentive on low-achieving students in rural China

In some accountability regimes, teachers pay more attention to higher achieving students at the expense of lower achieving students. The overall goal of this study is to examine, in this type of accountability regime, the impacts of a pay-for-percentile type scheme in which incentives exist for all students but which are larger for improving the achievement of lower achieving students. Analyzing data from a large-scale randomized experiment in rural China, we find that incentives improve average achievement by 0.10 SDs and the achievement of low-achieving students by 0.15 SDs. We find parallel changes in teacher behavior and curricular coverage. Taken together, the results demonstrate that incentive schemes can effectively address teacher neglect of low-achieving students

Cross-Effects in Microgravity Flows

Film growth by chemical/physical vapor deposition is a process of considerable interest in microgravity experiments. The absence of natural convection should allow better control of film growth processes but, in highly non-isothermal ampoules, thermal slip (creep) can become a matter of significant concern. The reported research is a theoretical and experimental investigation of the flow of gas/vapor mixtures under non-continuum conditions. The Boltzmann equation has been solved for a monatomic gas under non-condensing conditions and the various phenomenological coefficients have been computed. Computations for realistic potentials as well as for velocity and creep slip have been completed and the creep slip has been found to be dependent on the type of gas confirming the accuracy of previous variational results. The variational technique has been extended and planar flows calculated via the Burnett solutions. Velocity, diffusion and creep slips have been computed for gas mixtures and previously unknown dependencies of the creep slip on the mixture properties have been observed. Also for gas mixtures, an integral representation of the linearized Boltzmann operator has been developed for use in numerical and variational calculations for all intermolecular force laws. Two, two-bulb capillary systems have been designed, built and tested for the measurements of cross-flows; one of glass for isothermal measurements and one of stainless steel for non-isothermal measurements. Extensive data have been collected for Ar-He and N2-He mixtures at a variety of pressures and mole ratios. Viscosity, velocity slip coefficients and tangential momentum accommodation coefficients have been obtained from measurements with a spinning rotor gauge via a new theory that has been formulated for the spinning rotor gauge in the slip regime. The FIDAP fluid dynamics code has been applied to condensing flows in ampoules in the continuum regime and agreement obtained with the earlier work of Duval

Tracking the effects of COVID-19 in rural China over time

Background: China issued strict nationwide guidelines to combat the COVID-19 outbreak in January 2020 and gradually loosened the restrictions on movement in early March. Little is known about how these disease control measures affected the 600 million people who live in rural China. The goal of this paper is to document the quarantine measures implemented in rural China outside the epicenter of Hubei Province and to assess the socioeconomic effect of the measures on rural communities over time. Methods: We conducted three rounds of interviews with informants from 726 villages in seven provinces, accounting for over 25% of China’s overall rural population. The survey collected data on rural quarantine implementation; COVID-19 infections and deaths in the survey villages; and effects of the quarantine on employment, income, education, health care, and government policies to address any negative impacts. The empirical findings of the work established that strict quarantine measures were implemented in rural villages throughout China in February. Results: There was little spread of COVID-19 in rural communities: an infection rate of 0.001% and zero deaths reported in our sample. However, there were negative social and economic outcomes, including high rates of unemployment, falling household income, rising prices, and disrupted student learning. Health care was generally accessible, but many delayed their non-COVID-19 health care due to the quarantine measures. Only 20% of villagers received any form of local government aid, and only 11% of villages received financial subsidies. There were no reports of national government aid programs that targeted rural villagers in the sample areas. Conclusions: By examining the economic and social effects of the COVID-19 restrictions in rural communities, this study will help to guide other middle- and low-income countries in their containment and restorative processes. Without consideration for economically vulnerable populations, economic hardships and poverty will likely continue to have a negative impact on the most susceptible communities

Delayed intracardial shunting and hypoxemia after massive pulmonary embolism in a patient with a biventricular assist device

We describe the interdisciplinary management of a 34-year-old woman with dilated cardiomyopathy three months postpartum on a cardiac biventricular assist device (BVAD) as bridge to heart transplantation with delayed onset of intracardial shunting and subsequent hypoxemia due to massive pulmonary embolism. After emergency surgical embolectomy pulmonary function was highly compromised (PaO2/FiO2 54) requiring bifemoral veno-venous extracorporeal membrane oxygenation. Transesophageal echocardiography detected atrial level hypoxemic right-to-left shunting through a patent foramen ovale (PFO). Percutaneous closure of the PFO was achieved with a PFO occluder device. After placing the PFO occluder device oxygenation increased significantly (Δ paO2 119 Torr). The patient received heart transplantation 20 weeks after BVAD implantation and was discharged from ICU 3 weeks after transplantation

Hydrodynamic slip can align thin nanoplatelets in shear flow

The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids. Here we show, by combining non-equilibrium molecular dynamics and continuum simulations, that rigid nanoplatelets can attain a stable orientation for sufficiently strong flows. Such a stable orientation is in contradiction with the rotational motion predicted by classical colloidal hydrodynamics. This surprising effect is due to hydrodynamic slip at the liquid-solid interface and occurs when the slip length is larger than the platelet thickness; a slip length of a few nanometers may be sufficient to observe alignment. The predictions we developed by examining pure and surface-modified graphene is applicable to different solvent/2D material combinations. The emergence of a fixed orientation in a direction nearly parallel to the flow implies a slip-dependent change in several macroscopic transport properties, with potential impact on applications ranging from functional inks to nanocomposites.Energy Technolog

The impact of the Lesotho Child Grant Programme in the lives of children and adults with disabilities: Disaggregated analysis of a community randomized controlled trial

Globally, people with disabilities are disproportionally affected by poverty. Social protection policies, including cash transfers, are key strategies to address poverty “in all its forms”, but it is currently unclear how such programmes affect people with disabilities. This study examines differences in the impact of the Lesotho Child Grant Programme (CGP) on food security, health, education and livelihoods between people with and without disabilities using data from a community randomized control trial. Overall, this study finds the CGP had significant and differential impacts for people with disabilities across multiple health indicators (e.g. increased health expenditures, self-rated health, likelihood of seeking healthcare). The CGP also had an impact on food security, decreasing the number of months households with and without members with disabilities faced extreme food shortages. There was also a modest but significant and differential impact of the CGP on the engagement of people with disabilities in paid work. The CGP only had an impact on school enrolment for children without disabilities, however the difference in impact was non-significant and likely due to underpowered sample sizes. Overall, people with disabilities receiving the CGP still experienced high levels of absolute deprivation, and were generally still worse off compared to people without disabilities, indicating a need for adapted or complementary social protection and other poverty alleviation programmes