Reactor physics modelling of accident tolerant fuel for LWRs using ANSWERS codes

The majority of nuclear reactors operating in the world today and similarly the majority of near-term new build reactors will be LWRs. These currently accommodate traditional Zr clad UO2/ PuO2 fuel designs which have an excellent performance record for normal operation and most transients. However, the events at Fukushima culminated in significant hydrogen production and hydrogen explosions, resulting from high temperature Zr/steam interaction following core uncovering for an extended period. These events have resulted in increased emphasis towards developing more accident tolerant fuels (ATFs)-clad systems, particularly for current and near-term build LWRs. R&D programmes are underway in the US and elsewhere to develop ATFs and the UK is engaging in these international programmes. Candidate advanced fuel materials include uranium nitride (UN) and uranium silicide (U3Si2). Candidate cladding materials include advanced stainless steel (FeCrAl) and silicon carbide. The UK has a long history in industrial fuel manufacture and fabrication for a wide range of reactor systems including LWRs. This is supported by a national infrastructure to perform experimental and theoretical R&D in fuel performance, fuel transient behaviour and reactor physics. In this paper, an analysis of the Integral Inherently Safe LW R design (I2S-LWR), a reactor concept developed by an international collaboration led by the Georgia Institute of Technology, within a U.S. DOE Nuclear Energy University Program (NEUP) Integrated Research Project (IRP) is considered. The analysis is performed using the ANSWERS reactor physics code WIMS and the EDF Energy core simulator PANTHER by researchers at the University of Cambridge. The I2S-LWR is an advanced 2850 MWt integral PWR with inherent safety features. In order to enhance the safety features, the baseline fuel and cladding materials that were chosen for the I2S- LWR design are U3Si2 and advanced stainless steel respectively. In addition, the I S-LWR design adopts an integral configuration and a fully passive emergency decay heat removal system to provide indefinite cooling capability for a class of accidents. This paper presents the equilibrium cycle core design and reactor physics behaviour of the I2S-LWR with U3Si2 and the advanced steel cladding. The results were obtained using the traditional two-stage approach, in which homogenized macroscopic cross-section sets were generated by WIMS and applied in a full 3D core solution with PANTHER. The results obtained with WIMS/PANTHER were compared against the Monte Carlo Serpent code developed by VTT and previously reported results for the I2S-LWR. The results were found to be in a good agreement (e.g. < 200 pcm in reactivity) among the compared codes, giving confidence that the WIMS/PANTHER reactor physics package can be reliably used in modelling LWRs with ATFs.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1051/epjn/201601

Human Expeditions to Near-Earth Asteroids: Implications for Exploration, Resource Utilization, Science, and Planetary Defense

Over the past several years, much attention has been focused on human exploration of near-Earth asteroids (NEAs) and planetary defence. Two independent NASA studies examined the feasibility of sending piloted missions to NEAs, and in 2009, the Augustine Commission identified NEAs as high profile destinations for human exploration missions beyond the Earth-Moon system as part of the Flexible Path. More recently the current U.S. presidential administration directed NASA to include NEAs as destinations for future human exploration with the goal of sending astronauts to a NEA in the mid to late 2020s. This directive became part of the official National Space Policy of the United States of America as of June 28, 2010. With respect to planetary defence, in 2005 the U.S. Congress directed NASA to implement a survey program to detect, track, and characterize NEAs equal or greater than 140 m in diameter in order to access the threat from such objects to the Earth. The current goal of this survey is to achieve 90% completion of objects equal or greater than 140 m in diameter by 2020

Fermi Level Engineering of Passivation and Electron Transport Materials for p-Type CuBi₂O₄ Employing a High‐Throughput Methodology

Metal oxide semiconductors are promising for solar photochemistry if the issues of excessive charge carrier recombination and material degradation can be resolved, which are both influenced by surface quality and interface chemistry. Coating the semiconductor with an overlayer to passivate surface states is a common remedial strategy but is less desirable than application of a functional coating that can improve carrier extraction and reduce recombination while mitigating corrosion. In this work, a data‐driven materials science approach utilizing high‐throughput methodologies, including inkjet printing and scanning droplet electrochemical cell measurements, is used to create and evaluate multi‐element coating libraries to discover new classes of candidate passivation and electron‐selective contact materials for p‐type CuBi₂O₄. The optimized overlayer (Cu_(1.5)TiO₂) improves the onset potential by 110 mV, the photocurrent by 2.8×, and the absorbed photon‐to‐current efficiency by 15.5% compared to non‐coated photoelectrodes. It is shown that these enhancements are related to reduced surface recombination through passivation of surface defect states as well as improved carrier extraction efficiency through Fermi level engineering. This work presents a generalizable, high‐throughput method to design and optimize passivation materials for a variety of semiconductors, providing a powerful platform for development of high‐performance photoelectrodes for incorporation into solar‐fuel generation systems

A Piloted Flight to a Near-Earth Object: A Feasibility Study

This viewgraph presentation examines flight hardware elements of the Constellation Program (CxP) and the utilization of the Crew Exploration Vehicle (CEV), Evolvable Expendable Launch Vehicles (EELVs) and Ares launch vehicles for NEO missions

The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe

The preponderance of matter over antimatter in the early Universe, the dynamics of the supernova bursts that produced the heavy elements necessary for life and whether protons eventually decay --- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our Universe, its current state and its eventual fate. The Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed plan for a world-class experiment dedicated to addressing these questions. LBNE is conceived around three central components: (1) a new, high-intensity neutrino source generated from a megawatt-class proton accelerator at Fermi National Accelerator Laboratory, (2) a near neutrino detector just downstream of the source, and (3) a massive liquid argon time-projection chamber deployed as a far detector deep underground at the Sanford Underground Research Facility. This facility, located at the site of the former Homestake Mine in Lead, South Dakota, is approximately 1,300 km from the neutrino source at Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino charge-parity symmetry violation and mass ordering effects. This ambitious yet cost-effective design incorporates scalability and flexibility and can accommodate a variety of upgrades and contributions. With its exceptional combination of experimental configuration, technical capabilities, and potential for transformative discoveries, LBNE promises to be a vital facility for the field of particle physics worldwide, providing physicists from around the globe with opportunities to collaborate in a twenty to thirty year program of exciting science. In this document we provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess.Comment: Major update of previous version. This is the reference document for LBNE science program and current status. Chapters 1, 3, and 9 provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess. 288 pages, 116 figure

Gene-Based Tests of Association

Genome-wide association studies (GWAS) are now used routinely to identify SNPs associated with complex human phenotypes. In several cases, multiple variants within a gene contribute independently to disease risk. Here we introduce a novel Gene-Wide Significance (GWiS) test that uses greedy Bayesian model selection to identify the independent effects within a gene, which are combined to generate a stronger statistical signal. Permutation tests provide p-values that correct for the number of independent tests genome-wide and within each genetic locus. When applied to a dataset comprising 2.5 million SNPs in up to 8,000 individuals measured for various electrocardiography (ECG) parameters, this method identifies more validated associations than conventional GWAS approaches. The method also provides, for the first time, systematic assessments of the number of independent effects within a gene and the fraction of disease-associated genes housing multiple independent effects, observed at 35%–50% of loci in our study. This method can be generalized to other study designs, retains power for low-frequency alleles, and provides gene-based p-values that are directly compatible for pathway-based meta-analysis

Policy Entrepreneurship by International Bureaucracies: The Evolution of Public Information in UN Peacekeeping

The UN Secretariat’s role in the expansion of peacekeeping after the cold war is debated. Different theoretical accounts offer competing interpretations: principal–agent models and sociological institutionalism tend to emphasize the Secretariat’s risk-averse behaviour; organizational learning scholarship and international political sociology find evidence of the Secretariat’s activism; constructivism analyses instances of both. I argue that the UN Secretariat can be both enthusiastic and cautious about new tasks depending on the circumstances and the issue area. For example, UN officials have been the driving force behind the development of public information campaigns by peacekeeping missions aimed at the local population. During the cold war, it was not regarded as necessary for UN missions to communicate with the public in the area of operation: their interlocutors were parties to the conflict and the diplomatic community. With the deployment of the first multidimensional missions in the late 1980s and the early 1990s, UN staff realized the need to explain the organization’s role to the local population and provide information about UN-supported elections. In promoting this innovation, they played the role of policy entrepreneurs. The institutionalization of this innovation, however, was not an automatic process and required continuous advocacy by UN information staff