Questões de Concurso Sobre sinônimos | synonyms em inglês

Background

The Naval Nuclear Propulsion Program (NNPP) started in 1948. Since that time, the NNPP has provided safe and effective propulsion systems to power submarines, surface combatants, and aircraft carriers. Today, nuclear propulsion enables virtually undetectable US Navy submarines, including the sea-based leg of the strategic triad, and provides essentially inexhaustible propulsion power independent of forward logistical support to both our submarines and aircraft carriers. Over forty percent of the Navy's major combatant ships are nuclear-powered, and because of their demonstrated safety and reliability, these ships have access to seaports throughout the world. The NNPP has consistently sought the best way to affordably meet Navy requirements by evaluating, developing, and delivering a variety of reactor types, fuel systems, and structural materials. The Program has investigated many different fuel systems and reactor design features, and has designed, built, and operated over thirty different reactor designs in over twenty plant types to employ the most promising of these developments in practical applications. Improvements in naval reactor design have allowed increased power and energy to keep pace with the operational requirements of the modern nuclear fleet, while maintaining a conservative design approach that ensures reliability and safety to the crew, the public, and the environment. As just one example of the progress that has been made, the earliest reactor core designs in the NAUTILUS required refueling after about two years while modern reactor cores can last the life of a submarine, or over thirty years without refueling. These improvements have been the result of prudent, conservative engineering, backed by analysis, testing, and prototyping. The NNPP was also a pioneer in developing basic technologies and transferring technology to the civilian nuclear electric power industry. For example, the Program demonstrated the feasibility of commercial nuclear power generation in this country by designing, constructing and operating the Shipping port Atomic Power Station in Pennsylvania and showing the feasibility of a thorium-based breeder reactor.

In: Report on Low Enriched Uranium for Naval Reactor Cores. Page 1. Report to Congress, January 2014. Office of Naval Reactors. US Dept. of Energy. DC 2058 http://fissilematerials.org/library/doe14.pdf

Read the text below to answer the questions 11-15.

NASA Researchers Studying Advanced Nuclear Rocket Technologies

January 9, 2013

By using an innovative test facility at NASA’s Marshall Space Flight Center in Huntsville, Ala., researchers are able to use non-nuclear materials to simulate nuclear thermal rocket fuels - ones capable of propelling bold new exploration missions to the Red Planet and beyond. The Nuclear Cryogenic Propulsion Stage team is tackling a three-year project to demonstrate the viability of nuclear propulsion system technologies. A nuclear rocket engine uses a nuclear reactor to heat hydrogen to very high temperatures, which expands through a nozzle to generate thrust. Nuclear rocket engines generate higher thrust and are more than twice as efficient as conventional chemical rocket engines.

The team recently used Marshall’s Nuclear Thermal Rocket Element Environmental Simulator, or NTREES, to perform realistic, non-nuclear testing of various materials for nuclear thermal rocket fuel elements. In an actual reactor, the fuel elements would contain uranium, but no radioactive materials are used during the NTREES tests. Among the fuel options are a graphite composite and a “cermet” composite - a blend of ceramics and metals. Both materials were investigated in previous NASA and U.S. Department of Energy research efforts.

Nuclear-powered rocket concepts are not new; the United States conducted studies and significant ground testing from 1955 to 1973 to determine the viability of nuclear propulsion systems, but ceased testing when plans for a crewed Mars mission were deferred.

The NTREES facility is designed to test fuel elements and materials in hot flowing hydrogen, reaching pressures up to 1,000 pounds per square inch and temperatures of nearly 5,000 degrees Fahrenheit - conditions that simulate space-based nuclear propulsion systems to provide baseline data critical to the research team.

“This is vital testing, helping us reduce risks and costs associated with advanced propulsion technologies and ensuring excellent performance and results as we progress toward further system development and testing,” said Mike Houts, project manager for nuclear systems at Marshall.

A first-generation nuclear cryogenic propulsion system could propel human explorers to Mars more efficiently than conventional spacecraft, reducing crews’ exposure to harmful space radiation and other effects of long-term space missions. It could also transport heavy cargo and science payloads. Further development and use of a first-generation nuclear system could also provide the foundation for developing extremely advanced propulsion technologies and systems in the future - ones that could take human crews even farther into the solar system.

Building on previous, successful research and using the NTREES facility, NASA can safely and thoroughly test simulated nuclear fuel elements of various sizes, providing important test data to support the design of a future Nuclear Cryogenic Propulsion Stage. A nuclear cryogenic upper stage - its liquid- hydrogen propellant chilled to super-cold temperatures for launch - would be designed to be safe during all mission phases and would not be started until the spacecraft had reached a safe orbit and was ready to begin its journey to a distant destination. Prior to startup in a safe orbit, the nuclear system would be cold, with no fission products generated from nuclear operations, and with radiation below significant levels.

“The information we gain using this test facility will permit engineers to design rugged, efficient fuel elements and nuclear propulsion systems,” said NASA researcher Bill Emrich, who manages the NTREES facility at Marshall. “It’s our hope that it will enable us to develop a reliable, cost-effective nuclear rocket engine in the not-too-distant future."

The Nuclear Cryogenic Propulsion Stage project is part of the Advanced Exploration Systems program, which is managed by NASA’s Human Exploration and Operations Mission Directorate and includes participation by the U.S. Department of Energy. The program, which focuses on crew safety and mission operations in deep space, seeks to pioneer new approaches for rapidly developing prototype systems, demonstrating key capabilities and validating operational concepts for future vehicle development and human missions beyond Earth orbit.

Marshall researchers are partnering on the project with NASA’s Glenn Research Center in Cleveland, Ohio; NASA’s Johnson Space Center in Houston; Idaho National Laboratory in Idaho Falls; Los Alamos National Laboratory in Los Alamos, N.M.; and Oak Ridge National Laboratory in Oak Ridge, Tenn.

The Marshall Center leads development of the Space Launch System for NASA. The Science & Technology Office at Marshall strives to apply advanced concepts and capabilities to the research, development and management of a broad spectrum of NASA programs, projects and activities that fall at the very intersection of science and exploration, where every discovery and achievement furthers scientific knowledge and understanding, and supports the agency’s ambitious mission to expand humanity’s reach across the solar system. The NTREES test facility is just one of numerous cutting-edge space propulsion and science research facilities housed in the state-of- the-art Propulsion Research & Development Laboratory at Marshall, contributing to development of the Space Launch System and a variety of other NASA programs and missions.

Available in: http://www.nasa.gov