Radioisotope and Nuclear Technologies for Space Exploration
Radioisotope and Nuclear Technologies for Space Exploration
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用于太空探索的放射性同位素和核技术
DOI：
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发表时间：
2010
期刊：
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通讯作者：
R. O’Brien
中科院分区：
文献类型：
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作者：
R. O’Brien
放射性同位素热源和动力系统，传统上以钚-238为燃料，已被开发并用于航天器热管理，并在许多深空和行星科学飞行任务中提供电力。然而，裂变反应堆在空间的使用仅限于地球轨道上的高功率应用。美国原子能委员会先前进行的地面研究计划证明了核热火箭推进的原理，但迄今为止，核推进的飞行遗产仅限于核电推进。开发能够满足空间飞行严格要求的空间核系统和辅助部件至关重要。在所有可预见条件下的性能、寿命和操作安全性是必须考虑的基本因素。选择合适的材料和环境兼容性对于任何特定设计的成功至关重要。放射性同位素热源能够经受与发射有关的事故所带来的极端温度和机械负荷，这既是法律规定的，也是保护生命和地球环境所必需的。用于裂变系统的核燃料必须在事故期间提供同等保护，而整体设计确保反应堆保持安全配置。介绍了空间核系统的历史概况。传统和现代的系统设计和制造技术进行了讨论。适用的固态和机械功率转换方法进行了描述，并评估其性能。考虑了放射性同位素选择和热源封装结构对辐射安全的影响。确定了241 Am作为替代同位素燃料的可能性。其他候选同位素，如210 Po，242 Cm和244 Cm进行了评估。
出于安全原因，开发能够防止所封装的放射性材料被提取和分散的封装方法越来越具有吸引力。放电等离子烧结
(SPS)本发明提供了用于将放射性同位素材料封装在钨陶瓷-金属或金属陶瓷基体内的新颖、简单和快速的技术。通过蒙特-卡罗模拟的计算建模已经表明，在非均质钨金属陶瓷基质内封装放射性同位素可以减少传递到局部环境的中子、X射线和伽马射线辐射剂量。防止与制造相关的放射性同位素化合物的挥发是封装工艺成功的基础。SPS通过使用CeO 2作为放射性同位素化合物如PuO 2、AmO 2和UO 2的惰性模拟物而经验性地证明。氧化镅在钨基体中的化学相容性也通过差示扫描量热炉内的无压烧结来证明。放射性同位素封装技术的发展也证明了在高温空间动力和推进反应堆系统的金属陶瓷燃料制造的背景下。钨金属陶瓷燃料的使用可以消除历史上核热推进计划所经历的材料不相容性和故障。
最后，三个新的概念应用核能作为行星探测的一种使能技术。通过使用脉冲高功率热容放射性同位素源，提出了冰表面的熔体渗透和行星表面的长距离流动性。推进剂生产考虑就地资源利用。在“火星漏斗”的背景下，提出使用二氧化碳作为放射性同位素热火箭的推进剂。在火星取样返回使命下的单级表面上升飞行器的高温（3000 ℃）核热推进系统中也考虑了CO2推进剂。
Radioisotope heat sources and power systems, traditionally fuelled by 238Pu, have been developed and used for spacecraft thermal management and to provide electrical power during many deep space and planetary science missions. The use of fission reactors in space, however, has been limited to high power applications in Earth orbit. Previous ground based research programs conducted by the U.S. Atomic Energy Commission demonstrated the principal of nuclear thermal rocket propulsion but to date, flight heritage of nuclear propulsion has been limited to nuclear-electric propulsion. The development of space nuclear systems and tributary components that are capable of meeting the rigors of space flight is of paramount importance. Performance, lifetime and operational safety under all foreseeable conditions are essential considerations that must be made. The selection of appropriate materials and environmental compatibility is vital to the success of any given design. The ability for radioisotope heat sources to survive the extreme temperatures and mechanical loads associated with launch related accidents, is both legally mandated and necessary for the protection of life and the Earth’s environment. Nuclear fuels for fission systems must provide equal protection during accidents while the integral design ensures that a reactor remains in a safe configuration. A historical overview of nuclear systems for space is presented. Traditional and modern system designs and fabrication techniques are discussed. Applicable solid state and mechanical power conversion methods are described and their performances are evaluated. Consideration is made for the effect of radioisotope selection and heat source encapsulation architecture upon radiation safety. The identification of 241Am as an alternative isotope fuel is made. Other candidate isotopes such as 210Po, 242Cm and 244Cm are assessed.
The development of encapsulation methods that are resistant to the extraction and dispersion of the radioactive materials enclosed is increasingly attractive for security reasons. Spark Plasma Sintering
(SPS) processes are presented as novel, simple and rapid techniques for the encapsulation of radioisotopic materials within tungsten ceramic-metallic or cermet matrices. Computational modelling via Monte-Carlo simulation has shown that the encapsulation of radioisotopes within heterogeneous tungsten cermet matrices may reduce the neutron, X-ray and Gamma-ray radiation dose delivered to the localised environment. The prevention of fabrication related volatilisation of radioisotopic compounds is fundamental to the success of the encapsulation process. SPS is empirically demonstrated via the use of CeO2 as an inert simulant for radioisotopic compounds such as PuO2, AmO2 and UO2. The chemical compatibility of americium oxides within a tungsten matrix is also demonstrated through pressureless sintering within a Differential Scanning Calorimetric furnace. The techniques developed for radioisotope encapsulation are also demonstrated in context of cermet fuel fabrication for high temperature space power and propulsion reactor systems. The use of tungsten cermet fuels may eliminate material incompatibilities and failures experienced by historical nuclear thermal propulsion programs.
Finally, three novel concept applications of nuclear energy as an enabling technology for planetary exploration are presented. Melt penetration of icy surfaces and long range mobility on planetary surfaces is proposed via the use of pulsed high power heat capacitive radioisotope sources. In-situ resource utilization is considered for propellant production. The use of CO2 is proposed as a propellant for a radioisotope thermal rocket in the context of a ‘Mars Hopper’. A CO2 propellant is also considered in the context of a high temperature (3000°C) nuclear thermal propulsion system for a single stage surface ascent vehicle under a Mars sample return mission.