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The course focused on implementing a nuclear powered mission to Mars based on SOTA technology and near term deployable technologies. The conceptual design for the space application relies on the development of several key technologies. Though it is unclear if these technologies will be ready for a launch date of 2015, it is the feeling of the group that research in particular areas will allow for implementation in a manned mission within 50 years. The key development areas include high temperature TPV technology. TPV cells that operate in the range of 700 K may be required. Additionally, the use of a plutonium core allows for a small, compact, ultra high power density reactor unit. Currently, no space fission reactors have been fueled with plutonium, and some concerns exist with launching a system that has substantial activity prior to launch. Though our reactor, from a radiological standpoint appears safer than many RTGs, the fuel does at the time pose a concern. As for coolants, the design reference uses molten salt, though similiar to liquid metals in terms of heat transfer characteristics, materials development will be necessary to safeguard against corrosion. However, liquid metal alternatives, such as lithium, are proposed.
As for the surface application, an extra long life core was developed. Reactivity swing is mitigated by the use of an epithermal conversion scheme which allows for extra long life (~ 25 EFPY) with a small enough reactivity swing that ex-core control devices can be used. The design focuses on slow transients in an epithermal spectrum reactor. The use of a BeO radial reflector in a high L/D core increases the prompt fission time while limited conversion maintains large delayed neutron fraction. The surface PCU uses a simple CO2 Brayton cycle which makes the system insensitive to coolant leaks or ingress of Martian atmosphere.
The final design report can be downloaded here Final Report.
22.902 Fall 2003
The purpose of this design project is to continue work started in 22.033 in the arena of space nuclear power. The final report can be downloaded here. The contents of the report are summarized below.
Power Conversion Technology
Argon Brayton Cycle was analyzed for potential deployment. The cycle is acceptable for midrange powers (100 - 500 kW) However, to achieve multi-megawatt net work, coolant temperatures > 2000 K are required.
Thermionic power conversions systems were analyzed for potential deployment. Thermionics are ideal for low to midrange power operations (10 - 400 kW). To achieve 2 - 2.5 MW of net work, thermionic converters are in near direct contact with nuclear fuel at ~ 2400 - 2600 K with a boiling sodium coolant.
Liquid/Vapor metal rankine cycles were analyzed for potential deployment. Sodium, with a melting temperature of ~1000 K at near atmospheric pressure is an option of particular interest. Blending inert neutronic properties with excellent heat removal properties facilities the use of a fast UHPDC. The cycle appears capable of producing > 1 MW of power with coolant temperatures < 1200 K. The steeply sloping nature of the sodium T-s saturation line also makes sodium attractive from the standpoint of scalability to higher power with increasing temperature and pressure. At 1500 K, the sodium cycle is capable of producing 3.4 MW of work.
Radioisotope doping to prevent coolant freezing was evaluated. This approach only seems applicable to liquid LBE cooled systems.
Highly Enriched Uranium Fuel Ultra-High Power Density Space Reactor Physics Design
Previous work at MIT proposed a ultra-high power density plutonium fueled fast reactor for the space application. However, there are some concerns about launching a plutonium fueled core, and therefore, anaylses are conducted to assess the associated penalties with adapting the design for HEU (highly enriched uranium). Firstly, the highly reactive fuel allowed for a much more compact core, reducing shielding requirements and the overall mass of the system. Secondly, the presence of Pu240 in large quantities smoothed the reactivity swing of the core over life, thus reducing the burden on reactivity control devices. Though these trends are known, the exact magnitude of these penalties was established to assess the technical jusitifications for a plutonium based core in the paradigm of a cost benefit analysis.