Preliminary Design Study of an Innovative High-Performance Nuclear Thermal Rocket Utilizing LEU Fuel

摘要

A Nuclear Thermal Rocket (NTR) is a viable and efficient option for manned deep-space missions such as to Mars and beyond. The NTR technology has already been investigated and tested by the United States (US) and Russia. The representative US NERVA type reactors traditionally load hexagonal shaped fuel elements utilizing High Enriched Uranium (HEU) due to the imperative of making a high power reactor with a minimum size. This state-of-the-art NTR technology could be applicable with contemporary space vehicles. However, even though the NTR designs utilizing HEU is the best choice in terms of rocket performance and technical maturity, they inevitably arouse nuclear proliferation obstacles on all Research and Development (R&D) activities by civilians and non-nuclear weapon states, and potential commercialization. To cope with the security issue to use HEU, an innovative and high-performance NTR engine for future generations, Korea Advanced NUclear Thermal Engine Rocket utilizing Low Enriched Uranium fuel (KANUTER-LEU), is currently being designed at Korea Advanced Institute of Science and Technology (KAIST). The major design goals are to make use of a LEU fuel for its fairly compact reactor, but not to sacrifice the rocket performance relative to the traditional NTRs utilizing HEU. KANUTER-LEU mainly consists of a moderated Extremely High Temperature Gas cooled Reactor (EHTGR) utilizing a LEU fuel and H_2 propellant, a propulsion system housing a propellant feeding system, a regenerative nozzle assembly, and an optional electricity generation system as a bimodal engine. To implement a LEU fuel for the EHTGR, the KANUTER adopts W-UO_2 CERMET fuel to increase uranium density drastically and metal hydride moderators to thermalize neutrons in the core consequentially having a high neutron economy. The moderator and structural material selections also consider neutronic and thermo-physical characteristics to reduce non-fission neutron loss and reactor weight. The geometry design of fuel element and reactor focuses on protective cooling capability, fabricability and compactness. This paper presents the preliminary design study of KANUTER-LEU focusing on the neutronic and thermohydraulic features. The result shows comparable characteristics of high efficiency, compact and lightweight system despite the heavier LEU fuel utilization. The reference performance is theoretically estimated at a thrust of 50.0 kN, a thrust to weight ratio of 5.2 and a specific impulse of 912 s at the maximum power of 250 MW_(th).