Multi Megawatt Power System Analysis Report

Abstract

Missions to the outer planets or to near-by planets requiring short times and/or increased payload carrying capability will benefit from nuclear power. A concept study was undertaken to evaluate options for a multi-megawatt power source for nuclear electric propulsion. The nominal electric power requirement was set at 15 MW e with an assumed mission profile of 120 days at full power, 60 days in hot standby, and another 120 days of full power, repeated several times for 7 years of service. Of the numerous options considered, two that appeared to have the greatest promise were a gas-cooled reactor based on the NERVA Derivative design, operating a closed cycle Brayton power conversion system; and a molten lithium-cooled reactor based on SP-100 technology, driving a boiling potassium Rankine power conversion system. This study examined the relative merits of these two systems, seeking to optimize the specific mass. Conclusions were that either concept appeared capable of approaching the specific mass goal of 3-5 kg/kW e estimated to be needed for this class of mission, though neither could be realized without substantial development in reactor fuels technology, thermal radiator mass efficiency, and power conversion and distribution electronics and systems capable of operating at high temperatures. Though the gas-Brayton systems showed an apparent advantage in specific mass, differences in the degree of conservatism inherent in the models used suggests expectations for the two approaches may be similar. Brayton systems eliminate the need to deal with two-phase flows in the microgravity environment of space.iii CONTENTS

Multi-Megawatt Power System Trade Study

“…One uses a liquid-metal-cooled reactor and a metal vapor Rankine cycle power conversion system. The other uses Brayton cycle power conversion, but includes both gas-cooled and liquid-metal-cooled reactors (Longhurst, 2001c). In each case, two levels of availability were assumed regarding reactor fuel technology.…”

Thermal‐hydraulic analysis of an open‐grid megawatt gas‐cooled space nuclear reactor core

“…Numerous nuclear space reactors have been designed, manufactured and even launched over the last six decades 3 . Generally, the nuclear space reactor can be divided into three groups according to the cooling method, including heat pipe‐cooled reactor, 4 liquid metal‐cooled reactor, 5,6 and gas‐cooled reactor 7 …”

Multi-megawatt power system trade study

“…As part of the Special Purpose Fission Technology (SPFT) program conducted by the U. S. Department of Energy's Office of Nuclear Energy, Science and Technology (DOE-NE), an initial concept trade study was undertaken by the INEEL to evaluate feasibility, on the basis of specific mass, of two configurations of space nuclear power systems, subject to a set of operational constraints (Longhurst, 2001c).…”