High Temperature Heat Pipes for Space Fission Power

Abstract

Future space transportation and surface power applications will require small fission reactors for power generation. The fission reactors would generate up to 13kWt of power for the energy conversion system. The heat generated by the reactor would be collected and transferred by high temperature alkali metal heat pipes to a series of Stirling convertors or thermoelectric convertors for power generation. These heat pipes would be relatively long, 2 meters for a Stirling convertor design, and 4 m for a thermoelectric convertor design. Previous alkali metal heat pipe designs for spacecraft have used arterial, annular, or crescent wicks. All of these wicks can be difficult to fabricate for long heat pipes. Two other wick designs were examined in this study, grooved wicks, and self-venting arterial wicks. Artery de-priming by trapped vapor or non-condensable gas in an artery has been a single point failure for traditional arterial heat pipes. A self-venting arterial heat pipe has a screen artery that contains small venting pores in the evaporator section that allow for any trapped vapor or non-condensable gas (NCG) to escape. A trade study was conducted to compare the maximum transport and specific power for the self-vented artery, arterial, and grooved heat pipe designs. In all cases for a given diameter, the self-vented artery design carried the highest power, and had the highest specific power. Two 1-m long heat pipes were fabricated and tested, a self-venting wick and a grooved wick. The 1m long, 0.75in. (1.91cm) outer diameter sodium self-venting arterial heat pipe is capable of carrying 3.4kW of power at adverse elevations of up to 3.0in (7.62cm) without drying out. At an elevation of 5.0in (12.7cm), the self-venting arterial heat pipe is capable of carrying a maximum transport power of 1.4kW. Grooved heat pipes are typically used for spacecraft thermal control, since any NCG in the grooves can easily escape. The 1m long, 0.75in (1.91cm) outer diameter sodium grooved heat pipe is capable of carrying 846W, 546W and 346W at adverse elevations of 0.1in (0.25cm), 0.6in (1.52cm) and 1.0in (2.54cm), respectively.