J. Tom Sena

Review of liquid metal heat pipe work at Los Alamos

A survey of space‐power related liquid metal heat pipe work at Los Alamos National Laboratory is presented. Heat pipe development at Los Alamos has been on‐going since 1963. Heat pipes were initially developed for thermionic nuclear‐electrical power production in space. Since then Los Alamos has developed liquid metal heat pipes for numerous applications related to high temperature systems in both the space and terrestrial environments. Some of these applications include thermionic electrical generators, thermoelectric energy conversion (both in‐core and direct radiation), thermal energy storage, hypersonic vehicle leading edge cooling, and heat pipe vapor laser cells. Some of the work performed at Los Alamos has been documented in internal reports that are often little‐known. A representative description and summary of progress in space‐related liquid metal heat pipe technology is provided followed by a reference section citing sources where these works may be found.

Results of a first generation least expensive approach to fission module tests: Non-nuclear testing of a fission system

The use of resistance heaters to simulate heat from fission allows extensive development of fission systems to be performed in non-nuclear test facilities, saving time and money. Resistance heated tests on the Module Unfueled Thermal-hydraulic Test (MUTT) article has been performed at the Marshall Space Flight Center. This paper discusses the results of these experiments to date, and describes the additional testing that will be performed. Recommendations related to the design of testable space fission power and propulsion systems are made.

SAFE‐100 Module Fabrication and Test

Reliable, long‐life, low‐cost heat pipes can enable safe, affordable space fission power and propulsion systems. Advanced versions of these systems can in turn allow rapid access to any point in the solar system. Stainless steel heat pipe modules are being built at Advanced Methods and Materials for use in a non‐nuclear thermal hydraulic simulation of the SAFE‐100 reactor. SAFE‐100 is a near‐term, low‐cost space fission system demonstration. The heat pipes were designed to remove thermal power from the SAFE‐100 core, and transfer this power to an electrical power conversion system. These heat pipe modules are being delivered to NASA Marshall Space Flight Center to be filled and tested in a prototypical configuration during CY2003. The construction and test of a SAFE‐100 module prototype is described.

Sodium heat pipe module test for the SAFE-30 reactor prototype

Reliable, long-life, low-cost heat pipes can enable safe, affordable space fission power and propulsion systems. Advanced versions of these systems can in turn allow rapid access to any point in the solar system. Twelve stainless steel-sodium heat pipe modules were built and tested at Los Alamos for use in a non-nuclear thermohydraulic simulation of the SAFE-30 reactor (Poston et al., 2000). SAFE-30 is a near-term, low-cost space fission system demonstration. The heat pipes were designed to remove thermal power from the SAFE-30 core, and transfer this power to an electrical power conversion system. These heat pipe modules were delivered to NASA Marshall Space Flight Center in August 2000 and were assembled and tested in a prototypical configuration during September and October 2000. The construction and test of one of the SAFE-30 modules is described.

High temperature heat pipe experiments aboard the space shuttle

Although high temperature, liquid metal heat pipe radiators have become a standard component on most space nuclear power systems, there is no experimental data on the operation of these heat pipes in a zero gravity or micro gravity environment. Experiments to benchmark the transient and steady state performance of prototypical heat pipe space radiator elements are in preparation. Three SST/potassium heat pipes are being designed, fabricated, and ground tested. It is anticipated that these heat pipes will fly aboard the space shuttle in 1995. Three wick structures will be tested: homogeneous, arterial, and annular gap. Ground tests are described that simulate the space shuttle environment in every way except gravity field.

Sodium Compatibility Tests of MA‐ODS 754 and MA‐ODS 956 Alloys

Nickel based MA‐ODS 754 and iron based MA‐ODS 956 alloys were evaluated in a refluxing sodium environment. These materials possess properties such as high temperature creep strength and corrosion resistance that are potentially suitable for alkali metal heat pipes in planetary or deep space probes. The construction of reflux capsules made of these materials is described and the results of tests conducted in air are reported. The MA‐ODS 956 capsule had limited life, attributed in part, to the presence of aluminum as an alloy constituent. The MA‐ODS 754 capsule continued to operate normally after 5,500 hours at 940°C, 18 W/cm2 evaporator radial heat flux, and 862 W/cm2 axial heat flux at the evaporator exit.