Ground Testing NTP Systems: A Review of Potential Test Options and Recommendation on Preferred Approach

Abstract

The development of a nuclear thermal propulsion (NTP) system rests heavily upon being able to demonstrate performance of the system prior to launch. Since testing of nuclear thermal rocket (NTR) engines was suspended in 1972, a number of studies have been performed on ground test facility (GTF) needs and requirements. This paper provides a survey of the studies performed in recent years on concepts for ground testing and their current status. This paper identifies the most promising concepts and the advantages and disadvantages associated with each concept based on anticipated performance requirements for a nuclear thermal propulsion system. Detailed trade studies will need to be performed to support the decision making process. I. Introduction The U.S. Government, i.e., National Aeronautics and Space Administration (NASA), the Department of Energy (DOE), and the U.S. Air Force, initially sponsored the development of space NTP systems in the 1950s. These programs were initiated by Los Alamos National Laboratory (LANL) and Lawrence Livermore National Laboratory (LLNL), with the LANL program being selected to proceed with development of the NTP system. The research effort was called Rover and the development of the concept was called Nuclear Engine for Rocket Vehicle Application (NERVA). Testing of the concepts was performed at the Nuclear Rocket Development Station (NRDS) at the NTS. Under the Rover Program, four reactor test series (KIWI, Phoebus, Pewee-1 and Nuclear Furnace-1) were performed to demonstrate the basic nuclear technology. KIWI, Phoebus, and Pewee-1 were open cycle systems and exhausted their effluent into the atmosphere, whereas the Nuclear Furnace-1 used an effluent treatment system to treat the hydrogen effluent before discharge to the atmosphere. In all, 13 tests were conducted in the Rover Program. The NERVA Program focused on development of a flight-rated NTR using the technologies being demonstrated in the Rover Program. The NERVA Program was performed in parallel with the Rover Program, and several of the tests overlapped the research effort. The NERVA Program consisted of two projects, the Nuclear Reactor Experiment (NRX) and the Experimental Flight Engine Prototype (XEPrime). Both of these concepts used the open cycle with effluent being discharged to the atmosphere. Eight rocket reactor tests were performed in the NERVA Program. As environmental concerns were being raised in the U.S., continued open cycle testing of NTP systems was also being questioned. At the time of termination of the Rover and NERVA Programs in January 1973, effluent treatment systems were being developed for application to future NERVA test articles based on a smaller effluent treatment system (ETS) demonstrated on the Nuclear Furnace-1 reactor. The Nuclear Furnace-1 was a 44 MWt reactor used for testing fuel integrity and performance. The hydrogen effluent, after passing through the core, was sprayed with steam to cool the gas and remove any particles from the gas flow stream. A heat exchanger was then used to reduce the temperature further before the effluent was passed through a silica gel bed to remove the water and dissolved fission products. The noble gases were removed as the effluent passed through cryogenic, activated charcoal filter beds. The exiting hydrogen stream contained no detectable fission products. For the NERVA Program, seven effluent treatment system options were studied based on the type of fuel to be tested 1 . Beaded fuel was felt to have the highest integrity, and thus trapping of noble gases would not be required. All three concepts proposed for beaded fuel were based on passing the effluent gas through water, either through lutes, water spray, or an irrigated filter and HEPA filter systems. For