Nuclear Engine For Rocket Vehicle Application Research Articles

High-resolution thermal analysis of nuclear thermal propulsion fuel element using OpenFOAM

This paper conducts high-resolution thermal hydraulic analysis of a Nuclear Thermal Propulsion (NTP) Fuel Element (FE) using a finite volume approach. Recent NTP design efforts have focused on using low-enriched uranium (LEU) fuel as an alternative to the historical highly-enriched uranium (HEU) fuel. In addition to changing materials’ properties, variations in dimensions and flow characteristics are also considered. This makes the applicability of legacy experimental data questionable for the new LEU designs, as the data was generated for a specific range of design characteristics. Nowadays, there is limited accessibility to experimental capability under realistic hot hydrogen conditions. However, some experimental setups could be replaced or complemented by higher-order numerical analysis, which is the end objective of the computational framework developed here. This study implements a 3D conjugate heat transfer (CHT) numerical solver between solid and fluid regions using OpenFOAM Computational Fluid Dynamic (CFD) toolbox. The hydrogen flow in the fluid region is simulated using Reynolds-averaged Naiver-Stokes (RANS) model, while the solid region is modeled using a conduction heat transfer solver. The 3D simulation results are validated against experimental data obtained from the Nuclear Engine for Rocket Vehicle Application (NERVA) Nuclear Rocket Experimental (NRX) A6 program. The latter shares similar design parameters with modern NTP systems, such as dimensions and flow conditions. In addition, legacy heat transfer correlations were implanted in a reduced-order 1.5D semi-analytic solution, and the results were compared against the OpenFOAM solution. The results presented in this paper conclude that OpenFOAM can serve as a high-resolution thermal hydraulic code both for reproducing legacy experiments and educating reduced-order models.

Assessment of near-term fuel screening and qualification needs for nuclear thermal propulsion systems

Nuclear thermal propulsion (NTP) is an in-space propulsion technology capable of both high specific impulse (850–1000 s) and thrust (44–1112 kN), which can help reduce trip times for crewed missions beyond low Earth orbit. NTP technology has been demonstrated during historic programs. Over 20 ground test reactor experiments were performed, which demonstrated the prototypic reactor operations, during the Nuclear Engine for Rocket Vehicle Application (NERVA)/Rover program (1955–1972). Although historical programs have shown that NTP is a viable in-space propulsion technology, developing NTP in modern programs is contingent on the development and qualification of ultrahigh-temperature nuclear fuel technologies that can withstand engine operating conditions. In historical NTP development programs such as NERVA/Rover, prototypic reactor/engine schemes were ground tested to assess the overall system feasibility and to qualify the reactor fuel forms for eventual flight systems. Although this approach is effective to verify fuel performance under prototypic conditions, relying solely on full-scale NTP reactor tests as the pathway for verifying or qualifying fuel is inefficient and cost prohibitive today. Additionally, modern nuclear licensing requirements state that before test reactor approval, reactor components and fuel elements should be qualified via non-nuclear (out-of-pile) and nuclear (in-pile) testing under representative operating conditions. Using this methodology, fuel matures as production scale fabrication methods are established, and as produced fuel performance is demonstrated. This paper provides an overview of historical approaches to NTP fuel performance maturation, including fuel screening and qualification needs, and provides insight for establishing an efficient testing paradigm that can be implemented to rapidly and affordably develop NTP fuel forms for eventual qualification.

Modeling of corrosion-induced blockages on radiation heat transfer by using RELAP5-3D

Nuclear power propulsion for space applications is essential for long-term high payload missions. Several nuclear reactor types were investigated by the Nuclear Engine for Rocket Vehicle Application (NERVA) program of National Aeronautics and Space Administration (NASA). Due to the requirement of long-term missions, studies need to be conducted concerning the impact of planned/unplanned transients on nuclear thermal rockets. In this work, a system model based on RELAP5-3D is developed to simulate corrosion-induced blockages on the peripheral fuel elements of the Pewee I Test Reactor. In addition to the standard axial convective heat transfer, the model incorporates the radiation and conduction heat transfer across the radial direction. Steady-state conditions are achieved for the main thermal-hydraulic parameters. This work investigates the effect of radiation heat transfer across the gap between peripheral fuel elements and the inner core boundary wall caused by corrosion-induced fuel surface degradation of the coolant channel holes. Higher blockage ratios resulted in higher temperature rises across the coolant holes of the peripheral fuel elements. In addition, the pressure drop across the peripheral fuel element coolant holes was also larger at higher blockage ratios. For the channels undergoing blockages, their radiation heat transfer rate increases while their neighbors’ decreases. The temperature of the peripheral fuel elements will gradually get closer to the melting point of uranium carbide, especially when the coolant channels undergo the most severe blockage.

Design of a passive safety system for a nuclear thermal rocket

Long-term high payload missions necessitate the need for nuclear space propulsion. Several nuclear reactor types were investigated by the Nuclear Engine for Rocket Vehicle Application (NERVA) program of National Aeronautics and Space Administration (NASA). Study of planned/unplanned transients and their impact on nuclear thermal rockets is important due to the need for long-term missions. It has been determined that a loss-of-flow-accident (LOFA) is the most serious design basis accident that will affect nuclear thermal rockets. A safety system is needed to respond to a LOFA and to prevent the core from melting. In this paper, a special secondary loop has been designed that utilizes the existing components of the Pewee I reactor. In particular, the tie rod tubes are connected to a secondary loop with radiator tubes. A check valve is also present in the circuit to help facilitate natural circulation in one direction in the absence of gravity. The radiator tube heat transfer surface area was increased to the following specifications: (i) 2 times the heat transfer surface area (HTSA) of the tie rod tubes, (ii) 4 times the HTSA of the tie rod tubes, (iii) 6 times the HTSA of the tie rod tubes, (iv) 8 times the HTSA of the tie rod tubes, and (v) 10 times the HTSA of the tie rod tubes. The following expected results were achieved: (i) during both steady-state operation and post-LOFA decay heat removal, temperature of the tie rod can be kept below the material melting point; (ii) during both steady-state operation and post-LOFA decay heat removal, natural circulation can be facilitated with a decent flow rate; (iii) during post-LOFA decay heat removal, the coolant temperatures in the tie rod tubes decreases and the mass flow rate increases; and (iv) in the secondary system, the heat sinks are able to remove the heat generated by the heat sources, during both steady-state and transient operation. As far as minimum radiator HTSA is concerned, the radiator tubes need to have a HTSA of approximately twice of that of the tie rod tubes. This ensures the tie rod tubes won’t melt and there is a decent natural circulation flow rate.

Modeling Loss-of-Flow Accidents and Their Impact on Radiation Heat Transfer

Long-term high payload missions necessitate the need for nuclear space propulsion. The National Aeronautics and Space Administration (NASA) investigated several reactor designs from 1959 to 1973 in order to develop the Nuclear Engine for Rocket Vehicle Application (NERVA). Study of planned/unplanned transients on nuclear thermal rockets is important due to the need for long-term missions. In this work, a system model based on RELAP5 is developed to simulate loss-of-flow accidents on the Pewee I test reactor. This paper investigates the radiation heat transfer between the fuel elements and the structures around it. In addition, the impact on the core fuel element temperature and average core pressure was also investigated. The following expected results were achieved: (i) greater than normal fuel element temperatures, (ii) fuel element temperatures exceeding the uranium carbide melting point, and (iii) average core pressure less than normal. Results show that the radiation heat transfer rate between fuel elements and cold surfaces increases with decreasing flow rate through the reactor system. However, radiation heat transfer decreases when there is a complete LOFA. When there is a complete LOFA, the peripheral coolant channels of the fuel elements handle most of the radiation heat transfer. A safety system needs to be designed to counteract the decay heat resulting from a post-LOFA reactor scram.

Numerical Study of High-Temperature and High-Velocity Gaseous Hydrogen Flow in a Cooling Channel of a Nuclear Thermal Rocket Core

Two mathematical models (a one-dimensional (1D) and a two-dimensional (2D)) were adopted to study, numerically, the thermal-hydrodynamic characteristics of flow inside the cooling channels of a nuclear thermal rocket (NTR) engine. In the present study, only one of the cooling channels of the reactor core is simulated. The 1D model adopted here assumes the flow in this cooling channel to be unsteady, compressible, turbulent, and subsonic. The governing equations of the compressible flow in the cooling channel are discretized using a second-order accurate (MacCormack) finite-difference scheme. The steady-state results of the proposed model were compared to the predictions by a commercial CFD code. The 2D CFD solution was obtained in two domains: the coolant (gaseous hydrogen) and the ZrC fuel cladding. The wall heat flux which varied along the channel length (as described by the nuclear variation in the nuclear power generation) was given as an input. Numerical experiments were carried out using both codes to simulate the thermal and hydrodynamic characteristics of the flow inside a single-cooling channel of the reactor for a typical Nuclear Engine for Rocket Vehicle Application (NERVA)-type NTR engine. It is concluded that both models predict successfully the steady-state axial distributions of temperature, pressure, density, and velocity of gaseous hydrogen flow in the NTR cooling channel.

A feasibility study on low-enriched uranium fuel for nuclear thermal rockets – I: Reactivity potential

This paper is concerned with the possibility of implementing Low-Enriched Uranium (LEU) fuels in NERVA (Nuclear Engine for Rocket Vehicle Application) type Nuclear Thermal Rockets (NTR). It presents a detailed study of the requirements for implementing LEU in a NERVA type NTR revolving around the softening of the neutron spectrum. This work has been done to demonstrate the possibility to enhance the proliferation resistance of these nuclear space systems in the hope of fostering the groundwork for their eventual commercial use. The necessity of thermalizing the neutron spectrum is discussed along with a detailed study of various methods by which this can be achieved. The effect of minimizing non fission neutron loss through the selection of appropriate structural materials is then presented along with a cursory study of various options. Finally a reference conceptual reactor configuration is proposed and compared with previous NTR designs where its relative shortcomings and obvious advantages are presented and discussed. It is concluded that an LEU-NTR is not only a definite possibility, but also offers distinct advantages over existing Highly-Enriched Uranium (HEU) NTR designs, particularly the increased proliferation resistance of the system and the reduction of the fuel cost and development schedule. Finally, some suggestions are made for future work that would enable the progression of the current conceptual design to a more finalized reactor design.

Science in Flux: NASA's Nuclear Program at Plum Brook Station, 1955–2005 (review)

Reviewed by: Science in Flux: NASA’s Nuclear Program at Plum Brook Station, 1955–2005 Matthew H. Hersch (bio) Science in Flux: NASA’s Nuclear Program at Plum Brook Station, 1955–2005. By Mark D. Bowles . Washington, D.C.: National Aeronautics and Space Administration, 2006 Pp. xxix+335. $25. The image that graces the dust jacket of Science in Flux—a goofy 1959 rendering of an atomic spaceship—suggests not what one cold war nuclear research facility actually achieved, but everything it could not. Erected on an old TNT works in seismically somnolent Sandusky, Ohio, the federal government's Plum Brook Station operated only from 1963 to 1973, and it closed with neither a bang nor a whimper; rather, it disappeared into a probability cloud. According to Mark Bowles's exhaustive biography of this laboratory (winner of the 2005 Institute of Aeronautics and Astronautics History Manuscript Award), some labs have more to tell scholars through their disuse than through their use. Locals once feared that the National Aeronautics and Space Administration was hiding UFOs in Plum Brook's dormant containment vessels, but Bowles reveals more sinister ghosts lurking at the derelict station: low-level radiation and the decline of "big science." That said, Plum Brook achieved about as much as any laboratory founded on an intelligence failure. In the mid-1950s, belief that a nuclear-powered airplane was practical in the near-term—and that the Soviet Union already had one—triggered a crash program in radiation research by the precursor to NASA, the National Advisory Committee for Aeronautics. Although the experts were wrong on both counts, by the time Plum Brook's main fission reactor went critical, a contest to build spaceships had replaced the one for long-range airplanes, and NASA's only nuclear test facility appeared well suited to support this new effort. If many recall President John F. Kennedy's 1961 challenge to explore the Moon, Bowles remarks, few remember that Kennedy advocated, in the same speech, the development of nuclear-powered rockets. Beginning in 1963, Plum Brook's researchers studied the effects of neutron radiation—the "flux" of the book's title—on materials and components destined for atomic engines and other space-based reactors. As Bowles points out, though, Plum Brook science was both of flux and in flux. Where Plum Brook's original NACA mandate had weak technical underpinnings but a broad political mandate, projects like the Nuclear Engine for Rocket Vehicle Application (NERVA) were scientifically workable but shielded by paper-thin congressional support. By 1972, Plum Brook had become both peripheral to NASA's space exploration plans and, as radiation factory, a growing environmental menace. Already committed to funding the space shuttle, NASA pulled the plug on Plum Brook, mothballing the site instead of pursuing a more costly decommissioning. The facility [End Page 246] may yet prove useful, but it now sits, mostly dismantled, as part of NASA's Glenn (formerly Lewis) Research Center. Even though one might expect Plum Brook's staff to have been a fatalistic bunch, they wept when their world-class main reactor went cold. The facility's 700 researchers (most of them engineers) loved working at Plum Brook and were proud of its safety record. Even Myrna Steele liked being there, despite enduring endless teasing for being both a woman and—even worse—a physicist. Insightful insiders always suspected, however, that NASA might close the place at any time. While Plum Brook trained a generation of nuclear engineers and performed valuable materials tests and chemical analyses, the facility made no major scientific discoveries and took its research cues from elsewhere. Work on portable nuclear generators yielded usable space hardware, but NERVA never advanced beyond design studies and test reactors. Scattered around the world in labs and college campuses, research reactors produce no electricity, just data and headaches, and Bowles is quite right that few historians have written about them. Connecting Plum Brook's story to the growing body of work on engineering practice, twentieth-century technoscience, and nuclear history, Bowles deserves a great deal of credit for demonstrating such admirable fidelity to a challenging subject. His story has the narrative arc of an episode of VH1's...

Operational characteristics of nuclear rockets

The start-up, full-power operation, and shutdown (including afterheat removal from the nuclear reactor) stages of operation of the Nuclear Engine for Rocket Vehicle Application (NERVA) have been demonstrated in the technology program. Start-up is initiated by opening the valve that isolates the engine from the liquid-hydrogen run tank. Two engine systems with unfueled nuclear reactors have been used to investigate this portion of engine operation. A bootstrap technique has been developed that does not depend on auxiliary starting equipment. With the addition of a fueled reactor, as in NRX/EST or XE-P, the energy from the reactor is used to sustain operation or increase to full power. Operation at rated conditions can be sustained for long periods: NRX-A6 has demonstrated a reactor life of 1 hr. Throttling capability allows operation between 60% and 100% thrust at full specific impulse. After shutdown, a period of several days is needed to remove the delayed energy (radioactive decay) from the nuclear reactor by intermittently pulsing propellant through the reactor.

Problems of Nuclear Rockets

In man's effort to conquer space, he has relied on the same type of propulsion that powers cars, lawn mowers, jet planes, Piper Cubs, battleships and motor boats: chemical propulsion. For a long time to come, burning a fuel and controlling its combustion energy will be the way to boost a rocket into space. This may do for manned missions to the moon. But scientists and engineers at the National Aeronautics and Space Administration and the Atomic Energy Commission regard this method already as antiquated and uneconomical when it comes to missions deep in space. Over the last decade, AEC and NASA have spent $1.2 billion in developing the basic technology of the nuclear rocket; another $1 billion is needed to complete the project. It looks like it's around the corner, says Sen. John D. Pastore (D-R.I.) of the Joint Congressional Committee on Atomic Energy. We've been working on it for years, but where is it? The nuclear rocket, called NERVA (Nuclear Engine for Rocket Vehicle Application), has gone through all its preliminary design and testing stages, and the time from now until 1978-the current project completion date-will be taken up with getting it ready for flight. The rocket is expected to be ready in time to power a shuttle for ferrying men and cargo from low earth orbit to the space stations in high earth (geosynchronous) or lunar orbit, or to send payloads deeper into space on such missions as a trip to Mars for either a manned landing, an unmanned fly-by oI an instrumented sampling mission. Because of the trip time and the heavy payloads involved, NERVA is not only ideally suited for such a job but is considered critical to its success (SN: 9/20, p. 233). In all of these missions, a chemically powered shuttle rocket (SN: 1/3, p. 22) would first place the NERVA and its companion vehicle in low earth orbit. Then the rocket would blast off for its mission. When done it would return to low earth orbit, waiting for another payload tc be launched and docked to it. The nuclear engine, like other future space systems, is being designed with reusability as a guiding principle. Simply stated, the aim of reusability is to make a nuclear rocket engine that can be used a number of times. The idea is motivated by economics. Just as it would be uneconomical to build a car that could only make one round tripwhich is in essence what the present Apollo rockets do-NASA and the AEC want a nuclear engine that can be flown on several round trips. In no case in the foreseeable future is it envisioned for earth liftoff. The main reason is that chemically propelled rockets are adequate for that job, and present nuclear rocket capability would not provide significant advantages. Another reason is radioactivity, which could escape in small amounts to the launch area or in large amounts if an accident occurred. A nuclear rocket can carry heavier payloads on less fuel than a chemical rocket because of the nuclear engine's greater propulsion efficiency, or specific impulse. This is the tiube period in which one pound of thrust is produced by one pound of fuel. For the best chemical rocket using liquid hydrogen and oxygen, the specific impulse is about 450 seconds; NERVA'S specific impulse is nearly double that, 825 seconds, which means that one pound of propellant producing the same thrust as one pound of chemical fuel will last almost twice as long. The saving in fuel can go into carrying extra payload. As it now stands, NERVA iS comKlein: It's still a breadboard engine.