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NTP Engine System Design and Modeling
Abstract
View Video Presentation: https://doi.org/10.2514/6.2022-4373.vid Aerojet Rocketdyne (AR) has long had a vision for providing propulsion that permits exploration and extensive travel capability across the Solar System. AR’s history and current efforts include providing propulsion and power for NASA’s far-reaching exploration goals and science missions. These include propulsion for the return to the moon with the Space Launch System (SLS), battery and power systems for the International Space Station (ISS), propulsion for Mars landers, and power for Mars rovers (e.g., Perseverance) and propulsion to power deep space missions like New Horizon. AR has continued the race in developing advanced propulsion systems that help the USA and NASA advance their goal of getting humans to Mars by working on a High-Assay Low Enriched Uranium (HALEU) Nuclear Thermal Propulsion (NTP) system. Current mission studies are focused on Mars missions in the late 2030’s and beyond. NTP engine requirements (e.g., thrust size, Isp) have been connected to those current studies that have been on-going since 2019. Those studies have shown a wide range of thrust sizes (e.g., 12,500 to 25,000-lbf) which can close the architecture and vehicle design using a nuclear fuel material that is capable of high temperature (e.g., peak temperatures between 2,800 to 3,000-deg K) operation to achieve a specific impulse (Isp) at or above 900 seconds. Although Mars missions dominate where NTP shows high pay-off, cis-lunar missions where NTP can support faster 2-3 day missions and more cargo mass also show payoff versus typical chemical propulsion systems. The HALEU NTP designs continue to use hydrogen propellant as the coolant and can use either a Ceramic-Metallic, Ceramic-Ceramic, or Carbide based fuel. The new approach in 2021 for the NTP fuel arrangement utilizes discrete cylindrical assemblies in the moderator block. The grouping is optimized for achieving criticality, which produces the required power level but is similar to the previous approach of using hexagonal (prismatic form) fuel elements with hydrogen flowing in channels within the fuel assembly. Current work has extended the fuel and core designs beyond NTP fuels initially analyzed between 2017 to 2020 and have started looking at other fuels with Carbide material approaches since 2021. Engine design trades are still on going to identify the optimum core/engine system operating characteristics. The NTP design trades that are continuing rely heavily on thermodynamic cycle modeling that includes the neutronic design attributes of the fuel and how it operates within a reactor core design. This paper presents a discussion on the methods for NTP modeling of the engine system for both steady state and transient operation, examining start, shutdown and post-cool down operations. In addition to steady state and transient modeling architectures, the implications of capturing component design influences on the NTP design is discussed.
... This ensures a precise understanding of the working environment for the fuel elements. Belair [9] and Joyner [10] conducted overall performance simulations of a nuclear thermal rocket engine system. Duan performed a study on the reactor core, including neutron physics analyses under special conditions such as partial blockage, power variation, fuel element configurations, and moderator arrangements [11][12][13]. ...
... Under uniform inlet conditions, the temperature variations within coolant ch across different axial cross-sections are shown in Figure 13a. The temperature distri is relatively smooth in the central region of the fuel element (channels 1-7), while a temperature drop occurs in the outer region (channels [8][9][10][11][12][13][14][15][16][17][18][19]. Along the flow direc hydrogen, the temperature fluctuations transition from mild to severe, with the temperatures observed at the inner corners of the hexagonal prism (channels 8, 10, 16, and 18). ...
... Under uniform inlet conditions, the temperature variations within coolant channels across different axial cross-sections are shown in Figure 13a. The temperature distribution is relatively smooth in the central region of the fuel element (channels 1-7), while a sharp temperature drop occurs in the outer region (channels [8][9][10][11][12][13][14][15][16][17][18][19]. Along the flow direction of hydrogen, the temperature fluctuations transition from mild to severe, with the lowest temperatures observed at the inner corners of the hexagonal prism (channels 8, 10, 12, 14, 16, and 18). ...
Nuclear thermal propulsion, which uses a reactor core as the energy source of a nuclear thermal rocket, is expected to become an effective means of deep space exploration in the future. The reactor core can be damaged by a large temperature gradient. Thus, investigating the structural distribution of its internal components and understanding its flow and heat transfer characteristics is highly important. In this study, a 19-hole hollow hexagonal prism fuel element is selected for simulation. A new type of fuel element is proposed by changing the diameter of the channels in the work material, and the heat transfer characteristics are compared and analyzed. Compared with a conventional fuel element under uniform inlet conditions, when the inlet conditions and the diameter of the channel in the work material are changed, the peak temperature inside the fuel element decreases, but the overall temperature distribution is more uniform. Along the flow direction, the temperature distribution boundary is located at y = 300–500 mm. From the inlet to this position, the temperature distribution on the axial cross-section is uniform. From this position to the outlet, the temperature difference along the radial cross-section is significantly reduced, and the temperature fluctuation at the periphery of the fuel element is significantly improved. The research results can provide a reference for the design of fuel elements.
... Previously, a standard proportional integral (PI) controller for temperature and pressure demands was used in Ref. [1], with delays and oscillations being observed after any sudden change in demand. With the controller gains adjusted as a function of total power, near-perfect agreement between the demands and the responses was obtained [2]. Simultaneously, a limited delay and little to no overshoot were obtained in Ref. [3] by converting the chamber temperature signal to a power signal to use in a period-generated controller (PGC) [4]. ...
... In a nutshell, the proportional, integral and derivative terms respectively react to the current, past and future performance of the controller. Therefore, unless the gains are made time-dependent (as in Ref. [2]), a simple PI controller cannot perfectly anticipate any sudden change in demand. A derivative term adds anticipation and can also reduce overshoot but, in real systems, it can lead to instabilities due to instrumentation noise. ...
... The only demand is the chamber temperature. It is used directly by the temperature-driven component and indirectly by the reactivity-driven component after a conversion using Equations (2) and (3) is performed. The CD angle is computed by a weighted sum of both corrections terms: ...
In this work, a novel temperature-reactivity controller is introduced to rotate control drums based on a chamber temperature signal. It consists of two components: (1) a reactivity-driven proportional controller converting the temperature demand into a reactivity signal, and (2) a temperature-driven proportional-derivative controller which relies on a derivative term to anticipate sudden changes in demand and limit temperature overshoot. A weighting function is proposed to continuously transition from one component to the other.
Testing Of Feed System For Nuclear Propulsion Technology Under Consideration for Exploration Of Mars
- G V Konyukhov
- A I Belogurov
- K P Denisov
Decay Heat Estimates for MNR
- W Garland