Thermal Hydraulics and Structural Analysis of the Small Nuclear Rocket Engine (SNRE) Core

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

2012

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Nuclear rocket engines utilizing W-UO2 ceramic-metal (cermet) fuel are analyzed. A highly detailed Monte Carlo Neutron-Photon (MCNP) model of the reactor core is developed and exercised to determine the energy deposited in the various engine components via decelerating fission products and scattered neutrons and photons. These results are then used by the Nuclear Engine System Simulation (NESS) code to determine engine performance characteristics, determine thermodynamic state points throughout the cycle, and estimate engine mass. These engines are expander cycle based designs and utilize no tie-tubes to extract thermal energy from the reactor to drive the turbo-machinery.

Section: Ntr System Descriptionmentioning

confidence: 99%

Section: Ntr System Descriptionmentioning

confidence: 99%

Cycle Analysis of a 200MW Class CERMET Based NTR Engine

Fittje¹,

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

2012

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“…Further increases in edge coolant channel mass flow could move the maximum fuel temperature inside the fuel element, which would be beneficial. ANL200 [6] was designed for flow between fuel elements-unlike NERVA's SNRE [14] [31]. Small protrusions (5 mil height) on the fuel element's outer surface ensured a coolant flow passage even near the hot end where thermal expansion would otherwise force contact between neighboring elements and completely constrict flow through this gap.…”

Section: Resultsmentioning

confidence: 99%

“…This work is an extension of previous high-fidelity simulation and analysis of NERVA carbide fuel elements [14] [15]. Further, this work is part of a concerted effort to analyze cermet fuel elements; the thermodynamic cycle of this engine design (Table 1) is considered in Ref.…”

Section: Introductionmentioning

confidence: 99%

Thermal, Fluid, and Structural Analysis of a Cermet Fuel Element

Stewart¹,

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

2012

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This paper presents results and interpretation of a high-fidelity, multidisciplinary simulation of a cermet fuel element. The fluid, thermal, and structural equations are solved for a symmetric sub-region of a fast spectrum reactor core; detailed neutronic simulations provide heat deposition rates. Creep effects on stress are also simulated, as stresses are beyond elastic limits. The intent of this work is to predict maximum fuel temperature, variations in coolant exit temperature between channels, coating stress, and stress sources to evaluate and optimize cermet fuel element performance for Nuclear Thermal Propulsion reactors. The sources of mechanical stress in a fuel element are identified and their individual contributions are quantified. Temperature gradients and cladding-fuel thermal expansion mismatch are major sources of stress. Thick fuel element edge walls contribute to high fuel temperatures, high stresses, and low flow through edge coolant channels. NomenclatureA = constant in creep equation, MPa -n s -1 C p = specific heat, J/kg-K CTE = coefficient of linear thermal expansion, m/m-K E = modulus of elasticity (Young's modulus), GPa g = acceleration due to gravity, m/s 2 I sp = specific impulse, s k = coefficient of thermal conductivity, W/m-K k eff = thermal conductivity, effective value of cermet mixture, W/m-K k m = thermal conductivity of matrix (higher thermal conductivity metal matrix) , W/m-K k p = thermal conductivity of fuel particles, W/m-K %ΔL/L o = percentage change in length due to linear thermal expansion, % m = mass, kg = mass flow, kg/s MW = molecular weight, kg/mol MW t = megawatts of thermal energy, MW n = power law exponent in creep equation Q = activation energy, J/mol Re d = Reynolds number based on channel diameter R u = universal gas constant, J/mol-K T, T M , T ref = temperature, melting temperature, reference temperature, K %TD = percentage of theoretical density, % U = structural displacement, m V = fluid velocity, m/s V f,p , V f,1 = percent volume fraction of fuel particles, percent volume fraction of first mixture component, % ΔV= velocity increment for trajectory burn, m/s y + = normal boundary layer grid spacing at wall, normalized 2 z, r,θ = coordinates: axial, radial, and circumferential, m, deg α, α eff = coefficient of linear thermal expansion (CTE), effective CTE, m/m-K ε = emissivity, relative ability of a planar surface to emit radiation over all wavelengths = creep rate, 1/s γ = ratio of specific heats µ Poisson = Poisson's ratio µ = viscosity, Pa-s ρ, ρ o = density, theoretical density, kg/m 3 σ = stress, MPa Block = three symmetric sub-elements that combine to form the fuel element cross-section FE = fuel element A -25% B = metal matrix/ceramic particle mixture of metal A and ceramic B, % volume A /25% B = alloy of metals A and B, % volume % = compositions are percentage by volume, unless otherwise marked as % weight X 0 = subscript for theoretical density

“…The NASA Glenn Research Center (GRC) is leveraging this investment by creating and analyzing vehicle concepts based on NTR technology with the aid of the Nuclear Engine System Simulation (NESS) code. The primary focus of recent activities 3,4 at NASA GRC has been on benchmarking and upgrading methods, models, and analysis tools against the Small Nuclear Rocket Engine (SNRE) design 5 . Although never built, the SNRE has been the primary benchmark focus, primarily because of the maturity of the design and the available documentation regarding its preliminary design results.…”

mentioning

confidence: 99%

Evaluation of Recent Upgrades to the NESS (Nuclear Engine System Simulation) Code

Fittje¹,

44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

2008

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The Nuclear Thermal Rocket (NTR) concept is being evaluated as a potential propulsion technology for exploratory expeditions to the moon, Mars, and beyond. The need for exceptional propulsion system performance in these missions has been documented in numerous studies, and was the primary focus of a considerable effort undertaken during the Rover/NERVA program from 1955 to 1973. The NASA Glenn Research Center is leveraging this past NTR investment in their vehicle concepts and mission analysis studies with the aid of the Nuclear Engine System Simulation (NESS) code. This paper presents the additional capabilities and upgrades made to this code in order to perform higher fidelity NTR propulsion system analysis and design, and a comparison of its results to the Small Nuclear Rocket Engine (SNRE) design.