Dynamic Simulation of a Space Reactor System with Closed Brayton Cycle Loops

Abstract

A dynamic simulation model for space reactor power systems with multiple closed Brayton cycle loops for energy conversion is developed and demonstrated for a startup transient. The simulated power system employs a submersion-subcritical safe space S^4 reactor with a negative temperature reactivity feedback and has no singlepoint failures in reactor cooling and energy conversion. The S^4 reactor core is divided into three hydraulically independent sectors, and each sector has a separate closed Brayton cycle loop that is thermal-hydraulically coupled to a circulating liquid NaK-78 secondary loop with two water heat pipe heat rejection radiator panels. Each closed Brayton cycle loop has a Brayton rotating unit designed and optimized for high thermal efficiency and low specific mass (1:16 kg=kW e ). The reactor coolant and the closed Brayton cycle working fluid is a He-Xe binary gas mixture with a molecular weight of 40 g=mol. Results are presented for a startup transient of the S^4 closed Brayton cycle power system to full-power operation at a reactor thermal power 471 kW th , a Brayton rotating unit shaft speed of 45 krpm, and turbine and compressor inlet temperatures of 1149 and 400 K, respectively. At these conditions, the nominal electrical power and thermal efficiency of the power system are 130:8 kW e and 27.8%. NomenclatureC = compressor m = mass flow rate, kg=s m = normalized mass flow rate, kg=s, m m P ref =P o;in T o;in =T ref p P = pressure, Pa; electrical power, kW e P ref = reference pressure, 0.4 MPa T = temperature, K; turbine T ref = reference temperature, 400 K x = bleed fraction of working fluid at exit of Brayton rotating unit compressor = thermal or polytropic efficiency, % = pressure ratio ! = Brayton rotating unit shaft rotation speed, rad=s ! = normalized shaft rotation speed, rad=s, ! ! T ref =T o;in p Subscripts C = compressor e = electric G = generator in = turbine or compressor inlet o = stagnation or total P = polytropic Rx = reactor Sec = reactor sector, or BRU turbine inlet sys = power system th = thermal T = turbine

Uses of Liquid-Metal and Water Heat Pipes in Space Reactor Power Systems

“…The reactor core is divided into three hydraulically separate, but thermally and neutronically coupled sectors. Each reactor sector has a separate recuperated Closed Brayton Cycle (CBC) loop, with a turbo-machine unit for energy conversion (Gallo and El-Genk, 2009;El-Genk et al, 2010). Figure 29 presents a line diagram of one CBC loop in this power system.…”

“…A number of space reactor power system concepts have been developed or proposed with liquidmetal heat pipes for the passive and redundant removal and transport of the fission power generated in the reactor to the energy conversion subsystem (Angelo and Buden, 1985;El-Genk, 1994 and2008b;Ranken, 1982 andDeterman and Hagelston, 1992;, Poston et al, 2002;Ring et al, 2003; These heat pipes have also been considered for transporting waste heat from the energy conversion subsystems, and redundant and enhanced performance of heat rejection radiators. Energy conversion options considered for uses in space reactor power systems include Free-Piston Stirling Engine, FPSE (e.g., Angelo and Buden, 1985;Moriarty and Determan, 1989;Schreiber, 2001;Thieme et al, 2002 and2004;Schmitz et al, 1994 and2005), Thermoelectric (e.g., Ranken, 1982;Moriarty and Determan, 1989;Josloff et al, 1994;Marriott and Fujita, 1994;Caillat et al, 2000;Saber, 2003 and2005;Tournier, 2006b, El-Genk, 2008), Closed Brayton Cycle (CBC) with rotating turbo-machines (e.g., Harty and Mason, 1993;Shepard et al, 1994;Barrett and Reid, 2004;Barrett and Johnson, 2005;Gallo and El-Genk, 2009;El-Genk et al 2010;El-Genk, 1994 and2008), Potassium Rankine cycle (Angelo and Buden, 1985;Yoder and Graves, 1985;Bevard and Yoder, 2003), Thermionic (e.g., El-Genk and Paramonov, 1999;Ranken, 1990;…”

Thermal‐hydraulic analysis of an open‐grid megawatt gas‐cooled space nuclear reactor core

“…The three lowest specific mass belong to TEM, 11 S 4 , 12 and JIMO, 13 which are gas‐cooled reactors combined with dynamic thermal‐to‐electric conversion system. They have higher heat transfer coefficients, 14 including thermal‐to‐electric conversion coefficient and waste heat dissipation coefficient. Accordingly, the gas‐cooled reactor is the desirable choice for megawatt applications in space.…”

Thermal‐hydraulic analysis of gas‐cooled space nuclear reactor power system with closed Brayton cycle

“…A number of dynamic simulation models have been developed to study other integrated SNRPSs. A model for the SP‐100 system, a liquid lithium cooled reactor coupled to a TE energy conversion, was developed and successfully validated 26 . The Russian TOPAZ and TOPAZ‐II power systems, using thermionic fuel element (TFE) are the most technologically experienced and advanced space thermionic reactors .…”

“…For gas‐cooled SNRPS with CBC, Sandia national laboratories 34 developed a system model RPCSIM in SIMULINK platform and analyzed the startup transient of the gas‐cooled SNRPS. El‐Genk et al 26 developed a dynamic model DynMo‐CBC using SIMULINK and simulated the startup of the S 4 ‐CBC power system.…”