https://orcid.org/0009-0000-0092-7496
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Abstract
Microreactors comprise a new actively developing class of very small advanced reactors that have the potential to be an alternative to carbon-intensive energy technologies. A microreactor based on high-temperature gas reactor (HTGR) technology is a very promising advanced reactor with inherent safety, and it can couple with a closed Brayton cycle for higher efficiency. Since dynamics characteristics are fundamental to analyzing a power generation system and a reactor is the main source of the dynamics characteristics of a system, it is necessary to study a microreactor model suitable for system analysis. The main goal is to simulate the performance of the previously mentioned integrated system, focusing on the details of the power conversion unit while still ensuring acceptable calculation times. Hence, a simplified reactor model is needed that could supply sufficiently accurate values of pressure drop and heat transfer across the core. In this paper, by simplifying the physical processes in a microreactor, a dynamic model described by differential algebraic equations is obtained based on the lumped parameter modeling methodology and the basic conservation of fluid mass, momentum, and energy. Coupling thermal hydraulics with neutron kinetics, the temperature coefficient of reactivity and xenon poisoning are considered. Finally, the model is programmed and calculated using Modelica language. The transient responses of the main parameters under typical perturbations are analyzed, and the results show that the responses are correct. Because of the effect of reactivity feedback, fluctuations of the main parameters caused by microperturbations eventually tend to stabilize. In addition, the effects of negative reactivity introduced by xenon poisoning under two typical dynamic processes are analyzed. In power regulation, excess reactivity is required to compensate for the negative reactivity introduced by 135Xe. The model and results can properly predict the systematic parameters and serve as a basis for system analysis of microreactor coupling with the helium closed Brayton cycle.
Acronyms
| FP: | = | full power |
| HTGR: | = | high-temperature gas reactor |
| 135I: | = | iodine-135 |
| LWR: | = | light water reactor |
| ODE: | = | ordinary differential equation |
| RPV: | = | reactor pressure vessel |
| 135Xe: | = | xenon-135 |
Nomenclature
| A | = | = heat transfer area (m2) |
| Ac | = | = sectional area (m2) |
| C | = | = specific heat (J/kg·K) |
| c | = | = concentration of precursors |
| De | = | = diameter (m) |
| f | = | = flow friction resistance coefficient |
| G | = | = helium mass flow rate (kg/s) |
| HPC | = | = high-pressure compressor |
| I | = | = concentration of 135I |
| k | = | = ratio of specific heat |
| L | = | = length (m) |
| LPC | = | = low-pressure compressor |
| M | = | = mass (kg) |
| N | = | = shaft speed (rpm) |
| n | = | = neutron density |
| Nu | = | = Nusselt number |
| P | = | = reactor power (MW) |
| p | = | = pressure (Pa) or (bar) |
| Pr | = | = Prandtl number |
| Re | = | = Reynolds number |
| T | = | = temperature (K) or (°C) |
| u | = | = velocity (m/s) |
| V | = | = volume (m3) |
| X | = | = concentration of 135Xe |
Greek
| α | = | = heat transfer coefficient (W/m2·K); reactivity coefficient (1/K) |
| β | = | = delayed neutron fraction; leakage ratio |
| γ | = | = yield fraction |
| ε | = | = pebble bed porosity |
| η | = | = adiabatic efficiency |
| λ | = | = decay constant (s−1); conductivity (W/m·K) |
| μ | = | = dynamic viscosity (Pa·s) |
| ξ | = | = pressure-recovery coefficient |
| π | = | = pressure ratio |
| ρ | = | = reactivity; density (kg/m3) |
| Σ | = | = macroscopic cross section (m−1) |
| σ | = | = microscopic cross section (m2) |
| = | = neutron flux 1/(cm2·s) | |
| ψ | = | = friction resistance coefficient |
Subscripts
| av | = | = average value |
| C | = | = compressor |
| c | = | = core |
| cr | = | = core to reflector |
| d | = | = design value |
| f | = | = fuel; fission |
| i | = | = i’th group delayed neutron |
| m | = | = moderator |
| r | = | = relative value; reflector |
| rea | = | = reactor |
| T | = | = turbine |
| w | = | = metal wall |
| 0 | = | = rated value |
| 1 | = | = outlet of bottom of RPV |
| 2 | = | = outlet of coolant boreholes |
| 3 | = | = outlet of helium upper plenum |
| 4 | = | = outlet of pebble bed flow channel |
Disclosure Statement
The authors declare that the work described was original research that has not been published previously and is not under consideration for publication elsewhere, in whole or in part.
No potential conflict of interest was reported by the author(s).