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A New Uncertainty-Based Control Scheme of the Small Modular Dual Fluid Reactor and Its Optimization
Abstract and Figures
The small modular dual fluid reactor is a novel variant of the Generation IV molten salt reactor and liquid metal fast reactor. In the primary circuit, molten salt or liquid eutectic metal (U-Pu-Cr) is employed as fuel, and liquid lead works as the coolant in the secondary circuit. To design the control system of such an advanced reactor, the uncertainties of the employed computer model and the physicochemical properties of the materials must be considered. In this paper, a one-dimensional model of a core is established based on the equivalent parameters achieved via the coupled three-dimensional model, taking into account delayed neutron precursor drifting, and a power control system is developed. The performance of the designed controllers is assessed, taking into account the model and property uncertainties. The achieved results show that the designed control system is able to maintain the stability of the system and regulate the power as expected. Among the considered uncertain parameters, the reactivity coefficients of fuel temperature have the largest influence on the performance of the control system. The most optimized configuration of the control system is delivered based on the characteristics of uncertainty propagation by using the particle swarm optimization method.
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... The GB DT-based approach is exemplified on a case study concerning a small modular dual fluid reactor (SMDFR), originally presented in (Liu, Luo, and Macián-Juan 2021). ...
... The GB DT-based approach is here exemplified with reference to the risk monitoring of a SMDFR, whose structure is shown in Fig. 4 (Liu, Luo, and Macián-Juan 2021): the secondary coolant captures the heat produced within the molten salt fuel, and brings it to the heat exchangers and the conventional secondary loop (Lewitz et al. 2020). For the purposes of the presentation of the approach, the physical SMDFR is here simulated by a high-resolution model (Eltosohy et al. 2020). ...
... We consider a parallel arrangement of the models within the digital object (Fig. 3). A onedimensional lumped-parameter model of the actual reactor core dynamics is taken as the WB model in the model repository, made of the point kinetic and the thermohydraulic equations needed to describe the temperature profile and the normalized power inside the core (Liu, Luo, and Macián-Juan 2021). Only two coolant nodes and two fuel nodes are considered, thus reducing the number of differential equations in the system to be solved (Vajpayee et al. 2020). ...
Digital Twins (DTs) can enable real-time monitoring for improved risk assessment and tailored predictive maintenance of Nuclear Power Plants (NPPs). However, typical DTs are based on black-box models and their application is difficult to accept for such safety-critical systems. In this paper, we propose a grey-box DT comprised of: i) a real physical asset whose data/information is gathered from condition monitoring systems; ii) a dynamic white-box model of the NPP; and iii) a feedback loop that retroacts on the real asset. The grey-box DT-based approach is exemplified in a case study concerning a small modular dual fluid reactor (SMDFR) to show its applicability in NPPs.
... Liu et al. presented a small modular dual fluid reactor as a novel variant of the Generation IV molten salt reactor and the liquid metal fast reactor [13]. In the primary circuit, molten salt, or the liquid eutectic metal (U-Pu-Cr), is used as fuel, and liquid lead works as the coolant in the secondary circuit. ...
The main purpose of this special edition of “Advances in Fluid Power Systems” was to present new scientific work in the field of fluid power systems for the hydraulic and pneumatic control of machines and devices that are used in various industries [...]
A molten salt reactor (MSR) has unique safety and economic advantages due to the liquid fluoride salt adopted as the reactor fuel and heat carrier fluid. The operation scheme and control strategy of the MSR plant are significantly different from those of traditional solid-fuel reactors because of the delayed neutron precursors drift with the liquid-fuel flow. In this paper, a simulation platform of the MSR plant is developed to study the control characteristics under normal and accident conditions. A nonlinear dynamic model of the whole system is built in the platform consisting of a liquid-fuel reactor with a graphite moderator, an intermediate heat exchanger and a steam generator. A new control strategy is presented based on a feed-forward and feedback combined scheme, a power control system and a steam temperature control system are designed to regulate load changes of the plant. Three different types of operation conditions are simulated with the control systems, including transients of normal load-follow operation, a reactivity insertion accident and a loss of flow accident. The simulation results show that the developed control system not only has a fast load-follow capability during normal operation, but also has a good control performance under accident conditions.
There are many complex industrial hydraulic systems for which the detailed simulation of their behavior is computationally expensive. Fast three-dimensional (3D) computational approaches need to be developed that can offer the required degree of detail where it is needed, while being computationally efficient. One possibility is to establish multiscale models by developing coupled code systems based on one- or two-dimensional thermal-hydraulic modeling for less relevant system parts and 3D-computational fluid dynamics (CFD) for those locations where high accuracy is important. Despite the increased modeling accuracy achieved by such approaches, their results are always subjected to uncertainty. Safety relevant simulation results should therefore be qualified with uncertainty, so that decission makers can make use of them with the necessary assurance. In addition to uncertainty, sensitivity analysis based on statistical techniques can be applied to the simualtion results to identify weak points in the system design, to quantify the influences of local and global parameters on local/whole system thermal-hydraulics behavior, and to support the design and realization of experiments and measurements involving those systems.
In the frame of the EU-Project SESAME, an experimental facility named TALL-3D loop was built to provide experimental data for code validation and assessment in the simulation of liquid metal coolant loops. In the work presented in the paper a multiscale model of TALL-3D was built by using the coupled ATHLET-ANSYS CFX code system to perform flow simulations based on fast 3D-approaches and to conduct uncertainty and sensitivity analysis of the results. Based on information of the variability of input system parameters, a series of code simulations were performed for selected experimental scenarios to investigate the propagation of uncertainty in the coupled multiscale computational chain, and the uncertainty of the results was compared to the experimental data. It was found that the best-estimate results provided by the coupled code system, together with the uncertainty intervals (tolerance limits) were capable of bounding the experimental data. It is demonstrated that the Uncertainty Quantification (UQ) can be applied for the coupled code system and is able to quantify the simulation results with their uncertainties, which provide more comprehensive information of the real system. Sensitivity analysis allowed for the determination of the influences of input variables on the results, which can be used for the dimension reduction and provide a reference for the experimentalists and manufacturers to reduce the system uncertainty.
The Small Modular Dual Fluid Reactor (SMDFR) is a novel molten salt reactor based on the dual fluid reactor concept, which employs molten salt as fuel and liquid lead/lead-bismuth eutectic (LBE) as coolant. A unique design of this reactor is the distribution zone, which locates under the core and joins the core region with the inlet pipes of molten salt and coolant. Since the distribution zone has a major influence on the heat removal capacity in the core region, the thermal hydraulics characteristics of the distribution zone have to be investigated. This paper focuses on the thermal hydraulics analysis of the distribution zone, which is conducted by the numerical simulation using COMSOL Multiphysics with the CFD (Computational Fluid Dynamics) module and the Heat Transfer module. The energy loss and heat exchange in the distribution zone are also quantitatively analyzed. The velocity and temperature distributions of both molten salt and coolant at the outlet of the distribution zone, as inlet of the core region, are produced. It can be observed that the outlet velocity profiles are proportional in magnitude to the inlet velocity ones with a similar shape. In addition, the results show that the heat transfer in the center region is enhanced due to the velocity distribution, which could compensate the power peak and flatten the temperature distribution for a higher power density.
Design and safety analysis of the currently developed pool type liquid metal cooled fast nuclear reactors is currently impaired by limited operational experience for such systems and insufficient confidence in the predictive capabilities of the applied modelling. Understanding of pool-reactor thermal-hydraulics is crucial for assessment of reactor performance and passive safety systems reliability. Credibility of the analysis tools can be established in the process of code validation, which includes open and blind benchmarks against integral experiments.
TALL-3D is a lead-bismuth eutectic (LBE) loop built to provide experimental data for validation of standalone and coupled system thermal-hydraulics (STH) and computational fluid dynamics (CFD) codes. This paper summarizes the results of the open and blind benchmark exercise, performed using experimental data on natural circulation instability in liquid metal flows from the TALL-3D facility.
An approach for selection of experimental data for benchmark and tests for model input calibration is presented. A list of parameters, initial and boundary conditions are defined based on modelling limitations and sources of experimental uncertainty. A set of requirements and assessment criteria for the blind calculations were specified. Results of simulations are compared to experimental data. Implications of the benchmark test results for the codes validity and lessons learned are reported.
The Dual Fluid Reactor (DFR) is a fast reactor concept proposed by the Institute of Solid-state- and Nuclear physics (IFK) in Berlin. The design of DFR aims to combine the GenIV Molten Salt Reactor (MSR) and the Liquid-Metal Cooled Reactor (SFR, LFR), which means that the molten-salt fuel is no more used as coolant while the heat is removed in a separate loop by liquid lead, to improve these two concepts. Without control rods, DFR is given hope to react and take steps to the change of operation conditions automatically by its inertial negative temperature feedback. Since fuel and coolant are both liquid, the circulation speed of each liquid is considered capable to adjust operational parameters for DFR. The original design of a 3000MWth (Wang, 2017) and a downscaled version of 500MWth (He, 2016) were analyzed in the aspects of reactor physics and thermal-hydraulics. For the practical purpose, this paper has proposed a small modular version of the DFR, which has power output of 2MWth. The reactor with such power level is expected in various applications. Therefore, it is necessary to perform the more explicit analysis on the design than the previous ones. The analysis focuses on the neutronic calculations with the default fuel salt of U-Pu mixture under steady state conditions.
The Dual Fluid Reactor (DFR) is a fast reactor concept proposed by the Institute of Solid-state-and Nuclear physics (IFK) in Berlin. The design of DFR aims to combine the Gen-IV Molten Salt Reactor (MSR) and the Liquid-Metal Cooled Reactor (SFR, LFR), which means that the molten-salt fuel is no more used as coolant while the heat is removed in a separate loop by liquid lead, to improve these two concepts. Without control rods, DFR is given hope to react and take steps to the change of operation conditions automatically by its inertial negative temperature feedback. Since fuel and coolant are both liquid, the circulation speed of each liquid is considered capable to adjust operational parameters for DFR. The original design of a 3000MWth (Wang, 2017) and a downscaled version of 500MWth (He, 2016) were analyzed in the aspects of reactor physics and thermal-hydraulics. For the practical purpose, this paper has proposed a small modular version of the DFR, which has power output of 2MWth. The reactor with such power level is expected in various applications. Therefore, it is necessary to perform the more explicit analysis on the design than the previous ones. The analysis focuses on the neutronic calculations with the default fuel salt of U-Pu mixture under steady state conditions.
The dual fluid reactor (DFR) is a molten salt fast reactor developed by the Institut fuer Festkoerper‐Kernphysik (Berlin) on the basis of the Gen‐IV molten salt reactor and liquid metal–cooled reactor (sodium‐cooled fast reactor and lead‐cooled fast reactor) concepts. In the concept, the fuel is selected with the molten chloride salt and the coolant is the liquid lead. The article establishes the model for the reactor physics analysis and summarizes the preliminary performed calculations and the achieved results so far by the author on the steady‐state reactor physics behavior with the default fuel salt of U‐Pu mixture under zero‐flow‐velocity conditions. They include criticality calculation, neutron spectrum, spatial flux distribution, reaction rates and power distribution, nuclide importance, and temperature coefficient. The conclusion of the article evaluates the reactor physics behavior of the DFR concept and gives comments on the concept itself as well as on the future researches. The article is modified from a part of the PhD thesis of the first author (X. Wang). In this paper, the design of the novel molten salt reactor—dual fluid reactor (DFR)—was validated in the aspect of reactor physics in the steady state by performing a series of calculations including criticality, neutron spectra, temperature feedback coefficient, and sensitivity analysis. The results revealed that this design is feasible in the aspect and shows a sufficient neutronic stability facing possible changes in the fuel salt composition and the temperature fluctuation.
The dual fluid reactor (DFR) is a novel concept of a very high‐temperature (fast) reactor that falls off the classification of generation 4 international forum (GIF). DFR makes best of the two previous designs: molten salt reactor (MSR) and lead‐cooled fast reactor (LFR). In this paper, we present a new reactor design Dual Fluid Reactor metallic (DFRm) with the liquid eutectic U‐Cr metal fuel composition and the lead coolant of which general idea was patented recently. By performing the first steady state neutronic calculations for such a reactor (the neutron flux density as a function of energy, the burnup, the effective multiplication factor/reactivity), we show that this 250‐MWth reactor is critical, and that it can operate almost 20 years without refuelling. We also optimise the geometry (reflector thickness, fuel tubes pin pitch) with respect to the multiplication factor. The optimisation together with some other opportunities for the liquid metal fuel design (eg, the use of electromagnetic pumps to circulate the medium) allows DFRm to be of a small size. This rises economy of the construction as expressed nicely in terms of the energy return on invested (EROI) factor, which is even higher than for the molten salt fuel design (DFRs). Last but not least, we show that DFRm has all the (fuel, coolant, reflector) temperature coefficients negative, which is an important factor of the passive safety.
This article focuses on the validation of the basic design of the distribution zone of the Dual Fluid Reactor (DFR), which is based on the Generation IV Molten-Salt Reactor concept and the Liquid-Metal Cooled Reactor. The distribution zone located under the core joins the core and input pipes of both fluids. On the top of the core, another distribution zone specified for output is also symmetrically set up; however it will not be mentioned in the paper. This distribution zone partitions the inlet flow of the salt, determines the pressure and velocity distribution of the core inlet and influences the neutronic behaviors in the core. This article uses COMSOL as the tool to develop models and to study the pressure and velocity differences of fuel salt and coolant lead in the “original” and “alternative” configurations/designs of the distribution zone in the DFR concept. COMSOL is also used to determine the initial/boundary conditions of configuration variations of the distribution zone by hydraulic modelling and calculations. The simulation results are analyzed and the optimized design is delivered.