Molten Salt Loop Research Articles

Nitrate salt phase transition study for molten salt loop working fluid consideration

Nitrate salt phase transition study for molten salt loop working fluid consideration

UNITY: Kyoto Fusioneering’s Unique Integrated Testing Facility for Fusion Power Generation

One of the major research and development challenges on the critical path to achieving a fusion pilot plant is demonstrating the viability of power production from fusion. In August 2022, Kyoto Fusioneering launched the construction of the world’s first integrated testing facility for fusion power generation. The primary testing loop of the facility will initially adopt PbLi, with the prospect of adding an additional molten salt loop, with dimensions of around 5 × 5 × 3 m with a coolant inventory of approximately 100 L. To be completed in 2025, this facility will demonstrate (1) heat extraction from a mock-up blanket, (2) high-temperature heat transfer and exchange, (3) electricity generation from blanket heat, and (4) hydrogen isotope extraction under commercially relevant conditions—to be completed in time for the first-generation demonstration fusion plants. This facility is named UNITY, standing for Unique Integrated Testing facilitY to symbolize the integration of all critical components.

Steady state performance of molten salt natural circulation loop with different orientations of heater and cooler

Molten salts are proposed as a coolant and sensible heat storage medium for Solar Thermal Power Plant (STPP) as well as fuel and coolant for Molten Salt Reactor (MSR). The objective of the present study is to investigate the steady state behavior of molten salt in natural circulation flow condition along with effect of different orientations of heater and cooler on the steady state mass flow rate. For which a Molten Salt Natural Circulation Loop (MSNCL) has been setup with molten nitrate salt (mixture of Sodium Nitrate and Potassium Nitrate in 60:40 ratio by wt.) as working fluid. Steady state experiments in four different orientations of heater and cooler [Horizontal Heater Horizontal Cooler (HHHC), Horizontal Heater Vertical Cooler (HHVC), Vertical Heater Horizontal Cooler (VHHC) and Vertical Heater Vertical Cooler (VHVC)] have been performed and data generated are compared with the steady state correlations available in open literature which are derived considering either standard friction factor correlations or friction factor correlations deduced from their experiments and theoretical studies. Based on the deviations observed in the experimental values and correlation predictions, an improved formulation has been derived. The steady state formulation has been improved by incorporating Wall Thermal Inertia (WTI) effect and Heat Loss (HL) effect considering the importance of WTI & HL in dealing with high temperature molten salt loop. The improved formulation has been compared with the experimental results for different orientations of heater and cooler. Further, a new friction factor correlation has also been deduced from the experiments for vertical heater orientation. Description of MSNCL along with validation studies performed for different steady state correlation against experimental data generated in MSNCL, are reported in this paper.

Computational fluid dynamics analysis of the natural circulation system in vertical heater horizontal cooler (VHHC) molten salt loop

Molten salt has attracted the attention of researchers, especially as a coolant because of its characteristics. This study aimed to analyse the transient and steady-state of the natural circulation system in the molten salt loop with vertical heater and horizontal cooler using computational fluid dynamics. The computational fluid dynamics module in the COMSOL Multiphysics software was used to solve governing equations. Experimental data from several references were used as input data in modelling. The loop was modelled as a rectangular loop with Inconel 625 as the pipe material and molten salt (NaNO3+KNO3) as the working fluid. The variation of heater power was also carried out in modelling. The modelling results showed a good agreement with the experimental results. The results provided that the molten salt natural circulation loop with vertical heater and horizontal cooler showed good flow stability without reversal of flow direction.

Heat generation depth and temperature distribution in solar receiver tubes subjected to induction

Induction heating is commonly used in laboratory-scale facilities to replicate the heating conditions of the receiver tubes of concentrated solar power plants. This work aims at shedding light at the induction heating characteristics for such applications through the development of a multiphysics numerical model capable of replicating the experimental conditions of a molten salt loop locally heated by an induction heater. In the experiments, a stainless steel pipe is heated on its external surface by the induction heater, which is switched on and off during the experimental data acquisition while molten salts are continuously circulating in its interior. These conditions are replicated, for the first time, in a two-dimensional numerical domain fully coupling the electromagnetic and thermal physics, including thermally dependent material properties of the heated pipe. Once validated against the experiments, the numerical results revealed that the volumetric nature of the induction heating shall be considered for an accurate representation of the temperature profile inside the tube. As a novelty, different equivalent surface boundary conditions are presented and, despite the Gaussian-like behavior of the induction heating on the surface of the tube, the results indicate that there exists no equivalent wall boundary condition to fully replicate the temperature profile obtained with the induction heater. The effect of independently varying experimental parameters such as the geometry of the pipe (i.e., diameter and thickness) and its distance to the induction heating system is also evaluated. Using large diameters of the tube reduces the difference between the angular temperature profile obtained using induction heating and a simplified wall boundary condition. For small wall thicknesses, the induction heating is capable of penetrating along the whole thickness of the tube, the total heat generated in the volume of the tube being exposed to the counteracting effects of the volumetric generation and the enhancement of the heat dissipation by the molten salt, as both of them increase for small thicknesses. The distance of the inductor to the pipe wall appears to maintain the volumetric characteristics of the heating and only affects the induction heating magnitude and efficiency. • Fully coupled model of induction heating of a molten salt pipe is presented. • Induction promotes a volumetric heat generation in the pipe. • No equivalent surface heating can replicate induction heating. • Effect of different pipe geometries on the induction heating was characterized. • Induction reaches the whole pipe thickness for sufficiently thin tubes.

Experimental and numerical study of the heat transfer process during the startup of molten salt tower receivers

During the startup operation of molten salt solar tower plants, the tubes of the receiver are subjected to a high nonhomogeneous heat flux along with a low heat transfer coefficient to the air inside the tube, which results in a highly uneven angular temperature distribution. This uneven temperature distribution causes thermal stresses and tube deflection in the receiver. The most important constraint for the design and operation of central receivers is to keep the intercepting solar flux within the tube mechanical safety limits. In this work, an experimental facility consisting of a molten salt loop that simulates a solar tower receiver tube is used to measure the outer surface temperature and the deflection of the tube under the startup operating conditions of a solar tower power plant. An inverse heat transfer problem is applied to obtain the heat flux onto the receiver tube from the outer surface temperature measurements. To solve the inverse problem, a transient three-dimensional numerical model of an empty circular pipe subjected to a nonhomogeneous heat flux is developed. A good agreement between the experimental and calculated tube temperatures and deflection is observed, with differences of 7% and 10%, respectively. Moreover, the thermal stresses are calculated. It has been found that higher thermal stresses are obtained when the tube is preheated compared to the stress when the molten salt is flowing under similar heat flux conditions.

Experimental and numerical studies on natural circulation behavior of heat exchanger for molten salt loop

ABSTRACT In this study, the flow and heat transfer of a double molten salt working fluid heat exchanger (DHX) in a high-temperature molten salt natural circulation experimental loop were investigated both experimentally and numerically. The experimental results demonstrated that the actual heat transfer of the DHX was superior, and the heat transfer coefficient of the DHX tube increased with the heating power. The simulation results agreed strongly with experimental data, proving that the proposed model was reasonable and feasible. The temperature and velocity distributions were obtained, and the flow flux distribution in the DHX tube was uniform. These results provide a reference for the design of a double molten salt heat exchanger in the passive decay-heat removal system of a fluoride salt-cooled high-temperature reactor.

Novel parabolic trough power system integrating direct steam generation and molten salt systems: Preliminary thermodynamic study

A novel hybrid parabolic trough power system that integrates direct steam generation and molten salt systems is proposed in this study to stably and efficiently operate solar power plants. The feedwater from the power block is preheated and evaporated in a low temperature direct steam generation solar field. A high-temperature solar field using molten salt as heat transfer fluid is employed to superheat and reheat the steam to 540 °C. The heat transfer model based on energy conversion and balance is applied to numerically investigate the overall performance of various power plants. This paper presents a comparative study of the effects of different locations, steam turbines, and system configurations on the outputs of the power plants. The hybrid systems exhibit favorable system stability and reliability and an excellent overall performance. The molten salt loop percentages of hybrid systems with and without reheat section are only 45.1% and 37.4%, which lead to low energy loss in the operation period and low molten salt freezing protection energy. The annual thermal energy productions of the hybrid systems with and without the reheat section in Tonopah are 685.1 and 691.7 GWh, and the percentages of energy required for freezing protection of those systems are 3.2% and 2.7%, respectively. The hybrid systems with reheat section exhibit optimal electricity production and economic performances compared with those of other configurations. The electricity production increments of novel systems in Tonopah and Lhasa are 14.0% and 14.8%, respectively, compared with those of molten salt systems.

Inverse heat problem of determining unknown surface heat flux in a molten salt loop

Inverse heat transfer problems typically rely on temperature measurements for estimating unknown boundary heat flux, such as that in the water tubes of steam boilers or central receivers in solar tower power plants. In this work, an experimental facility consisting of a molten salt loop that simulates a tube of a solar tower receiver is presented to obtain the outer tube surface temperatures under solar tower power plant operating conditions. The external surface f the pipe in the test section is heated in a controlled manner with an induction heater, which provides a very high nonuniform heat flux. An inverse thermal method has been applied to obtain the incident heat flux onto the receiver tube from the outer surface temperature measurements. To solve the inverse problem, a transient two-dimensional numerical model of a circular pipe flowing molten nitrate salt and subjected to a nonhomogeneous circumferential heat flux has been developed. The heat flux calculation with the inverse method is in accordance with the heat flux estimation based on the calibration of the induction heater. A good agreement between the experimental and calculated temperatures is observed. Furthermore, the deflection of the tube caused by the nonhomogeneous heat flux is measured and is compared to the deflection calculated from the radial temperature profile from the inverse problem solution, and a good agreement between both results is observed.

Experimental and theoretical studies on the natural circulation behavior of molten salt loop

Molten salts are increasingly getting attention as a coolant and storage medium in solar thermal power plants and as a liquid fuel, blanket and coolant in High Temperature Reactors (HTR). A Molten Salt Natural Circulation Loop (MSNCL) has been setup for thermal hydraulics, instrument development and material related studies relevant to HTR and solar power plants. The loop mainly consists of heated section, air heat exchanger, valves, various tanks and argon gas control system. All the components and piping of the loop are made of Inconel 625. Steady state natural circulation experiments at different power level have been performed in the loop. Transient studies for startup of natural circulation, loss of heat sink, heater trip and step change in heater power have also been carried out. A one dimensional code LeBENC, developed in-house to simulate the natural circulation characteristics in closed loops, has been validated with the experimental data obtained from MSNCL. This paper deals with the description of the loop and experimental studies carried out in the loop. Detailed validation of the LeBENC code with the experimental data has also been discussed in the paper.

Validation of electro-thermal simulation with experimental data to prepare online operation of a molten salt target at ISOLDE for the Beta Beams

The main objective of the Beta Beams is to study oscillation property of pure electrons neutrinos. It produces high energy beams of pure electron neutrinos and anti-neutrinos for oscillation experiments by beta decay of 6He and 18Ne radioactive ion beams, stored in a decay ring at γ=100. The production of 6He beam has already been accomplished using a thick beryllium oxide target. However, the production of the needed rate of 18Ne has proven to be more challenging. In order to achieve the requested yield for 18Ne a new high power target design based on a circulating molten salt loop has been proposed. To verify some elements of the design, a static molten salt target prototype has been developed at ISOLDE and operated successfully. This paper describes the electro-thermal study of the molten salt target taking into account the heat produced by Joule effect, radiative heat exchange, active water cooling due to forced convection and air passive cooling due to natural convection. The numerical results were compared with the available experimental data in order to validate the model. This approach allows one to improve the reliability of the model, which will help to predict the thermo-mechanical impact of the required targets for future facilities such as HIE-ISOLDE and the Beta-Beams.

Fabrication of the Hydrogen Recovery Unit in the Molten Salt Loop Orosh<sup>2</sup>i-1 and Preliminary Evaluation for Hydrogen Transfer

Fabrication of the Hydrogen Recovery Unit in the Molten Salt Loop Orosh<sup>2</sup>i-1 and Preliminary Evaluation for Hydrogen Transfer

水素・熱回収両立試験溶融塩ループOrosh2i-1における水素回収部の設計と製作

水素・熱回収両立試験溶融塩ループOrosh2i-1における水素回収部の設計と製作

水素・熱回収両立試験溶融塩ループOrosh2i-1 における水素回収部の水素透過能

水素・熱回収両立試験溶融塩ループOrosh2i-1 における水素回収部の水素透過能

Experimental research on molten salt thermofluid technology using a high-temperature molten salt loop applied for a fusion reactor Flibe blanket

Experimental research on molten salt thermofluid technology using a high-temperature molten salt loop (MSL) is described in this paper. The MSL was designed to be able to use Flibe as a coolant, however, a simulant, heat transfer salt (HTS) has to be used alternatively since Flibe is difficult to operate under avoiding a biohazard of Be. Experiment on heat-transfer enhancement, that is required for applying to cool the high heat flux components of fusion reactors, is ongoing. Preliminary experimental results showed that an internal structure of a mixing chamber in the MSL was important to obtain accurate bulk temperatures under severe thermal conditions. For operating the loop, careful handling are needed to proceed how to melt the salt and to circulate it in starting the operation of the MSL. It is concluded that several improvements proposed from the present experiences should be applied for the future Flibe operation.

Design and development of the Flibe blanket for helical-type fusion reactor FFHR

Blanket design is in progress in helical-type compact reactor FFHR-2. A localized blanket concept is proposed by selecting molten-salt Flibe as a self-cooling tritium breeder from the main reason of safety: low tritium solubility, low reactivity with air and water, low pressure operation, and low MHD resistance which is compatible with the high magnetic field design in force-free helical reactor (FFHR). Numerical results are presented on nuclear analyses using the MCNP-4B code, on thermal and stress analyses using the ABAQUS code, and heat exchange efficiency from Flibe to He. R&D programs on Flibe engineering are also in progress in material dipping-tests and in construction of molten salt loop. Preliminary results in these experiments are also presented.