Liquid level detection device for molten salt pumps

Abstract

To provide a liquid level detection device of a molten salt pump capable of correctly detecting a liquid level of molten salt in a conductive manner, even if moisture included in water dilution molten salt evaporates and condenses in the pump.SOLUTION: A liquid level detection device 1 detecting liquid level height of molten salt in a pump chamber 3 of a molten salt pump 104 is equipped with a pump chamber 3 sucking / discharging molten salt, an impeller 9 that rotates around a rotary shaft 23 penetrating the pump chamber 3, a pump chamber mechanism seal 11 that is provided around an outer periphery of a penetrating portion of the rotary shaft 23, and a gas introducing port 13 that fills gas into the pump chamber 3 and maintains the liquid level height of the molten salt below the pump chamber mechanical seal. The liquid level detection device 1 is equipped with a common electrode 17 electrically grounded, a detection electrode 19 in which at least a part of a surface exposed into the pump chamber 3 is covered by an insulation layer 46, and a liquid level meter 21 that detects the height of a lower end 55 of the detection electrode 19 as the liquid level height of the molten salt when the common electrode 17 and the detection electrode 19 are electrically connected through the molten salt.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a liquid level detection device for a molten salt pump.

Background Art

[0002] Molten salt is a salt composed of cations and anions that is solidified at normal temperature but melts into a molten state when the temperature reaches a certain level or higher. Among molten salts, there is a substance called HTS (Heat Transfer Salt) that is used as a sensible heat type heat medium that stores and releases heat without undergoing a phase change, and is used to heat heat exchangers, reactors, etc. Examples of HTS include a mixture of sodium nitrite, sodium nitrate, and potassium nitrate. This mixture is also called Niter, which is derived from the English name of potassium nitrate crystals.

[0003] When using molten salt such as HTS as a heat medium, a molten salt pump is required to send HTS from a heating device that heats HTS to a heating target or a heat preservation target. The structure of the molten salt pump can be exemplified by a centrifugal pump. On the other hand, since HTS is a material that solidifies when the temperature drops below a certain level, the molten salt inhaled and discharged by the molten salt pump that sends HTS will contact the components that make up the pump, such as mechanical seals, and solidify when the temperature drops below a certain level. In this state, the solidified molten salt adheres to the mechanical seal, causing problems such as the drive shaft supported by the mechanical seal not being able to move, or the lubricating oil leaking from the damaged part due to the adhered molten salt damaging the mechanical seal. Therefore, the molten salt pump requires a structure that prevents such components from contacting HTS. For example, in Patent Document 1, the inside of the molten salt pump is filled with gas to pressurize the molten salt downward, and the liquid level of the molten salt in the chamber is pushed below the mechanical seal, which is the bearing of the rotation axis of the impeller, to prevent the molten salt from contacting the mechanical seal. More specifically, the liquid level of the molten salt is measured by a level switch inside the pump, the filling amount of the gas is adjusted based on the measurement result, and the liquid level height is adjusted by maintaining the pump internal pressure at a pressure intermediate between the tank liquid level and the lift pressure and pump circulation liquid pressure between the pumps. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-231874 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Liquid level detection devices include a common electrode that is grounded and a conductive type that detects the liquid level of the molten salt by measuring the height of the lower end of the detection electrode when current is passed through the molten salt. There are also water-diluted molten salts, which are diluted with water to lower the freezing point. However, when attempting to detect the liquid level using a conductive liquid level detection device while simultaneously drawing in / discharging a water-diluted molten salt with a molten salt pump, water vapor evaporated from the molten salt may condense and connect the detection electrode and the molten salt pump, creating a conductive connection between them. In this case, even though the actual liquid level of the molten salt is lower than the lower end of the conductive detection electrode, the liquid level detection device may incorrectly detect the liquid level as corresponding to the lower end of the conductive detection electrode, resulting in an inaccurate detection of the liquid level.

[0006] The present invention has been made in view of the above problems, and aims to provide a liquid level detection device for a molten salt pump that can accurately detect the liquid level of the molten salt in a conductive manner, even when the water contained in the water-diluted molten salt evaporates and condenses inside the pump. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention provides a pump chamber for drawing in / discharging a molten salt diluted with water, an impeller positioned in the pump chamber that draws in / discharges the molten salt by rotating around a rotating shaft that passes through the pump chamber and whose axial direction is upward, a pump chamber mechanical seal provided around the outer circumference of the part in which the rotating shaft passes through the pump chamber, and a liquid level adjustment means for filling the pump chamber with inert gas to push down the molten salt and maintain the liquid level of the molten salt in the pump chamber below the pump chamber mechanical seal, wherein a mixture of sodium nitrite, sodium nitrate, and potassium nitrate is used as the molten salt, and the heating temperature of the molten salt diluted with water is 400°C to 500°C. ℃ A liquid level detection device for a molten salt pump in the range of a molten salt pump, for detecting the liquid level of the molten salt in the pump chamber, comprising: a rod-shaped common electrode that protrudes downward from above the pump chamber into the interior of the pump chamber and is electrically grounded; a rod-shaped detection electrode that protrudes downward from above the pump chamber into the interior of the pump chamber and is connected to the pump chamber via an insulating member, with at least a portion of the surface of the surface exposed in the pump chamber, excluding the lower end, covered by an insulating layer; and a liquid level gauge that is electrically connected to the common electrode and the detection electrode, and detects the height of the lower end of the detection electrode in the pump chamber as the liquid level of the molten salt when the common electrode and the detection electrode conduct electricity through the molten salt, wherein the insulating layer is made of alumina. [Effects of the Invention]

[0008] In this invention, even if the water contained in the water-diluted molten salt evaporates and condenses near the detection electrode, the condensation occurs between the insulating layer covering the surface of the detection electrode and the inner wall of the pump chamber. As a result, the insulating layer prevents current from flowing between the pump chamber and the detection electrode via the condensed water. Therefore, erroneous detection of the liquid level by the liquid level gauge, which occurs when the pump chamber and detection electrode are energized through condensed water, is prevented, and the liquid level of the molten salt can be accurately detected using a conductive method. Therefore, according to the present invention, it is possible to provide a liquid level detection device for a molten salt pump that can accurately detect the liquid level of the molten salt in a conductive manner, even when the water contained in the water-diluted molten salt evaporates and condenses inside the pump. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of a molten salt circulation system using a molten salt pump equipped with a liquid level detection device according to the first embodiment of the present invention. [Figure 2] Figure 1 is a longitudinal cross-sectional view showing the molten salt pump, with the motor and rotating shaft shown in the front view. [Figure 3] Figure 1 is an enlarged view of the vicinity of the detection electrode, with the detection electrode and terminals shown in a side view. [Figure 4] This figure shows a molten salt pump equipped with a liquid level detection device according to a second embodiment of the present invention, and corresponds to Figure 3 in the first embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail based on the drawings. First, with reference to Figures 1 and 2, a schematic configuration of a molten salt circulation system 100 using a molten salt pump 104 equipped with a liquid level detection device 1 according to the first embodiment of the present invention will be described.

[0011] Here, as an example of a circulation system 100, a system is shown in which a water-diluted molten salt, which is obtained by diluting HTS (a type of molten salt) with water, is circulated, and the water-diluted HTS is used to heat and maintain the temperature of the HTS-using equipment 103.

[0012] As shown in Figure 1, the circulation system 100 includes an HTS tank 101, a molten salt pump 104, HTS usage equipment 103, and an expansion tank 105. The HTS tank 101 stores the water-diluted HTS and is a device that adjusts the temperature and concentration of the water-diluted HTS by heating it or diluting it with water.

[0013] The HTS tank 101 shown in Figure 1 comprises a storage tank 102, a heater 115, a power supply 117, a water injection pipe 119, and a vent pipe 121. The storage tank 102 is a container for storing the water-diluted HTS, and in Figure 1, it is illustrated as a horizontally placed cylindrical container with hemispherical ends. The heater 115 is a device for heating the water-diluted HTS and is placed inside the storage tank 102. The heater 115 can use any known heating method as long as it can raise the water-diluted HTS to the desired temperature. In Figure 1, a resistance heating type is illustrated as the heater 115. The power supply 117 is a power supply that drives the heater 115, and if the heater 115 is a resistance heating type, it is the power supply that energizes the heater 115 to heat it. The water injection pipe 119 is a pipe that injects the dilution water used to dilute the water-diluted HTS into the storage tank 102, and in Figure 1, it is connected to the upper end of the storage tank 102. The vent pipe 121 is a pipe that releases gases such as water vapor from inside the storage tank 102 to the atmosphere, and is connected to the storage tank 102 via a dust collector such as a cyclone (not shown).

[0014] The molten salt pump 104 is a pump for circulating the heated water-diluted HTS within the circulation system 100. The suction port 5 shown in Figure 2 is connected to the storage tank 102 via the piping 107 through which the heated water-diluted HTS flows, and the pump draws in the heated water-diluted HTS and discharges it from the discharge port 7 at a desired flow rate.

[0015] The HTS-using equipment 103 shown in Figure 1 is equipment that utilizes the heat of water-diluted HTS heated by the heater 115 of the HTS tank 101. More specifically, HTS-using equipment 103 is equipment that uses water-diluted HTS as a heat transfer medium to heat the fluids used in the equipment, such as heat exchangers and reactors.

[0016] The HTS usage equipment 103 is connected to the discharge port 7 shown in FIG. 2 of the molten salt pump 104 via a pipe 108, and the heated water-diluted HTS discharged by the molten salt pump 104 flows in via the pipe 108. In FIG. 1, a bypass pipe 109 branches off from the pipe 108 midway. The bypass pipe 109 is a pipe that returns the heated water-diluted HTS discharged by the molten salt pump 104 to the HTS tank 101 without sending it to the HTS usage equipment 103, and the downstream end is connected to the storage tank 102 of the HTS tank 101. Valves (not shown) are provided at the portion closer to the HTS usage equipment 103 than the connection portion of the pipe 108 with the bypass pipe 109 and in the bypass pipe 109. When stopping the operation of the circulation system 100, by closing the valve of the pipe 108 and opening the valve of the bypass pipe 109, the water-diluted HTS discharged by the molten salt pump 104 is returned to the HTS tank 101 without being sent to the HTS usage equipment 103.

[0017] Also, when the flow rate of the heated water-diluted HTS discharged by the molten salt pump 104 is too large with respect to the flow rate of the heated water-diluted HTS required by the HTS usage equipment 103 during the operation of the circulation system 100, both the valve of the pipe 108 and the valve of the bypass pipe 109 are opened. Thereby, by returning a part of the heated water-diluted HTS discharged by the molten salt pump 104 to the HTS tank 101, the flow rate of the heated water-diluted HTS flowing from the pipe 108 into the HTS usage equipment 103 is reduced.

[0018] The expansion tank 105 is a siphon breaker that sucks in the heated water-diluted HTS remaining in the HTS-using facility 103 and returns it to the HTS tank 101 when the operation of the circulation system 100 is stopped. Specifically, the expansion tank 105 is connected to the HTS-using facility 103 via a pipe 111 through which the heated water-diluted HTS flows during the operation of the circulation system 100. The expansion tank 105 is connected to the storage tank 102 of the HTS tank 101 via a pipe 113 through which the heated water-diluted HTS flows. The expansion tank 105 is further connected to the storage tank 102 via an equalizing pipe 123. The equalizing pipe 123 is a pipe through which gas flows to equalize the gas pressures in the HTS tank 101 and the expansion tank 105. In this way, the expansion tank 105 always functions as a siphon breaker so that the flow path of the heated water-diluted HTS does not act as a siphon by equalizing the gas pressures in the HTS tank 101 and the expansion tank 105 with the equalizing pipe 123.

[0019] When the circulation system 100 is operated with this configuration, the water-diluted HTS heated to a desired temperature by the heater 115 circulates through the molten salt pump 104 as HTS tank 101 → molten salt pump 104 → HTS-using facility 103 → expansion tank 105 → HTS tank 101. In FIG. 1, it circulates in the order of the arrows A1 → A2 → A3 → A5 → A6. At this time, the heated water-diluted HTS warms the fluid in the HTS-using facility 103. Also, a part of the heated water-diluted HTS discharged from the molten salt pump 104 as necessary flows from the bypass pipe 109 in the direction of A4 in FIG. 1 and returns to the HTS tank 101. In this configuration, in order to lower the freezing point of the HTS to an easily handled temperature, it is necessary to dilute the HTS by injecting a diluting water in an amount that does not impair the performance as a medium of the HTS from the water injection pipe 119 into the HTS tank.

[0020] The above is the description of the schematic configuration of the molten salt circulation system 100 using the molten salt pump 104 provided with the liquid level detection device 1 according to the first embodiment. Next, referring to FIGS. 2 and 3, the details of the structures of the molten salt pump 104 and the liquid level detection device 1 will be described.

[0021] The molten salt pump 104 shown in Figure 2 is a centrifugal pump and comprises a pump chamber 3, an impeller 9, a rotating shaft 23, a motor 27, a pump chamber mechanical seal 11, a shaft chamber 25, a motor chamber 29, a gas inlet 13, a gas outlet 15, and a liquid level detection device 1.

[0022] Pump chamber 3 is a container for drawing in and discharging water-diluted HTS, and in Figure 2, its vertical cross-section is elliptical. Pump chamber 3 has an intake port 5 on its bottom surface for drawing in water-diluted HTS, and an outlet port 7 on its side surface for discharging water-diluted HTS. In some cases, pump chamber 3 is provided with a partition plate 31 to mitigate a rapid rise in the liquid level of water-diluted HTS in pump chamber 3 when the amount of water-diluted HTS being drawn in increases rapidly. However, since the partition plate 31 has an opening, the partition plate 31 does not constitute a watertight compartment within pump chamber 3, and the liquid level of water-diluted HTS in pump chamber 3 does not differ in height depending on the location. Pump chamber 3 is also provided with a drain pipe (not shown) to discharge water-diluted HTS in pump chamber 3 when the molten salt pump 104 is stopped, so that water-diluted HTS does not remain in pump chamber 3 and solidify when the molten salt pump 104 is stopped and the circulation system 100 is stopped.

[0023] The impeller 9, also called the impeller, rotates within the pump chamber 3, drawing the diluted HTS into the pump chamber 3 through the inlet 5 and then discharging it through the outlet 7 using centrifugal force generated in the HTS. The impeller 9 is circular in plan view, with blades arranged on its surface. The impeller 9 shown in Figure 2 is located on the underside of the pump chamber 3, directly above the inlet 5, with its underside facing the inlet 5. The impeller 9 shown in Figure 1 rotates upward, in this case vertically, as its central axis. A centrifugal pump in which the axis of rotation of the impeller 9 is oriented vertically is also called a vertical pump.

[0024] The rotating shaft 23 is the axis that rotates the impeller 9, and the impeller 9 rotates around the rotating shaft 23. The rotating shaft 23 has its axial direction upward, in this case vertically, and passes through the upper end of the pump chamber 3. The lower end of the rotating shaft 23 is fastened to the rotation center of the impeller 9 with bolts or the like.

[0025] Motor 27 is an electric motor that generates power to rotate the impeller 9 and is located above the pump chamber 3. The output shaft of motor 27 is connected to the upper end of the rotating shaft 23, and the power generated by motor 27 is transmitted to the impeller 9 via the rotating shaft 23.

[0026] The pump chamber mechanical seal 11 is a mechanical shaft sealing device that prevents oil for lubricating the rotating shaft 23 from leaking into the pump chamber 3 from the portion where the rotating shaft 23 penetrates the pump chamber 3, and is installed around the outer circumference of the portion where the rotating shaft 23 penetrates the pump chamber 3.

[0027] The shaft chamber 25 is a cylindrical container with closed upper and lower ends that surrounds the rotating shaft 23 which extends upward through the pump chamber 3. The rotating shaft 23 passes through the upper and lower ends of the shaft chamber 25. A pump chamber mechanical seal 11 is provided around the outer circumference of the lower end penetration, and a shaft chamber mechanical seal 12 is provided around the outer circumference of the upper end penetration. The shaft chamber mechanical seal 12, like the pump chamber mechanical seal 11, is a mechanical shaft sealing device that prevents oil for lubricating the rotating shaft 23 from leaking out of the shaft chamber 25 from the portion where the rotating shaft 23 passes through the shaft chamber 25. The lower end of the shaft chamber 25 is fastened to the upper end of the pump chamber 3 with bolts or the like (not shown). Inside the shaft chamber 25, cooled lubricating oil is constantly circulated while the molten salt pump 104 is in operation in order to maintain lubrication and cooling performance for the pump chamber mechanical seal 11 and the shaft chamber mechanical seal 12. The motor chamber 29 is a container that houses the motor 27, and is located above the pump chamber 3 and the shaft chamber 25. Its lower end is fastened to the upper end of the shaft chamber 25 with bolts or the like (not shown).

[0028] The gas inlet 13 is a gas pipe that fills the pump chamber 3 with gas, pressurizing the water-diluted HTS with gas pressure and pushing it down as shown by the white arrow Z1 in Figure 2, thereby lowering the liquid level of the water-diluted HTS in the pump chamber 3 below the pump chamber mechanical seal 11. The gas inlet 13 penetrates the outer wall of the pump chamber 3 and connects the inside and outside of the pump chamber 3. The upstream end of the gas inlet 13, that is, the end of the gas inlet 13 outside the pump chamber 3, is connected to a gas supply source such as a compressor via a solenoid valve (not shown). In this configuration, when the liquid level of the water-diluted HTS is about to exceed the height of the pump chamber mechanical seal 11, the solenoid valve is opened to fill the pump chamber 3 with gas and lower the liquid level of the water-diluted HTS. The gas used for filling can be any gas that does not react with the materials that make up the HTS or pump room 3; for example, an inert gas such as nitrogen gas can be used.

[0029] The gas outlet 15 is a pipe that exhausts the gas inside the pump chamber 3 to the outside of the pump chamber 3, and it penetrates the outer wall of the pump chamber 3, connecting the inside and outside of the pump chamber 3. The gas outlet 15 is equipped with a solenoid valve (not shown), and when the liquid level of the water-diluted HTS falls below a predetermined height, the solenoid valve opens to exhaust the gas inside the pump chamber.

[0030] In this way, by introducing gas from the gas inlet 13 and pushing down the water-diluted HTS, the liquid level of the water-diluted HTS in the pump chamber 3 can be maintained below the pump chamber mechanical seal 11 while simultaneously drawing in / discharging the water-diluted HTS. Therefore, the gas inlet 13 functions as a liquid level adjustment means that maintains the liquid level of the water-diluted HTS in the pump chamber 3 below the pump chamber mechanical seal 11. Furthermore, if the liquid level of the water-diluted HTS in the pump chamber 3 is pushed down too much, the gas is exhausted from the gas outlet 15 to prevent the liquid level of the water-diluted HTS from dropping too low and becoming unable to be discharged. In addition, to prevent water-diluted HTS from flowing into the gas inlet 13 and gas outlet 15, the installation height of the gas inlet 13 and gas outlet 15 is higher than the maximum liquid level of the water-diluted HTS in the pump chamber 3 that is allowed when the molten salt pump 104 is running. Furthermore, the pressure of the gas introduced from the gas inlet 13 is adjusted to be higher than the pressure of the gas in the pump chamber 3.

[0031] The liquid level detection device 1 is a device that detects the liquid level of the water-diluted HTS in the pump chamber 3. The pressure of the gas filling the pump chamber 3 through the gas inlet 13 must be higher than the pressure of the gas in the pump chamber 3 and is determined by the liquid level of the water-diluted HTS. Therefore, the liquid level detection device 1 is electrically connected to a solenoid valve (not shown) or a control unit that operates the solenoid valve, which is connected to the gas inlet 13 or gas outlet 15, and transmits the detected liquid level to them. In addition, the molten salt pump 104 stops operation if the liquid level of the water-diluted HTS in the pump chamber 3 is about to exceed the height of the pump chamber mechanical seal 11, or if it is too low to discharge the water-diluted HTS. Therefore, the liquid level detection device 1 is also electrically connected to a control unit (not shown) that controls the drive of the motor 27 of the molten salt pump 104, and transmits the detected liquid level. However, the flow rate control of the water-diluted HTS drawn in / discharged by the molten salt pump 104 by the motor 27 and the control of the liquid level of the water-diluted HTS by the gas inlet 13 may be controlled independently.

[0032] The liquid level detection device 1 shown in Figures 2 and 3 is a conductive type that detects the liquid level of the water dilution HTS by measuring the height of the lower end 55 of the detection electrode 19 when current is passed through the water dilution HTS to the grounded common electrode 17 and the ungrounded detection electrode 19. Therefore, the liquid level detection device 1 comprises a common electrode 17, a detection electrode 19, and a liquid level gauge 21.

[0033] The common electrode 17 is a rod-shaped conductive electrode that protrudes downward from above the pump chamber 3 into the interior of the pump chamber 3 and is electrically grounded. Specifically, the common electrode 17 is grounded by being electrically connected to the pump chamber 3. The common electrode 17 is the electrode that indicates the reference potential, in this case 0V, when the liquid level detection device 1 detects the liquid level height of the water-diluted HTS. Therefore, when detecting the liquid level height of the water-diluted HTS, it is necessary for the common electrode 17 to always be in contact with the water-diluted HTS. For this reason, the height of the lower end of the common electrode 17 corresponds to the minimum liquid level height L0 of the water-diluted HTS in the pump chamber 3 that is allowed when the molten salt pump 104 is driven.

[0034] The common electrode 17 can be made from any known material that is conductive, does not deteriorate with water dilution HTS, and does not deform or deteriorate due to the temperature and atmosphere of the gas in the pump room 3 when the circulation system 100 is in operation. For example, austenitic stainless steels such as SUS304 and SUS316 can be used as examples of materials for the common electrode 17.

[0035] The detection electrode 19 is a rod-shaped conductive electrode that protrudes downward from above the pump chamber 3 into the interior of the pump chamber 3 and is connected to the pump chamber 3 via an insulating member. It is generally made of the same material as the common electrode 17. As shown in Figure 3, a terminal 53 for connecting a wire when connecting to the liquid level gauge 21 is provided at the upper end of the detection electrode 19. A terminal 53 is also provided at the upper end of the common electrode 17. To describe the connection structure between the detection electrode 19 and the pump chamber 3 in more detail, a circular opening 41 is provided near the side end of the upper end of the pump chamber 3, as shown in Figure 3. Furthermore, a tubular electrode housing tube 51 is provided that protrudes upward from the opening 41 and communicates with the pump chamber 3 through the opening 41. The electrode housing tube 51 is a tube that fixes the detection electrode 19 and comprises a lower electrode housing tube 43, an upper electrode housing tube 45, fastening bolts 47, and an insulating sleeve 49.

[0036] The lower electrode housing tube 43 is a tube fixed to the pump chamber 3, and its axial lower end is fitted into the inner circumference of the opening 41 and connected by welding or the like. The axial upper end 43a of the lower electrode housing tube 43 has threads on its inner circumference.

[0037] The upper electrode housing tube 45 is a component that supports the detection electrode 19. The upper electrode housing tube 45 has threads on the outer circumference of its axial lower end 45a, and the threads on the outer circumference of the lower end 45a engage with the threads on the inner circumference of the upper end 43a of the lower electrode housing tube 43, thereby fixing it to the lower electrode housing tube 43. The upper electrode housing tube 45 also has threads cut into the inner circumference of its upper end 45b.

[0038] The fastening bolt 47 is a component that supports the insulating sleeve 49 and the detection electrode 19 and fixes them to the upper electrode housing tube 45, and is a bolt having a through hole 47a formed in the axial direction. The fastening bolt 47 is fixed to the upper electrode housing tube 45 by screwing the threads 47b formed on the outer circumference of the bolt into the threads on the inner circumference of the upper end 45b of the upper electrode housing tube 45.

[0039] The insulating sleeve 49 is a tube that acts as an insulating member, insulating and connecting the fastening bolt 47 and the detection electrode 19. The outer diameter of the insulating sleeve 49 is approximately the same as the inner diameter of the through hole 47a of the fastening bolt 47, and it is fixed by fitting or screwing into the through hole 47a of the fastening bolt 47. The inner diameter of the insulating sleeve 49 is approximately the same as the outer diameter of the detection electrode 19, and the detection electrode 19 is fixed to the electrode housing tube 51 by being inserted into the inner circumference of the insulating sleeve 49 and fitted into place.

[0040] The insulating sleeve 49 is made of an insulating material that has sufficient strength to hold the detection electrode 19; for example, alumina (Al2O3) can be used. The lower electrode housing tube 43, the upper electrode housing tube 45, and the fastening bolt 47 may be made of a conductive material.

[0041] Similarly, the common electrode 17 is also fixed to the electrode housing tube 51. However, since the common electrode 17 is a grounded electrode and may be electrically connected to the pump chamber 3, a conductive sleeve may be provided instead of the insulating sleeve 49, or it may be directly fixed to the fastening bolt 47.

[0042] The liquid level gauge 21 shown in Figure 2 is a device for detecting the liquid level of the water-diluted HTS in the pump chamber 3, and is electrically connected to the common electrode 17 and the detection electrode 19. The liquid level gauge 21 is a conductive type that detects the height of the lower end 55 of the detection electrode 19 in the pump chamber 3 as the liquid level of the water-diluted HTS when the common electrode 17 and the detection electrode 19 are conductive through the water-diluted HTS.

[0043] For example, if the liquid level of the water-diluted HTS in the pump chamber 3 is the liquid level L1 shown in Figure 2, the common electrode 17 is in contact with the water-diluted HTS, but the detection electrode 19 is not. Therefore, the common electrode 17 and the detection electrode 19 do not conduct electricity through the water-diluted HTS, and the liquid level gauge 21 does not detect the height of the lower end 55 of the detection electrode 19 as the liquid level of the water-diluted HTS.

[0044] On the other hand, when the liquid level of the water-diluted HTS in the pump chamber 3 reaches a liquid level L2, which is the same height as the lower end 55 of the detection electrode 19 in Figure 2, both the common electrode 17 and the detection electrode 19 come into contact with the water-diluted HTS. As a result, the common electrode 17 and the detection electrode 19 become electrically connected through the water-diluted HTS. Therefore, the liquid level gauge 21 detects the height of the lower end 55 of the detection electrode 19 as the liquid level of the water-diluted HTS.

[0045] Since the liquid level detection device 1 is conductive, it can only detect two states: whether there is conductivity between the common electrode 17 and the detection electrode 19 via the water dilution HTS, or whether there is conductivity or not. Therefore, one detection electrode 19 can only detect one liquid level. For example, the single detection electrode 19 shown in Figure 2 can only detect whether the liquid level is above L2 or below L2. Therefore, if you want to detect multiple liquid level heights, you need to install multiple detection electrodes 19 in the pump chamber 3 so that the height of the lower end 55 of the detection electrode 19 is positioned at the height corresponding to the liquid level height to be detected, and electrically connect them to the common electrode 17 and the liquid level gauge 21 with wires or the like.

[0046] Here, as shown in Figure 3, at least a portion of the surface of the detection electrode 19 that is exposed inside the pump chamber 3, excluding the lower end 55, is covered with an insulating layer 46. The reason for covering the detection electrode 19 with an insulating layer 46 in this manner will now be explained. When the water-diluted HTS is circulated within the circulation system 100, water may evaporate from the water-diluted HTS within the circulation system 100. If the evaporation occurs within the pump chamber 3, the evaporated water remains in the pump chamber 3 as water vapor. However, as shown in Figure 2, the height of the water-diluted HTS in the pump chamber 3 is maintained below the pump chamber mechanical seal 11 by filling it with gas. Therefore, the wall portion of the pump chamber 3 near the pump chamber mechanical seal 11 and the wall portion near the upper end of the detection electrode 19, such as the electrode housing tube 51, are not in contact with the water-diluted HTS and are at a lower temperature than the wall portion in contact with the water-diluted HTS.

[0047] Therefore, as shown by the dashed line in Figure 3, if water vapor condenses into liquid condensed water 81 near the detection electrode 19 through heat exchange with the atmosphere via the wall, the condensed water 81 may condense in such a way that it connects the detection electrode 19 and the inner wall of the pump chamber 3. In this case, since the detection electrode 19 and the pump chamber 3 are electrically connected, the detection electrode 19 and the common electrode 17 are also electrically connected via the pump chamber 3. Therefore, even if the lower end 55 of the detection electrode 19 is not in contact with the water dilution HTS at the time the condensed water 81 is generated, the liquid level gauge 21 may mistakenly detect the liquid level of the water dilution HTS as being at the liquid level of the lower end 55 of the detection electrode 19. In particular, as shown in Figure 3, the radial gaps between the detection electrode 19 and the electrode housing tube 51, such as the gaps 82, 83, and 84 between the detection electrode 19 and the electrode housing tube 51, are small in size and are also farther horizontally from the pump chamber 3. Therefore, water vapor condenses easily, and as the water vapor condenses to connect the detection electrode 19 and the inner wall of the pump chamber 3, false detection of the water level by the liquid level gauge 21 is likely to occur.

[0048] For example, suppose that the detection electrode 19, which detects a liquid level exceeding the maximum allowable liquid level height for the molten salt pump 104, is connected to the pump chamber 3 via the condensed water 81. In this case, even if the lower end 55 of the detection electrode 19 is not in contact with the water-diluted HTS, the liquid level gauge 21 will incorrectly detect that the liquid level in the pump chamber 3 has exceeded the maximum liquid level height. Furthermore, the control device for the motor 27 of the molten salt pump 104 stops operation when the liquid level detected by the liquid level gauge 21 exceeds the maximum permissible liquid level, in order to prevent parts such as the pump chamber mechanical seal 11 from coming into contact with the water dilution HTS. Therefore, if the detection electrode 19, which detects a height exceeding the maximum liquid level, becomes conductive with the pump chamber 3 via the condensed water 81 and incorrectly detects that the liquid level has exceeded the maximum liquid level, the control device for the molten salt pump 104 will stop the operation of the molten salt pump 104. As a result, if the condensed water 81 makes contact between the detection electrode 19 and the pump chamber 3, there is a risk that the circulation system 100 will stop operating. In order to restart the circulation system 100 in this state, it is necessary to wait until the condensed water 81 that is making contact between the detection electrode 19 and the pump chamber 3 is removed naturally by falling under its own weight, which can make restarting very time-consuming and labor-intensive. In addition, when the operation of the molten salt pump 104 stops, water-diluted HTS accumulates inside the pipes 107 and 108 and inside the molten salt pump 104. As a result, while waiting for the condensed water 81 to be removed naturally in order to restart, the accumulated water-diluted HTS may solidify if it falls below its freezing point, potentially blocking the inside of the pipes 107 and 108 and the inside of the molten salt pump 104.

[0049] Therefore, in the first embodiment, at least a portion of the surface of the detection electrode 19 that is exposed inside the pump chamber 3, excluding the lower end 55, is covered with an insulating layer 46. Here, "exposed surface" refers to the surface that is not covered by the insulating sleeve 49. In this configuration, even if the water contained in the water-diluted HTS evaporates and condenses near the detection electrode 19, it condenses between the insulating layer 46 and the inner wall of the pump chamber 3 or the inner wall of the electrode housing tube 51. Therefore, as shown in Figure 3, the insulating layer 46 prevents current from flowing through the condensed water 81 between the pump chamber 3 and the detection electrode 19. Therefore, erroneous detection of the liquid level by the liquid level gauge 21, which occurs when the pump chamber 3 and the detection electrode 19 are energized with condensed water 81, can be prevented, and the liquid level of the water-diluted HTS can be accurately detected using a conductive method. Therefore, the liquid level detection device 1 can accurately detect the liquid level of the water-diluted HTS, which is a water-diluted molten salt, in a conductive manner, even if the water contained in the water-diluted HTS evaporates and condenses in the pump chamber 3.

[0050] It should be noted that in addition to conductive types, there are also impedance-type liquid level detection devices that use electrodes. An impedance-type device detects the liquid level from the impedance between two electrodes. In the case of an impedance-type device, even if condensed water 81 causes conductivity between the detection electrode 19 and the pump chamber 3, the impedance detected at that time is different from the impedance when conductivity occurs via the water dilution HTS, so false detection of the liquid level due to condensed water 81 does not occur. For this reason, the configuration in which at least a portion of the surface of the detection electrode 19 exposed in the pump chamber 3, excluding the lower end 55, is covered with an insulating layer 46, as in this embodiment, is applicable only to conductive-type liquid level detection devices 1 and not to impedance-type devices. Furthermore, while typical molten salt pumps have a maximum liquid level of around 300 mm, when detecting the liquid level of an HTS (High Temperature System) of this height using an impedance-type detection method, the impedance changes depending on the concentration and temperature of the HTS water dilution, leading to large errors in liquid level measurement. Therefore, impedance-type liquid level detection devices are unsuitable as liquid level detection devices for molten salt pumps like the one in this embodiment because their detection accuracy is lower than that of conductive-type liquid level detection devices. Moreover, impedance-type liquid level detection devices that can be used to detect the liquid level of relatively high-temperature liquids such as molten salt are significantly more expensive than conductive-type liquid level detection devices, making them unsuitable in terms of cost as well.

[0051] The material constituting the insulating layer 46 is preferably an insulating material that can prevent current from flowing through the condensed water 81 between the pump chamber 3 and the detection electrode 19, and that does not deteriorate due to the temperature or atmosphere inside the pump chamber 3. Alumina is an example of such a material, but a material to which SiO2 or the like has been added may also be used.

[0052] Furthermore, the insulating layer 46 shown in Figure 3 exemplifies a thermal spray coating of an insulator. In this configuration, even if the water contained in the diluted HTS evaporates and condenses near the detection electrode 19, the thermal spray coating on the surface of the detection electrode 19 acts as an insulating layer 46, preventing current from flowing between the pump chamber 3 and the detection electrode 19 via the condensed water 81. Furthermore, in this configuration, since the insulating layer 46 is a thermal spray film, the surface of the detection electrode 19 and the insulating layer 46 can be brought into close contact, and there is no risk of condensed water 81 entering through the gap between the insulating layer 46 and the detection electrode 19 and conducting electricity between the detection electrode 19 and the pump chamber 3 via the condensed water 81.

[0053] If the insulating layer 46 is a thermal spray film, an example of an insulating film can be one in which alumina has been thermal sprayed. Furthermore, an example of a thermal spraying method is atmospheric plasma spraying (ASP). If the insulating layer 46 completely covers the surface of the detection electrode 19 exposed inside the pump chamber 3, the water-diluted HTS will not be able to conduct electricity with the detection electrode 19, and the liquid level height cannot be detected. Therefore, it is necessary to cover the portion of the surface exposed inside the pump chamber 3 other than the lower end 55 corresponding to the liquid level height to be detected.

[0054] The insulating layer 46 may cover all parts of the surface of the detection electrode 19 exposed in the pump chamber 3, except for the lower end 55 corresponding to the liquid level to be detected. However, there is a limit to the size of the condensed water 81 that can be generated. Therefore, if the surface of the detection electrode 19 is separated from the inner walls of the pump chamber 3 and the electrode housing tube 51 to a certain extent, even if condensed water 81 adheres to the detection electrode 19, the distance to the inner walls of the pump chamber 3 and the electrode housing tube 51 is too great for the condensed water 81 to connect these inner walls with the detection electrode 19. Therefore, the insulating layer 46 should be provided in an area where the shortest distance between the outer surface of the detection electrode 19 and the inner circumference of the opening 41 and / or the inner circumference of the electrode housing tube 51 is less than or equal to a predetermined upper limit distance.

[0055] For example, Figure 3The distance D1 shown is the distance between the outer surface of the detection electrode 19 and the inner circumference of the electrode housing tube 51, and is also called the creepage distance. If the upper limit of a predetermined range for the creepage distance is distance D1, then the outer surface of the detection electrode 19 at the position of distance D1 must be provided with an insulating layer 46. Also, the outer surface of the detection electrode 19 at the position of distance D2 shown in Figure 3 must be provided with an insulating layer 46 because the shortest distance from the electrode housing tube 51 is less than or equal to the upper limit distance D1. On the other hand, the outer surface of the detection electrode 19 below the position of distance D2 shown in Figure 3 does not need to be provided with an insulating layer 46 because the distance from the inner circumference of the opening 41 and the inner circumference of the electrode housing tube 51 are both longer than the upper limit distance D1.

[0056] Thus, the gap between the inner wall of the pump chamber 3 and the electrode housing tube 51 and the detection electrode 19 is narrow, and the insulating layer 46 may be provided only in the portion where condensed water 81 may cause electrical conductivity between the pump chamber 3 and the detection electrode 19 when water vapor evaporated from the water-diluted HTS condenses. In this configuration, the insulating layer 46 is not provided in areas where there is no possibility of conductivity between the pump chamber 3 and the detection electrode 19 due to condensed water 81. Therefore, the amount of insulating layer 46 can be reduced compared to the case where all exposed parts other than the lower end 55 are covered with the insulating layer 46, thereby reducing costs.

[0057] Shortening the upper limit distance for the insulating layer 46 reduces the amount of insulating layer 46 needed, thereby lowering costs. However, shortening it too much may cause condensed water 81 to conduct electricity between the pump chamber 3 and the detection electrode 19, leading to erroneous detection of the liquid level. Therefore, the upper limit distance is set by balancing cost with the reliability required to prevent erroneous detection of the liquid level. Specifically, the area where the insulating layer 46 is provided should preferably have an upper limit of 8 mm or less, even when cost is a priority. In other words, an upper limit of 8 mm is preferable. A limit of 18 mm or less is even preferable, as it allows for a high level of balance between cost and reliability. Furthermore, if reliability in preventing false detection of liquid level height is a priority, a limit of 20 mm or less is also acceptable. Furthermore, even when there are multiple detection electrodes 19, it is preferable to cover all detection electrodes 19 with the insulating layer 46. When there are multiple detection electrodes 19, the upper limit distance covered by the insulating layer 46 is the same for all detection electrodes 19. On the other hand, since the common electrode 17 is a grounded electrode, it does not need to be covered with the insulating layer 46.

[0058] Furthermore, as shown in Figure 3, the upper end of the insulating layer 46 must be in contact with the lower end of the insulating sleeve 49. This is to prevent condensed water 81 from entering between the upper end of the insulating layer 46 and the insulating sleeve 49 and causing electrical contact between the pump chamber 3 and the detection electrode 19. Furthermore, the radial thickness of the insulating layer 46 must be at least such that the detection electrode 19 is not exposed on the surface of the covering in order to prevent electrical conductivity between the pump chamber 3 and the detection electrode 19. However, if the covering thickness is too thick, the insulating layer 46 may interfere with the electrode housing tube 51, preventing the detection electrode 19 from being housed in the electrode housing tube 51, or the insulating layer 46 may become heavy and prone to peeling. Therefore, the thickness of the insulating layer 46 should be appropriately selected within a range that prevents electrical conductivity between the pump chamber 3 and the detection electrode 19, allows the detection electrode 19 to be housed in the electrode housing tube 51, and does not cause the insulating layer 46 to peel off. The above is a detailed explanation of the structure of the molten salt pump 104 and the liquid level detection device 1.

[0059] Thus, according to the first embodiment, the detection electrode 19 of the liquid level detection device 1, which detects the liquid level height of the water-diluted HTS in the pump chamber 3 of the molten salt pump 104, has at least a portion of its surface, excluding the lower end 55, covered with an insulating layer 46.

[0060] In this configuration, even if the water contained in the water-diluted HTS evaporates and condenses near the detection electrode 19, it condenses between the insulating layer 46 and the inner wall of the pump chamber 3. As a result, the insulating layer 46 prevents current from flowing between the pump chamber 3 and the detection electrode 19 via the condensed water 81. Therefore, the pump chamber 3 and the detection electrode 19 are energized through the condensed water 81, which prevents the liquid level gauge 21 of the liquid level detection device 1 from misdetecting the liquid level, and allows for accurate detection of the liquid level of the water-diluted HTS using a conductive method. Therefore, the liquid level detection device 1 can accurately detect the liquid level of the water-diluted HTS in a conductive manner, even if the water contained in the water-diluted HTS evaporates and condenses in the pump chamber 3.

[0061] Next, the structure of the liquid level detection device 1a according to the second embodiment will be described with reference to Figure 4. In the liquid level detection device 1a according to the second embodiment, instead of an insulating spray film of an insulator, an insulating tube 61, which is a tubular insulator, is used as the insulating layer 46, as in the first embodiment. In the second embodiment, elements that perform the same functions as in the first embodiment will be given the same numbers, and the parts that differ mainly from the first embodiment will be described.

[0062] As shown in Figure 4, the liquid level detection device 1a according to the second embodiment includes an insulating tube 61, an upper end cap 67, and a lower end cap 65. The insulating tube 61 is a tubular insulator. In this configuration, the detection electrode 19 is inserted through the hollow portion of the insulating tube 61, so that the insulating tube 61, acting as an insulating layer 46, covers the area around the detection electrode 19.

[0063] In this configuration, even if the water contained in the diluted HTS evaporates and condenses near the detection electrode 19, the insulating tube 61 provided around the outer circumference of the detection electrode 19 acts as an insulating layer 46, preventing current from flowing between the pump chamber 3 and the detection electrode 19 via the condensed water 81. Therefore, the pump chamber 3 and the detection electrode 19 are energized by the condensed water 81, which prevents erroneous detection of the liquid level by the liquid level gauge 21 of the liquid level detection device 1a, and allows for accurate detection of the liquid level of the molten salt using a conductive method. The material constituting the insulating tube 61 should have sufficient strength to maintain its shape as a tube and should not be altered by the temperature inside the pump chamber 3 or by the water dilution HTS. Specifically, alumina may be used as in the first embodiment, but a material to which SiO2 or the like has been added may also be used.

[0064] The upper end cap 67 is a component that fixes the insulating tube 61 to the detection electrode 19 by filling the gap G when the inner diameter D3 of the insulating tube 61 is larger than the outer diameter D4 of the detection electrode 19, and a radial gap G is provided between the insulating tube 61 and the detection electrode 19.

[0065] More specifically, the upper end cap 67 is cylindrical, with an outer diameter greater than or equal to the inner diameter D3 of the insulating tube 61, and an inner diameter less than or equal to the outer diameter D4 of the detection electrode 19. Furthermore, as shown in Figure 4, the upper end cap 67 is fitted into the gap G between the upper end of the insulating tube 61 and the detection electrode 19, thereby fixing the insulating tube 61 to the detection electrode 19.

[0066] For example, if the distance D1 shown in Figure 4 is the upper limit of a predetermined range when covering the insulating layer 46, the shortest distance between the upper end cap 67 and the inner circumference of the electrode housing tube 51 is usually less than or equal to D1. Therefore, the upper end cap 67 is made of an insulator such as alumina. Also, the upper end of the upper end cap 67 must be in contact with the lower end of the insulating sleeve 49. This is to prevent condensed water 81 from entering between the upper end of the upper end cap 67 and the insulating sleeve 49 and causing electrical conductivity between the pump chamber 3 and the detection electrode 19. If the outer diameter of the insulating sleeve 49 is greater than or equal to the inner diameter D3 of the insulating tube 61, the insulating sleeve 49 may be used as the upper end cap 67, and the upper end of the insulating tube 61 may be fitted to the lower end of the insulating sleeve 49.

[0067] The lower end cap 65 is a component that fixes the insulating tube 61 to the detection electrode 19 when the inner diameter D3 of the insulating tube 61 is larger than the outer diameter D4 of the detection electrode 19, and a radial gap G is provided between the insulating tube 61 and the detection electrode 19 by filling the gap G.

[0068] More specifically, the lower end cap 65 is also cylindrical, with an outer diameter greater than or equal to the inner diameter D3 of the insulating tube 61, and an inner diameter less than or equal to the outer diameter D4 of the detection electrode 19. Furthermore, as shown in Figure 4, the lower end cap 65 is fitted into the gap G between the lower end of the insulating tube 61 and the detection electrode 19, thereby fixing the insulating tube 61 to the detection electrode 19.

[0069] The lower end cap 65 must be an insulator such as alumina if the shortest distance between the outer surface of the detection electrode 19 and the opening 41 at the installation position is less than or equal to the upper limit distance. However, the position where the lower end cap 65 is provided is near the lower end 55 of the detection electrode 19 and is in contact with the water-diluted HTS, so usually the shortest distance is longer than the upper limit distance. In this case, the lower end cap 65 may be a conductor, for example, austenitic stainless steel, similar to the detection electrode 19.

[0070] Thus, even when a radial gap G is provided between the insulating tube 61 and the detection electrode 19, the insulating tube 61 can be fixed to the detection electrode 19 by providing an upper end cap 67 and a lower end cap 65. The upper end cap 67 also provides insulation by sealing the gap G between the insulating tube 61 and the detection electrode 19, preventing condensed water 81 from entering the gap G and making contact with the pump chamber 3. Furthermore, the lower end cap 65 seals the gap between the insulating tube 61 and the detection electrode 19, preventing condensed water 81 from entering the gap G and making contact with the pump chamber 3.

[0071] Therefore, even if the inner diameter D3 of the insulating tube 61 is larger than the outer diameter D4 of the detection electrode 19, the surface of the detection electrode 19 can be covered with the insulating tube 61 as long as the insulating tube 61 is small enough to fit into the electrode housing tube 51.

[0072] Furthermore, if the inner diameter D3 of the insulating tube 61 is less than or equal to the outer diameter D4 of the detection electrode 19, no gap G will occur, and the insulating tube 61 can be fitted onto the detection electrode 19. In this case, the upper end cap 67 and the lower end cap 65 are unnecessary. Furthermore, the area in which the insulating tube 61 and the upper end cap 67 cover the detection electrode 19 is the same as in the first embodiment, and is an area in which the shortest distance between the outer surface of the detection electrode 19 and the inner circumference of the opening 41 or the inner circumference of the electrode housing tube 51 is less than or equal to a predetermined upper limit distance.

[0073] Thus, according to the second embodiment, the detection electrode 19 of the liquid level detection device 1a, which detects the liquid level height of the water-diluted HTS in the pump chamber 3 of the molten salt pump 104, has at least a portion of its surface, excluding the lower end 55, covered by an insulating tube 61. Therefore, it produces the same effects as the first embodiment.

[0074] Furthermore, whether the insulating layer 46 is a thermal spray coating of an insulator, as in the first embodiment, or an insulating tube 61, as in the second embodiment, can be appropriately selected considering the advantages of each. For example, when the insulating layer 46 is a thermal spray coating of an insulator, as in the first embodiment, the insulating layer 46 can be brought into close contact with the surface of the detection electrode 19. Therefore, compared to the second embodiment, it is advantageous in that there is no risk of condensed water 81 entering through the gap between the insulating layer 46 and the detection electrode 19 and conducting electricity between the detection electrode 19 and the pump chamber 3.

[0075] On the other hand, when the insulating layer 46 is made of an insulating tube 61, as in the second embodiment, the insulating tube 61 itself can maintain its shape as a tube. Therefore, compared to the case where the insulating layer 46 is a thermal spray film, the insulating layer 46 has higher strength and is advantageous in that it is less likely to collapse and peel off from the detection electrode 19. In addition, depending on the outer diameter of the detection electrode 19, commercially available alumina tubes or the like can be used as the insulating tube 61. In this case, there is no need to manufacture an insulating tube 61 specifically for the detection electrode 19, which is advantageous in terms of cost and man-hours when providing the insulating tube 61 to the detection electrode 19. [Examples]

[0076] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the circulation system 100 shown in Figure 1, the molten salt pump 104 shown in Figure 2 was used to draw in and discharge water-diluted molten salt, and the liquid level height of the water-diluted molten salt was detected. The specific procedure is as follows.

[0077] (Comparative example) A molten salt motor pump manufactured by Teikoku Electric Works, Ltd. was used as the molten salt pump 104, and a conductive type liquid level detection device was prepared as the liquid level detection device 1. Four electrodes made of SUS316 with a diameter of 4 mm and lengths of 230 mm, 295 mm, 340 mm, and 390 mm were prepared as the detection electrodes 19. In addition, a common electrode made of SUS316 with a diameter of 4 mm and length of 390 mm was prepared as the common electrode 17, and these electrodes were mounted on the molten salt motor pump. However, the common electrode 17 and the four detection electrodes 19 were not coated with an insulating layer 46. Next, a molten salt was prepared with a composition of 40% by mass sodium nitrite, 7% by mass sodium nitrate, and 53% by mass potassium nitrate, with a freezing point of 150°C. Water was added to this molten salt to create an 85% by mass diluted molten salt. The freezing point of this diluted molten salt was approximately 70°C. Next, this diluted molten salt was heated to a temperature of 400°C to 500°C and circulated through the circulation system 100 using a molten salt motor pump. Furthermore, inert gas was filled into the molten salt motor pump as a gas to maintain the liquid level in the pump chamber 3 below the pump chamber mechanical seal 11. However, after the start of the test, the liquid level gauge 21 detected a liquid level exceeding the maximum allowable liquid level, even though the liquid level of the molten salt in the molten salt motor pump should have been below the maximum allowable liquid level. As a result, the molten salt motor pump made an emergency stop. Upon withdrawing the detection electrode 19 from the molten salt motor pump, which had been emergency stopped, and examining both the detection electrode 19 and the inside of the molten salt motor pump, it was found that water was adhering to both the detection electrode 19 and the surface of the motor pump opposite the detection electrode 19. Furthermore, the liquid level of the molten salt had not reached the maximum liquid level. Therefore, it was considered that the adhering water had energized the detection electrode 19 and the molten salt motor pump, causing the liquid level gauge 21 to misdetect the liquid level. Thus, when the surface of the detection electrode 19 was not covered with the insulating layer 46, the liquid level of the water-diluted molten salt could not be accurately detected by a conductive liquid level detection device.

[0078] (Example 1) On the outer circumference of the detection electrode 19 of the liquid level detection device 1, alumina was applied as an insulating layer 46 to the exposed surface at the shortest distance of 18 mm or less from the opening 41 and / or the electrode housing tube 51 by atmospheric pressure plasma spraying to a thickness that did not expose the detection electrode 19. Otherwise, the water-diluted molten salt was circulated using a motor pump for molten salt under the same conditions as the comparative example. As a result, even in a situation where the liquid level of the molten salt in the molten salt motor pump should have been below the maximum liquid level after the start of the test, the liquid level gauge 21 detected a liquid level below the maximum liquid level, and the molten salt motor pump did not have to be stopped in an emergency. Therefore, by covering the surface of the detection electrode 19 with an insulating layer 46 which is a thermal spray layer, the liquid level height of the water-diluted molten salt could be accurately detected by the conductive liquid level detection device 1.

[0079] (Example 2) As an insulating tube 61 covering the detection electrode 19 of the liquid level detection device 1, an alumina protective tube (model 2551-2373-03, part number SSA-S 6C, inner diameter 9 mm, outer diameter 13 mm) manufactured by Hagitec Co., Ltd. was prepared. In addition, an alumina tube with an outer diameter of 9 mm and an inner diameter of 4 mm was used as the upper end cap 67, and SUS316 with an outer diameter of 9 mm and an inner diameter of 4 mm was used as the lower end cap 65 to fix the insulating tube 61 around the outer circumference of the detection electrode 19. The position where the insulating tube 61 was installed was on the exposed surface on the outer circumference of the detection electrode 19 such that the shortest distance to the opening 41 and / or electrode housing tube 51 was 18 mm or less. Otherwise, the water-diluted molten salt was circulated using a motor pump for molten salt under the same conditions as the comparative example. As a result, even in a situation where the liquid level of the molten salt in the molten salt motor pump should have been below the maximum liquid level after the start of the test, the liquid level gauge 21 detected a liquid level below the maximum liquid level, and the molten salt motor pump did not have to be stopped in an emergency. Therefore, by covering the surface of the detection electrode 19 with the insulating tube 61, the liquid level height of the water-diluted molten salt could be accurately detected by the conductive liquid level detection device 1a.

[0080] From the above results, it was found that when detecting the liquid level of the water-diluted molten salt in the pump using a conductive liquid level detection device while drawing in / discharging the water-diluted molten salt with a motor pump for molten salt, accurate detection is not possible unless the surface of the detection electrode 19 is covered with an insulating layer 46. [Explanation of Symbols]

[0081] 1, 1a: Liquid level detection device 3: Pump Room 5: Inlet 7:Discharge port 9: Impeller 11: Pump chamber mechanical seal 12: Axle chamber mechanical seal 13: Gas inlet 15: Gas outlet 17: Common electrode 19: Detection electrode 21:Liquid level gauge 23: Rotation axis 25: Axis chamber 27: Motor 29: Motor Room 31: Partition plate 41: Opening 43: Lower electrode housing tube 43a: Upper end 45: Upper electrode housing tube 45a: Bottom end 45b: Upper end 46: Insulating layer 47: Fastening bolts 47a: Through hole 47b: Screw 49: Insulating sleeve 51: Electrode housing tube 53: Terminal 55: Bottom edge 61: Insulating tube 65: Bottom end cap 67: Top end cap 81: Condensed water 82, 83, 84: Gap 100: Circulation System 101: HTS Tank 102: Storage tank 103: Equipment using HTS 104: Molten salt pump 105: Expansion Tank 107, 108, 111, 113: Piping 109: Bypass piping 115: Heater 117: Power supply 119: Water injection pipe 121: Bent pipe 123 :Pressure equalization pipe

Claims

1. A molten salt pump comprising: a pump chamber for drawing in / discharging molten salt diluted with water; an impeller positioned in the pump chamber that draws in / discharges the molten salt by rotating around a rotating shaft that passes through the pump chamber with its axial direction facing upward; a pump chamber mechanical seal provided around the outer circumference of the part of the pump chamber through which the rotating shaft passes; and a liquid level adjustment means for filling the pump chamber with inert gas to push down the molten salt and maintain the liquid level of the molten salt in the pump chamber below the pump chamber mechanical seal, wherein a mixture of sodium nitrite, sodium nitrate, and potassium nitrate is used as the molten salt, and the heating temperature of the molten salt diluted with water is in the range of 400°C to 500°C, wherein the liquid level detection device for a molten salt pump detects the liquid level of the molten salt in the pump chamber. A rod-shaped common electrode is provided, which is electrically grounded and protrudes downward from above the pump chamber into the interior of the pump chamber. A rod-shaped detection electrode is provided, which protrudes downward from above the pump chamber into the interior of the pump chamber, is connected to the pump chamber via an insulating member, and at least a portion of the surface of the surface exposed inside the pump chamber, excluding the lower end, is covered with an insulating layer. The pump chamber is equipped with a liquid level gauge that is electrically connected to the common electrode and the detection electrode, and detects the height of the lower end of the detection electrode in the pump chamber as the liquid level of the molten salt when the common electrode and the detection electrode are electrically connected through the molten salt, A liquid level detection device for a molten salt pump, characterized in that the insulating layer is made of alumina.

2. The liquid level detection device for a molten salt pump according to claim 1, wherein the insulating layer is a thermal spray film of an insulator coated on the surface of the detection electrode.

3. The liquid level detection device for a molten salt pump according to claim 1, wherein the insulating layer is an insulating tube which is a tubular insulator, and the insulating layer covers the area around the detection electrode by inserting the detection electrode through the hollow portion of the insulating tube.

4. The inner diameter of the insulating tube is larger than the outer diameter of the detection electrode, and a radial gap is provided between the insulating tube and the detection electrode. A cylindrical upper end cap, which is an insulator, is fitted into the gap between the upper end of the insulating tube and the detection electrode to fix the insulating tube to the detection electrode, A cylindrical lower end cap that is fitted into the gap between the lower end of the insulating tube and the detection electrode, thereby fixing the insulating tube to the detection electrode, A liquid level detection device for a molten salt pump according to claim 3, comprising:

5. The aforementioned detection electrode is A tubular electrode housing tube, which protrudes upward from an opening provided in the pump chamber and communicates with the pump chamber through the opening, is fixed inside the tube via an insulating sleeve, which is an insulating tube. The insulating layer is A liquid level detection device for a molten salt pump according to any one of claims 1 to 4, wherein the device is provided in a region where the shortest distance between the outer surface of the detection electrode and the inner circumference of the opening and / or the inner circumference of the electrode housing tube is 20 mm or less.

6. The insulating layer is The liquid level detection device for a molten salt pump according to claim 5, wherein the detection electrode is provided in a region where the shortest distance between the outer surface of the detection electrode and the inner circumference of the opening and / or the inner circumference of the electrode housing tube is 18 mm or less.

7. The insulating layer is The liquid level detection device for a molten salt pump according to claim 5, wherein the detection electrode is provided in a region where the shortest distance between the outer surface of the detection electrode and the inner circumference of the opening and / or the inner circumference of the electrode housing tube is 8 mm or less.

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