Patent Description:
When a severe accident occurs in a nuclear power plant, a core is exposed and finally melt due to a coolant loss of a primary loop system of the nuclear power plant, and the core corium will eventually collapse into the lower head of RPV (reactor pressure vessel). If the core corium cannot be cooled in time, the corium will eventually melt through the lower head of the RPV because of the core decay heat, thus the core melt falls in the reactor pit and may possibly melt through a bottom plate of a containment, resulting in a large leakage of radioactive substance in the end.

To solve the problems above, a reactor pit water injection system is designed in current nuclear power plant to inject water into the reactor pit to submergie the pit, such that the lower head of the RPV is cooled. The design and construction of the reactor pit water injection system in the prior art is obtained through one-dimensional and two-dimensional test and theoretical design.

As shown in <FIG>, a test section in a prior art for processing a two-dimensional heating test consists of a copper heating section <NUM> and a stainless-steel flow channel <NUM>. The copper heating section <NUM> is used to simulate a wall surface of the RPV heated by the core melt when an accident occurs, and the stainless-steel flow channel <NUM> is used to simulate a flow channel outside the lower head of the RPV A width of the copper heating section <NUM> is the same from the top to the bottom, and a heating rod and a thermocouple are inserted from a side surface and are arranged parallel to a heating surface. During the test, all cooling water entering the flow channel <NUM> of the test section from an inlet at a bottom of the test section can only flow in one direction from the bottom to the top of the test section in the narrow flow channel, so that the three-dimensional flow state of an outer wall surface of the lower head of the RPV under a real condition cannot be simulated, thereby a great difference is existed with the actual flow condition.

Examples of devices for simulating the heat flux of a nuclear reactor are described in the applications <CIT>, <CIT> and <CIT>, as well as in the publication<NPL>.

A technical problem to be solved in the present invention is to provide a heating and temperature measuring device for simulating PRV heat exchange characteristics when an accident occurs, and a test system for simulating RPV heat exchange characteristics of a nuclear power plant.

A technical solution adopted by the present invention to solve the technical problem is to provide a heating and temperature measuring device for simulating RPV heat exchange characteristics when an accident occurs, wherein the heating and temperature measuring device includes a tube portion, a hemispherical lower head connected to a lower end of the tube portion, a heating assembly for heating the lower head, and a temperature measuring assembly disposed in the lower head;
the temperature measuring assembly is configured to monitor a temperature change in a wall thickness direction of the lower head to monitor a surface temperature change of the lower head. An inner wall surface of the lower head is provided with a number of temperature measuring holes along a spherical center direction of the lower head. Corresponding to the heating assembly, a number of heating holes are provided in the inner wall surface of the lower head along a spherical center direction of the lower head.

Preferably, the temperature measuring assembly includes a number of sets of thermocouples, and each set of thermocouple includes two thermocouples, and the thermocouple is inserted in the lower head perpendicular to an inner wall surface of the lower head.

Preferably, the thermocouples are inserted in the temperature measuring holes one by one; depths of the two temperature measuring holes corresponding to each set of thermocouples are different.

Preferably, the depths of the two temperature measuring holes corresponding to each set of thermocouples are <NUM>-<NUM>, <NUM>-<NUM> respectively.

Preferably, the lower head is provided with an annular recess on an inner wall surface adjacent to an opening side, and the lower head is separated into a non-heating section and a heating section respectively on an upper side and a lower side of the recess; the lower head is connected with the tube portion via the non-heating section, and the heating assembly and the temperature measuring assembly are disposed in the heating section.

Preferably, the heating and temperature measuring device further includes a sealing assembly disposed between the tube portion and the lower head; the sealing assembly includes a sealing flange, a high temperature resistant elastic gasket and a number of sets of locking members;
a lower end surface of the tube portion is welded to an upper surface of the sealing flange; a lower surface of the sealing flange is provided with a convex annular step, an end surface of the opening side of the lower head is provided with an annular groove, the high temperature resistant elastic gasket is disposed in the annular groove, and the annular step is tightly abutted against the high temperature resistant elastic gasket and fits within the annular groove; the locking members extends through the sealing flange and the non-heating section of the lower head.

Preferably, a number of first locking holes are provided in the sealing flange spaced along a circumference direction of the sealing flange and extending through an upper surface and a lower surface thereof, the non-heating section of the lower head is provided with a number of second locking holes spaced along a circumference direction of the lower head and communicated with the first locking holes correspondingly, and the second locking hole extends downward to be communicated with the recess from the end surface of the opening side of the lower head.

Preferably, the annular groove is located outside the second locking hole.

Preferably, the high temperature resistant elastic gasket is a graphite gasket.

Preferably, the tube portion is a stainless-steel tube, and the lower head is a hemispherical copper shell.

The present invention further provides a test system for simulating RPV heat exchange characteristics of a nuclear power plant, including the heating and temperature measuring device, a pit simulator, an insulation layer simulator and a cooling tank simulator; wherein the heating and temperature measuring device is configured as a RPV simulator and is suspended in the pit simulator, the insulation layer simulator is disposed on an outer periphery of the RPV simulator, and the cooling tank simulator is disposed on an outer periphery of an upper end of the RPV simulator;
a cooling water flow channel is defined between the insulation layer simulator and the RPV simulator, and a water injection space is defined between the insulation layer simulator and an inner wall surface of the pit simulator; a water inlet communicating the cooling water flow channel with the water injection space is provided at a bottom of the insulation layer simulator, so that cooling water in the water injection space is able to enter the cooling water flow channel through the water inlet, and the cooling water is heated outside the lower head of the RPV simulator to generate a steam-water two-phase flow; an upper end of the insulation layer simulator is provided with an exhaust outlet communicated with the cooling water flow channel, the steam-water two-phase flow flows upward along the cooling water flow channel and then is separated to steam and water when flowing through the exhaust outlet, and the liquid water falls into the cooling tank simulator.

Preferably, the cooling tank simulator includes an annular tank body and a first heat exchanger, a liquid level of the tank body is kept below the exhaust outlet, and the first heat exchanger is disposed in the tank body and below the liquid level thereof.

Preferably, the cooling tank simulator further includes a spray mechanism and/or a second heat exchanger disposed in the tank body and located above the exhaust outlet.

Preferably, a pit wall of the pit simulator is provided with at least one water inlet communicated with the water injection space for accessing the cooling water.

Preferably, the pit simulator, the RPV simulator, the insulation layer simulator and the cooling tank simulator are arranged in a ratio of <NUM>:<NUM> to sizes of the corresponding prototypes respectively.

Preferably, the test system further includes a water return line disposed outside the pit simulator; an upper end of the water return line is communicated with the cooling tank simulator, and a lower end of the water return line is communicated with the water injection space.

The present invention has the following beneficial effects: the present invention is configured to simulate a process that a high temperature core melt is transferred to a wall surface of the RPV(reactor pressure vessel) and flows outside the wall surface of the RPV under a severe accident condition of a nuclear power plant, so that to study the distribution of CHF(critical heat flux) and three-dimensional cooling water flow characteristics at different positions on an outer wall surface of the RPV under a three-dimensional flow condition, thereby providing data support for studying the effectiveness of a severe accident mitigation system -a pit water injection system.

The present invention will now be further described with reference to the accompanying drawings and embodiments, and in the drawings:.

To clearly understand the technical features, objectives and effects of the invention, specific embodiments of the invention will now be described in detail with reference to the accompanying drawings.

As shown in <FIG>, a test system for simulating RPV heat exchange characteristics of a nuclear power plant in an embodiment of the present invention includes a heating and temperature measuring device <NUM>, a pit simulator <NUM>, an insulation layer simulator <NUM>, and a cooling tank simulator <NUM>. The heating and temperature measuring device <NUM> serves as a RPV simulator and is suspended in the pit simulator <NUM>. The insulation layer simulator <NUM> is provided on an outer periphery of the RPV simulator. The cooling tank simulator <NUM> is disposed on an outer periphery of an upper end of the RPV simulator.

A cooling water flow channel <NUM> is defined between the insulation layer simulator <NUM> and the RPV simulator (the heating and temperature measuring device <NUM>), and a water injection space <NUM> is defined between the insulation layer simulator <NUM> and an inner wall surface of the pit simulator <NUM>. A water inlet <NUM> is provided at a bottom of the insulation layer simulator <NUM> and communicates the cooling water flow channel <NUM> with the water injection space <NUM>, so that the cooling water in the water injection space <NUM> is able to enter the cooling water flow channel <NUM> through the water inlet <NUM>. An upper end of the insulation layer simulator <NUM> is provided with an exhaust outlet <NUM> communicated with the cooling water flow channel <NUM>. The cooling water in the cooling water flow channel <NUM> is heated outside the RPV simulator to form a steam-water two-phase flow, and the steam-water two-phase flow flows upward along the cooling water flow channel <NUM> and then is separated to steam and water when flowing through the exhaust outlet <NUM>, and the liquid water falls into the cooling tank simulator <NUM>.

As an embodiment, the pit simulator <NUM>, the RPV simulator (the heating and temperature measuring device <NUM>), the insulation layer simulator <NUM> and the cooling tank simulator <NUM> are respectively arranged in a ratio of <NUM>:<NUM> to the corresponding prototypes.

Wherein, the heating and temperature measuring device <NUM> serves as the RPV simulator and is configured to simulate heat exchange characteristics of the reactor pressure vessel (RPV) under an accident. As shown in <FIG> and <FIG>, the heating and temperature measuring device <NUM> includes a tube portion <NUM>, a hemispherical lower head <NUM>, a heating assembly (not shown in the drawings) and a temperature measuring assembly. The tube portion <NUM> is a non-heating portion, and an upper end thereof is enclosed by an end cover, etc. The lower head <NUM> is connected to a lower end of the tube portion <NUM> to enclose the lower end of the tube portion <NUM>. The heating assembly heats the lower head <NUM>, enabling a three-dimensional heating section formed on the lower head <NUM>, thereby a heat transfer of the lower head of the RPV and a three-dimensional flow characteristics of an outer wall surface of the RPV can be completely simulated when a serious accident occurs. The temperature measuring assembly is disposed in the lower head <NUM>, and is configured to monitor a temperature change in a wall thickness direction of the lower head <NUM> to monitor a surface temperature change of the lower head <NUM>. Thereby, a real-time temperature measuring, a real-time monitor of a heating state and a stable measurement of a heat flux of different regions within a heating section <NUM> are realized, and the disturbance of a heating rod to the temperature measuring is avoided.

The cooling water in the cooling water flow channel <NUM> is generally heated outside the lower head <NUM> to generate a steam-water two-phase flow. The cooling water can flow in any direction outside a spherical surface of the lower head <NUM>, thus a three-dimensional flow state of an outer wall surface of the lower head of the RPV is able to be simulated under a real condition, which is more consistent with the actual flow situation.

Specifically, the tube portion <NUM> may be formed by two or more axial sections sequentially connected in an axial direction, thereby facilitating providing sufficient space for installing the heating assembly and arranging wires and the like, and realizing the operability for an operator.

Alternatively, in the heating and temperature measuring device <NUM>, the tube portion <NUM> may be a stainless-steel tube, and the lower head <NUM> may be a hemispherical copper shell.

The heating assembly may be disposed in the lower head <NUM>, and may include a number of heating rods to heat the lower head <NUM>. The heating rods are inserted into the lower head <NUM> vertical to an inner wall surface of the lower head <NUM>. By a uniform arrangement of a plurality of (eg. hundreds of, or thousands of) the heating rods in the lower head <NUM>, regional fine heating can be achieved with a maximum heating heat flux of <NUM>. 0MW/m<NUM>.

As shown in <FIG>, corresponding to the heating assembly, a number of heating holes <NUM> are uniformly provided in an inner wall surface of the lower head <NUM> along a spherical center direction of the lower head <NUM>. The heating hole <NUM> is a blind hole not extending through an outer wall surface of the lower head <NUM>. Each heating rod is inserted into a corresponding heating hole <NUM>.

Since the heating hole <NUM> into which the heating rod is inserted is a blind hole, the processing and installation error of the heating rod and the heating hole <NUM> needs to be strictly controlled, to prevent the heating rod from being pushed out by remaining air in the blind hole when heating, and to ensure sufficient contact between the heating rod and an inner wall surface of the heating hole <NUM> when being expanded. By controlling a distance between the heating rod and the heating hole <NUM>, the influence of the blind hole on ejection of the heating rod when being heated is achieved, and the heating expansion fitness is achieved, and the burnout possibility of the heating rod is effectively reduced.

Furthermore, in the heating and temperature measuring device <NUM>, the lower head <NUM> is connected to the lower end of the tube portion <NUM> in a sealing mode. During a test process, the lower head <NUM> and the tube portion <NUM> are submerged in water, and a large number of heating rods are installed in the lower head <NUM>. During the test operation, a body of the lower head <NUM> has a great temperature gradient and a sealing surface being deformed, thus a good sealing of a contact surface between the lower head <NUM> and the tube portion <NUM> is required, to prevent leakage of the contact surface from damaging the device.

To achieve a sealed connection between the lower head <NUM> and the tube portion <NUM>, the heating and temperature measuring device <NUM> further includes a sealing assembly <NUM> disposed between the tube portion <NUM> and the lower head <NUM>. To reduce the deformation of the sealing surface caused by the transmission of the heat generated by the heating assembly to the sealing assembly, the lower head <NUM> may include a non-heating section <NUM> and a heating section <NUM>. The non-heating section <NUM> is located adjacent to and configured for being matched with the sealing assembly <NUM>, and the heating section <NUM> is configured for installing the heating assembly therein. The heating hole <NUM> is defined in the heating section <NUM>.

A thickness of the heating section <NUM> of the lower head <NUM> is determined by a length of the heating rod, a heating capacity, the number of the heating holes <NUM> and a required space of the heating holes <NUM>. If the wall thickness of the heating section <NUM> is larger, then the length of the heating rod is larger, and the inner space of the heating section <NUM> is less, thus there is no enough space for drilling a larger number of the heating holes <NUM>. If the wall thickness of the heating section <NUM> is smaller, then there is enough space inside the heating section <NUM> for drilling, but the heating capacity and the surface heating power of the heating rod have higher requirement since the length of the heating rod is smaller. Therefore, factors such as the heating design capacity of the heating rods and the number of the heating rods etc. should be fully considered in selecting the wall thickness of the heating section <NUM>. The relationship of the thickness of the lower head <NUM> and the depth and the quantity of the heating hole <NUM> are mutual coupling: <NUM>) when a radius of the lower head <NUM> is defined, the thickness of the lower head <NUM> determines the depth of the heating hole <NUM>, and the installation spaces and amounts of the heating holes <NUM> and heating rod wires; <NUM>) a diameter and a heating length of the heating rod are determined by a power, a heating section and a manufacturing process of the heating rod. The thickness of the lower head <NUM> and the depth and the quantity of the heating hole <NUM> can be determined by considering the above factors overall.

In the present embodiment, the wall thickness of the lower head <NUM> (the wall thickness of the heating section <NUM>) is <NUM>-<NUM>. The heating hole <NUM> has a depth of <NUM>-<NUM> with a tolerance of ± <NUM>, an inner diameter of <NUM>-<NUM> with a tolerance of -<NUM> to +<NUM>, and a perpendicularity of <NUM>. The inner wall surface of the heating hole <NUM> should be smooth, scratch free and has a roughness of <Ra1. Correspondingly, the heating rod has a total length of ≤ <NUM>, a heating length of <NUM>-<NUM>, and an outer diameter of <NUM>-<NUM> with a tolerance of -<NUM> to +<NUM>. A rated power of the heating rod can be selected at ~<NUM>.

Specifically, the lower head <NUM> is provided with an annular recess <NUM> on an inner wall surface adjacent to an opening side thereof, and the lower head is separated by the recess <NUM> into the non-heating section <NUM> and the heating section <NUM> respectively on an upper side and a lower side of the recess <NUM>. The lower head <NUM> is connected with the tube portion <NUM> via the non-heating section <NUM>, and the heating assembly is disposed in the heating section <NUM>. The heating section <NUM> occupies a large volume of the lower head <NUM> and is a hemispherical three-dimensional section. The non-heating section <NUM> and the heating section <NUM> are connected by a side wall thinned by the recess <NUM>, thereby reducing a contact area between the non-heating section <NUM> and the heating section <NUM>. The non-heating section <NUM> acts as an isolation function and provides conditions for the installation of the sealing assembly <NUM> at the same time.

In the heating section <NUM> of the lower head <NUM>, a number of the heating rods are evenly spaced and inserted into the corresponding heating holes <NUM>. The heating section <NUM> may further include a number of heating units, and each heating unit has a plurality of the heating rods therein. To facilitate a power control of each heating unit, the heating rods of different heating units may be connected to different power controllers according to the actual requirements. For example, the powers of the heating rods of the adjacent heating units are different, and by performing heating power controls of different units, to control the temperatures of different units in the entire heating section <NUM>.

As shown in <FIG> and <FIG>, the sealing assembly <NUM> includes a sealing flange <NUM>, a high temperature resistant elastic gasket <NUM> and a number of sets of locking members <NUM>. The sealing flange <NUM> fits between the tube portion <NUM> and the lower head <NUM>, and a lower end surface of the tube portion <NUM> is welded to an upper surface of the sealing flange <NUM>. A lower surface of the sealing flange <NUM> cooperates with an end surface of the opening side of the lower head <NUM>. Specifically, the lower surface of the sealing flange <NUM> is provided with a convex annular step <NUM>, and the end surface of the opening side of the lower head <NUM> is provided with an annular groove <NUM>. The high temperature resistant elastic gasket <NUM> is disposed in the annular groove <NUM>, and the annular step <NUM> is tightly abutted against the high temperature resistant elastic gasket <NUM> and fits within the annular groove <NUM>, to realize a concace-convex sealing fit between the sealing flange <NUM> and the lower head <NUM>.

Preferably, in the present embodiment, the high temperature resistant elastic gasket <NUM> is a graphite gasket.

A number of sets of the locking members <NUM> are spaced distributed along a circumference direction of the sealing flange <NUM>. Each set of locking member <NUM> extends through the sealing flange <NUM> and the non-heating section <NUM> of the lower head <NUM>, to firmly lock the sealing flange <NUM> with the lower head <NUM>, thereby to firmly lock the tube portion <NUM> with the lower head <NUM>. The locking member <NUM> may include a bolt and at least one nut mating therewith.

Corresponding to the locking member <NUM>, a number of first locking holes <NUM> are provided in the sealing flange <NUM> spaced along the circumference direction of the sealing flange <NUM> and extending through an upper surface and a lower surface thereof. The non-heating section <NUM> of the lower head <NUM> is provided with a number of second locking holes <NUM> spaced along the circumference direction of the lower head <NUM>, and the second locking hole <NUM> is communicated with the first locking hole <NUM> correspondingly.

Wherein, the first locking hole <NUM> is located inside the annular step <NUM> along a radial direction of the sealing flange <NUM>. Correspondingly, the second locking hole <NUM> is inside the annular groove <NUM> along a radial direction of the lower head <NUM>. Otherwise, the annular groove <NUM> is located outside the second locking hole <NUM>.

Particularly, the second locking hole <NUM> extends downward to be communicated with the recess <NUM> from the end surface of the opening side of the lower head <NUM>, forming a shape of through hole. The second locking hole <NUM>, of a through hole shape, enables a lower end of the bolt of the locking member <NUM> to extend into the recess <NUM>, thereby a nut can be screwed with the lower end of the bolt, combined with a nut assembled on an upper end of the bolt, to form a double head locking. It provides a better bolt fastening than in a blind hole, and improves the fastening between the sealing flange <NUM> and the lower head <NUM>.

Furthermore, since the heating section <NUM> of the lower head <NUM> is located below the recess <NUM>, the recess <NUM> is able to reduce the heat transfer of the heating section <NUM> to a flange surface, thereby to decrease the expansion degree of the sealing flange <NUM>, and to ensure the connection sealing performance.

The temperature measuring assembly may include a number of sets of thermocouples, and each set of thermocouple includes two thermocouples. The thermocouples are inserted in the lower head <NUM> perpendicular to an inner wall surface of the lower head <NUM>. Specifically, the thermocouple is inserted in the heating section <NUM> of the lower head <NUM>.

Corresponding to the temperature measuring assembly, an inner wall surface of the lower head <NUM> is provided with a number of temperature measuring holes <NUM> along a spherical center direction of the lower head <NUM>, and each thermocouple is inserted into a corresponding temperature measuring hole <NUM>. Corresponding to two thermocouples being configured as one set, every two temperature measuring holes <NUM> are also configured as one set, and are arranged corresponding to the two thermocouples of each set of thermocouples. Depths of the two temperature measuring holes <NUM> corresponding to each set of thermocouples are different, so that insertion depths of the two thermocouples of each set of thermocouples are different and serve as a set of temperature measuring points.

In the present embodiment, corresponding to the wall thickness of the lower head <NUM>, the depths of the two temperature measuring holes <NUM> corresponding to each set of thermocouples may be <NUM>-<NUM>, <NUM>-<NUM> respectively.

As shown in <FIG>, in the present embodiment, the two temperature measuring holes <NUM> corresponding to each set of thermocouples are arranged in a center position of a region surrounded by four heating holes <NUM>, so that each set of thermocouples is located in a center position of a region surrounded by four heating rods. In the lower head <NUM>, the area enclosed by four heating rods has the largest space, thus to facilitate the arrangement and insertion of the thermocouples, and the four heating rods are of the same power.

The two thermocouples of each set of thermocouples are arranged along the spherical center direction with the same tilt angle.

As shown in <FIG>, by the insertion of the plurality of heating rods in the corresponding heating holes <NUM> and the uniform arrangement of the plurality of heating rods in the lower head <NUM>, the heating section <NUM> of the lower head <NUM> can be divided into a plurality of equal temperature distribution regions <NUM> (the regions defined by dashed lines in <FIG>) along the spherical center direction. In the lower head <NUM>, the temperature measuring points of the two thermocouples <NUM> are arranged in the equal temperature distribution region <NUM>, and the depths of the temperature measuring holes corresponding to the two thermocouples <NUM> are different.

During the test, a thermal flow density qi of the equal temperature distribution region <NUM> is obtained by Fourier formula:
<MAT>.

In the above formula, qi is the thermal flow density of the equal temperature distribution region <NUM>, in W/m<NUM>; ti is a measured value of the thermocouple with a smaller depth of one set of thermocouples, and t<NUM> is a measured value of the thermocouple with a larger depth of one set of thermocouples; λ is a thermal conductivity (integral average) of a copper; and △l is a depth difference of the two thermocouples in one set of thermocouples, in mm.

Wherein λ is obtained by the following formula:
<MAT>.

Furthermore, as shown in <FIG>, in the test system, the cooling tank simulator <NUM> includes an annular tank body <NUM> disposed at an outer periphery of an upper end of the heating and temperature measuring device <NUM> and a first heat exchanger <NUM> disposed in the tank body <NUM>.

The exhaust outlet <NUM> is communicated with an inner space of the tank body <NUM>, and the liquid level of the tank body <NUM> is kept below the exhaust outlet <NUM> to keep the exhaust outlet <NUM> clear during the test. The first heat exchanger <NUM> is disposed below the liquid level in the tank body <NUM>. The first heat exchanger <NUM> may include a plurality of cooling tubes for the cooling water flowing and heat exchanging with the water in the tank body <NUM>. The cooling tube may be annularly arround the outer periphery of the upper end of the heating and temperature measuring device <NUM>.

The cooling tank simulator <NUM> further includes a spray mechanism <NUM> and / or a second heat exchanger <NUM> disposed in the tank body <NUM> and located above the exhaust outlet <NUM>, and is configured for cooling the vapor discharged from the exhaust outlet <NUM>, so that the vapor condenses into liquid and falls into the tank body <NUM>. The second heat exchanger <NUM> may be arranged with reference to the first heat exchanger <NUM>.

A pit wall of the pit simulator <NUM> may be provided with at least one water inlet (not shown in the drawings) communicated with the water injection space <NUM> for accessing cooling water. During the test, the cooling water is fed into the water injection space <NUM> through the water inlet. When the test is finished, the water inlet may act as a water outlet to drain off water, or a water outlet <NUM> can be provided at a bottom of the pit simulator <NUM> to drain off water. Of course, the cooling water may alternatively be fed into the tank body <NUM> through the spray mechanism <NUM> of the cooling tank simulator <NUM> or a interface of the tank body <NUM>, and then the cooling water flows into the water injection space <NUM>.

To facilitate observing the inner condition of the pit simulator <NUM> during the test, at least one observing window <NUM> may be provided on a pit wall of the pit simulator <NUM>. Observing window may also be provided on a wall surface of the tank body <NUM> of the cooling tank simulator <NUM>.

Furthermore, the test system of the invention further includes a water return line (not shown in the drawings) disposed outside the pit simulator <NUM>. An upper end of the water return line is communicated with the cooling tank simulator <NUM>, and a lower end of the water return line is communicated with the water injection space <NUM>. Corresponding to the water return line, a first interface <NUM> is provided at a lower end of the tank body <NUM> of the cooling tank simulator <NUM>, and a second interface <NUM> is provided at a lower end of a pit wall of the pit simulator <NUM>, and the water return line is formed by communicating the pipe between the first interface <NUM> and the second interface <NUM>. During the test, the cooling water of the tank body <NUM> can flow back into the water injection space <NUM> through the water return line.

The test system of the present invention can simulate a whole process of a pit water injection of a nuclear power plant when a severe accident occurs, mainly simulate a process and a flow direction of the cooling water when being injected into the pit and then being heated in the channel outside the lower head of the RPV and the insulation layer of the RPV to form steam-water two-phase flow, and obtain the heat flux of the lower head by real time monitor, thereby the heating characteristics of different regions of a wall surface of the RPV and the two-phase flow characteristics of an outer wall surface of the lower head of the RPV can be studied. Meanwhile, a test, such as a CHF experiment under natural cycle and forced cycle conditions, or a temperature response test under false water injection condition or the like, can be conducted.

Claim 1:
A heating and temperature measuring device (<NUM>), for simulating reactor pressure vessel (RPV) heat exchange
characteristics when an accident occurs, wherein the heating and temperature measuring device (<NUM>) comprises a tube portion (<NUM>), a hemispherical lower head (<NUM>) connected to a lower end of the tube portion (<NUM>), a heating assembly for heating the lower head (<NUM>) and a temperature measuring assembly disposed in the lower head (<NUM>);
and
the temperature measuring assembly is configured to monitor a temperature change of the lower head (<NUM>) in a wall thickness direction to monitor a temperature change of a surface of the lower head (<NUM>),
wherein an inner wall surface of the lower head (<NUM>) is provided with a number of temperature measuring holes (<NUM>) along a spherical center direction of the lower head (<NUM>), and
corresponding to the heating assembly, a number of heating holes (<NUM>) are provided in the inner wall surface of the lower head (<NUM>) along a spherical center direction of the lower head (<NUM>).