Core catcher system and control method thereof

Abstract

A core catcher system according to an embodiment of the present invention, which prevents unnecessary supply of cooling water from a cooling water tank, comprises: a core molten material monitoring sensor assembly including an expansion sensor and a stress sensor which are attached to the outer wall of the lower portion of a nuclear reactor, an infrared sensor which measures a temperature of a reactor cavity, and a wind pressure-wind velocity sensor for measuring an air flow in the reactor cavity; a determination unit for determining whether the outputs of the expansion sensor and the stress sensor are equal to or greater than a predetermined value and whether the outputs of the infrared sensor and the wind pressure-wind velocity sensor are equal to or greater than a predetermined value in the core molten material monitoring sensor assembly; and a control unit for operating a valve unit of the cooling water tank for supplying cooling water to a core catcher when the determination unit determines that any one of the output values of the expansion sensor and the stress sensor is equal to or greater than the predetermined value and any one of the output values of the infrared sensor and the wind pressure-wind velocity sensor is equal to or greater than the predetermined value.

Description

Core catcher system and its control method

[0001] The present invention relates to a core catcher system and a control method thereof, and more specifically, to a core catcher system and a control method thereof that can solve the problem of coolant from a reloading tank being unnecessarily supplied to a core catcher by adding another type of sensor, improving the logic of a control unit, and introducing a judgment unit.

[0002] A severe accident in a nuclear power plant is considered to have occurred when the core exit temperature reaches 649℃. If core cooling fails and the severe accident continues, the core melt will be redistributed to the lower part of the reactor, pierce the reactor vessel, and fall into the reactor cavity.

[0003] A core catcher is installed in the reactor cavity as a severe accident response facility, and after the core melt falls onto the core catcher structure, the coolant shut-off valve is automatically opened to supply coolant to the reload water tank.

[0004] As illustrated in Fig. 1, the prior art (registered patent 10-2514705, core catcher system with improved operational safety) uses an expansion detection sensor (511) and a stress detection sensor (512) attached to the lower outer wall of the reactor, and an infrared sensor (520) for measuring the temperature of the reactor cavity, and the control unit (60) that operates the coolant shut-off valve operates the valve unit (40) to open it when two or more of the three sensors (50) reach the set value.

[0005] As illustrated in Fig. 2, coolant is supplied when the expansion detection sensor (511) and the stress detection sensor (512) reach the set values. However, even if the expansion detection sensor (511) and the stress detection sensor (512) reach the set values, the core cooling strategy is successful, so the reactor vessel is not damaged and core molten material does not flow out.

[0006] That is, the strategy of continuously supplying coolant into the reactor vessel must be maintained, but the problem arises that coolant from the reload water tank is unnecessarily supplied to the core catcher.

[0007] Therefore, the control logic must be improved so that an automatic start signal is generated only in situations where coolant supply to the core catcher is absolutely necessary.

[0008] In addition, since the infrared sensor (520) has a shortened lifespan and its operational reliability is not secured when installed in a high-radiation area, such as a reactor cavity, it is necessary to add another type of sensor that is robust to radiation.

[0009] The present invention has been devised to solve such problems, and the purpose of the present invention is to provide a core catcher system and a control method thereof that can solve the problem of coolant from a reloading tank being unnecessarily supplied to a core catcher by adding a different type of sensor, improving the logic of a control unit, and introducing a judgment unit.

[0010] A core catcher system for preventing unnecessary supply of coolant from a coolant tank according to one embodiment of the present invention is characterized by including a core melt monitoring sensor assembly including an expansion detection sensor and a stress detection sensor attached to a lower outer wall of a nuclear reactor, an infrared sensor for measuring a temperature of a nuclear reactor cavity, and a wind pressure and velocity sensor for measuring an airflow in the nuclear reactor cavity; a determination unit for determining whether an output of the infrared sensor or an output of the wind pressure and velocity sensor received from the core melt monitoring sensor assembly is equal to or greater than a predetermined value; and a control unit for operating a valve unit of a coolant tank for supplying coolant to a core catcher when the determination unit determines that one of the output values ​​of the expansion detection sensor and the stress detection sensor is equal to or greater than the predetermined value and one of the output values ​​of the infrared sensor and the wind pressure and velocity sensor is equal to or greater than the predetermined value.

[0011] A control method of a core catcher system according to one embodiment of the present invention comprises the steps of: a step in which an expansion detection sensor detects a change in expansion of an outer wall of a reactor, and a stress detection sensor detects a change in stress of the outer wall of the reactor; a step in which an infrared sensor measures a temperature of a reactor cavity located below the reactor, and a wind pressure and speed sensor measures a speed and pressure of airflow in a reactor cavity area located below the reactor; a step in which a determination unit determines whether at least one of the result values ​​measured by the infrared sensor and the wind pressure and speed sensor is greater than or equal to a predetermined value; and a step in which a control unit commands an operation of a valve unit of a coolant tank connected to the core catcher to supply coolant to the core catcher when at least one of the result values ​​measured by the expansion detection sensor and the stress detection sensor is greater than or equal to the predetermined value and the determination unit determines that an AND condition in which at least one of the result values ​​measured by the infrared sensor and the wind pressure and speed sensor is greater than or equal to the predetermined value.

[0012] According to a core catcher system and a control method thereof that prevents unnecessary supply of coolant from a coolant tank according to one embodiment of the present invention, the problem of coolant from a rechargeable water tank being unnecessarily supplied to a core catcher can be solved by adding a different type of sensor, improving the logic of a control unit, and introducing a judgment unit.

[0013] Figure 1 is a drawing explaining a core catcher system of the prior art.

[0014] Figure 2 is a drawing showing the control logic of a core catcher of the prior art.

[0015] FIG. 3 is a drawing showing a core catcher system according to one embodiment of the present invention;

[0016] FIG. 4 is a diagram showing the control logic of a core catcher according to one embodiment of the present invention, and

[0017] Figure 5 is a flowchart showing a control method of a core catcher system according to one embodiment of the present invention.

[0018] Hereinafter, with reference to the attached drawings, an embodiment of the present invention will be described in detail so that those skilled in the art can easily implement the invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0019] Additionally, throughout the specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0020] FIG. 3 is a drawing showing a core catcher system according to one embodiment of the present invention, and FIG. 4 is a drawing showing the control logic of a core catcher according to one embodiment of the present invention.

[0021] First, the core catcher system (1) may include a core catcher placed at the bottom of a reactor vessel, a cooling water tank that supplies cooling water to the core catcher, a valve unit (40) installed in a connecting pipe between the core catcher and the cooling water tank, a core melt monitoring sensor assembly (50), and a control unit (60).

[0022] The above core catcher is located at the bottom of the reactor and comes into contact with the molten material of the reactor in the event of a major accident to cool the molten material, and the above coolant tank contains coolant to be supplied to the core catcher.

[0023] The coolant tank may be, but is not limited to, an in-line refueling water storage tank (IRWST), and the coolant tank may be located above the coolant flow path.

[0024] The core melt monitoring sensor assembly (50) includes a reactor sensor (510) installed in the reactor vessel, a cavity sensor (520) installed in the cavity between the reactor vessel and the core catcher, and a wind pressure and velocity sensor (530) for measuring air flow in the cavity area.

[0025] The above reactor sensor (510) detects physical changes in the reactor, and in particular, detects physical changes caused by temperature changes in the reactor. The reactor sensor (510) includes an expansion detection sensor (511) that detects expansion changes in the outer wall of the reactor and a stress detection sensor (512) that detects stress changes in the outer wall of the reactor.

[0026] The expansion detection sensor (511) may be provided as a piezoelectric element positioned between the outer wall of the reactor and the insulation, and the stress detection sensor (512) may be provided as a strain gauge positioned between the outer wall of the reactor and the insulation.

[0027] The above-mentioned joint sensor (520) senses the temperature of the reactor cavity located at the bottom of the reactor and may be provided as an infrared sensor.

[0028] The above wind pressure and speed sensor (530) measures the speed and pressure of the air current formed from the bottom to the top in the cavity between the reactor vessel and the core catcher when the extremely high temperature core molten material falls through the reactor vessel and out due to the rapid temperature difference with the atmospheric temperature.

[0029] The number of the above wind pressure sensors is at least 2 and does not need to be limited to 2.

[0030] The expansion detection sensor (511), stress detection sensor (512), cavity sensor (520), and wind pressure / wind speed sensor (530) described above adopt different measurement principles.

[0031] In addition, the measurement locations are also different. Some or all of the expansion detection sensor (511), stress detection sensor (512), cavity sensor (520), and wind pressure / wind speed sensor (530) may be provided in multiple units.

[0032] The above control unit (60) connects the expansion detection sensor (511) and the stress detection sensor (512) with an OR condition, and the output of the infrared sensor (520) or the output of the wind pressure sensor (530) is configured as an AND condition through the judgment unit (70) to operate the valve unit (40).

[0033] The judgment unit (70) determines whether the rate of change in the output value of the infrared sensor (520) or wind pressure sensor (530) increases above a certain standard.

[0034] As shown in Fig. 4, in order for the control unit (60) to operate the valve unit (40), the OR condition that the result value of at least one of the expansion detection sensor (511) and the stress detection sensor (512) is greater than or equal to a predetermined value must be satisfied, and the judgment unit (70) must determine that the result value of at least one of the infrared sensor (520) and the wind pressure sensor (530) is greater than or equal to a predetermined value must be satisfied.

[0035] Therefore, the valve unit (40) does not operate only under the condition that the result values ​​of the expansion detection sensor (511) and the stress detection sensor (512) are higher than a predetermined value.

[0036] Now, referring to FIG. 5, a method for controlling a core catcher system according to one embodiment of the present invention will be described.

[0037] As illustrated in FIG. 5, in a control method of a core catcher system according to an embodiment of the present invention, an expansion detection sensor (511) detects a change in expansion of the outer wall of a reactor, a stress detection sensor (512) detects a change in stress of the outer wall of a reactor (S11), and detects whether an OR condition in which at least one of the measured values ​​by the expansion detection sensor (511) and the stress detection sensor (512) is greater than a predetermined value is met (S12).

[0038] An infrared sensor (520) measures the temperature of the reactor cavity located at the bottom of the reactor, and a wind pressure and wind speed sensor (530) measures the speed and pressure of air flow in the reactor cavity area located at the bottom of the reactor (S21).

[0039] The judgment unit (70) is electrically connected to the infrared sensor (520) or the wind pressure and speed sensor (530) and determines whether at least one of the measured results by the infrared sensor (520) or the wind pressure and speed sensor (530) is greater than a predetermined value (S23).

[0040] If the judgment unit (70) determines that at least one of the measured values ​​by the infrared sensor (520) or the wind pressure / wind speed sensor (530) is not greater than a predetermined value, it determines whether the rate of change in the measured value measured by the infrared sensor (520) or the wind pressure / wind speed sensor (530) is at a certain level, for example, has a certain slope (S31).

[0041] The control unit (60) is an OR condition in which at least one of the result values ​​measured by the expansion detection sensor (511) and the stress detection sensor (512) is greater than or equal to a predetermined value, and an AND condition in which the judgment unit (70) determines that at least one of the result values ​​measured by the infrared sensor (520) or the wind pressure and wind speed sensor (530) is greater than or equal to a predetermined value (S32), or even if at least one of the result values ​​measured by the infrared sensor (520) or the wind pressure and wind speed sensor (530) is not greater than or equal to the predetermined value in the step (S31), if the change rate of the measured value measured by the infrared sensor (520) or the wind pressure and wind speed sensor (530) is greater than or equal to a predetermined level, the control unit (60) commands the valve unit (40) to supply cooling water to the core catcher (S33).

[0042] The control unit (60) prevents the valve unit (40) from operating if the measured values ​​by the expansion detection sensor (511) and the stress detection sensor (512) are not all equal to or greater than a predetermined value, and the measured values ​​by the infrared sensor (520) and the wind pressure and wind speed sensor (530) are not all equal to or greater than a predetermined value, or if at least one of the measured values ​​by the infrared sensor (520) and the wind pressure and wind speed sensor (530) in the step (S31) is not equal to or greater than a predetermined value and the change rate of the measured values ​​by the infrared sensor (520) and the wind pressure and wind speed sensor (530) is not equal to or greater than a predetermined level (S34).

[0043] When the extremely high temperature core melt falls through the reactor vessel and out, the measured values ​​by the infrared sensor (520) in the cavity between the reactor vessel and the core catcher and the output values ​​of the airflow speed and pressure measured by the wind pressure and speed sensor (530) in the cavity area rapidly increase.

[0044] Therefore, reliability can be increased because the judgment unit (70) does not only judge the output value itself, but also calculates the rate of change of the output value and judges whether it is above a certain level, and the control unit (60) controls whether or not the valve unit (40) operates.

[0045] Therefore, by adding different types of sensors, improving the logic of the control unit, and introducing a judgment unit, the problem of coolant from the reload tank being unnecessarily supplied to the core catcher can be solved.

[0046] According to a core catcher system and a control method thereof that prevents unnecessary supply of coolant from a coolant tank according to one embodiment of the present invention, the problem of coolant from a rechargeable water tank being unnecessarily supplied to a core catcher can be solved by adding a different type of sensor, improving the logic of a control unit, and introducing a judgment unit.

Claims

1. A core melt monitoring sensor assembly including an expansion detection sensor and a stress detection sensor attached to a lower outer wall of a reactor, an infrared sensor for measuring a temperature of a reactor cavity, and a wind pressure and velocity sensor for measuring an airflow of the reactor cavity; a judgment unit for judging whether an output of the infrared sensor or an output of the wind pressure and velocity sensor received from the core melt monitoring sensor assembly is equal to or higher than a predetermined value, and a control unit for operating a valve unit of a coolant tank which supplies coolant to a core catcher when the judgment unit determines that one of the output values ​​of the expansion detection sensor and the stress detection sensor is equal to or higher than the predetermined value and one of the output values ​​of the infrared sensor and the wind pressure and velocity sensor is equal to or higher than the predetermined value.

2. In paragraph 1, The above judgment unit is a core catcher system that judges whether the output value change rate of the infrared sensor or the wind speed and pressure sensor increases above a certain standard.

3. In the control method of the core catcher system, A step in which an expansion detection sensor detects a change in expansion of the outer wall of a reactor, and a stress detection sensor detects a change in stress of the outer wall of a reactor; A step in which an infrared sensor measures the temperature of a reactor cavity located below the reactor, and a wind pressure and speed sensor measures the speed and pressure of airflow in a reactor cavity area located below the reactor; A step in which the judgment unit determines whether at least one of the results measured by the infrared sensor and the wind pressure and wind speed sensor is greater than a predetermined value; A method for controlling a core catcher system, comprising the step of: when at least one of the result values ​​measured by the expansion detection sensor and the stress detection sensor is greater than or equal to a predetermined value, and when the judgment unit determines that at least one of the result values ​​measured by the infrared sensor and the wind pressure and wind speed sensor is greater than or equal to a predetermined value as an AND condition, the control unit commands the valve unit of the cooling water tank connected to the core catcher to operate so as to supply cooling water to the core catcher.

4. In paragraph 3, A control method for a core catcher system further comprising a step of determining whether a rate of change in the measured values ​​measured by the infrared sensor and the wind pressure and wind speed sensor is above a predetermined level, if the judgment unit determines that at least one of the measured values ​​by the infrared sensor and the wind pressure and wind speed sensor is not above a predetermined value.

5. In paragraph 4, A control method for a core catcher system, comprising the step of commanding the valve unit to operate to supply cooling water to the core catcher when the determination unit determines that the rate of change in the measured values ​​by the infrared sensor and the wind pressure and wind speed sensor is above a predetermined level, even if at least one of the measured values ​​by the infrared sensor and the wind pressure and wind speed sensor is not higher than a predetermined value.

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