Radiation-resistant multiplexer measurement system and nuclear power plant

Abstract

To provide a radiation-resistant multiplexer measurement system and the like capable of high-precision measurements over a long period of time, even in high-radiation environments, while reducing measurement errors caused by fluctuations in the on-resistance of the multiplexer.SOLUTION: A radiation-resistant multiplexer measurement system 1000 includes: thermocouples 1a to 1d that convert physical quantities, including temperature, into analog electrical signals and output them in a PCV103; and multiplexers 2a and 2b selectively output the outputs of the thermocouples 1a to 1d; and a piece of measuring instruments 102 that converts the output signals from the multiplexers 2a and 2b into physical quantities, and controls the output selection of the multiplexers 2a and 2b under a non-radiation environment. The measuring instruments 102 include: a resistance measurement unit 6 that measures the resistance values of the multiplexers 2a and 2b; and a temperature measurement unit 5 that corrects the output signals of the multiplexers 2a and 2b while referring to a calibration table 8 describing the correspondence between the resistance values and the correction coefficients of the output signals and converts the same into a physical quantity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a radiation-tolerant multiplexer measurement system and a nuclear power plant. [Background technology]

[0002] An example of a situation where it is necessary to maintain circuit devices in a radiation environment is a nuclear power plant. In environments exposed to radiation, such as nuclear power plants, semiconductor elements contained in electronic circuits of measuring instruments deteriorate due to the ionizing effect of radiation, making it difficult to use electronic circuits, especially in high-radiation environments.

[0003] For example, to consolidate the vast amount of cables within a plant, it is effective to reduce wiring by using a multiplexer, which is an electronic circuit using semiconductors, but for the reasons mentioned above, it is difficult to apply this to nuclear power plants.

[0004] In nuclear power plants and other radiation-using facilities, various sensors are installed to measure plant and facility processes, including temperature sensors, pressure sensors, flow rate sensors, radiation sensors, and vibration sensors. To strengthen the safety of nuclear power plants, the demand for increasing the number of sensors inside the PCV (Primary Containment Vessel) is increasing year by year, but because the size of the PCV penetration is limited, there is a limit to the number of cables that can pass signals from the sensors, making it difficult to easily increase the number of sensors.

[0005] Patent Document 1 describes a device for reducing the number of cables. The device described in Patent Document 1 includes a first multiplexer that switches between and captures voltage signals from multiple thermocouples, an amplifier that amplifies the voltage signals, an analog-to-digital converter that converts the amplified voltage into a digital value, a corrector that corrects the digital value signal according to the ambient temperature and type of each thermocouple, and a second multiplexer that sequentially switches between passing a small DC current through a high-resistance resistor for open circuit detection to each of the thermocouples. The second multiplexer is used to individually detect open circuits in multiple thermocouples. By passing a small current only when open circuit detection is performed, it is possible to eliminate voltage signal errors caused by variations in the resistance values ​​of the thermocouples.

[0006] However, when a semiconductor multiplexer is installed inside a PCV, which is a high-radiation environment, radiation exposure causes a charge accumulation effect. This is an effect in which gamma rays irradiating the insulating film of the semiconductor generate electron-hole pairs, and holes with particularly low mobility are trapped in the insulating film. These trapped holes are called trapped charges, and they degrade the physical properties (such as mobility) of the interface between the insulating film and the semiconductor. For this reason, it has been difficult to implement a general-purpose multiplexer using Si semiconductors inside a PCV. As a semiconductor material other than Si, silicon carbide (SiC) is expected to have high environmental resistance, and devices with excellent radiation resistance, such as field effect transistors (MOSFETs: Metal-Oxide-Semiconductor Field Effect Transistors) and SiC-MOS capacitors, have been reported. However, SiC has the disadvantage of having lower channel mobility and higher on-resistance compared to Si due to the large number of interface defects that affect channel resistance compared to Si.

[0007] A multiplexer has variations in on-resistance for each channel, and in order to reduce the errors caused by these variations, a device is described in which a voltage follower is inserted between the multiplexer and the analog-to-digital converter (Patent Document 2).

[0008] Non-Patent Document 1 describes a thermocouple measurement system that uses a multiplexer configured with Si-CMOS (Complementary MOS). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 62-75326 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-192973 [Non-Patent Document 1] Low Power Multichannel Thermocouple Measurement System with Cold Junction Compensation; Analog Devices, Circuit Note CN-0354,2017 Summary of the Invention [Problem to be solved by the invention]

[0010] When multiplexers made of semiconductor materials with excellent radiation resistance, such as SiC, are used to reduce the number of cables in measurement systems for nuclear power plants, especially in temperature measurement systems using thermocouples, a problem arises: the high on-resistance of the multiplexer. Even though SiC has excellent radiation resistance, the on-resistance can fluctuate as the cumulative amount of radiation exposure increases, and the magnitude of the change is large because the absolute value is large. A large on-resistance causes significant voltage attenuation due to voltage division with the input resistance of downstream circuits, such as operational amplifiers. Furthermore, while a minute current of 1 μA or less is typically used for open circuit detection, this also increases the voltage signal error, which is multiplied by the on-resistance.

[0011] Patent Document 1 describes a configuration in which a thermocouple and a multiplexer are combined, and describes signal correction, but does not include any description that takes into account the on-resistance of the multiplexer.

[0012] In Patent Document 2, a voltage follower is added to reduce errors caused by the on-resistance of the multiplexer. This reduces the voltage attenuation caused by the voltage division described above, but it does not reduce errors caused by the open circuit detection current.

[0013] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a radiation-resistant multiplexer measurement system and a nuclear power plant that can reduce measurement errors due to fluctuations in the on-resistance of a multiplexer and perform high-precision measurements over a long period of time even in a high-radiation environment. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a measuring instrument that, in a high radiation environment, comprises a plurality of sensors that convert physical quantities including temperature into analog electrical signals and output the signals, and a multiplexer that selectively outputs the outputs of the plurality of sensors, and, in a non-radiation environment, converts the output signals from the multiplexer into physical quantities and controls the output selection of the multiplexer, wherein the measuring instrument comprises a resistance measuring unit that measures the resistance value of the multiplexer, and a physical quantity measuring unit that corrects the output signal of the multiplexer by referring to a calibration table that describes the correspondence between the resistance value and a correction coefficient for the output signal, and then converts the output signal into a physical quantity. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a radiation-resistant multiplexer measurement system and a nuclear power plant that can reduce measurement errors due to fluctuations in the on-resistance of a multiplexer and perform highly accurate measurements over a long period of time even in a high radiation environment. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of a calibration table of the radiation-tolerant multiplexer measurement system according to the first embodiment of the present invention. [Figure 3] 4 is a control sequence of the radiation-tolerant multiplexer measurement system according to the first embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing a calibration table that takes into account the multiplexer temperature value of the radiation-tolerant multiplexer measurement system according to the second embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a third embodiment of the present invention. [Figure 7] FIG. 10 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a fourth embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a fifth embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing the configuration of a main part of a nuclear power plant according to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and can be combined with other embodiments or modified as desired without departing from the technical spirit of the present invention. In the following embodiments, when necessary for convenience, the description will be divided into multiple sections or embodiments, but unless otherwise expressly stated, they are not unrelated to each other, and one is a partial or complete variation, detail, supplementary explanation, etc. of the other. Furthermore, in the following embodiments, when the number of elements (including the number, numerical value, amount, range, etc.) is mentioned, it is not limited to that specific number, and may be greater than or less than the specific number, unless otherwise specified or clearly limited in principle. Furthermore, in the following embodiments, it goes without saying that the components (including elementary steps, etc.) are not necessarily essential, unless otherwise specified or clearly considered essential in principle. Similarly, in the following embodiments, when the shape, positional relationship, etc. of components, etc. are mentioned, it is intended to include those that are substantially approximate or similar to the shape, etc., unless otherwise specified or clearly considered not essential in principle. The same applies to the above numerical values ​​and ranges. In addition, in all the drawings for explaining the following embodiments, components having the same functions are generally designated by the same reference numerals, and repeated explanations thereof will be omitted.

[0018] (First embodiment) 1 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a first embodiment of the present invention. The radiation-tolerant multiplexer measurement system of this embodiment measures temperatures at multiple locations inside a PCV, which is in a high radiation environment. For simplicity of explanation, this example will be described assuming that four thermocouples are used to measure temperatures at four locations.

[0019] As shown in FIG. 1, the radiation-resistant multiplexer measurement system 1000 includes a PCV 103 (containment vessel) and a measuring instrument 102.

[0020] <pcv103> The PCV 103 includes thermocouples 1a to 1d (plurality of sensors) installed at various locations within the PCV, and a multiplexer module 101 connected to the thermocouples 1a to 1d to selectively output thermocouple signals. The thermocouples 1a to 1d convert physical quantities such as temperature into analog electrical signals and output them.

[0021] The multiplexer module 101 includes multiplexers 2a and 2b. The multiplexers 2a and 2b are the main components of the multiplexer module 101 and are mounted on a printed circuit board or the like. The multiplexers 2a and 2b are made of a semiconductor material with excellent radiation resistance, such as SiC. The multiplexers 2a and 2b selectively output the outputs of the thermocouples 1a to 1d (plurality of sensors). The multiplexers 2a and 2b are connected to the positive and negative terminals of the thermocouples 1a to 1d, respectively, and receive power from a power supply 9 in the measuring instrument 102. The multiplexers 2a and 2b selectively output thermocouple signals to the measuring instrument 102 in accordance with a switching instruction 51 from a temperature measurement unit 5 in the measuring instrument 102.

[0022] <Measuring Instrument 102> The measuring instrument 102 converts the output signals from the multiplexers 2a and 2b into physical quantities and controls the output selection of the multiplexers. For example, the measuring instrument 102 converts thermocouple signals into temperature values ​​and issues switching instructions and power supply to the multiplexer module 101.

[0023] The measuring instrument 102 includes a temperature measuring unit 5 (physical quantity measuring unit), a resistance measuring unit 6, switches 7a and 7b, a memory unit (not shown) that stores a calibration table 8, and a power supply unit 9. The radiation-resistant multiplexer measurement system 1000 only needs to be able to utilize the information in the calibration table 8, which is stored in a memory unit that can be read by the temperature measuring unit 5. This memory unit may be located anywhere, such as on the cloud. The temperature measurement unit 5 corrects the output signals of the multiplexers 2a and 2b by referring to the calibration table 8, and then converts them into physical quantities. The temperature measurement unit 5 also controls the selection of the outputs of the multiplexers 2a and 2b.

[0024] In the normal <temperature measurement mode>, the thermocouple signal input to the measuring instrument 102 is sent to the temperature measurement unit 5 via switches 7a and 7b, and is converted into a temperature value according to the voltage value of the thermocouple signal and a correction value described below. Resistance value information 54 measured by the resistance measurement unit 6 is sent via the temperature measurement unit 5 to a calibration table 8 (FIG. 2) that describes the relationship between the resistance value and the correction coefficient. The temperature measurement unit 5 reads out the correction value information 55 corresponding to the resistance value information 54 from the calibration table 8, calculates the temperature value using the read correction value information 55, and thereafter changes the correction value used in accordance with fluctuations in the resistance value.

[0025] The resistance measurement unit 6 measures the resistance values ​​of the multiplexers 2a and 2b. The resistance measurement unit 6 is provided to measure the on-resistance fluctuations of the multiplexers 2a and 2b, and in the <resistance measurement mode>, the switches 7a and 7b are switched by a switching instruction 52 from the temperature measurement unit 5, and resistance measurement is started by a measurement instruction 53 also from the temperature measurement unit 5.

[0026] The resistance measurement unit 6 may measure the resistance by passing a known constant current and observing the voltage generated at both ends of the signal path. The measured resistance is the total resistance of the signal path, which is the sum of the on-resistances of the multiplexers 2a and 2b, the switches 7a and 7b, the resistance of the thermocouple, and the resistance of the compensation leads. The calibration table 8 must be created taking these factors into consideration.

[0027] The voltage value measured by the resistance measurement unit 6 is added to the signal voltage value of the thermocouple, so the voltage value fluctuates depending on the temperature change around the thermocouple. Therefore, it is advisable to adjust the current value so that the measured voltage value is sufficiently larger than the signal voltage value of the thermocouple (for example, several tens of μA to several mA).

[0028] The switches 7a and 7b switch between a path connecting the multiplexers 2a and 2b to the resistance measurement unit 6 and a path connecting the multiplexers 2a and 2b to the temperature measurement unit 5. Here, it is preferable to maintain symmetry between the two signal paths between the positive and negative terminals of thermocouple 1a and temperature measurement unit 5. Specifically, they should be arranged adjacent to each other with equal lengths as much as possible. This improves resistance to external electromagnetic noise. The same applies to thermocouples 1b to 1d.

[0029] The calibration table 8 describes the correspondence between the resistance value and the correction coefficient of the output signal. 2 is a diagram showing an example of the calibration table 8. The calibration table 8 holds correction coefficients C1 to CN for each of the resistance values ​​R1 to RN. The resistance values ​​R1 to RN correspond to the resistance value information 54 in FIG. 1, and the correction coefficients C1 to CN correspond to the correction value information 55 in FIG. 1.

[0030] When creating calibration table 8, multiplexers 2a and 2b may be replaced with resistance components with known constants, and a system in which a thermocouple and a temperature measurement unit are directly connected may be used as a reference to obtain correction values ​​while changing the constants of the resistance components. Also, calibration table 8 may contain correction values ​​corresponding to each resistance value, and if the resistance value measured by resistance measurement unit 6 is an intermediate value in the table, linear interpolation may be performed, or the correction value may be created as an approximate function of the resistance value.

[0031] The temperature measurement unit 5, resistance measurement unit 6, switches 7a and 7b, and calibration table 8 as a whole constitute a functional unit that measures the multiplexer resistance value and corrects the output signal of the multiplexer by referring to the calibration table 8.

[0032] To ensure high reliability, the radiation-tolerant multiplexer measurement system 1000 includes an open-circuit detection function (e.g., a high-resistance resistor) in the temperature measurement unit 5 to detect open circuits in the signal path between the thermocouples 1a-1d and the temperature measurement unit 5, which consists of multiplexers, compensation wires, and other components. The open-circuit detection function connects the signal path to a positive or negative power supply voltage via a high-resistance resistor, and detects an open circuit in the signal path by causing the voltage signal to swing to its maximum or minimum value. It can also detect a failure of the MOSFETs that make up the multiplexers 2a and 2b, resulting in an open circuit between the source and drain. The disadvantage of this open-circuit detection function is that it causes a small current to flow through the signal path, resulting in a voltage signal error that is multiplied by the total resistance of the signal path, including the on-resistance of the multiplexers 2a and 2b. However, by performing the correction described above, highly accurate temperature measurement is possible even when on-resistance fluctuations due to radiation exposure occur.

[0033] The operation of the radiation-tolerant multiplexer measurement system 1000 configured as described above will now be described.

[0034] FIG. 3 shows a control sequence of the radiation-tolerant multiplexer measurement system 1000. The input channels of the multiplexers 2a and 2b connected to the thermocouples 1a, 1b, 1c, and 1d shown in FIG. 1 will be described as ch1, ch2, ch3, and ch4, respectively. The temperature measurement unit 5 has a <temperature measurement mode> for performing temperature measurement in normal use, and a <resistance measurement mode> for measuring the resistance of the multiplexers 2a and 2b.

[0035] First, the temperature measurement unit 5 ends the normal <temperature measurement mode> at any timing, starts the <resistance measurement mode> (S200), and sends a switching instruction to the switches 7a and 7b (S201).

[0036] The switches 7a and 7b switch from the normal temperature measurement path to the resistance measurement path in accordance with a switching instruction from the temperature measurement unit 5 (S202). After a certain period of time, the temperature measurement unit 5 sends a switching instruction to the multiplexers 2a and 2b to switch the path to ch1 (S203).

[0037] The multiplexers 2a and 2b receive the switching instruction from the temperature measurement unit 5 and switch the path to ch1 (S204). After a certain time, the temperature measurement unit 5 sends an instruction to start resistance measurement to the resistance measurement unit 6 (S206). The resistance measurement unit 6 starts resistance measurement and sends information about the measured resistance value to the temperature measurement unit 5 (S207).

[0038] The temperature measurement unit 5 sends the resistance value information of the resistance measurement unit 6 to the calibration table 8 (S208). The calibration table 8 searches for a correction value corresponding to this resistance value (S209) and sends the obtained correction value back to the temperature measurement unit 5 (S210).

[0039] The temperature measurement unit 5 updates the correction value used in temperature calculation when the ch1 path is selected to the obtained value (S211). With the above, the flow of ch1 in the <resistance measurement mode> is completed, and the flow moves to ch2.

[0040] As a flow for ch2, the temperature measurement unit 5 sends a switching instruction to the multiplexers 2a and 2b to switch the path to ch2 (S212). Thereafter, the same flow as ch2 → ch3 → ch4 is continued, and after updating the ch4 correction value, the temperature measurement mode is resumed (S251). The temperature measurement unit 5 sends a switching instruction to the switches 7a and 7b (S252), and the switches 7a and 7b switch from the resistance measurement path to the temperature measurement path in accordance with this switching instruction (S253). After a certain period of time, the temperature measurement unit 5 sends a switching instruction to the multiplexers 2a and 2b to switch the path to ch1 (S254).

[0041] The multiplexers 2a and 2b receive the switching instruction from the temperature measurement unit 5 and switch the path to ch1 (S255). After a certain period of time, the temperature measurement unit 5 calculates the temperature of the ch1 path using the correction value (S256). With the above, the flow of ch1 in the <temperature measurement mode> is completed, and as the flow of ch2, the temperature measurement unit 5 sends a switching instruction to the multiplexers 2a and 2b to switch the path to ch2 (S257).

[0042] Thereafter, the same flow as ch2 → ch3 → ch4 → ch1 →... is repeated to measure and calculate the temperature of each channel.

[0043] The appropriate frequency for running the <Resistance Measurement Mode> depends on the radiation level in the environment where the multiplexer module is installed, but once a week or once a month is sufficient.

[0044] [Advantages of the first embodiment] As described above, the radiation-resistant multiplexer measurement system 1000 includes, in a PCV 103 that is in a high radiation environment, thermocouples 1a to 1d (plurality of sensors) that convert physical quantities including temperature into analog electrical signals and output the signals, and multiplexers 2a and 2b that selectively output the outputs of the thermocouples 1a to 1d. The radiation-resistant multiplexer measurement system 1000 also includes, in a non-radiation environment, a measuring instrument 102 that converts output signals from the multiplexers 2a and 2b into physical quantities and controls the selection of the outputs of the multiplexers 2a and 2b. The measuring instrument 102 includes a resistance measuring unit 6 that measures the resistance values ​​of the multiplexers 2a and 2b, and a temperature measuring unit 5 (physical quantity measuring unit) that corrects the output signals of the multiplexers 2a and 2b by referring to a calibration table 8 (FIG. 2) that describes the correspondence between the resistance values ​​and the correction coefficients of the output signals, and then converts the corrected signals into physical quantities.

[0045] This configuration can reduce temperature measurement errors caused by multiplexer resistance components in the radiation-tolerant multiplexer measurement system 1000. This reduces measurement errors caused by fluctuations in the on-resistance of the multiplexers 2 a and 2 b, which use semiconductor materials such as SiC, and provides a temperature measurement system that can perform high-precision measurements over a long period of time even in a high-radiation environment.

[0046] As described above, resistance measurement using this embodiment produces various effects that contribute to higher reliability. It can detect not only breaks in conductor cables and board wiring, but also open circuit faults between the source and drain of MOSFETs that make up a multiplexer. It can also detect faults that increase the transition time of channel switching due to an increase in the gate resistance of the MOSFET.

[0047] Furthermore, if the temperatures of the thermocouples installed at each location are all different, it is possible to detect abnormalities in the transition time by observing the temperature change caused by channel switching using the temperature measurement unit 5. However, if the temperatures of each thermocouple are almost the same, it is difficult to detect abnormalities. Therefore, by inserting different resistive elements into each channel of the multiplexers 2a and 2b to make the apparent on-resistance different, and checking the responsiveness of the resistance value output to channel switching in the resistance measurement mode, abnormalities can be detected. To achieve this effect, it is desirable to increase the frequency of the resistance measurement mode more than described above.

[0048] (Second embodiment) 4 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a second embodiment of the present invention, in which the same components as those in FIG. 1 are given the same reference numerals and overlapping explanations will be omitted.

[0049] The radiation-tolerant multiplexer measurement system 1000A differs in configuration from the radiation-tolerant multiplexer measurement system 1000 shown in Fig. 1 in that a thermocouple 11 (temperature sensor) is disposed within the multiplexer module 101A. The thermocouple 11 is disposed near the multiplexers 2a and 2b so that the ambient temperature of the multiplexers 2a and 2b can be measured. Thermocouple signal 56 of thermocouple 11 is input to temperature measurement section 5A (physical quantity measurement section) in measuring instrument 102A, and is converted into a temperature value (multiplexer temperature) according to the voltage value.

[0050] FIG. 5 is a diagram showing a calibration table 8A that takes into account the multiplexer temperature values. The resistance values ​​of multiplexers 2a and 2b vary depending on the multiplexer temperature, so calibration table 8A has table data of correction coefficients C11 to CNM for multiplexer temperatures T1 to TM and resistance values ​​R1 to RN. Calibration table 8A shown in FIG. 5 adds the correspondence between the ambient temperature of the multiplexer and the correction coefficient of the output signal in addition to the resistance values ​​R1 to RN to calibration table 8 shown in FIG.

[0051] The temperature value (multiplexer temperature) of the thermocouple 11 is sent to a calibration table 8A, which describes the relationship between the resistance value, temperature value, and correction coefficient, as temperature and resistance value information 54A, together with resistance value information 54 measured in the <resistance measurement mode>. The temperature measurement unit 5A reads correction value information 55 from the calibration table 8A, calculates the temperature value using the read correction value information 55, and thereafter changes the correction value used in accordance with fluctuations in the resistance value and temperature value.

[0052] [Effects of the second embodiment] The radiation-resistant multiplexer measurement system 1000A is provided with thermocouples 11 (temperature sensors) near the multiplexers 2a and 2b that measure the ambient temperatures of the multiplexers 2a and 2b. A calibration table 8A (FIG. 5) describes the correspondence between the ambient temperatures of the multiplexers and the correction coefficients of the output signals, in addition to the resistance values. The physical quantity measurement unit refers to the calibration table that describes the correspondence, corrects the output signals of the multiplexers 2a and 2b, and then converts them into physical quantities.

[0053] By configuring it in this manner, the radiation-resistant multiplexer measurement system 1000A can achieve the same effects as the first embodiment, i.e., reduce temperature measurement errors caused by multiplexer resistance components, reduce measurement errors caused by fluctuations in the on-resistance of the multiplexers 2a and 2b, and enable high-precision measurements over a long period of time even in a high-radiation environment.

[0054] In addition to the effects of the first embodiment, it is also possible to determine whether the ambient temperature of the multiplexers 2a and 2b is within the temperature range in which the multiplexers 2a and 2b can operate normally, and notify the host system of this.

[0055] To improve reliability, the radiation-tolerant multiplexer measurement system 1000A is equipped with an open circuit detection function in the temperature measurement unit 5A that detects open circuits in the signal path between the thermocouples 1a-1d and the temperature measurement unit 12, which is made up of the multiplexers 2a and 2b and compensation wires. By performing the above-described correction for the voltage signal error caused by the minute current for this open circuit detection, highly accurate temperature measurement becomes possible even if there are fluctuations in the ambient temperature of the multiplexers 2a and 2b or fluctuations in the on-resistance due to radiation exposure.

[0056] As described above, the radiation-resistant multiplexer measurement system 1000A reduces measurement errors caused by fluctuations in the on-resistance of the multiplexer due to radiation exposure or temperature fluctuations, and provides a temperature measurement system that can perform high-precision measurements over a long period of time even in high-radiation environments.

[0057] (Third embodiment) 6 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a third embodiment of the present invention, in which the same components as those in FIG. 4 are given the same reference numerals and overlapping descriptions will be omitted.

[0058] The radiation-resistant multiplexer measurement system 1000B differs in configuration from the radiation-resistant multiplexer measurement system 1000A shown in Figure 4 in that a thermocouple 11 (temperature sensor) and a heater 12 (temperature regulator) are arranged in the multiplexer module 101B, and a heater control unit 23 (control unit) is arranged in the measuring instrument 102B. The thermocouple 11 is disposed near the multiplexers 2a and 2b so as to measure the ambient temperature of the multiplexers 2a and 2b. The heater 21 is also disposed near the multiplexers 2a and 2b so as to heat the multiplexers 2a and 2b. The heating operation of the heater 21 is controlled by a heater control unit 23 in the measuring instrument 102B. The heater control unit 23 starts and stops the operation of the heater 21 and controls the amount of heating power in response to a heating instruction 71 from the temperature measuring unit 22.

[0059] The temperature measurement unit 5B (physical quantity measurement unit) ends the normal resistance measurement mode at any timing, stops temperature measurement by the thermocouples 1a to 1d, and starts the charge refresh mode. It sends a heating instruction 71 to the heater control unit 23. The heater control unit 23 starts the operation of the heater 21 with any amount of heating power in accordance with the heating instruction 71.

[0060] The temperature measurement unit 22 adjusts the heating instruction 71 so that the temperature value converted according to the thermocouple signal voltage value of the thermocouple 11 becomes an arbitrary set temperature (for example, several hundred degrees Celsius).

[0061] By heating for a certain period of time in this manner, the charge accumulated in the multiplexers 2a and 2b due to radiation exposure can be refreshed, and fluctuations in on-resistance can also be alleviated. After the certain period of time has elapsed, the operation of the heater 21 is stopped, and after the ambient temperature of the multiplexers 2a and 2b returns to the temperature before heating, the charge refresh mode is terminated, the normal temperature measurement mode is resumed, and temperature measurement using the thermocouples 1a to 1d is started.

[0062] Here, if a heating / cooling device such as a Peltier module (temperature regulator) is used instead of the heater 21, the temperature of the multiplexers 2a and 2b can be kept constant in the normal temperature measurement mode, thereby reducing the temperature dependency of the multiplexers 2a and 2b.

[0063] [Effects of the third embodiment] The radiation-resistant multiplexer measurement system 1000B includes a heater 12 (temperature regulator) for heating or cooling the multiplexers 2a and 2b, located near the multiplexers 2a and 2b. The measuring instrument 102B is equipped with a heater control unit 23 (control unit) that heats the heater 12 or controls the heater 12 or Peltier module (temperature regulator) to maintain a predetermined temperature, and when measuring the resistance values ​​of the multiplexers 2a and 2b, the temperature measurement unit 5B (physical quantity measurement unit) measures the resistance values ​​of the multiplexers 2a and 2b after heating the multiplexers 2a and 2b, or measures the resistance values ​​of the multiplexers 2a and 2b while maintaining them at a predetermined temperature.

[0064] With this configuration, by heating the multiplexers 2a and 2b and measuring their resistance after heating, it is possible to refresh the charge accumulated in the multiplexers 2a and 2b due to radiation exposure and reduce on-resistance fluctuations. Also, by maintaining the multiplexers 2a and 2b at a constant temperature and measuring their resistance in that state, it is possible to reduce the temperature dependence of the multiplexers 2a and 2b. As a result, the output signals of the multiplexers 2a and 2b can be corrected more accurately, and temperature measurement errors caused by the resistance components of the multiplexers can be further reduced.

[0065] As described above, the radiation-tolerant multiplexer measurement system 1000B can refresh the charge accumulated by radiation exposure and mitigate the on-resistance fluctuation, thereby reducing measurement errors and providing a temperature measurement system that can perform high-precision measurements over a long period of time even in a high-radiation environment.

[0066] (Fourth embodiment) 7 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a fourth embodiment of the present invention, in which the same components as those in FIG. 1 are given the same reference numerals and overlapping explanations will be omitted.

[0067] The radiation-tolerant multiplexer measurement system 1000C differs in configuration from the radiation-tolerant multiplexer measurement system 1000 shown in Fig. 1 in that a power supply voltage change instruction 81 is sent from a temperature measurement unit 5C (physical quantity measurement unit) in a measuring instrument 102C to a power supply unit 9C. Unlike the power supply unit 9 (Figs. 1, 4, and 6), the power supply voltage of the power supply unit 9C is variable.

[0068] Upon receiving a request from the higher-level system, the temperature measurement unit 5C ends the normal temperature measurement mode and starts the resistance measurement mode. The temperature measurement unit 5C sends a power supply voltage change instruction 81 to the power supply unit 9C to increase the power supply voltage (for example, from 3.3 V to 5 V). The power supply unit 9C changes the power supply voltage supplied to the multiplexers 2a and 2b in accordance with the power supply voltage change instruction 81.

[0069] Here, the signal voltage value of the switching instruction 82 from the temperature measurement unit 5C to the multiplexers 2a and 2b may be changed in conjunction with each other. After that, as in the first embodiment, resistance measurement is performed for each channel of the multiplexers 2a and 2b (FIG. 3), and after updating each correction value, the <high-precision temperature measurement mode> is started. The <High Precision Temperature Measurement Mode> is the same as the normal <Temperature Measurement Mode> except that it uses a large power supply voltage. When a request to return to the normal <Temperature Measurement Mode> is received from the host system, the mode transitions to the normal <Temperature Measurement Mode> via the <Resistance Measurement Mode>.

[0070] In general, in a multiplexer made of semiconductors, increasing the power supply voltage reduces the on-resistance and reduces measurement errors, but there is a trade-off in that the device lifespan is shortened, so the power supply voltage cannot be easily increased. However, in nuclear power plant applications, emergency situations may arise in which more accurate temperature measurement is required for a short period of time, and this embodiment is designed to address such emergency situations. Conversely, there may also be cases in which operation is performed with lower-precision temperature measurement during normal times, in which case the device lifespan can be extended by controlling the power supply voltage to a low level.

[0071] [Effects of the fourth embodiment] The radiation-resistant multiplexer measurement system 1000C includes a measuring instrument 102C that includes a power supply unit 9C that supplies power to the multiplexers 2a and 2b, and the power supply unit 9C increases or decreases the supply voltage to the multiplexers 2a and 2b based on instructions from a temperature measurement unit 5C (physical quantity measurement unit).

[0072] With this configuration, in the <high-precision temperature measurement mode>, a large power supply voltage is used, which reduces the on-resistance and further reduces measurement errors. On the other hand, in the <resistance measurement mode>, the output signals of the multiplexers 2a and 2b are corrected by resistance measurement similar to the first to third embodiments. In this case, the life of the device can be extended.

[0073] As described above, the radiation-tolerant multiplexer measurement system 1000C can adaptively change the measurement accuracy as needed, and furthermore, it can reduce measurement errors caused by fluctuations in on-resistance due to radiation exposure of the multiplexer, thereby providing a temperature measurement system that operates normally even in high-radiation environments.

[0074] (Fifth embodiment) 8 is a diagram showing the configuration of a radiation-tolerant multiplexer measurement system according to a fifth embodiment of the present invention, in which the same components as those in FIG. 1 are given the same reference numerals and overlapping explanations will be omitted. In this embodiment, in order to improve reliability, temperature measurements at multiple locations inside the PCV, which is in a high radiation environment, are made redundant so that operation can continue in the remaining systems even if a single failure occurs in one system. For simplicity of explanation, the radiation-resistant multiplexer measurement system 1000 described in the first embodiment is made quadruple.

[0075] As shown in FIG. 8, the radiation-resistant multiplexer measurement system 1000D includes multiplexer modules 141-1 to 141-4 with thermocouples, each of which is composed of four thermocouples and two multiplexers, in the PCV 103 to configure a quadruple system. The multiplexer modules with thermocouples 141-1 to 141-4 each include thermocouples 1a to 1d installed at various locations within the PCV, and a multiplexer module 101 connected to the thermocouples 1a to 1d to selectively output thermocouple signals.

[0076] The radiation-tolerant multiplexer measurement system 1000D includes measuring instruments 142-1 to 142-4 connected to the thermocouple-equipped multiplexer modules 141-1 to 141-4, respectively, and a management device 143 that manages the measuring instruments 142-1 to 142-4. Measuring instruments 142-1 to 142-4 are the same as measuring instrument 102 shown in Fig. 1. That is, measuring instruments 142-1 to 142-4 each include a temperature measurement unit 5, a resistance measurement unit 6, switches 7a and 7b, a calibration table 8, and a power supply unit 9. The operations of the multiplexer modules with thermocouples 141-1 to 141-4 and the measuring instruments 142-1 to 142-4 are the same as those shown in the first embodiment.

[0077] Upon receiving instructions 92-1 to 92-4 from the management device 143, each temperature measurement unit 5 sends the resistance value and disconnection status of the multiplexer that it has grasped to the management device 143 together with the channel number as multiplexer information 91-1 to 91-4.

[0078] The management device 143 manages the multiplexer information 91-1 to 91-4 from each temperature measurement unit 5 in an integrated manner, and sends alarms such as disconnection and increased resistance to a higher-level system. The management device 143 may set an arbitrary threshold value for the resistance value, determine that a failure has occurred when the resistance value exceeds the threshold value, and notify the upper system of an alarm of a multiplexer failure. The management device 143 also displays multiplexer information for each system and each channel to an operator, and sends instructions 92-1 to 92-4 to each temperature measurement unit 41-1 to 41-4 upon request from the upper system.

[0079] Here, since there is a causal relationship between the increase in resistance value and the cumulative amount of radiation exposure, the correlation between the increase in resistance value and the cumulative amount of radiation exposure can be measured in advance, and the cumulative amount of radiation exposure can be estimated by referring to the results and notified to a higher-level system. In addition, although the explanation here is that multiplexer modules are used for all four systems, it goes without saying that the effect of reducing the number of cables can be achieved even if, for example, a multiplexer module is not used for just one system and the thermocouple signal is input directly to the temperature measurement unit.

[0080] [Effects of the fifth embodiment] The radiation-resistant multiplexer measurement system 1000D includes a plurality of combinations of thermocouple-equipped multiplexer modules 141-1 to 141-4 having multiplexers 2a and 2b similar to those of the first to third embodiments and measuring instruments 142-1 to 142-4, and includes a management device 143 that manages and controls the plurality of measuring instruments 142-1 to 142-4.

[0081] By configuring it in this way, the radiation-resistant multiplexer measurement system 1000D is made redundant so that operation can continue in the remaining system even if a single failure occurs, while reducing measurement errors caused by fluctuations in on-resistance due to radiation exposure to the multiplexer, thereby providing a temperature measurement system that can perform high-precision measurements over a long period of time even in high-radiation environments.

[0082] (Sixth embodiment) FIG. 9 is a diagram showing the configuration of a main part of a nuclear power plant 2000 according to a sixth embodiment of the present invention. The nuclear power plant 2000 of this embodiment is equipped with radiation-resistant multiplexer measurement systems 1000 (FIG. 1), 1000A (FIG. 4), 1000B (FIG. 6), 1000C (FIG. 7), and 1000D (FIG. 8) that measure physical quantities such as the temperatures of the reactor containment vessel, the reactor pressure vessel, and the pressure suppression chamber.

[0083] Specifically, the nuclear power plant 2000 is provided with various sensors installed in a boiling water reactor (BWR) for safety monitoring and control, and measures various physical quantities. A BWR comprises a PCV158 (containment vessel), a reactor pressure vessel 157 built into the PCV158, and a pressure suppression chamber 159 connected to the reactor pressure vessel 157, and generates electricity by rotating a turbine generator using steam generated directly from cooling water inside the reactor pressure vessel 157. In the event of a loss of primary coolant accident, the leaking steam and hot water are guided from PCV 158 to the pressure suppression chamber 159, where they are cooled and condensed to prevent the pressure inside the vessel from increasing.

[0084] The nuclear power plant 2000 generates electricity by rotating a turbine generator using steam generated from cooling water in the PCV 158, and prevents the pressure inside the PCV 158 from increasing by guiding the flowing steam and hot water from the PCV 158 to the pressure suppression chamber 159 where it is cooled and condensed, and measures physical quantities such as the temperatures of the PCV 158, the reactor pressure vessel 157, and the pressure suppression chamber 159.

[0085] PCV158 has temperature sensors 153 (multiple sensors), image sensors 154 (multiple sensors), and SRM (Source Range Monitor: neutron source range monitor) 155 (multiple sensors) placed in various locations, and these sensor signals are collected by multiplexer modules 101 (Figures 1 and 7), 101A (Figure 4), 101B (Figure 6), and 141-1 to 141-4 (Figure 8), and then input to measuring instruments 102 (Figure 1), 102A (Figure 4), 102B (Figure 6), 102C (Figure 7), and 142 (Figure 8) through a through hole 156 opened in PCV158.

[0086] The temperature sensor 153 and the image sensor 154 respectively monitor the temperature and state inside the PCV 158. The SRM 155 measures the amount of neutrons inside the reactor when the reactor is in a low power state, such as when the reactor is started or stopped, and issues an alarm if it detects an excessive amount of neutrons.

[0087] The operations of multiplexer modules 101 (FIGS. 1 and 7), 101A (FIG. 4), 101B (FIG. 6), and 141-1 to 141-4 (FIG. 8) and measuring instruments 102 (FIG. 1), 102A (FIG. 4), 102B (FIG. 6), 102C (FIG. 7), and 142 (FIG. 8) are as described in each embodiment.

[0088] In this embodiment, a small number of representative sensor types have been used for explanation, but the present invention is not limited to these and can be applied to a large number of different types of sensors.

[0089] [Effects of the Sixth Embodiment] The nuclear power plant 2000 is a nuclear power plant including a PCV 158 (a reactor containment vessel), a reactor pressure vessel 157 built in the PCV 158, a pressure suppression chamber 159 connected to the reactor pressure vessel 157, and radiation-resistant multiplexer measurement systems 1000, 1000A, 1000B, 1000C, and 1000D that measure physical quantities including temperatures of the PCV 158, the reactor pressure vessel 157, and the pressure suppression chamber 159. The radiation-resistant multiplexer measurement systems 1000, 1000A, 1000B, 1000C, and 1000D convert the physical quantities including the temperature into analog electrical signals within the PCV 103, which is in a high radiation environment. The measuring instrument 102 includes thermocouples 1a to 1d (plurality of sensors) that convert and output the outputs of the thermocouples 1a to 1d, and multiplexers 2a and 2b that selectively output the outputs of the thermocouples 1a to 1d. The measuring instrument 102 converts the output signals from the multiplexers 2a and 2b into physical quantities in a non-radiation environment and controls the selection of the outputs of the multiplexers 2a and 2b. The measuring instrument 102 includes a resistance measuring unit 6 that measures the resistance values ​​of the multiplexers 2a and 2b, and a temperature measuring unit 5 (physical quantity measuring unit) that corrects the output signals of the multiplexers 2a and 2b by referring to calibration tables 8 and 8A (FIGS. 2 and 5) that describe the correspondence between the resistance values ​​and correction coefficients of the output signals, and then converts them into physical quantities.

[0090] By configuring in this manner, the nuclear power plant 2000 can reduce measurement errors caused by on-resistance fluctuations due to radiation exposure of multiplexers made of semiconductor materials such as SiC, and can provide a wiring-saving system that can perform high-precision measurements over a long period of time even in a high-radiation environment.

[0091] The present invention is not limited to the configurations described in the above embodiments, and the configurations can be appropriately changed without departing from the gist of the present invention as set forth in the claims. There are various types of SiC, and any type can be applied.

[0092] Although the example of application to a boiling water reactor (BWR) as a nuclear power plant has been explained, the system can also be applied to pressurized water reactors (PWR) and other reactors. In other words, the radiation-resistant multiplexer measurement system can be applied to pressurized water reactors (PWR) and other reactors.

[0093] The above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0094] 1a~1d Thermocouples (multiple sensors) 2a, 2b multiplexer 5,5A,5B,5C Temperature measurement section (physical quantity measurement section) 6 Resistance measurement section 7a, 7b switches 8,8A Calibration Table 9,9C power supply section 11 Thermocouple (temperature sensor) 12 Heater (temperature regulator) 23 Heater control unit (control unit) 101, 101A, 101B Multiplexer Module 102, 102A, 102B, 102C, 142, 142-1~4 Measuring instruments 103,158 PCV (Primary Containment Vessel) 141-1~4 Multiplexer Module with Thermocouple (Multiplexer Module) 143 Management device 157 Reactor Pressure Vessel 159 Suppression Chamber 153 Temperature Sensor (Multiple Sensors) 154 Image Sensor (Multiple Sensors) 155 SRM (Multiple Sensors) 1000, 1000A, 1000B, 1000C, 1000D Radiation-Tolerant Multiplexer Measurement System 2000 Nuclear Power Plant

Claims

1. A system including a plurality of sensors that convert physical quantities including temperature into analog electrical signals and output the analog electrical signals in a high radiation environment, and a multiplexer that selectively outputs the outputs of the plurality of sensors; a measuring instrument that converts an output signal from the multiplexer into a physical quantity and controls output selection of the multiplexer in a non-radiation environment; The measuring instrument is a resistance measurement unit that measures the resistance value of the multiplexer; a physical quantity measuring unit that refers to a calibration table in which a correspondence relationship between the resistance value and a correction coefficient of the output signal is described, corrects the output signal of the multiplexer, and then converts the corrected signal into a physical quantity. A radiation-tolerant multiplexer measurement system comprising:

2. The measuring instrument includes a switch that switches between a path connecting the multiplexer and the resistance measuring unit and a path connecting the multiplexer and the physical quantity measuring unit.

2. The radiation-tolerant multiplexer measurement system according to claim 1.

3. a temperature sensor disposed near the multiplexer for measuring the ambient temperature of the multiplexer; the calibration table describes a correspondence relationship between the ambient temperature of the multiplexer and a correction coefficient of the output signal in addition to the resistance value; The physical quantity measuring unit corrects the output signal of the multiplexer by referring to the calibration table in which the correspondence relationship is described, and then converts the corrected output signal into a physical quantity.

2. The radiation-tolerant multiplexer measurement system according to claim 1.

4. a temperature regulator for heating or cooling the multiplexer is provided in the vicinity of the multiplexer; the measuring instrument includes a control unit that heats the temperature regulator or controls the temperature regulator to maintain a predetermined temperature; When measuring the resistance value of the multiplexer, the physical quantity measuring unit measuring the resistance of the multiplexer after heating the multiplexer; or The resistance value of the multiplexer is measured while the multiplexer is maintained at a predetermined temperature.

2. The radiation-tolerant multiplexer measurement system according to claim 1.

5. the measuring instrument includes a power supply unit that supplies power to the multiplexer; The power supply unit increases or decreases the supply voltage of the multiplexer in response to an instruction from the physical quantity measurement unit.

2. The radiation-tolerant multiplexer measurement system according to claim 1.

6. a plurality of combinations of the multiplexer and the measuring instrument; A management device that manages and controls a plurality of the measuring instruments is provided.

2. The radiation-tolerant multiplexer measurement system according to claim 1.

7. A reactor containment vessel; a reactor pressure vessel housed in the reactor containment vessel; a pressure suppression chamber connected to the reactor pressure vessel; a radiation-resistant multiplexer measurement system that measures physical quantities including temperatures of the reactor containment vessel, the reactor pressure vessel, and the pressure suppression chamber, the radiation-hard multiplexer measurement system, a plurality of sensors configured to convert physical quantities including temperature into analog electrical signals and output the analog electrical signals, and a multiplexer configured to selectively output the outputs of the plurality of sensors, within the reactor containment vessel; a measuring instrument that converts an output signal from the multiplexer into a physical quantity and controls output selection of the multiplexer in a non-radiation environment; The measuring instrument is a resistance measurement unit that measures the resistance value of the multiplexer; a physical quantity measuring unit that refers to a calibration table in which a correspondence relationship between the resistance value and a correction coefficient of the output signal is described, corrects the output signal of the multiplexer, and then converts the corrected signal into a physical quantity. A nuclear power plant characterized by:

8. The measuring instrument includes a switch that switches between a path connecting the multiplexer and the resistance measuring unit and a path connecting the multiplexer and the physical quantity measuring unit.

8. The nuclear power plant according to claim 7.

9. a temperature sensor disposed near the multiplexer for measuring the ambient temperature of the multiplexer; the calibration table describes a correspondence relationship between the ambient temperature of the multiplexer and a correction coefficient of the output signal in addition to the resistance value; The physical quantity measuring unit corrects the output signal of the multiplexer by referring to the calibration table in which the correspondence relationship is described, and then converts the corrected output signal into a physical quantity.

8. The nuclear power plant according to claim 7.

10. a temperature regulator for heating or cooling the multiplexer is provided in the vicinity of the multiplexer; the measuring instrument includes a control unit that heats the temperature regulator or controls the temperature regulator to maintain a predetermined temperature; When measuring the resistance value of the multiplexer, the physical quantity measuring unit measuring the resistance of the multiplexer after heating the multiplexer; or The resistance value of the multiplexer is measured while the multiplexer is maintained at a predetermined temperature.

8. The nuclear power plant according to claim 7.

11. the measuring instrument includes a power supply unit that supplies power to the multiplexer; The power supply unit increases or decreases the supply voltage of the multiplexer in response to an instruction from the physical quantity measurement unit.

8. The nuclear power plant according to claim 7.

12. a plurality of combinations of the multiplexer and the measuring instrument; A management device that manages and controls a plurality of the measuring instruments is provided.

8. The nuclear power plant according to claim 7.

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