Method and system for automatic control for safe discharge of gaseous radwaste

Abstract

A radioactive waste treatment control system may include a sensor unit that measures the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration of gaseous waste passing through a HEPA filter, a discharge valve that opens and closes the atmospheric discharge path of the gaseous waste, a memory that stores instructions, and a processor. The system forms a discharge path for the gaseous waste through either a first train line or a second train line that is identically configured and redundant with each other. When the automatic mode is selected among the automatic mode and the manual mode, the system compares the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration measured by the sensor unit with corresponding preset reference values ​​to determine whether the gaseous waste is in a safe state for discharge into the atmosphere. If it is determined that the gaseous waste is in a safe state, the system opens the discharge valve to discharge the gaseous waste into the atmosphere, and if it is determined that the gaseous waste is not in a safe state, the system outputs an alarm and controls the system to restrict the opening of the discharge valve.

Description

Technology Field

[0001] The present invention relates to the field of gaseous radioactive waste treatment control for nuclear facilities.

[0002] More specifically, the invention relates to an automatic control method and system for the safe discharge of radioactive waste, which measures multiple state parameters of gaseous waste passing through a HEPA filter and comprehensively evaluates them, and automatically controls the discharge of gaseous waste into the atmosphere only when it is confirmed to be in a safe state. Background Technology

[0004] Gaseous radioactive waste may be generated during the operation of nuclear facilities, including nuclear power plants. This gaseous waste can be released into the atmosphere only when it is in a safe state that meets certain standards regarding radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration. Therefore, a process of measuring these various conditions and determining safety is required prior to releasing the gaseous waste.

[0005] Conventionally, the emission control of such gaseous waste relied primarily on manual operation by workers or was carried out through single-loop controllers separated for each individual parameter. In this case, since each parameter is managed individually, it is difficult to make a comprehensive judgment of multiple states, and frequent worker intervention is required, which can lead to reduced operational efficiency.

[0006] Furthermore, since the emission of gaseous waste is an operation directly related to safety, measures to ensure safety are required to allow emissions to continue without interruption even if a malfunction occurs in the equipment forming the emission path. However, conventional separated control methods had limitations in achieving both such safety and automation simultaneously. The problem to be solved

[0008] The present invention aims to provide a method and system for automatically controlling the discharge of gaseous waste into the atmosphere only when a safe state is confirmed, by measuring the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration of gaseous waste passing through a HEPA filter and comprehensively determining the results.

[0009] In addition, the present invention aims to prevent gaseous waste in an unsafe state from being discharged into the atmosphere by sequentially determining a plurality of measurement parameters according to a preset priority to determine safety status, and outputting an alarm and restricting the opening of a discharge valve if the state is not safe.

[0010] Furthermore, the present invention aims to ensure safety and continuity in the discharge operation of gaseous waste by forming a discharge path through a first train line and a second train line that are identically configured and redundant with each other, and by switching the discharge path to the other line in the event of a malfunction in either line. However, this objective is exemplary and does not limit the scope of the present invention. means of solving the problem

[0012] A radioactive waste treatment control system may include a sensor unit that measures the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration of gaseous waste passing through a HEPA filter, a discharge valve that opens and closes the atmospheric discharge path of the gaseous waste, a memory that stores instructions, and a processor. The system forms a discharge path for the gaseous waste through either a first train line or a second train line that is identically configured and redundant with each other. When the automatic mode is selected among the automatic mode and the manual mode, the system compares the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration measured by the sensor unit with corresponding preset reference values ​​to determine whether the gaseous waste is in a safe state for discharge into the atmosphere. If it is determined that the gaseous waste is in a safe state, the system opens the discharge valve to discharge the gaseous waste into the atmosphere, and if it is determined that the gaseous waste is not in a safe state, the system outputs an alarm and controls the system to restrict the opening of the discharge valve. Effects of the invention

[0014] The automatic control method and system for the safe discharge of radioactive waste according to the present invention has the effect of preventing gaseous waste in an unsafe state from being discharged into the atmosphere by comprehensively determining a plurality of state parameters of gaseous waste and ensuring that discharge occurs only when it is confirmed to be in a safe state.

[0015] In addition, the present invention can reduce operator intervention and improve operational efficiency by automating emission control that previously relied on manual operation by an operator or isolated single-loop control.

[0016] Furthermore, the present invention has the effect of ensuring safety and continuity in the discharge operation of gaseous waste by forming a discharge path through a redundant train line and switching to another line in the event of an anomaly. Of course, the scope of the present invention is not limited by this effect. Brief explanation of the drawing

[0018] FIG. 1 is a block diagram illustrating the configuration of a radioactive waste treatment control system according to one embodiment. FIG. 2 illustrates the gaseous waste emission control operation of a radioactive waste treatment control system according to one embodiment. FIG. 3 illustrates a humidity and oxygen concentration-based judgment operation of a radioactive waste treatment control system according to one embodiment. FIG. 4 illustrates the opening of a discharge valve and operation verification operation of a radioactive waste treatment control system according to one embodiment. FIG. 5 illustrates an input configuration and a logical operation structure for automatic discharge control of a radioactive waste treatment control system according to one embodiment. FIG. 6 illustrates a drain valve control structure based on the water tank level of a radioactive waste treatment control system according to one embodiment. Specific details for implementing the invention

[0019] FIG. 1 is a block diagram illustrating the configuration of a radioactive waste treatment control system according to one embodiment.

[0020] Referring to FIG. 1, the system (100) may include a sensor unit (110), a valve driving unit (120), a memory (130), and a processor (140). The configuration shown in FIG. 1 is merely an example and is not limited thereto, and the system (100) may omit some of the configurations shown in FIG. 1 or include additional configurations not shown in FIG. 1.

[0021] According to one embodiment, the sensor unit (110) can measure the state of gaseous waste that has passed through a HEPA filter. The sensor unit (110) may include a radiation detector for measuring radiation dose, a temperature sensor for measuring temperature, a pressure sensor for measuring pressure, a flow sensor for measuring flow rate, a hydrogen concentration sensor for measuring hydrogen concentration, and an oxygen concentration sensor for measuring oxygen concentration. The sensor unit (110) may further include a humidity sensor for measuring the humidity of the gaseous waste. The sensor unit (110) can transmit the measured value to a processor (140). The types of sensors included in the sensor unit (110) are merely examples and are not limited thereto, and may vary depending on the settings.

[0022] According to one embodiment, the valve driving unit (120) can open and close the discharge path of gaseous waste under the control of the processor (140). The valve driving unit (120) may include a discharge valve that opens and closes the discharge path of gaseous waste into the atmosphere. The valve driving unit (120) may further include an open limit switch that detects the open state of the discharge valve and a close limit switch that detects the closed state of the discharge valve. The valve driving unit (120) can open the discharge valve by receiving an open command from the processor (140). The valve driving unit (120) can transmit signals from the open limit switch and the close limit switch to the processor (140). Through this, the valve driving unit (120) can enable the actual open / closed state of the discharge valve to be verified by the processor (140).

[0023] According to one embodiment, the memory (130) can store instructions required for the operation of the system (100). The memory (130) can store setting values ​​including a reference value, humidity reference value, oxygen reference value, holding time, verification time, and operating cycle corresponding to each measurement parameter. The memory (130) can store the history of measurement values ​​received from the sensor unit (110) and the discharge operation. The memory (130) may include high-speed random access memory, a magnetic disk, ROM, RAM, or flash memory.

[0024] The processor (140) can control the overall operation of the system (100) by executing instructions stored in the memory (130). The processor (140) can receive a measurement value from the sensor unit (110) and determine whether the gaseous waste is in a safe state by comparing the measurement value with a reference value. Depending on the result of the determination, the processor (140) can transmit an opening command to the valve driving unit (120) or limit the opening of the discharge valve. The processor (140) can check the actual open / closed state of the discharge valve based on the signal of the limit switch received from the valve driving unit (120). The processor (140) can control the formation of a discharge path through either of the first train line and the second train line, which are identically configured and redundant with each other.

[0025] According to one embodiment, the system (100) can manage the water level of a water tank that stores condensate generated during the treatment process of gaseous waste. The system (100) can receive a measurement signal corresponding to the water level of the water tank from a water level sensor included in the sensor unit (110). The system (100) can compare the measured water level with a preset water level reference value. If the measured water level is above the water level reference value, the system (100) can open a drain valve to discharge the condensate stored in the water tank. If the measured water level drops below the water level reference value, the system (100) can close the drain valve. At this time, the water level reference value may include 70 percent, which is merely an example and is not limited thereto, and may vary depending on the setting. Through this, the system (100) can prevent the water level of the water tank from rising excessively.

[0026] According to one embodiment, the system (100) can control multiple control targets involved in the treatment of gaseous waste by integrating them into a single control system. Conventionally, each control target could be controlled individually by a single-loop controller separated from one another. In this case, the state of each control target is managed individually, making it difficult to make a comprehensive judgment. The system (100) can perform measurement, judgment, and control continuously within a single control system. The system (100) can automatically perform discharge operations based on measurement values ​​in automatic mode without individual operation by a manager. Through this, the system (100) can reduce manager intervention and improve operational efficiency.

[0028] FIG. 2 illustrates the gaseous waste emission control operation of a radioactive waste treatment control system according to one embodiment.

[0029] The operations described through FIG. 2 can be implemented based on instructions that can be stored in memory (e.g., memory (130) of FIG. 1). The order of each operation of FIG. 2 may be changed, some operations may be omitted, and some operations may be performed simultaneously.

[0030] In operation 210, the system (100) can measure a plurality of measurement parameters, including radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration of gaseous waste that has passed through a HEPA filter, through a sensor unit. The system (100) can perform the measurement by receiving a measurement signal corresponding to each parameter from a sensor unit positioned downstream of the HEPA filter. The sensor unit may include a radiation detector for measuring radiation dose, a temperature sensor for measuring temperature, a pressure sensor for measuring pressure, a flow rate sensor for measuring flow rate, a hydrogen concentration sensor for measuring hydrogen concentration, and an oxygen concentration sensor for measuring oxygen concentration. The system (100) can store the measured plurality of measurement parameters as input values ​​for subsequent judgment. Through this, the system (100) can identify the state of the gaseous waste as a plurality of items rather than a single item.

[0031] In operation 220, the system (100) can form a discharge path for gaseous waste through either a first train line or a second train line that are identically configured and redundant with each other. The first train line and the second train line can be composed of hardware of the same configuration, and while one line is in operation, the other line can stand by as a backup line. The system (100) can set one of the two lines as a discharge path based on the manager's selection input or preset conditions. Through this, the system (100) can form a structure that allows discharge to continue through the other line even if a malfunction occurs in one line.

[0032] In operation 230, when the automatic mode is selected among the automatic mode and manual mode, the system (100) can determine whether the gaseous waste is in a safe state to be discharged into the atmosphere by comparing the measured radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration with preset reference values ​​corresponding to each. The system (100) can read preset reference values ​​for each measurement parameter from memory and perform comparison operations. The system (100) can determine that the gaseous waste is in a safe state if all of the multiple measurement parameters satisfy their respective reference values. The system (100) can determine that the gaseous waste is not in a safe state if any of the multiple measurement parameters do not satisfy the corresponding reference value. Each reference value is merely an example and is not limited thereto, and may vary depending on the settings.

[0033] In operation 240, if the system (100) determines that the gaseous waste is in a safe state, it can open the discharge valve to discharge the gaseous waste into the atmosphere. If the system (100) determines that the gaseous waste is not in a safe state, it can output an alarm and restrict the opening of the discharge valve. If the system (100) determines that the gaseous waste is in a safe state, it can transmit an opening command to the discharge valve to open the discharge path. If the system (100) determines that the gaseous waste is not in a safe state, it can keep the discharge valve in a closed state and output an alarm through a display device or an alarm device. Through this, the system (100) can discharge only gaseous waste that meets safety standards into the atmosphere.

[0034] According to one embodiment, a radioactive waste treatment control system (100) may include a sensor unit that measures the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration of gaseous waste that has passed through a HEPA filter, a discharge valve that opens and closes the path for discharging the gaseous waste into the atmosphere, a memory that stores instructions, and a processor. The system (100) forms a discharge path for gaseous waste through either a first train line or a second train line that is identically configured and redundant with each other, and when the automatic mode is selected among the automatic mode and manual mode, it determines whether the gaseous waste is in a safe state for discharge into the atmosphere by comparing the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration measured by the sensor unit with corresponding preset reference values, and if it is determined that the gaseous waste is in a safe state, it opens the discharge valve to discharge the gaseous waste into the atmosphere, and if it is determined that the gaseous waste is not in a safe state, it outputs an alarm and controls the system to restrict the opening of the discharge valve.

[0035] According to one embodiment, the system (100) may receive a measurement value regarding oxygen concentration from an external source. The system (100) may receive a signal corresponding to the oxygen concentration from a client or an external system. The system (100) may output an alarm if the received oxygen concentration is greater than or equal to a preset oxygen alarm threshold value. The system (100) may process the received oxygen concentration within a range from 0 percent to 100 percent. In this case, the oxygen alarm threshold value may include 40 percent, which is merely an example and is not limited thereto, and may vary depending on the settings. Through this, the system (100) can utilize the oxygen concentration information provided from an external source for emission determination and alarm processing.

[0036] According to one embodiment, the system (100) may control gaseous waste that has passed through a HEPA filter. The HEPA filter may refer to a high-efficiency filter that captures fine particulate matter contained in the gas. The system (100) may measure the state of the gaseous waste at the downstream end of the HEPA filter. Thus, the value measured by the system (100) may reflect the state after the particulate matter has been primarily removed.

[0037] According to one embodiment, a plurality of measurement parameters measured by the system (100) may represent different physical properties. Radiation dose may represent the radioactivity level of the gaseous waste. Temperature and pressure may represent the thermal and mechanical state of the gas. Flow rate may represent the amount of gas flowing per unit time. Hydrogen concentration and oxygen concentration may represent the composition of the gas. The system (100) can utilize these values ​​together to determine the state of the gaseous waste in a multifaceted way.

[0038] According to one embodiment, automatic mode may refer to an operational state in which the system (100) continuously performs measurement, judgment, and control without individual operation by the manager. Manual mode may refer to a state in which discharge operation is performed according to the manager's operation. In automatic mode, the system (100) may automatically perform a comparison between the measured value and the reference value. The reference value may refer to a limit value at which each parameter is considered safe. The system (100) may open the discharge valve only when all parameters satisfy the reference value. Through this, the system (100) can prevent the discharge of unsafe gas. If the state is not safe, the system (100) may output an alarm to allow the manager to be aware of the situation.

[0039] According to one embodiment, the system (100) compares radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration sequentially with corresponding reference values ​​according to a preset priority, and performs a comparison with the measurement parameter of the next priority when the measurement parameter of the preceding priority satisfies the reference value, and controls the system to determine the gaseous waste to be in a safe state when the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration all satisfy their respective reference values, and determines that the gaseous waste is not in a safe state when any one of the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration does not satisfy the reference value.

[0040] According to one embodiment, the system (100) may compare multiple measurement parameters sequentially according to a preset priority without comparing them simultaneously. The priority may refer to the order in which each parameter is compared. The system (100) may compare the next-ranked parameter only if the parameter of the preceding rank satisfies a reference value. That is, if the preceding rank does not satisfy the reference value, the system (100) may not perform a comparison of subsequent ranks. Such sequential comparison may have the effect of reducing unnecessary operations.

[0041] According to one embodiment, the system (100) may terminate the judgment when any one parameter falls below a standard. Thus, the system (100) can quickly determine whether it is safe. Additionally, the system (100) can identify at which stage the failure to meet the standard occurred. Through this, the system (100) can identify the parameter that has failed. The system (100) may determine that the gaseous waste is in a safe state when all parameters satisfy the standard values ​​in sequence. The order of comparison is merely an example and is not limited thereto, and may vary depending on the settings.

[0042] According to one embodiment, the system (100) can control gaseous waste introduced from a source to be discharged after passing through a plurality of pretreatment facilities. The treatment path controlled by the system (100) may include a drying facility for removing moisture from the gaseous waste, an adsorption facility for adsorbing components contained in the gaseous waste, and a HEPA filter for capturing particulate matter. The system (100) can perform measurements and determine a safe state for the gaseous waste that has passed through the HEPA filter. The system (100) can allow the gaseous waste that has undergone such pretreatment to be discharged into the atmosphere when it is determined to be in a safe state. The types and arrangement of facilities constituting the treatment path are merely examples and are not limited thereto, and may vary depending on the settings.

[0044] FIG. 3 illustrates a humidity and oxygen concentration-based judgment operation of a radioactive waste treatment control system according to one embodiment.

[0045] The operations described through FIG. 3 can be implemented based on instructions that can be stored in memory (e.g., memory (130) of FIG. 1). The order of each operation of FIG. 3 may be changed, some operations may be omitted, and some operations may be performed simultaneously.

[0046] In operation 310, the system (100) can additionally measure the humidity of the gaseous waste through the sensor unit. The system (100) can receive a measurement signal corresponding to the humidity of the gaseous waste from a humidity sensor included in the sensor unit. The system (100) can store the measured humidity as an input value for subsequent comparison judgment. Through this, the system (100) can utilize humidity as an additional judgment item in addition to the multiple parameters measured earlier.

[0047] In operation 320, the system (100) can compare the measured humidity with a preset humidity reference value and output a humidity alarm if the measured humidity is greater than or equal to the humidity reference value. The system (100) can read the humidity reference value stored in memory and compare it with the measured humidity. The system (100) can output a humidity alarm through a display device or an alarm device if the measured humidity is greater than or equal to the humidity reference value. At this time, the humidity reference value may include 60 percent, which is merely an example and is not limited thereto, and may vary depending on the settings.

[0048] In operation 330, the system (100) can count the elapsed time from the point in time when a state in which the measured oxygen concentration is greater than or equal to a preset oxygen reference value begins. The system (100) can count the elapsed time by comparing the measured oxygen concentration with the oxygen reference value and driving a timer when the oxygen concentration becomes greater than or equal to the oxygen reference value. The system (100) can use the counted elapsed time as an input value for comparison with a preset maintenance time. At this time, the oxygen reference value may include 30 percent, which is merely an example and is not limited thereto, and may vary depending on the setting.

[0049] In operation 340, the system (100) may determine that the gaseous waste is not in a safe state and output an oxygen alarm if the state in which the measured oxygen concentration is above the oxygen reference value persists continuously for longer than a preset maintenance time. The system (100) may reset the elapsed time count if the state in which the measured oxygen concentration is above the oxygen reference value is resolved before the maintenance time is reached. The system (100) can distinguish between instantaneous fluctuations and continuous abnormal states by determining whether the state in which the oxygen concentration is above the oxygen reference value persists without interruption during the maintenance time. Through this, the system (100) can prevent unnecessary alarm outputs caused by temporary fluctuations in the measured value. At this time, the maintenance time may include 10 minutes, but this is merely an example and is not limited thereto and may vary depending on the settings.

[0050] According to one embodiment, the system (100) further measures the humidity of gaseous waste through a sensor unit, compares the measured humidity with a preset humidity reference value, outputs a humidity alarm if the measured humidity is greater than or equal to the humidity reference value, compares the measured oxygen concentration with a preset oxygen reference value, checks the elapsed time from the point when the state in which the measured oxygen concentration is greater than or equal to the oxygen reference value begins, determines that the gaseous waste is not in a safe state and outputs an oxygen alarm if the state in which the measured oxygen concentration is greater than or equal to the oxygen reference value continues continuously for longer than a preset maintenance time, and can reset the count of the elapsed time if the state in which the measured oxygen concentration is greater than or equal to the oxygen reference value is resolved before reaching the maintenance time. The humidity reference value may include 60 percent, the oxygen reference value may include 30 percent, and the maintenance time may include 10 minutes.

[0051] According to one embodiment, the system (100) may additionally measure humidity in addition to the parameters measured earlier. Humidity may indicate the degree of moisture contained in the gas. The system (100) may output a humidity alarm if the humidity is above a reference value. Since gas with high humidity can affect downstream equipment, the system (100) may keep humidity as a separate management item.

[0052] According to one embodiment, the system (100) can determine the oxygen concentration based on duration rather than instantaneous value. The system (100) can count the elapsed time from the point when the oxygen concentration exceeds a reference value. The counting of the elapsed time can be implemented by driving a timer. The system (100) can determine that the state is not safe only when this state persists for longer than the maintenance time. The system (100) can reset the count if the oxygen concentration drops below the reference value before reaching the maintenance time. This duration-based determination can have the effect of distinguishing between temporary fluctuations and actual abnormal conditions. The oxygen concentration may fluctuate instantaneously during the measurement process. The system (100) may not react immediately to short fluctuations. Therefore, the system (100) can prevent unnecessary alarms from being frequently output. The humidity reference value, oxygen reference value, and maintenance time are merely examples and are not limited thereto, and may vary depending on the settings.

[0053] According to one embodiment, the system (100) may set different maintenance times for oxygen concentration depending on the measured humidity. When the measured humidity is above a humidity reference value, the system (100) may set the maintenance time applied to the state where the oxygen concentration is above the oxygen reference value to be shorter than when the measured humidity is below the humidity reference value. A state of high humidity may mean a state where the condition of gaseous waste is relatively likely to deviate from the normal range. In such cases, the system (100) may observe the state where the oxygen concentration is above the oxygen reference value for a shorter period of time and then determine that it is not a safe state. In this way, the system (100) may change the judgment criteria of another measurement parameter according to the state of one measurement parameter, thereby making judgments by linking multiple measurement parameters together.

[0054] According to one embodiment, the system (100) sets one of the first train line and the second train line as a discharge path for gaseous waste according to the selection input of a manager, counts the accumulated operating time of the line set as the discharge path, and when the accumulated operating time reaches a preset operating cycle, switches the discharge path to the other line and resets the accumulated operating time so that the first train line and the second train line are alternately set as discharge paths in units of operating cycles, and when at least one of the following is detected is a discrepancy between the opening command of a valve provided on the line set as the discharge path and the actual opening / closing state, failure to receive measurement parameters of the line, and tripping of a device provided on the line, it is determined that an abnormality has occurred in the line, and the line determined to have an abnormality is excluded from the discharge path and the other line is set as the discharge path so that the discharge of gaseous waste is maintained.

[0055] According to one embodiment, the first train line and the second train line handled by the system (100) may refer to two lines having the same configuration. The two lines may be configured for redundancy. Redundancy may refer to a configuration that enhances safety by having two or more facilities with the same function. The system (100) may keep the remaining line as a reserve while operating one line.

[0056] According to one embodiment, the system (100) can count the accumulated operating time of a line set as a discharge path. The accumulated operating time may refer to the sum of the times the line is used as a discharge path. When the accumulated operating time reaches an operating cycle, the system (100) can switch the discharge path to another line. After switching, the system (100) can reset the accumulated operating time. Through this, the two lines can be used alternately in units of operating cycles. This alternating operation can have the effect of preventing the load from being concentrated on one line. Additionally, the system (100) can secure time to inspect the unused line.

[0057] According to one embodiment, the system (100) may determine an abnormality in the line based on specific reasons. The system (100) may determine an abnormality when the valve opening command does not match the actual open / closed state. The system (100) may determine an abnormality when measurement parameters of the line are not received. The system (100) may determine an abnormality when a trip of a device equipped in the line is detected. A trip may mean that the device stops operation for protection. If at least one of these reasons is detected, the system (100) may exclude the line in question from the discharge path. The system (100) may set the remaining line as the discharge path to maintain discharge.

[0058] According to one embodiment, the system (100) can first check whether the remaining line is normal before switching the discharge path to the remaining line when the accumulated operating time reaches the operating cycle. The system (100) can check the open / closed status of the valve provided in the remaining line and check whether the measurement parameters of the remaining line are received normally. The system (100) can confirm that the remaining line is normal if the valve provided in the remaining line operates normally and the measurement parameters are received normally. The system (100) can switch the discharge path to the remaining line if it is confirmed that the remaining line is normal. If the system (100) confirms that the remaining line is not normal, it can postpone the switching of the discharge path and maintain discharge through the current line. By checking the normality of the line to be switched in advance in this way, the system (100) can prevent a situation where discharge is not performed normally after the switch.

[0060] FIG. 4 illustrates the opening of a discharge valve and operation verification operation of a radioactive waste treatment control system according to one embodiment.

[0061] The operations described through FIG. 4 can be implemented based on instructions that can be stored in memory (e.g., memory (130) of FIG. 1). The order of each operation of FIG. 4 may be changed, some operations may be omitted, and some operations may be performed simultaneously.

[0062] In operation 410, the system (100) sets the automatic mode, the line forming the discharge path, and the purge switch being in the ON state as basic conditions for opening the discharge valve, and can check whether the basic conditions are satisfied. The system (100) can determine whether all three conditions are met by checking the mode selection input, the line selection input, and the state of the purge switch, respectively. If any of the three conditions are not met, the system (100) may not proceed to the determination of opening the discharge valve. Through this, the system (100) can prevent unintended discharge through multi-stage interlock conditions.

[0063] In operation 420, the system (100) may output an opening command for the discharge valve on the condition that basic conditions are met and that the gaseous waste is determined to be in a safe state and this state is maintained continuously for a preset verification time. The system (100) counts the verification time from the point at which the safe state is determined and may output an opening command if the safe state is maintained during the verification time. The system (100) may not output an opening command if the safe state is resolved before the verification time has elapsed. Through this, the system (100) can prevent discharge from occurring when the safe state is temporarily measured.

[0064] In operation 430, the system (100) can verify the actual open / closed state of the discharge valve based on signals received from the open limit switch and the close limit switch provided on the discharge valve after the output of the open command. The system (100) can verify the actual open / closed state of the discharge valve by receiving a signal indicating an open state from the open limit switch or a signal indicating a closed state from the close limit switch. The system (100) can use the verified actual open / closed state as an input value for comparison with the open command. Through this, the system (100) can verify whether the open command led to the operation of the actual valve.

[0065] In operation 440, the system (100) can maintain the discharge of gaseous waste by determining that the discharge valve is normally open when the open command and the confirmed actual open / closed state match each other. The system (100) can determine that the discharge valve is normally open when the open limit switch detects an open state in response to the open command. When the system (100) determines that it is normally open, it can continue the discharge of gaseous waste through the discharge path. Through this, the system (100) can ensure that discharge is carried out in a verified normal state.

[0066] In operation 450, if the open command and the confirmed actual open / closed state do not match, the system (100) determines that there is an operational abnormality of the discharge valve and outputs a valve operation abnormality alarm, isolates the line in question from the discharge path, and can re-establish the discharge path for gaseous waste through the remaining line. The system (100) can determine that there is an operational abnormality of the discharge valve if the open limit switch fails to detect the open state even though an open command has been output. The system (100) can exclude the line determined to be operationally abnormal from the discharge path and set the remaining redundant line as the discharge path. Additionally, the system (100) can output a system isolation alarm if the close limit switch fails to detect the closed state. Through this, the system (100) can ensure the safety and continuity of discharge even if an operational abnormality of the discharge valve occurs.

[0067] According to one embodiment, the discharge valve may be equipped with an opening limit switch for detecting the open state of the discharge valve and a closing limit switch for detecting the closed state of the discharge valve. The system (100) selects an automatic mode, selects a line forming a discharge path, and sets the purge switch to be in the ON state as a basic condition for opening the discharge valve; outputs an opening command for the discharge valve under the condition that the basic condition is satisfied and the state in which the gaseous waste is judged to be in a safe state is continuously maintained for a preset verification time; after outputting the opening command, checks the actual open / closed state of the discharge valve based on signals received from the opening limit switch and the closing limit switch; if the opening command and the confirmed actual open / closed state match each other, it determines that the discharge valve is normally open and maintains the discharge of the gaseous waste; if the opening command and the confirmed actual open / closed state do not match each other, it determines that there is an operational abnormality of the discharge valve and outputs a valve operation abnormality alarm; isolates the corresponding line from the discharge path and re-forms the discharge path of the gaseous waste through the remaining line; and if the closing limit switch fails to detect the closed state, it outputs a system isolation alarm.

[0068] According to one embodiment, the system (100) can check whether basic conditions are satisfied before opening the discharge valve. Here, the basic conditions may refer to preconditions for allowing discharge. The system (100) may set the selection of an automatic mode, the selection of a discharge line, and the ON state of a purge switch as basic conditions. The purge switch may refer to a switch that allows the discharge operation of gaseous waste. The system (100) may enter the opening judgment only when all three conditions are met. These multi-stage conditions may have the effect of preventing unintended discharge.

[0069] According to one embodiment, the system (100) may output an opening command when the safety state is continuously maintained for a verification time. The verification time may refer to the time for determining whether the safety state has been maintained at a reliable level. The system (100) may not output an opening command if the safety state is resolved before the verification time has elapsed. Through this, the system (100) can prevent discharge from occurring when it is instantaneously measured to be safe.

[0070] According to one embodiment, the system (100) can verify whether the valve actually operated as commanded after outputting an opening command. An opening limit switch may refer to a switch that detects that the valve is open. A closing limit switch may refer to a switch that detects that the valve is closed. The system (100) can check the actual open / closed state of the valve from the signals of the two switches. If the opening command and the actual open / closed state match, the system (100) can determine that it is normally open. If the two do not match, the system (100) can determine that there is an operational abnormality in the valve.

[0071] According to one embodiment, the system (100) may output a valve operation abnormality alarm if it determines that there is an operation abnormality. The system (100) may isolate the corresponding line from the discharge path. The system (100) may reconfigure the discharge path to the remaining redundant line. Such verification and switching can have the effect of ensuring the safety and continuity of discharge even in situations where there is a discrepancy between the command and the actual operation. Additionally, the system (100) may output a system isolation alarm if the closing limit switch fails to detect the closed state. Through this, the system (100) can help an administrator verify that the valve is not completely closed.

[0072] According to one embodiment, the system (100) may continue to measure a plurality of measurement parameters while discharging gaseous waste by opening the discharge valve, and determine whether to maintain the discharge based on the measured values. If any of the plurality of measurement parameters measured after the discharge valve is opened changes to a state where they do not meet the corresponding reference value, the system (100) may determine that the gaseous waste is not in a safe state and close the discharge valve. The system (100) may output a closure command to the discharge valve and then check whether the discharge valve is actually closed based on a signal received from the closure limit switch. The system (100) may determine that the discharge has stopped if it is confirmed that the discharge valve is closed through the closure limit switch. If the system (100) outputs a closure command but it is not confirmed that the discharge valve is closed through the closure limit switch, the system (100) may output a system isolation alarm. The system (100) can prevent unsafe gaseous waste from being continuously discharged even if the state of the gaseous waste changes during discharge by continuously monitoring measurement parameters and verifying whether the discharge valve is closed during discharge.

[0074] FIG. 5 illustrates an input configuration and a logical operation structure for automatic discharge control of a radioactive waste treatment control system according to one embodiment.

[0075] Referring to FIG. 5, the system (100) can control the opening of the exhaust valve (580) based on inputs from a mode selection unit (510), a train selection unit (520), a control selection unit (530), a fuzzy switch (540), an oxygen concentration input unit (550), a time delay element (560), and a logic operation unit (570). The configuration shown in FIG. 5 is merely an example and is not limited thereto, and may vary depending on the settings.

[0076] According to one embodiment, the mode selection unit (510) may select the operating mode of the system (100) as either an automatic mode or a manual mode. The automatic mode may refer to an operating state in which the system (100) continuously performs measurement, judgment, and control without individual operation by the manager. The manual mode may refer to a state in which discharge operation is performed according to the operation of the manager. Unlike manual control by a conventional separate single-loop controller, the system (100) can control multiple control targets by integrating them into a single control system in the automatic mode. The system (100) can perform subsequent automatic discharge control only when the automatic mode is selected through the mode selection unit (510).

[0077] According to one embodiment, the train selection unit (520) may select either a first train line or a second train line, which are identically configured and redundant with each other, as a discharge path. The first train line and the second train line may be made of hardware of the same configuration. The two lines may be configured for redundancy. The system (100) may form a discharge path for gaseous waste through the line selected via the train selection unit (520). The system (100) may keep the other line as a reserve while one line is in operation. The system (100) may switch the discharge path to the other line in the event of an abnormality in the line currently in operation.

[0078] According to one embodiment, the control selection unit (530) may receive a control location of the system (100). The control selection unit (530) may include a hand switch indicating the control location. The control selection unit (530) may receive a control location selected as either local or remote. Local may refer to a location where control is performed in the field. Remote may refer to a location where control is performed remotely. The system (100) may determine the subject of control according to the control location selected through the control selection unit (530).

[0079] According to one embodiment, the purge switch (540) may be selected as either an ON state that allows the discharge of gaseous waste or an OFF state that does not allow it. Purge may refer to the operation of releasing gaseous waste into the atmosphere through a discharge path. The system (100) may set the purge switch (540) being in the ON state as a basic condition for opening the discharge valve. The system (100) may determine that the basic condition for opening the discharge valve is satisfied when the automatic mode is selected, the line forming the discharge path is selected, and the purge switch (540) being in the ON state are all established together.

[0080] According to one embodiment, the oxygen concentration input unit (550) may receive a signal regarding the oxygen concentration of gaseous waste. The oxygen concentration input unit (550) may receive an oxygen concentration signal from the outside, which may be indicated by a dotted line. The system (100) may receive a signal from the oxygen concentration input unit (550) indicating that the oxygen concentration is above a reference value. The system (100) may output an alarm if the received oxygen concentration is above an oxygen alarm reference value. At this time, the oxygen alarm reference value may include 40 percent, which is merely an example and is not limited thereto, and may vary depending on the settings.

[0081] According to one embodiment, the system (100) may generate an output when an input signal persists for a preset time or longer. The time delay element (560) may be implemented as an off-delay method that maintains the output for a preset time after the input is removed. Through the time delay element (560), the system (100) may process the signal when the state in which the oxygen concentration is above a reference value persists for a duration longer than the maintenance time. The system (100) may not process the signal if the state in which the oxygen concentration is above the reference value is resolved before reaching the maintenance time. Through this, the system (100) can distinguish between instantaneous fluctuations in oxygen concentration and a continuous abnormal state. The maintenance time may include 10 minutes, which is merely an example and is not limited thereto, and may vary depending on the settings.

[0082] According to one embodiment, the logic operation unit (570) can perform operations on inputs from the mode selection unit (510), the train selection unit (520), the control selection unit (530), the fuzzy switch (540), and the time delay element (560). The logic operation unit (570) can perform a logical AND operation that generates an output when all input conditions are satisfied. The system (100) can comprehensively determine multiple input conditions through the logic operation unit (570). The system (100) can control the opening of the discharge valve (580) based on the output of the logic operation unit (570).

[0083] According to one embodiment, opening the discharge valve (580) may mean an operation of opening the discharge valve according to the output of the logic operation unit (570). The system (100) may open the discharge valve and discharge gaseous waste into the atmosphere when the output of the logic operation unit (570) occurs. The system (100) may keep the discharge valve in a closed state when the output of the logic operation unit (570) does not occur. Through this, the system (100) may discharge gaseous waste only when safety standards are met and basic conditions are established.

[0084] According to one embodiment, the system (100) can receive measurement values ​​together from sensor units (110) provided in each of the first train line and the second train line, which are configured identically and redundantly, and can determine the reliability of the measurement by comparing the measurement values ​​of the two lines. The first train line and the second train line may each be equipped with sensor units (110) of the same configuration. While operating one of the two lines as a discharge path, the system (100) can receive measurement values ​​from the sensor unit (110) of the line set as the discharge path and measurement values ​​from the sensor unit (110) of the line waiting as a reserve line for the same measurement parameter. The system (100) can calculate the difference between the measurement values ​​received from the two lines for the same measurement parameter and compare the calculated difference with a preset allowable error.

[0085] According to one embodiment, the system (100) can determine that a measurement value is a reliable value if the difference between the two lines is within the allowable error. The system (100) can determine whether the gaseous waste is in a safe state by comparing the measurement value determined to be a reliable value with a reference value. If the difference between the two lines exceeds the allowable error, the system (100) can determine that an abnormality has occurred in either of the two lines' sensor units (110) and output a sensor abnormality alarm.

[0086] According to one embodiment, when a sensor malfunction is detected, the system (100) may use the measurement value of the two lines that is closer to the direction in which the gaseous waste is judged to be in a non-safe state for determining the safety state. For example, for a measurement parameter that is judged to be safe when the measurement value is below a reference value, the system (100) may use the larger value of the two measurement values ​​for determining the safety state. For a measurement parameter that is judged to be safe when the measurement value is above a reference value, the system (100) may use the smaller value of the two measurement values ​​for determining the safety state. By using such more conservative measurement values, the system (100) can prevent unsafe gaseous waste from being incorrectly judged to be in a safe state even if one of the sensor units (e.g., sensor unit (110) of FIG. 1) malfunctions in a direction that outputs a safer value than the actual one. The system (100) may mark the line where a sensor malfunction is detected as a line requiring inspection and set the line judged to be normal as a discharge path to maintain the discharge of gaseous waste.

[0088] FIG. 6 illustrates a drain valve control structure based on the water tank level of a radioactive waste treatment control system according to one embodiment.

[0089] Referring to FIG. 6, the system (100) can control the opening and closing of the drain valve based on inputs from a mode selection unit (610), a control selection unit (620), a water level high detection unit (630), a water level low detection unit (640), a drain valve opening / closing command unit (650), a water level-based control logic unit (660), an opening limit switch (670), a closing limit switch (680), a water level high-high detection unit (690), and a water level low-low detection unit (695). The configuration shown in FIG. 6 is merely an example and is not limited thereto, and may vary depending on the settings.

[0090] According to one embodiment, the mode selection unit (610) may select an operation mode for the drain valve as either an automatic mode or a manual mode. When the automatic mode is selected through the mode selection unit (610), the system (100) can automatically open and close the drain valve based on the water level. When the manual mode is selected, the system (100) can open and close the drain valve according to the operation of the manager.

[0091] According to one embodiment, the control selection unit (620) may select a control position for the drain valve as either local or remote. The system (100) may determine the subject of control according to the control position selected through the control selection unit (620).

[0092] According to one embodiment, a water level high detection unit (630) can detect whether the water level of a water tank is above a first high reference value. A water tank may refer to a tank that stores condensate generated during the treatment process of gaseous waste. The system (100) may receive a signal from the water level high detection unit (630) indicating that the water level is above the first high reference value. At this time, the first high reference value may include 70 percent, which is merely an example and is not limited thereto, and may vary depending on the setting.

[0093] According to one embodiment, the water level low detection unit (640) can detect whether the water level of the water tank is below a first low reference value. The system (100) can receive a signal from the water level low detection unit (640) indicating that the water level is below the first low reference value. At this time, the first low reference value may include 20 percent, which is merely an example and is not limited thereto, and may vary depending on the setting.

[0094] According to one embodiment, the water level-based control logic unit (660) can perform calculations on signals from the water level high detection unit (630) and the water level low detection unit (640). The system (100) can generate a signal to open the drain valve when the water level becomes greater than or equal to a first high reference value through the water level-based control logic unit (660). The system (100) can generate a signal to close the drain valve when the water level becomes less than or equal to a first low reference value. The system (100) can invert the signal from the water level low detection unit (640) and use it for calculations. Through this, the system (100) can maintain the water level within a certain range by opening the drain valve when the water level rises above the first high reference value and closing the drain valve when the water level falls below the first low reference value.

[0095] According to one embodiment, the drain valve opening / closing command unit (650) may output an opening command or a closing command for the drain valve based on a signal from the water level-based control logic unit (660). The system (100) may open or close the drain valve through the drain valve opening / closing command unit (650). The system (100) may open the drain valve to discharge the condensate stored in the water tank.

[0096] According to one embodiment, an open limit switch (670) can detect the open state of the drain valve. A closed limit switch (680) can detect the closed state of the drain valve. The system (100) can determine the actual open / closed state of the drain valve based on signals received from the open limit switch (670) and the closed limit switch (680). The system (100) can determine normal operation if the command for the drain valve matches the actual open / closed state. If the command for the drain valve does not match the actual open / closed state, the system (100) can determine that there is a valve operation abnormality and output an alarm. The system (100) can light an indicator lamp indicating openness when the drain valve is open, and light an indicator lamp indicating closedness when the drain valve is closed.

[0097] According to one embodiment, the second high-level detection unit (690) can detect whether the water level of the water tank is above a second high-high reference value. The system (100) can output a water level upper limit alarm when it receives a signal from the second high-level detection unit (690) indicating that the water level is above the second high-high reference value. In this case, the second high-high reference value may include 80 percent, which is merely an example and is not limited thereto, and may vary depending on the setting.

[0098] According to one embodiment, the second low-level detection unit (695) can detect whether the water level of the water tank is below a second low-low reference value. The system (100) can output a water level lower limit alarm when it receives a signal from the second low-level detection unit (695) indicating that the water level is below the second low-low reference value. At this time, the second low-low reference value may include 10 percent, which is merely an example and is not limited thereto, and may vary depending on the settings. The system (100) can help an administrator check for abnormal water level conditions outside the normal control range through the second high-level detection unit (690) and the second low-level detection unit (695).

[0099] According to one embodiment, the system (100) can determine in advance whether a safe state is maintained by calculating the trend of change over time for each of a plurality of measurement parameters, including radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration of gaseous waste that has passed through a HEPA filter, in addition to determining only whether the current measurement value meets a reference value. When an automatic mode is selected, the system (100) can collect measurement values ​​of each measurement parameter from the sensor unit (110) at preset unit time intervals. The system (100) can store the collected measurement values ​​in a time series in the memory (130) along with the measurement time. The system (100) can calculate the amount of change in the measurement value per unit time by dividing the difference between the most recent measurement value and the previous measurement value among the stored time series measurement values ​​by the unit time. The system (100) can calculate a trend of change indicating whether the measurement value is changing in a direction approaching the reference value or in a direction moving away from the reference value through the sign of the calculated amount of change.

[0100] According to one embodiment, the system (100) may determine that a measurement parameter is in a pre-warning state if, even when the current measurement value meets a reference value, the magnitude of the calculated change amount is greater than or equal to a preset change amount reference value and the measurement value changes in a direction approaching the reference value. If there is a measurement parameter determined to be in a pre-warning state, the system (100) may output a pre-warning alarm so that the manager is aware that the measurement parameter may soon deviate from the reference value. The system (100) may calculate a predicted time when the measurement value is expected to reach the reference value by dividing the difference between the current measurement value and the reference value by the calculated change amount. If the calculated predicted time is within a preset time, the system (100) may perform a preparatory operation to switch the line forming the discharge path to the remaining line. The preparatory operation may include an operation to check in advance the valve status of the line waiting as a reserve line and the reception status of the measurement parameter.

[0101] According to one embodiment, the system (100) may switch the discharge path to the remaining line where the preparation operation is completed when any one of the plurality of measurement parameters is determined to be in a non-safe state because it actually deviates from a reference value. Through this trend-based prior judgment and preparation operation, the system (100) can reduce the time required to switch the discharge path compared to the case where a response begins only after the measurement value deviates from the reference value. The system (100) can maintain the continuity of discharge by reducing the time during which the purging operation of gaseous waste is interrupted.

[0103] Although the embodiments have been described above with reference to the limited drawings, those skilled in the art can apply various technical modifications and variations based on the above. For example, suitable results may be achieved even if the described techniques are performed in a different order than described, and / or if the components of the described system, structure, device, circuit, etc. are combined or assembled in a form different from described, or replaced or substituted by other components or equivalents.

Claims

Claim 1 A radioactive waste treatment control system comprises a sensor unit that measures the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration of gaseous waste passing through a HEPA filter, a discharge valve that opens and closes the atmospheric discharge path of said gaseous waste, a memory that stores instructions, and a processor. When said instructions are executed by said processor, said system forms a discharge path of said gaseous waste through either a first train line or a second train line that is identically configured and redundant with each other. When said automatic mode is selected among automatic mode and manual mode, said radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration measured by said sensor unit are compared with corresponding preset reference values ​​to determine whether said gaseous waste is in a safe state to be discharged into the atmosphere. If said gaseous waste is determined to be in the safe state, said discharge valve is opened to discharge said gaseous waste into the atmosphere. If said gaseous waste is determined not to be in the safe state, an alarm is output and said discharge valve is opened. Control to limit, further measure the humidity of the gaseous waste through the sensor unit, compare the measured humidity with a preset humidity reference value, output a humidity alarm if the measured humidity is greater than or equal to the humidity reference value, compare the measured oxygen concentration with a preset oxygen reference value, check the elapsed time from the point at which the state in which the measured oxygen concentration is greater than or equal to the oxygen reference value begins, and if the state in which the measured oxygen concentration is greater than or equal to the oxygen reference value continues continuously for longer than a preset maintenance time, determine that the gaseous waste is not in a safe state and output an oxygen alarm, and if the state in which the measured oxygen concentration is greater than or equal to the oxygen reference value is resolved before reaching the maintenance time, reset the count of the elapsed time.A radioactive waste treatment control system in which, when the measured humidity is greater than or equal to the humidity reference value, the maintenance time for the measured oxygen concentration is set shorter than when the measured humidity is less than the humidity reference value, wherein the humidity reference value includes 60 percent, the oxygen reference value includes 30 percent, and the maintenance time includes 10 minutes. Claim 2 A radioactive waste treatment control system according to claim 1, wherein the instructions, when executed by the processor, control the system to sequentially compare the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration with corresponding reference values ​​according to a preset priority, perform a comparison with the measurement parameter of the next priority if the measurement parameter of the preceding priority satisfies the reference value, determine the gaseous waste to be in the safe state if the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration all satisfy their respective reference values, and determine the gaseous waste not to be in the safe state if any one of the radiation dose, temperature, pressure, flow rate, hydrogen concentration, and oxygen concentration does not satisfy the reference value. Claim 3 delete Claim 4 In claim 1, the instructions, when executed by the processor, set either the first train line or the second train line as the discharge path for the gaseous waste according to the selection input of the administrator terminal of the system, count the accumulated operating time of the line set as the discharge path, and when the accumulated operating time reaches a preset operating cycle, switch the discharge path to the remaining line and reset the accumulated operating time so that the first train line and the second train line are alternately set as the discharge path in units of the operating cycle, and determine that an abnormality has occurred in the line if at least one of a discrepancy between the opening command and the actual opening / closing state of the valve provided on the line set as the discharge path, non-reception of measurement parameters of the line, and tripping of the device provided on the line is detected, exclude the line determined to have an abnormality from the discharge path and set the remaining line as the discharge path so that the discharge of the gaseous waste is maintained, and before the accumulated operating time reaches the operating cycle and the discharge path is switched to the remaining line, the valve provided on the remaining line A radioactive waste treatment control system that checks the open / closed state and the reception state of the measurement parameters of the remaining one line, and controls the discharge path to be switched to the remaining one line when it is confirmed that the remaining one line is normal. Claim 5 In claim 1, the discharge valve is equipped with an opening limit switch for detecting the open state of the discharge valve and a closing limit switch for detecting the closed state of the discharge valve; and the instructions, when executed by the processor, set the system as a basic condition for opening the discharge valve that the automatic mode is selected, the line forming the discharge path is selected, and the purge switch is in the ON state, and output an opening command for the discharge valve under the condition that the basic condition is satisfied and the state in which the gaseous waste is judged to be in the safe state is continuously maintained for a preset verification time, and after outputting the opening command, check the actual open / closed state of the discharge valve based on signals received from the opening limit switch and the closing limit switch, and if the opening command and the confirmed actual open / closed state match each other, determine that the discharge valve is normally opened and maintain the discharge of the gaseous waste, and if the opening command and the confirmed actual open / closed state do not match each other, determine that there is an operational abnormality of the discharge valve and output a valve operation abnormality alarm, isolate the corresponding line from the discharge path, and then through the remaining one line, the gas A radioactive waste treatment control system that reshapes the discharge path of waste, outputs a system isolation alarm when the closure limit switch fails to detect a closed state, closes the discharge valve when any of a plurality of measurement parameters measured for the gaseous waste after the discharge valve is opened changes to a state where it does not satisfy a corresponding reference value, and controls the system isolation alarm to output when it is not confirmed through the closure limit switch that the discharge valve is closed.

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