JPH0452432B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is suitable for diagnosing water quality abnormalities in nuclear power plants, such as boiling water nuclear power plants, by detecting the ion concentration in the water supply system and condensate system, and detecting the cause of abnormalities in the water supply system and condensate system. Regarding the method. In order to ensure safety, nuclear power plants use strict monitoring systems to monitor the operating status of nuclear plants from all angles, with the aim of early detection of abnormalities in nuclear plants. If ionic components are mixed in as impurities in the cooling water of the condensate system and water supply system (hereinafter referred to as the condensate water supply system), which are the primary systems of the nuclear reactor, they may accelerate corrosion of the equipment piping in the primary system or may be carried into the reactor. There is a concern that as a result of the ion components being activated, the radiation dose rate in the primary system will increase and the fuel rods will be damaged. Therefore, although an underwater abnormality such as an increase in ionic components in the cooling water does not lead to a serious accident that would lead to core damage, it can make the operation, maintenance, and inspection work of a nuclear plant difficult. It is desirable to detect abnormalities early and reliably. Therefore, it is being considered to detect abnormalities in nuclear power plants using a method as shown in FIG. As shown in FIG. 1, this method consists of two stages, in which the presence or absence of an abnormality is detected in the first stage, and the cause and degree of the abnormality are determined in the second stage. In other words, in the first stage, gross state quantities such as radiation dose rate, electrical conductivity (hereinafter referred to as "conductivity"), and PH, which are state quantities that alone can only reveal the presence or absence of abnormalities in the plant, are evaluated. The measured gross state amount is compared with the gross amount reference value corresponding to the operating state of the nuclear reactor to determine whether there is an abnormality in the condensate water supply system. In the second stage, if it is determined that there is an abnormality in the condensate water supply system in the first stage, detailed elemental quantity analysis such as radioactivity analysis by nuclide and elemental analysis of radioisotopes in the cooling water is performed, The current pattern of element quantities is compared with the normal pattern of the plant to accurately determine abnormalities in the condensate water supply system, as well as to determine the cause and extent of the abnormality. This elemental quantity is a state quantity that indicates the element that is the cause of abnormality in a nuclear power plant, that is, elemental concentration, radioactivity concentration by nuclide, etc., and is obtained by off-line analysis of substances sampled from the plant. Unlike gross quantities such as conductivity, which can be quickly accessed online, analyzing elements takes time. Therefore, when using the method shown in Figure 1, it is often necessary to perform a new analysis of the element quantities and make a final judgment after detecting an abnormality from the gross quantity measurements. When determining an abnormality, it requires time to analyze the amount of elements, so it has the disadvantage of being accompanied by a time delay. In particular, in the case of water quality abnormalities in the condensate water supply system, leakage of seawater in the condenser, elution of metals such as iron due to corrosion of pipes and valves, etc. There are a wide variety of possible causes of abnormalities, such as contamination of regenerated liquid after chemical regeneration using a method of regeneration, and there are many types of substances that can cause abnormalities, so analytical operations often require time. The present invention was made in order to eliminate the drawbacks of the prior art, and it is possible to easily detect the cause of water quality abnormality in a nuclear reactor plant using only measured values related to gross amount that can be measured online. The purpose is to provide a diagnostic method. An object of the present invention is to provide a water quality abnormality diagnosis method that can identify multiple causes of water quality abnormalities in a nuclear power plant. An object of the present invention is to provide a water quality abnormality diagnosis method that can quantitatively grasp the degree of an identified abnormality in water quality in a nuclear power plant. The present invention creates a basic vector by comparing it with the standard ion concentration in water under normal conditions based on the increase/decrease in the ion concentration in water based on the cause of the abnormality assumed in advance, and measures this basic vector at multiple locations in the piping system. The system is designed so that the cause of water quality abnormality can be easily detected by comparing it with a measurement vector created based on the measured ion concentration. The present invention detects the ion concentration in water flowing in one direction through a piping system at multiple locations in the piping system,
A measurement vector created by comparing the detected ion concentration with the standard ion concentration in a normal state, and a basic vector created by comparing the ion concentration in the water caused by the abnormality assumed in advance and the standard ion concentration. , when the measured vector does not match the basic vector but has a non-zero element, a composite vector obtained by combining the plurality of basic vectors is used. The system is configured so that multiple causes of water quality abnormalities can be detected by comparing the vector and the measured vector. The present invention detects the ion concentration in water flowing in one direction through a piping system at multiple locations in the piping system,
A measurement vector created by comparing the detected ion concentration with the standard ion concentration in a normal state, and a basic vector created by comparing the ion concentration in the water caused by the abnormality assumed in advance and the standard ion concentration. , and after identifying multiple causes of abnormality, derive simultaneous equations that hold between the electrical conductivity detected at multiple locations in the piping system and the respective ion concentrations corresponding to the detected causes of abnormality,
The structure is such that the degree of each abnormality can be evaluated by solving the simultaneous equations. A preferred embodiment of the method for diagnosing water quality abnormalities in a nuclear power plant according to the present invention will be described in detail with reference to the accompanying drawings. Figure 2 shows the measurement locations in an example in which the water quality abnormality diagnosis method for a nuclear power plant according to the present invention is applied to the condensate water supply system of a nuclear reactor, and Figure 3 shows the measurement locations used for implementing the water quality abnormality diagnosis method. This figure shows an example of a measuring device that performs measurements. In FIG. 2, steam generated in a nuclear reactor 10 is sent to a turbine 14 through a main steam pipe 12 to drive the turbine, and then condensed in a condenser 16 to condense water. After that, the condensate is pumped to the condensate pump 18
After removing crud and ions in a filter demineralizer 20 and a condensate demineralizer 22, the water is sent to a low pressure heater 24. The condensate is then sent to the high-pressure heater 28 by the water supply pump 26, heated, and supplied to the nuclear reactor 10 as a coolant. Note that the symbols 30, 32, 3 shown in the figure
Reference numerals 4, 36, and 38 indicate measurement locations for measuring the ion concentration in water in this condensate water supply system. Each of the above measurement locations 30, 32, 34, 36,
The ion detector installed at 38 is the first ion detector, which consists of a thermocouple 40 and a PH meter 42, as shown in Figure 3.
At least one of the detector 44 and the second detector 48 composed of the thermocouple 40 and the conductivity meter 46 is installed, and the first detector 44 and the second detector 48 are installed.
The detector 48 may be installed at the same measurement location.
Further, the number of these detectors must be equal to or larger than the type of abnormality cause assumed in advance, which will be described later. The above-mentioned thermocouple 40, PH meter 42, conductivity meter 46
are each connected to an analog-to-digital converter 50, and the detected analog quantities are converted into digital quantities. The detected value converted into a digital quantity is then input to the process computer 54 via the interface 52. The process computer 54 performs predetermined arithmetic processing based on the input detection values, displays the results on a display 56, and stores the measurement data and the arithmetic results in a storage medium 58 made of magnetic tape or the like. Note that, for example, fundamental vectors as shown in the following table are input in advance to the storage medium 58. The fundamental vector has conductivity and PH as components.

[Table] The above table is based on the fact that the causes of water quality abnormalities in condensate water supply systems are broadly classified into the following four types. The first case is when seawater leaks into the condenser 16 and sodium chloride is mixed into the condensate.
In this case, there is concern that corrosion of non-rusting steel, which is often used for piping, valves, etc. in nuclear power plants, will be accelerated due to the contamination of chlorine ions, leading to an accident. Sodium chloride mixed into the condensate due to seawater leak is a neutral salt produced from a strong acid and a strong alkali. At this time, the PH of the condensate does not change, but the conductivity increases. Therefore, measurement location 3
At 0, only the increase in conductivity is measured.
However, since the sodium chloride mixed in the condensate is removed in the condensate demineralizer 22, after the measurement location 34 on the outlet side of the condensate demineralizer 22,
It will show normal condensate conductivity and pH. One of the fundamental vectors obtained in this way is the first one in the table.
This is the basic vector that causes the abnormality to be the seawater leak shown in the first row. The second case is when metal ions such as iron and cobalt are mixed into the cooling water (condensate) due to corrosion in the piping, valves, etc. of the condenser 16, the low-pressure heater 24, and the high-pressure heater 28. These metal ions in the cooling water adhere to fuel rods in the reactor and become radioactive, and the activated radioactive metal ions are then released into the reactor water and circulated together with the reactor water.
This deposits on pipes, valves, etc. of the recirculation system and increases the surface radiation dose rate in the recirculation system. Therefore, regarding the elution of metal ions due to corrosion, it is important to accurately determine the location of corrosion in order to safely operate a nuclear reactor. The elution of this metal ion is performed by hydroxide ion according to the following reaction formula.
Accompanied by the generation of OH ^- . M→M ²⁺ +2e ^- ...(1) 2H ₂ O+2e ^- →H ₂ +2OH ^- ...(2) Here M means a metal element, and the elution of divalent metal ions was explained above. ,1
The same applies to the elution of valent, trivalent, etc. metal ions. Therefore, when metal ions are eluted from equation (2), the PH of the coolant shifts to the alkaline side. The basic vector of water quality abnormalities based on the elution of metal ions will be explained based on a table, taking as an example the case where Fe is eluted in a condenser. When Fe ions (e.g. Fe ²⁺ ) are eluted in the condenser 16,
As mentioned above, the pH of cooling water increases due to the generation of OH ^- . Therefore, at the measurement point 30, an increase in conductivity and an increase in PH are observed, and the element of conductivity and the element of PH at the measurement point 30 of the fundamental vector are set to 1 and +1, respectively. However, since these Fe ions and hydroxide ions are removed in the condensate demineralizer 22, the vector elements are set to 0 at each subsequent measurement location. The third and fourth causes are due to leakage of the regeneration liquid of the ion exchange resin used in the condensate demineralizer 22. To regenerate the ion exchange resin used in the condensate demineralizer 22, after separating the condensate demineralizer from the condensate system and separating it into an anion exchange resin and a cation exchange resin, the anion exchange resin is This is carried out by backwashing with an aqueous sodium hydroxide solution, and the cation exchange resin is backwashed with an aqueous sulfuric acid solution. After the regeneration work has been completed, the condensate demineralizer is cleaned in order to prevent the remaining regenerated liquid from mixing with the primary cooling water.
After thoroughly washing each exchange resin with pure water, the anion exchange resin and the cation exchange resin are uniformly mixed and returned to the condensate system. However, if cleaning is insufficient, sodium hydroxide or sulfuric acid, which accelerates corrosion of stainless steel used in piping, etc., will be mixed into the cooling water. When the regeneration liquid is mixed into the cooling water, the PH of the cooling water increases when sodium hydroxide mixes into the cooling water, and the PH of the cooling water decreases when sulfuric acid mixes into the cooling water.
For this reason, when sodium hydroxide mixes into the cooling water in the brine desalination unit 22, the conductivity at the measurement location 34 increases, and the PH also increases.
As shown in the table, the vector element at the outlet of the condensate demineralizer has a conductivity of 1 and a PH of +1. and,
Since the sodium hydroxide mixed in the cooling water is supplied to the reactor 10 without being removed, the conductivity at the measurement locations 36 and 38 remains 1. When sulfuric acid is mixed into the cooling water in the condensate demineralizer 22, the conductivity increases and the pH decreases. Therefore, the vector elements in this case are as shown in the table. As described above, for the seven types of abnormality causes assumed in advance, basic vectors whose elements are electrical conductivity and PH corresponding to changes in ions due to these abnormal causes are created as shown in the table, and are stored in the storage medium 58. input. Next, an embodiment of the water quality abnormality diagnosis method will be described according to the flowchart shown in FIG. Figure 4 shows
This is a flowchart using PAD display (References, Journal of Information Processing Society of Japan, published in 1980, 21(4), p.259, Mura,
Written by Kawai, Horikoshi, and Tsutsumi, Program Analysis
Design and create programs with Diagrams). First, each measurement location 30, 32, 34, 36, 3
Detection signals from the first and second detectors installed at 8, that is, the detection signals from the thermocouple 40, PH meter 42, and conductivity meter 46, are sequentially input to the process computer 54 for each measurement location. be done. The process computer 54 calculates the difference from the set reference temperature of the cooling water based on the detection signal from the thermocouple 40 based on each input detection signal. Then, the process computer 54
The actually measured values of the conductivity and PH of the cooling water are corrected to the values of the conductivity and PH at the aforementioned reference temperature. Next, the process computer 54 calculates the electrical conductivity and pH of the cooling water at the reference temperature stored in the storage medium 58 at each measurement location, that is, the pure water.
, and the difference between the corrected conductivity of the cooling water and PH. When the absolute value determined by the process computer 54 is within the error range of the measured value set in advance, the element of the corresponding vector component corresponding to the measurement location of the measured value is set to 0.
shall be. On the other hand, when the absolute value of the calculated difference exceeds the preset error range of the measured value,
Determine the conductivity and PH of pure water from the corrected conductivity and PH values.
Depending on the sign of the difference after subtracting the value, the corresponding vector element at each measurement location is +1 or -
1. In this way, measurement vectors corresponding to the basic vectors shown in the table above are created. Process computer 54 then corresponds and compares the measured vectors with the fundamental vectors stored in storage medium 58 . When the measured vector does not correspond to any of the basic vectors shown in the table, it is confirmed that no abnormality has occurred in the cooling water of the condensate water supply meter, and this fact is displayed on the display 56. At this time, when comparing the fundamental vector and the measured vector, it is possible that the measured vector and the fundamental vector do not match due to a plurality of abnormal causes. Therefore, when the measurement vector includes at least one non-zero element, a composite vector of the basic vectors is created and compared with the measurement vector. This basic vector composition is performed as follows. If at least one conductivity element corresponding to each measurement location among the plurality of basic vectors extracted for synthesis includes 1, the element related to the electrical conductivity at that measurement location in the composite vector is set to 1. Then, regarding the elements of PH, take the sum of all the elements of PH at each measurement location of each basic vector,
The sum is the element of the composite vector. By sequentially comparing the composite vector obtained in this way with the above-mentioned measured vectors, it becomes possible to identify all the causes of the abnormality. Once the cause of the abnormality is clarified in this way, as mentioned in the creation of the basic vector,
The ionic components that cause water quality abnormalities, that is, the types of ions, become clear. Therefore, as shown in FIG. 5 using Fe ²⁺ ions as an example, since the conductivity difference or PH difference in the cooling water with respect to pure water is determined, the ion concentration in the cooling water can be obtained. In addition, if the standard measurement temperature at each measurement location is different, the standard conductivity in the coolant can be calculated using the following formula using the conductivity per unit gram equivalent shown in Figure 6. can be calculated. K= 〓 ⁱ Α _i C _i ...(3) where K is the electrical conductivity (μS/cm), A is the ultimate equivalent electrical conductivity (μS・cm ² /g equivalent), and C is the ion concentration (g equivalent weight/cm ³ ), i indicates the number of each measurement location. However, abnormalities in water quality can usually be detected immediately after the abnormality occurs, and therefore, taking into account that the ion concentration of the substance causing the water quality abnormality is small, in equation (3), Correction terms that are nonlinear are omitted. In addition, if water quality abnormalities occur due to a combination of multiple causes, ions generated by the abnormal causes occurring on the condenser 16 side, which is the upstream side shown in Fig. 2, will sequentially progress to the downstream side. Therefore, simultaneous equations are created based on the indicated values of conductivity and/or PH at each measurement location, and the degree of each abnormality can be evaluated by solving these simultaneous equations. In this way, in this example, when measuring the electrical conductivity at each measurement location, the cooling water used as the sample was measured without being cooled to a low temperature such as room temperature. Thus, the indicated value of the conductivity difference increases, and the lower limit of detection can be improved. Especially in normal nuclear power plants,
The temperature of the cooling water near the outlet of the high-pressure heater 28 shown in Figure 2 is as high as 215°C, so it is normally
Compared to the measurement value at 25℃ specified by JIS, sensitivity is 4/3 to 3/2 times higher for metal ions, and even more sensitive for sodium chloride, sodium hydroxide, and sulfuric acid. The sensitivity is significantly improved, and the sensitivity is approximately 7 times higher. In addition, when measuring conductivity and PH, the temperature of the cooling water is measured at the same time, and the temperature of the conductivity and PH is corrected, but the temperature change of the cooling water during steady operation is only a few degrees Celsius. Even without temperature correction, the measurement error can be kept within a few percent. Moreover, the conductivity meter, which is already used for continuous measurement as a measurement device in nuclear power plants, and
By using only a PH meter, it is possible to continuously detect water quality abnormalities, and also to monitor the cause and extent of the abnormality. For this reason, the period of time that conventionally required several days for element quantity analysis to elucidate the cause of an abnormality is greatly shortened, and the cause can be determined almost instantly (within a few seconds). Therefore, it is possible to speed up the response to the cause of water quality abnormality, and it is possible to greatly improve the reliability of the operation of the nuclear power plant. Furthermore, even if a complex water quality abnormality occurs based on multiple causes of abnormality, monitoring can be carried out by breaking down each cause of the abnormality by comparing the composite vector of the basic vectors and the measured vector. I can do it. Therefore, compared to the conventional method of detecting abnormalities in a nuclear power plant by measuring only the gross state quantity at one point in the piping system, detection accuracy can be greatly improved. In other words, metal elution from piping, etc. is unavoidable to the extent that it does not cause water quality abnormalities, and the increase in electrical conductivity from pure water due to these eluted metals acts as a measurement error, so the criteria for determining abnormalities such as seawater leaks had no choice but to set a high value. For example, the concentration of metal ions eluted from the condenser is approximately 10 ppb.
Therefore, the conductivity of cooling water is approximately 0.5 μS higher than that of pure water. As a result, in the case of conventional seawater leaks, the abnormality detection level was approximately 60 ppb of sodium chloride concentration, taking into consideration the elution of metal ions from the condenser, but according to this example, the elution It is possible to separate the conductivity fluctuations caused by accompanying metal ions, and the abnormality detection level for seawater leaks can be reduced to approximately 10 ppb, making it possible to improve sensitivity by approximately 6 times. As a result, it became possible to detect water quality abnormalities at an early stage. As explained above, according to the present invention, it is possible to compare the measurement vector with the fundamental vector corresponding to the increase/decrease in the measurement value related to the gross amount, which can be measured online including the conductivity and PH at a plurality of measurement locations in the piping system. Therefore, water quality abnormalities can be easily detected. If the measured vector does not match the basic vector, but it has a non-zero element, multiple abnormalities in water quality can be detected by composing multiple basic vectors and comparing the resulting composite vector with the measured vector. The cause can be identified. Furthermore, after identifying multiple causes of the abnormality, derive simultaneous equations that hold between the electrical conductivity detected at multiple locations in the piping system and the respective ion concentrations corresponding to the detected causes of the abnormality, and solve the simultaneous equations. This makes it possible to quantitatively understand the extent of identified abnormalities in water quality.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of a conventional water quality abnormality diagnosis method for a nuclear power plant, FIG. 2 is a diagram showing an example of a measurement location according to the water quality abnormality diagnosis method for a nuclear power plant according to the present invention, and FIG. A diagram showing an example of a measuring device for carrying out a method for diagnosing water quality abnormalities in a nuclear power plant, Fig. 4 is a flowchart using a PAD display of the method for diagnosing water quality abnormalities in a nuclear power plant according to the present invention, and Fig. 5 shows Fe ²⁺ ion concentration. FIG. 6 is a diagram showing the relationship between temperature change and ultimate equivalent conductivity. 10... Nuclear reactor, 16... Condenser, 20... Filter demineralizer, 22... Condensate demineralizer, 24...
Low pressure heater, 28...High pressure heater, 30,3
2, 34, 36, 38...Measurement location, 42...PH
Total, 46...Conductivity meter.

Claims (1)

[Scope of Claims] 1. A method for diagnosing water quality abnormality in a nuclear power plant in which the cause of water quality abnormality is detected by detecting the ion concentration in water flowing in one direction through a piping system, wherein the ion concentration in the water is measured at multiple points in the piping system. Detected in
A measurement vector created by comparing the detected ion concentration with the standard ion concentration in a normal state, and a basic vector created by comparing the ion concentration in the water caused by the abnormality assumed in advance and the standard ion concentration. A water quality abnormality diagnosis method for a nuclear power plant, characterized in that the cause of water quality abnormality is detected by comparing . 2. The method for diagnosing water quality abnormalities in a nuclear power plant according to claim 1, characterized in that electrical conductivity and pH are used as detection indicators for the ion concentration in the water. 3. In a water quality abnormality diagnosis method for a nuclear power plant, which detects the cause of water quality abnormality by detecting the ion concentration in water flowing in one direction through a piping system, the ion concentration in the water is detected at a plurality of locations in the piping system,
A measurement vector created by comparing the detected ion concentration with the standard ion concentration in a normal state, and a basic vector created by comparing the ion concentration in the water caused by the abnormality assumed in advance and the standard ion concentration. , when the measured vector does not match the basic vector but has a non-zero element, a composite vector obtained by combining the plurality of basic vectors is used. A method for diagnosing water quality abnormalities in a nuclear power plant, characterized in that a plurality of causes of water quality abnormalities are detected by comparing the measured vector and the measured vector. 4. The method for diagnosing water quality abnormalities in a nuclear power plant according to claim 3, characterized in that electrical conductivity and pH are used as detection indicators for the ion concentration in the water. 5. In a water quality abnormality diagnosis method for a nuclear power plant, which detects the cause of water quality abnormality by detecting the ion concentration in water flowing in one direction through a piping system, the ion concentration in the water is detected at a plurality of locations in the piping system,
A measurement vector created by comparing the detected ion concentration with the standard ion concentration in a normal state, and a basic vector created by comparing the ion concentration in the water caused by the abnormality assumed in advance and the standard ion concentration. , and after identifying multiple causes of abnormality, derive simultaneous equations that hold between the electrical conductivity detected at multiple locations in the piping system and the respective ion concentrations corresponding to the detected causes of abnormality,
A water quality abnormality diagnosis method for a nuclear power plant, characterized in that the degree of each abnormality is evaluated by solving the simultaneous equations. 6. The method for diagnosing water quality abnormalities in a nuclear power plant according to claim 5, characterized in that electrical conductivity and pH are used as indicators for detecting the ion concentration in the water.