JPH063484A - Primary reactor cooling system water quality estimation method - Google Patents

Abstract

(57) [Summary] (Corrected) [Purpose] Using the calculation results obtained by simulation and the measured values outside the core, the water quality of the reactor core and its vicinity can be accurately measured in real time within a practical range. Estimate high and map the distribution of reactor water components on the screen to enhance the operability of the reactor. [Structure] This calculation is performed by simulating how the water quality at each site in the reactor changes when the amount of hydrogen injection is changed depending on the design and operating conditions of each plant. The result is stored in the storage device 22. The water quality distribution in the pressure vessel 26 having a solution that agrees with the actual measurement value by the water quality measuring device 23 outside the core is searched out from the calculation result by using the arithmetic device 21. When there is no matching solution, the distribution including the measured value is obtained from the calculation result by the interpolation method. [Effect] Since the water quality of each region in the furnace is accurately estimated in real time, water quality control such as hydrogen injection can be performed under optimum conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water quality control system for reactor cooling water, and particularly to water quality suitable for diagnosing water quality at various parts of a reactor during hydrogen injection for preventing stress corrosion cracking of a boiling water reactor. Concerning how to guess.

[0002]

2. Description of the Related Art Stress corrosion cracking (SC
When C) is suppressed by controlling the water quality, it is considered to keep the dissolved oxygen concentration in the reactor water at a certain value (20 ppb) or less. Therefore, in recent years, in many boiling water nuclear power plants, it has been performed to inject hydrogen into the primary cooling system to reduce the dissolved oxygen concentration.

When the plant design, operating conditions, impurity concentration in the reactor water, etc. change, the concentrations of oxygen, hydrogen peroxide, etc. in the reactor water change. In particular, in the vicinity of the core, as a result of the reactor water being strongly irradiated with neutrons and gamma rays, oxygen and hydrogen peroxide that corrode the structural material, or various reactive radicals are formed. Therefore, it is necessary to accurately know the concentration distribution of dissolved oxygen and the like in the reactor water in order to effectively perform hydrogen injection.

However, it is impossible with the present technology to measure the concentration of the reactor water component by placing the device directly in the core part. This is because the reactor core cannot be stably installed for a long period of time due to strong radiation in addition to high temperature and high pressure. Therefore, the water quality is measured after guiding the primary cooling water from the core to the outside through a long sampling pipe. However, with this method, since the radiation dose and temperature differ depending on the core region, the concentration of the reactor water component changes until it exits the sampling pipe, and it is not possible to correctly see the water quality in the core.

In the present situation where the direct concentration cannot be measured, it is an effective method to increase the safety of the nuclear reactor by estimating the situation in the core by simulation. At the current technical stage, it is possible to calculate the concentration distribution of reactor water components with a certain degree of accuracy by a simulation that models the environmental conditions inside the reactor such as radiation dose. Japanese Laid-Open Patent Publication No. 61-86688 proposes a method of estimating the water quality by adjusting specific parameters during simulation so as to correspond to measured values such as oxygen concentration every moment. However, this method is not realistic because it does not guarantee the existence of solutions that take time to calculate.

Further, Japanese Patent Application No. 3-264512 proposes that a specific water quality factor at a specific site is adopted as a reference, and that the water quality is controlled by making a judgment by using a measured value by a sensor group and a simulation result. ing.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to use the calculation results obtained by simulation and the measured values outside the core in real time to determine the water quality of the primary reactor cooling system, especially the core and its vicinity. Another object of the present invention is to provide an embodiment suitable for application to Japanese Patent Application No. 3-26451, which is estimated with high accuracy in a practical range.

Another object of the present invention is to estimate the water quality,
It is to improve the operability of the reactor by mapping the distribution of reactor water components on the screen.

Another object of the present invention is, on the contrary, to calculate the hydrogen injection amount necessary for maintaining a good core environment from the estimated water quality and finely control the injection amount.

[0010]

The present invention is to estimate the water quality distribution of the primary cooling system by using the measured values outside the core. This is done by the following procedure. It is necessary to calculate in advance how the water quality will change in each part of the reactor when the hydrogen injection amount is changed in accordance with the design and operating conditions of each plant. The calculation result is stored in the storage device. The water quality distribution in the pressure vessel having a solution that agrees with the water quality measurement result outside the core is searched from the calculation results. When there is no matching solution, the calculated result is used to obtain the distribution including the measured value by an appropriate interpolation method.

Further, in the present invention, the obtained water quality distribution in the reactor is averaged for each of the pre-divided regions, and the average value is mapped in the diagram representing the nuclear reactor on the display device.

Further, in the present invention, the required hydrogen injection amount is calculated from the estimated core water quality environment, and the opening / closing of the valve of the hydrogen injection device is controlled. At this time, taking advantage of the fact that it can be estimated in real time, the hydrogen injection amount is always fed back.

[0013]

[Operation] When simulation is performed with the calculation code, the actual measurement values are not used as boundary conditions to perform calculations on the spot. Calculate the component concentration distribution. Then, from the obtained calculation results of the concentration distribution of the oxidizing component, the one that matches the measured value is searched for, or the water quality distribution including the measured value is obtained by the interpolation method. As a result, it is possible to obtain a solution without spending much calculation time.

[0014]

EXAMPLE An estimation method will be described using the estimation algorithm of water quality in the core shown in FIG. FIG. 2 shows the concept of inference, which is used as a supplement to the algorithm. First, in order to evaluate the water quality environment in the core, it is decided which concentration of the reactor water component should be used as the estimation standard. This is called the index component concentration. The index component concentration is
Oxidizing component concentration such as hydrogen peroxide concentration, oxygen concentration or effective oxygen concentration is used. For example, this is the effective oxygen concentration at the core entrance. This value cannot be measured directly with current technology. Here, the effective oxygen concentration [O
₂ ] eff is oxygen concentration [O ₂ ] and hydrogen peroxide concentration [H ₂ O ₂ ]
Is defined as follows.

[O ₂ ] eff = [O ₂ ] + [H ₂ O ₂ ] / 2 (Chemical formula 1) Regarding the hydrogen concentration, the measurement result and the analysis result may not exactly match the hydrogen injection amount. . This is because some of the constants for each plant required for the calculation have not been obtained accurately, and the actual hydrogen consumption may differ from the calculation. Even in such a case, the relative relationship between the calculated values of the oxidative components at each site is reliable, so if the concentration at a specific site is known, calibrate the calculation results using that value to obtain other values. The value of the part of can be obtained. That is, the measured value of the concentration of the reducing component,
Ignore the compatibility with the calculated values and simplify the logic of estimating the water quality by focusing only on the concentration of oxidizing components.

Next, the concentration of this index component is measured at a certain position outside the core where the water quality can be accurately measured, and is input to the arithmetic unit online.

For each operating plant, the water quality when the amount of hydrogen injection into the feed water is systematically changed under the design and operating conditions of each reactor is the primary cooling with the core inlet as the origin. Calculate for each position of the system. This is C
Let _l (X; P) {l = 0, N}. X is the distance from the core inlet origin, N is the number of calculations with different hydrogen injection amounts, and P is
Represents parameters other than the hydrogen injection amount. The obtained results are stored in the storage device as a database. C
_l (X; P) corresponds to what is drawn by four solid lines in FIG. 2 as the calculation for each hydrogen concentration. Below, P is assumed to be constant and expressed as C _l (X).

The concentration distribution of the reactor water component is estimated as follows using the database and the actual measurement value.

First, at the position x ₁ corresponding to the measurement point, when the hydrogen injection amount was gradually increased from 0 ppb, the measured value Cobs (x ₁ ) was C _i (x ₁ ) ≦ Cobs (x ₁ ). <C _{i + 1} (x ₁ ) ... (Equation 1) Calculated values for two consecutive injection amounts sandwiching the measured value, C _i (x ₁ ), C _{i + 1} (x ₁ ) Find out. In FIG. 2, where on the alternate long and short dash line the measured value is to be found is to be searched. Then, two calculated values sandwiching the measured value are proportionally distributed to calculate a proportional coefficient, and the concentration at a position other than the measured point is calculated using i in the database and the calculated value at the (i + 1) th hydrogen injection amount. The coefficient k (x ₁ ) of proportional distribution is k (x ₁ ) = (Cobs (x ₁ ) −C _i (x ₁ )) / (C _{i + 1} (x ₁ ) −C _i (x ₁ )) ... ( It is obtained by the formula 2). Therefore, the estimated concentration C at any position x
(x) is obtained by the following equation.

C (x) = k (x ₁ ) (C _{i + 1} (x) −C _i (x)) + C _i (x) (Equation 3) This is the hydrogen injection corresponding to the measured value in FIG. When the quantity exists, it corresponds to the case of Xppb between 0 ppb and 100 ppb, and the broken line is calculated.

When C _i (x ₁ ) = Cobs (x ₁ ) ... (Equation 4), C _i (x) is a concentration distribution for a certain hydrogen injection amount including an actually measured value. In FIG. 2, the measured value exists on the intersection of the solid line and the alternate long and short dash line.

The function used for the interpolation method may be of a higher order, but this is sufficient considering the error in the calculation itself.

An estimated value of the effective oxygen concentration at the core inlet can be obtained from the concentration distribution obtained by the above method. FIG. 3 is a graph and table showing the results of the estimation. At this time, what is shown in the graph is how the effective oxygen concentration changes with the distance from the core in the primary cooling system, calculated by changing the hydrogen injection amount (solid line) and the measured value (black circle). And the estimated concentration distribution (broken line). The table also shows the values of hydrogen, oxygen, hydrogen peroxide, and effective oxygen concentration at each position of the primary cooling system when the effective oxygen concentration is used as the estimation standard.

FIG. 4 shows an algorithm for mapping the concentration distribution after estimating the water quality. First, the index component concentration as a reference for estimation is selected, and the concentration of the index at each position of the primary cooling system is estimated using the estimation algorithm described above.
The estimation result is shown in a graph and a table as shown in FIG. Here, in order to intuitively grasp the concentration distribution in the reactor pressure vessel and allow the operator to make a proper judgment, the pressure vessel is color-coded in the figure. This is done in FIG. In this embodiment, the densities are divided into 11 levels and the colors are associated with the respective density ranges. The color was substituted by the letters ak. In order to see what the concentration distribution of the primary cooling system looks like, it is divided into the following areas and displayed. That is, the boiling channel region 5, the bypass channel region 4, the upper plenum region 7, the riser outlet region 8, the mixing plenum region 9, the downcomer region 10, the recirculation system region 13, the jet pump outlet region 11, and the lower plenum region 12 Is. An average value is calculated for each area using the estimated density distribution, and the color is determined according to the calculated value. Which color the density range corresponds to is shown in the color palette 2 which is the density display portion. As a result, it is possible to visually grasp how the water quality in each region in the furnace is. The density display may be performed not by color classification but by changing the shade of color or the design.

When it is desired to see how the components other than the index component are distributed, the component desired to be viewed is selected from the menu 1 shown on the screen 15 and input. Further, when the user wants to see the previously displayed graph and table (FIG. 3) again, it can be selected from the menu 1. Furthermore, it is also possible to select and display the concentration distribution of the components in the reactor water when hydrogen is not injected. All operations required for screen display can be selected from menu 1.

FIG. 6 shows how the present invention is applied to the water quality control of a boiling water reactor. 26 is a pressure vessel, 16 is a turbine, 17 is a condenser, 18 is a condensate purification system, 19 is a water supply pump, and 25 is a recirculation pump. The measuring device 23 is installed at a certain point in the recirculation system. The measuring device 23 is connected to the arithmetic device 21 online, and the measurement result is input every moment. The arithmetic unit 21 calculates the concentration distribution of the reactor water component of the entire primary cooling system in real time from the measured values using the database stored in the storage unit 22, and displays the display unit 2
Map to 4 above. SCC at a part of the core 27
If the estimated water quality deviates from the set value, the optimal index concentration to prevent
Calculate the hydrogen injection amount that satisfies the set concentration in the core,
The opening amount of the valve of the hydrogen injection device 20 is adjusted. At this time, the actual measurement value can be fed back while performing fine control. FIG. 7 is an algorithm showing the control concept.

[0027]

According to the present invention, since the distribution of reactor water quality in the reactor can be estimated in real time, the water quality can be determined by a technique such as hydrogen injection by focusing on the material at any position of the reactor. Feedback control is possible and the corrosive environment in the furnace can be clearly captured.

[Brief description of drawings]

FIG. 1 is a flowchart for estimating water quality in a reactor.

FIG. 2 is a characteristic diagram for estimating water quality in a reactor.

FIG. 3 is a characteristic diagram of estimation results.

FIG. 4 is a flowchart of a water quality screen display.

FIG. 5 is an explanatory diagram of a mapping example.

FIG. 6 is a block diagram of an embodiment of a boiling water reactor.

FIG. 7 is a flowchart of water quality control.

[Explanation of symbols]

16 ... Turbine, 17 ... Condenser, 18 ... Condensate purification system, 1
9 ... Water supply pump, 20 ... Hydrogen injection device, 21 ... Arithmetic device, 22 ... Storage device, 23 ... Water quality measuring device, 24 ... Display device, 25 ... Recirculation pump, 26 ... Pressure vessel, 27 ... Core.

Claims (4)

[Claims] 1. A measuring unit for measuring the reactor water quality factor of the primary cooling system outside the nuclear reactor core, and for each predetermined region in the primary cooling system including the reactor core, based on the measured data by the measuring unit. A method for estimating water quality of a primary reactor cooling system, which comprises estimating the concentration of oxidizing components in reactor water. 2. A method for estimating water quality of a primary reactor cooling system, which displays the concentration of constituents in reactor water estimated in claim 1 on a screen. 3. The reactor according to claim 1, wherein the two-dimensional cross-sectional view of the reactor is divided into regions by using the estimated concentration of the constituents in the reactor water at a specific site, and the oxidizability is obtained by changing the color coding, shading and pattern of each region. A method for estimating the water quality of a primary reactor cooling system that displays the concentrations of components. 4. The method for estimating the water quality of a reactor primary cooling system according to claim 1, wherein the injection amount of the water quality easing agent is determined by using the estimated concentration of the constituent in the reactor water at the specific site.