JP2014202552A - Method for removing silica in nuclear reactor coolant purification system and method for estimating silica adsorption amount - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silica removal method capable of efficiently removing silica from a nuclear reactor water.SOLUTION: A silica removal method for removing silica from a nuclear reactor water exchanges an ion exchange resin, provided on a filter demineralizer constituting a nuclear reactor coolant purification system for purifying reactor water, for new one, at the time when a silica adsorption amount peaks, to remove silica from reactor water. In this case, silica adsorbed on the ion exchange resin is removed before re-emitted by substitution with other anions having strong adsorption power, and therefore silica can be efficiently removed from the reactor water. This leads to a slower rise of silica concentration of the reactor water after the exchange and leads to a longer period of time to reach a control value which requires next exchange. Thus, the number of exchanges of ion exchange resins can be reduced more than before.

Description

  The present invention relates to a method for removing silica contained in reactor water in a reactor coolant purification system of a boiling water nuclear power plant and a method for estimating the silica adsorption amount of an ion exchange resin.

  In boiling water nuclear power plants, silica contained in reactor water is adsorbed and removed by the ion exchange resin on the filter surface of the filter demineralizer to keep the silica concentration in the reactor water below the control value. This is because when the silica concentration in the reactor water is high, there is a concern about adverse effects on structural materials such as stress corrosion cracking (for example, the filtration desalination apparatus 11 of Patent Document 1 below).

Japanese Patent Laid-Open No. 7-104095

  Since the exchange capacity of the ion exchange resin on the filter surface decreases as the silica adsorption amount increases, in general, as shown in FIG. 2, the silica concentration of the reactor water at the outlet of the filtration desalination apparatus is Until the control value is reached, continue to use ion exchange resin (mixed resin of anion exchange resin and cation exchange resin). When the silica concentration reaches the control value, the old ion exchange resin is discarded and new ion exchange is performed. Replaced with resin. After the exchange, since the ion exchange resin adsorbs silica, the silica concentration of the reactor water at the outlet of the filtration desalination apparatus is once lowered. After that, when the use is continued, the silica concentration of the reactor water at the outlet of the filtration desalination apparatus gradually increases, and when the silica concentration reaches the control value, the ion exchange resin is replaced again.

  By the way, the adsorptive power of anions to ion exchange resins (anion exchange resins) is low in the order of chlorine (low) <silica <nitric acid <sulfuric acid <chromic acid (high). After the exchange, silica having a larger total amount contained in the reactor water than the other anions is once attached to the ion exchange resin. However, by adsorbing silica and other anions contained in the reactor water, the ion exchange resin reaches the total exchange capacity, and when the silica adsorption amount reaches a peak, it is once adsorbed to the ion exchange resin. Silica is replaced with anions such as chromic acid having a high adsorptive power, and is released again into the reactor water (see FIG. 11).

Therefore, in the method of exchanging the ion exchange resin when the silica concentration reaches the control value, the silica adsorption amount of the ion exchange resin at the time of the exchange is greatly reduced from the peak due to the re-release of the silica described above. Since silica cannot be efficiently removed, the number of exchanges of the ion exchange resin increases, and there is a problem that the amount of radioactive waste (ion exchange resin discarded by exchange) increases.
This invention is completed based on the above situations, Comprising: It aims at removing a silica efficiently from nuclear reactor water.

  The present invention relates to a silica removal method for removing silica from reactor water, wherein an ion exchange resin provided in a filtration desalination apparatus constituting a reactor coolant purification system for purifying reactor water is used as a silica adsorption amount. The silica is removed from the reactor water by exchanging at the time when reaches a peak. By doing so, since more silica can be removed from the reactor water by exchanging the ion exchange resin once, with no or little re-release of silica, the number of ion exchange resin exchanges can be reduced. The peak (maximum) means the amount of silica adsorbed when the ion exchange resin reaches the total exchange capacity (adsorption saturation).

The following configuration is preferable as an embodiment of the present invention.
The silica adsorption amount of the ion exchange resin is estimated based on the silica concentration of the inlet water of the filtration demineralizer and the silica concentration of the outlet water of the filtration demineralizer. In this way, even when the silica adsorption amount of the ion exchange resin cannot be directly measured, the timing at which the silica adsorption amount of the ion exchange resin peaks can be specified.

  The present invention is a method for estimating the amount of silica adsorbed by ion-exchange resin fat provided in a filtration desalination apparatus constituting a reactor coolant purification system, and is based on the amount of increase / decrease per unit time of silica relative to a reactor. The first relational expression for determining the change in the silica concentration of the reactor water, the equilibrium constant of the silica adsorption reaction to the ion exchange resin, the hydroxide ion concentration of the inlet water of the filtration desalination apparatus, and the silica load And the second relational expression for determining the silica concentration of the outlet water of the filtration demineralizer based on the remaining exchange capacity of the ion exchange resin, the silica concentration of the inlet water of the filtration demineralizer, Based on the silica concentration of the outlet water of the salt device, the silica adsorption amount of the ion exchange resin fat is estimated using a third relational expression for obtaining the amount of change in the silica adsorption amount of the ion exchange resin fat.

  According to the present invention, silica can be efficiently removed from reactor water. Thereby, the frequency | count of replacement | exchange of ion exchange resin reduces, and the generation amount of radioactive waste can be reduced.

System configuration diagram of a boiling water reactor disclosed in the embodiment Figure showing the transition of the silica concentration of reactor water when the ion exchange resin is replaced when the silica concentration of the reactor water reaches the control value Figure showing the change in the silica concentration of reactor water when the ion exchange resin is replaced when the amount of silica adsorbed on the ion exchange resin reaches its peak The figure which shows the description list of each term which comprises Numerical formula 1 Block diagram showing water circulation in a boiling water nuclear power plant The figure which shows the description list of each term which comprises Numerical formula 2 The figure which shows the description list of each term which comprises Numerical formula 3-Numerical formula 8. Block diagram showing the electrical configuration of the simulation device Table summarizing calculation conditions and variables required for simulation Table summarizing calculation results obtained by simulation The figure which shows a mode that the silica adsorbed on the ion exchange resin is replaced with chromic acid

<One Embodiment>
An embodiment of the present invention will be described with reference to FIGS.
1. System configuration of boiling water nuclear power plant FIG. 1 is a system configuration diagram of a boiling water nuclear power plant. The boiling water nuclear power plant is composed of a boiling water reactor (hereinafter simply referred to as a nuclear reactor) 1, a turbine 2, a condenser 3, a condensate filtration device 4, a condensate demineralizer 5, and a feed water heater 6. Has been. Then, the steam generated in the nuclear reactor 1 is sent to the turbine 2 and then condensed in the condenser 3 to become condensate. It is formed so as to return to the nuclear reactor 1 as feed water through the feed water heater 6. The condensate demineralizer 5 is provided with a filter having a particulate ion exchange resin (anion exchange resin and cation exchange resin). It is the structure which suppresses the silica concentration of water.

  Further, the reactor coolant purification system (purification system for purifying the reactor water) 7 includes a filtration desalination apparatus 11 comprising a precoat resin tower 12 and a purification pump 8 for circulating the reactor water to the precoat resin tower 12. It has. The precoat resin tower 12 has a plurality of precoat filters implanted in a tank in which reactor water circulates. The precoat filter has a configuration in which an ion exchange resin is attached to the outer surface of a cylindrical element. The ion exchange resin is an ion exchange resin in which a powdered anion exchange resin and a cation exchange resin are mixed, and the anion containing silica is adsorbed by the anion exchange resin. It is configured to adsorb and remove cations and maintain high purity of the reactor water.

  Therefore, when the purification pump 8 is driven and the reactor water is passed through the precoat type powder mixing resin tower 12, impurities such as silica and radioactivity are adsorbed on the ion exchange resin of the precoat filter. Such impurities and radioactivity are removed, and the reactor water becomes purified treated water. And this treated water becomes a system which joins the above-mentioned water supply and returns to the nuclear reactor 1. Reference numeral 13 denotes a recirculation pump of the reactor coolant recirculation system.

2. Silica Removal Method from Reactor Water In the silica removal method disclosed in the present embodiment, the precoat type resin tower 12 of the filtration desalination apparatus 11 constituting the reactor coolant purification system 7 that purifies the reactor water is used. Silica is efficiently removed from the reactor water by exchanging the provided ion exchange resin when the silica adsorption amount reaches a peak. The peak (maximum) means the time when the ion exchange resin reaches the total exchange capacity (adsorption saturation) or the silica adsorption amount at that time.

  In this case, more or less silica is removed from the reactor water with no or less silica re-release. Therefore, since the increase in the silica concentration of the reactor water becomes slow after the ion exchange resin is replaced, the number of ion exchange resin replacements can be reduced as compared with the conventional case.

  For example, when the ion exchange resin is replaced when the silica concentration in the reactor water reaches the control value (conventional case), the number of replacements per year is 7 as shown in FIG.

  On the other hand, if the ion exchange resin is exchanged at the peak of the amount of silica adsorbed, at the initial stage when the reactor water contains a lot of silica, before the silica concentration in the reactor water reaches the control value, The ion exchange resin will be exchanged, and the exchange interval will be shortened.

  However, each time the ion exchange resin is replaced, the increase in the silica concentration of the reactor water becomes slow, and if the replacement is repeated to some extent, the time until the silica concentration of the reactor water reaches the control value becomes longer. As shown, the number of exchanges per year is four. Therefore, it is possible to reduce the number of exchanges of the ion exchange resin as compared with the conventional case.

  By the way, since the filtration desalination apparatus 11 contains high radioactivity, there exists a situation that the silica adsorption amount of an ion exchange resin cannot be measured directly. Therefore, in the present embodiment, the silica adsorption amount of the ion exchange resin is determined based on the silica concentration of the inlet water of the filtration demineralizer 11 (silica concentration at the point P1 shown in FIG. 1) and the outlet water of the filtration demineralizer 11. It is estimated based on the silica concentration (silica concentration at the point P2 shown in FIG. 1).

  If it demonstrates concretely, the nuclear reactor water also contains the radioactivity similarly to the filtration desalination apparatus 11, but the radioactivity contained in the reactor water is lower than that of the filtration demineralization apparatus 11. Therefore, the silica concentration can be measured. Therefore, if the silica concentration of the inlet water of the filtration desalting apparatus 11 and the silica concentration of the outlet water of the filtration desalting apparatus 11 are respectively specified by measurement or the like, the silica adsorption to the ion exchange resin based on the following formula 1 It is possible to determine the amount of change (amount of change with respect to time). The explanation of each term in Equation 1 is shown in FIG.

  Therefore, the silica adsorption amount of the ion exchange resin can be estimated by integrating the change amount of the silica adsorption amount calculated from Equation 1 with time.

  On the other hand, the peak of the silica adsorption amount can be obtained by subtracting the adsorption amount of other anions when reaching the total exchange capacity from the total exchange capacity of the ion exchange resin. In addition, the adsorption amount of the other anion with respect to ion exchange resin can be calculated | required from the density | concentration of each anion in the entrance / exit of the filtration desalination apparatus 11, and it is also possible to use an experimental value and experience value. The total exchange capacity of the ion exchange resin can be calculated based on the exchange capacity of the ion exchange resin (anion exchange resin) per unit weight and the weight of the ion exchange resin.

  Therefore, when the numerical value obtained by converting the silica adsorption amount estimated from Equation 1 into a molar concentration (hereinafter referred to as silica load amount) continues to use the ion exchange resin until reaching the peak, and when the silica load amount reaches the peak, It is only necessary to replace the ion exchange resin.

  Moreover, although the example which calculates the silica adsorption amount of ion exchange resin using the measured value of the silica concentration of the inlet water of the filtration desalination apparatus 11 above and the outlet water was demonstrated, the silica adsorption amount of ion exchange resin was demonstrated. It is also possible to obtain from simulation without using the measured value of silica concentration.

3. FIG. 5 is a block diagram showing water circulation in a portion related to a change in the silica concentration of reactor water in a boiling water nuclear power plant.

  As shown in FIG. 5, silica enters and exits (increase / decrease) in the nuclear reactor 1 and the intake amount X (first term on the right side of Equation 2 below) taken in through the feed water and the main flow out to the turbine 2 side. The outflow amount Y contained in the vapor and flowing out (the second term on the right side of the following formula 2) and the adsorption removal amount Z (the third side on the right side of the following formula 2) adsorbed and removed by the ion exchange resin in the filtration desalting apparatus 11 Section).

Therefore, as shown in Equation 2 below, the product of the change in the reactor water silica concentration and the reactor water retention amount (ΔC _RW · V) is the amount of increase / decrease per unit time of silica relative to the reactor 1, specifically Is the amount of outflow Y per unit time that goes out to the turbine 2 side from the amount of intake X per unit time taken in through the feed water, and the unit that is adsorbed and removed by the ion exchange resin in the filtration demineralizer 11 It is equal to the amount obtained by subtracting the adsorption removal amount Z per hour. Formula 2 corresponds to the “first relational expression” of the present invention. Also, explanation of each term in Equation 2 is shown in FIG.

  Formula 3 is a formula for obtaining the silica load of the ion exchange resin (the silica adsorption amount converted to the molar equivalent per ion exchange resin). Equation 4 shows the silica concentration of the outlet water of the filtration desalting apparatus 11, the equilibrium constant of the silica adsorption reaction to the ion exchange resin (term 1 on the right side of the expression 4), and the hydroxide ions of the inlet water of the filtration desalting apparatus 11. Concentration (term 2 on the right side of Formula 4), silica load (numerator on the right side 3 of Formula 4), and the remaining exchange capacity of the ion exchange resin (total exchange capacity minus all anions including silica) Thing: a formula to be calculated based on the denominator of the third term on the right side of Formula 4.

  Equation 5 is an equation in which the amount of change in the silica adsorption amount of the ion exchange resin is calculated from the silica concentration of the inlet water and the silica concentration of the outlet water of the filtration desalting apparatus 11. Formula 4 is an example of the “second relational expression” in the present invention, and Formula 5 is an example of the “third relational expression” in the present invention.

  Equations 6 to 9 are equations for obtaining increments of the loadings of chromate ions, sulfate ions, nitrate ions, and chloride ions. Moreover, the description of each term of Formula 3 to Formula 8 is shown in FIG.

  FIG. 8 is a block diagram of the simulation apparatus 50. The simulation device 50 includes a calculation unit 51, a storage unit 53, an input unit 55 such as a keyboard and a mouse, and a display unit 57. The storage unit 53 stores simulation software for calculating the silica concentration of the reactor water, the silica concentration of the outlet water of the filtration desalting apparatus 11, and the silica adsorption amount of the ion exchange resin based on the above-described Equations 1 to 9. Has been.

  Then, after starting the simulation software, when the calculation conditions such as the constants and parameters shown in FIG. 9 and the initial values of the variables are input, the calculation unit 51 uses the formulas 1 to 9 to calculate the reactor water silica. The concentration, the silica concentration of the outlet water of the filtration desalting apparatus 11, the silica adsorption amount to the ion exchange resin, and the silica load amount are automatically calculated, and the results are displayed on the display unit 57 (see FIG. 10).

  The constant is a condition in which the numerical value is fixed among the calculation conditions necessary for executing the simulation. In this example, as shown in FIG. 9, the feed water flow rate, the amount of water retained in the reactor, the reactor water Hydroxide ion concentration, Reactor water chromate ion concentration, Reactor water sulfate ion concentration, Reactor water nitrate ion concentration, Reactor water chloride ion concentration, Reactor water carryover rate, Filtration removal The purification flow rate of the salt device 11, the ion exchange resin loading amount, the total exchange capacity of the ion exchange resin, and the equilibrium constant of the silica adsorption reaction of the ion exchange resin are set as constants. The parameters are conditions that can be appropriately changed by the operator. In this example, as shown in FIG. 9, the silica concentration of the water supply and the date and time of replacement of the ion exchange resin are used as parameters. The variables are values that change from simulation to simulation. In this example, the silica concentration in the reactor water, the chromate ion loading, the sulfate loading, the nitrate loading, and the chloride loading of the ion exchange resin. It is the amount, the silica concentration of the outlet water of the filtration demineralizer 11, the silica adsorption amount to the ion exchange resin, and the load amount.

  In the present embodiment, the silica concentration of the reactor water, the silica concentration of the outlet water of the filtration demineralizer 11, and the silica adsorption amount of the ion exchange resin can be simulated. Therefore, it is possible to estimate the replacement time of the ion exchange resin and the number of replacements per predetermined period (in this example, one year) before the operation of the boiling water nuclear power plant. It is effective for creating. In addition, it becomes possible to estimate the point in time when the amount of silica adsorbed by the ion exchange resin reaches a peak, and by performing the ion exchange resin exchange operation at that point, silica can be efficiently removed from the reactor water.

4). Description of Effects In this embodiment, silica can be efficiently removed from the reactor water, so that the number of ion exchange resin exchanges can be reduced. Therefore, the amount of radioactive waste (ion exchange resin discarded by exchange) can be reduced.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) The present invention only needs to replace the ion exchange resin when the silica adsorption amount of the ion exchange resin reaches its peak. For example, after the ion exchange resin is replaced, the outlet water of the filtration demineralizer 11 The ion exchange resin may be replaced when the silica concentration of the water and the silica concentration of the inlet water are equal. This is because, after the exchange of the ion exchange resin, while the exchange capacity of the ion exchange resin remains, the ion exchange resin continues to adsorb the silica, so that the silica concentration in the outlet water of the filtration desalination apparatus 11 is substantially zero. Become. Then, when the exchange capacity of the ion exchange resin is lost and the ion exchange resin is no longer capable of adsorbing silica, the reactor water containing silica taken into the filtration demineralizer 11 is directly discharged out of the apparatus. It will be. Therefore, when the silica adsorption amount reaches a peak, the outlet water concentration of the filtration desalting apparatus 11 and the inlet water concentration are approximately the same.

1 ... Boiling water reactor 2 ... Turbine 3 ... Condenser 4 ... Condensate filtration device 5 ... Condensate demineralizer 6 ... Feed water heater 7 ... Atom Furnace coolant purification system 8 ... Purification pump 11 ... Filtration demineralizer 12 ... Precoat type resin tower

Claims (3)

A silica removal method for removing silica from reactor water,
Silica is removed from the reactor water by replacing the ion exchange resin provided in the filtration desalination equipment that constitutes the reactor coolant purification system that purifies the reactor water when the silica adsorption reaches its peak. Silica removal method characterized by performing.   The silica adsorption amount of the ion exchange resin is estimated based on the silica concentration of the inlet water of the filtration demineralizer and the silica concentration of the outlet water of the filtration demineralizer. Silica removal method. A method for estimating the amount of silica adsorbed on an ion exchange resin fat provided in a filtration desalination apparatus constituting a reactor coolant purification system,
Based on the amount of silica increase / decrease per unit time relative to the reactor,
Based on the equilibrium constant of the silica adsorption reaction to the ion exchange resin, the hydroxide ion concentration of the inlet water of the filtration demineralizer, the silica loading, and the remaining exchange capacity of the ion exchange resin, the filtration A second relational expression for determining the silica concentration of the outlet water of the desalinator,
Based on the silica concentration of the inlet water of the filtration desalination apparatus and the silica concentration of the outlet water of the filtration desalination apparatus, a third relational expression for determining the amount of change in the silica adsorption amount of the ion exchange resin fat is used. ,
A silica adsorption amount estimation method for estimating a silica adsorption amount of the ion-exchange resin fat.

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