KR20090022449A - Reduction method of spent resin generated from steam generator blowdown demineralizers of pwr nuclear power plants - Google Patents

Abstract

A method for reducing spent resin generated in blowdown demineralizer of steam generator of atomic power plant is provided to reduce low-level radioactive waste by increasing a life cycle of resin for a blowdown demineralizer. A blowdown demineralizer is continuously operated after saturation of a water pH adjuster. A life cycle of a resin for the blowdown demineralizer is increased. The water pH adjuster is NH4+ or ETA(Ethanol Amine). A concentration of an outlet of the blowdown demineralizer is Na+, Cl- >= 5ppb. A secondary decision reference concentration of the outlet of the blowdown demineralizer is SO4-2 >= 5ppb, is C.C(Cation Conductivity) >= 0.3us/cm, and is a reference of resin replacing.

Description

Reduction Method of Spent Resin Generated from Steam Generator Blowdown Demineralizers of PWR Nuclear Power Plants}

The present invention relates to a method for reducing waste gas from desorption generation of a steam generator of a nuclear power plant, and more specifically, to a secondary system water quality management of a nuclear power plant and a cycle of using a resin for desalting to suppress environmental emissions of radioactive materials. It has been greatly increased to reduce the low-level radioactive wastes caused by this, which greatly improves the quality and reliability of the product so that users can plant a good image.

As you may know, Units 3 and 4 in Kori Nuclear Power Plant used ammonia, a secondary corrosion inhibitor (pH regulator), to adjust the pH of the plant water using AVT (All Volatile Treatment) (hereinafter referred to as 'AVT'). Since 2013, ETA (Ethanol Amine) (hereinafter referred to as 'ETA'), which is known to perform better than ammonia, has been changed. In the steam generator, ETA has lower volatility and weak basicity than ammonia, so the ETA concentration in the steam generator should be operated higher than the ammonia treatment to maintain the proper pH range. [Table-1 below. Reference].

[Table 1] Comparison of ion load of secondary system before and after AVT replacement

As a result, the cation load of the steam generator withdrawal system demineralizer increased about 2 times and the amount of waste resin generated increased 2 times. Waste resin from steam generator withdrawal desalter is higher than natural radioactivity level because of radioactive material from primary side to secondary side and meets most of self-disposal standard of radiation. As such, most of the waste resin used in the SG withdrawal system is a waste subject to self-disposal, but when the waste resin is incinerated according to the environmental law treatment standard, the radioactive material is concentrated, so it is not easy to process the incineration ash.

The amount of steam generator blow-out desalination waste resin was about 15 tons, which is 65% of the total waste resin every year at the time of ammonia treatment, but it increased to more than 20 tons after changing the secondary corrosion inhibitor to ETA-AVT. See Table-2 below.

[Table 2] Development of Waste Resin 3,4

The problem is that the ion exchange resin of the steam generator take-off and desorption traps impurity ions such as Na and Cl in the secondary water and instead produces hydrogen ions. The latter stage decontamination coefficient (DF: inlet concentration / outlet concentration) was applied. At this time, the decontamination criteria were applied comprehensively to Na which was present as an impurity in the unused new resin. As a result, the replacement cycle of the resin was shorter than necessary, and the amount of SG take-off and debasement waste resin generated was about 6 times higher than the expected amount, which was very disadvantageous in terms of economic efficiency and operability.

Looking at the existing SG desalter resin replacement criteria of domestic nuclear power plants, the resin replacement criteria is based on the point that the ion exchange resin in the desalter can no longer remove impurities in the extraction water, so that the system water quality cannot be improved. The indication that the debase resin has lost its ability to remove has been empirically judged as Na + leakage. Replacement criteria other than Na + leakage vary from plant to plant, and there is no specific evaluation data on the resin's performance deterioration. See Table-3 below.

[Table 3] SG Extraction Desalter Replacement Standard by Domestic Nuclear Power Plant

As shown in the domestic nuclear power plant replacement standard of Table-3, in case of shear desalter in SG withdrawal desalter, there is no cation decontamination factor criterion that can determine whether saturation of cationic impurities is present, or even if the replacement criterion value is different, anion impurities In some cases, there is no concentration standard to determine whether Criteria for rear desalter replacement are more varied but less consistent than shear desalters.

As described above, the SG take-off debase waste resin has a large amount of generation, and many problems have arisen in its treatment and disposal.

The present invention has been made to solve all the problems of the prior art as described above, by improving the replacement criteria of the steam generator take-out desalination resin of Kori 3, 4 to eliminate the performance impact of the resin due to the corrosion inhibitor and saturation ETA operation The first purpose is to provide a method for determining the resin purification capacity consumed to enable this, and the second purpose is to allow the impurities to be introduced into the water quality of the secondary during the resin replacement process as the replacement cycle is greatly extended. By minimizing the method, the steam generator corrosion conditions can be improved, and the ETA unsaturated operation generated a large amount of waste resin, but by reducing the amount of waste resin to one-sixth, the ETA saturation operation was possible. The third object of the present invention for this purpose is to replace the Na decontamination coefficient (DF) ≤ 1 or the cationic conductivity (CC) applied in nuclear power plants other than the ring 3, 4 groups to be applied as a replacement standard for steam generator take-out desalination The decontamination coefficient reaches the replacement standard because ETA pushes out Na, which is an impurity in the resin, despite the ability to sufficiently remove Na, Cs, and other impurities in the system due to the effect of Na ions present as impurities in the new resin itself. The reason why there was an unreasonable point to replace the resin was to use the desalter outlet Na concentration standard, which can be judged as the point at which Na, which has a low selectivity and the highest content, leaks into the inlet of the resin tower in use. The upper limit value for maintaining the system water quality was derived and this value was set as the replacement reference value. In addition, the fourth object of the present invention is a resin ion exchange reaction experiment using Cs, which is known to have the worst removal property among radioactive materials in order to confirm the water retention of the steam generator withdrawal debasement decontamination coefficient of FSAR. In the case of Cs exchange capacity was not detected below 50%, experimentally proved that up to 70% of the ion exchange capacity satisfies the decontamination factor 10 or more. In addition, the fifth objective is that the anion resin contains impurities such as Cl-, NO3-, and SO4-2 like the cation resin, and the replacement criteria for the anion resin is the deionizer of Cl- which is the least selective among the secondary anion management items in nuclear power plants. The exit concentration was applied. In addition, the sixth objective is to determine the ion molar ratio (Molar) by determining the Cl-concentration outlet Cl- concentration as in the cation resin replacement standard, considering the impurity component included in the new resin itself as in the case of Na-ion. Ratio) was made constant. In addition, the seventh objective of the present invention can be selected as SO4-2 and cation conductivity (CC) as an indicator of performance degradation of the anion resin, but since the cation conductivity is a mixed electrical conductivity of several anions and cations, it is determined the exact performance degradation of the anion resin Although it is difficult to apply it as a standard, as a supplementary criterion to confirm the decrease of the anion resin performance, the standard of SO4-2 concentration and cationic conductivity (CC) at the desalter outlet where SG water quality is satisfied is prepared. And the eighth purpose is to charge the demineralizer by mixing a cation resin and an anionic resin, the maximum usable time of the demineralizer is when the ion exchange capacity of the two resins are lowered. If the cation resin is capable of removing impurities, the anion exchange resin should be replaced, that is, discarded, even if it has sufficient impurities. Therefore, in order to maximize the operation period of the demineralizer and to minimize the waste resin generated in a situation where the volume capacity in the demineralizer is limited, the time points for demineralization of the cationic resin and the anionic resin should be equalized. To this end, the ratio of cation and anion exchange resin to be charged in the demineralizer is determined by taking into account the concentration of impurities in the system water removed from the demineralizer. Provided are methods for reducing base generation waste balance.

In order to achieve the above object, the present invention increases the resin service life by operating the water quality pH regulator until after saturation in operating the effluent demineralizer of the nuclear power plant steam generator. Provides a way to reduce

As described in detail above, the present invention improves the replacement criteria of the steam generator withdrawal and desalination resins of Kori 3 and 4 to eliminate the performance effects of resins due to corrosion inhibitors, and to determine the consumed resin purification ability to enable ETA saturation operation. To provide.

In addition, the present invention can improve the corrosion condition of the steam generator by minimizing the influx of impurities in the chemicals during the resin replacement process into the water quality of the secondary side as the replacement cycle is greatly extended, and ETA unsaturated operation Although the waste resin was generated, the ETA saturation operation was enabled, which drastically reduced the amount of waste resin produced to one-sixth of the original amount.

The present invention also applies the replacement criteria based on the Na decontamination coefficient (DF) ≤ 1 or the cationic conductivity (CC) applied in nuclear power plants other than the 3, 4 rings, as impurities in the new resin itself. Despite the ability to sufficiently remove Na, Cs, and other impurities in the system due to the effect of Na ions, the decontamination coefficient reaches the replacement criteria because ETA pushes out Na, which is an impurity in the resin. Maintaining the system water quality properly is based on the desalter outlet Na concentration standard, which can be judged as the point at which Na, which has a low selectivity and the highest content among the impurities flowing into the inlet of the resin tower in use, is unreasonable. The upper limit value was derived and this value was set as the replacement reference value.

In addition, the present invention is a Cs exchange capacity in a resin ion exchange reaction experiment using Cs, which is known to have the worst removal property among radioactive materials in order to confirm the water retention of the steam generator withdrawal and debasement decontamination coefficients of the Kori Nuclear Power No. 3 and 4 Safety Analysis Report (FSAR). It was not detected below 50% and experimentally proved that up to 70% of the ion exchange capacity satisfies the decontamination factor of 10 or more.

In addition, the present invention includes impurities such as Cl-, NO3- and SO4-2 in the anion resin as well as the cationic resin. It was applied at a concentration.

In addition, in the present invention, the Cl-decontamination coefficient (DF) is also determined by considering the impurity components included in the new resin itself as in the case of Na ions. ) To be constant.

In addition to the present invention, SO4-2 and cationic conductivity (CC) may be selected as an indicator of deterioration of the anion resin, but since the cationic conductivity is a mixed electrical conductivity of various anions and cations, the present invention may be applied as a criterion for deterioration of anion resin. Although it is difficult to determine the anion resin performance, the standard of SO4-2 concentration and cationic conductivity (CC) at the desalter outlet where SG water quality is satisfied is established as an auxiliary decision criterion for confirming the decrease of anion resin performance.

In addition, the present invention is filled with a deionizer mixed with a cationic resin and an anionic resin, the maximum usable time of the demineralizer is the time when the ion exchange capacity of the two resins are low. If the cation resin is capable of removing impurities, the anion exchange resin should be replaced, that is, discarded, even if it has sufficient impurities. Therefore, in order to maximize the operation period of the demineralizer and to minimize the waste resin generated in a situation where the volume capacity in the demineralizer is limited, the time points for demineralization of the cationic resin and the anionic resin should be equalized. To this end, it is a very useful invention in which the ratio of the cation and anion exchange resin to be charged in the demineralizer is changed in the steam generator take-out demineralizer resin mixing ratio of Kori Nuclear Power Nos. 3 and 4 in consideration of the impurity concentration in the plant water removed from the demineralizer.

Hereinafter, described in detail with reference to the accompanying drawings a preferred embodiment of the present invention for achieving this effect are as follows.

1 is a model diagram of an ion exchange resin saturation experimental apparatus to support the theory of the present invention.

Figure 2 is a photograph of the actual experimental apparatus installation used in the present invention.

Figure 3 is a Cs selectivity seal in the resin saturated with the steam generator extraction system of the present invention

        Test result graph.

Figure 4 is ETA +, Na +, NH ₄ +, Cs + ion in the hydrogen ion (H +) saturated resin of the present invention

        Selectivity experiment results graph.

5 is a result of the selectivity experiment of the Cs ion in the ETA, Na, NH ₄ saturated resin of the present invention

        Laugh.

Figure 6 is a graph showing the ETA-Na breakthrough curve of the cationic resin of the present invention.

Method for reducing the extraction desalination generating waste resin of the steam generator of the nuclear power plant applied to the present invention is configured as shown in Figs.

In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

The following terms are terms set in consideration of functions in the present invention, which may vary depending on the intention or custom of the producer, and their definitions should be made based on the contents throughout the specification.

Hereinafter, the results of the resin exchange experiment of each ion, which is the basis of the resin replacement criterion that does not consider the effects of ammonia and ETA, which are pH adjusting agents of the leachate demineralizer, will be described in detail as follows.

In order to confirm the operability and the resin characteristics after the point of steam generator withdrawal from the nuclear power plant saturation with ETA, the experiment was performed as shown in FIGS. 1 and 2.

1) Cs + collection experiment of resin saturated with secondary system water

2) High concentration simulation sample exchange test [Refer to Table 4]

3) Cs + exchange reaction of saturated ETA resin

Experimental method was used to test the performance of the ion exchange resin KSM 0119 (1993), the experimental conditions were adjusted as follows.

1) Ion exchange resin amount: 40ml (H + type cation exchange resin, manufacturer: Purolite)

2) Sample volume: 60 liters

3) Mixed solution: ETA + 122.18ppm, Na + 46ppm, Cs + 265.8ppm, NH3 34ppm

4) Flow rate: 50ml / min

5) Resin layer column: 20φ glass tube specified in KSM

[Table 4] Ion Concentration Conditions in High Concentration Experiments

3 is a test result for qualitatively confirming the Na + and Cs + trapping ability of the resin saturated with the system water as saturated with ETA 3,400ppb, ammonia 230ppb, Na + 0.3ppb of the secondary system of Kori Nuclear Power Plant No. 3 The simulated sample (adding 2 ppm of Cs + to the system water) was poured into the resin. The results showed that Cs + did not leak at all until 50 liters of the simulated solution had been consumed. The decontamination coefficient of Cs + was very high.The Na concentration at the outlet of the experimental column increased slowly in proportion to the increase of ETA concentration and the concentration was 0.3. The decontamination coefficient was about 0.1 based on the increase from ppb to 3 ppb.

Based on this experiment, the higher Na + concentration at the outlet than the Na + concentration inflowed into the experimental column did not indicate that the inflow of Na + exited the column, but the Na + present as impurities in the resin itself.

Figure 4 shows the results of the exchange experiment of the high concentration simulated impurity solution, in this experiment was intended to shorten the experiment time to obtain the results by reducing the experimental resin capacity and increasing the virtual system ion concentration. To this end, the chemical capacity added to the secondary system was 30 times higher than the resin capacity (30 ml), which is equivalent to about 1 / 0,000 of 2.5 m3, which is the charge of the steam generator withdrawal and desulfation cation resin of nuclear power plants. The experiment was performed.

First, the selectivity of the total ions for the resin was shown to be the largest Cs as follows [Fig. 4 and 5].

∴ Ion selectivity: Cs +> Na +> NH4 +> ETA +> H +

The most selective Cs in the resin exchange reaction of ions showed the sigmoid, the resin breakthrough curve of a single species, as if not affected by the coexisting ETA +, NH4 +, and Na +. This is because Cs + has the strongest ion selectivity whether the resin is Na + or saturated with ETA +. When the simulated concentration of Cs + was tested at 1 meq / ℓ lower than 2 meq / ℓ, the saturation period was doubled and the Cs + breakthrough site was doubled.

The breakthrough curve of the Na breakthrough curve shows that Na + is more selective than ETA + and ammonia, causing breakthrough later than ETA or ammonia. If Cs + was not used in the experiment, the breakthrough curve of Na would appear as the breakthrough curve of Cs, but the breakthrough of Na appeared earlier than the Cs + breakthrough because of Cs + injected into the experimental solution to confirm the conservativeness of the decontamination coefficient for radioactive material. , Na + breakthrough peaked at 2.4 meq / l higher than the experimental solution concentration of 2.0 meq / l due to Na + pushed away by Cs +, and then returned to the inlet solution concentration. In addition, the location of the Na + peak point coincides with a Cs + concentration of 1.0 meq / l (50% of the inlet concentration), indicating that Na is being pushed out by Cs +.

This phenomenon shows that when the power plant steam generator breaks down and leaks, the contaminated steam generator system that passed through the desalting plant has the ability to remove radioactive ions, such as H + resin, without depending on the desalting service life. . In other words, the experimental results show that the steam generator withdrawal water can capture the radioactive material determined by the debase capacity for the radioactive material regardless of the H + type, the ETA + type or the Na + type. In addition, the Na + concentration graph in the beginning of the breakthrough is slightly convex, which is the result of the amount of Na + contaminated with resin eluted by ETA and NH4 + combined with the Na + component in the sample.

ETA + breakthrough curves showed slightly weaker resin selectivity than ammonia. Initially, all four chemical concentrations were the same at 2.0 meq / l, but the final concentrations of ETA and ammonia were less than 2.0 meq / l, which was volatile ammonia and ETA after 10 hours of experimentation. Seems to have decreased slightly. In addition, in the breakthrough curve of each chemical species, the arrival time of 50% of the inlet concentration was (ETA + + NH4 +): Na +: Cs + = (1 + 1) T: 3T: 4T. This phenomenon is caused by large ion selectivity values between ETA + / NH4 +, Na + and Cs +. When Na + or Cs + enters the resin column, if Na + or Cs + has low selectivity ions such as ETA or ammonia, It takes the place and instead pushes ammonia or ETA, which is a low selectivity material.

In nuclear power plants injected with ETA, NH4 + is injected with NH4 + mixed with ETA, or is a decomposition product of hydrazine injected for oxygen removal. In the NH4 + breakthrough curve, NH4 + leaks slightly later than ETA, which leaks only slightly later, since the exchange reaction with the resin is more active than ETA. However, the peak breakthrough time, which is the total breakthrough curve, is faster at NH4 + because ETA is more strongly bound to Na + or Cs + than NH4 +. That is, the exchange reaction between the two ions is determined by the reaction rate and chemical stability.

As described above, the experimental result that the ETA saturation operation is valid through the selectivity and breakthrough curve experiments for the four ions that can be considered in the secondary system of nuclear power plants can be obtained.

5 is an experiment for confirming the Cs + trapping ability of the resin saturated with ETA +, NH4 + and Na + and Na +, and the new resin is sufficiently saturated with 2.0 meq / L of ETA +, NH4 + and Na + solution in advance, and further Cs + 2 meq / L was dissolved in the experimental solution to obtain a breakthrough curve.

The Cs breakthrough curve was S-shaped like the exchange of a new resin. However, the breakthrough curve was slightly lowered due to ETA +, NH4 +, and Na having higher selectivity than the H-ion saturated resin, but the decontamination coefficient of Cs was about 10, similar to that of the H-type resin. This shows that the effluent demineralizer is saturated with Na and has the ability to remove Cs sufficiently even at the point of replacement.

The Na exchange reaction was found to be less saturated than the intention to use a resin sufficiently saturated with ETA, NH4 + and Na + at the beginning of the experiment as shown in the saturation curve. However, as the experiment progressed, the concentration of effluent continued to increase due to Na + pushed into Na + and Cs +, and peaked at the point when ETA and NH4 + concentration reached equilibrium. This is because the concentration change of Cs appears before the Cs + concentration of 1.0 meq / L, which is the largest position, because Na + appears at the outlet of the desalination after exchanging with ETA + / NH4 +. Based on these phenomena, the NH4 + concentration was higher than the ETA concentration in the ETA + and NH4 + exchange experiments. The exchange selectivity with the resin was NH4 + ≥ ETA. However, given that the species to be removed are Na + and Cs +, ETA or NH4 + does not have to be removed from the resin.

The configuration of the above-described technology of the present invention is described in more detail as follows.

First, the present invention is to operate the water quality pH regulator until after saturation in operating the extraction water desalination unit of the steam generator of the nuclear power plant to increase the service life of the resin. In this case, the water pH adjusting agent is characterized in that NH ₄ ⁺ or ETA is used.

In other words, the secondary system water quality management of Kori Units 3 and 4 has been converted from Ammonia-AVT to ETA-AVT based on domestic and international studies since 2002. The water quality management data before and after conversion are shown in Table 6 below. Changes in the water quality category showed that the pH in the steam generator increased from 9.2 to 9.6, while the ammonia concentration was lowered to 1/3, and the ETA was maintained at about 3,500 ppb. Most other impurity concentrations are similar before and after changes in water quality management.

[Table 5] Secondary Water Quality Standards of Kori Unit 4 and Water Quality Management Data Before and After ETA Treatment

For the ETA saturation operation of Kori Units 3 and 4, it is necessary to evaluate the water quality of the major water quality factors, and the evaluation results meet the “SG Steam side and Feedwater AVT Chemistry Guidelines” in Table 6 below. At the same time, it should be possible to achieve the purpose that water quality can reasonably achieve. To this end, the review contents and results of each water quality item are as follows.

Table 6SG Steam side and Feedwater AVT Chemistry Guidelines

1) pH (hydrogen ion concentration)

The piping and tank materials of the secondary nuclear power plant are made of carbon steel and stainless steel, and the minimum corrosion rate range of iron alloy is pH 9.6 or more. Therefore, in the absence of copper alloys such as rings 3 and 4, maintaining the pH range of the entire secondary system above pH 9.6 can minimize general corrosion and flow corrosion of the material. If the steam generator blow-out desalinater is operated with saturated ETA, the system pH is higher than if it is removed, which is beneficial to the system. Especially in the case of the pipe after the desalinater, the pH was near neutral because the ETA was removed before. When the ETA is passed through to increase the pH has the effect of improving the pH weak part of the desorption end.

In other words, ETA saturation operation keeps the pH of all secondary systems in a region where the corrosion rate is minimized, so saturation operation is better for corrosion prevention operation of system materials.

2) Cation Conductivity

The cation conductivity can indirectly estimate the impurity concentrations of anions such as Cl-, F-, HSiO2-, SO4-2, and organic acids.In particular, the increase in Cl-concentration in case of seawater leakage in the condenser heat exchanger ( It is a quick way to detect spikes.

The cationic conductivity (C.C) of ring 4 is about 0.1 μmhos / cm, which is 1/20 of the secondary water quality standard (2.0 μmhos / cm), indicating that anion impurities are kept low in the steam generator system. In ETA saturation operation, ETA leaks from the demineralizer and increases in concentration, but ETA, which is a cation, does not affect the water quality of cation conductivity. However, the concentration of organic acid (formic acid, glycolic acid), which is a by-product of ETA pyrolysis, increased slightly, resulting in an increase in the cationic conductivity (C.C) value. The cationic conductivity (C.C) of Ring 4 increased slightly from 0.09 to 0.1, but it was kept below the water quality standard, so there was no effect on the overall water quality.

3) Total Ion Conductivity

The total ion conductivity is used to determine the total ion content using the conductivity of cations and anions in water, and the total conductivity limit is given as the minimum value because the pH regulator should be kept above a certain concentration in the secondary system water. In other words, the total conductivity of Kori 3, 4 water supply was determined to be 2.5 μmohs / cm or more, which is to determine whether ETA is properly injected. If the effluent demineralizer is operated with saturated ETA, the concentration is maintained even without additional injection of ETA, which is advantageous in terms of operation and water quality management.

4) Na ions

Na on the secondary side of the nuclear power plant is concentrated in the internal space of the steam generator to create a strong alkali (pH 10 or higher) environment. According to the corrosion test results of the steam generator tube, NaOH, which is a strong alkaline component at high temperature, is inter-granular attack. Cause corrosion. IGA corrosion conditions require a pH higher than 10. The minimum Na concentration of this condition is about 2,300 ppb, depending on the relationship between NaOH and pH in Table-7. However, Kori 3, 4 SG water quality standard is less than 20ppb, and according to Kori 4, SG leachate operation results, Na concentration is about 0.2ppb, about 1/100 of the limit. If it is concentrated to 110,000 times (2300ppb ÷ 0.2ppb) in the SG gap, it does not exceed pH 10. Therefore, it is judged that there is no possibility of alkali corrosion. In the gap, Cl-, SO4-2, organic acid, etc. coexist to neutralize the alkali effect of Na + (see Table -8). Saturation of ETA slightly increases the concentration of Na + in the outlet side of the SG take-off demineralizer due to Na + contaminated with resin. The leaked Na is combined with the condenser water of the condenser to be diluted and then removed when passing through the CPP demineralizer. If some Na is bypassed by partial operation of CPP, it will enter the steam generator but will eventually be captured again in the blowout debase.

[Table 7] Relationship between NaOH concentration and pH

[Table 8] Relationship between Na and Cl concentrations and pH

5) Hydrochloric acid ion (Cl-)

Cl-, like Na +, has a latent concentration phenomenon in the crevices of the steam generator and, according to experiments, can cause pitting of Alloy 600, an SG tubular, under acidic and oxidative conditions. It is known that there is no viscosity problem due to Cl- at the reducing condition or the pH of 8.5 or higher which is the secondary water quality condition of the nuclear power plant. In ring 3 and 4 water quality, reducing atmosphere is controlled by hydrazine, and pH 8.5 maintenance is controlled by ETA and some ammonia. In other words, the hydrochemical limit in nuclear power plants is about 20 ppb and the actual operating level is 0.3 ppb, so there is no point corrosion caused by Cl-. That is, even if the effluent desalter is operated in saturated ETA, there is no effect on Cl concentration of the system, and the ETA saturation operation reduces the amount of ETA chemicals injected into the system, and Cl, which is an impurity of the chemical, can suppress the inflow into the system. That is, the ETA saturation operation can further reduce the Cl- concentration of the system water.

6) sulfate ion

SO4-2 is latent in crevices in the steam generator like Cl- and accelerates local corrosion of Alloy 600 above 1,000 ppb. As a result, the nuclear hydration limit is 20 ppb, which is 1/50 of 1,000 ppb, and actual operating performance is 0.3 ppb. Therefore, since the water quality of SO4-2 is operated within the limits, there is no risk of corrosion, and even if the desalting unit is operated after saturation with ETA, the amount of ETA chemical introduced into the system is reduced, thereby preventing SO4-2 inflow of chemical impurities. In other words, the desalting ETA saturation operation contributes to the reduction of SO4-2 concentration in the system water quality, which is positive in terms of system water quality improvement.

7) Dissolved Oxygen

Oxygen is strictly controlled because it reacts with metal to form a stable oxide, which impairs the properties of the original material. However, in terms of water quality management, dissolved oxygen is not related to the ion exchange reaction of the demineralizer and thus has no effect due to the ETA saturation operation. On the contrary, air is introduced into the system when the demineralizer resin is replaced. The longer the replacement cycle, the less chance there is for inflow.

As a result of reviewing the seven major water quality items for the secondary system water quality of Kori Units 3 and 4, the ETA saturation operation of the blow-out desalter prevents the inflow of impurities contained in the new ETA and lowers the concentration of impurities in the system. In addition, it was found to be positive for the system operation by reducing the amount of ETA used.

In addition, in order to confirm the water retention of the steam generator withdrawal and debasement decontamination coefficient of the Kori Nuclear Power Plant No. 3 and 4 Safety Analysis Report (FSAR), the Cs exchange capacity was less than 50% in the resin ion exchange reaction experiment using Cs, which is known to have the worst removal property among radioactive materials. Was not detected, and up to 70% of the ion exchange capacity satisfies the decontamination factor of 10 or more.

In addition, the steam generator withdrawal and desalination removal capacity has 25 times the removal capacity of the total amount of soluble cations leaking to the fuel, assuming 1% nuclear fuel damage, which is a design criterion.In this case, the decontamination coefficient of FSAR is very large. The condition 100 was fully satisfied.

Therefore, in the conventional operation method, ETA and ammonia were injected into the steam generator by using a chemical injection pump in the secondary system feed water to adjust the pH of the steam generator and the secondary system water, and some ETA and ammonia were discharged through the lower part of the steam generator. The discharged ETA was collected in the desalter. When the debase is saturated with the collected ETA or ammonia, it has been wrongly determined that Na, Fe, or Cs ions, etc., which are impurities in the plant water, cannot be removed anymore, but have been replaced with ETA or ammonia injected through the chemical injection system. Saturated demineralizers were operated continuously until they were saturated with impurities such as Na and Fe which are actual impurities in the plant water.

In another aspect, the present invention provides a method for reducing the desalination generating waste resin of the steam generator of the nuclear power plant, characterized in that the concentration of the demineralizer outlet using the water quality pH regulator is Na +, Cl-≥ 5 ppb.

In the present invention, the secondary determination reference concentration of the desalter outlet using the water quality pH adjusting agent is SO ₄ ^-2 ≥ 5 ppb, and is based on the resin replacement judgment standard. It will provide a way to reduce the risk.

In addition, in the present invention, the auxiliary determination standard concentration of the desalter outlet using the water quality pH adjusting agent is based on the resin replacement judgment standard based on the cation conductivity (CC) ≥ 0.3㎲ / cm. Provided are methods for reducing base generation waste balance.

This will be described in more detail as follows.

In other words, the existing information related to the performance of the secondary system demineralization of nuclear power plants has been known that the Na + selectivity is higher than that of hydrogen ions (H +) but lower than that of ammonia and ETA. When saturated with ETA, as shown in a report published by the US Electric Power Research Institute (EPRI) [TR-107199], Na has a lower selectivity to the resin than ETA, pushed out by ETA, and shows a peak at breakthrough (Fig. 6). Since then, the Na + trapping capacity of the resin is lost, and it is understood that Na entering the demineralizer inlet immediately exits.

It is an object of the present invention to provide a method for determining the consumed resin purifying capacity so that the ETA saturation operation can be performed without removing the performance influence of the resin due to the corrosion inhibitor as a replacement standard of the steam generator take-out demineralized resin.

Existing criteria: SG withdrawal demineralization inlet and outlet Na DF (decontamination factor) ≤ 1

Criteria for improvement: SG withdrawal debase exit Na +, Cl- ≥ 5 ppb

(Secondary ^{_{criteria: SO 4 - 2 ≥ 5 ppb}} , CC ≥ 0.3㎲ / ㎝)

In order to achieve the above object, the present invention provides a replacement standard based on a cationic conductivity (CC) applied to a nuclear power plant other than Na decontamination coefficient (DF) ≤ 1 or rings 3 and 4, which is applied as a replacement standard for steam generator take-out desalination. Due to the effects of Na ions present as impurities in the new resin itself, there was an unreasonable need to replace the steam generator even if the water quality is good.

As a solution to this problem, the desalter outlet Na concentration, which is a criterion that can be judged as the point at which Na, which has a low selectivity and the highest content among the impurities flowing into the inlet of the resin tower, is used, is based on 5 ppb or more. [Outlet Na concentration: ≥ 5 ppb] was applied as a replacement standard for the cation resin.

The replacement criteria for SG take-off demineralization resins of domestic nuclear power plants is defined as the condition that demineralization resins cannot remove harmful impurities in the system water. Since the SG extraction debase resin is a mixed phase, it is composed of a cation and an anion resin.

○ Cationic Resin Replacement Criteria

Since the most difficult ions of secondary system impurities to be removed from the cationic resin are Na, the replacement criteria by Na encompasses the replacement criteria due to deterioration of the cation resin. The reason for setting replacement criteria by Na is as follows. In the case of increasing Na concentration in the system, the increase in Na in SG water, in particular, may lead to seawater leakage, impurities from chemicals such as ETA, leaks from contaminated resins with high Na content, leaks of hidden SG tubules, and resins. The decontamination coefficient of the membrane (mainly channeling phenomenon) may be the cause. For this reason, the Na decontamination coefficient of SG take-off debasement has been used as a criterion for judging resin performance. Since the leakage of steam generator withdrawal was due to contaminated Na, the intrinsic removal capacity of the debase resin was not lost. Improper replacement means that the replaced new resin will consume ETA chemicals, increasing the chemical injection volume and further introducing impurities into the steam generator.

The cationic resin, which is newly discovered in the process of the present invention, captures Na better than ETA, and when the cationic resin is saturated with ETA injected to adjust pH in the plant water, the leakage of Na is introduced into the demineralization inlet, which is an impurity contained in the plant water. Since the cationic impurities push out ETA collected in the resin or Na previously existed in the resin, not Na introduced, the debase resin replacement criteria should be set in consideration of this phenomenon. In principle, the following points were established:

A) ETA, a pH regulator in the secondary system water, is not considered to be removed from the demineralizer. It circulates with the tree.

B) Na leakage in the new resin is not related to the saturation time of the resin. Therefore, the effect of leakage is excluded from the desalter replacement criteria, but should be considered in terms of the Na concentration control of the tree.

C) Impurity removal should be an active process. Even if the influx of impurities in the system increases suddenly due to external inflow, the impurities naturally decrease with the decontamination factor in the desalting machine in proportion to the flow rate of the tree water over time. The selectivity of various ions has been demonstrated in the experiment. The decontamination coefficient of Na is above 10 but is evaluated conservatively as 10.

Taking into account the above principles, there are water quality management standards set for each of the stop, start and output stages during the operation of the nuclear power plant. [Cleaning of impurities during start-up, prevention of SG inflow of leaked seawater, and primary coolant radioactive material when SG customs are broken. Capabilities such as removal should be secured.

[Table 9] Steam Generator Water Quality Standards by Nuclear Power Plant Output Status

Based on the above conditions, the water quality standard of the cationic resin of the SG withdrawal demineralizer was determined as follows.

A) Concentration considering the decontamination factor of Na is 10ppb or less under conditions of Na concentration of 100ppb or less, which is the SG withdrawal water quality standard at the highest start or stop, and Na 100ppb or less, which is the two-step concentration limit for normal operation. Satisfy

B) At the output condition of 30% or more, the desalter outlet Na concentration limit is 2 ppb, which satisfies the decontamination factor 10 of 20 ppb, the steam generator water quality limit, and 3 ppb, which is the concentration value due to Na leakage as impurities during saturation of ETA. Satisfies Na 5 ppb or less

[Na maximum leakage concentration 3ppb Basis: refer to EPRI report (NP-7380 Figure B-3)]

Among the above two methods, the strict water quality standard is less than 5 ppb, so the improvement of cation resin replacement was selected as the exit Na concentration of SG take-off demineralizer above 5 ppb.

I. Anion Resin Replacement Criteria

Like the cationic resin, the anion resin contains impurities such as Cl-, NO _3- , and SO ₄ -2, and the replacement criteria for the anion resin also monitors the least selective items among the secondary anion management items in the nuclear power plant. Is universally valid.

The selectivity of ions for anion resins is as follows according to the data of several experiments.

Anion-selective sequence: OH- <F- <Cl- <Br- <NO3- <I- <SO 4 -2

In the anion resin, the main impurities such as Cl-, NO ₃ -and SO ₄ -2 are included as the cation resin, so the replacement criteria also indicate the de-mineralization outlet concentration of Cl- which has the lowest selectivity in the secondary control items of nuclear power plants. It is reasonable to select. The decontamination coefficient criterion can be measured to have a low decontamination coefficient due to contaminated Cl resin such as Na of the cationic resin. The replacement criterion is that the pH of the phylogenetic tree caused by the two ions, as shown in relation to the Na and Cl concentrations in Table 8, is that the outlet concentration of Cl- is 5 ppb or more so that the abundance of the phylogenetic tree is proportional to the cation Na. Because change is the least.

In addition, SO4-2, which is mostly detected in the steam generator system of nuclear power plants, is more removed than anion resin due to its selectivity compared to other anions, but sometimes the debris of the cation resin is decomposed after being introduced into the steam generator. Therefore, the determination of sulfate ion as a replacement standard for demineralizer is less valid than that of Cl- ion.

However, in most nuclear power plants, SO4 concentration is managed in consideration of water quality degradation caused by resin inflow, so it is set as a desaltering decontamination standard separately. Nevertheless, if it was set as a resin replacement criterion, the SO4-2 concentration at the outlet of the blow-out debasement was set to 5 ppb or more like other ion concentration limits. The reason for this value is that the system quality control standard is the same as Na and Cl.

Another water quality factor that can monitor anion concentrations is cation conductivity (CC). CC shows the change in the total concentration of anion impurities such as Cl-, F-, HSiO _3- , SO ₄ -2 and organic acids. Previously, the cation conductivity value was a good indicator for monitoring water impurities.

However, in recent years, it is reasonable to directly determine the performance of anion resin by measuring the concentration before and after the debasement to accurately analyze trace impurities, so CC can be used to determine the trend of water quality change for online monitoring. It is reasonable to refer to the criteria only. If the SG effluent is selected as a resin replacement criterion, a value of 0.3 uS / cm or more, which is the water quality limit of the effluent system, is valid. Based on this value, various impurities that may be present in the secondary system as shown in Table Ⅵ-2] - is a _{(Cl-, HSiO 3, SO 4} -2, an organic acid), the concentration of the conductivity calculated theoretically when the order of 5ppb.

[Table 10] Cationic Conductivity Calculation Table for Impurity Ion Concentration

In another aspect, the present invention is characterized in that the water mixing ratio of the demineralizer using the water pH adjuster to adjust the cation resin volume to anion resin volume 1 to 1 to increase the resin service period of the nuclear power plant steam generator take-out debase It provides a method for reducing the generated waste balance.

The present invention is characterized in that the water mixing ratio of the demineralizer using the water pH adjuster is adjusted to cation resin volume to anion resin volume of 3 to 1 to increase the resin service period. It provides a method for reducing the generated waste balance.

This will be described in more detail as follows.

That is, the deionizer ion exchange resin is mixed with a resin for removing cations and a resin for removing anions. The period of use is inversely proportional to the ion concentration of the plant water passing through it. If the ratio of cations and anions in the plant water differs, the ion exchange capacity is determined by the capacity of the resin that is saturated first, that is, the ion concentration contained in the plant water. So, by filling the resin according to the ratio of cation concentration and anion concentration in the system water, the saturation point is reached almost simultaneously to maximize the utilization rate.

Previously, the resin blending ratio of the extraction water demineralizer was regarded as the cation loading of ETA and ammonia as pH adjusters. When the ETA and ammonia were not regarded as ionic loads, a new mixing ratio had to be set. For this purpose, the mixing ratio of ion exchange resin was calculated based on the data of domestic power plant operation. In addition, the effects of organic acid, which is a degradation product, are considered in the ETA environment.

Since the plant complies with the water quality standard, it operates within the standard value, so the relevant standard value or limit value is used. In the absence of a reference value, it is assumed to be a conservative maximum or five times more conservative than the measured results. (For example, the concentration of organic acid is approximately five times that of the research report “Applied to Ring 1 ETA.”).

The calculations show that the total cation load is about 115 x 10 ^-9 eq / l, considering the ETA load, and about 3.78x 10 ^-9 eq / l when not considered.

The anion load is 3.67 x 10 ^-9 eq / l regardless of the intensity ETA. When the concentration of the organic acid is conservatively 5 times, it is about 7.80 × 10 ⁻⁹ eq / L.

Under these conditions, the required ratio of cationic resin and anionic resin is 30: 1 when considering ETA load, and about 1: 2 when ETA is not considered.

Computationally, if ETA is not considered, anion resin is needed 2 ~ 3 times more than cation resin.

The ratio of resin mixture by ionic strength ignoring ETA is as follows.

Cationic resin: Anionic resin = 1: 2

However, in actual operating environments, the ionic strength of cationic materials should be considered somewhat conservatively. This is because ETA and ammonia have stronger ionic strength and resin selectivity than H ions of pure water, and have elution to push out ions trapped in the cationic resin even though the resin selectivity is weaker than Na or metallic ions.

And, unlike other impurities, the organic acid as an anion is highly volatile, and has a higher rate of removal from the plural demineralizer (CPP) through a condenser together with steam. Considering this phenomenon, the actual cation resin ratio should be higher than the calculated value. In consideration of the elution of ETA, when the elution factor is 2 to 6 times, on the contrary, the cation resin is 1 to 3 times higher than the anion resin. Therefore, the resin blending ratio of the SG take-off demineralizer is presented as the optimum blending ratio of cation resin to anion resin = 1 to 3: 1.

[Table 11] Ion Load on Plant Water

Table 12 Ion Exchange Resin Requirement for System Water Ion Load

○ Cation exchange resin specification

-Grade: AMBERLITE IRN-77 equivalent, Ionic Form: H +,

Total exchange capacity: 1.8 eq / ℓ

○ anion specifications

-Grade: AMBERLITE IRN-78 equivalent, Ionic Form: OH,

Total exchange capacity: 1.2 eq / ℓ

The optimum resin mixing ratio of the steam generator blow-out debaseper of nuclear power plant is presented as follows.

Existing Mixing Ratio: Positive / Anionic Resin Mixing Ratio 10: 1

Improvement Mixing Ratio: Positive / Anionic Resin Mixing Ratio 1-3: 1

On the other hand, the present invention may be variously modified and may take various forms in applying the above configuration.

And it is to be understood that the invention is not limited to the specific forms referred to in the above description, but rather includes all modifications, equivalents and substitutions within the spirit and scope of the invention as defined by the appended claims. It should be understood that.

The technical idea of the method for reducing the extraction and desalination generation waste balance of the steam generator of the nuclear power plant of the present invention can actually repeat the same result, and in particular, by implementing the present invention, it can contribute to industrial development by promoting technological development. It is well worth protecting.

Claims (7)

A method for reducing the blow-out desalination generation wastewater of a nuclear power plant steam generator, characterized by increasing the service life of the nuclear power plant steam generator by operating the water quality pH regulator until after saturation. According to claim 1, The water quality pH adjusting agent is NH ₄ ⁺ or ETA, characterized in that the method for reducing the outgoing debase generation waste resin of the steam generator steam generator. The method according to claim 1 or 2, The concentration of the demineralizer outlet using the water quality pH adjusting agent is Na +, Cl- ≥ 5 ppb, characterized in that the method for reducing the extraction desalination generating waste resin of the steam generator steam generator. The method according to claim 1 or 2, Auxiliary determination standard concentration of the demineralizer outlet using the water pH adjuster is SO ₄ ^-2 ≥ 5 ppb, which is based on the resin replacement judgment criteria. Way. The method according to claim 1 or 2, Auxiliary determination reference concentration of the demineralizer outlet using the water quality pH adjusting agent is cation conductivity (CC) ≥ 0.3 kW / cm, and is based on the resin replacement judgment criteria. Method for abatement. The method according to claim 1 or 2, Reducing deodorization generation waste resin of the nuclear power plant steam generator characterized in that the resin usage period is increased by adjusting the water mixing ratio of the demineralizer using the water quality pH adjusting agent to 1 to 1 volume of cation resin to volume of anion resin. Way for you. The method according to claim 1 or 2, Reducing deodorization generation waste resin of the nuclear power plant steam generator characterized in that the resin usage period is increased by adjusting the water mixing ratio of the demineralizer using the water quality pH adjusting agent to 3 to 1 volume of cation resin to volume of anion resin. Way for you.