JPS6235079B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for recovering boric acid from radioactive waste.

Conventionally, a system has been proposed that uses a reverse osmosis membrane to recover boric acid from waste liquid discharged from nuclear power plants [Patent Application No. 80468/1983
No. 12559) - This publication states that the product stream of a reverse osmosis membrane module (the flow that permeates through the membrane) is approximately 90% of the volume of the effluent fed to the module and approximately 90% of the volume of the boric acid in the effluent. This system has advantages such as a reduction in the number of drums of waste and a reduction in the capacity of the solidification equipment. However, on the other hand, reverse osmosis equipment requires attached tanks, pumps, heat exchangers, chiller cooling equipment, etc., and also requires demineralization towers and membrane cleaning equipment as auxiliary processing, making it a complex equipment. It cannot be denied that there were drawbacks such as increased equipment costs, increased installation space, and operational complexity.

Therefore, the present inventor has conducted research to provide a method that can obtain the same effect as the reverse osmosis described above using simpler equipment, but the anion exchange resin adsorbs boric acid depending on the temperature of the inflow liquid. The present invention was achieved by paying attention to the fact that boric acid has the property of desorption and desorption, and succeeded in utilizing this for the recovery of boric acid from radioactive waste liquid.

That is, the present invention provides (1) that the anion exchange resin adsorbs only anionic substances in the waste liquid, such as borate ions, chloride ions, and iodine ions, while allowing the others to pass through; The strength of adsorption is borate ion < chloride ion < iodine ion, with boric acid being the weakest, and the temperature dependence of adsorption and desorption of boric acid is more pronounced than other ions.
Boric acid can be desorbed with hot water at a relatively low temperature (about 60 to 70 degrees Celsius). (Chloride ions and iodine ions have extremely high adsorption strength to ion exchange resins, and their temperature dependence is also very high. 60 because there is no
It takes advantage of two properties of anion exchange resins: they are not desorbed in hot water of ~70°C.
Radioactive waste liquid discharged from nuclear power plants
The anions in the waste liquid are brought into contact with an anion exchange resin at a low temperature of about 10°C, and the anions in the waste liquid are adsorbed by the resin. Then, pure water heated to about 60 to 70°C is passed through the resin that has adsorbed the anions, and only boric acid is added. The present invention relates to a method and apparatus for recovering boric acid from waste liquid by repeating the desorption operation.

An example of the boron adsorption characteristics of the above anion exchange resin is schematically shown in FIG. In the figure, the horizontal axis represents the amount of boron adsorbed to the resin, and the vertical axis represents the boron concentration in the effluent. The point at which the supply of waste liquid is started is point A, and the boron concentration in the effluent at this time is sufficiently low. As the adsorption of boron to the resin progresses, the boron concentration in the effluent gradually increases on the low temperature section adsorption curve 1 and reaches the set point B. At this time, when heated primary system pure water (water of good quality that has been desalinated and degassed so that it can be supplied to the primary coolant circulation system of the nuclear reactor) is passed through, the adsorption curve at the high temperature part Moving to point C on 2, the boron concentration in the effluent is sufficiently high to allow effective boric acid recovery. As boron is desorbed, the boron concentration in the effluent gradually decreases on adsorption curve 2, and when it reaches point D, it moves to point A by passing the cooled waste liquid, and by repeating this operation, it moves to point A. Then boric acid is recovered. That is, points A→B→C→D→A on the characteristic curve are repeated by waste liquid treatment and boric acid recovery. In addition, since this curve changes using temperature as a parameter, it is possible to select an appropriate temperature and resin amount according to the target recovery rate of boric acid. Furthermore, the lifespan of the resin is regulated by ions other than boric acid (mainly chlorine ions and iodine ions) in the waste liquid that are not desorbed.
The amount of these ions contained in this waste liquid is
Since the amount is relatively small at less than ppm, a relatively large amount of such ions are adsorbed to the resin, and it takes a long time for the resin to reach the end of its life, which affects the adsorption and desorption performance of boric acid. Therefore, even if the used resin is replaced at this point, it will not lead to the generation of a large amount of secondary waste. When regenerating, use NaOH
Anions can be removed by passing a few percent solution through the tube. As the anion exchange resin in the present invention, any commercially available anion exchange resin may be used.

FIG. 2 shows a system for recovering boric acid from radioactive waste liquid using a demineralization tower according to the present invention.

In a conventional nuclear power plant, a waste liquid containing boric acid, chloride ions, and iodine ions stored in a waste liquid hold-up tank 10 is passed through a filter 12 by a waste liquid supply pump 11, and then directly sent to an evaporator 16 for evaporation. was. However, since it contains a large amount of boric acid, the concentration limit depends on the boric acid, and radioactive substances and chemical components to be removed cannot be efficiently concentrated.

The present invention eliminates this drawback by performing desalination treatment using a resin as a pretreatment for the evaporation treatment, and allows the evaporation treatment to be carried out efficiently and at the same time, it is possible to recover boric acid in the waste liquid.

The outline of the present invention will be explained below.

The waste liquid containing boric acid stored in the waste liquid hold-up tank 10 is passed through a filter 12 by a pump 11.
is supplied to The waste liquid coming out of the filter is cooled by the cooler 1 with cold water from the cold water supply device 14.
After adjusting the temperature to an appropriate temperature, for example 10° C., in Step 3, the mixture is passed through a demineralization tower 15 filled with an anion exchange resin. While passing through this anion exchange resin, anionic substances (boric acid ions, chloride ions, iodine ions, etc.) in the waste liquid are adsorbed and removed. After passing through the demineralization tower 15, the waste liquid passes through the post-filter 17 and then to the evaporator 16.
for efficient concentration treatment. After such a sequence of treatments is carried out intermittently, valves V ₁ and V ₃ are closed and valves V ₂ and V ₄ are opened.

Good quality water (does not contain boric acid) that matches the quality of water used as a primary coolant is sent from the primary system pure water tank through the line to the warmer 18, where it is heated to an appropriate temperature using hot water circulating through the line. After adjusting the temperature to 60°C, it is sent to a demineralization tower 15. In this operation, among the anionic substances adsorbed in the demineralization tower, only boric acid is desorbed due to changes in ambient temperature, but other substances (chlorine ions, iodine ions, etc.) remain adsorbed on the resin. That is, boric acid alone can be effectively transferred into high-quality water, and boric acid in waste liquid can be effectively recovered.

The recovered water containing boric acid coming out of the desalination tower 15 is cooled to room temperature in the cooler 19, which uses cooling water circulating through the line, and then sent from the line to the primary coolant storage tank. Reuse within the feed plant. After the boric acid has been sufficiently desorbed, the demineralization tower is switched to the system for passing waste liquid again and used repeatedly.

1000 ~ as boron as above
2000ppm (boric acid concentration 5800~
Boric acid recovery rate when radioactive waste liquid containing boric acid, Cl ^- 10 ppm or less, and I ^- 10 ppm or less is treated at a waste liquid cooling temperature of 4 to 10 °C and a pure water heating temperature of 60 to 70 °C. is shown below.

Boric acid recovery rate varies depending on operational conditions. That is, Diaion SAN-1 is used as an anion exchange resin.
(Mitsubishi Kasei, trade name) in the boron adsorption curve in Figure 3, if the amount of boric acid adsorbed by the resin is around 20g/, for example, in the effluent (4℃)
The boron concentration is 100-200 ppm, Cl ^- and I ^- are zero, and 90-95% boric acid and 100% Cl ^- and I ^- are adsorbed (recovered) on the resin. However, in this case, the amount of boric acid desorbed by heated pure water is as small as 250 to 500 ppm, and a relatively large amount of pure water is required for desorption. On the other hand, the boron concentration in the effluent (4℃) is 500~
600ppm, Cl ^- and I ^- become zero, Cl ^- and I ^-
100% can be removed, but only 50-70% of boric acid can be recovered. However, in this case pure water (60℃)
The desorbed boron concentration in is 1500-2000 ppm, desorbed Cl ^-
and desorption I ^- are both zero, allowing effective addition. Furthermore, in the former case, a larger amount of resin is required than in the latter case for the same amount of waste liquid treated.

When the same type of anion exchange resin as above is used and the waste liquid cooling temperature is set to 10°C, almost the same results are obtained as shown in FIG. 4.

Practically speaking, it is appropriate to vary the amount of boron adsorption between 20 and 30 g/g and recover 70 to 80% of boric acid on average.

With the present invention, it is possible to obtain the same effects as using a reverse osmosis device, such as reducing the number of waste drums and the capacity of solidification equipment, and the equipment is relatively simple and easy to operate. The effect is produced.

Furthermore, by using this system as a pretreatment for the evaporator, chlorine ions contained in the waste liquid can be removed, and the additional effect is that it can also solve the corrosion problem caused by the concentration of chlorine ions in the evaporator. You can also expect

[Brief explanation of the drawing]

FIGS. 1, 3, and 4 are graphs showing examples of boron adsorption curves on anion exchange resins, and FIG. 2 is a flow sheet showing an outline of the method of the present invention.

Claims (1)

[Scope of Claims] 1. A nuclear reactor in which anionic substances are adsorbed through an anion exchange resin through the cooled radioactive waste liquid in the treatment of radioactive waste liquid containing boric acid, chloride ions, and iodine ions, and then heated. A method for recovering boric acid from radioactive waste liquid, which consists of repeating the process of passing primary pure water through the process. 2. When treating radioactive waste liquid containing boric acid, chloride ions, and iodine ions, anion exchange resin passes through the cooled radioactive waste liquid to adsorb anionic substances, and then the waste liquid is evaporated and concentrated.
A method for treating radioactive waste liquid that consists of repeatedly collecting boric acid by passing it through heated primary purified water from a nuclear reactor through a resin that has adsorbed anionic substances. 3 A system consisting of a waste liquid storage tank, a cooling device, an anion exchange resin filled desalination device, and an evaporation device, a clean water supply device, a heating device, an anion exchange resin filled desalination device, a cooling device, and a cooling water storage tank. This radioactive waste liquid treatment system uses a common anion exchange resin-filled desalination system and is connected by a switching valve.