JPS6180096A - Method of reducing radioactive waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to the disposal of radioactive waste by effectively reusing unreacted chemicals in the recycled waste liquid of ion exchange resin from ion exchange equipment containing radioactive materials. Concerning how to reduce the amount.

[Conventional technology]

Conventionally, in condensate desalination equipment for condensate purification systems in BWR type nuclear power plants, for example, in order to prevent seawater leakage and ensure the purity of outlet water, ion exchange resin is Therefore, in the recycled waste liquid generated at this time, unreacted chemicals (caustic soda or sulfuric acid) remain in the amount of over 95% of the amount passed.

The recycled waste liquid of the ion exchange resin containing this unreacted agent is sent as is to the waste treatment system, where it is evaporated and concentrated and finally converted into sulfuric acid. However, these waste materials are radioactive and cannot be easily divided into two parts for disposal, so at present they are only being accumulated inside the power plant, and it is difficult to divide these radioactive wastes into two parts. This is one of the important issues as it is related to environmental issues.

[Structure of the invention]

In a method for purifying a liquid containing a radioactive substance by ion exchange, the present invention divides the recycled waste liquid generated when regenerating an ion exchange resin into the recycled waste liquid discharged at the beginning of the regeneration and the recycled waste liquid discharged afterwards. The method is characterized in that the regenerated waste liquid is divided and discharged at the initial stage of regeneration, and the unreacted drug is recovered by electrodialysis, and the regenerated waste liquid discharged thereafter is left as is and both are reused as the next regeneration agent. This is a way to reduce radioactive waste.

Since the method of dividing radioactive waste into two has become a serious social problem, the present inventors believe that even if the method of dividing radioactive waste into two is not completely solved, if the amount of waste to be divided into two can be reduced, The present invention was developed while conducting various studies on ways to reduce the amount of regeneration waste liquid discharged during ion exchange resin regeneration in order to reduce the storage volume of substances.

The ion load during normal operation at nuclear power plants, etc. is
In order to prevent seawater leakage and maintain the purity of the outlet water, it is necessary to keep the ion load of the ion exchange resin small during regeneration of the ion exchange resin. For this reason, each desalination tower is operated at 45,000 μs/1-711-1.
The consumption of regeneration agent in the regeneration agent solution (usually 8% 80. and 4% Naoll) during regeneration is approximately 4-
As little as 5%, a large amount of unreacted drug, ie sulfuric acid or caustic soda, is present in the regeneration effluent.

The following table shows the relationship between the amount of drug in the regeneration drug solution (drug passing amount) and the amount of unreacted drug present in the regeneration waste liquid during normal ion exchange resin regeneration.

The recycled waste liquid contains a large amount of unreacted regenerant as shown in the table above, so it is possible to use the recycled waste liquid repeatedly. Impurities in the condensate supplied to the column, such as Na, Oa, Fθ
, C/, etc., not only reduces the regeneration level of the ion exchange resin, but also increases the dose rate of the environment as radioactive materials are concentrated in proportion to impurities in the recycled waste liquid when used repeatedly. increases, which is not desirable in terms of radiation exposure reduction measures.

And the above Na contained in the recycled waste liquid.

Impurities such as Ca, Pe, and O/2 appear in the recycled waste liquid relatively early after the start of the regeneration operation, and after that, unreacted chemicals with few impurities flow out from the regeneration tower as the recycled waste liquid. Focusing on this point, the present invention divides and collects the regenerated waste liquid into two parts: a regenerated waste liquid with many impurities and a waste liquid with few impurities, which are discharged in the early stage of regeneration.・At the same time as concentration, the latter is recovered as it is, and in the next regeneration, first the latter is used to regenerate the first half, and then the unreacted drug purified by electrodialysis and the new drug solution for replenishment are used to regenerate the second half. It performs regeneration.

In addition, when the recycled waste liquid is divided into two, it is possible to collect about 1/3 or less of the total recycled waste liquid as the initially discharged recycled waste liquid, but in order to ensure the removal of impurities, Preferably, the amount of K is about 4.

〔Example〕

Next, the present invention will be explained in detail based on the drawings.

The ion exchange resin to be regenerated (hot water ion exchange resin or anion exchange resin) introduced into the ion exchange resin regeneration tower 1 is first treated with the ion exchange resin used in the latter half of the previous regeneration of the ion exchange resin in the waste liquid receiving tank 2. The regenerated waste liquid is supplied to the regeneration tower IK through the pipe 12 by a pump, and the regenerated waste liquid discharged from the regeneration tower is supplied to the regeneration tower IK through the pipe 12. and 11, and is stored in the waste liquid receiving tank 3.

Next, the recovered chemical liquid stored in the recovered chemical tank 7, collected by electrodialysis from the waste liquid used in the first half of the previous regeneration, is regenerated together with the new regenerated chemical liquid supplied from the pipe 20 via the pump a pipe 19. The recycled waste liquid is supplied to the column 1 to regenerate the ion exchange resin in the column, and the recycled waste liquid discharged from the raw tube 9 is stored in the raw liquid receiving tank 2 via the pipe 10, and the waste liquid is used in the first half of the next regeneration. . On the other hand, the recycled waste liquid used in the first half of the regeneration stored in the waste liquid receiving tank 3 is transferred to the waste liquid tank 4 by the pump P, and then circulated to the desalination chamber of the electrodialysis tank 5 by the pump P. The purified water in the recovery liquid tank 6 is circulated through the anode chamber, cathode chamber, and concentration chamber by the pump 4 and subjected to electrodialysis to purify and recover the drug in the recycled waste liquid, and the recovered drug solution is recovered from the recovery liquid tank 6. It is temporarily stored in the chemical tank 7, and after checking the concentration, it is used in the second half of the next regeneration process together with the newly supplied chemical solution via the pipe 19 by the pump P.

Furthermore, the recovered waste liquid from the electrodialysis tank is discharged to the waste treatment process through a pipe 23, while the waste liquid generated by the washing water supplied through the pipe 8 after regenerating the ion exchange resin is discharged through the pipe 9 and the pipe 22. Discharged to waste treatment process.

It goes without saying that it is necessary to provide two systems for recovery of drugs by electrodialysis for negative and positive ion exchange resin regeneration waste liquids.

Although any type of electrodialysis tank may be used, recovery of HIF304 and NaOH from ion exchange resin regeneration waste liquid will be explained using the most typical electrodialysis equipment.

The fs2 diagram shows mainly Fl, B 04 and Nl!, which is the recycled waste liquid of cation exchange resin. Figure 5 shows the state in which horse No. 80 is recovered from a solution containing L1804.
FIG. 3 is a diagram showing a state in which NaOH is recovered from a solution containing lt.

The dialysis tank is equipped with a pair of anodes and a cathode at both ends, between which a large number of anion exchange membranes and cation exchange membranes C are arranged alternately. A cathode chamber is formed between the cathode and the cation exchange membrane.

To explain based on FIG. 2, the cation exchange resin regenerated waste liquid is introduced into the demineralization chamber (undiluted solution chamber) through the pipe 33, and is circulated through the pipe 34 to the pipe 33. It is led to the bipolar chamber and the concentration chamber and circulated through tube 32 to 51. During this time, ions such as 804-, Ha'', H+, etc. move in the direction of the arrow, but while Qa- remains in the stock solution chamber, that is, while the opposition ■+ is high, the mobility in H+ and Na is large. There is also a difference; only H+ moves, while most of Na moves.As a result, pure H@so can be obtained in the concentration chamber.However, if the recovery rate of sulfuric acid is 90% or more, Care must be taken because the concentration in ■ in the stock solution chamber becomes diluted and Na begins to move into the recovered sulfuric acid.

Next, to explain the recovery of NaOH based on FIG.
stock solution chamber) K is introduced and circulated through the pipe 44 to the pipe 43,
The NaOH recovery liquid is led from the pipe 41 to both electrode chambers and the concentration chamber, and is circulated to the pipe 41 via the pipe 42. During this time Na”
, Cl-.

Each ion such as OH- moves in the direction of the arrow, but while Na remains in the stock solution chamber, that is, while the opposing OH- is high, there is a difference in the mobility of OH- and Cl-, and OH- Only Cl- moves, and Cl- hardly moves.

Therefore, a pure NaOH solution can be obtained in the concentration chamber. However, when the recovery rate of NaOH becomes 90% or more, the OR- concentration in the stock solution chamber becomes small and pat- begins to move into the recovered NaOH solution, so care must be taken.

By the electrodialysis method explained above, the recovery rate is about 74% with a recovery rate of about 90% from the recycled ion exchange resin waste liquid with a sulfuric acid concentration of 565%.
of pure sulfuric acid can be recovered, and NaOH concentration is 2.9%.
Similarly, approximately 55% pure caustic soda can be recovered from the anion exchange resin regeneration waste solution.

〔Effect of the invention〕

When using the method of the present invention, it is possible to obtain a regeneration efficiency equivalent to that of conventional regeneration methods in terms of resin regeneration efficiency.

Further, according to the present invention V, the number of drums that are the final solidified product is calculated as shown in the table below.

As mentioned above, it is possible to reduce the amount by about 78% compared to the conventional method.
Considering the difficulty and high cost of final halving of drums,
It has sufficient economic efficiency.

The present invention has the following advantages compared to a method in which all unreacted drugs from recycled waste liquid are recovered by electrodialysis.

1) Since it is only necessary to electrodialyze about half of the unreacted drug in the following amount, the scale of the electrodialysis equipment becomes about 4 or less, and the running cost such as electricity cost and membrane replacement cost also becomes 4 or less.

2) If the latter half of the unreacted chemical solution is recycled during maintenance or failure of the electrodialyzer, the amount of final waste can be reduced to about 1/2.

Of course, the reverse is also possible, increasing the margin of the device.

[Brief explanation of the drawing]

Figure 1 is a schematic flow diagram for explaining the method of the present invention, and Figures 2 and 3 are diagrams showing the recovery of H, EI04 from cation exchange resin recycled waste liquid, and anion exchange resin recycled waste liquid, respectively. FIG. 3 is a diagram showing a state in which NaOH is recovered.

Claims (1)

[Claims] 1. In a method for purifying a liquid containing a radioactive substance by ion exchange, the regenerated waste liquid generated when regenerating the ion exchange resin is divided into two: a regenerated waste liquid that is discharged at the beginning of the regeneration, and a regenerated waste liquid that is discharged afterwards; Reducing radioactive waste by collecting unreacted chemicals from the recycled waste liquid discharged at the beginning of regeneration using electrodialysis, and then reusing the recycled waste liquid as it is as it is for the next regeneration chemical. how to.