JPH11109092A - Processing method for radioactive material-containing waste liquid using reverse osmosis membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the control of processing equipment by measuring the concentration of Na in waste liquid before and after passing a reverse osmosis membrane (RO membrane), and evaluating the degradation status of the RO membrane from the permeability of Na calculated from the measured value. SOLUTION: Raw water containing radioactive material is once received in a washing drain tank 1, and supplied to an RO membrane 3 by a high pressure pump 2 for waste liquid transport. Electric conductivity and Na concentration of the raw water is measured at a measurement position 7 upstream of the RO membrane 3, and electric conductivity and Na concentration of the processed water is measured at a downstream measurement position 8 and radioactivity is measured with a radiation monitor 6. Although in this example, the electric conductivity of the permeated water at the time of integral processing amount of 600 m<3> is below the discharge standard, radioactive material is detected in the radioactivity measurement, and Na permeability is 60% at this moment, and it is lower than initial performance. By this constitution, the degradation of processing performance of radioactive material in the RO membrane which can not be grasped in the conventional electric conductivity measurement can be easily detected, and the control of the processing equipment can be easily and smoothly performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a waste liquid containing radioactive substances such as washing wastewater in a nuclear facility by using a reverse osmosis membrane, and more particularly, to an improved method for evaluating the state of degradation of a reverse osmosis membrane in use. The present invention relates to a method for treating a radioactive substance-containing waste liquid.

[0002]

2. Description of the Related Art Reverse osmosis (hereinafter referred to as RO) is one of the methods for treating wastewater containing radioactive substances such as washing wastewater in nuclear facilities (nuclear power plants).
(Abbreviated as a film). In these treatment systems, the soundness (deterioration state) of the membrane during operation (during use) was evaluated based on the conductivity of permeated water (treated water). That is, the conductivity of the permeated water was measured, and when the value exceeded a certain reference value, it was determined that the stock solution was leaking due to membrane damage, aging, etc., and the membrane was replaced.

[0003]

FIG. 2 shows an example of a schematic system diagram of a radioactive substance-containing waste liquid treatment facility using an RO membrane used in a nuclear power plant. In the equipment shown in FIG. 2, a waste liquid (washing wastewater) containing a radioactive substance is once received in a washing wastewater tank 1 and supplied to the RO membrane 3 by a wastewater transfer high-pressure pump 2. The treated water that has passed through the RO membrane 3 is continuously and automatically measured by a conductivity meter 4, and is discharged to a permeated water tank 5 when the conductivity is equal to or less than a reference value.
Further, the treated water discharged to the permeated water tank 5 is checked for radioactivity by the radiation monitor 6, and is finally discharged if it is below the release reference value. Here, the determination of whether or not discharge is possible is based on whether or not the radioactivity is finally detected by the radiation monitor 6 at or above the reference value, as described above. However, there is a possibility that the radioactivity cannot be released, that is, radioactivity is detected. That is, even if the RO film is determined to be healthy (continuous use) by the conductivity management, a radioactive substance that does not contribute much to the conductivity actually penetrates, and is finally detected by the radiation monitor 6. Release may not be possible. in this case,
The RO film cannot be used continuously, and it is necessary to replace it with a new film.

As described above, when an RO membrane is used in a treatment system for handling radioactive waste liquid, the actual state of the membrane (deterioration, damage, etc.) is determined by the method of confirming the integrity of the membrane based on electrical conductivity used in the general industry. May not be accurately understood. The present invention, in view of the state of the prior art, can accurately evaluate the performance deterioration state of an RO membrane in a treatment facility for radioactive substance-containing waste liquid, and can easily manage the treatment facility. It is an object to provide a processing method.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted various studies on a process for treating a waste liquid containing a radioactive substance by an RO membrane, and measured the transmittance of Na contained in the waste liquid. By doing so, it was found that the film deterioration state (change with time) can be accurately grasped. That is, the present invention relates to a method for treating a radioactive substance-containing waste liquid using a reverse osmosis membrane, wherein the Na concentration in the waste liquid before and after passing through the reverse osmosis membrane is measured, and the Na concentration is calculated based on the Na transmittance calculated from the measured value. This is a method for treating a radioactive substance-containing waste liquid, wherein the state of deterioration of the permeable membrane is evaluated.

[0006] In the method of the present invention, the radioactive material containing
It is a radioactive element contained in waste liquid ⁶⁰Co,¹³⁷Cs, etc.
Metal ions show similar membrane permeability to Na ions.
And the permeability of Na coexisting in the waste liquid containing radioactive substances.
Evaluate reverse osmosis membrane degradation by measuring excess rate
I am trying to do it. Specifically, before and after the RO film
To measure the Na concentration in the solution and calculate the Na transmittance.
You. From the situation of this change in transmittance, the RO film is damaged or deteriorated.
Can be evaluated.

Usually, the liquid to be treated by the RO membrane in a nuclear power plant mainly consists of washing wastewater (washing wastewater) and contains NaCl which is a human sweat component.
What is necessary is just to measure this Na concentration. It should be noted that N
When a is not contained, NaCl or the like is appropriately added,
The concentrations of Na in the raw water and the treated water may be measured and compared.

The performance of an RO membrane is generally expressed as a desalination rate (a ratio of a salt concentration in a permeated water to a salt concentration in a raw water).
Confirmation (inspection) of the initial performance after film production is also made with salt (= N
aCl) is measured. Therefore, the performance evaluation of the RO film actually used is also N
By measuring and performing the transmittance of “a”, it is possible to consistently manage and grasp the state of deterioration from the time of film production to the time of use of the film by the same means. In addition, it is possible to confirm film deterioration that cannot be detected by simple conductivity management.

In carrying out the method of the present invention, the electric conductivity meter 4 is replaced with N in the conventional equipment shown in FIG.
Only by installing the a meter, it is possible to check the deterioration state of the RO film over time while minimizing the remodeling range from the conventional equipment.

[0010]

EXAMPLES The method of the present invention will be described more specifically with reference to the following examples. (Example 1) A waste liquid treatment test was performed using an RO membrane facility used in a washing and drainage treatment system at one of domestic nuclear power plants. The schematic system diagram is shown in FIG. The test operation involves cleaning the wastewater once containing radioactive
And supplied to the RO membrane 3 by the high-pressure pump 2 for transferring waste liquid. The conductivity and Na concentration of the raw water (liquid to be treated) are measured at the measurement position 7 on the upstream side of the RO film 3, and the conductivity and Na concentration of the treated water are measured at the measurement position 8 on the downstream side of the RO film 3. At the same time, the radioactivity was measured by the radiation monitor 7, and the relationship among the integrated processing amount of the liquid to be processed and the conductivity, Na transmittance, and radioactivity was confirmed. Table 1 shows the results.

[0011]

[Table 1]

As can be seen from the results in Table 1, the conductivity of the permeated water is 4 at the time when the integrated treatment amount of the raw water is 600 m ^3.
6.3 μS / cm, which is less than 450 μS / cm, which is the standard for release to the permeated water tank 5 downstream, so that the processing itself is continuously performed. In the check, radioactive substances were detected and release was impossible. On the other hand, the Na transmittance at this time is 60%.
Which is clearly lower than the initial performance (1%). From the above, it can be seen that film deterioration that cannot be confirmed only by the conventional conductivity management can be performed by measuring Na.

[0013]

According to the method of the present invention, it is possible to easily detect the deterioration of the processing performance of radioactive substances of the RO film, which could not be grasped by the conventional management by conductivity measurement, and to easily detect the radioactive substance-containing waste liquid. Management of processing equipment can be performed easily and smoothly. The method of the present invention is particularly suitable for treating cleaning wastewater in a nuclear power plant.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram of a facility for treating radioactive substance-containing waste liquid according to an embodiment of the present invention.

FIG. 2 is a schematic system diagram of a conventional radioactive substance-containing waste liquid treatment facility.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/44 ZAB C02F 1/44 ZABK

Claims (1)

[Claims] In a method of treating a radioactive substance-containing waste liquid using a reverse osmosis membrane, the Na concentration in the waste liquid before and after passing through the reverse osmosis membrane is measured, and the Na concentration calculated from the measured value is measured.
A method for treating a radioactive substance-containing waste liquid, wherein the degradation state of the reverse osmosis membrane is evaluated based on transmittance.