JPS60210800A - Method of removing radioactive element in waste liquor - 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 The present invention relates to a method for removing radioactive elements that can economically reduce the concentration of radioactive elements in waste liquid containing radioactive elements to below the emission standard value.

Waste liquid generated from medical institutions and research facilities often contains large amounts of radioactive elements due to the use of radioactive isotopes. When discharging such waste liquid out of the system, it is necessary to reduce the concentration of radioactive elements in the waste liquid so as not to adversely affect the environment (so as to satisfy the discharge standard value).

For this reason, the above facilities are equipped with radioactive element removal equipment that uses an attenuation method, a dilution method, or a combination of both methods. However, if the former method is adopted, the waste liquid must be stored for a long period of time until the concentration of radioactive elements in it decays below the standard value, which requires a large-capacity storage tank. There is. On the other hand, the latter method dilutes the waste liquid with water to reduce the concentration of radioactive elements to below the standard value, so the equipment size is smaller than the attenuation method, but it has the disadvantage of requiring a large amount of dilution water and the total amount being regulated. The problem is that it does not fit in with the recent way of thinking. That is, in all conventional methods, there is no guarantee that waste liquid treatment can be carried out economically.

The present invention was completed as a result of repeated studies under these circumstances, and is intended to economically and reliably lower the concentration of radioactive elements in radioactive element-containing waste liquid.

The method of the present invention, which has achieved the above object, circulates the radioactive element-containing waste liquid via the first adsorption part and adsorbs the radioactive element to the first adsorption part, thereby reducing the radioactive element concentration of the waste liquid in the circulation line. When the detected concentration is below the standard value, the waste liquid is discharged from the system, and from the change in the detected concentration, taking into account the adsorption capacity of the first adsorption section, the waste liquid is sent to the circulation line via the second adsorption section. The gist is that the radioactive element concentration of the waste liquid in the circulation line is continuously detected after switching.

This has made the equipment more compact, reduced water consumption, and made it possible to process radioactive elements more reliably.

The configuration and effects of the method of the present invention will be explained below with reference to the drawings. In the following explanation, the treatment of waste liquid containing radioactive iodine will be used as an example, but since the object of the present invention is not limited to radioactive iodine, the types of elements to be treated will be The technical scope of the present invention includes making various design changes depending on the concentration and concentration.

FIG. 1 is an explanatory diagram showing the basic configuration of an apparatus for removing unformed radioactive substances for carrying out the present invention. In addition to accommodating the second adsorption tower 2, a waste liquid storage tank 3 is formed at the bottom of the hood F. By forming the tapered part f, consideration is given so that all the liquid components collected in the hood F, such as washing water, are introduced into the waste liquid storage tank 3. A first circulation line M drawn out from the bottom of the waste liquid storage tank 3
At the same time, the latter half of the first line is branched into a 2-inch line m1 and a line m2, which are connected to the top of the first adsorption tower 1 and the second adsorption tower 2, respectively, and The line m1 and line m2 drawn from the bottom are the second line N.
monitor 4, which is the radioactive iodine concentration measuring section.
The waste liquid is returned to the waste liquid storage tank 3 via the third line N'. Further, a discharge line K is branched from point G on the third line N'. Furthermore, 12th in M, 2nd line N' + discharge 2 in K and line m 1 y m 2 s n I
Hn 2 has solenoid valves e, d, c*a, respectively.
1 t a'2 * b 1 and b2 are interposed.

When carrying out the method of the present invention using the removing device S having the above configuration, a 1 tbl of the electromagnetic valves.

d and e are opened while a2 + b2 and C are closed, and a waste liquid containing radioactive iodine is introduced into the waste liquid storage tank 3. Next, by starting the pump P, the waste liquid is introduced into the first adsorption tower 1 via the first line M and the line ml, and after radioactive iodine is adsorbed and removed, it is extracted to the line nl. Then, the waste liquid is introduced into the monitor 4 via the 22nd inn N, and the radioactive iodine concentration in the waste liquid is detected. If the detected concentration exceeds the discharge standard value, the solenoid valve C is closed and the solenoid valve d is closed. While it is left open, the waste liquid flows to the third line N' and is refluxed to the waste liquid storage tank 3. Hereinafter, this will be referred to as the first circulation line. In this way, the circulation of waste liquid through the first circulation line is repeated, and when it is found that the concentration detected on monitor 4 has decreased to below the discharge standard value, monitor 4
Solenoid valve C is opened based on the command from solenoid valve d.
is closed, and the waste liquid is discharged from the system through the discharge line K. When all the waste liquid in the waste liquid storage tank 3 has been treated (or when the amount of waste liquid in the waste liquid storage tank 3 has decreased by a predetermined amount),
A new waste liquid is introduced into the waste liquid storage tank 3, and the solenoid valve C is closed again, and the solenoid valve d is opened to continue the same circulation process as described above. On the other hand, if the radioactive undeposited capacity of the first adsorption tower 1 reaches a saturated state while the waste liquid treatment is repeated, the detected concentration will no longer be low -F'L even if the waste liquid is further circulated. Alternatively, the detected concentration may become high due to some other circumstances.

When such a state is detected by the monitor 4, the solenoid valves al and bl are closed according to a command from the monitor 4, while the solenoid valves a2+b2 are opened, and the waste liquid storage tank 3 is closed.
The waste liquid is introduced from the 12th inn M to 2 inn m2, and the radioactive iodine is removed through the second adsorption tower 2.
2, the second line N, the monitor 4 and the third line N' are refluxed to the waste liquid storage tank 3. In this way, the second adsorption tower 2
When the concentration detected by the monitor 4 drops below the discharge standard value, the solenoid valve C is opened in the same manner as described above, while the solenoid valve d is closed, and the waste liquid is discharged from the system through the discharge line K. Release water. In the above embodiment, the solenoid valve opening/closing control circuit opens the solenoid valve d and closes the solenoid valve C when the detected concentration on the monitor 4 is higher than the discharge standard value, and when the detected concentration is below the discharge standard value. is configured so that solenoid valve d is closed and solenoid valve C is opened, so even if the radioactive iodine concentration in the waste liquid changes slightly, the waste liquid will not be discharged from the removal device until it exceeds the discharge standard value. It circulates and is not discharged outside the system. If the concentration detected by the monitor drops from a value higher than the discharge standard value to below the discharge standard value, the solenoid valve C is opened as described above and the waste liquid is discharged out of the system. In the flow path between C, there is waste liquid whose detected concentration value is higher than the discharge standard value, and this waste liquid is discharged at the same time. Environmental pollution caused by this can be prevented by, for example, a dilution method, but it is necessary to set the discharge standard value on the monitor to be stricter than the actual standard, or to open and close the solenoid valve COD that is required for the circulating waste liquid to flow through the flow path. This can be dealt with by taking time into account and delaying the process.

Next, when the waste liquid treatment for the batch is completed by the second adsorption tower 2 as described above, the first adsorption tower
Adsorption tower 1 is replaced. That is, washing water W is added to the waste liquid storage tank 3.
is introduced, and while monitoring the monitor 4, the cleaning water is manually circulated using the second adsorption tower 2, and the cleaning waste liquid is appropriately discharged to the outside of the system through the discharge line. At this time, the adsorption capacity of the second adsorption tower 2 is still sufficient, so that the radioactive iodine concentration in the washing waste liquid can be sufficiently reduced.

Further, in order to wash the inside of the hood F, if necessary, washing water W may be sprayed from above the hood F. When cleaning is completed, the inlet/outlet 5 of the hood F is opened, the adsorption unit of the first adsorption tower 1 is removed and carried out of the hood F, and a new adsorption unit is loaded into the first adsorption tower 1, and the inlet/outlet 5 is closed. do.

When restarting waste liquid treatment using the removal device S after replacing the adsorption tower in this way, the second adsorption tower 2 is regarded as the first adsorption tower 1 before restart, and the first adsorption tower 1 is also replaced with the second adsorption tower 1. Regarded as adsorption tower 2, solenoid valve al.

Switch the control circuits of a2, bl and b2. Furthermore, it is also possible to provide a third adsorption tower so as to prepare for breakthrough of the second adsorption tower. The following explanation shows the case where the third adsorption tower is installed for another purpose.

The configuration of the present invention is basically the same as shown above, but in order to automatically clean the inside of the removal device S, a third suction dedicated for cleaning is provided in the 7-door F as shown in Fig. 2. A column 6 is provided, to which a line m3 branched from the 12th inn M and a line n3 merging with the second line N are connected, respectively, and a line m
3 r n 3 may be provided with solenoid valves a3 and b3. This is called a removal device S', but the procedure for using the first adsorption tower 1 and the second adsorption tower in the removal device S', in other words, how to assemble the fourth circulation line and the second circulation line, is the same as in the case of the removal device S. There is no difference. However, the usage procedure after the residual waste liquid in the removal device S' is treated and discharged using the second adsorption tower 2 is different. That is, after that, the cleaning water W is introduced into the waste liquid storage tank 3, and the solenoid valves a3+b31d,
Open only e, 4th line M, line m3+n3+2nd
The cleaning water is circulated by assembling a third circulation line from the second line N and the third line N', and while the concentration is similarly detected by the monitor 4, the cleaning wastewater whose concentration is below the standard concentration is discharged. If the concentration detected by the monitor becomes higher than the discharge standard value during cleaning, the discharge is stopped and the fluid is sent to the third circulation line again. When the cleaning is completed, the first adsorption tower 1 whose adsorption capacity is saturated is replaced.

As mentioned above, by using the third adsorption tower 6 exclusively for cleaning, the cleaning effect of the lines through which waste liquid flows, the pump, and the inside of the hood F can be more completely achieved, so that the replacement work of the adsorption tower can be performed safely. I can do it.

The circulation line of the present invention is implemented by the apparatus as exemplified above, but it is also possible to make the first to third (or more if necessary) circulation lines independent of each other and provide a monitor for each.
The present invention also includes making only the cleaning line completely independent, and not dedicating the cleaning line and using each line in sequence as the currently used line, backup line, and cleaning line, for example.

Examples of adsorbents for adsorbing radioactive iodine include silver-impregnated activated carbon, silver zeolite, and ion exchange resins, among which silver-impregnated activated carbon is particularly recommended since it has the largest equilibrium adsorption amount. By the way, the ability of silver-impregnated activated carbon to adhere to radioactivity increases almost proportionally as the silver content increases, but at the same time, the price also increases, so it is uneconomical to increase the content unnecessarily. Therefore, it is recommended that the silver-impregnated activated carbon has sufficient adsorption capacity and the price is not so high, that is, the silver content is about 0.5 weight. The typical properties of such silver-impregnated activated carbon are shown in Table 1 below.

Furthermore, when filling the above-mentioned silver-impregnated activated carbon to form an adsorption unit, it is desirable to fill the adsorption unit so that the packing density is approximately 0.5 kg/1.

Furthermore, in the above example, an adsorption tower was formed using only an adsorption unit filled with an adsorbent, but for example, in addition to proteins (e.g. albumin), waste liquid discharged from medical institutions contains general Since impurities are often included, when forming an adsorption tower, it is desirable to divide the adsorption unit and arrange adsorption layers corresponding to each adsorbent.

Although the explanation so far has shown a column-type adsorption section in which waste liquid is introduced from the top and extracted from the bottom, the adsorption section may be one in which the above-mentioned adsorption units are arranged horizontally.

In addition, as the monitor 4 for detecting the radioactive iodine concentration, a Ge semiconductor detector, a NaI scintillation counter, etc. can be used. Furthermore, when carrying out the method of the present invention, it is desirable to maintain a negative pressure in the hood F to prevent the radioactive iodine in the hood F from leaking out of the system, thereby completely preventing leakage of radioactive iodine. In order to do this, it is recommended to install an outer hood that surrounds each line including hood F, monitor 4, pump P, etc.

The present invention is configured as described above, and can obtain the effects summarized below.

(1) Since the radioactive elements in the waste liquid are adsorbed and removed, unlike the attenuation method, a large-scale storage tank is not required, and the treatment can be completed in a short time, and unlike the dilution method, a large amount of dilution water is not required. Not needed. That is, it is possible to economically remove radioactive elements.

(2) Since the waste liquid is discharged from the system only when the concentration detected by the monitor falls below the discharge standard value, it can greatly contribute to the prevention of environmental pollution.

(3) When it is confirmed from the change in concentration detected by the monitor that the adsorption capacity of the first adsorption part has reached a saturated state, the circulation line is switched to the second adsorption part and introduced into the removal equipment. It is possible to reliably reduce the concentration of radioactive elements in the waste liquid to below the discharge standard value and discharge it out of the system.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams showing a removal apparatus for carrying out the method of the present invention. 1... First adsorption tower 2... Second adsorption tower 3... Waste liquid storage tank 4... Monitor 5... Inlet/outlet 6... Third adsorption tower M... First circulation line N ...Second circulation line applicant Kobe Steel, Ltd.

Claims (1)

[Claims] While circulating the radioactive element-containing waste liquid via the first adsorption part, the radioactive element is adsorbed to the first adsorption part, and the radioactive element concentration of the waste liquid in the circulation line is detected, and when the detected concentration becomes below the reference value. Then, the waste liquid is discharged to the outside of the system, and based on the change in the detected concentration, the adsorption capacity of the first adsorption part is taken into consideration, and the radioactive element in the waste liquid in the circulation line is switched to the circulation line passing through the second adsorption part. A method for removing radioactive elements from waste liquid, characterized by detecting the concentration.