JPS61194398A - Decontaminator for material to be treated contaminated by radioactivity - 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 [Technical Field of the Invention] The present invention is a method for decontaminating radioactively contaminated tanks, piping, valves, etc. in a nuclear facility. Related to decontamination equipment for processed materials.

[Technical background of the invention and its problems] In general, radioactivity accumulates in tanks, piping, valves, etc. installed in raw materials facilities as the facility is operated, and empty wires at the installation location accumulate. As the bottle becomes taller, maintenance work becomes difficult. For this reason, tanks with high radioactivity levels,
When workers enter the high-sensitivity area where piping, valves, etc. are installed, decontamination is carried out to lower the radioactivity level.

In addition, if a defect occurs in a tank, pipe, valve, etc. and it becomes necessary to replace it with a new one, the removed tank, pipe, valve, etc. will be transported and stored as low-level waste. It is necessary to carry out decontamination to make this possible.

However, since radioactivity permeates the inner material of tanks, piping, valves, etc. (hereinafter referred to as objects to be treated), complete decontamination cannot be achieved by simply removing the radioactivity deposited on the surface. It is not possible to do so, and it is necessary to dissolve the object itself and remove the surface layer that has been penetrated by radioactivity.

Regarding this radioactive decontamination, chemical decontamination methods and electrical decontamination methods using chemical decontamination agents such as acids are known.

Although the former method is highly applicable to processing large equipment with complex shapes, it has the drawbacks of extremely slow decontamination speed and relatively low decontamination coefficient.

On the other hand, although the latter electric decontamination method has a high decontamination speed and a high decontamination coefficient, it has a complicated shape and has problems in application to large objects to be treated.

Furthermore, the decontamination agents used in chemical decontamination equipment and electrolytic decontamination equipment deteriorate and accumulate radioactivity, making decontamination impossible, resulting in an increase in secondary waste.・[Objective of the Invention] The present invention has been made based on the above circumstances, and its purpose is to reliably dissolve the inner surface of the object to be treated, where radioactivity permeates into the material itself, and to overcome the drawbacks of the conventional example. Even large equipment and items with complex shapes were completely decontaminated.

The decontamination agent can be recycled to reduce the radioactivity level to the background level, and the amount of secondary waste generated can be minimized. It is an object of the present invention to provide a decontamination device for a workpiece contaminated with radioactivity, which can reduce the oxidizing power so that there is no problem in treating the used decontamination agent as waste liquid.

[Summary of the invention] That is, the present invention is directed to polyvalent oxidation states in an aqueous solution.

an electrolytic tank for adjusting an acidic solution-based electrolyte in which a metal compound having a metal with a low oxidation state is dissolved; A radioactively contaminated workpiece is provided so that the electrolytic solution flows in from a liquid input line connected to the tank, and a three-way valve is connected between the workpiece and the electrolytic tank. a reduction treatment tank connected from the other side of the three-way valve via a waste liquid return line, and an electrolytic waste liquid reduced in this reduction treatment tank from the waste liquid return line connected to the reduction treatment tank. This is an apparatus for decontaminating a workpiece contaminated with tlIII, characterized in that it is equipped with a waste liquid line that flows out through the workpiece. .

The object to be treated is characterized in that it has a shape such as a tank, piping, or valve in which the electrolyte is stored.

According to the present invention, it is possible to reliably dissolve the inner surface of the object to be treated whose material itself is permeated with radioactivity, and it is also possible to completely decontaminate even large objects with complex shapes and reduce the radioactivity level. At the same time, since decontamination is carried out while regenerating the decontamination agent, the amount of secondary waste generated after use and use of the decontamination agent (electrolyte) can be minimized.

Furthermore, in order to avoid problems in the waste liquid treatment system when the used decontamination agent that has removed radioactivity from the object to be treated is treated as waste liquid, Ce4+ in the decontamination agent can be reduced to C6J4.

Furthermore, by providing a filter, it is possible to prevent the radiation surface and impurities from adhering to the electrode, so C
e4+ can be efficiently played back.

[Embodiment 1 of the Invention] Hereinafter, an embodiment of the decontamination apparatus for a workpiece contaminated with radioactivity according to the present invention will be described with reference to the drawings.

FIG. 1 is a system diagram of the apparatus according to the present invention, and FIGS. 2 and 3 are characteristic diagrams comparing and showing the stirring effect of the apparatus in FIG. 1.

Reference numeral 1 is an electrolytic cell, and inside the electrolytic cell 1 there is, for example, Ce.
"-Ce"-HNO3 solution electrolyte 2 and anode.

3 and a cathode 4 are housed therein. Further, reference numeral 5 denotes a tank-shaped object to be treated, and the electrolytic tank 1 is placed inside this object to be treated 5.
The electrolyte 2 inside is flowed in through the inflow line 21. The object to be processed 5 has a shape in which an electrolytic solution 2 is stored, and a heater 18 for heating the electrolytic solution 2 is inserted therein.

Further, a return line 22 is provided for returning the electrolyte 2 in the object 5 to the electrolytic cell 1. This return line 22
A pump 6, a filter 7, and a three-way valve 8 are connected in this order. Further, a waste liquid reduction line 23 is connected to the other side of the three-way valve 8, and this waste liquid reduction line 23 is connected to the lower part of the reduction treatment tank 9.

A pair of electrodes consisting of an anode 10 and a cathode 11 are provided within this reduction treatment tank 9. Reference numeral 13 is an adjustment tank;
The electrolytic solution 2 is adjusted and stored in the adjustment tank 13.

The adjustment tank 13 has a liquid supply line 25 having a liquid supply pump 14.
is connected, and the electrolytic solution 2 in the adjustment tank 13 is supplied to the electrolytic tank 1 through the liquid supply line 25 by the liquid supply pump 14. Further, a stirring line 26 is provided branching from the discharge side of the pump 14, and the stirring line 26 is connected to the adjustment tank 13. Further, a circulation line 21 is connected to the side surface of the electrolytic cell 1, and the electrolytic solution 2 that has overflowed the electrolytic cell 1 is supplied to the object to be processed 5 through the inflow line 21. It was connected to the adjustment tank 13. The stirring unit 26 is the liquid supply pump 1
A part of the electrolytic solution 2 from which the electrolyte 4 has been discharged is ejected into the adjustment tank 13 through the stirring line 26. Further, the adjustment tank 13 is provided with a heater 19, which heats the electrolytic solution 2 to increase the production speed of the electrolytic solution 2. The cerium regeneration anode 3 and the cerium regeneration cathode 4 of the electrolytic cell 1 are supplied with direct current ff1il! 12. - A return line 22 is connected to the object to be treated 5, and the electrolytic solution 2 contained in the object to be treated 5 is ejected from the lower part of the electrolytic cell 1 through a filter 7 by a circulation pump 6.

On the other hand, by switching the three-way valve 8 provided in the return line 22, the return line 22 is connected to the waste liquid reduction line 23. It passes through and is ejected from the lower part of the reduction treatment tank 9. A reduction treatment anode 10 and a reduction treatment cathode 11 of the reduction treatment tank 9 are connected to a DC power source 12 . A waste liquid return line 24 is connected to the reduction treatment tank 9,
The electrolyte 2 that has overflowed the reduction treatment tank 9 is returned to the object to be treated 5 through the waste liquid return line 24 .

When the reduction process of converting Ce4÷ contained in the electrolytic solution 2 to ce'' is completed, the electrolytic solution 2 is transferred to a wastewater treatment system (not shown) using the existing wastewater line 29 connected to the object to be treated 5. The heater 18 in the object to be treated 5 is used to increase the temperature of the electrolytic solution 2 and speed up the decontamination speed.

An exhaust gas line 27 is connected to the upper part of the electrolytic cell 1 and the reduction treatment tank 9, and the H2O-11NO:l generated from the electrolytic solution 2 is
The steam and mist pass through the exhaust gas line 27 and are condensed in the condenser 15, and are collected into the electrolytic cell 1 through the condensate return line 28. L-120 that could not be recovered
-HNO3 vapor and mist are sucked into the exhaust blower 17 and recovered by the demister 16.

In the decontamination apparatus for a radioactively contaminated workpiece according to the present invention configured as described above, first, Ce (NO3)3 is heated to a predetermined temperature by the heater 19 in the adjustment tank 19 for a predetermined number of times, and then H2O - Dissolve in HNO3 solution, adjust the electrolyte, and pass it through the liquid supply line 25 by the liquid supply pump 14 to the electrolytic cell 1.
The electrolytic solution 2 contained in the object to be treated 5 and adjusted by the circulation pump 6 is ejected from the lower part of the electrolytic cell 1 through the return line 22, and the electrolytic solution is circulated between the electrolytic cell 1 and the object to be processed 5 through the circulation line 21. 2 is heated to a predetermined temperature by the heater 18, and the inside of the electrolytic cell 1 is brought to negative pressure by the exhaust gas 10a 17. At the same time, when N pressure is applied between the cerium regeneration anode 3 and the cerium regeneration cathode 4 by the DC N source 12 and a current with a predetermined current density is passed, the following reaction occurs, and the Ce trigram becomes Ce4
Oxidizes to +-.

Cerium regeneration anode ce” 4064÷+6− −−・−−−−
−, < 1)20H−→H20+(1/2)02
(↑)−+2e−・・・・・・・・・・(2) Cerium regeneration cathode H+ +6− →(1/2) H2(↑) ・−・
-(3) The production reaction of Ce4+ in the cerium regeneration anode 3 depends on the speed at which ce" diffuses and reaches the anode surface. Therefore, if the electrolytic solution 2 is spouted from the bottom of the electrolytic cell 1 and stirred, It has the effect of promoting the Ce4+ production reaction.

Further, the following reaction occurs on the inner surface of the object to be processed 5 immersed in the electrolytic solution 2, and the radioactivity and metal (M) adhering to the surface are dissolved and contamination is removed.

M + Ce” −> M + +
Ce j+ −・−−−−−−・− (4−) After circulating the electrolyte 2 for a predetermined period of time, the radiation activity attached to the surface of the object 5 and the contamination layer on the surface are removed, and the radioactivity level is reduced. Will there be a significant decline? . .

On the other hand, since a voltage is constantly applied from the DC N source 12 and a current of a predetermined current density is passed through the Ce" which has been reduced by reacting with the object to be treated 5, the reaction of equation (7) occurs. Ce4
Generate +. In addition, since oxides such as iron floating in the electrolyte 2 are recovered by the filter 7 provided in the return line 22, it is possible to prevent oxides such as iron from adhering to the cerium regeneration anode 3. , it is possible to efficiently generate <Ce'+.

When decontamination with the electrolytic solution 2 has been completed, the two-way valve 8 is switched to transfer the electrolytic solution 2 contained in the object 5 to the circulation line 22 and the waste liquid reduction line 23 using the circulation pump 6.
The electrolytic solution 2 is ejected from the lower part of the reduction treatment tank 9 through the heater 18 and circulated between the reduction treatment tank 9 and the object to be treated 5 through the waste liquid return line 24. The electrolyte 2 is heated to a predetermined temperature by the heater 18. Make it negative pressure. At the same time DC-
An anode 10 for reduction treatment and a cathode 11 for reduction treatment by a source 12
When a voltage is applied between them and a current with a predetermined current density is passed, the following reaction occurs, and Ce4+, which has oxidizing power, is reduced to Qe, which has no oxidizing power.

Anode 201-de for reduction treatment -+H20+ (1/2) 02
(↑) +20! ”−・・・・・・・・・(5
) Cathode for reduction treatment Ce ” +e −→Ce ” −−= (6
)1-1” +e −→(1/2) H2(↑)−(7
) The reaction for producing CeJ+ at the cathode 11 for reduction treatment is based on CeJ+.
- Depends on the rate at which 4+ diffuses and reaches the cathode surface.

In addition, if the electrolytic solution 2 is jetted out from the lower part of the reduction treatment tank 9 and stirred, it has the effect of promoting the reaction for producing Ce notes.

When Ce4+ in the electrolytic solution 2 becomes equal to or higher than the predetermined sy1, the circulation pump 6 is stopped to complete the reduction process of the electrolytic solution 2, and electrolysis is carried out from the existing waste liquid pipe 29 connected to the object to be treated 5. Send liquid 2 to the waste liquid treatment system.

In addition, as in the case of regenerating Ce4+, in order to recover oxides such as iron floating in the electrolytic solution 2 with the filter 7 provided in the circulation return line 22, the reduction treatment anode 10
It is possible to prevent oxides such as iron and the like from adhering to the surface, and it is possible to efficiently reduce <Ce'+ to Ca''.

Incidentally, both the electrolysis tank 4f11 and the reduction treatment tank 9 are provided with a drain line, and the electrolytic solution 2 remaining in the tank is transferred to the object to be processed 5.

On the other hand, +20-=HNO3 vapor and mist generated from the electrolytic solution 2 pass through the exhaust gas line 27 connected to the upper part of the electrolytic solution 4! It passes through and is collected in the electrolytic cell 1. The 1lzo-HNO3 vapor and mist that could not be completely recovered are sucked into the exhaust blower 17 and sent to the demister 1.
It is recovered by 6.

In addition, the electrode materials for cerium regeneration are HNO3 and Ce4.
Use materials such as platinum, titanium, etc. that exhibit corrosion resistance to strong oxidizing agents such as + and are not polished by electrolysis.

On the other hand, when using a metal material with a high oxygen overvoltage such as graphite, gold, platinum, etc. for the anode 10 for reduction treatment, Ce 3 ÷ C 6,4
Since the proportion of current used for oxidation to + increases, the current efficiency for oxygen production decreases. Therefore, it is important that the anode 10 for reduction treatment is made of a material in which Ce 3" is difficult to convert into Ce 4+, that is, a metal material or metal oxide material with a low oxygen overvoltage. Generally, the magnitude of the oxygen current and pressure is graphite, Gold, platinum, palladium, cadmium, platinum (plated), silver, lead, nickel, copper, iron, and cobalt decrease in this order.To improve the current efficiency of reduction treatment,
The material of the anode 10 for reduction treatment has an absolute value of oxygen overvoltage of ce
It is necessary to use a material whose absolute value is smaller than the absolute value of the voltage at which Ce' is oxidized to ten.

Next, regarding the cathode 11 for reduction treatment, if a metal material with low hydrogen overvoltage is used, such as platinum, iron, or nickel, the proportion of current used to generate hydrogen will be lower than the reduction of CeA+ to Ce''. Ce 4+ becomes Ce
The efficiency of the current reduced to 5+ deteriorates. Therefore, it is important that the reduction treatment cathode 11 be made of a material that does not easily generate hydrogen, that is, a metal material or metal oxide material that has a high hydrogen overvoltage. In general, the magnitude of hydrogen overvoltage is platinum black, rhodium, gold, tungsten, smooth platinum, nickel,
Dried budden, iron, silver, aluminum, beryllium, niobium, tantalum, copper, graphite, bismuth, lead, tin, indium, thallium, mercury, and cadmium.

In order to improve the current efficiency of reduction treatment, the reduction treatment cathode 1
The material No. 1 needs to be a material in which the absolute value of the hydrogen overvoltage is greater than the absolute value of the voltage at which Ce4+ is reduced to Ce squares.

Furthermore, a stirrer or the like may be used to stir the electrolytic solution.

Next, the results of an experiment conducted to confirm the effects of the above embodiment will be explained with reference to FIGS. 2 and 3.

In FIG. 2, line a shows electrolysis without stirring, and line a shows electrolysis with stirring. Note that the vertical axis represents Ce4+ in the electrolyte.
The concentration and current efficiency are shown on the horizontal axis, and the electrolysis time is shown on the horizontal axis.

The electrolytic conditions are Ce (No3>3' degree 0.8m
Ce4+ was generated by electrolyzing an electrolytic solution with an electrolytic solution temperature of 80° C. and a current density of 0.3 A/c/i at 0° C./J2 and a HNO3 concentration of 2 mol/i. The amount of Ce 4+ produced was determined by analysis using potentiometric titration, and the current efficiency η was determined as follows.

77 = 96485x Ce'+Generation It (wo
n/ffl) x electrolyte volume (bu)/electrolysis time (5
ec) X current (A) As is clear from Figure 2, if electrolysis is carried out by stirring the electrolyte, efficient
and can be played.

Next, FIG. 3 will be explained. Based on the results in Figure 2, Ce
4+ concentration 0.4mon/A, HtlO311 degrees 2I
Heat the electrolyte of IIO to 80℃ to remove contaminated metals (S).
US304.2 B x S ch40x 500) was immersed, and Ce4+ was simultaneously regenerated at a current density of 0.3 Acif.

Curve C shows the case where the metal to be processed is immersed without stirring the electrolytic solution, curve 1Iad shows the case where the metal to be processed is immersed while stirring the electrolytic solution, and the horizontal line e shows the background. Note that the vertical axis is the γ-ray strength f! ! (The horizontal axis shows the decontamination time.

As is clear from FIG. 3, by stirring the electrolytic solution and immersing the metal to be treated, it is possible to reduce the amount of surface contamination to the background level within 60 minutes of FrR during decontamination. 12 when the metal to be treated is immersed in the electrolyte without stirring
Even after 0 minutes of decontamination, it was not observed that the amount of surface contamination was reduced to the background level.

[Effect of the invention 1 As described above, the present invention is capable of dissolving the inner surfaces of tanks and the like that are objects to be treated using a Ce3+Ce4+-FINO3 solution system, and of dissolving Ce3+Ce4+-FINO3 solution system.
This is a decontamination device that uses a redox (electrolytic oxidation-reduction) reaction that can regenerate 4+.

Therefore, according to the present invention, it is possible to efficiently generate and regenerate <ce'> by stirring and stirring the electrolyte, and moreover, by collecting oxides such as iron with a filler, it is possible to transfer them to the electrode. It is possible to prevent the adhesion of impurities, and moreover, it is possible to regenerate efficiently <ce'+.

In addition, it is possible to reliably dissolve the inner surfaces of objects to be treated whose materials themselves are penetrated with radioactivity, and it is possible to completely decontaminate large equipment and objects with complex shapes, reducing radioactivity levels to background levels. can.

Furthermore, by recycling and using the decontamination agent, the amount of secondary waste generated can be minimized.

Furthermore, before the used decontamination agent, which contains a large amount of radioactivity removed from the object to be treated, is transferred to the waste liquid treatment system, the Ce4+ contained in the decontamination agent is reduced to Ce5+, so the waste liquid It will not corrode processing equipment.

In addition, in the above example, ce”-Ce” was used as the electrolyte.
-HNO3 solution system is explained, but is not limited thereto.When a metal compound in a low oxidation state is dissolved in water and an acid, it becomes a metal ion in a low oxidation state in the solution.CrS
+ or V4+ can be used. In addition to nitric acid, sulfuric acid or hydrochloric acid can be used as the acidic solution. and,
Highly oxidized metal ions are Ce'+, Ce4+,
Cr't for Cr J+, ■ for v4÷.

Furthermore, as the object to be treated, in addition to metals, objects contaminated with radioactivity attached or deposited on the surface of resin can also be used.

[Brief explanation of drawings]

Figure 1 shows an embodiment of the decontamination equipment for radioactively contaminated objects according to the present invention, and Figures 2 and 3 are for detailed explanation of the present invention. , FIG. 2 is a characteristic diagram showing the relationship between electrolysis time and Ce4+ concentration, and FIG. 3 is a characteristic diagram showing the relationship between decontamination time and reduction in the amount of surface contamination. 1...... Electrolytic cell 2... Electrolyte 3... Cerium regeneration anode 4...
......Cerium regeneration cathode 5...
・・・・・・Metal to be processed 6・・・・・・・・・・・・
Circulation pump 7...Filter 8...Three-way valve 9...Reduction tank 10... ...
......Anode 11 for reduction treatment...
・・・Reduction treatment cathode 12・・・・・・・・・DC power supply 13・・・・・・・・・Adjustment tank 14・・・・・・・・・・・・・・・Liquid supply pump 15...
・・・・・・・・・Capacitor 16・・・・・・・・・・
...Demister 17...Exhaust blower 18...Heater 19...Heater 21... ......Inflow line 22...
・・・・・・Return line 23・・・・・・・・・
...Waste liquid return line 24...Waste liquid return line 25...... Liquid supply line 2
6...... Stirring line 27...
・・・・・・Exhaust gas line 28・・・・・・・・・
...Condensate return line 29...Waste liquid line Applicant Toshiba Corporation Representative for Japan Atomic Energy Corporation Patent attorney Satoshi Suyama - Figure 2 Electrolysis time (hr) 3 Figure decontamination time (minutes)

Claims (7)

[Claims] (1) An adjustment tank for adjusting the concentration of an acidic electrolyte in which a metal compound in a low oxidation state of a metal with a multivalent oxidation state is dissolved in an aqueous solution, and the electrolyte in this adjustment tank is supplied as a liquid. an electrolytic cell into which the electrolytic solution flows through a line; a radioactively contaminated object to be treated that is provided so that the electrolytic solution flows into the electrolytic cell through an inflow line connected to the electrolytic cell; A return line is connected between the two through a three-way valve, a reduction treatment tank is connected from the other side of the three-way valve through a waste liquid reduction line, and the electrolytic waste liquid reduced in this reduction treatment tank is transferred to the reduction treatment tank. 1. A decontamination device for a workpiece contaminated with radioactivity, comprising: a wastewater return line connected to a wastewater return line that flows out through the workpiece. (2) Removal of a radioactively contaminated object as set forth in claim 1, wherein the object has a shape such as a tank, piping, or a valve in which an electrolytic solution is stored. Dyeing equipment. (3) When a metal compound in a low oxidation state is dissolved in water or an acid, it becomes a metal ion in a low oxidation state Ce^3^
Decontamination of a workpiece contaminated with radioactivity according to claim 1, characterized in that it is at least one compound selected from +, Cr^3^+, and V^4^+. Device. (4) The apparatus for decontaminating a workpiece contaminated with radioactivity according to claim 1, wherein the acidic solution is a solution containing any one of nitric acid, sulfuric acid, and hydrochloric acid. (5) The decontamination device for a workpiece contaminated with radioactivity according to claim 1, wherein the adjustment tank is provided with a stirring line. (6) The decontamination device for a workpiece contaminated with radioactivity according to claim 1, wherein a pair of electrodes consisting of an anode and a cathode are provided in the reduction treatment tank. (7) A capacitor and a demister are sequentially connected to the electrolytic cell through an exhaust gas line, and the demister is connected to a condensate return line communicating with the electrolytic cell. A decontamination device for objects to be treated that are contaminated with the radioactivity described above.