JPH01318999A - Chemical decontamination - Google Patents

Abstract

PURPOSE:To enable a decontamination with a small amount of decontaminant by inserting a filling material at a center part of an equipment and/or a piping to which a radioactive substances stick and by inducing a chemical decontaminant into the above-mentioned equipment and/or piping under the said situation. CONSTITUTION:A filling material 2 is inserted into a large diameter piping 1 of an object of decontamination. Under this situation, a liquid decontaminant is circulated through a gap between the filling material 2 and the piping 1. In this way, a volume of the piping 1 is reduced in substance therefore an amount of the decontaminant can be reduced as much as the reduced volume of the piping. Also a concentration of the decontaminant can be increased therewith a decontamination effect can be improved.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for chemical decontamination of equipment, piping, etc. in a nuclear facility.

(Prior Art) At nuclear facilities, radioactive materials adhere to equipment, piping, etc., so there is concern about radiation exposure for workers working there. Therefore, chemical decontamination is being carried out as a means of removing these radioactive deposits and reducing exposure. Chemical decontamination is broadly divided into concentrated chemical decontamination, in which the concentration of decontamination agent is as high as several percent, and dilute chemical decontamination, in which the concentration of the decontaminating agent is less than 1%, and each type has its own characteristics in terms of decontamination methods and waste liquid treatment methods. In some cases, decontamination agents are classified based on whether they are recycled or not. For example, in decontamination methods where the decontamination agent is not regenerated during decontamination, regardless of whether it is concentrated or diluted,
The maximum (equivalent) amount of decontamination agent corresponding to the amount of decontamination solution adhering to the object to be decontaminated, or more, is required. on the other hand,
Among dilute decontamination agents, in decontamination methods that regenerate the decontamination agent, the concentration of the decontamination agent is constant regardless of the amount of decontamination solution to be decontaminated, and the ion exchange resin used to regenerate the decontamination agent Decontamination is carried out by increasing the amount according to the amount of decontamination solution.

Therefore, if the decontamination agent is not regenerated during decontamination work, the amount of deposits to be dissolved in the object to be decontaminated must be ascertained, and the stoichiometric It is necessary to supply a larger amount of the decontamination agent component to the object to be decontaminated than the equivalent amount determined by .

(Problem to be Solved by the Invention) As mentioned above, the amount of decontaminating agent and the concentration of decontaminating agent are basically determined based on the amount of deposits to be dissolved and the dissolving ability of the decontaminating agent. Decontamination work may not necessarily be carried out under optimal conditions, depending on the volume of the container and the amount of deposits.

For example, an example of two pipes having different volumes and different amounts of deposits to be dissolved is shown below. Note that the concentration of the decontamination agent used here is 1 to 8%, and the dissolving ability of the decontamination agent is defined as "concentration 1".
% decontamination agent can dissolve 1/10 fVh of deposits with a liquid volume of 1.

Piping A: Pipe diameter dcm, length 1cm.

Deposits m mIRg/7 Pipe B: Pipe diameter 4 dCrR, length decrement 1° Deposits 1 1/8 m4/d In pipe A, the amount of deposits to be dissolved is large compared to the volume of the object to be decontaminated. Piping B has a large volume to be decontaminated, but the amount of deposits to be dissolved is small. Internal surface area of each pipe.

The volume inside the pipe and the amount of deposits are as follows.

Evidence Δ Piping internal surface area S1 = πdlaA Piping internal volume V1 = 1/4πd22CrIt3 Amount of deposits M1 = πdIl-TrLη [Toyota pipe internal surface area 52-4πd deficient ad = 4 S1 pipe internal volume V2 = 4πd21crn3 = 16V1 deposits IM2
= 1/27rd 12 · mmg = 1/21'vh The upper limit of the decontamination agent concentration is determined based on limitations such as the solubility of the decontamination agent components or the solubility of dissolved deposits. If there is a lot of deposits like in pipe A, even the upper limit of the decontamination agent concentration of 8% cannot dissolve all the deposits.
1 to lyse 8/10 tVh), lysis cannot be completed in one decontamination. Therefore, it is necessary to repeat decontamination until there are no more deposits. On the other hand, although the volume of pipe B to be decontaminated is large, the amount of deposits to be dissolved is small. Such conditions occur during tank decontamination and large-diameter piping decontamination. In this example, the decontamination agent concentration determined from the decontamination material obtained from stoichiometric estimation is approximately 0.3% (because the decontamination agent concentration is 1% and the liquid volume v1 dissolves 1/10 fVh of deposits). , decontamination agent 1%, liquid volume v2 is 16/1
Can dissolve 0M1 deposits. The amount of deposit is 1/
2 Mt, about 0.3% is sufficient for liquid IV2. ), the concentration is lower than the lower limit of 1% decontamination agent concentration at which decontamination can be carried out effectively. However, if the decontamination concentration is increased to 1% or more in order to increase the efficiency of decontamination,
Supplying an excess amount of decontamination agent than the stoichiometrically required amount of decontamination agent results in waste of the agent and an increase in the amount of waste.

In other words, although it is necessary to repeat decontamination under the conditions of pipe A, it does not mean that more decontamination agent is supplied than necessary, and the amount of waste is naturally generated from the amount of deposits present on the object to be decontaminated. This is the amount. However, if pipe B is to be effectively decontaminated, it is necessary to inject a large amount of decontaminating agent in excess of the equivalent amount, and the injection of the excess decontaminating agent generates excess waste.

In general, the higher the flow rate of the decontamination agent, the higher the decontamination effect, and the faster the decontamination can be completed, so pipe B
If the flow rate is increased to perform effective decontamination under these conditions, a large-capacity pump will be required because the volume is large compared to the surface area.

The present invention was made in view of the above circumstances, and aims to perform chemical decontamination of equipment, piping, etc. efficiently while reducing the amount of decontamination liquid, and to roughly reduce the amount of decontamination waste. This is the purpose.

[Structure of the Invention] (Means for Solving the Problems) The present invention performs chemical decontamination by placing a filler inside the object to be decontaminated so as to reduce the volume of the object. That is, the present invention provides a chemical decontamination method for equipment, piping, etc., in which radioactive materials are removed by flowing a chemical decontamination agent into equipment, piping, etc. to which radioactive materials have adhered. A device characterized by the insertion of a filling in such a way that the contact between its internal surface and the chemical decontamination agent is not obstructed.

Concerning chemical decontamination methods for piping, etc.

(Function) In the present invention, for example, as shown in the piping cross-sectional view of FIG.
Since the filling material 2 is placed inside the pipe 1, the volume of the pipe is reduced, and the amount of decontamination liquid can be reduced. Since the decontamination agent concentration can be increased and the decontamination agent flow rate can be increased by decreasing the amount of decontamination liquid, the decontamination effect can be improved. Note that the reference numeral 3 in FIG. 1 is a spacer provided so that the filler 2 does not come into contact with the inner surface of the pipe and obstruct the flow of the decontamination liquid.

Next, FIG. 2 shows the relationship between the diameter of the pipe, the inner surface area of the pipe, the amount of liquid, and the concentration of the decontaminating agent, assuming that the amount of adhesion per unit area of the pipe is equal. As is clear from this figure, as the diameter increases, the amount of decontamination liquid relative to the surface area inside the pipe increases, and therefore the concentration of decontamination agent decreases. By reducing the volume to be decontaminated by placing filler in the piping, it is possible to set the optimal conditions for the amount of decontamination agent corresponding to the deposits and the decontamination concentration suitable for decontamination.

(Example) Embodiments of the present invention will be described with reference to the drawings.

Human Dan■Hoshizufu Yaseiyu Figure 3 shows an example of decontamination of large-diameter pipes filled with fillers.

A filling material 2 is inserted into a large-diameter pipe 1 of an object to be decontaminated. The filling 2 is flammable and at a decontamination temperature (-generally 80-120
It is made of a material such as polycarbonate that is heat resistant up to temperatures up to 30°F (°C). Additionally, nitrogen is fed into the filling. Nitrogen is used here because some decontamination agents have a strong reducing power, and when they come into contact with air, they oxidize and decontamination performance decreases, so if the gas leaks from the filling, it will not be a problem. This is to prevent this from happening. If the decontamination agent does not cause any change in decontamination performance even when exposed to air, it may be filled with air. A spacer 3 is attached to the outside of the filling so that the decontaminating agent can pass between it and the inner surface of the pipe.

In decontamination, the filling material 2 is inserted into the piping 1 to be decontaminated, nitrogen is sent from the nitrogen cylinder 4, and the filling material 2 is installed inside the decontamination object. Desalinated water is filled into a decontamination line consisting of a decontamination target 1, a circulation pump 5, and a decontamination tank 6, and is circulated by the circulation pump 5 while being heated by a heater 7. Depending on the characteristics of the decontamination agent, degassing may be performed by injecting nitrogen gas. The decontamination agent is injected into the decontamination system from the decontamination tank 8 when the temperature of the decontamination system increases. Subsequent decontamination can be carried out in the same manner as normal chemical decontamination.

When the decontamination is completed, the decontamination waste liquid is sent to the waste liquid processing device 9 and treated in a manner appropriate for each decontamination waste liquid.

For example, in the intensive decontamination method shown in FIG. 4, the decontamination waste liquid is received in the waste liquid receiver tank 10, and the decontamination system is cleaned by flushing or the like. The concentration device 11 performs concentration and desalination using a reverse osmosis membrane, a concentrator, etc.

The concentrated waste liquid is solidified in the assimilation treatment device 12.

Further, in the dilute decontamination method shown in FIG. 5, waste liquid is treated by the ion exchange resin column 13, and the object 1 to be decontaminated is washed with the demineralized water generated therein. The used ion exchange resin is treated as waste in a resin waste treatment system 14.

Next, for such large-diameter piping, the decontamination conditions when no filler was added (P) and when it was filled (Q) were compared, and the results are shown in Table 1. The two pipes have the same shape,
The amount of deposits to be removed is equal in both cases.

Table 1 (P) (Q) Surface area 200072000 ci
Volume 5000cm3 1000
cm3 Amount of deposits (per unit area) 1■/cri
1rn'j/7〃 (total amount > 2SF
2g Required amount of decontamination agent (as 100%) 209
2Cj (J decontamination agent concentration (equivalent concentration) 0.4%
2.0%〃 (Using concentration) 1.0% 2.5%
Decontamination agent injection amount: 50g By adding 25g of filler, the volume of the pipe increases from 5000ff3 to 10
It decreased to 1000C. Since the amount of deposits is the same, the required amount of decontamination agent is both equal to 20g, but the volume (i.e. liquid volume)
are different, so the decontamination agent equivalent concentration for P is 0.4%, but for Q it is 2.0%. Since the actual concentration of the decontamination agent used is in the range of 1 to 8%, P will be lower than this, while Q will be at an appropriate concentration. When the decontamination agent equivalent concentration is lower than the usage concentration as in P, the decontamination is carried out at the lower limit of the decontamination usage concentration range, and the usage concentration for P is 1%.

Therefore, the amount of decontamination agent injected is 5000 x 0.01
=50(0). In Q this is i ooo xo,
025=25(0). Therefore, in P, an extra amount of decontamination agent is injected, whereas in Q, not only can such waste be avoided, but also the decontamination speed can be increased because the decontamination agent concentration is increased. This is because the decontamination speed increases as the decontamination agent concentration increases.

In addition to increasing concentration, there are other effects of adding fillers. This is shown in Table 2.

Table 2 (P) (Q) Surface area 2000CrA2000c
d Volume 5000cm3 100
0cm” Decontamination agent concentration (use concentration) 1.0% 2.5
% Decontamination agent injection IJ 50g 25g Decontamination flow rate 15 Time required for temperature rise Long Short waste liquid tank storage 51 Waste liquid concentration ratio Small Large amount of purification ion exchange resin 21 Time required for purification 91.7 (Numbers without units are relative values) As is clear from Table 2, one of the effects is a reduction in the amount of decontamination liquid, which is advantageous in increasing the temperature of the decontamination agent. That is, since the amount of decontamination liquid is small, the temperature can be easily raised.

In addition, a decrease in the amount of decontamination liquid results in a decrease in waste liquid, which has the effect of reducing the waste liquid tank capacity and reducing the waste liquid concentration rate. The dilute chemical decontamination method results in a reduction in the purification time using the ion exchange resin and a reduction in the amount of the ion exchange resin. FIG. 6 shows the relationship between decontamination agent concentration and purification time with and without packing.

As shown in this figure, the cleaning time is reduced in the presence of packing.

In addition, if there is a filler, the flow rate of the decontamination agent on the inner surface of the pipe becomes faster even with the same pump flow rate, and therefore the decontamination rate also becomes faster.

Figures 7 and 8 show examples of tank decontamination. The tank has a large volume compared to the surface area to be decontaminated.
Problems such as a large amount of waste liquid have arisen. In Fig. 7, a filler 16 and a spacer 18 that match the tank shape are installed in the tank 1.
5, and the decontamination agent is circulated by the pump 17. In FIG. 9, a spherical filler 19 is submerged in the tank to reduce the amount of decontamination agent injected. With this method, there is no need to prepare fillers according to the shape of the tank, and any shape or size can be decontaminated using the same method.

[Effects of the Invention] As explained above, according to the present invention, decontamination effects can be achieved without using excess decontamination agent in decontaminating large-capacity equipment and pipes such as large-diameter pipes and tanks. can be improved in various ways. Additionally, the amount of waste generated by decontamination can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a pipe for explaining the present invention in detail, and Fig. 2 shows the pipe diameter, the amount of liquid in the pipe, the surface area inside the pipe, and the decontamination agent assuming that the amount of adhesion per unit area of the pipe is equal. Figure 3 is a diagram showing the relationship with concentration, Figure 3 is a system diagram for decontamination of large-diameter piping to explain one embodiment of the present invention, Figures 4 and 5 are diagrams showing other decontamination methods of the present invention. A system diagram showing an example, FIG. 6 is a diagram showing the relationship between decontamination agent purification time and decontamination agent concentration with and without filling, and FIGS. 7 and 8.
The figure is a diagram showing an embodiment of the present invention in the case of decontaminating a tank. 1... Piping (object to be decontaminated) 2, 16.19... Filler 3.18... Spacer 4... Nitrogen cylinder 6... Decontamination tank 7... Heater 8... Decontamination agent tank 9... Waste liquid treatment device 11... Concentration device 12... Solidification device 13... Ion exchange resin tower 15... Tank (object to be decontaminated) (8733) Agent Patent attorney Boar Yoshiaki Mata (and others)
1 person) Fig. 1 Piping test (relative value) Fig. 2 Fig. 3 Fig. 4 Nurification time jump (relative value)

Claims (1)

[Claims] (1) In a chemical decontamination method for equipment, piping, etc. that removes radioactive materials by flowing a chemical decontamination agent into equipment, piping, etc. that has radioactive materials attached, the internal surface of the equipment, piping, etc. A chemical decontamination method for equipment, piping, etc., characterized by inserting a filler so as not to prevent contact with the decontaminating agent.