JPH04313391A - Sodium azide decomposing equipment - Google Patents

Abstract

PURPOSE:To surely decompose sodium azide while restraining the quantity of generated gas and to improve safety by continuously supplying sodium nitrite and nitric acid causing decomposition reaction with liquid to be treated to a reaction tank. CONSTITUTION:Liquid to be treated is continuously supplied little by little to a specified quantity to a reaction tank 3 and sodium nitrite and nitric acid are continuously supplied to a specified quantity to the reaction tank 3. Generated gas part is continuously exhausted by vent piping 6 and liquid part whose sodium azide concentration has been notably lowered by accelerated decomposition reaction is transferred to a waste liquid tank. Thereby sodium azide is gradually decomposed and can be surely removed to improve safety in treating the liquid part after decomposition treatment. And the quantity of generated gas is restrained to improve offgas processability by making continuous decomposition reaction treatment.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a sodium azide decomposition device, and more particularly to a technique for stabilizing sodium azide contained in a liquid to be treated by continuously or intermittently decomposing it. It is something.

0002

2. Description of the Related Art Spent nuclear fuel used in nuclear power plants is subjected to so-called reprocessing to separate and recover uranium and plutonium. In this case, the Purex method is said to be effective as a reprocessing method, and for example, it uses tributyl phosphate (TBP) as a solvent and a hydrocarbon such as dodecane as a diluent to reprocess spent nuclear fuel. Through contact, extraction and recovery of plutonium, uranium, etc. is carried out.

[0003] Hydrazine is used in the plutonium/uranium extraction step in these reprocessing processes, and ammonia (NH3), hydrogen azide (HN3), etc. are produced by decomposition of this hydrazine. Among these, hydrogen azide becomes sodium azide (NaN3) in a stable state by back extraction with a basic solution during solvent washing. Based on its own stability, this sodium azide is difficult to decompose even during alkaline cleaning, so its concentration tends to be high.

On the other hand, if various treatments are carried out while maintaining a high concentration of sodium azide in the radioactive waste liquid, in the presence of acids, the explosive hydrazoic acid and heavy metals interact with each other to increase sensitivity. Therefore, it is desirable to decompose sodium azide or to reduce the concentration of sodium azide.

Conventionally, as a method for decomposing sodium azide, sodium nitrite (NaNO2) was mixed with nitric acid (
It is believed that it is effective to add HNO3) to produce a decomposition action based on the following decomposition reaction formula to achieve a stable state. NaN3 +NaNO2 +2HNO3 →2Na
NO3 +N2 +N2O +H2O Through this chemical reaction, sodium nitrate, water, N2 gas, and N2O gas are generated, and sodium nitrate is dissolved in water or the like and retained in this state.

[0006]

However, when sodium azide is decomposed, about 0.7 liters of gas is generated per 1 gram of NaN3, as is clear from the above decomposition reaction formula. Therefore, when a large amount of alkaline cleaning waste liquid is treated at one time, the chemical reactions mentioned above are thought to proceed rapidly, resulting in the generation of huge amounts of N2 gas and N2O gas, which is common in reprocessing plants. If you try to process it by combining it with the off-gas of In addition, the latter method of lowering the concentration of sodium azide generates a large amount of diluted radioactive waste liquid, which is difficult to manage, impairs economic efficiency, and is impractical.

The present invention was made in view of the above-mentioned circumstances; (1) To improve safety by reliably decomposing sodium azide; (2) To decompose sodium azide continuously or intermittently while suppressing the amount of gas generated. The purpose is to carry out processing, etc.

[0008]

[Means for Solving the Problems] The sodium azide decomposition apparatus according to the present invention includes two means for solving the problems. The first means consists of a liquid to be treated storage tank that stores a liquid to be treated containing sodium azide, a reaction tank connected to the liquid to be treated tank and into which the liquid to be treated is fed, and an interior of the liquid that is connected to the reaction tank. A sodium nitrite supply system and a nitric acid supply system that continuously supply a decomposition reaction accelerating liquid to cause a decomposition reaction, a vent pipe that is connected to the upper space of the reaction tank and discharges gas, and a storage tank for the liquid to be treated. A quantitative supply means interposed between the reaction tank and continuously supplying a small amount of the liquid to be treated to the reaction tank; and a quantitative supply means connected to the reaction tank to continuously feed the liquid after the decomposition reaction. The sodium azide decomposition device is equipped with a waste liquid tank. The second means includes a liquid to be treated storage tank that stores a liquid to be treated containing sodium azide, a reaction tank that is connected to the liquid to be treated and temporarily stores the liquid to be treated in small portions, and a reaction tank that is connected to the liquid to be treated and temporarily stores the liquid in small quantities. A sodium nitrite supply system and a nitric acid supply system that supply a decomposition reaction accelerating liquid to the temporarily stored liquid to be treated to cause a decomposition reaction, and a vent pipe that is connected to the upper space of the reaction tank and discharges gas. The sodium azide decomposition apparatus is configured to include a waste liquid tank which is connected to the reaction tank and into which the liquid after the decomposition reaction is intermittently fed.

[0009]

According to the first means, the liquid to be treated is fed into the liquid to be treated storage tank and is continuously fed into the reaction tank little by little by the operation of the quantitative supply means. When the sodium nitrite supply system and the nitric acid supply system operate to supply a decomposition reaction promoting solution to the reaction tank in an amount commensurate with the small amount of the liquid to be treated, a decomposition reaction of the liquid to be treated occurs, and this decomposition reaction generates The gas is continuously discharged little by little through the vent piping. Then, the liquid after the decomposition reaction, in which the concentration of sodium azide has been significantly reduced by the promotion of the decomposition reaction, is continuously transferred to the waste liquid tank. The liquid to be treated is supplied to these reaction tanks, the generated gas is removed, and the liquid after decomposition is discharged continuously, and the liquid with the sodium azide concentration reduced to the desired concentration is sent to the waste liquid tank. will be transferred to. According to the second means, the liquid to be treated stored in the liquid to be treated storage tank is intermittently fed into the reaction tank in small amounts based on the volume of the reaction tank. With the liquid to be treated stored in the reaction tank, the sodium nitrite supply system and the nitric acid supply system are operated to supply a decomposition reaction accelerating liquid in an amount commensurate with the amount of the liquid to be treated to the reaction tank. A decomposition reaction occurs, and the gas generated by this decomposition reaction is discharged through the vent pipe. When the decomposition of sodium azide in the liquid to be treated stored in the reaction tank is completed by promoting the decomposition reaction, the liquid in the reaction tank is transferred to the waste liquid tank, and the next liquid to be treated is By repeating the process of feeding the liquid into the reaction tank again and decomposing it, the decomposition process of the liquid to be treated in the liquid to be treated storage tank is carried out intermittently and sequentially.

0010

[Example] <One Example> An example of the sodium azide decomposition apparatus according to the present invention will be described below with reference to FIG.

In FIG. 1, reference numeral 1 indicates a storage tank for the liquid to be treated, and 2
3 is a quantitative supply means, 3 is a reaction tank, 4 is a sodium nitrite supply system, 5 is a nitric acid supply system, 6 is a vent pipe, 7 is a stirring device, 8 is a waste liquid tank, 9 is a transfer pipe, 10 is a transfer pump, 11
is a quantitative container, 12 is a liquid supply pipe, 13 is a return flow pipe, 14 is a liquid distribution pipe, 15 is a treated liquid supply system, 16 is an off-gas treatment system, R is a treated liquid, and X is a waste liquid (radioactive waste liquid). It is.

The liquid to be treated storage tank 1 includes a liquid to be treated supply system 1
The liquid to be treated R containing sodium azide is connected to 5.
is sent in and stores a large amount of liquid R to be treated,
The liquid returned from the quantitative supply means 2 is also stored as a liquid to be treated.

The quantitative supply means 2 is arranged to be interposed between the liquid to be treated storage tank 1 and the reaction tank 3, and continuously supplies a small amount of the liquid to be treated R to the reaction tank 3. The quantitative supply means 2 includes a transfer pipe 9 connected to the liquid to be treated storage tank 1 and a liquid to be treated R disposed in the middle of the transfer pipe 9.
A transfer pump 10 for continuously transferring the liquid R, a metering container 11 to which the liquid to be treated R is supplied via the transfer piping 9, and a transfer pump 10 for transferring the liquid stored in the metering container 11 to the reaction tank 3. It is configured by a liquid supply pipe 12 provided therein.

The reaction tank 3 is connected to the quantitative supply means 2, and is used to continuously decompose and react the stored liquid R to be treated. In the reaction tank 3, a sodium nitrite supply system 4, a nitric acid supply system 5, a vent pipe 6, and a liquid transfer pipe 14 are arranged in a connected state, and the liquid to be treated R etc. stored therein are connected. A stirring device 8 for stirring is provided.

The sodium nitrite supply system 4 and the nitric acid supply system 5 add and supply sodium nitrite (NaNO2) and nitric acid (HNO3) as a decomposition reaction accelerating liquid into the reaction tank 3, as described above. , which produces a decomposition action based on the above-mentioned decomposition reaction formula.

The vent pipe 6 is connected between the upper space of the reaction tank 3 and the off-gas treatment system 11.

The waste liquid tank 8 is connected to the reaction tank 3 via a liquid transfer pipe 14, and is used to store liquid components (waste liquid X, radioactive waste liquid) after the decomposition reaction.

The transfer pump 10 is, for example, an air lift pump, and the transfer pipe 9 and the liquid supply pipe 12 are connected as necessary.
and is disposed in the liquid transfer pipe 14 to transfer the liquid to be treated R and the like.

The liquid to be treated R fed into the liquid to be treated storage tank 1 is continuously fed into the reaction tank 3 little by little by operating the quantitative supply means 2. In this case, in the example shown in FIG. 1, by operating the two transfer pumps 10, the liquid to be treated is transferred from the storage tank 1 to the quantitative container 11, and from the quantitative container 11 to the reaction tank 3. , the amount supplied to the metering container 11 is slightly increased, and the amount (surplus) of the liquid to be treated R that exceeds the amount transferred to the reaction tank 3 is transferred to the liquid to be treated storage tank through the return flow piping 13 such as a siphon pipe. Set it back to 1. In other words, the amount transferred from the quantitative container 11 to the reaction tank 3 is defined as the quantitative supply amount.

Under the condition that the liquid to be treated R is stored in the reaction tank 3 and supplied in fixed quantities, the sodium nitrite supply system 4 and the nitric acid supply system 5 are operated to remove the small amount stored in the reaction tank 3. A saturated solution of NaNO2 and a saturated solution of HNO3 are used as decomposition reaction accelerating liquid in proportion to the liquid R to be treated.
is continuously supplied to the reaction tank 3 to cause a decomposition reaction of the liquid R to be treated.

In this case, the supply state of the decomposition reaction accelerating liquid is as follows:
NaNO2 is placed near the supply position of the liquid to be treated R to the reaction tank 3.
The saturated solution of NaNO2 is supplied near the mixed solution of the liquid to be treated R and the saturated solution of NaNO2, and the stirring device 7 is operated to promote stirring of the mixed solution. . Also, settings are made to feed a saturated solution of NaNO2 in a slightly larger amount than the specified amount (relative amount to HNO3).

[0022] NaNO2 and HNO3 are added to the liquid R to be treated.
The gases generated by the decomposition reaction based on the decomposition reaction formula described above, N2 gas and N2O gas, are sent to the off-gas treatment system 16 via the vent pipe 6, and are subsequently treated as off-gas. The amount of gas generated in this case is given by the amount of supplied liquid R to the reaction tank 3 and the supplied amount of the decomposition reaction promoting liquid. The fixed amount of R is set, and the gas is continuously supplied in small quantities to the vent pipe 6.
is discharged from. In this way, the supply of the liquid R to be treated to the reaction tank 3, the removal of the generated gas, the discharge of the decomposed liquid, etc. are carried out continuously.

The liquid after the decomposition reaction in which the concentration of sodium azide has been reduced to the desired concentration by the decomposition reaction of NaN3 in the reaction tank 3 is transferred via the liquid transfer pipe 14 by the operation of the transfer pump 10. and are sequentially transferred to the waste liquid tank 8.

When a decomposition reaction of NaN3 contained in the liquid to be treated R is caused, NaN3 is removed from the liquid to be treated R from the beginning by the decomposition reaction based on the decomposition reaction formula described above.
is removed, while NaNO3 and H2O
will be generated and mixed into the alkaline cleaning waste liquid, but if, for example, sodium azide with a concentration of about 0.4 mol/liter is decomposed and removed to about 1/100th of its concentration, the liquid volume will be substantially reduced. There is almost no change in the above. In addition, NaNO3 is dissolved in water, etc., and is collected together with other liquid components as a radioactive waste liquid at an appropriate time.

<Other Embodiments> Hereinafter, other embodiments of the sodium azide decomposition apparatus according to the present invention will be described with reference to FIG.

In the example shown in FIG. 2 (another embodiment), compared to the example shown in FIG. By this operation, an appropriate amount of the liquid R for decomposition reaction is intermittently fed and temporarily stored, and during this temporary storage, the liquid R to be decomposed is subjected to a decomposition reaction. Therefore, the reaction tank 3 is set to have a relatively smaller volume than the liquid storage tank 1 (for example, set to a volume of 10% or less).

The sodium nitrite supply system 4 and the nitric acid supply system 5 supply sodium nitrite (NaNO2) and nitric acid (HNO3) as a decomposition reaction promoting liquid inside the reaction tank 3.
) is added and supplied in an amount commensurate with the temporary storage amount of the liquid to be treated R, thereby producing a decomposition action based on the above-mentioned decomposition reaction formula.

By the operation of the transfer pump 10, an appropriate amount of the liquid to be treated R is sent into the reaction tank 3 and temporarily stored, and then NaNO2 is used as a decomposition reaction accelerating liquid.
A saturated solution of R and HNO3 are supplied at intervals in this order to cause a decomposition reaction of the liquid R to be treated. In other words, by operating the sodium nitrite supply system 4, NaNO
2 is fed in a slightly larger amount than the specified amount (relative amount to HNO3) to mix it with the liquid to be treated R, and then, by operating the nitric acid supply system 5, the liquid to be treated in the reaction tank 3 is HNO3 is added to a mixture of R and a saturated solution of NaNO2 to cause a decomposition effect based on the decomposition reaction formula described above, and the generated N2 gas and N
2O gas is passed through the vent pipe 6 to the off-gas treatment system 1
6, and thereafter treated as off-gas. In this case, by feeding a slightly larger amount of NaNO2 than the specified amount, the decomposition reaction of NaN3 is made smooth.

The amount of gas generated during the decomposition reaction of NaN3 in the example shown in FIG. It is given by the amount of the liquid R stored in the reaction tank 3 and the amount of NaNO2 and HNO3 supplied. As mentioned above, when the amount of NaNO2 is slightly higher than the specified amount, by setting the amount of HNO3 to the specified amount, the amount of N in the liquid to be treated R in the reaction tank 3 can be reduced.
The entire amount of aN3 can be decomposed. Therefore, the storage amount of the liquid R to be treated in the reaction tank 3 (in other words, the amount of decomposition processed at one time) is set mainly in consideration of the amount of generated gas, that is, the influence on the off-gas treatment system 16.

The decomposition reaction of NaN3 in the reaction tank 3 takes place relatively quickly, so when a specified amount of the decomposition reaction accelerating liquid is gradually supplied to the reaction tank 3, the liquid to be treated R stored in the reaction tank 3 is As the sodium azide concentration gradually decreases, the amount of gas generated per unit time gradually decreases to zero. In this state, the liquid stored in the reaction tank 3, in other words, the liquid after the decomposition reaction, is transferred to the waste liquid tank 8 via the liquid transfer pipe 14 by the operation of the transfer pump 10, and the inside of the reaction tank 3 is emptied. state.

[0031] Then, by operating the transfer pump 10 again, an appropriate amount of the liquid to be treated R is sent into the reaction tank 3, and the process of performing the decomposition reaction treatment is repeated intermittently.

By repeating these decomposition reaction treatments in appropriate amounts depending on the volume of the reaction tank 3, the entire amount of sodium azide mixed in the liquid to be treated R is decomposed and its concentration becomes zero. Or, a state in which the sodium azide concentration is significantly reduced is reached.

In addition, in the present invention, the following technique can be adopted instead of the above-mentioned embodiment. (1) Each transfer pump 10 may be configured with a different type of pump. (2) Omitting the transfer pump 10 and supplying the liquid downstream using a siphon pipe or the like. (3) The quantitative supply means 2 may be constructed using another method.

[0034]

Effects of the Invention The first invention, that is, the sodium azide decomposition apparatus according to claim 1, includes a liquid to be treated storage tank for storing the liquid to be treated, a reaction tank into which the liquid to be treated is fed, and a decomposition reaction promoting device. A sodium nitrite supply system and a nitric acid supply system that supply the liquid, a vent pipe, a quantitative supply means that continuously supplies a small amount of the liquid to be treated, and a waste liquid tank into which the liquid after the decomposition reaction is continuously fed. Since it is equipped with the following, the following effects are achieved. (1) The liquid to be treated is continuously supplied to the reaction tank, so that sodium azide is decomposed little by little and can be reliably removed from the liquid to be treated, and the sodium azide concentration in the liquid to be treated can be reduced. By lowering the temperature, it is possible to improve the safety in processing the liquid after decomposition treatment. (2) By feeding the amount to be treated into the reaction tank little by little and performing decomposition reaction treatment continuously, the amount of gas generated can be suppressed and off-gas treatment performance can be improved. (3) By continuously decomposing the liquid to be treated,
By bringing a series of processes online, it is possible to simplify the sodium azide decomposition treatment facility. (4) The increase in liquid volume due to decomposition reaction treatment is suppressed, and the amount of radioactive waste liquid does not increase. In the second invention, that is, in the sodium azide decomposition apparatus according to claim 2, a to-be-treated liquid storage tank that stores the to-be-treated liquid;
A reaction tank that temporarily stores small amounts of the liquid to be treated, a sodium nitrite supply system and a nitric acid supply system that supply a decomposition reaction accelerating liquid, a vent pipe, and a waste liquid tank into which the liquid after the decomposition reaction is intermittently fed. Since it is equipped with the following, the following effects are achieved. (1) For the liquid to be treated stored in the reaction tank, the entire amount or an amount close to this amount of sodium azide is reliably decomposed and the sodium azide in the liquid to be treated is removed, and the objective is to be achieved. The safety after decomposition treatment can be improved by lowering the concentration to a certain level. (2) By intermittently feeding the liquid to be treated in small quantities into the reaction tank and subjecting it to decomposition reaction treatment, the amount of gas generated at one time can be suppressed and off-gas treatment performance can be improved. (3) By dividing the liquid to be treated into multiple portions and decomposing them in small amounts at intervals, it is possible to easily check the progress of the decomposition treatment and improve reliability during decomposition.

[Brief explanation of drawings]

FIG. 1 is a wiring diagram showing an embodiment of a sodium azide decomposition device according to the present invention.

FIG. 2 is a wiring diagram showing another embodiment of the sodium azide decomposition device according to the present invention.

[Explanation of symbols]

1 Liquid to be treated storage tank 2 Quantitative supply means 3 Reaction tank 4 Sodium nitrite supply system 5 Nitric acid supply system 6 Vent piping 7 Stirring device 8 Waste liquid tank 9 Transfer piping 10 Transfer pump (air lift pump) 11 Quantitative container 12 Liquid supply piping 13 Flow piping 14 Liquid transfer piping 15 Treated liquid supply system 16 Off-gas treatment system R Treated liquid X Waste liquid (radioactive waste liquid)

Claims (2)

[Claims] Claim 1: A liquid to be treated storage tank for storing a liquid to be treated containing sodium azide, a reaction tank connected to the liquid to be treated tank and into which the liquid to be treated is fed, and a reaction tank connected to the reaction tank and inside the liquid to be treated. A sodium nitrite supply system and a nitric acid supply system that continuously supply a decomposition reaction accelerating liquid to cause a decomposition reaction, a vent pipe that is connected to the upper space of the reaction tank and discharges gas, and a storage tank for the liquid to be treated. A quantitative supply means that is interposed between the tank and continuously supplies a small amount of the liquid to be treated to the reaction tank, and a waste liquid that is connected to the reaction tank and into which the liquid after the decomposition reaction is continuously fed. An apparatus for decomposing sodium azide, comprising: a tank. 2. A liquid to be treated storage tank for storing a liquid to be treated containing sodium azide, a reaction tank connected to the liquid to be treated and temporarily storing the liquid to be treated in small portions, and connected to the reaction tank. a sodium nitrite supply system and a nitric acid supply system that supply a decomposition reaction accelerating liquid to the temporarily stored liquid to be treated to cause a decomposition reaction; and a vent pipe that is connected to the upper space of the reaction tank and discharges gas. 1. An apparatus for decomposing sodium azide, comprising a waste liquid tank connected to a reaction tank and into which a liquid after a decomposition reaction is intermittently fed.