JPH0664189B2 - Waste solvent treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention dissolves spent nuclear fuel generated in a nuclear power plant or the like in an aqueous solution of nitric acid in a reprocessing step, and then uses a solution of tributyl phosphate and a diluent to produce U , A method for treating a waste solvent for recovering a highly pure diluent from a waste solvent containing tributyl phosphate extracted with a radioactive substance such as Pu and a diluent.

More specifically, spent nuclear fuel generated in a nuclear power plant, etc. is dissolved in a nitric acid aqueous solution in the reprocessing step, and then a solution consisting of tributyl phosphate and a diluent is added.
When recovering a diluent from a waste solvent containing tributyl phosphate extracted with radioactive materials such as U and Pu and a diluent by using a thin film evaporation type distillation apparatus, the distillate vapor from the distillation apparatus is partially condensed, By refluxing to the waste solvent supply section of the distillation apparatus, it is possible to recover a high-purity diluent without lowering the distillation rate, and to provide a method for treating a waste solvent which enables a smooth distillation operation.

[Conventional technology]

Spent nuclear fuel, which is generally generated in nuclear power plants, is dissolved in an aqueous nitric acid solution in the reprocessing step, and then tributyl phosphate (hereinafter abbreviated as “TBP”) and a diluent (dodecane, kerosene, C _{10 to} C ₁₄ hydrocarbons). U, Pu, etc. are extracted by a solvent consisting of By the above operation
TBP and diluent solvent are nitric acid, decomposition products of TBP or diluent (dibutyl phosphate, monobutyl phosphate, dodecanone, dodecanol, phosphate ester, hydrocarbon) due to radiation and heat, and complex with dibutyl phosphate or phosphate ester, etc. And the inorganic substances (Zr, R
h, Nb, Ru, U, Pu, etc.), water, nitric acid, etc. (hereinafter “degradation products”)
That is) will be contained in trace amounts.

It can be easily carried out by using a thin film evaporation type distillation apparatus as a method for recovering a diluent from a waste solvent containing TBP that easily causes thermal decomposition as described above and a degradation product that promotes thermal decomposition of TBP. Found.

However, in the method in which the waste solvent is simply supplied to the thin film evaporation type distillation apparatus and distilled, a high-purity diluent cannot be recovered unless multiple thin film evaporation type distillation apparatuses are installed and multistage distillation is performed. Therefore, there was a problem that enormous equipment cost and operation cost were required.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned problems, to collect a high-purity diluent without lowering the distillation rate with a single thin-film evaporation type distillation apparatus, and to carry out the distillation operation smoothly. The purpose of the present invention is to provide a method for treating a waste solvent that can be used.

[Means for solving problems]

That is, the present invention, the spent nuclear fuel generated in a nuclear power plant or the like is dissolved in a nitric acid aqueous solution in the reprocessing step,
Then, a solution of tributyl phosphate and a diluent is used to extract radioactive materials such as U and Pu, and then tributyl phosphate,
When recovering the diluent from the waste solvent containing the diluent by using a thin film evaporation type distillation apparatus, the distillate vapor from the distillation apparatus is condensed and is allowed to reflux to the waste solvent supply section of the distillation apparatus. A method for treating a waste solvent is provided.

Here, it is necessary to use a thin film evaporation type distillation apparatus which has a short residence time of the solvent in the apparatus, has no local abnormal retention, and has a high evaporation efficiency. As for this device, in view of the fact that it has been put to practical use as a production device and the results of its use, the Chemical Engineering Handbook (December 25, 1980, published by Maruzen Co., Ltd.), page 406. It is preferable to use an agitated thin film evaporation type distillation apparatus as described in FIG.

The dephlegmator has a simple structure, does not abnormally retain condensate, and has a good cooling effect. For example, the Chemical Engineering Handbook (December 1980)
25th. Issued by Maruzen Co., Ltd.) Use the structure as described on page 365.

In the treatment of the waste solvent, as shown in FIG. 1, a stirring thin film evaporation type distillation apparatus 1 having a rotating rotor 1a, a partial condenser 2 having a reflux rate adjusting valve 2a, and a pre-compressor 3 are used. The distillate vapor of the distillation apparatus 1 is supplied to the partial condenser 2, the liquid condensed by the partial condenser is supplied to the waste solvent supply section of the distillation apparatus 1, and the undivided vapor is supplied to the pre-condenser 3. It is preferable to use an apparatus having a configuration in which the pipe is connected to

Purity of the diluent (low boiling point component of the decondensate) by refluxing a part of the decondensate to the waste solvent supply part of the distillation device and recovering the remaining part of the decondensate together with the distillate. The recovery rate of the diluent can be improved by increasing the recovery rate of the diluent and recovering the decrease in the recovery amount of the diluent by recovering the remainder of the partial contraction liquid.

The partial condensation reflux rate is the amount of partial condensation reflux liquid / (the amount of partial condensation reflux liquid + the amount of partial condensation distillate), and when the value is 0.1 or less, the reflux ratio is too small to improve the separation performance by partial condensation reflux. I can't. Also, 0.7
In the above case, the partial condensed reflux liquid is evaporated in the distillation apparatus from the supply amount of the waste solvent, and the evaporation capacity of the distillation apparatus cannot be effectively utilized.

Therefore, it is preferable to set the partial condensation reflux rate in the range of 0.1 or more and 0.7 or less.

When the partial condensation temperature is less than 30 ° C, the partial condensation reflux rate is 1.00 even if the distillation pressure in the stirred thin film evaporation type distillation apparatus is 0.5 torr, so the total condensation is completed, so the objective of improving the separation performance by partial condensation reflux is achieved. Can't do it. Also, 200 ℃
If the distillation pressure exceeds 20 torr, the partial reflux ratio is 0
Therefore, the partial reflux does not occur at all, and it becomes impossible to maintain the above range of the optimal partial reflux rate.

Therefore, the partial condensation temperature is preferably set in the range of 30 ° C or higher and 200 ° C or lower.

〔Example〕

Distillation conditions Distillation equipment inner diameter: 50mm Distillation temperature: 150 ℃ Distillation pressure: 5torr Rotor speed: 450R.PM Under the above conditions, using the device shown in Fig. 1, 70% by volume of dodecane and TBP The results shown in Table 1 could be obtained by distilling Samples 1 to 3 in which the fractional reflux ratio was changed with the waste solvent containing 30% by volume and 0.1% by volume or less of the deteriorated product.

As is clear from the above results, the partial condensation reflux rate was 0.23 to
When distilled at 0.54, it was possible to recover dodecane with a purity of about 99% or higher.

On the other hand, in the distillation method without partial reflux, only dodecane having a purity of about 90% could be recovered as shown in sample 4 in Table 1.

〔The invention's effect〕

In the present invention, when the diluent is recovered from the waste solvent containing tributyl phosphate, the diluent and the like as described above by using the thin film evaporation type distillation apparatus, the distillate vapor from the distillation apparatus is condensed and the distillation is performed. By refluxing the waste solvent in the apparatus, the following effects can be obtained.

(1) It is possible to recover a high-purity diluent such as dodecane without lowering the distillation rate by using one thin film evaporation type distillation apparatus.

(2) Since the distillation temperature, which is a distillation condition, can be set low and the distillation pressure can be set high, the diluent can be recovered without causing decomposition of TBP.

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing one embodiment of an apparatus for carrying out the processing method of the present invention. 1: Thin film evaporation type distillation device, 2: Partial condenser, 1a: Rotor, 2a: Reflux control valve, 3: Total condenser.

Claims (3)

[Claims] 1. A thin film evaporation type distillation apparatus from a waste solvent containing tributyl phosphate and a diluent, in which spent nuclear fuel is dissolved in an aqueous nitric acid solution in a reprocessing step, and then radioactive materials are extracted with a solution consisting of tributyl phosphate and a diluent. A method for treating a waste solvent, characterized in that when the diluent is recovered by using, the distillate vapor from the distillation apparatus is partially condensed and refluxed to the waste solvent supply section of the distillation apparatus. 2. The method according to claim 1, wherein a part of the partial condensed liquid is refluxed to the waste solvent supply part of the distillation apparatus, and the remaining part of the partial condensed liquid is collected together with the distillate. Waste solvent treatment method. 3. The partial condensation reflux ratio (ratio of the partial condensation reflux liquid amount to the total amount of the partial condensation reflux liquid amount and the partial condensation distillate amount) of the reflux is
The method for treating a waste solvent according to claim 1 or 2, wherein the method is 0.1 to 0.7.