CN111474234A - Method for analyzing content of trace plutonium in large amount of uranium in nuclear fuel post-processing flow - Google Patents

Abstract

The invention belongs to the technical field of analytical chemistry, and relates to an analysis method for content of trace plutonium in a large amount of uranium in a nuclear fuel post-processing flow, which sequentially comprises the following steps of (1) taking a certain volume of sample, adding concentrated nitric acid to adjust the concentration of the nitric acid to 1-2 mol/L, (2) adding a sodium nitrite solution into the sample, uniformly mixing and placing for a period of time, (3) adding an extracting agent into the sample for extraction, centrifugally separating, removing a water phase and retaining an organic phase, (4) washing the organic phase for 2-5 times by using a washing solution, removing the water phase after each washing, retaining the organic phase, (5) diluting the organic phase by using isopropanol, and analyzing the diluted organic phase by using ICP-MS (inductively coupled plasma Mass Spectrometry) provided with an organic sample introduction system.

Description

A method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process

technical field

The invention belongs to the technical field of analytical chemistry, and relates to a method for analyzing the content of trace plutonium in a large amount of uranium in a nuclear fuel reprocessing process.

Background technique

The control requirements for plutonium in uranium products in nuclear fuel reprocessing are very strict. In the uranium products in the post-processing process, the concentration of uranium is several tens of grams per liter, and the ratio of uranium to plutonium exceeds 1×10 ⁹ . A large amount of uranium interferes greatly with the analysis of trace amounts of ²³⁹ Pu. To accurately determine the plutonium concentration of the sample solution, it is necessary to The uranium and plutonium can be separated after a strict uranium and plutonium separation pretreatment process. Therefore, a good pretreatment process for the separation of uranium and plutonium is the key to the accuracy of the analytical data. However, there are many samples that need to be analyzed in nuclear fuel reprocessing. Some intermediate samples and samples at all levels are limited by technology and equipment, and the sample sampling amount is small, which cannot meet the volume requirements of the analyzed samples.

At present, there are two main methods for the analysis of plutonium in uranium products: one is the radioactivity method, and the other is the ion exchange-mass spectrometry method.

The radioactivity method uses TTA extractant to separate plutonium from a large amount of uranium, and takes an appropriate amount of the extractant to make an alpha radiation source on a special stainless steel plate, and then uses alpha energy spectrum to measure the activity of plutonium-239. This method requires a sample volume of 5-50ml, and the sample volume is large; the pretreatment process of uranium and plutonium separation requires means such as evaporation, extraction and concentration, and the operation steps are complicated; due to the self-absorption of α caused by the salt-containing components of the radioactive source, the The measurement result of the activity is low, so the analytical error is large and the sensitivity is low (the analytical error is greater than 10%, and the analytical lower limit is 1×10 ^-9 g/L) (see: [1] Guo Kuisheng, Wu Jizong, Liu Huanliang. Anion chromatography separation- Determination of trace amounts of Pu in high-level radioactive waste by α counting method[J]. Atomic Energy Science and Technology. 1997, 31(5): 435; System design and application [D]. Beijing: China Institute of Atomic Energy, 2005.).

The ion-exchange-mass spectrometry method is that after adjusting the acid value of the sample, the tetravalent plutonium is adsorbed through the ion-exchange column to realize the separation of uranium and plutonium, and then the plutonium is desorbed from the ion-exchange column with dilute nitric acid, and finally the concentration of plutonium is analyzed by mass spectrometry. The pretreatment process of the separation of uranium and plutonium in this method includes adsorption, leaching, elution and other processes. The process is complicated, and the pretreatment of a single sample takes 2-4 hours; the sample consumption is large, requiring 5-50ml; the sample with low plutonium concentration , during the adsorption, washing and elution process of ion exchange, a part of plutonium will be lost, resulting in low analysis results (see: Li Lili, Li Jinying, Zhao Yonggang, etc. Separation of trace plutonium in uranium matrix [J]. Nuclear Chemistry and Radiochemistry, 2007, 29(3):135-140.).

Therefore, the above methods all have the disadvantages of large analysis error, large sampling amount, complicated separation process and long operation time when analyzing nuclear fuel reprocessing process samples.

The full name of TTA is ² -thiopheneformyl trifluoroacetone, which is widely used in the extraction and separation of plutonium in nitric acid medium. Taking advantage of the extraction characteristics of TTA in a 1mol/L nitric acid system, plutonium can be extracted with TTA, and more than 99% of plutonium can be separated from uranium.

Inductively coupled plasma mass spectrometry (ICP-MS) is an instrument that can be used to determine ultra-trace elements and isotope ratios. Its advantages are: very low detection limit (up to ng/ml or lower), small matrix effect, The spectral lines are simple, and many elements can be determined simultaneously. An ICP-MS equipped with an organic sampling system can analyze trace elements in organic phase samples.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for analyzing the trace plutonium content in a large amount of uranium in the nuclear fuel reprocessing process, so that the trace plutonium content in the large amount of uranium in the nuclear fuel reprocessing process can be carried out simply, quickly, accurately, with less sample volume and less interference. analysis.

In order to achieve this purpose, in a basic embodiment, the present invention provides a method for analyzing the content of trace plutonium in a large amount of uranium in a nuclear fuel reprocessing process, the analysis method sequentially comprising the following steps:

(1) Take a certain volume of sample, add concentrated nitric acid to adjust the concentration of nitric acid to 1-2mol/L (sample sampling volume is generally 1-5ml; adding concentrated nitric acid to adjust acid to 1-2mol/L is because the extraction agent TTA-xylene In the solution with 1-2mol/L nitric acid concentration, the extraction and distribution ratio of plutonium is the highest);

(2) Add sodium nitrite solution to the sample, mix well and place for a period of time (TTA-xylene only extracts tetravalent plutonium, and the oxidative property of sodium nitrite can keep plutonium in tetravalent);

(3) After adding an extractant to the sample for extraction, centrifuge, remove the water phase, and retain the organic phase (remove the raffinate water phase, because uranium only exists in the water phase, and removing the water phase can realize the separation of uranium and plutonium) ;

(4) Wash the organic phase with the washing solution 2-5 times, remove the aqueous phase after each washing, and retain the organic phase (the washing solution is used to wash and extract the organic phase, which can reduce the uranium entrained in the organic phase and reduce the interference of uranium on plutonium). );

(5) The organic phase was diluted with isopropanol, and the diluted organic phase was analyzed by ICP-MS equipped with an organic sampling system.

In a preferred embodiment, the present invention provides a method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (1), a 1-5ml sample is taken, and concentrated nitric acid is added to a concentration of 8-12mol /L, the concentration of uranium in the sample is 50-90g/L, and the concentration of plutonium is 1.5×10 ^-6 -5×10 ^-8 g/L.

In a preferred embodiment, the present invention provides a method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (2), 0.03-0.07ml of 0.5-1.5mol/L of 0.03-0.07ml is added to the sample Sodium nitrite solution, mix well and leave for 2-10 minutes.

In a preferred embodiment, the present invention provides a method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (3), the extraction agent is 0.4-0.6mol/LTTA-xylene Solution, add volume of 0.4-0.6ml.

In a preferred embodiment, the present invention provides a method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (3), the extraction time is 7-15 minutes, and the centrifugal separation is 2000-4000 rpm Centrifugation for 1-3 minutes at a rotational speed of 1/min (extraction for 7-15 minutes is to ensure sufficient extraction of Pu(IV) by TTA-xylene).

In a preferred embodiment, the present invention provides a method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (4), the washing solution is 0.8-1.2 mol/L nitric acid, and each The washing time is 4-6min.

In a preferred embodiment, the present invention provides a method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (5), the dilution ratio is 10-50 times.

In a preferred embodiment, the present invention provides a method for analyzing trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (5), an aqueous plutonium standard solution of isopropanol is prepared for ICP-MS analysis work curve drawing.

In a preferred embodiment, the present invention provides a method for analyzing the content of trace plutonium in a large amount of uranium in a nuclear fuel reprocessing process, wherein in step (5), the organic sampling system is supplied with oxygen (the introduction of oxygen The organic phase can be fully burned. On the one hand, the ICP-MS flame can be stabilized and not easily extinguished. On the other hand, due to the sufficient combustion of the organic phase, the carbon atoms are turned into carbon dioxide, so as to avoid the blockage caused by carbon deposition at the outlet of the instrument, and improve the ICP-MS performance. sensitivity).

The beneficial effect of the present invention is that, by using the method for analyzing the trace plutonium content in a large amount of uranium in the nuclear fuel reprocessing process of the present invention, it is simple, fast and accurate to carry out the nuclear fuel reprocessing process trace in a large amount of uranium with less sample amount and less interference. Analysis of plutonium content.

The analysis method of the present invention can meet the requirement of analyzing the concentration of trace plutonium in the sample containing a large amount of uranium in the post-processing process. The analytical lower limit of plutonium analysis by this method can reach 1×10 ^-10 g/L, the analytical error is 5%, and the analytical precision is much higher than that of the radioactive analysis method; the required sample volume is only 0.5-5ml; one batch of uranium-plutonium The separation process can operate 8-16 samples at the same time, and the entire uranium and plutonium separation pretreatment process takes no more than 1 hour. The analyst can complete the pretreatment separation of several samples at a time according to the analysis requirements (in a thermal experiment, Analysts can pretreat up to 40 samples in an 8-hour working time), so compared to radioanalytical methods and ion exchange methods, the preprocessing separation time is greatly shortened, the sample consumption is greatly reduced, the loss of plutonium is small, and the analysis error somewhat reduced.

The analysis method of the invention selects TTA extractant to realize the separation of uranium and plutonium, and then analyzes the plutonium by inductively coupled plasma mass spectrometry equipped with an organic phase sampling system, which greatly shortens the pretreatment time for the separation of uranium and plutonium, improves the analytical sensitivity, and reduces the sample consumption. quantity. The method successfully determined the trace plutonium concentration in a batch of samples containing a large amount of uranium in the thermal experiment of the reprocessing process.

Detailed ways

The specific embodiments of the present invention will be further described below with reference to the examples.

Example 1:

(1) Take 5ml of simulated sample (wherein the concentration of uranium is 50g/L, and the concentration of plutonium is 5.12×10 ^-8 g/L), and 1.2ml of 10mol/L nitric acid is added to make the solution acidity reach 2mol/L;

(2) add 0.05ml 1mol/L sodium nitrite solution, mix and place for 2 minutes, and oxidize plutonium to tetravalent;

(3) adding extractant 0.5mol/LTTA-xylene solution 0.5ml to extract Pu(IV) for 10min, centrifuging for 2min at 3000 rpm, discarding the water phase to realize the separation of uranium and plutonium;

(4) washing the organic phase three times with 1 mol/L nitric acid for 5 minutes each time to elute a small amount of uranium entrained in the organic phase;

(5) Take 0.1ml of organic phase and dilute it to 2.5ml with isopropanol, analyze the plutonium concentration with ICP-MS equipped with an organic sampling system (preparing the aqueous plutonium standard solution of isopropanol and carry out the working curve of ICP-MS analysis) Drawing, the organic sampling system was fed with oxygen), the analyzed plutonium concentration was 5.26×10 ^-8 g/L, and the relative standard deviation was 2.73%.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their technical equivalents, the present invention is also intended to include such modifications and variations. The above-mentioned embodiments or implementations are merely illustrative of the present invention, and the present invention may also be implemented in other specific forms or other specific forms without departing from the gist or essential characteristics of the present invention. Accordingly, the described embodiments are to be regarded in all respects as illustrative and not restrictive. The scope of the present invention should be indicated by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims (9)

1. A method for analyzing the content of trace plutonium in a large amount of uranium in a nuclear fuel reprocessing process is characterized by sequentially comprising the following steps:

(1) taking a certain volume of sample, and adding concentrated nitric acid to adjust the concentration of the nitric acid to 1-2 mol/L;

(2) adding sodium nitrite solution into the sample, uniformly mixing and standing for a period of time;

(3) adding an extracting agent into a sample for extraction, performing centrifugal separation, removing a water phase, and retaining an organic phase;

(4) washing the organic phase with a washing solution for 2-5 times, removing the aqueous phase after each washing, and retaining the organic phase;

(5) the organic phase was diluted with isopropanol and the diluted organic phase was analyzed by ICP-MS equipped with an organic sampling system.

2. The method according to claim 1, wherein in the step (1), 1 to 5ml of the sample is taken, and concentrated nitric acid is added to the sample in an amount of 8 to 12 mol/L, the sample has a uranium concentration of 50 to 90 g/L, and a plutonium concentration of 1.5 × 10^-6-5×10^-8g/L。

3. The analytical method according to claim 1, wherein in the step (2), 0.03 to 0.07ml of 0.5 to 1.5 mol/L mol sodium nitrite solution is added to the sample, and the mixture is left to stand for 2 to 10 minutes.

4. The analytical method according to claim 1, wherein in the step (3), the extractant is a 0.4 to 0.6 mol/L TTA-xylene solution, and the volume of the extractant added is 0.4 to 0.6 ml.

5. The analytical method of claim 1, wherein: in the step (3), the extraction time is 7-15 minutes, and the centrifugal separation is carried out for 1-3 minutes at the rotating speed of 2000-4000 revolutions per minute.

6. The analytical method according to claim 1, wherein in the step (4), the washing solution is 0.8 to 1.2 mol/L of nitric acid, and each washing time is 4 to 6 min.

7. The analytical method of claim 1, wherein: in the step (5), the dilution multiple is 10-50 times.

8. The analytical method of claim 1, wherein: and (5) drawing a working curve for ICP-MS analysis of the aqueous plutonium standard solution prepared into the isopropanol.

9. The analytical method of claim 1, wherein: and (5) introducing oxygen into the organic sample introduction system.