Keep things in order: the laser will make it safer to control the processing of nuclear waste

Russian scientists have proposed a laser method that allows faster and more accurate control of spent nuclear fuel reprocessing. The technology makes it possible to track the composition of solutions and the content of various components in them in almost real time without sampling and adding reagents. In the future, the development will make it possible to more quickly identify deviations in the technological process, reduce the number of operations with radioactive materials and reduce the formation of additional radioactive waste. At the same time, the new method should remain economically affordable, taking into account the cost of purchasing additional components and equipment maintenance, experts told Izvestia.

Optical control of nuclear waste recycling

Scientists from Sechenov University, together with colleagues from the Breakthrough Company and the High-tech Scientific Research Institute of Inorganic Materials named after Academician A.A. Bochvar (JSC VNIINM), have developed an optical approach for continuous monitoring of spent nuclear fuel reprocessing processes. It combines two spectroscopic methods and allows you to simultaneously monitor the state of the organic extractant, that is, a special substance that is used to extract uranium, and the composition of the aqueous phase without adding reagents and complex sample preparation.

The researchers proposed to control the two phases using different optical methods. The composition of the organic phase was evaluated using Raman spectroscopy, which analyzes the characteristic scattering of light by molecules. The method made it possible to determine the concentration of tributyl phosphate, one of the main extractants used in nuclear fuel reprocessing. The median measurement error was about 1%.

Laser spark emission spectroscopy (LIBS) was used to analyze the aqueous phase. A short laser pulse creates a microscopic plasma region in the liquid, and the composition of the solution and the concentration of the elements contained in it can be determined by the spectrum of its glow. When tested on model solutions with elements simulating fission products, the average measurement error was 4-8%.

— The main idea of the work is to receive information about two flows of the same technological process in almost real time. Raman spectroscopy shows what happens to the extractant, and LIBS shows which elements remain in the aqueous phase. In the future, such measuring modules can be moved outside the zone with a high radiation background, leaving only measuring cells in the process line. This will reduce the number of operations with samples and make it faster to notice deviations in the process," Gleb Budylin, Ph.D., head of the Laboratory of Clinical Biophotonics at the Institute of Regenerative Medicine at Sechenov University, told Izvestia.

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So far, the technology has been tested on laboratory installations and simplified model solutions. Real technological environments are much more complex: they contain more components at the same time, and optical signals can be influenced by acidity, radiolysis products, and other factors.

—The use of rapid online monitoring methods for spent nuclear fuel reprocessing products, which include the proposed development, not only reduces the process time, but also significantly reduces the dose burden on laboratory personnel, and reduces the amount of waste generated during the analysis process," said Deputy General Director of JSC VNIINM, winner of the National Award. in the field of future technologies, the "Challenge" is Mikhail Skupov.

The next stage is to test the method on multicomponent and irradiated media, as well as to adapt the equipment for remote work in real production conditions.

Prospects for a new method of non-destructive testing

Taking into account the complexity of the object and the risks involved in working with it, it is advisable to carry out analytical control using remote methods. They make it possible to monitor process parameters without exposing personnel to additional radiation exposure and observing established safety standards, said Stepan Kalmykov, Academician and Vice-President of the Russian Academy of Sciences, Head of the Department of Radiochemistry at the Lomonosov Moscow State University Faculty of Chemistry, winner of the National Prize in the Field of Future Technologies "Challenge".

"The proposed complex based on nonlinear optics methods, in particular laser spectrometry and laser breakdown, can be a solution to this problem," the scientist commented.

The concentration control method seems to be quite effective and simple, which is especially important when working with such objects, said Mikhail Volkov, a leading researcher at the Technetium Chemistry Laboratory of the Institute of Physics and Technology of the Russian Academy of Sciences.

"Such methods make it possible to control the processes of extraction and radiolytic aging of organic components in situ, that is, directly in the working environment," the specialist said.

The main advantage of online monitoring devices is that there is no need to take and prepare samples. This makes it possible to practically eliminate or significantly reduce the formation of secondary liquid radioactive solutions, which inevitably occur with traditional methods of destructive analysis, said Konstantin Dvoeglazov, an expert at JSC VNIINM.

According to him, when introducing the technology into production practice, difficulties may arise: in particular, it will be necessary to install additional measuring cells in technological equipment.

— Also, the exact cost of the devices is still unknown, taking into account the purchase of additional components and their maintenance, — the expert noted.

The results are published in the journal Applied Spectroscopy.