Innovations in glass: Rosatom scientists immured radioactive waste in a borosilicate matrix

An innovative unit for the vitrification of radioactive waste has been put into operation at the Siberian Chemical Combine. It was designed at VNIINM and the Radium Institute.

For many years, in special furnaces at Mayak, waste from spent nuclear fuel processing has been enclosed in a matrix of aluminophosphate glass. But these are highly active materials, and during the processing of regenerated uranium, medium-active ones are formed. Mayak furnaces vitrify about 80 kg of radioactive waste per hour. So much is not generated from recycling. We needed less productive and more compact equipment. In addition, borosilicate glass is refractory - it requires a temperature much higher than aluminophosphate. A new technical solution was proposed by scientists VNIINM them. Bochvar and the Radium Institute. Khlopin.

Cold - hot

For the radiochemical plant of the Siberian Chemical Combine, scientists proposed a liquid radioactive waste vitrification unit with induction heating. The technology of induction melting in a hot crucible is not new in principle, it has been used in France for more than 40 years, it has been mastered in the UK and India. “But in our country, this is the first implementation at the existing radiochemical production,” emphasizes Ilya Skrigan, head of the Laboratory of Technology and Solidification Processes of the Radium Institute. “For Russia, this is important in terms of technical development in general and RW vitrification technology in particular.”

The peculiarity of the Russian installation is that it has two different melting units: with a hot crucible and with a cold one. Nodes can turn on in turn and simultaneously. The hot crucible was developed at the Radium Institute, and the cold crucible at VNIINM. The Bochvarians also designed peripheral and supporting systems: batch evaporation, preparation and batching units, a transport system, gas cleaning systems, remote automated control, sealing, decontamination and certification units for containers with glass, etc.

“The unit not only solves the problems of the Regenerate project, but is also being tested on medium-level waste,” says Dmitry Suntsov, head of the high-level waste management department at VNIINM. “And at the experimental demonstration power complex of the Siberian Chemical Plant, we will have to work with highly active ones.”

The hot crucible is heated to 1150 °C by an alternating magnetic field. “Liquid RW and granules of glass-forming components — steklofrits“ are loaded in portions, — Ilya Skrigan describes the process. — The crucible transfers heat to the glass, radioactive waste is included in the glass matrix, forming a single structure that is safe for the environment. The melt is drained into a receiving can, the can is sealed, decontaminated, certified and sent to storage.”

The cold crucible remains cold even during the hottest moments of work. “Melting is carried out in an apparatus with water-cooled walls. The electromagnetic field through the gaps in the crucible delivers heat directly to the molten glass,” says Dmitry Suntsov.

Melt test

It is important that the metal from which the cold crucible is made is not exposed to the corrosive glass melt. “When the melt approaches the water-cooled walls of the melter, it solidifies and ceases to be corrosive,” explains Dmitry Suntsov. “The frozen thin layer of glass on the walls of the melter is called the skull, it does not affect the melting in any way, but protects the crucible from corrosion.”

The melter with a hot crucible also has advantages: it is easier to operate, the energy consumption is three to four times less than that of a unit with a cold crucible. The Radium Institute had difficulties at first. “We used cast crucibles, and they deformed during the tests,” recalls Ilya Skrigan. — We switched to crucibles made by welding. The experimental sample easily withstood 300 hours of testing. The full resource is not yet clear, but we expect about 5,000 hours.”

Both units will be used at the Siberian Chemical Combine. Operation will show which is more reliable. “Specialists of the radiochemical plant are already working independently with the installation, and we consider this a great merit of the plant's staff,” says Dmitry Suntsov. “Large enterprises struggle to innovate, but in our case, everything went great.”

Source: https://strana-rosatom.ru/