Installation has begun of a new electric furnace – the EP 250/6 – at Russia’s Mayak Production Association in Ozersk. This is part of a major upgrade of Mayak’s technology for high-level waste (HLW) processing involving vitrification. Its previous electric furnace – the EP-500/5 – was closed in 2020 after four years of operation during which 141m Curies of activity contained in liquid solutions obtained from used fuel was vitrified.

In 2021 Mayak developed design documentation for two new unique types of melter to provide its radiochemical facility with modern HLW vitrification units. These are an EP-250/6 type melter for producing alumino-phosphate glass and a small-sized EPM type melter for producing borosilicate glass. The designs were developed based on the experience of operating five EP-500 electric furnaces, as well as prototypes that had been tested on the experimental stands of the enterprise.

The new vitrification complex at the radiochemical plant was designed by JSC RaoProekt. The design capacity of the new complex is 490 tonnes of vitrified HLW a year. Commissioning was scheduled for 2028 but work is significantly ahead of schedule.

The original vitrification complex was put into commercial operation in 1987. The vitrification method involves melting alumino-phosphate glass in electric furnaces where it is mixed with solutions of radioactive waste and fluxing additives. The glass melt containing HLW is then poured into special containers where it solidifies to form of a mechanically strong and chemically stable monolith. The filled containers are placed in metal cases. After three containers are filled, the canister is closed with a lid, sealed and transported to the special storage site for vitrified HLW.

The last EP-500/5electric was put into operation at the end of 2016 in workshop 4 of the radiochemical plant. The previous four electric furnaces have been mothballed at the installation site after their service life expired. The new complex will include a unified transport and technological system associated with the main technological redistribution of radiochemical production. All the ceramic melters in it will be replaceable – when they are worked out, they will be dismantled, fragmented, packed in containers and transferred to storage at the Federal State Unitary Enterprise National Operator RAO.

The new complex is designed to solve environmental problems related to the immobilisation of liquid radioactive waste (RW) that was accumulated in the early years of the enterprise. It will use two types of ceramic melters: high-performance ones, such as EP-250 electric furnaces for producing alumino-phosphate glass, and small ones for producing borosilicate glass. The high-performance ones are intended for processing liquid HLW accumulated from the previous activities of the enterprise, as well as from processing special types of used nuclear fuel. The small ones will be used for vitrification of waste from reprocessing used fuel from power reactors.”

Mayak was originally established in the late 1940s to produce plutonium for the Soviet nuclear industry. The main directions of the current activities include: fulfilment of the state defence order for the production of components of nuclear weapons; transportation and processing of used fuel; production and sale of isotope products; mechanical engineering and instrument making; research and production activities; and the solution of nuclear legacy problems.

Like weapons production sites worldwide, there was little attention to safety in the early years and unregulated disposal of HLW left large areas highly contaminated. This was exacerbated in 1957 by the explosion of a waste tank. Mayak has since faced a huge remediation task, with which it is making positive headway. In 2015, after years of work and huge expense it completed the mothballing and remediation of Lake Karachai on the site where HLW had been dumped and which had been described by the Washington, DC-based Worldwatch Institute as the most polluted spot on Earth.

As Alexander Akintsev, head of the department for the development and reconstruction of the radiochemical plant, explained, instead of constructing a new building, equipping it with equipment with engineering systems, the new electric will be mounted in the same building, where its predecessors are mothballed, as part of the technical re-equipment of the existing glazing complex. This will not only reduce the time needed to put the furnace into operation, but also significantly save the resources of the enterprise.

The EP-250/6 power project was developed by Mayak’s Design & Design Department (UPC – Upravleniem po Proektirovaniu y Konstruirovaniu) together with specialists from the design department of the radiochemical plant. “The work is carried out according to industrial standards in a small room and in cramped conditions, but is not interrupted for a minute,” said Viktor Aksenov, master of construction and installation work. “We are participating in a unique project for the first time and we often have to find solutions to non-standard situations. So far we're ahead of the schedule.” Commissioning of the EP-250/6 is now expected in 2025.

Image: Installation of the EP 250/6 electric furnace at Russia’s Mayak Production Association in Ozersk (courtesy of Rosatom)