The operation of the electric furnace revealed a number of shortcomings in its design, primary among which were the less-than-optimal location of the electrode racks and their inefficient cooling. These factors led to the unplanned shutdown of the first electric furnace and the reconstruction of the backup unit.
Trial run operations in the vitrification section began in September 1990, and in January 1991 the rebuilt EP-500/1-r furnace was put back in operation. Tests on model solutions were conducted over the next six months, and in July 1991 the unit began processing high-level wastes, with these operations continuing for five and a half years. The second unit in the vitrification section, which included two electric furnaces—EP-500/3 and EP-500/4—was put into operation in 2001.
The design for the vitrification section is based on the process of electric arc melting of phosphate glass from waste solutions and flux additives in an electric glass furnace using direct electric heating. As illustrated in Figure 1, the basic technical outline of the process for the vitrification of high-level radioactive wastes includes the following elements:
solution preparation section, including a chain of various containment vessels
vitrification section, including an electric furnace with systems for solution correction, glass pouring, power supply, and cooling
gas treatment section, consisting of a number of gas cleaning devices and filters
transport section, including a moving conveyer, a chamber for the assembly of cases, and a protective shield
storage facility for the vitrified wastes
The technical process is carried out as follows. Liquid radioactive wastes from the repository go into a vessel where the solutions are prepared for processing. In this vessel the solution mixture is brought to a specific standard through the addition of calculated amounts of phosphoric acid and sodium nitrate. After being prepared in this manner, the solution is transferred through a number of vessels into an automated displacement elevator, from which the solution flows into the electric furnace directly onto the surface of the molten glass. At the same time that the radioactive waste solution is released into the furnace, the solution is dosed with a reducing agent (ethylene glycol) in order to create a loose foamy layer on the molten surface and reduce unwanted movement of radionuclides.
When the solution contacts the molten surface, there follows a sequence of processes by which the solution is turned to steam, the salts are dried and denitrated, and the oxides are melted. The resulting steam gas mixture moves through a gas pipe into the gas treatment system, which consists of the following devices: a sparger-refrigerator, crude and fine purification filters, ruthenium tetroxide extraction columns, and a fine purification filter and an absorption