NRA: The storage of spent nuclear fuel should not cause concern among the population

The storage and disposal of nuclear fuel should not cause concern among the population. The possibilities for storing the spent nuclear fuel at the site of the Kozloduy NPP are until 2032. The National Repository for Low and Medium Level Storage of Radioactive Waste is also in the process of being put into operation. By the end of 2026, the waste from the repository in Novi Khan should also be removed, which will subsequently remain only as a facility as a source of ionizing radiation, which will be under the control of the relevant authorities. Experts from the Nuclear Regulatory Agency (NRA) commented on this to journalists. The management of the nuclear waste located on the site of the nuclear power plant is carried out by the operator of the nuclear facilities, and outside these sites - by DP RAO.

The difficult geopolitical situation raises more and more questions regarding the spent nuclear fuel from units 5 and 6 of the Kozloduy NPP. However, there are solutions, and trusting some self-proclaimed "experts" often does not solve, but inflames the situation. It is also important to know that the process of building a nuclear power plant, and in particular the 7th and 8th units on the territory of Kozloduy, contains in itself the issue of the storage, processing, and subsequently the burial of nuclear waste and in especially spent nuclear fuel (SNF).

Spent nuclear fuel can be stored temporarily, but European and international requirements recommend a reprocessing and disposal process. This is contained in the nuclear fuel cycle itself (closed and open). The closed nuclear cycle covers the processes of extraction, processing and conversion of uranium, uranium-235 enrichment, nuclear fuel production, operation, temporary storage of spent nuclear fuel (SNF), operation, SNF processing, disposal), explained the deputy chairman of AAR Borislav Stanimirov.

The temporary or intermediate storage of nuclear fuel is carried out in the near-reactor pools, with the minimum aging time being 3 or 4 years, depending on the type of nuclear cartridges. In addition, there is also temporary storage in the so-called wet DHW depending on the resource of the facility. Temporary storage also envisages storage for SNF with "dry storage" type technology in CONSTOR 440 containers (dry COG), where the storage period is 50 years.

Regardless of which of the options will be chosen, it is necessary to carry out the process of burying the nuclear waste in the future, Stanimirov said. For the time being, care must be taken of the highly vitrified waste, which is to be returned after processing by the Russian side. According to Stanimirov, the spent nuclear fuel can be stored in the wet HOG until 2032. Until then, however, there must be a solution for dry storage. In response to a question, he specified that according to the contract with the Russian company TVEL, our country can export SNG for processing in 2025 or in the years after. Of course, everything depends on the geopolitical situation, which at the moment remains quite complicated. The last fuel removal took place in 2022, when 192 cartridges were exported.

The removal process itself is very complicated. It is not by chance that it is recorded that it can only take place twice a year, explained Stanimirov. On the occasion of the upcoming replacement of the fuel of the sixth unit of the plant with that of the French Framatom, and in response to a question, he specified that, in principle, there are talks about processing the fuel of VVER-1000, but the process itself is very long, and it is yet to be decided still the very process of storage, processing, burial. The chairman of the NRA, Tsanko Bachiiski, explained that there is a special methodology for VVER-1000, which is yet to be adopted, and it foresees the volume, method of waste return, activity, etc... "We can safely keep our fuel for many years, creating conditions for safe storage," Bachiiski assured. He was adamant that the storage of spent nuclear fuel is now safe and there is enough time to decide on final disposal.

Meanwhile, according to the latest annual report of the NRA, at the end of last year, a total of 122 baskets (covers) containing 924 cartridges from VVER-1000 reactors and 1268 cartridges from VVER-440 reactors are stored underwater in the HOG. 19 "Constor 440/84" containers containing a total of 1,596 VVER-440 reactor cassettes are stored in HSSOYAG.

In the past period, a total of 120 spent fuel cartridges were transported from units 5 and 6 of the Kozloduy NPP for storage in the HOG.

According to Stanimirov, the process of reprocessing nuclear fuel includes disassembling the fuel cartridges, extracting uranium and plutonium from the fuel tablets, as well as storing the extracted nuclear material, producing nuclear fuel with the extracted enriched uranium, producing nuclear fuel containing plutonium (MOX fuel). This is followed by vitrification of highly active radioactive waste (RAW) obtained during the processing of the fuel pellets.

Long-term storage or the so-called "burial" of SNF before the actual process goes through a stage of vitrified high-level waste storage in a deep geological disposal facility. The disposal of the spent fuel cartridges after their interim storage, without reprocessing, in a facility for deep geological disposal can also be carried out.

Meanwhile, NRA experts dispelled doubts regarding the popular compatibility of "American" and "Russian fuel" disposal. As they explained, here the dependence is not on the "homeland" of the fuel, but on the activity contained in the waste, as well as on a number of other elements that are understandable to the experts, but not to the people who use them depending on their political views.

Boryana Chakalova from the Directorate of Radiation Protection at the NRA, for her part, focused on the world burial methods, which provide for surface burial, silo storage and trench storage. She focused on the experience of Japan, France, South Africa, the United States, South Korea and Spain with the repositories they built for surface burial. At the moment, however, all countries, in order to guarantee security in the long term, are directed to the so-called mining-type storage, which are being built in three stages, the most advanced at the moment being Finland. This type of storage can be built depending on what the rock type is - crystalline (granitic) rocks, sedimentary rocks and salt formations. The research process itself takes a considerable amount of time. As an example, she gave Finland with the Onkalo repository. According to Chakalova, Finland started the site selection process as early as 1983-1985, and out of 100 specified sites, the selection was reduced to only 6, so that in the period from 1992 to 2000, they would go through two stages of characterization. Through a research laboratory in the Onkalo repository itself in Finland, it was only in 2004 that real activity began, which continues to this day. There is one research laboratory at a depth of 420 meters underground and another at a depth of 520 meters. The actual commissioning is only planned for 2026.

Chakalova specified that the issue of so-called drilling burial is currently being studied, but it is still experimental and is being worked on.

In our country, there is still no in-depth study on the disposal of nuclear waste, but it is time to start one. It is assumed, but only to the extent that there are opportunities for such in the northwestern part of Bulgaria due to the type of rock formations.

As for the storage of medium and low-level waste in Bulgaria, the chairman of the NRA, for his part, specified that this issue can now be considered resolved. Bachiyski specified that this will take place at the "Radiana" site, which is located on the territory of the "Kozloduy" NPP. All medium and low-level waste from the entire territory of Bulgaria will be stored there. There is also an option for storage expansion. An operating license is expected next year. The opening itself is planned to take place towards the end of this year at best.