Kozloduy NPP is exploring the possibility of storing the Russian TVSA-12 heat-separating cartridges in its spent fuel repository

The possibility of storing the spent heat-separating cartridges TVSA-12 in a spent fuel repository (SFR) is among the topics discussed by the Kozloduy NPP, writes the specialized publication atominfo.ru. The development is based on a presentation given at the Bulatom conference and is published on the organization's website - https://www.bulatom-bg.org/.

Russian TVSA-12 fuel has been used at the sixth unit of the plant since 2016, when the first batch of these cartridges was loaded into the reactor core. This enabled the unit to operate at 104% power over a 4-year fuel cycle with an annual recharge of 42 cartridges.

In 2020, the first batch of spent TVSA-12 was removed from the unit. They are now in the cooling pool of the power unit. In the future, a task has been set to move the spent fuel cartridges TVSA-12 to the water storage for spent fuel of the plant.

Water reservoir

The initial schematic design of the water SFR was developed by the Soviet Institute "Glavtechstroyproekt" in 1968.

The need for a water storage facility at the Kozloduy NPP was confirmed 10 years ago, based on the requirements for the return of spent nuclear fuel from Bulgaria to the Soviet Union.

Spent fuel from the VVER-440 units could be stored in the pools for up to three years, while the available containers allowed the transport of fuel only after five years of storage, which led to the requirement to create an intermediate storage facility in a water pool at the site.

The Soviet VNIPIET and the Bulgarian company Energoproekt were responsible for the final development of the storage project. The storage facility's capabilities were expanded for spent nuclear fuel from the VVER-1000.

The water reservoir was built in the southwestern part of the site. It has four pools filled with water, which also contain containers with spent fuel cartridges, the publication states.

Justification for storage

The use of the water storage (SFR) for intermediate storage of spent TVSA-12 cartridges requires a preliminary safety justification.

A report on the topic of the Bulatom conference at the beginning of June was presented by Venelin Rusanov, chief expert in the Nuclear Energy Directorate at the Abilico company.

The rapporteur's conclusions are generally expected - no blocking factors have been found from the point of view of safety for the storage of spent TVSA-12.

For example, you can look at the table with calculations for storage options. It can be seen that the effective multiplication factor in none of the variants exceeds 0.92. It should be noted that the calculations used the model TVCA-12 B46H6, that is, cartridges with the highest enrichment.

In the data provided by the lecturer are also estimates of the impact of various errors, calculations of energy releases and activities, as well as doses to personnel.

He noted that for all possible water storage configurations of the TVSA-12 spent fuel cartridges, the value for the various filling configurations of the SFR fuel storage pool would not exceed 0.95.

The energy release and activity during aqueous storage of container 37/3 with 12 spent fuel cartridges TVCA-12, which have been stored in the storage pool for six years, will not exceed the limits for the aqueous storage for GHG. Collective and individual doses for staff will also not exceed established limits.

Thus, it can be concluded that the spent TVSA-12 cartridges, after being in the spent fuel pool of Unit 6 of the Kozloduy NPP, will be moved to a water storage facility at the plant.

But what will be done with these tapes further remains unknown, the publication concludes.