Recently, specialists of the State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS) jointly with the representatives of the Society for Facilities and Reactors Safety of Germany (GRS) presented a jointly developed draft report "Analysis of Factors Determining Shelter Object Safety" as part of the new Safe Confinement".

The new Safe Confinement (NSC) is designed on the basis of the boundary conditions for the current and potentially hazardous impacts of the Shelter object.

If the boundary conditions are met, the environment is protected; the permissible release of radioactive substances from the NSC does not exceed the norm. The same is applicable to the radiation protection of Arch employees.

Current impact of the Shelter object is represented by the radioactive substances release into NSC, release of ionizing radiation into workplaces and the temperature and humidity regime. Potential impact is criticality occurrence, collapse of structures, fire and explosion.

"The Shelter object condition can be considered as safe if its safety indicators do not exceed the limiting conditions", - said Sergey Kondratiev, the head of SSTC decommissioning department. "Together with GRS, we collected all the limiting design conditions and developed approaches to definition of criteria for the further safe operation of the facility."

During the project implementation, risks were identified that may occur in process of the Shelter object unstable structures dismantling.

The work will be performed with the dust suspension inside the Arch. At that time ventilation will function with the use of filters. At the same time, air contamination within the main volume of the Arch should not exceed 210 Bq/m3. Release of radioactive substances from the Shelter object in its steady state should be much less; its limiting value makes 30 Bq/m3. "If filters are not used – the release under such contamination will be hazardous", - said Sergey Kondratiev.

According to the expert, in rooms and in zones with high surface contamination it is necessary to take all possible actions to prevent the spread of dust.

At the same time, the Center’s expert asserts, that no significant changes in release of ionizing radiation from the Shelter object are forecasted over the time. NSC design provides the shielding of personnel workplaces. In addition, adds Sergei Kondratyev, to prevent possible moisture condensation on the Arch internal lining, it is stipulated to heat air in the annular space of NSC.

"During the project, we also identified those risks that require further investigation" - continues expert of SSTC NRS. In particular, these are the risks of internal structures collapse in case of an earthquake, as well as a fire occurrence of in the Shelter premises with high degree of contamination.

In general it is proposed to establish to the design following types of criteria: safety of the building structures, fuel-containing materials, liquid radioactive waste accumulations within the Shelter; prevention of air contamination; explosion and fire safety; forecasting of the Shelter object safe state.

To date, works to complete New Safe Confinement construction and prepare its commissioning are underway. The preliminary date is established as 30 November 2017.

The report "Analysis of the factors determining the Shelter object safety as part of the New Safe Confinement" was positively assessed by the meeting participants. In future this document will be used in the Safety Analyzes performance, the Shelter object investigation plans development, as well as in the regulatory documents development.

Material of SSTC NRS