Nuclear safety

Nuclear accident - an accident resulting in damage to fuel elements (fuel rods), which exceeds the established limits of safe operation, and caused by nuclear physics processes due to a violation of control and management of a fission chain reaction in the core and / or the formation of a critical mass during refueling, transportation and storage fuel rods, as well as violation of heat removal from fuel rods.

NPP safety is ensured through the consistent implementation of the concept of defense in depth, based on the use of a system of physical barriers to the spread of radioactive substances and ionizing radiation, as well as a system of technical and organizational measures to protect physical barriers and maintain their effectiveness, in order to protect personnel, the public and the environment. environment.

The system of successive physical barriers of the NPP power unit includes a fuel pellet, a fuel rod cladding, a boundary of the primary coolant circuit, a hermetic enclosure of the reactor plant, and biological protection.

If it is revealed that any physical barrier or means of its protection provided for by the NPP project is inoperable, according to the conditions of safe operation, the operation of the NPP power unit at capacity is prohibited.

The defense in depth strategy is implemented at five levels:

-Level 1. Prevention of disruptions to normal operation;

-Level 2. Ensuring safety in case of violations of normal operation and prevention of emergency situations;

-Level 3. Prevention and elimination of accidents;

-Level 4. Management of beyond design basis accidents;

-Level 5: Emergency preparedness and response.

The main document that determines the safe operation of the reactor plant and the power unit as a whole is the technological procedure for the safe operation of the power unit (TRBE). The TRBE defines the limits and conditions for the safe operation of a power unit, contains the requirements and basic methods for the safe operation of a power unit, as well as the general procedure for performing operations related to the safety of a nuclear power plant.

The main state regulatory documents that define the requirements for ensuring nuclear safety of nuclear power plants are:

"Substantial regulations for the safety of nuclear power plants" NP 306.2.141-2008;

"Rules for Nuclear Safety of Reactor Installations of Nuclear Power Plants with Reactors with Water under Pressure" NP 306.2.145-2008;

"Vimogi security for the hour of occasion with nuclear fire" NP 306.2.221-2019;

“Technical operation of power stations and networks. Rules” GKD 34.20.507-2003, rev. 2019;

“Introduction to nuclear fire. Fire rewitching in the VVER-1000 reactor. Nomenclature of operational neutron-physical investigations and experiments” SE “NAEC “Energoatom”, 2018 SOW NAEK 064:2016.

On the basis of the above documents, a list of nuclear hazardous work (i.e., work that can lead to a nuclear accident) is developed and agreed upon in the prescribed manner, and relevant regulations, programs and instructions have been developed, compliance with which guarantees the accident-free performance of nuclear hazardous work at stages of transportation, reloading, operation and storage of nuclear fuel. The documentation must include information on the goals and conditions for conducting nuclear hazardous work, safety measures, the distribution of duties and responsibilities during the performance of work, the procedure for performing operations, as well as the criteria for and monitoring the successful completion of work.

Protected Equipment

The operating organization has defined special requirements for protected equipment.

Protected equipment is the minimum set of operable system equipment that ensures the operability of the system associated with the performance of critical safety functions for the shutdown state of the reactor plant.

The critical safety functions for the shutdown state of the reactor plant are:

subcriticality;

coolant supply;

heat sink from fuel assemblies.

Violation of critical safety functions refers to the inability of the system to perform the corresponding critical safety function. Protected equipment can be classified as part of the following systems:

-cooldown of the cooling pool;

-emergency cooling of the low-pressure core;

-emergency cooling of the high-pressure core;

-technical water supply of responsible consumers;

-instrumentation in the scope of protected equipment;

-reliable power supply;

-neutron flux control equipment, neutron flux control system during nuclear fuel reloading;-

-measuring the concentration of boron in the primary circuit;

-level control of pressurizer, reactor and spent fuel pool;

-temperature control at the exit from the core.

Physical barriers must be used to restrict access to the protected equipment area and prevent unauthorized contact with the protected equipment and its control keys. Protected equipment must be marked with placards reading “WARNING! EQUIPMENT IN WORK”, which are posted:

-for equipment;

-at the entrance to the premises with equipment, with a list of the protected equipment located in the premises;

-on switches, control cabinets.

If it is determined that the work along the line may affect the protected equipment or the place of work is located within the zone of the protected equipment, a note is made in the order in the column “Special conditions”: “Perform measures to prevent unintentional impact on the protected equipment”.

For personnel and contractors who perform work on protected equipment or in the area where protected equipment is located, targeted briefings on the safety of such work should be carried out.