Shelter Safety System

The constructions and systems constructed at the Shelter during the period of beyond design basis accident management, which happened on April 26, 1986 at the Unit No 4 of Chernobyl NPP are designed for mitigation of its consequences.

These constructions and systems were created in specific conditions. They carry out safety functions and current operation of the Shelter.

For the Shelter object the following safety functions are determined:

Control (management) function of the Shelter

Control of the Shelter object state as well as its radiation impact to the staff, population and environment.
The control function of the fuel-containing materials’ state includes the control of the following parameters in rooms with fuel-containing materials:
density of neutron flux;
exposure dose rate of gamma radiation.

For the performance of this function the following systems are used:

information-measuring system “Finish-R”;
control system of fuel containing materials “Signal”

The control function of the other Shelter state parameters includes the control of hydrogen concentration and deformation (displacement) of building constructions too.

Scheme of the dust suppression system

Confining function of the Shelter

Prevention and limitation of spread of radioactive substances located in the Shelter object and ionizing radiations beyond the fixed confines.
For the performance of this function the following systems (components) of the Shelter are used:
modernized dust suppression system;
system of exhaust ventilation and gas purification system;
system of liquid radioactive waste collection and removal.

Protective function of the Shelter

Insurance of the fuel containing materials condition, including prevention of self-sustained chain reaction initiation, when systems (components) are able to perform the confining function.
The function of FCM sustenance in sub-critical state includes the supply of neutron-absorbing solutions in rooms containing FCM to the surface of FCM aggrelations. For its performance the following systems are used:
system of nitrate gadolinium solution supply;
installation of operative injection of neutron-absorbing solution;
modernized dust suppression system.

Supporting function of the Shelter

Support of constructions and systems (components) carrying out the safety functions by power, operating environment and making of other conditions necessary for their operation.
Main technological functions for the Shelter object systems:
control of the Shelter object state, including the control of fuel-containing materials state and control of the radiation-technological, environmental and non-spreading of radioactive contaminations.
retention of radioactive substances and ionizing radiation in the fixed confines and quantities;
maintenance of fuel-containing materials in the sub-critical state;
provision of operated constructions and systems (components) of the Shelter object with power, operating environment and creation of conditions for their operation;
mitigation of consequences of potential accidents.

Main systems and constructions of the Shelter that carry out the safety functions
The following is related to the systems and constructions carrying out the safety functions:
systems of fuel-containing materials control IMS “Finish-R”, FCM CS “Signal”
control system of gas-aerosol release activity through the ventilation stack-2;
control system of hydrogen concentration in the Unit 4 CH;
localizing construction;
dust suppression system;
system of exhaust ventilation and gas purification;
systems of LRAW collection and removal;
system of nitrate gadolinium solution supply;
installation of operative injection of neutron-absorbing solution
fire fighting system;
power supply system.

Besides, the following systems are staying in the suspended condition at the Shelter:
cooling of the Unit No 4 reactor sub-foundation plate;
temperature control of the Unit No 4reactor sub-foundation plate;
intake ventilation PR-1.
This page presents a description of the Shelter systems carrying out the safety function as well as other Shelter object systems.
Systems described above, were created at the Shelter during management of a beyond design basis accident; they were meant for mitigation of its consequences. Systems were created under specific conditions, caused by the extreme urgency of work implementation, insufficient information about the systems layout, radiation danger in the places intended for assemblage and actuation, etc. They possess shortages, indicated in the wording of section; as a result of it, they do not meet the requirements for safety in full.

At present, body of the Shelter systems provides with observance of limits for Shelter safe operation, partially reasoning from substantively technical abilities, but not from safety criteria, which have not been esmimated for Shelter yet. Therefore, they can not be considered the safety related systems, but operate a function of safety, i.e., special concrete goals and methods of their realization within the obtaining a common purpose – the Shelter object safety operation.