RITM-200N | SMRs & ADVANCED REACTORS


core reactivity control and compensation during load following operations and as a result, generation of liquid radioactive waste is restricted.


● Two independent electromechanical systems for reactivity control have been envisaged in the RITM- 200N design which are based on diverse operating principles. A fast-acting emergency protection (EP) system ensures injection of absorber rods (AR) into the core throughspring action (the drives are released from electromagnets as they are de-energized) and a system of compensation of reactivity by ARs of compensating grids (CG). The insertion of CGs is driven by gravity. An electro-mechanical system of control includes six drives with ARs for EP and twelve drives with ARs for CG. The electro-mechanical system performs control functions during normal operation and protective safety functions by tripping the reactor on an emergency signal.


The reactor is placed in a leak-tight steel envelope (the primary containment) to localise any possible radioactive releases. It is designed for an internal pressure of up to 0.9 MPa (abs). The dimensions of the steel envelope for the RITM-200N are Φ8.7m× 21m. This leak-tight steel envelope of the reactor plant is a cylindrical protective shell with an elliptical bottom and a neck in the upper part with a detachable connection to the elliptical lid. The internal volume of the steel envelope is divided with biological protection blocks into two rooms: the equipment room and the reactor room. The main volume is occupied by the equipment room, below which there is a reactor room under the biological protection blocks. Division into two separate sealed rooms makes it possible to carry out repairs or replace equipment. The supporting foundation structure for the reactor


vessel, the equipment of the primary circuit systems and dry biological protection units is the metal water shield tank, which contains caissons to accommodate the integral reactor, pressurizer system equipment, and equipment of the purification and cooling down system. In the upper part of equipment room, the heat removal


system equipment, such as the heat exchangers, fans and ducts, are located. Access to the equipment room is provided from a sanitary access control room. The equipment room also has hatches for inspecting the reactor room using periscopes and manholes.


Safety in design The safety design philosophy of the RITM-200 reactor is based on achieving higher reliability by implementing the


following principles: ● Defense-in-depth ● Inherent self-protection ● Redundancy and diversity ● Physical separation and independence ● Protection against external events ● Elimination of common-cause failure ● Incorporation of proven features


The “defense-in-depth” principle is the cornerstone of the safety principles adopted in the RITM-200, with the implementation of several levels of protection including successive barriers against the release of radioactive substances to the environment. This principle is applied for three fundamental safety functions – reactivity control,


cooling the fuel and confining radioactive substances with the aim of ensuring protection of population, personnel and the environment. This includes accident prevention as well as accident mitigation. The principle calls for a more extensive consideration of the possibilities of multiple failures and the use of diversified means to fulfil the three fundamental safety functions mentioned above. The inherent safety properties of the reactor are aimed at limiting the energy release, rise in pressure and temperature, heating rates and extent of the fuel damage. They also prevent the development of initiating events and accident conditions, limit their consequences without the participation of operator for a long time. The inherent safety features incorporated into the design


are as follows: ● Negative temperature coefficient of reactivity of the fuel and coolant which limits power rise


● High thermal conductivity of fuel composition that eliminates hot spots


● High thermal capacity of the primary circuit which increases the time available for safety systems to respond


● Integral reactor configuration almost eliminates large break loss of coolant accidents


An adequate combination of redundancy and diversity has been adopted in the design. Spatial separation has been applied for the safety systems, while support functions such as power, control, cooling are independent to the largest possible extent. Special emphasis has been placed on the redundancy and diversity of electrical power supplies. External events such as a possible aircraft crash, seismic events, flood, tornado, or fire have also been considered for the safety structures. The combination of both passive and active safety systems ensures a higher level of safety for a wide range of postulated accident scenarios. RITM-200N includes the following safety systems to


mitigate design basis accidents: ● For emergency shutdown of the reactor and maintaining


it in a subcritical state, the design envisages two independent electromechanical shutdown systems - active and passive.


● Heat removal from the reactor with intact primary circuit is carried out with an active system through the heat exchanger of the purification and cooling loop (through the intermediate circuit of the safety system and the process water of safety system as well as with a passive heat removal system (PHRS).


● Heat removal from the reactor in case of a loss of coolant accident (LOCA) is carried out through an active safety injection system; an active cooling system through a process condenser, as well as with a passive pressurised hydraulic accumulators and a passive heat removal system (PHRS).


● Heat removal from the spent fuel pool is ensured through an active cooling system for the spent fuel pool.


● Release of fission products is kept within established limits with the help of the steel enclosure of the reactor, the hermetic containment of the reactor building and passive autocatalytic recombiners (PAR).


The following safety systems are designed to mitigate beyond design basis accidents (design extension conditions):


www.neimagazine.com | May 2024 | 39


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53