Core vessel integrity

Besides it was required to develop and modify core components (fuel sub-assemblies, control rod guide tubes and control rods), to explore and modify electrical drives of sodium pumps, to modify a reactor refuelling system, to construct advanced failed fuel detection systems, to design and construct advanced reactor vessel integrity inspection systems, reactor vessel and auxiliary primary sodium pipeline displacement measurement systems, to remarkably improve water-sodium reaction detection systems of the water-sodium steam... 

The vessel extension allows also to reduce the neutron irradiation intensity of critical weld between the supporting shell and the shell of nozzles zone. Owing to this, the margin is increased for the vessel integrity under pressurised thermal shock. The vessel extension allowed to increase the coolant inventory between the core top and the lower generant of the inlet nozzle, that is, to improve the core cooling conditions under loss-of-coolant accidents. 

GV of small volume, ensuring prevention of core dry out during accidents with loss of the reactor vessel integrity. 

A reactor caisson and a system of water supply to the reactor caisson supporting the reactor vessel integrity and core melt in-vessel retention in severe beyond design basis accidents and... 

Maintaining the reactor vessel integrity and retaining core materials inside the vessel ... 

The capability to flood the reactor cavity prevents the failure of the reactor vessel given a severe accident. The vessel and its insulation are designed so that the water in the cavity is able to cool the vessel and prevent it from failing that is, in-vessel retention (IVR). By maintaining die vessel integrity, the core debris in the vessel eliminates the potential of a large release due to ex-vessel phenomena and its potential to fail the containment. 

Some Beyond Design Basis fault sequences could result in a core melt in such circumstances reactor vessel integrity and therefore prevention of a large release of radioactivity is maintained by flooding the reactor cavity with water, thereby cooling the vessel by evaporation within its insulation. Changes have been made to the flow path between the outside of the reactor vessel and the reactor vessel insulation, and testing has confirmed the robustness of the heat transfer required for in-vessel retention (Section IB. 1.5 ofReference 6.1). 

As a consequence of the extremely low probability of core damage and the capability of the MARS concept to confront even severe accidents while maintaining the reactor vessel integrity, licensing of a MARS NPP does not require any off-site emergency planning. 

The reactor vessel integrity will be retained by core cooling through the reactor vessel wall, even if severe accidents occur. 

Computer sensitivity studies show that hole size strongly affects the fraction of fission products released from the containment. The failure location determines mitigation due to release into another building in which condensation and particulate removal occur. The quantity released depends on the time of containment fails relative to reactor vessel failure. If containment integrity is maintained for several hours after core melt, then natural and engineered mechanisms (e.g., deposition, condensation, and filtration) can significantly reduce the quantity and radioactivity of the aerosols released to the atmosphere. 

Either to reduce the size so much that core melt accidents almost certainly can be contained by the vessel used (this involves maximum unit sizes of 50-100 MW in a traditional design, while the pebble-bed reactor may circumvent this limitation, if the integrity of the pebbles can be guaranteed),... 

A cut-away schematic of a BWR equipped with external coolant pumps is shown in Fig. 17. The recirculation system comprises the external piping, pumps, and valves located at the lower region of the vessel. The penetrations through the bottom of the vessel that contain the control rod drive mechanisms that are vital for controlling the reactivity of the core are not shown in Fig. 17. Of particular importance, as far as the integrity of the reactor is concerned, is the control rod drive tubes and related mechanisms, because they are in contact with the coolant and... 

The project of BRUS-150 integral type reactor of 500 MW thermal power and 150 MW electric power has been developed. The core, steam generators, pumps and all lead-bismuth loops are located in the reactor vessel, so that leak-proof vessel contains total amount of lead-bismuth. BRUS-150 reactor can be also used for transmutation of minor actinides accumulated in WWER type reactors and for utilization of weapon grade plutonium (for the main characteristics -see Table 2.2)... 

The design of RI SVBR-75 have two-circuit scheme of LBC heat removal for the primary circuit and steam-water for the secondary circuit. The integral design of the pool type is used for the RI primary circuit (see Fig. 2). It enables to mount die primary circuit equipment inside the one vessel. RI SVBR-75 includes the removable part with the core (the reactor itself), 12 SG modules with compulsory circulation over the primary circuit and natural circulation over the secondary circuit, 2 main circulation pumps (MCP) for LBC circulation over die primary circuit, devices for controlling the LBC quality, the in-vessel radiation protection qrstem and buffer reservoir which are the parts of the main circulation circuit (MCC). 

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