According to an embodiment, a nuclear plant has: an outer well; an in-Containment Atmosphere Dilution System to inject a gas that has a low concentration of oxygen in the outer well into a containment vessel; an accumulator containing pressurized oxygen therein; and a passive containment cooling system including: a scrubbing pool arranged in the outer well; a cooling water pool installed above a dry well and the outer well; a heat exchanger partly submerged in a cooling water; a wet well gas supply pipe that is connected to an inlet plenum of the heat exchanger at one end and connected to a wet well gas phase at the other end; and a gas vent pipe that is connected to an outlet plenum of the heat exchanger at one end and is submerged in the scrubbing pool at the other end.

According to an embodiment, a nuclear plant has: an outer well; an in-Containment Atmosphere Dilution System to inject a gas that has a low concentration of oxygen in the outer well into a containment vessel; an accumulator containing pressurized oxygen therein; and a passive containment cooling system including: a scrubbing pool arranged in the outer well; a cooling water pool installed above a dry well and the outer well; a heat exchanger partly submerged in a cooling water; a wet well gas supply pipe that is connected to an inlet plenum of the heat exchanger at one end and connected to a wet well gas phase at the other end; and a gas vent pipe that is connected to an outlet plenum of the heat exchanger at one end and is submerged in the scrubbing pool at the other end.

A containment vessel has an inner shell covering a reactor pressure vessel and an outer shell forming an outer well which is a gas-tight space covering the horizontal outer periphery of the inner shell. The inner shell has a first cylindrical side wall surrounding the horizontal periphery of the reactor pressure vessel, a containment vessel head which covers the upper part of the reactor pressure vessel, and a first top slab connecting in a gas-tight manner the periphery of the containment vessel head and the upper end of the first cylindrical side wall. The outer shell has a second cylindrical side wall surrounding the outer periphery of the first cylindrical side wall, and also has a second to slab connecting in a gas-tight manner the vicinity of the upper end of the second cylindrical side wall and the first cylindrical side wall.

A containment vessel has an inner shell covering a reactor pressure vessel and an outer shell forming an outer well which is a gas-tight space covering the horizontal outer periphery of the inner shell. The inner shell has a first cylindrical side wall surrounding the horizontal periphery of the reactor pressure vessel, a containment vessel head which covers the upper part of the reactor pressure vessel, and a first top slab connecting in a gas-tight manner the periphery of the containment vessel head and the upper end of the first cylindrical side wall. The outer shell has a second cylindrical side wall surrounding the outer periphery of the first cylindrical side wall, and also has a second to slab connecting in a gas-tight manner the vicinity of the upper end of the second cylindrical side wall and the first cylindrical side wall.

A passive containment cooling system (PCCS) condenser, for reducing some non-condensable gases in the PCCS, includes a first and a second stage condenser that each include channels in fluid communication between an inlet and an outlet header. The inlet header of the first stage condenser is configured to receive a fluid mixture through a first inlet opening. The channels are configured to condense water from the fluid mixture flowing through the channels from the inlet header to the outlet header, respectively, of the first and second stage condenser. The PCCS condenser includes a catalyst in at least one of the outlet header of the first stage condenser or the inlet header of the second stage condenser. The catalyst catalyzes a reaction for forming water from hydrogen and oxygen in the fluid mixture. The outlet header of the second stage condenser is in fluid communication with a combined vent-and-drain line.

A passive containment cooling system (PCCS) condenser, for reducing some non-condensable gases in the PCCS, includes a first and a second stage condenser that each include channels in fluid communication between an inlet and an outlet header. The inlet header of the first stage condenser is configured to receive a fluid mixture through a first inlet opening. The channels are configured to condense water from the fluid mixture flowing through the channels from the inlet header to the outlet header, respectively, of the first and second stage condenser. The PCCS condenser includes a catalyst in at least one of the outlet header of the first stage condenser or the inlet header of the second stage condenser. The catalyst catalyzes a reaction for forming water from hydrogen and oxygen in the fluid mixture. The outlet header of the second stage condenser is in fluid communication with a combined vent-and-drain line.

Hydrogen explosion safety in premises of the containment dome (CNT) at nuclear power plants (NPP) with water-cooled power reactor (VVER). The method for ensuring hydrogen explosion safety at nuclear power plants comprises ventilation of premises of the nuclear reactor premises and hydrogen recombination in premises of the nuclear reactor premises by its catalytic oxidation. In accordance with the declared solution, a reflector is placed on the way of potentially emergency propagation of a pressure hydrogen-containing steam-gas jet, apertures are made in the walls between premises of the nuclear reactor containment dome with a size equal to minimum 35% of the surface area of the said walls, while excess heat is withdrawn in areas of potential localization of hydrogen-containing steam-gas mixture burning sources.

Hydrogen explosion safety in premises of the containment dome (CNT) at nuclear power plants (NPP) with water-cooled power reactor (VVER). The method for ensuring hydrogen explosion safety at nuclear power plants comprises ventilation of premises of the nuclear reactor premises and hydrogen recombination in premises of the nuclear reactor premises by its catalytic oxidation. In accordance with the declared solution, a reflector is placed on the way of potentially emergency propagation of a pressure hydrogen-containing steam-gas jet, apertures are made in the walls between premises of the nuclear reactor containment dome with a size equal to minimum 35% of the surface area of the said walls, while excess heat is withdrawn in areas of potential localization of hydrogen-containing steam-gas mixture burning sources.

An igniter apparatus which generates a high speed buoyancy induced vortex to funnel hydrogen and air from the surrounding onto the igniter core where an igniter core heats up to the auto ignition temperature by the exothermic catalytic oxidation of hydrogen on its surface. Water (vapor) is formed as the product, which inhibits the oxidation reaction, if not stripped away from the catalyst surface. The high velocity of the vortex ensures the stripping of the boundary layer of steam that is formed by the reaction, thus ensuring more active sites are available for hydrogen oxidation. The vortex is formed by channeling an upward draft into a vortex by guided fins. The upward draft is formed by a plate, which is also coated with a hydrogen recombination catalyst. The plate becomes hot by the same catalytic oxidation reaction in the presence of air containing hydrogen.

An igniter apparatus which generates a high speed buoyancy induced vortex to funnel hydrogen and air from the surrounding onto the igniter core where an igniter core heats up to the auto ignition temperature by the exothermic catalytic oxidation of hydrogen on its surface. Water (vapor) is formed as the product, which inhibits the oxidation reaction, if not stripped away from the catalyst surface. The high velocity of the vortex ensures the stripping of the boundary layer of steam that is formed by the reaction, thus ensuring more active sites are available for hydrogen oxidation. The vortex is formed by channeling an upward draft into a vortex by guided fins. The upward draft is formed by a plate, which is also coated with a hydrogen recombination catalyst. The plate becomes hot by the same catalytic oxidation reaction in the presence of air containing hydrogen.