Patent Number: 
Section: claims

1. An operating floor confinement that constitutes part of a nuclear plant, the nuclear plant including:a reactor pressure vessel that houses a core;a dry well housing the reactor pressure vessel and having a top slab;a wet well housing a suppression pool in its lower portion and a gas phase in its upper portion;a LOCA vent pipe connecting the dry well and the suppression pool;a containment vessel that includes at least the dry well, the LOCA vent pipe and the wet well;a containment vessel head;a main steam line; anda reactor building including an equipment area that houses a section of the main steam line, whereinthe operating floor confinement is fluidically isolated from the equipment area of the reactor building and forms a pressure boundary that has pressure resistance that is at least the same level as that of the containment vessel and a leakage protection function, wherein the operating floor confinement comprises:a reactor well that surrounds the containment vessel head and is in contact with the containment vessel via the containment vessel head,an operating floor that is provided around the reactor well, the operating floor having a larger area than a cross-sectional area of the dry well, wherein the operating floor constitutes a part of the pressure boundary and has no staircase, elevator, elevator shaft, or equipment hatch that communicates with the equipment area of the reactor building,a sidewall that surrounds the operating floor, the sidewall being arranged wider than the cross-sectional area of the dry well, wherein the sidewall constitutes a part of the pressure boundary and has no blowout panel,a ceiling that is provided on an upper portion of the sidewall, constitutes a part of the pressure boundary and has no blowout panel,a fuel pool extending horizontally beyond the top slab of the dry well and constituting a part of the pressure boundary,a dryer and separator pit extending horizontally beyond the top slab of the dry well and constituting a part of the pressure boundary,an equipment hatch that is provided on the sidewall,an air lock that is provided on the sidewall,a penetration line that passes through the sidewall, andan isolation valve that is provided on the penetration line. 2. The operating floor confinement according to claim 1, further comprisingan external venting system that includes an external vent pipe, which penetrates the pressure boundary of the operating floor confinement and communicates with outside, and an external vent isolation valve, which is provided on the external vent pipe in order to vent, to the outside, atmosphere of the operating floor confinement. 3. The operating floor confinement according to claim 1, further comprising:a reactor well overflow section that is provided between the reactor well and the fuel pool;a fuel pool overflow section that is provided on the fuel pool; andan operating floor drain pit that is provided inside the operating floor confinement in such a way as to make a dent in part of the operating floor. 4. The operating floor confinement according to claim 3, further comprising:a drain pipe having one end opened inside the operating floor drain pit while another end is connected to the wet well; anda drain isolation valve that is provided on the drain pipe. 5. The operating floor confinement according to claim 4, further comprising:a connecting vent pipe having one end opened in the atmosphere of the operating floor confinement while another end is connected to the containment vessel; anda connecting vent isolation valve that is provided on the connecting vent pipe, whereinan opening of the connecting vent pipe inside the operating floor confinement is located higher than an opening of the drain pipe inside the operating floor drain pit. 6. The operating floor confinement according to claim 1, wherein a portion of the sidewall includes the airlock and the equipment hatch, whereinthe portion of the sidewall is shared with an auxiliary access building that is built adjacent to the reactor building, whereineach floor of the auxiliary access building communicates with each floor of the equipment area of the reactor building,an elevator is provided in the auxiliary access building to allow operators to go upstairs and downstairs,a staircase is provided in the auxiliary access building to allow operators to go upstairs and downstairs,an equipment access lock is provided on a wall of the auxiliary access building,a shaft is provided in the auxiliary access building adjacent to the equipment access lock and through each floor of the auxiliary access building,an equipment hatch is provided on a top floor of the auxiliary access building, whereinequipment, as well as workers, can be moved in and out to the operating floor confinement via the auxiliary access building. 7. The operating floor confinement according to claim 6, whereinthe auxiliary access building further includes a blowout panel on a sidewall of the auxiliary access building. 8. A nuclear plant comprising:a core;a reactor pressure vessel that houses the core;a dry well housing the reactor pressure vessel and having a top slab;a wet well housing a suppression pool in its lower portion and a gas phase in its upper portion;a LOCA vent pipe connecting the dry well and the suppression pool;a containment vessel that includes at least the dry well, the LOCA vent pipe and the wet well;a containment vessel head;a main steam line;a reactor building including an equipment area that houses a section of the main steam line; andan operating floor confinement that is fluidically isolated from the equipment area of the reactor building and forms a pressure boundary that has pressure resistance that is at least the same level as that of the containment vessel and a leakage protection function, wherein the operating floor confinement includes:a reactor well that surrounds the containment vessel head, constitutes the pressure boundary and is in contact with the containment vessel via the containment vessel head,an operating floor that is provided around the reactor well, the operating floor having a larger area than a cross-sectional area of the dry well, wherein the operating floor constitutes a part of the pressure boundary and has no staircase, elevator, elevator shaft, or equipment hatch that communicate with the equipment area of the reactor building,a sidewall that surrounds the operating floor, the sidewall being arranged wider than the cross-sectional area of the dry well, wherein the sidewall constitutes a part of the pressure boundary and has no blowout panel,a ceiling that is provided on an upper portion of the sidewall, constitutes a part of the pressure boundary and has no blowout panel,a fuel pool extending horizontally beyond the top slab of the dry well and constituting a part of the pressure boundary,a dryer and separator pit extending horizontally beyond the top slab of the dry well and constituting a part of the pressure boundary,an equipment hatch that is provided on the sidewall,an air lock that is provided on the sidewall,a penetration line that passes through the sidewall, andan isolation valve that is provided on the penetration line.