Abstract: A nuclear reactor cooling system comprises a containment area, an In-Containment Refueling Water Storage Tank (IRWST), and a discharge pipe. The containment area is formed to enclose a reactor coolant system. The IRWST is disposed outside the containment area. The discharge pipe discharges steam from the containment area to refueling water in the IRWST when an accident occurs. A steam intake pipe has one end in fluid connection with an upper space of the IRWST, and another end in fluid connection with a radioactive substance reduction tank which stores cooling water. The steam intake pipe allows steam to flow from the upper space of the IRWST into the cooling water in the reduction tank.

Abstract: A nuclear reactor containment atmospheric filter system includes dedicated piping, valves, a control system, and a chemical injection system. An outlet of the piping can release atmospheric effluent from a reactor containment vessel into a lower portion of a spent fuel pool. The chemical injection system can release a chemical into the spent fuel pool to facilitate a reaction with the released atmospheric effluent. The reaction can assist in neutering deleterious environmental impact of the atmospheric effluent. The filter system can filter and cool contaminated air and steam vapor released from the reactor containment vessel, and prevent vessel overpressure and radioactive release.

Abstract: A hot water storage device having a vessel includes a first section formed from a molded material and a second section formed from a molded material. An open end of the first section is sealingly engaged with an opposing open end of the second section to form the vessel. The first and second sections each have a generally cylindrical body portion and a closed end, comprising a head portion. The vessel includes a water inlet aperture molded into the first or second section and a water outlet aperture molded into the first or second section and wherein the inlet and outlet apertures are located on the body portion proximal to a tangent line between the body portion and the head portion.

Abstract: Internal head vents are usable in nuclear reactors and include piping inside of the reactor pressure vessel with a vent in the reactor upper head. Piping extends downward from the upper head and passes outside of the reactor to permit the gas to escape or be forcibly vented outside of the reactor without external piping on the upper head. The piping may include upper and lowers section that removably mate where the upper head joins to the reactor pressure vessel. The removable mating may include a compressible bellows and corresponding funnel. The piping is fabricated of nuclear-reactor-safe materials, including carbon steel, stainless steel, and/or a Ni—Cr—Fe alloy. Methods install an internal head vent in a nuclear reactor by securing piping to an internal surface of an upper head of the nuclear reactor and/or securing piping to an internal surface of a reactor pressure vessel.

Abstract: A nuclear reactor includes a pressure vessel and a nuclear reactor core disposed in the pressure vessel. A subterranean containment structure contains the nuclear reactor. An ultimate heat sink (UHS) pool is disposed at grade level, and an upper portion of the subterranean containment structure defines at least a portion of the bottom of the UHS pool. In some embodiments, the upper portion of the subterranean containment structure comprises an upper dome, which may protrude above the surface of the UHS pool to define an island surrounded by the UHS pool. In some embodiments, a condenser comprising a heat exchanger including hot and cold flow paths is disposed inside the subterranean containment structure; and cooling water lines operatively connect the condenser with the UHS pool.

Abstract: A power module includes a containment vessel completely submerged in a pool of liquid, and a support structure located at or above an approximate midpoint of the containment vessel, or center of gravity of the power module. The power module is supported by the support structure in combination with a buoyancy force of the pool of liquid acting on the containment vessel.

Abstract: Heat from an ex-vessel mass of core material is removed to cooler regions of a containment envelope via liquid and/or vapor phase transport. Various aspects provide for contacting the ex-vessel core material with a material having properties including melting point, boiling point, and condensation kinetics such that condensation of the material in cooler regions of the containment envelope is at least as fast as evaporation of the material due to heat absorption from the core material and associated species.

Abstract: A pressure vessel, including: a body portion; and an inclined nozzle projecting from the body portion along an axis inclined relative to an inner surface of the body portion, wherein: a through hole of a circular section is formed through both the body portion and the inclined nozzle. At an intersecting portion between the inner surface of the body portion and a surface surrounding the through hole, there are formed round portions. The radius of each of the round portions at two positions in a major axis direction is smaller than the radius of each of round portions.

Abstract: In a nuclear reactor building of a steel plate concrete structure that houses a pressure containment vessel formed with a plurality of penetration ports penetrating the pressure containment vessel on the periphery thereof and includes a biological shielding wall disposed outside the pressure containment vessel. The pressure containment vessel is vertically divided into a plurality of blocks so that each of the blocks has one or more pressure containment vessel penetration ports arranged on a same horizontal plane, and the reactor building including the biological shielding wall is divided into a plurality of modules by the horizontal plane.

Abstract: The invention relates to a sealing element fastening system for at least one sealing element of a pressure vessel, which has at least one opening and a sealing part, in particular a cover, provided for the opening. In the operating state of the pressure vessel each sealing element is at least partially inserted in an accommodating groove in the sealing part and corresponding sealing element fastening devices are positioned in each case in an indentation in the sealing part. The indentations are in each case sealed by a fill element in the operating state of the pressure vessel.

Abstract: Disclosed is an advanced process that relates to the enhanced production of energy using the integration of multiple thermal cycles (Brayton and Rankine) that employ multiple fuels, multiple working fluids, turbines and equipment. The method includes providing a nuclear reactor, reactor working fluid, heat exchangers, compressors, and multiple turbines to drive compressors that pressurize a humidified working fluid that is combusted with fuel fired in at least one gas turbine. The turbine(s) provide for electrical energy, processes or other mechanical loads.

Abstract: According to an embodiment, a nuclear reactor containment vessel has: a primary reactor containment vessel which contains a nuclear pressure vessel; a secondary reactor containment vessel and which is disposed outside the primary reactor containment vessel which has the pressure resistant properties and the leak-tightness which are equivalent to those of the primary reactor containment vessel; an air bag which is disposed within the secondary reactor containment vessel and which, when a failure occurs in primary reactor containment vessel, expands while receiving and encapsulating a high pressure gas discharged from the inside of the primary reactor containment vessel; and a gas phase vent pipe which connects the primary reactor containment vessel and the air bag.

Abstract: An integrated reactor missile shield and crane assembly (IRMSCA) is disclosed and claimed. The IRMSCA replaces the existing concrete missile shields and reactor services crane. The IRMSCA is moveable such that the missile shield can be moved away from the reactor head, allowing the integral crane to lift the control rod drive mechanism components and other routine loads at the refueling cavity.

Abstract: The invention relates to a pressurised water nuclear reactor vessel, comprising: an outer casing which comprises at least one cylindrical shell and a dished bottom head, a core support plate, a vessel bottom head space being delimited between the support plate and the dished bottom head, the support plate being perforated with holes for circulation of the primary coolant which place the vessel bottom head space in communication with the core, a calming device which is arranged in the vessel bottom head space, wherein the calming device comprises at least one calming plate which is substantially perpendicular relative to the centre axis of the vessel and a plurality of calming holes, the calming holes being provided in the calming plate and being capable of calming the primary coolant by passing the fluid through the holes.

Abstract: A nuclear reactor having a coolant flow deflector secured to a reactor core barrel in line with a coolant inlet nozzle. The flow deflector redirects incoming coolant down an annulus between the core barrel and the reactor vessel. The deflector has a main body with a front side facing the fluid inlet nozzle and a rear side facing the core barrel. The rear side of the main body has at least one protrusion secured to the core barrel so that a gap exists between the rear side of the main body adjacent the protrusion and the core barrel. Preferably, the protrusion is a relief that circumscribes the rear side of the main body.

Abstract: In a nuclear reactor building of a steel plate concrete structure that houses a pressure containment vessel formed with a plurality of penetration ports penetrating the pressure containment vessel on the periphery thereof and includes a biological shielding wall disposed outside the pressure containment vessel. The pressure containment vessel is vertically divided into a plurality of blocks so that each of the blocks has one or more pressure containment vessel penetration ports arranged on a same horizontal plane, and the reactor building including the biological shielding wall is divided into a plurality of modules by the horizontal plane.

Abstract: A covering element for a reactor core of a nuclear installation provides a secure and tight closure of the reactor core in an operating state and at the same time being simple and cost effective to produce. The covering element is easily disassemblable during maintenance or loading processes and provides good possibilities for intervention in the reactor core. For this purpose, the covering element has a closure head and a separate support ring. The support ring is joined form-lockingly and/or force-lockingly to the closure head.

Abstract: A covering element for a reactor core of a nuclear installation provides a secure and tight closure of the reactor core in an operating state and at the same time being simple and cost effective to produce. The covering element is easily disassemblable during maintenance or loading processes and provides good possibilities for intervention in the reactor core. For this purpose, the covering element has a closure head and a separate support ring. The support ring is joined form-lockingly and/or force-lockingly to the closure head.

Abstract: A nuclear reactor and method for generating energy from fertile and fissile nuclear fuel material. The reactor may comprise a pressure vessel for housing a nuclear reactor core, the vessel having a lower vessel with an upwardly facing opening and a vessel closure head having a sealable access port. The vessel closure head may be positionable in differing positions relative to the lower vessel so that differing portions of the interior of the pressure vessel may be accessed through the access port. The lower vessel may include penetrations for lateral insertion of one or more reactor control blades into the interior of the lower vessel.

Abstract: The invention relates first of all to a method for manufacturing a pressure vessel of a pressurized-water reactor of a nuclear power station, which pressure vessel comprises a pressure resistant casing and which is being used filled with a medium in high pressure in order to utilize heat, being generated as a result of a nuclear reaction taking place in an internal space (13) of the pressure vessel, by means of a heat exchange arrangement or like, being in connection with the pressure vessel. A casing of a pressure vessel (1) of a pressurized water reactor, is being manufactured from two or more shell structures (5, 6) existing one within the other, whereby an essentially lower pressure than the pressure existing in an internal space (13) of the pressure vessel is being arranged in an intermediate space (12) between the shell structures. The invention relates also to a pressure vessel of a pressurized-water reactor of a nuclear power station and to use of a multiwalled pressure vessel for the above purpose.

Abstract: Marking of the cuts which have to be made, cutting of the section at two ends, removal of the section which has to be replaced, bevelling of the joint ends of the parts remaining after the section has been cut out from the pipe, adjustment of a new or replacement section for length and bevelling of its joining ends and positioning and narrow bevel welding of the ends joining the replacement section to the ends of the remaining parts of the pipe are performed outside the pipe. Within the pipe operations of machining and inspecting an internal part of the joining ends welded together are performed by remote control in a programmed way by introducing and positioning means for working within the pipe from a component of the primary circuit.

Abstract: A transport or storage cask comprises a cask body, a modular thermal conducting and shielding system and a mechanical attachment. The modular thermal conducting and shielding system includes a modular fin and a modular neutron shield. The mechanical attachment retains the modular thermal conducting and shielding system to the cask body. The modular fin is disposed between the modular neutron shield and the cask body. The modular fin is capable of dissipating thermal energy from the cask body.

Abstract: In a nuclear reactor, cooled by pressurized water, an apparatus is employed for replacing a section of a primary circuit primary pipe that interconnects first and second components of a primary circuit. The apparatus cuts out and removes a section of the primary pipe. Supports are provided for the end parts of a new replacement section in a position held by the removed pipe. The apparatus bevel welds the end parts of the new replacement section of the primary pipe to confronting corresponding ends of the remaining primary pipe. Means are provided to work within the pipe along the entire length of the interior surface of the primary pipe and is introduced through one of first and second components of the primary circuit to a location within the welded replacement pipe section.

Abstract: Marking of the cuts which have to be made, cutting of the section at two ends, removal of the section which has to be replaced, bevelling of the joint ends of the parts remaining after the section has been cut out from the pipe, adjustment of a new or replacement section for length and bevelling of its joining ends and positioning and narrow bevel welding of the ends joining the replacement section to the ends of the remaining parts of the pipe are performed outside the pipe. Within the pipe operations of machining and inspecting an internal part of the joining ends welded together are performed by remote control in a programmed way by introducing and positioning means for working within the pipe from a component of the primary circuit.

Abstract: A reactor pressure vessel supports the flanges of a core barrel assembly and an upper support plate. These flanges have aligned holes for diverting inlet coolant water to the vessel head for cooling the head. The aligned holes have different cross-sectional areas for controlling unexpected backflow of coolant water from the vessel head around the periphery of the upper support plate.

Abstract: A seal plate for repairing damaged areas in a pressure vessel cladding includes a first side and an opposing second side and a sealing portion located on the second side, with the sealing portion circumscribing the seal plate. The seal plate also includes a seal lip extending from a periphery of the sealing portion and a cavity located in the second side, with the cavity circumscribed by the sealing portion. The seal plate further includes at least one purge port extending from the first side to the cavity. Each purge port is in fluid communication with the cavity.

Abstract: A reactor closure head assembly has guide tube nozzles which are integral with the reactor closure head. A dome-shaped forging having a concave surface is prepared with extra thickness equal to or greater than the desired nozzle height. Nozzles having bores therethrough are machined opposite the concave surface. Weld buttering is applied to the ends of the nozzles, the concave surface is clad with a corrosion resistant layer, and the forging is then heat treated. A guide tube flange is attached to the ends of the nozzles. The surfaces of the nozzle bores are covered with a protective layer which is preferably applied without heating, for example by electrochemical deposition, thereby avoiding the need for subsequent post weld heat treatment.

Abstract: A reactor pressure vessel supports the flanges of a core barrel assembly and an upper support plate. These flanges have aligned holes for diverting inlet coolant water to the vessel head for cooling the head. The aligned holes have different cross-sectional areas for controlling unexpected backflow of coolant water from the vessel head around the periphery of the upper support plate.

Abstract: A compact metal containment vessel, for a boiling water nuclear reactor, includes in one exemplary embodiment, a bottom head, a removable top head, and a substantially cylindrical sidewall extending from the bottom head to the top head. The bottom head, top head and cylindrical sidewall define a containment cavity sized to receive and enclose a reactor pressure vessel. The containment vessel has a pressure rating of at least about 50 atmospheres atm.

Abstract: The present invention provides a boiling water reactor nuclear power plant in which a reactor core support plate, upper grid plate, and a reactor core consisting of fuel assemblies supported by these plates are provided in the inner base portion of a nuclear reactor pressure vessel. Control rod guide tubes and a reactor core shroud are positioned over the upper grid plate, and a control rod drive mechanism is provided further above same, whereby the control rods can be inserted from above the reactor core, and natural circulation of cooling water inside the reactor can be achieved by means of a chimney effect of the control rod guide tubes. According to the above structure, there can be provided a compact and economical nuclear power plant.

Abstract: Passive emergency cooling in response to a loss of coolant accident (LOCA) in a PWR, having an integral reactor pressure vessel incorporating the steam generators and housed in a small high pressure containment vessel, is provided by circulating cooling water through the steam generators and heat exchangers in an external tank to cool the reactor vessel at a rate sufficient to lower the pressure in the reactor vessel below that in containment to reverse mass flow out of the reactor vessel and keep the reactor core covered without the addition of makeup water. Suppression tanks inside the small high pressure containment structure limit peak blowdown pressure in containment and provide flood-up water and gravity fed makeup water to cool the core. Diverse cooling is provided by natural circulation of air, and if needed, water, over the spherical containment structure.

Abstract: The present invention, in one form, is a natural circulation reactor having, in one embodiment, a layer of high aluminate cement concrete disposed between an uninsulated steel liner and a prestressed concrete reactor vessel. The prestressed concrete reactor vessel includes a concrete shell having a cavity therein. The steel liner is positioned in the cavity and spaced from the concrete shell so that an insulating chamber is formed between the steel liner and the concrete shell. The insulating chamber is filled with high aluminate cement concrete which is configured to substantially insulate the concrete shell from the steel liner and to transfer loads such as pressure from the liner to the concrete shell.

Abstract: A reactor pressure vessel with an upper support plate, in which an equalization opening is provided as a bypass is described. A process for temperature equalization between an upper dome chamber above a support plate and a lower chamber below it is described. It is proposed that the cross section of the equalization opening be variable as a function of the temperature, so that the flow of medium between the upper dome chamber and the lower chamber is varied as a function of the temperature.

Abstract: A reactor pressure vessel with an upper support plate, in which an equalization opening is provided as a bypass is described. A process for temperature equalization between an upper dome chamber above a support plate and a lower chamber below it is described. It is proposed that the cross section of the equalization opening be variable as a function of the temperature, so that the flow of medium between the upper dome chamber and the lower chamber is varied as a function of the temperature.

Abstract: A liquid metal nuclear reactor is described. The reactor includes a concrete reactor silo, and at least one primary vessel located in the reactor silo and coupled to a reactor shield deck. Each primary vessel is substantially surrounded by a containment vessel in a spaced apart relationship. The reactor also includes a heat removal system which includes a guard vessel substantially surrounding each containment vessel in a spaced apart relationship, at least one inlet conduit in fluid communication with the ambient atmosphere outside the nuclear reactor, and at least one outlet conduit in fluid communication with the ambient atmosphere outside the nuclear reactor. A fluid flow heat transferring flowpath is formed by the inlet conduits, the space intermediate the guard vessel of each primary vessel and the containment vessel of each primary vessel and the outlet conduits.

Abstract: A reactor pressure vessel (RPV) for a nuclear reactor that permits measurement of the flow through each reactor internal pump (RIP) is described. The reactor pressure vessel also includes at least one reactor internal pump that includes an impeller and a pump diffuser. At least two seal rings extend circumferentially around an outer surface of the diffuser housing outer wall and are located in circumferential grooves in the housing outer wall. At least one lateral bore extends through the housing outer wall into a diffuser housing longitudinal flow passage. Each lateral bore is located in an area between two adjacent seal rings, with each inter-seal ring area containing one lateral bore. At least one pressure tap bore extends from the outer surface of the RPV bottom head petal, through the pump deck to an inner surface of a pump deck opening. Each pressure tap bore is aligned with an area in the RIP containing a corresponding lateral bore.

Abstract: A forged nozzle shell course for a pressure vessel includes shell course comprising at least one reinforcement portion extending radially outward from an outer surface of the shell course with each reinforcing portion including a nozzle having a radius. The nozzle includes a bore extending from an outside surface of the reinforcing portion to an inside surface of the shell course, and at least one extension attachment surface located adjacent to and coaxial to the bore. The reinforcing portion having a longitudinal dimension equal to about 2.0 times the radius of the nozzle, and a circumferential dimension equal to about 1.5 times the radius of the nozzle, measured from the centerline of the nozzle bore.

Abstract: A forged upper shroud section which may be machined from a single piece rectangular cross-section ring forging and includes a circular flange and a cylindrical shell is described. Openings and slots are machined into the flange to align and support the shroud head. A groove is machined along an inside surface of the cylinder section, and the groove may be used to support top guide grid (not shown). An end of the cylinder section is machined with a weld prep for attachment to the core section of the shroud.

Abstract: A top guide to shroud head interface is described. In one embodiment, the interface includes a top guide that includes a flange that is configured to engage a corresponding flange of the shroud head. The top guide flange includes a plurality of frusto-conical shaped guide pins extending from the top surface of the flange. The shroud head flange includes a plurality of guide pin openings configured to align with the guide pins located on the top guide flange. Each guide pin opening includes a frusto-conical portion that extends through the flange from the bottom surface of the shroud head flange and has a slope equal to the slope of the frusto-conical pins. Each guide pin opening also includes a cylindrical portion that extends from the small base of the frusto-conical portion of the guide pin opening to the top surface of the shroud head flange.

Abstract: An integral stub tube which simplifies the reactor pressure vessel fabrication process, provides a structural transition between the penetration and head, and facilitates future remote inspection of the attachment weld is described. In one embodiment, a stub tube is machined into the bottom head dome. Specifically, a penetration is formed in the bottom head dome by a bore having a stub tube portion. The stub tube portion has a cylindrical shape and a length of the stub tube portion is selected to provide a transition between a penetration housing and an adjacent portion of bottom head dome. The penetration housing extends through the penetration, in the dome. A weld attaches the stub tube portion to the penetration housing.

Abstract: An integrated head assembly for a nuclear reactor pressure vessel includes a closure head with CRDM assemblies extending upwardly from the head. A CRDM seismic support disposed above the closure head provides lateral support for the CRDM assemblies. The seismic support also has air flow holes which communicate with the interior of a shroud enclosing the CRDMs and extending upwardly from the closure head to the seismic support. The shroud has an air port in direct air flow communication with the surrounding atmosphere so that the closure head, shroud and seismic support define an air flow passageway directly communicating with the surrounding atmosphere via the air port and without the extensive ductwork and, therefore, with substantially less power. A missile shield disposed above and in air flow communication with the seismic support provides a lightweight, compact physical barrier for removing energy from dislocated objects such as CRDM drive rods.

Abstract: A pressure testing apparatus can pressure test separately a first object having a width and a height and a second object having a width and a height. The first object can be, for example, a fiber optic repeater; the second object can be, for example, a fiber optic branch unit. The pressure testing apparatus has a testing vessel and an adaptor. The testing vessel has a chamber with an inner width corresponding to the width of the first object and a first gap. The adaptor can be selectably insertable into the chamber of the testing vessel and has an inner width and an outer width. The outer width of the adaptor corresponds to the inner width of the chamber of the testing vessel and a second gap. The inner width of the adaptor corresponds to the width of the second object and a third gap.

Abstract: The invention pertains to a building, particularly in the context of a nuclear installation. The building is formed with an outer shell and an inner shell which form an intermediate space therebetween. A sealing element is disposed in the intermediate space. The sealing element is gas tight, it envelopes the inner shell, and it is largely freely movable perpendicularly to the surfaces of the shells defining the intermediate space. Pressure fluctuations, particularly pressure waves, originating on the inside of the building are received and equalized by the sealing element, while the gas-tightness of the sealing element is largely assured.

Abstract: A bottom head to shell junction assembly which, in one embodiment, includes an annular forging having an integrally formed pump deck and shroud support is described. In the one embodiment, the annular forging also includes a top, cylindrical shaped end configured to be welded to one end of the pressure vessel cylindrical shell and a bottom, conical shaped end configured to be welded to the disk shaped bottom head. Reactor internal pump nozzles also are integrally formed in the annular forging. The nozzles do not include any internal or external projections. Stubs are formed in each nozzle opening to facilitate welding a pump housing to the forging. Also, an upper portion of each nozzle opening is configured to receive a portion of a diffuser coupled to a pump shaft which extends through the nozzle opening. Diffuser openings are formed in the integral pump deck to provide additional support for the pump impellers. The diffuser opening is sized so that a pump impeller can extend at least partially therethrough.

Abstract: A reactor vessel seal for temporarily sealing a reactor pressure vessel from a water-filled refueling canal above the reactor pressure vessel. The reactor vessel seal is installed in place of the removable reactor pressure vessel closure head for inspecting/servicing the reactor vessel. The reactor seal comprises a seal cap having a surface connected to a flange which is complementary to the upper flange of the reactor pressure vessel. A seal is located between the seal cap flange and the upper flange of the reactor pressure vessel. A lifting rig is connected to the seal cap for lifting the seal cap and placing it in position, with the seal cap flange in alignment with the reactor vessel upper flange, such that the seal located between the seal cap flange and the reactor pressure vessel upper flange is compressed by hydrostatic pressure from water in the water-filled refueling canal acting on the surface of the seal cap as water in the reactor pressure vessel is evacuated.

Abstract: An irradiated steel pressurized nuclear reactor pressure vessel 10 is provided with a crack initiation retarding and crack extension retarding reactor vessel integrity girdle 20 or 120 made up of shoes or links 22, with mechanical take up joints (26 to 34a or 126 to 134a). Instead of pivoted shoe links 22, the girdle 120 may be made using constricting roller chain links 122. In any event, crack initiation and crack extension which may result from pressure loading or vessel material embrittled in the beltline region by neutron bombardment is retarded by maintenance of a prestress under the nozzles during all periods of operation of the reactor.

Abstract: A pressure vessel apparatus for containing fluid under high pressure and temperature including pressure surges caused by in-vessel explosions includes a vessel main body, a vessel top body and a vessel head. Elongated tendons interconnect the vessel main body to the vessel top body and elongated tendons with removable anchors also connect the vessel head to the vessel top body. The tendons with insulated protecting sleeves connecting the vessel main body to the vessel top body are chosen to allow the vessel top body to temporarily separate from the vessel main body before the vessel head separates from the vessel top body. These tendons may be mounted directly, on springs, or on dampers in order to provide optimum (minimum) response to the postulated load cases.

Abstract: Pressure vessel apparatus includes upper and lower pressure vessel housings maintained together under pressure by tendons. Bellows are connected to the pressure vessel housings in order to provide leaktight barriers, and to permit motion of the pressure vessel housings. The tendons are divided into two sets, with the tendons of each set of tendons being stressed differently than the tendons of the other set of tendons. The apparatus when utilized as a nuclear reactor pressure vessel includes a core catcher with flotation pool connected to and disposed below the pressure vessel housings and defining a core catcher interior in communication with the pressure vessel interior for receiving core material from the pressure vessel interior resulting from reactor melt-down.

Abstract: A reactor pressure vessel for a nuclear reactor includes an upper part and a lower part. At least the lower part has first subregions with a lesser wall thickness and second subregions with a greater wall thickness. The lesser wall thickness is selected for a rated operation. The first subregions are formed by recesses in the outer surface of the wall.

Abstract: A nuclear reactor vessel cavity seal plate. An annular support plate is positioned over the cavity between the reactor vessel and the shield structure and seal welded to the shield structure. Inner and outer support rings attached to the annular plate are supported by the existing beams in the annular cavity. A U-shaped flexible annular expansion ring positioned between the annular plate and reactor vessel flange has its inner diameter seal welded to the reactor vessel flange and its outer diameter seal welded to the annular plate. Ports in the annular plate provide access to nuclear instruments below the annular plate. A cover plate is removably attachable to each port to seal the ports. A closable drain is provided in the annular expansion ring. This provides a permanent seal plate that allows flooding of the cavity for refueling with it being necessary to remove only the cover plates for normal reactor operations.