Abstract: Disclosed is a water jet peening method that includes the steps of: preparing a water jet peening apparatus having a supporting member, a first divider plate, a nozzle support body, and a second divider plate; inserting the water jet peening apparatus into a piping in which a structure or electronic device is mounted that is susceptible to damage by a jet of water discharged from a jet nozzle or by shock waves; disposing either the first divider plate or the second divider plate between the jet nozzle and the structure or electronic device; filling water into an internal area formed in the piping between the first divider plate and the second divider plate; and subjecting the inner surface of the piping to water jet peening by allowing the jet nozzle to discharge a jet of water into the water in the internal area.

Abstract: A top head of a reactor pressure vessel includes control rod drive mechanism (CRDM) penetration pipes arranged in a square grid-like pattern. The CRDM penetration pipes are joined with one another by a tube support member. The top head is placed on a tank and water is filled in an inner region of the tank and the top head. A travel apparatus moves a nozzle lifting and lowering apparatus to a predetermined location. A lifting and lowering mechanism of the nozzle lifting and lowering apparatus lifts a jet nozzle above the tube support member among the neighboring four CRDM penetration pipes. An ejection outlet of the jet nozzle is directed to a weld between one of the CRDM penetration pipes and the top head, and a water jet is ejected. A nozzle turning mechanism turns the jet nozzle, and WJP is executed sequentially to the four CRDM penetration pipes.

Abstract: A chamber having a water jet generation apparatus and a mesh installed inside is pushed against a surface of a peening object. A rotary vane of the water jet generation apparatus, disposed in a region in the chamber between the mesh and the chamber, is rotated to generate a water jet flowing toward the peening object in one region in the chamber, the one region is a region closer to the peening object than the mesh. A plurality of shots 4 put in the region 30A moves toward the peening object along with the water jet and collides with the surface of the peening object. After the collision, the shots move toward the mesh along with the water jet. Compression residual stress is given to the surface of the peening object with which the shots have collided. Thus, spreading of contaminants peeled off from a peening object can be prevented.

Abstract: A water jet peening apparatus (WJP apparatus) includes a seating member, rotating portion set to it, and first and second injection nozzles. A hoisting apparatus is attached to the rotating portion, and the first and second injection nozzles are attached to a nozzle arm. The WJP apparatus is gone down in a reactor vessel (RV) by crane operation, and the seating member is seated on a bottom mounted instrumentation nozzle welded to a bottom head of the RV. By the hoisting apparatus, the nozzle arm is gone down and the first and second injection nozzles are gone down. The first injection nozzle is inserted into the bottom mounted instrumentation nozzle and the second injection nozzle is set outside the bottom mounted instrumentation nozzle. High-pressure water is jetted from the first and second injection nozzles, and WJP is implemented for both of the inner and outer surfaces of the welding area of the bottom mounted instrumentation nozzle.

Abstract: In a water jet peening apparatus, a high-pressure under-water pump is installed on an upper end of a casing and an injection nozzle drive mechanism equipped with an injection nozzle is attached to the casing. A high-pressure hose whose one end is connected to the high-pressure under-water pump is disposed in the casing and the other end of the high-pressure hose is connected to the injection nozzle. The casing is seated at an upper end of a control rod drive mechanism housing and the high-pressure under-water pump is driven. The high-pressure water pressurized by the high-pressure under-water pump is supplied to the injection nozzle through the high-pressure hose in the casing and is jetted toward the weld portion between the control rod drive mechanism housing and a stub tube. The time required for a water jet peening operation can be shortened.

Abstract: An evaluation method of residual stress in water jet peening includes a step of creating an analytical model including meshes according to a water jet peening (WJP) object, the shape of a nozzle, and an injection distance, a step of inputting WJP execution conditions, a step of calculating the internal pressure pBi of a cavitation bubble and a bubble number density ngi through jet flow analysis for a jet flow jetting from the nozzle, a step of calculating cavitation energy according to the internal pressure pBi of a cavitation bubble and a bubble number density ngi (S4), a step of calculating the burst energy of cavitation bubbles from the cavitation energy C, and a step of calculating the compressive residual stress of the WJP object from the collapse pressure of cavitation bubbles. Accordingly, the residual stress of the WJP object can be evaluated precisely in a shorter time.

Abstract: A chamber having a water jet generation apparatus and a mesh installed inside is pushed against a surface of a peening object. A rotary vane of the water jet generation apparatus, disposed in a region in the chamber between the mesh and the chamber, is rotated to generate a water jet flowing toward the peening object in one region in the chamber, the one region is a region closer to the peening object than the mesh. A plurality of shots 4 put in the region 30A moves toward the peening object along with the water jet and collides with the surface of the peening object. After the collision, the shots move toward the mesh along with the water jet. Compression residual stress is given to the surface of the peening object with which the shots have collided. Thus, spreading of contaminants peeled off from a peening object can be prevented.

Abstract: A high-pressure water jet is injected from a nozzle scanned and a shock wave generated due to the collapse of bubbles included in the water jet is impacted on a WJP execution object. Tensile residual stress close to the surface of the WJP execution object is improved to compressive residual stress. The shock wave is detected by a pressure sensor and a shock wave generation frequency is obtained. Whether the obtained shock wave generation frequency is larger than a set value or not is decided. When the shock wave generation frequency is larger than the set value, a high-pressure pump is stopped and the injection of the water jet from the nozzle is stopped. When the shock wave generation frequency is equal to or smaller than the set value, the operation condition of the high-pressure pump is changed.

Abstract: An evaluation method of residual stress in water jet peening includes a step of creating an analytical model including meshes according to a water jet peening (WJP) object, the shape of a nozzle, and an injection distance, a step of inputting WJP execution conditions, a step of calculating the internal pressure pBi of a cavitation bubble and a bubble number density ngi through jet flow analysis for a jet flow jetting from the nozzle, a step of calculating cavitation energy according to the internal pressure pBi of a cavitation bubble and a bubble number density ngi (S4), a step of calculating the burst energy of cavitation bubbles from the cavitation energy C, and a step of calculating the compressive residual stress of the WJP object from the collapse pressure of cavitation bubbles. Accordingly, the residual stress of the WJP object can be evaluated precisely in a shorter time.

Abstract: A high-pressure water jet is injected from a nozzle scanned and a shock wave generated due to the collapse of bubbles included in the water jet is impacted on a WJP execution object. Tensile residual stress close to the surface of the WJP execution object is improved to compressive residual stress. The shock wave is detected by a pressure sensor and a shock wave generation frequency is obtained. Whether the obtained shock wave generation frequency is larger than a set value or not is decided. When the shock wave generation frequency is larger than the set value, a high-pressure pump is stopped and the injection of the water jet from the nozzle is stopped. When the shock wave generation frequency is equal to or smaller than the set value, the operation condition of the high-pressure pump is changed.

Abstract: A method of performing maintenance on a structural member inside a reactor pressure vessel includes lowering an annular guide rail having a second lug until the guide rail rests on an upper flange of a core shroud provided inside the reactor pressure vessel, detachably mounting the second lug of the guide rail to a first lug mounted on the core shroud, positioning a discharging nozzle at a position at which compressive remaining stress is added to a surface of the core shroud by moving the discharging nozzle in a radial direction and an axial direction of the core shroud by a discharging nozzle moving apparatus mounted on a turnable revolving on the guide rail and discharging water to add compressive remaining stress to a surface of the core shroud from the discharging nozzle.

Abstract: A preventive maintenance apparatus for structural members inside a nuclear reactor pressure vessel includes a ring-shaped guide rail having a plurality of lugs which is placed on an upper flange of a core shroud provided inside a reactor pressure vessel. At least some of lugs separately engage with a plurality of guide rods provided on an inner surface of the reactor pressure vessel. A turntable is rotated on the guide rail. A first discharging nozzle moving apparatus placed on the turntable moves a first discharging nozzle for adding compressive remaining stress to an outer surface of the core shroud in a radial direction of the core shroud and in an axial direction of the core shroud. A second discharging nozzle moving apparatus placed on the turntable moves a second discharging nozzle for adding compressive remaining stress to an inner surface of the core shroud in a radial direction of the core shroud and in an axial direction of the core shroud.

Abstract: An apparatus preventive maintenance having a driving mechanism capable of driving a jet nozzle 24 to cause it to travel upward-and-downward, to rotate and to swing is settled on the top of a housing in the bottom portion of a reactor pressure vessel and on a hole for a fuel support piece, water pumped by a high pressure pump is spouted from a jet nozzle, and cavitation bubbles generated during the spouting are supplied to the positions to be treated for preventive maintenance, such as housings in the bottom portion of the reactor pressure vessel. Therewith, the residual tensile stress in the position to be treated is improved in a releasing direction by the energy generated by the collapsing of the cavitation bubbles.