Abstract: An underwater laser processing system has a laser torch; a laser torch driving mechanism for changing a laser emission position of the laser torch; and a chamber with one end opened to an external environment, which contains the laser torch; wherein a partitioning wall for preventing permeation of water is provided between a free end of the chamber and the laser torch. The system is used for detecting a sensitized portion and repairing it at one time using a sensitization detecting arrangement. Moreover, it is used for forming an alloying layer by melting a sprayed coating film, and for forming a new surface layer by emitting a laser beam through a solution containing a metal component.

Abstract: A submerged laser beam irradiation equipment provides a high quality submerged laser beam processing of a submerged workpiece using only a small amount of a gas. The submerged laser beam irradiation equipment has: a focus lens for focusing a laser beam; a mirror tube which houses the lens; a first nozzle operating to cover the front end of the mirror tube in an irradiating direction of the laser beam; a skirt portion provided at the front end of the first nozzle for preventing water intrusion thereinto; and a shutter mechanism operable to open and close and provided between said skirt portion and said mirror tube for preventing water intrusion into said mirror tube.

Abstract: Disclosed is a highly reliable weld repairing method to repair a crack defect in structures and apparatus inside pressure vessels of nuclear reactors, while preventing generation of new crack defects in the structures and apparatus during the repairing. These structures and apparatus are made of any of stainless steel and Ni-base alloys, and are irradiated with high energy corpuscular ray during operating period of the reactor. The repairing method includes the steps of eliminating a region of the structure or the apparatus including a portion having the crack defect, and executing spot welding at a surface of the region continuously or interruptedly in a manner so as to form a first welded layer in a manner that each of the spot welded spots is half-overlapped with adjacent welded spots. Additionally, welding for forming at least a second layer, on the first welded layer, so that the at least a second layer is not deeper than a weld penetration thickness of the first welded layer can be performed.

Abstract: By applying spot welding along a crack which has occurred in an austenitic stainless steel structure without use of welding material so that spot welds are connected, melting and solidifying of the crack can be achieved, thereby to provide a metal structure which is rich with delta ferrite of the austenitic stainless steel structure or prevent propagation of the crack by enclosing it into the interior of the austenitic stainless steel structure.

Abstract: A water jet peening method in which a pressurized water jet flow containing cavities is jetted through a nozzle having a velocity increasing orifice portion and a horn-like jetting hole formed continuously with the velocity increasing orifice portion to impinge against a surface of a metallic material immersed in water and to cause the cavities to collapse at the surface of the metallic member, and a tensile plastic deformation is caused in a surface layer of the metallic material by a local high pressure generated by the impingement and the collapse so that a residual tensile stress in the surface of the metallic member is reduced. In this method, the nozzle is vibrated so that vibration-induced cavities are formed in the vicinity of a nozzle wall surface, and the vibration-induced cavities are caused to impinge against the surface of the metallic member by the pressurized water jet flow containing cavities.

Abstract: A method for improving a property of a weld of an austenitic stainless steel which is a part of a structure being brought into contact with a corrosive fluid at a region having been affected by welding heat on both of opposed surfaces, comprising the steps of: cooling said thermally affected region on one of said opposed surfaces; and simultaneously with said cooling step, applying a melting treatment to the other surface, thereby changing the melting treatment portion into a micro structure that contains delta (.delta.) ferrite and is superior in corrosion resistance property. The latter surface is improved in high tensile stress generated by the welding work. Namely, its stress is reduced. The melting heat for said melting treatment is obtained by application of high density energy.

Abstract: A water sealing device suitable for use when a control rod drive housing welded to a stub tube and extends through a wall of a reactor pressure vessel is replaced, singly or with the stub tube, by a new one, including a sealing cylinder temporarily inserted in a control rod guide tube opening for providing a cylindrical space in which the control rod drive housing is located to shut out water in a core from the vicinity of the control rod drive housing.

Abstract: A method of repairing the housing of a control rod driving system of a nuclear reactor, the housing being inserted through the wall of a pressure vessel of the reactor into a cylindrical sleeve secured to the inner surface of the vessel, which housing is jointed by welding to the cylindrical sleeve. The method comprises the steps of: cutting the housing in the circumferential direction of the housing at a position defined between the weld joint and the inner surface of the reactor vessel and surrounded by the cylindrical sleeve, thereby to divide the housing into a first housing part still attaching to the weld joint and another removable housing part; removing the removable other housing part; inserting a second housing part into said cylindrical sleeve through the wall of the nuclear reactor vessel; and uniting the first housing part and the second housing part by welding thereby to form a new housing for the control rod driving system.

Abstract: In a method of correcting a distorted pipe end to an original substantially true circular cross-section, external loads are applied to the outer peripheral surface of the pipe adjacent to the end thereof to forcibly deform the pipe end to the substantially true circular cross-section. The external loads are maintained to keep this substantially true circular cross-sectional shape while an internal pressure is applied to the inner peripheral surface of the pipe end until a circumferential stress produced in the pipe reaches an amount which exceeds the yield stress of the pipe to give a radial permanent deformation to the pipe for thereby producing a circumferentially uniformly distributed residual stress in the pipe.

Abstract: In welding tubular members of stainless steel, metal is deposited by build-up welding on a portion of the inner surface of each tubular member adjacent an edge thereof where welding gives a heat affection and exposed to a corrosive fluid when in service, and melting a portion of the inner surface of each tubular member in a zone adjacent to the metal deposited by build-up welding and affected by the heat of the build-up welding, said portion being exposed to the corrosive fluid when in service. Following the completion of these two steps, the tubular members of stainless steel are welded at the edges thereof to be joined. The method has the effect of preventing the occurrence of stress corrosion cracking at the inner surface of the piping which is near the joint and exposed to the corrosive fluid.