Westinghouse Electric Corporation

Dennis J Cadwell

Richard D Franklin

Stanley Kmonk

Stephen J Ferlan

Method is disclosed herein for removing debris from nuclear fuel assemblies which have been in service in a nuclear reactor. The method generally comprising immersing the fuel assembly in a pool of water which may be the cask loading pit of a nuclear facility, securing the fuel assembly in a spent fuel rack, enveloping the spent fuel rack in a rectangular sleeve in order to isolate the water surrounding the fuel assembly from the balance of the water in the cask loading pit, and discharging a series of pressure pulses into the isolated water from a pressure pulse source to create shock waves that exert momentary forces on the fuel rods sufficient to dislodge debris therefrom but insufficient to create a liftoff between the fuel rods and the spring fingers of the grids which retain them within the fuel assembly.

Pressure pulse method for removing debris from nuclear fuel assemblies

Both a method and system are disclosed herein for removing debris from nuclear fuel assemblies which have been in service in a nuclear reactor. The method generally comprising immersing the fuel assembly in a pool of water which may be the cask loading pit of a nuclear facility, securing the fuel assembly in a spent fuel rack, enveloping the spent fuel rack in a rectangular sleeve in order to isolate the water surrounding the fuel assembly from the balance of the water in the cask loading pit, and discharging a series of pressure pulses into the isolated water from a pressure pulse source to create shock waves that exert momentary forces on the fuel rods sufficient to dislodge debris therefrom but insufficient to create a liftoff between the fuel rods and the spring fingers of the grids which retain them within the fuel assembly.

Pressure pulse method and system for removing debris from nuclear fuel

A nuclear reactor fuel assembly spacer grid having grid straps and a first type of spring clip. The grid straps define standard cells enclosing fuel rods and thimble cells enclosing control rod guide thimbles. The spring clip is bent to widthwise encircle a grid strap and has its two ends welded together. The first type of spring clip is used at a location on a grid strap having a standard cell and an adjacent thimble cell. The spring clip has a spring portion compressibly contacting the fuel rod in the standard cell. The spring clip also has a pair of separated flat portions straddling the control rod guide thimble in the thimble cell so as not to interfere with the guide thimble. The spring clip is made of a material having good radiation stress relaxation properties.

Nuclear reactor fuel assembly spacer grid

An improved control rod guide tube for use in a fuel assembly in a nuclear reactor. The guide tube extends the complete length of the fuel assembly and has its upper end fastened in a cylindrical housing by swaging the guide tube material into grooves formed in the housing walls. To eliminate wear on the guide tube inner walls caused by hydraulic induced vibratory forces on a control rod adapted to move therein, a thin-walled chrome plated sleeve is threaded into the top end of the guide thimble and extends downwardly a distance sufficient to be engaged by the control rod during reactor operation. The sleeve serves as a highly resistant wear surface between the control rod and walls on the guide tube in the fuel assembly.

Nuclear fuel assembly wear sleeve

A design of fuel assembly control rod guide thimble which includes insets or indentations which project inwardly from the upper end of the guide thimble and extend longitudinally of the thimble for about the same distance traversed by a control rod movable therein. These preferentially formed discrete indented areas or insets within the guide thimble provide for controlled localized control rod to guide thimble wear. The insets minimize wear at the control rod-guide thimble interface by lowering the normal load and encouraging the control rod into a line contact wearing mode. Additional insets may be remotely installed after irradiation if desired.

Control rod guide thimble for nuclear reactor fuel assemblies

A top nozzle for a nuclear reactor fuel assembly which includes an orifice plate designed to receive control rod guide tubes extending upwardly from the top of the fuel assembly. Nozzle pin extensions connected to the orifice plate are axially coextensive with the guide tubes and project upwardly through a top nozzle hold-down plate, and through openings in the upper core plate in the reactor. The hold-down plate is spring biased into an upper core plate engaging position and since the pin extensions are adapted to move in the core plate and against the action of the springs, the top nozzle thus becomes effective in accommodating upwardly acting hydraulic forces which tend to lift the fuel assembly, and to accommodate differential expansion of parts in the fuel assembly as compared to the core barrel in which the assembly is located. The number of pins disposed in the hold-down plate move in slots formed in each of the guide tube extensions and the uppermost position of the fuel assembly is determined when the pin is in the bottom of its slot in each of the guide tubes.

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Plum Borough, PA, United States of America

Dennis J Cadwell