Westinghouse Electric Corporation

Westinghouse Electric Company LLC

David A Boatwright

Wade H Widener

Kenneth K Klapper

Robert Duncan

Paul M Evans

Denis Yeo

Michael Anthony Marzean

Jacob X Huang

Harry A Pearce

Paul Marcus Evans

A top end plug design for a nuclear fuel rod or control rod that maximizes the fuel rod length and internal volume for high burn-up, but limits plenum spring melting for eutectic formation margin. The press fit length of the top end plug is increased to increase the distance from the center of heat from the TIG welding process that seals the end plug to the cladding, to the back face of the end plug. A hole in the back of the end plug is enlarged to recover the volume loss from the press fit length increase.

Nuclear fuel element

A fuel assembly for a nuclear reactor that employs dissimilar materials for the fuel assembly grid and the control rod guide thimbles. The guide thimbles are secured to the grid employing a through grid cell sleeve that is welded to the grid and spot weld rings that are secured over the sleeve and welded directly to the guide tube through windows in the sleeve.

Nuclear reactor fuel assembly

A trepan is provided in a flat end face of an end plug about an external opening of an axial bore through the end plug. The trepan includes an annular groove encircling the external opening and an annular end face portion extending between the annular groove and the external opening. The ratio of the depth of the groove to the diameter of the annular end face portion of the trepan is within a range of from about 1:3 to 1:6. The ratio of the depth of the groove to the width thereof is within a range of from about 1:1 to 1:2. When an axially-directed welding arc is applied to the trepan in the flat end face of the end plug a melting of the material of the trepan into the end face occurs which forms a weld seal such that the trepan is replaced by a shallow concavity overlying the weld seal and extending across the region substantially encircled originally by the annular groove of the trepan.

Fuel rod end plug welding method

A method of forming a gripper cavity in a nuclear fuel rod end plug includes the basic steps of providing an end plug blank having an internal bore of substantially uniform diameter that opens at an annular outer rim on the end plug blank, cold forming the end plug blank to produce an intermediate end plug in which the annular outer rim is transformed into a conical outer rim having a rounded internal surface that defines an inlet opening to the internal bore of a diameter less than that of the internal bore, and removing an external layer of material from the intermediate end plug and an internal layer of material from the rounded internal surface of the conical outer rim to produce a finished end plug having an internal gripper cavity composed of the internal bore and a cylindrical internal surface defining the inlet opening to the internal bore and being of smaller diameter than the internal bore.

Method of forming a gripper cavity in a fuel rod end plug

An end cap is mounted on a fuel rod gripper to cover the end portions of fingers thereon to minimize impacts with grid cell dimples. The fingers are defined by circumferentially-spaced and longitudinally-extending slots in the gripper which permit the finger end portions to radially expand and retract between corresponding expanded and collapsed conditions. The end cap includes a body having a forward camming portion and a rearward mounting portion. The rearward mounting portion is hollow and configured to fit over and cover the end portions of the gripper fingers with the forward camming portion extending forwardly thereof. Also, circumferentially-spaced and longitudinally-extending attachment flutes are disposed internally of the hollow mounting portion of the body and project radially inwardly therefrom. The flutes are configured to releasably fit within the respective slots of the gripper when the finger end portions thereof are in the expanded condition and to be retained therein when the finger end portions are in the retracted condition.

Fuel rod gripper end cap for minimizing impact with grid cell dimples

An end stop is adapted for engaging the sealing plug positioned in the end of a nuclear fuel rod and so as to permit the evacuation of the fuel rod to facilitate girth welding of the plug onto the rod, and to permit pressurization of the fuel rod and an enclosing welding chamber to facilitate the seal welding closure of the axial opening in the end stop. The end stop includes an axial passage extending therethrough having a welding electrode coaxially positioned therein to facilitate the seal welding closure of the fuel rod sealing plug. An air channel extends between the axial passage and an outlet on the surface of the end stop. A one-way valve is positioned in the air channel for permitting the free passage of a gas from the axial passage to the outlet into the welding chamber while precluding passage of a gas in the reverse direction.

End stop for welding sealing plugs of nuclear fuel rods

An end cap is mounted on a fuel rod gripper to cover the end portions of fingers thereon to minimize impacts with grid cell dimples. The fingers are defined by circumferentially-spaced and longitudinally-extending slots in the gripper which permit the finger end portions to radially expand and retract between corresponding expanded and collapsed conditions. The end cap includes a body having a forward camming portion and a rearward mounting portion. The rearward mounting portion is hollow and configured to fit over and cover the end portions of the gripper fingers with the forward camming portion extending forwardly thereof. Also, circumferentially-spaced and longitudinally-extending attachment flutes are dispsoed internally of the hollow mounting portion of the body and project radially inwardly therefrom. The flutes are configured to releasably fit within the respective slots of the gripper when the finger end portions thereof are in the expanded condition and to be retained therein when the finger end portions are in the retracted condition.

An end plug is welded to a nuclear fuel rod tube by a girth weld having a melt-zone arcuately extending through the tube wall and into the plug, wherein the melt-zone and the end of the tube are separated by a predetermined distance. The distance is chosen such that heat is dissipated from the weld-zone to prevent damage to the rod and to prevent damage to the weld end stop. This weld enables the use of a substantially solid cylindrical end plug having a first end disposed inside the tube, a second end, and a hollow cavity extending to the second end for axially aligning the cylinder and fuel rod with a frictionally engaging weld stop during formation of the girth weld.

End plug weld for nuclear fuel rod

A welding apparatus includes a housing defining a welding chamber and an access opening at one end thereof. The access opening allows an end of a tube fitted with an end plug to pass into and from a welding position within the chamber. An end stop for supporting the end plug at the welding position is rotatably mounted to the housing and disposed in the chamber opposite from and axially aligned with the chamber access opening. The end stop has an annular collar-like portion adapted to fit over and engage the exterior of the end plug. The end stop also has an inner hollow tube-like portion adapted to fit into a central passage of the end plug and engage the interior of the end plug. The end stop has an orifice adapted to supply flow of inert cover gas into the end plug central passage and therefrom into the tube interior to purge air therefrom. Also, a welding assembly having an electrode with a leading end is mounted on a carriage which, in turn, is mounted on the housing for moving the welding assembly toward and away from welding chamber and thereby moving the electrode leading end toward and away from the tube and end plug between respective extended working position and retracted non-working positions. A drive mechanism is operable to rotate the tube and thereby rotate the tube end and end plug within the welding chamber and therewith the end stop engaged with the end plug.

Burnable absorber rod end plug welding apparatus and method

A welding apparatus has a welding chamber with an access opening allowing passage of a cladding tube end fitted with an end plug to a welding position therein. A rotatable end plug stop assembly disposed in the chamber and axially aligned with the access opening is adapted to engage the end plug when inserted in the welding chamber. An end of a electrode of a girth welding assembly disposed in the welding chamber adjacent to the rotatable end plug and tube end and in generally orthogonal relation thereto is operable to form a girth weld circumferentially joining the end plug and cladding tube end. An end seal welding assembly mounted to the end plug stop assembly and having an electrode with an end disposed adjacent to and in axial alignment with an axial bore of the end plug is operable to form an end seal weld therein. The end seal welding assembly also defines a path for flow of a fill gas along the electrode and both into the welding chamber and the end plug axial bore before formation of the end seal weld therein. The end plug stop assembly includes an end stop which receives an end seal welding electrode and flow of fill gas along the electrode, and an end plug-engaging insert adapted to fit in the end stop and engage the end plug leading end portion.

Fuel rod end plug welding apparatus and method

A nuclear fuel rod loader for pulling fuel rods into a fuel assembly skeleton has a rod gripper with slots defining fingers. The rod gripper passes through the grids of the skeleton on its way to a fuel rod magazine. An inner shaft of the rod gripper spreads open the fingers to engage a groove in the cavity of the end plug of the fuel rod. The rod gripper is retracted, pulling the coupled fuel rod into the fuel assembly skeleton. The rod gripper has a chamfer surface at the closed slot end of each slot to avoid the rod gripper damaging a dimple during entry into the grids of the fuel assembly skeleton. The rod gripper has a stress relief surface at the closed slot end of each slot to avoid failure in the flexing fingers.

Nuclear fuel rod loader for pulling fuel rods into a fuel assembly

An improved end plug for attachment on an end of a cladding tube of a nuclear fuel rod facilitates using a gripper tool for loading the fuel rod into a nuclear fuel assembly. The end plug includes an inner portion adapted to be inserted into the end of the tube and an outer portion adapted to extend from the end of the tube when the inner portion is inserted therein. The outer plug portion has a body part disposed adjacent the tube end and a leading part disposed remote from the tube end. The leading part of the outer plug portion has a hollow interior cavity defined therein, an exterior annular truncated surface defined on a terminal end thereof and an exterior annular tapered surface defined on a lateral side thereof. The exterior tapered surface extends between and merges with the body part and the exterior truncated surface and provides sufficient angular inclination so as to facilitate insertion of the end plug when mounted on the fuel rod tube end into the fuel assembly. The interior cavity in the leading part has an inner end, an outer opening defined at and surrounded by the exterior annular truncated surface and an interior annular wall surface interconnecting the inner end and the outer opening. An undercut annular groove is defined in the interior wall surface of the cavity, has a larger diametrical size than the interior wall surface and is spaced from the cavity opening. The groove is engageable by the gripper tool when fitted through the cavity opening for loading the fuel rod into the nuclear fuel assembly. The leading part has a thickness between the exterior tapered surface thereon and the interior cavity undercut groove therein which is less than the radius of the groove and greater than the width of the exterior truncated surface, and the interior wall surface of the cavity has an axial length between the exterior truncated surface and the undercut groove which is greater than the axial width of the groove, such that the leading part is provided with sufficient wall structure laterally surrounding the interior cavity to react the forces created by engagement of the gripper tool within the cavity groove.

End plug with truncated tapered leading end configuration

An apparatus for applying an end plug to a nuclear fuel rod tube end includes a stationary base, a support carriage and a track assembly mounting the support carriage on the base for reciprocal movement relative to the base. The apparatus also includes a plugger guide supported on the carriage for movement therewith. The plugger guide has an elongated central bore with one end for receiving the end plug and an opposite end for receiving the tube end. The plugger guide contains a plurality of sets of bearings in spaced axial positions along the bore which adapts it to guide the tube end toward the end plug for application of the end plug into the tube end as the carriage is moved.

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Columbia, SC, United States of America

David A Boatwright