Westinghouse Electric Corporation

John V Miller

William R Carlson

Robert K Gjertsen

Donald G Sherwood

Terry L Schulz

Denis J Altman

Allen L Morris

Eric D Rinker

Michael B Yarbrough

Steven J Lovasic

William R Snyder

Hybrid nuclear reactor grey rods are described, wherein geometric combinations of relatively weak neutron absorber materials such as stainless steel, zirconium or INCONEL, and relatively strong neutron absorber materials, such as hafnium, silver-indium cadmium and boron carbide, are used to obtain the reactivity worths required to reach zero boron change load follow. One embodiment includes a grey rod which has combinations of weak and strong neutron absorber pellets in a stainless steel cladding. The respective pellets can be of differing heights. A second embodiment includes a grey rod with a relatively thick stainless steel cladding receiving relatively strong neutron absorber pellets only. A third embodiment includes annular relatively weak netron absorber pellets with a smaller diameter pellet of relatively strong absorber material contained within the aperture of each relatively weak absorber pellet. The fourth embodiment includes pellets made of a homogeneous alloy of hafnium and a relatively weak absorber material, with the percentage of hafnium chosen to obtain the desired reactivity worth.

Hybrid nuclear reactor grey rod to obtain required reactivity worth

A vent system for controlling hydraulically actuated drive means for selectively moving pluralities of rod clusters respectively connected to the plurality of drive means between fully inserted positions within the lower barrel assembly of the vessel in telescoping relationship with fuel rod assemblies contained therein, and a fully withdrawn position. Each drive means responds to the reactor coolant fluid pressure and includes a leakage passage and an outlet channel through which a leakage flow may pass under control of the vent system, the latter comprising a valve arrangement, flow restrictors and a common orifice through which the outlet channels are selectively connected to essentially ambient pressure, for establishing a pressure differential within each drive means producing a net force for moving the drive rods and associated clusters to the withdrawn position at which the drive means mechanically latch the fully withdrawn clusters for mechanically supporting same in the fully withdrawn position. The valve arrangement may be selectively actuated to reestablish the pressure differential within each drive means thereby to raise the associated drive rods and release same from the mechanically latched positions, after which the valve arrangement is selectively operated to establish pressure equilibrium within the drive means to permit the corresponding drive rods and associated control rod clusters to fall by force of gravity to the fully inserted positions thereof. Display indications and control panel operation provide for operator sensing of the rod cluster positions and control of the valve arrangement.

Vent system for displacer rod drive mechanism of pressurized water

A fuel assembly includes top and bottom nozzles, elongated hollow control rod guide thimbles extending longitudinally between and rigidly interconnecting the top and bottom nozzles such that together they form a rigid structural skeleton of the fuel assembly, transverse grids being supported on the guide thimbles at axially spaced locations therealong between the top and bottom nozzles, fuel rods extending through and being supported by the grids between the top and bottom nozzles so as to extend in generally side-by-side spaced relation to one another and to the guide thimbles, and elongated solid tie rods extending longitudinally between the top and bottom nozzles and through and rigidly interconnected with the grids so as to extend in generally side-by-side spaced relation to one another, to the fuel rods and to the guide thimbles so as to bolster the stiffness of the structural skeleton of the fuel assembly. Each of the guide thimbles has a cross-sectional size which occupies a position in the fuel assembly substantially equivalent to the positions of more than one of the fuel rods, whereas each of the tie rods has a cross-sectional size which occupies a position in the fuel assembly substantially equivalent to the position of only one of the fuel rods. While each guide thimble has a cross-sectional size which is larger than the cross-sectional size of each tie rods, the cross-sectional area of the tie rod is substantially equal to the cross-sectional area of the guide thimble.

Nuclear fuel assembly incorporating primary and secondary structural

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Munhall, PA, United States of America

John V Miller