Neutron absorber pellets with modified microstructure
AssigneeWestinghouse Electric Corp.
InventorKenneth C. Radford
Life of this patent
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Abstract
An improved annular burnable poison pellet of aluminum oxide-boron carbide (Al.sub.2 O.sub.3 --B.sub.4 C) adapted for positioning in the annular space of concentrically disposed zircaloy tubes. Each tubular pellet is fabricated from Al.sub.2 O.sub.3 powders of moderate sintering activity which serves as a matrix for B.sub.4 C medium size particle distrbution. Special pellet moisture controls are incorporated in the pellet for moisture stability and the pellet is sintered in the temperature range of 1630.degree.-1650.degree. C. This method of fabrication produces a pellet about 2 inch long with a wall thickness of about 0.020 inch to 0.040 inch. Fabricating each pellet to about 70% theoretical density gives an optimum compromise between fabricability, microstructure, strength and moisture absorption.
Claims11
A sintered burnable absorber pellet for use in a nuclear reactor fuel assembly comprising:
- a body of burnable absorber material adapted for positioning in the space between a pair of metal rods in said assembly, said material including aluminum oxide which serves as a matrix for a neutron absorbing compound selected from the group of boron, gadolinium, samarium, cadmium, europium, hafnium and indium, and
- a sintering additive in said material for limiting the moisture adsorption of said material after sintering, said additive including silica containing compounds having an equivalent SiO.sub.2 content of at least 1 wt.% of said material.
A sintered burnable absorber for use in a nuclear reactor fuel assembly comprising
- a sintered pellet of burnable absorber material including moderately sinterable aluminum oxide and boron carbide particles of about 5 to 20 .mu.m size for establishing a theoretical density of about 70% in the pellet, and
- an additive of about 3-4 wt.% silicic acid for modifying the open surface areas in the pellet and providing adequate moisture stability to the pellet.
The process of manufacturing a burnable absorber pellet comprising the steps of:
- mixing a sinterable alumina powder with about 15 wt.% boron carbide of about 5 to 20 .mu.m particle size and an additive sintering aid including silica containing compounds having an equivalent SiO.sub.2 content of at least 1 wt.% of the pellet for imparting moisture stability to the pellet;
- spray drying the foregoing mixture, forcing the mixture into a pellet and isostatically pressing the pellet into a unified mass,
- sintering the pellet at a temperature of 1625.degree. C..+-.25.degree. C. in an inert gas;
- grinding the pellet to a substantially uniform diameter, and thereafter annealing the pellet to remove strain energy introduced during grinding.
Dependencies are inferred from the claim text.