Nuclear reactor grid strip cantilever spring with nonuniform material characteristics
AssigneeCombustion Engineering, Inc.
InventorPatrick A. Perrotti
Life of this patent
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Abstract
A metal component (10) having non-uniform material characteristics which cause the component to undergo differential growth upon exposure to a neutron flux, and a process for producing such a component. The invention is useful for making metal components for use in nuclear reactors, particularly fuel assembly cantilever grid springs (12). By cold working a portion (40) of a cantilever spring on the convex side of the curved region of the spring, a spring can be provided which has a smaller reduction in preload upon exposure to radiation than a conventional cantilever spring.
Claims18
A grid strip for a nuclear reactor fuel assembly, the grid strip having a plurality of loaded metal cantilever springs which grow and relax when subjected to irradiation, each spring having a first end portion connected to the grid strip, a second end portion with an unattached terminal end, a length extending along the spring from the first end to the second end, and a thickness, the first end portion including a first curved portion which is curved in a first direction and the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, the first curved portion having a first layer including a convex exterior surface and a second layer including a concave exterior surface, the first and second layers being opposite each other in a direction parallel to the thickness of the spring, the first layer having different material characteristics than the second layer such that upon irradiation of the grid strip the relaxation of the spring is at least partially offset by differential growth of the first and second layers, the second end portion having substantially uniform material characteristics throughout its thickness.
A loaded metal nuclear reactor cantilever grid spring which grows and relaxes as a result of irradiation, the spring having a length, a thickness, a supported first end portion and a second end portion with an unsupported terminal end, the first end portion including a first curved portion which is curved in a first direction and the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, the first curved portion including a first layer having a convex exterior surface and a second layer having a concave exterior surface, the first and second layers being opposite each other in a direction parallel to the thickness of the spring, the first layer having different material characteristics than the second layer such that upon irradiation of the grid spring, any relaxation in the spring is at least partially offset by differential growth of the first and second layers, the second end portion having a substantially uniform composition and substantially uniform material characteristics throughout its thickness.
A process for minimizing the loss in load of a zirconium cantilever spring, the spring having a length, a thickness, a supported first end portion and an opposite second end portion with un unsupported terminal end, the first end portion including a first curved portion which is curved in a first direction and has opposite convex and concave exterior surfaces, the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, the process comprising the step of shot peening the convex exterior surface of the first end portion without shot peening the second end portion to form a shot peened layer which extends through only part of the thickness of the first curved portion, the degree of shot peening being sufficient to result in differential growth of the first and second layers of the spring upon exposure to a neutron flux.
In a metal cantilever grid spring for use in a nuclear reactor fuel assembly, the spring being formed from a metal which grows as a result of exposure to radiation and comprising a supported first end portion and a second end portion with an unattached terminal end, the first end portion including a first curved portion which is curved in a first direction and the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, the first curved portion including a concave exterior surface and an opposite convex exterior surface, the improvement wherein the first curved portion of the spring includes a first layer including the convex exterior surface and a second layer including the concave exterior surface, the first and second layers each having a length and being opposite each other in a direction parallel to the thickness of the curved portion, the first layer having been specially treated to experience an increase in length upon exposure to a neutron flux which is sufficiently different from the increase in length of the second layer upon exposure to the neutron flux to result in a lower rate of radiation-induced loss in spring load of the spring than the rate of radiation-induced load loss of a spring which does not have a curved portion with a specially treated first layer, the second layer and the second end portion remaining untreated.
A component for use in a nuclear reactor fuel assembly having a cantilevered portion, the cantilevered portion being formed from a metal which grows as a result of exposure to a neutron flux, the cantilevered portion having a length, a thickness, a supported first end portion, and an opposite second portion with an unsupported terminal end, the first end portion including a first curved portion which is curved in a first direction and the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, the first curved portion including a first layer having a convex exterior surface and a second layer having a concave exterior surface, the first and second layers being opposite each other in a direction parallel to the thickness of the spring, the first and second layers having different material characteristics such that upon irradiation of the grid spring any relaxation in the spring is at least partially offset by differential growth of the first and second layers, the second end portion having a substantially uniform composition and substantially uniform material characteristics throughout its thickness, the degree of curvature of the first curved portion changing upon exposure to a neutron flux due to differential growth of the first and second layers.
A method of making a cantilevered metal component for use in a nuclear reactor, comprising:
- obtaining a component which is formed from metal that grows as a result of exposure to radiation, the component having a length, a thickness, a supported first end portion and an opposite second end portion with an unsupported terminal end, the first end portion including a first curved portion which is curved in a first direction and has opposite concave and convex exterior surfaces, the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, and
- cold working the convex exterior surface of the first curved portion without cold working the second end portion to result in the first curved portion having a first degree of curvature and to impart to the first curved portion characteristics sufficient to cause the degree of curvature of the first curved portion to increase to a second degree of curvature upon exposure to a neutron flux.
A fuel assembly for use in a nuclear reactor, comprising a metal component, the component having a cantilevered portion including:
- an attached first end portion which is connected to a support,
- an opposite second end portion with an unattached terminal end,
- the first end portion including a first curved portion which is curved in a first direction and the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, the first curved portion including a shot peened first layer including a convex surface, and a second layer overlapping the first layer in a direction which is parallel to the thickness of the curved portion and including a concave surface, the first layer growing at a different rate than the second layer upon exposure to a neutron flux, the second end portion having substantially uniform material characteristics throughout its thickness.
A process for producing a pre-load retaining nuclear reactor grid spring for supporting a fuel rod, comprising the steps of:
- (a) obtaining a grid spring having a length, a thickness, a supported first end portion and an opposite second end portion with an unsupported terminal end, the first end portion including a first curved portion which is curved in a first direction and has opposite concave and convex exterior surfaces, the second end portion including a second curved portion which is curved in a second direction which is opposite to the first direction, and
- (b) shot peening the convex exterior surface of the first curved portion without shot peening the concave exterior surface and the second end portion to form a shot peened layer which extends through only part of the thickness of the first curved portion.
Dependencies are inferred from the claim text.