KINETICALLY APPLIED GRADATED Zr-Al-C OR Ti-Al-C CERAMIC OR AMORPHOUS OR SEMI-AMORPHOUS STAINLESS STEEL WITH NUCLEAR GRADE ZIRCONIUM ALLOY METAL STRUCTURE

Abstract

A composition and method of kinetically depositing the composition to form a coating onto an exterior surface of a zirconium alloy cladding of a light water nuclear reactor which at least partially adheres to the exterior surface. The coating composition includes a first component and a second component. The first component is selected from the group consisting of zirconium, zirconium oxide and mixtures thereof. The second component is selected from the group consisting of Zr.sub.2AlC ceramic, Ti.sub.2AlC ceramic, Ti.sub.3AlC.sub.2 ceramic, Al.sub.2O.sub.3, aluminum, zirconium silicide, amorphous and semi-amorphous alloyed stainless steel, and mixtures of Zr.sub.2AlC ceramic, Ti.sub.2AlC ceramic and Ti.sub.3AlC.sub.2 ceramic. The coating has a gradient emanating from the exterior surface of the cladding toward an exposed outer surface of the coating such that percent by weight of the first component decreases and the second component increases from the exterior surface of the cladding toward the exposed outer surface of the coating.

Claims

1. A coating composition for kinetic deposition on an exterior surface of a zirconium alloy cladding to form a coating which at least partially adheres to said exterior surface, the zirconium alloy cladding inherently having a zirconium oxide-containing layer thereon, the coating composition comprises: a first component selected from the group consisting of zirconium, zirconium oxide and mixtures thereof; and a second component selected from the group consisting of Zr.sub.2AlC ceramic, Ti.sub.2AlC ceramic, Ti.sub.3AlC.sub.2 ceramic, Al.sub.2O.sub.3, aluminum, zirconium silicide, amorphous or semi-amorphous alloyed stainless steel, and mixtures of Zr.sub.2AlC ceramic, Ti.sub.2AlC ceramic and Ti.sub.3AlC.sub.2 ceramic, wherein, the coating formed by the coating composition has a gradient emanating from the exterior surface of the cladding toward an exposed outer surface of the coating such that percent by weight of the first component decreases from the exterior surface of the cladding toward the exposed outer surface of the coating and percent by weight of the second component increases from the exterior surface of the cladding to the exposed outer surface of the coating, based on total weight of the coating composition.

2. The coating composition of claim 1, wherein the coating at least partially penetrates the zirconium oxide-containing layer.

3. The coating composition of claim 1, wherein the coating is formed by one or more passes of a kinetic deposition technique.

4. The coating composition of claim 3, wherein a first pass may include kinetically depositing the coating composition to form a first layer which comprises from about 75% to about 100% by weight of the first component and from about 0% to about 25% by weight of the second component based on total weight of the coating composition.

5. The coating composition of claim 3, wherein a final pass may include kinetically depositing the coating composition to form the exposed outer surface which comprises from about 75% to about 100% by weight of the second component and from about 0% to about 25% by weight of the first component based on total weight of the coating composition.

6. The coating composition of claim 1, wherein a portion of the coating composition mixes with the zirconium oxide-containing layer to form an integrated layer.

7. The coating composition of claim 1, wherein the coating is from about 5 to about 100 micrometers in thickness.

8. The coating composition of claim 1, wherein the coating is from about 5 to about 50 micrometers in thickness.

9. A coated zirconium alloy cladding, comprising: an uncoated zirconium alloy cladding; a zirconium oxide-containing layer existing on the uncoated zirconium alloy cladding; a coating having a gradient and a thickness, applied to the uncoated zirconium alloy cladding with the zirconium oxide-containing layer existing thereon, the coating comprising: a first component selected from the group consisting of zirconium, zirconium oxide and mixtures thereof; and a second component selected from the group consisting of Zr.sub.2AlC ceramic, Ti.sub.2AlC ceramic, Ti.sub.3AlC.sub.2 ceramic, Al.sub.2O.sub.3, aluminum, zirconium silicide, amorphous or semi-amorphous alloyed stainless steel, and mixtures of Zr.sub.2AlC ceramic, Ti.sub.2AlC ceramic and Ti.sub.3AlC.sub.2 ceramic, wherein, the thickness of the coating emanates from the exterior surface of the cladding toward an exposed outer surface of the coating, such that percent by weight of the first component decreases from the exterior surface of the cladding toward the exposed outer surface of the coating, and percent by weight of the second component increases from the exterior surface of the cladding to the exposed outer surface of the coating, to form the gradient.

10. The coated zirconium alloy cladding of claim 9, wherein the coating at least partially penetrates the zirconium oxide-containing layer.

11. The coated zirconium alloy cladding of claim 9, wherein the coating is formed by one or more passes of a kinetic deposition technique.

12. The coated zirconium alloy cladding of claim 11, wherein a first pass includes depositing the coating to form a first layer which comprises from about 75% to about 100% by weight of the first component and from about 0% to about 25% by weight of the second component based on total weight.

13. The coated zirconium alloy cladding of claim 11, wherein a final pass includes depositing the coating to form the exposed outer surface which comprises from about 75% to about 100% by weight of the second component and from about 0% to about 25% by weight of the first component based on total weight.

14. The coated zirconium alloy cladding of claim 9, wherein a portion of the coating mixes with the zirconium oxide-containing layer to form an integrated layer.

15. The coated zirconium alloy cladding of claim 9, wherein the coating is from about 5 to about 100 micrometers in thickness.

16. The coated zirconium alloy cladding of claim 9, wherein the coating is from about 5 to about 50 micrometers in thickness.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

[0014] FIG. 1 is a cross-section view of a coated zirconium alloy substrate in accordance with the prior art;

[0015] FIG. 2 is a cross-section view of a coated zirconium alloy substrate in accordance with certain embodiments of the invention; and

[0016] FIG. 3 is a block diagram of a method of applying a coating material employing a kinetic deposition technique in accordance with certain embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] The invention provides a coating composition which includes a zirconium compound and a compound which protects the cladding surface from bulk oxidation. The coating composition is deposited on an exterior surface of a zirconium alloy cladding, e.g., tube. The deposition can be performed using various conventional techniques, such as a kinetic deposition technique (referred to as cold spray). The zirconium alloy cladding tube typically has a zirconium-oxide layer inherently formed on at least a portion of its exterior surface. Deposition of the coating composition results in a coating being formed on at least a portion of the exterior surface of the zirconium alloy cladding tube.

[0018] The zirconium alloy cladding is positioned in the core of a light water nuclear reactor, such as a pressurized water reactor (PWR) or a boiling water reactor (BWR). Thus, the cladding is exposed to a high temperature and pressure water environment.

[0019] The coating composition of the invention includes a first component and a second component. The first component includes zirconium, zirconium oxide or mixtures thereof. The second component includes Zr.sub.2AlC ceramic, Ti.sub.2AlC ceramic, Ti.sub.3AlC.sub.2 ceramic, Al.sub.2O.sub.3, aluminum, zirconium silicide (ZrSi.sub.2), amorphous or semi-amorphous alloyed stainless steel, or mixtures of Zr.sub.2AlC, Ti.sub.2AlC and Ti.sub.3AlC.sub.2.

[0020] Since the zirconium alloy cladding inherently has at least partially formed on its exterior surface a zirconium oxide-containing layer or film, the coating composition is actually deposited on and adhered to this zirconium oxide-containing layer. Deposition of the coating composition of the invention results in a gradient coating or matrix that emanates from the exterior surface of the zirconium alloy cladding to an outer exposed surface of the coating. This gradient coating is effective to eliminate bulk oxidation of the zirconium alloy cladding upon exposure to PWR or BWR conditions, e.g., coolant that circulates in the reactor core. The gradient of the coating is such that the amount or weight percent (based on total weight of the coating composition) of each of the first and second components increases or decreases as the coating thickness emanates from the surface of the coating which is adjacent to or near the zirconium alloy cladding surface toward the exposed outer surface of the coating. In certain embodiments, the amount of the first component decreases as the coating thickness emanates from the surface adjacent to or near the zirconium alloy cladding surface toward the exposed outer coating surface, and the amount of the second component increases as the coating thickness emanates from the surface adjacent to or near the zirconium alloy cladding surface toward the exposed outer coating surface. Further, the decrease in the amount of the first component may correspond to the increase in the amount of the second component. For example, when the weight percent of the first component decreases from about 75% by weight at the surface of the coating adjacent to or near the cladding surface to about 10% by weight at the exposed outer surface, the weight percent of the second component correspondingly increases from about 25% by weight at the surface of the coating adjacent to or near the cladding surface to about 90% by weight at the exposed outer surface of the coating. In certain embodiments, the weight percent of each of the first and second components may decrease and increase, respectively, such that the first component is present on the exposed outer surface of the coating in an amount of about 0% by weight and the second component is present on the exposed outer surface of the coating in an amount of about 100% by weight.

[0021] The coating composition may be deposited onto the exterior surface of the zirconium alloy cladding to form the gradient coating by employing various coating techniques known in the art. In certain embodiments, the coating composition is deposited using a conventional kinetic deposition technique which generally includes directing particulate material by a gas stream toward a substrate. In accordance with the invention, typically, the coating composition is propelled by a propulsive gas stream toward the zirconium alloy cladding. The first and second components of the coating composition may each be propelled separately or they may be propelled together, e.g., in a blend or mixture. The coating composition may be propelled at room temperature or may be pre-heated to an elevated temperature, e.g., at or above the melting temperature of the first and second components. Without intending to be bound by any particular theory, it is believed that this method of kinetic deposition is capable of at least partially disrupting the zirconium-oxide layer which is inherently formed on the zirconium alloy cladding such that the resulting coating is firmly bonded, e.g., atom-to-atom, to the cladding surface.

[0022] The gradient coating may be formed in several passes or in a single pass. In certain embodiments wherein several passes are employed, the first pass includes an excess amount of the first component. That is, the first component is present in greater than about 50% by weight based on total weight of the coating composition. In other embodiments, the first component in the first pass may be present in about 75% by weight or greater based on total weight of the coating composition. The remainder of the coating composition being composed of the second component. In certain embodiments, the first pass includes about 100% by weight of the first component and about 0% by weight of the second component based on total weight of the coating composition. In each subsequent pass, the amount of the first component decreases and the amount of the second component increases. In certain embodiments, the amount by which the first component decreases is equal to the amount by which the second component increases.

[0023] In alternate embodiments, a single pass technique is employed. In these embodiments, the amount (e.g., percent by weight) of each of the first and second components in the coating composition is continually varied to produce the gradient coating.

[0024] The kinetic deposition methodology of the invention produces an integrated gradient coating that is richer in the first component, e.g., the zirconium or zirconium oxide, in the portion of the coating that is closer to the substrate, e.g., zirconium alloy cladding, and richer in the second component, e.g., the oxidation resistant material, in the portion of the coating that is nearer the exposed surface of the coating. In certain embodiments in accordance with the invention, the first component is present in excess (e.g., as compared to the second component) near the zirconium alloy cladding surface and the presence of the first component decreases throughout the coating thickness such that the exposed surface of the coating has an excess of the second component. Without intending to be bound by any particular theory, it is believed that the increased presence of the first component adjacent to or near the cladding tube surface enhances incorporation of the gradient coating onto and into the surface, as the coating composition is chemically similar to the zirconium alloy cladding composition and, gradually changes the thermal expansion and radiation swelling characteristics to minimize thermal and radiation stresses during operation.

[0025] In certain embodiments of the invention, the gradient coating of the invention is created by kinetically depositing a first layer of the coating composition which includes from about 50% to about 100% or from greater than about 50% to about 100% or from about 75% to about 95% by weight of the first component, and from about 0% to about 50% or from about 0% to less than about 50% or from about 5% to about 25% by weight of the second component, based on total weight of the coating composition. In certain embodiments, the first component is zirconium alloy. Subsequently, additional layers of the coating composition may be deposited on the first layer. In certain embodiments, in each of the additional layers, the amount of the first component will successively decrease and the amount of the second component will successively increase. As a result, the exposed outer surface of the coating is composed of an excess of the second component such that it retains the oxidation resistant behavior of the second component while a base is present (e.g., underlying layers) that is rich in zirconium, i.e., the first component.

[0026] The method of the invention is generally directed to depositing an oxidation resistant material into a zirconium oxide layer, such that the oxidation resistant material ultimately penetrates into the zirconium substrate resulting in strong adhesion, and the oxidation resistant material deposited on the exposed outer coating surface provides a dense oxidation resistant surface that protects the underlying substrate from the nuclear reactor environment.

[0027] FIG. 2 shows an integrated gradient coating deposited on a zirconium alloy substrate 10 in accordance with certain embodiments of the invention. In FIG. 2, a coating layer 20 containing zirconium alloy, e.g., the first component is applied to the zirconium alloy substrate 10. The zirconium alloy substrate 10 includes an oxidation layer 12 thereon. The coating layer 20 is adjacent to the oxidation layer 12. Within the coating layer 20 is an integration layer 22. Without intending to be bound by any particular theory, it is believed that a portion of the coating layer 20 mixes together or integrates with a portion of the oxidation layer 12, to form the integration layer 22 adjacent to the oxidation layer 12, which may penetrate within the zirconium alloy substrate 10. The zirconium (e.g., the first component) content of the coating layer 20 increases toward the zirconium alloy substrate 10 as shown by arrow 24 and the non-zirconium species (e.g., the second component) content increases toward the outside surface 26 as shown by arrow 28.

[0028] Typically, the gradient coating layer 20 is deposited and the integration layer 22 formed as a result of several passes of the kinetic deposition technique described herein. Each successive deposition increases in the non-zirconium alloy species, e.g., the second component, and decreases in zirconium alloy, e.g., the first component, content. In certain embodiments, a single pass deposition technique may be employed where the coating composition itself is altered in a continuous manner such that multiple passes are not required. The thickness of the coating layer 20 may vary and in certain embodiments is less than or equal to about 100 micrometers thick, or more preferably from about 5 to about 100 micrometers thick, or from about 5 to about 50 micrometers thick.

[0029] The higher concentration of zirconium alloy, e.g., the first component, near the base of the coating layer 20, e.g., its presence in excess as compared to the second (non-zirconium) component, and its presence in general, reduces thermal stresses incorporated by the kinetic deposition technique and in operation, reduces thermal coefficient and radiation swelling mismatches between the corrosion resistant additive, e.g., the second component, and the zirconium alloy cladding, thus increasing the propensity of the coating layer 20 to adhere to the zirconium alloy cladding 10.

[0030] The gradient coating of the invention provides numerous benefits over known corrosion resistant coatings. For example, known coatings may be applied on top of, e.g., overlay, the oxidation layer resulting in poor adhesion and failure. In the invention as shown in FIG. 2, the gradient coating provides oxidation resistant material directly into the oxidation layer which ultimately penetrates into the zirconium alloy cladding resulting in strong adhesion and a dense oxidation resistant surface that protects the underlying cladding from the reactor environment.

[0031] FIG. 3 shows a method of depositing a coating composition, e.g., the first and second components, in accordance with certain embodiments of this invention. A zirconium alloy tube 30 is supplied. A coating composition 32 is supplied to a Kinetic Cold Spray or Thermal Spray Deposition Process (KCS/TSDP) 34. The KCS/TSDP provides or deposits the coating composition 32 to form a gradient coating 36.

[0032] While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.