Patent Application
20110146597
The subject matter disclosed herein relates generally to boiling water reactors and more specifically to systems and methods for securing a riser brace to a riser pipe in a boiling water reactor.
Boiling water reactors typically include a coolant recirculation system providing forced convection flow through the core. A portion of the water flowing through the downcomer annulus is withdrawn from the reactor vessel via a recirculation water outlet and is fed under pressure into a plurality of jet pump assemblies distributed about the core shroud within the downcomer annulus. The jet pump assemblies produce a forced convection flow through the core, providing the required reactor core water flow.
The riser pipe of a jet pump assembly is supported and stabilized within the reactor vessel by a riser brace attached to the riser pipe and to an attachment wall, the attachment wall typically being the reactor vessel wall. The riser brace provides lateral and radial support to the riser pipe. In addition, the riser brace is designed to accommodate the differential thermal expansion resulting from reactor start-up and heat-up, and to accommodate the flow-induced vibration incumbent in the reactor water circulation system due to reactor recirculation pumps.
Commonly, the riser brace is attached to the riser pipe and to the attachment wall by being welded to the riser pipe and to the attachment wall. The riser brace is normally attached to the riser pipe via a weld. However, cracks have been known to develop in these welds. Also, intergranular stress corrosion cracking (IGSCC) resulting from corrosion, radiation, and/or stress occurs in the welds between the riser brace and the riser pipe. Cracks can grow in size and reach critical sizes for mechanical fatigue crack to the detriment of the jet pump assembly.
Accordingly, there is a need for reinforcing the weld between a riser pipe and a riser brace of a jet pump assembly, including mitigating or repairing a cracked weld to maintain structural integrity of the jet pump assembly and to avoid excessive vibration of the riser pipe or brace. There is an additional need for redundant structural support to the weld between a riser pipe and riser brace. Previously proposed designs are complicated, requiring the inlet mixer to be removed. Previous designs must also be extremely accurate to fit correctly and must be machined in the field for each particular application.
The various embodiments overcome the shortcomings of the prior art by providing an apparatus and method that mechanically reinforces the weld between a riser pipe and riser braces in boiling water reactors. The installation of the system is simple and allows for minute adjustments and error correction without having to machine parts. It also allows for installation without inlet mixer removal. Cost cutting aspects are found in the absence of a need for specific machining and particular training.
According to an exemplary embodiment, an assembly for securing a riser brace to a riser pipe includes brackets configured to engage a yoke of the riser brace and clamp bands that are configured to extend around the riser pipe and connect to the brackets. The assembly also includes a connection that connects the assembly as a unit and is configured to adjust the tightness of the assembly around the riser pipe and riser brace.
The foregoing has broadly outlined some of the aspects and features of the various embodiments, which should be construed to be merely illustrative of various potential applications. Other beneficial results can be obtained by applying the disclosed information in a different manner or by combining various aspects of the disclosed embodiments. Other aspects and a more comprehensive understanding may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings, in addition to the scope defined by the claims.
As required, detailed embodiments are disclosed herein. It must be understood that the disclosed embodiments are merely exemplary of various and alternative forms. As used herein, the word “exemplary” is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. In other instances, well-known components, systems, materials, or methods that are know to those having ordinary skill in the art have not been described in detail in order to avoid obscuring the present disclosure. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art.
A boiling water reactor 10 shown in
The jet pump assembly 18 includes a riser pipe 22 and inlet mixers 24a, 24b, each which extends substantially vertically in the annular region 16. The inlet mixers 24a, 24b are positioned on opposite sides of the riser pipe 22. Lateral support for the inlet mixers 24a, 24b is provided by restrainer supports 30a, 30b respectively attached between the inlet mixers 24a, 24b and the riser pipe 22.
A transition piece 32 connects the upper end of the riser pipe 22 and the upper ends of the inlet mixers 24a, 24b. The lower end of the riser pipe 22 includes an elbow 34 that curves toward and extends through the wall 36 of reactor pressure vessel 12 to a recirculation inlet nozzle (not shown) outside of the wall 36. The lower ends of the inlet mixers 24a, 24b include diffusers 26a, 26b that are mounted over holes in a pump deck 28. The pump deck 28 connects a bottom portion of the core shroud 14 with the reactor pressure vessel 12.
The riser pipe 22 is supported and stabilized within the annular region 16 by a riser brace assembly 40 and a riser brace 42. Referring to
The brackets 44a, 44b are configured to slip onto or around the riser brace 42. Each bracket 44 includes a recess 60 that is configured to receive a corner of the yoke 50 and separates upper and lower portions of the bracket 44. The illustrated brackets 44 each include studs 62 and nuts 64 that facilitate securing the clamp bands 46a, 46b to the brackets 44a, 44b and tightening the clamp bands 46 and brackets 44 around the riser brace 42 and riser pipe 22. In alternative embodiments, a connection between a bracket and a clamp band can be made with other mechanical fasteners, welds, mechanical connections, hooks, clips, combinations thereof, and the like. Brackets and clamp bands, or portions of each, can be integrally formed pieces. In alternative embodiments, an assembly of brackets and clamp bands can be tightened around the riser pipe and riser brace using a worm gear and the like. In general, one or more connections that connect the assembly as a unit are configured to adjust the tightness of the assembly around the riser pipe and riser brace.
Recess 60 maintains the position of the bracket 44 at the corner of the yoke 50. In alternative embodiments, the bracket has a C-shaped cross-section such that the recess is configured to receive an end of the yoke 50 and can be adjustably positioned along the length of the yoke 50.
The clamp bands 46a, 46b are shaped to be complementary to the convex curvature of the riser pipe 22 and include flanges 70 with apertures 72 that are configured to receive the studs 62. The clamp bands 46a, 46b are sufficiently flexible to be used with riser pipes of different diameters.
The riser brace 42 is welded to the riser pipe 22 and the wall 36. The brackets 44a, 44b and clamp bands 46a, 46b or the riser brace assembly 40 are installed to support the welds. In alternative embodiments, the riser brace 42 is welded to the wall 36 and the brackets 44a, 44b and clamp bands 46a, 46b secure the riser brace 42 to the riser pipe 22 without the need for welds. One advantage of the riser brace assembly 40 is that it is configured to be installed without removing the inlet mixers 24a, 24b. Exemplary methods of installing the riser brace assembly 40 to support the riser pipe 22 and riser brace 42 are now described in further detail.
As shown in
The brackets 44a, 44b attach to the shroud side of the yoke 50 with the yoke 50 being received in the recesses 60 and the studs 62 extending toward the wall 36. The clamp bands 46a, 46b are placed against the attachment wall 36 side of the riser pipe 22 with a stud 62 of each of the brackets 44a, 44b received in the apertures 72. The nuts 64 attach to the studs 62 to secure the clamp bands 46a, 46b to the brackets 44a, 44b. The nuts 64 are tightened to frictionally secure the riser brace 42 against the riser pipe 22. Tightening the nuts 64 pulls the clamp bands 46a, 46b and the brackets 44a, 44b together, which causes the brackets 44a, 44b to force the riser brace 42 against the riser pipe 22.
The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
