Jet pump clamp and method for use in nuclear reactor jet pumps

Abstract

The jet pump clamp fits onto the modified jet pump assembly at the junction of the riser pipe and the restraint fitting. The clamp can secure the restraint fitting and riser pipe, preventing the restraint fitting from moving while relieving the weld between the same stresses. The clamp can include multiple members on either side of the restraint fitting that fit onto the surface of the riser pipe. When these members are drawn together by the clamping action, the underlying riser pipe is compressed. Similarly, vertically adjustable members can seat on and / or through the restraint fitting to hold the fitting stable. The jet pump assembly can be prepared by forming a groove in the riser pipe, a hole in the restraint fitting, and a spherical depression. The clamp can be installed in the grooves and holes during installation or during a maintenance outage at a commercial nuclear power plant.

Description

Technical Field

[0004] , , , , , ,

[0003]

[0001] FIG. 1A is a front view of a related art boiling water reactor (BWR) jet pump assembly 8. The main components of the jet pump assembly 8 include a riser tube 3 inserted into each diffuser 2 and two inlet mixers 4. The shroud support plate 1 receives the fluid from the diffuser 2, supports it, and allows the flow of the jet pump drive fluid through an annular portion that houses the jet pump assembly 8. The jet pump restraint fitting 5 is welded to the riser tube 3 to stabilize the movement of the inlet mixer 4 and reduce the movement and leakage of the slip joint present at the interface between the inlet mixer 4 and the diffuser 2. The restraint fitting 5 minimizes the relative movement between the inlet mixer 4 and the restraint fitting 5 and minimizes leakage and damage around the slip joint.

[0002] FIG. 1B is a top view of the jet pump restraint fitting 5 as seen from line B - B of FIG. 1A. As seen in FIG. 1B, each fitting 5 can be welded directly to opposite side surfaces of the outer periphery of the riser tube 3. One or more guide ears 6 and / or other alignment structures can keep the inlet mixer 4 and the diffuser 2 properly aligned and / or securely confined by the corresponding fitting 5. Non - Patent Document 1 and Non - Patent Document 2 describe the operation of other related art jet pump assemblies, and their entirety is incorporated herein by reference.

Background Art

[0003] This background serves as a useful baseline or starting point for a better understanding of several exemplary embodiments described hereinafter. Except for specifically identified third - party subject matter that may be separately filed, this background and the figures are by the inventors created for the purposes of this application. What is included in this application is not necessarily known or represented as prior art.

Summary of the Invention

[0004] Exemplary embodiments include a jet pump clamp, an improved jet pump assembly containing the same, and methods for forming and installing such a clamp and assembly in a nuclear reactor. The exemplary embodiment clamp is attachable to a riser pipe and a restraint fitting joined to the riser pipe. The clamp can completely replace welds and other connections between the restraint fitting and the riser pipe, relieving pressure in the same area and holding the fitting and the riser pipe in a fixed orientation. The clamp can also compress the riser pipe within the clamp, relieving vertical strain on the pipe that can contribute to crack propagation. The exemplary embodiment jet pump assembly can include recesses on the outer surface of the riser pipe that receive portions of the clamp and vertically secure the pipe and clamp. Different members of the clamp can be drawn together vertically to compress the pipe vertically through these recesses. The assembly can further include a clamp restraint fitting having one or more vertical holes through which the clamp can pass and seat. The exemplary embodiment clamp can include retaining members that adjust vertically to fit the restraint fitting and can seat on either side of the restraint fitting hole. This allows for omnidirectional fixation of the restraint fitting and riser pipe. The clamp of the exemplary embodiment can be tightened and held in place via a variety of structures, including an adjustable draw bolt that passes through all structures, which can be tightened with a threaded crimp nut. The draw bolt and any other biasing structure can be seated against the clamp body and restraint fitting with a washer that conforms to the body and fitting surfaces, including partially spherical surfaces.

[0005] The exemplary method can prepare and / or attach clamp components to a jet pump assembly. The exemplary method can be performed at any time during fabrication, installation, or maintenance outage of the jet pump assembly. The riser pipe groove and restraint fitting hole, and their associated surfaces, can be formed by any forming process, including forging and machining. The clamp can then be attached to the groove and hole(s) in any manner and ultimately biased to impart internal compression to the riser pipe about the restraint fitting while holding the fitting and riser pipe relatively immobile. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] GL STEVENS et al, “Jet Pump Flaw Evaluation Procedures” 8th International Conference on Nuclear Engineering, Jan. 2000 [Non-patent document 2] G. SOTO-MENDOZA et al., “Cross Flow Analysis over the Jet Pumps of a BWR-5 Reactor” Science and Technology of Nuclear Installations, Vol. 2021, Mar. 27, 2021 [Brief explanation of the drawings]

[0007] Exemplary embodiments will become more apparent from a detailed description of the accompanying drawings, in which like elements are represented by like reference numerals, which are given by way of illustration only and therefore not by way of limitation to the terms they depict.

[0008] [Figure 1A]FIG. 1 is an illustration of a related art jet pump assembly used in nuclear power plants. [Figure 1B] FIG. 1B shows details of the related art jet pump assembly of FIG. 1A. [Figure 2] FIG. 2 is an illustration of an example embodiment riser pipe formed by an example method. [Figure 3] 1A-1C are illustrations of exemplary embodiment restraints formed by exemplary methods. [Figure 4] FIG. 1 is a perspective view of an exemplary embodiment jet pump clamp. [Figure 5] FIG. 5 is a side view of the jet pump clamp of the exemplary embodiment of FIG. 4. [Figure 6] FIG. 6 is a top view of the exemplary embodiment jet pump clamp of FIG. 5. [Figure 7] FIG. 1 is an explanatory diagram showing an example of an embodiment of a jet pump clamp installed on a riser pipe of a jet pump in a nuclear reactor. DETAILED DESCRIPTION OF THE INVENTION

[0009] Because this is a patent document, general broad rules of interpretation should be applied when reading this document. Everything described and shown herein is an example of the subject matter of the claims appended hereto. Specific structural and functional details disclosed herein are merely for the purpose of illustrating how to make and use the examples. Several different embodiments and methods not specifically disclosed herein may fall within the scope of the claims. Thus, the claims may be embodied in many alternative forms and should not be interpreted as limited to only the examples set forth herein.

[0010] Membership terms such as "consisting of," "including," "having," or "together" reflect the presence of the stated features, characteristics, steps, operations, elements, and / or components, but do not, by themselves, preclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and / or groups thereof. Rather, exclusive modifiers such as "only" and "singular" may preclude the presence and addition of other subjects in the modifier. The use of open-ended terms such as "may" or "can" reflects optionality, such as the absence of a modifier, but the absence of an open-ended term does not reflect compulsion. In listing items in the exemplary embodiments, conjunctions and inclusive terms such as "and," "together," and "or" include all combinations of one or more of the listed items without excluding items not listed. The use of "etc." is defined as "et cetera" and indicates the inclusion of all other elements belonging to the same group of the preceding items in any "and / or" combination(s). The modifiers "first," "second," "another," etc. do not restrict the modified items to any order. These terms are used only to distinguish one element from another. When there is a "second" or higher ordinal number, there simply must be that many elements, not necessarily a difference or other relationship between those elements.

[0011] When an element is "connected," "coupled," "on," "attached," "secured," or otherwise related to another element, it may be directly connected to the other element, or there may be intervening elements. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements. Other words used to describe relationships between elements should be interpreted similarly (e.g., "between" vs. "directly between," "adjacent" vs. "directly adjacent," etc.).

[0012] As used herein, singular forms such as "a," "an," and "the" are intended to include both the singular and the plural unless the context clearly indicates otherwise. Indefinite articles such as "a" and "an" introduce or refer to any modified term, whether previously introduced or not, while definite articles such as "the" refer to the same previously introduced term. Relative terms such as "almost" and "more," and terms of degree such as "approximately" and "substantially" reflect a 10% variation in the modified value, or a full range of imprecision that still achieves the functionality of the modified term as understood by those skilled in the art in the technical context. Precision and non-variation are expressed in opposing terms such as "exactly."

[0013] As used herein, "axial" and "vertical" refer to the same up-down direction oriented along the reactor's longitudinal axis, often oriented in the direction of gravity. A "lateral" direction is perpendicular to the "axial" direction and is a side-to-side direction at a particular axial height, while a "radial" direction is a specific lateral direction extending perpendicular to and directly away from the reactor's longitudinal axis.

[0014] The structures and operations described below may occur out of the order depicted and / or noted in the figures. For example, two operations and / or figures shown in succession may in fact be performed simultaneously or in the reverse order depending on the functionality / acts involved. Similarly, individual operations within the exemplary methods described below may be performed iteratively, individually, or sequentially to provide a loop or other sequence of operations apart from the precise operations described below. Any embodiment or method having the features and functionality described below, in any workable combination, should be presumed to be within the scope of the exemplary embodiments.

[0015] The present inventors have recognized that the riser pipes and restraint fittings of nuclear reactor jet pumps are susceptible to material degradation and failure due to the unique operating conditions in the jet pumps. The welds securing the restraint fittings to the riser pipe, known as RS-6 / 7 welds, run longitudinally and laterally through the base of the restraint fitting and are subject to intergranular stress corrosion cracking due to flow-induced vibrations and reactor conditions. These cracks can contribute to fatigue cracking in the riser pipe itself due to pressure within the riser pipe. The present inventors have recognized a need to completely eliminate such joint welds and secure the restraint fittings and riser pipe within a jet pump assembly while applying pressure to the riser pipe to avoid fatigue. To overcome these newly recognized challenges, as well as others, the present inventors have developed the exemplary embodiments and methods described below to address these and other challenges recognized by the inventors with unique solutions enabled by the exemplary embodiments.

[0016] The present invention is a jet pump clamp and a method of using the jet pump clamp to form a jet pump assembly. In contrast to the present invention, the few exemplary embodiments and exemplary methods described below are only a subset of the variety of different configurations that can be used as and / or in conjunction with the present invention.

[0017] FIG. 2 illustrates the structure of an exemplary method for preparing a jet pump assembly for clamping according to an exemplary embodiment. As shown in FIG. 2, at least one of an upper groove 301 and a lower groove 302 is formed in the riser pipe 3 of the jet pump assembly of the nuclear reactor. In this manner, the riser pipe 3 of FIG. 1A is modified to the riser pipe 3 of the exemplary embodiment of FIG. 2 that is compatible with the clamping of the exemplary embodiment. If the riser pipe 3 extends vertically, the grooves 301 and / or 302 may extend laterally or have a depth with a width extending about the circumference of the riser pipe 3. The assembly including the riser pipe 3 may be similar to an existing assembly in a U.S. commercial boiling water reactor plant or an existing assembly in a new plant with a jet pump assembly. The upper groove 301 may be formed above the restraint fitting 5, and the lower groove 302 may be formed below the restraint fitting 5.

[0018] Grooves 301 and 302 may be any distance from the restraint fitting 5 to match the positioning of the exemplary embodiment clamp described below. Grooves 301 and 302 may be any length and depth, for example, approximately 75 degrees each around the surface of the riser pipe 3 centered at the midpoint of the restraint fitting 5 where it joins to the riser pipe 3, and less than a half-inch deep, to similarly match the tongue(s) of the exemplary embodiment clamp described below. While only a single continuous groove can be used, multiple grooves can also be formed from dashes, countersunk spots, or other shapes and numbers that allow for joining to the riser pipe 3. Grooves 301 and 302 do not have to extend completely through the material of the riser pipe 3 to maintain a closed flow path within the riser pipe 3, in which case they can have any depth that maintains the structural integrity of the riser pipe 3. Grooves 301 and / or 302 can be formed by any process, including welding or cutting with a laser torch, machining such as electrical discharge machining, chemical etching, forging the pipe 3 with grooves 301 and / or 302, etc. In an exemplary method, grooves 301 and 302 may be formed during manufacture of riser pipe 3, during installation of riser pipe 3 in a reactor, after operation of riser pipe 3 in an existing reactor, such as during a maintenance outage, or at any other time.

[0019] FIG. 3 illustrates another configuration of an exemplary method for preparing a jet pump assembly for clamping according to an exemplary embodiment. As shown in FIG. 3, at least one of a left clamp hole 502 and a right clamp hole 504 is formed in the restraint fitting 5 of the jet pump assembly of the nuclear reactor. In this manner, the restraint fitting 5 of FIG. 1B is formed in the restraint fitting 5 of the exemplary embodiment of FIG. 3 to fit the clamp of the exemplary embodiment. The holes 502 and / or 504 extend completely vertically through the fitting 5. For example, the holes 502 and / or 504 can be on a flat bib or gauge on the lateral side of the fitting 5. The restraint fitting 5 and the assembly including the same can be similar to an existing assembly in a U.S. commercial boiling water reactor plant or an existing assembly in a new plant with a jet pump assembly. The holes 502 and 504 can be located anywhere in the restraint fitting 5 to match the locations of the clamps of the exemplary embodiment described below. The left clamp hole 502 and the right clamp hole 504 may be formed equidistant from the midpoint of the restraint fitting 5 welded to the riser pipe 3 (FIG. 1A), as shown in FIG. 3, for example.

[0020] Bushing seats 501 and 503 may be formed about respective holes 502 and 504 to provide an improved fit and clamping surface for structures mating thereto, including the exemplary embodiment clamps described below. For example, seats 501 and 503 may be spherical or elliptical cross-sectional surfaces centered about holes 502 and 504 on both the upper and lower sides of fitting 5. Neither seat 501 and / or 503 may extend completely through fitting 5, which may maintain the thickness of fitting 5 in order to maintain the structural integrity of fitting 5.

[0021] Holes 502 and / or 504 can be any shape, such as holes one inch (approximately 2.54 centimeters) in diameter or less, to similarly mate with the bolt(s) or other penetration structure of the exemplary embodiment clamp described below. While only a single hole can be used, any number of holes with any seating surface can be formed in any shape and number that allows restraint fitting 5 to pass through. Holes 502 and 504 and seats 501 and 503 can be formed by any process, including welding or cutting with a laser torch, machining such as electrical discharge machining, chemical etching, forging restraint fitting 5 with holes, etc. In an exemplary method, holes and seats 501-504 can be formed during the manufacture of restraint fitting 5, during installation of fitting 5 into a reactor, after fitting 5 is in operation in an existing reactor such as during a maintenance outage, or at any other time.

[0022] An exemplary method can form holes in restraint fitting 5 and grooves in riser pipe 3 simultaneously or at separate times. For example, holes 502 and 504 can be machined in restraint fitting 5 during manufacturing, and grooves 301 and 302 can be machined in riser pipe 3 during maintenance when exemplary embodiment clamps are installed. Although the holes and grooves are shown from one side in Figures 2 and 3, symmetrical or separate holes and grooves can be formed on the other side of riser pipe 3 and restraint fitting 5 to accommodate exemplary embodiment clamps, described below. Similarly, these holes and grooves on the other side can be formed simultaneously or at separate times.

[0023] FIG. 4 is an illustration of an exemplary embodiment jet pump clamp 100 usable in an exemplary manner. FIG. 4 is a perspective view of the exemplary embodiment clamp 100, FIG. 5 is a top view of the clamp 100 showing the upper riser pipe clamp member, and FIG. 6 is a side view of the clamp 100. As shown in FIG. 4, the exemplary embodiment jet pump clamp 100 includes a lower clamp member 101 and an upper clamp member 102. The clamp members 101 and 102 are configured to fit and securely fit onto the riser pipe 3 ( FIG. 1A ) of a jet pump assembly, allowing for the application of external and internal forces to the pipe 3. To achieve this, the clamp members 101 and 102 include tongues 105 and 106 extending from inner surfaces 107 and 108 that fit around the riser pipe. The tongues 105 and 106 are configured to seat into grooves 301 and 302 ( FIG. 2 ) formed in the riser pipe 3 ( FIG. 2 ) by an exemplary method. Thus, tongues 105 and 106 can have any shape or size that fits into the groove (and vice versa) to prevent unrestricted vertical movement of clamping members 101 and 102 relative to the pipe. Similarly, multiple tongues 105 and 106 can be used to fit into different grooves formed on different sides of the riser pipe. While inner surfaces 107 and 108 are shaped and sized to fit around the riser pipe, they can have any desired additional shape. For example, inner surfaces 107 and 108 can have an inner diameter sized to directly contact and bias against the outer periphery of the riser pipe, or inner surfaces 107 and 108 can be completely spaced from the riser pipe except for tongues 105 and 106, or they can only selectively contact the riser pipe, for example, by appropriate size and extension.

[0024] The clamp members 101 and 102 can expand or open via rotation, tightening, etc., relative to the joint, or can be multi-piece to fit around the tongues 105 and 106 and secure with the riser pipe. An exemplary method is to position each clamp member 101 and 102 relative to a respective groove on the riser pipe and engage the tongues 105 and 106 into the respective grooves, thereby fastening, closing, joining, or otherwise securing the clamp members 101 and 102 vertically to the riser pipe. For example, as shown in FIG. 4 , the clamp fastener 112 of the upper clamp member 102 and the clamp fastener 111 of the lower clamp member 101 can be inserted into respective pockets of the multi-piece members, drawing the pieces together and ultimately securing the same laterally. As best seen in FIGS. 5 and 6 , multiple clamp fasteners 112 can be used on each member to secure the pieces of each member from each side.

[0025] The clamp fasteners 111 and 112 can use any configuration to secure the upper and lower clamp members 102 and 101 to the riser pipe. For example, two clamp fasteners 111 and two clamp fasteners 112 can be used on opposite sides of the respective clamp members 101 and 102. Each clamp fastener 111 and 112 can use a pull bolt with a nut on one end and a threaded end on the other end that passes completely through a matching hole in the member 101 / 102. A crimp nut with an opposing internal thread rides on the threaded end and can laterally tighten the bolt. In the illustrated manner, once the desired tightening is reached, the crimp nut can deform onto the pull bolt, preventing further rotation and loosening. To increase and / or match the surface area between the clamp fasteners and the clamp members, washers, e.g., those with a spherical cross-sectional surface or other shape that matches the pocket surface surrounding the hole in the member 101 and 102, can be placed under each end of the crimp nut and bolt nut. As mentioned above, any other fasteners may be used, including ratchets, cinches, vise jaws, etc., that allow the attachment of clamp members 101 and 102 relative to the riser pipe to be secured perpendicularly to the grooves of the same riser pipe.

[0026] In an exemplary method, the upper clamp member 102 and the lower clamp member 101 can even be vertically connected and compressed together. Such joining can be performed at any time before or after the clamp members are vertically secured to the riser pipe. Compression or biasing of the upper clamp member 102 and the lower clamp member 101 can be performed after they are joined to the riser pipe to apply a compressive vertical force to the riser pipe.

[0027] For example, as shown in FIG. 4, vertical connectors 120 can vertically couple and / or secure the lower clamp member 101 to the upper clamp member 102. The vertical connectors 120 can pass through matching bosses or pockets in the members 101 and 102 to vertically couple and align the members. Multiple vertical connectors 120 can be used, evenly spaced relative to the exterior of the upper clamp member 102, such as the four connectors 120 shown in FIG. 6. Each vertical connector 120 can use a draw bolt with a nut on one end and a threaded end on the other, which passes completely through a matching hole in the members 101 / 102. A crimp nut with an opposing internal thread rides on the threaded end and can laterally tighten the bolt. When the desired tightening is reached in the illustrated manner, the crimp nut can deform onto the draw bolt, preventing further rotation and loosening. Washers, for example, those having a spherical cross-sectional surface or other shape that matches the pocket surface surrounding the holes in members 101 and 102, can be placed at each end under the crimp nut and bolt nut to increase and / or match the surface area between the vertical connector and the clamping member. Other connectors, including ratchets, cinches, vise jaws, etc., that allow for vertical fixation and potentially further vertical clamping of members 101 and 102 relative to the riser pipe can also be used.

[0028] The flexibility of the clamping members 101 and 102 and the joint structures therein allows the exemplary method to install the members together or separately on the riser pipe and still impart the desired compression to the riser pipe below at any stage. For example, the lower clamping member 101 can be installed separately on the riser pipe and secured to the same via the tongue 105 and groove 302 ( FIG. 2 ). The upper clamping member 102 can be installed separately on the riser pump and similarly secured. One or more vertical connectors 120 can then be connected between the installed clamping members 101 and 102, regardless of their final vertical position, to pull the members 101 and 102 vertically together or apart and apply similar forces to the underlying riser pipe to which they are secured. Attaching the illustrated embodiment clamp 100 to the underlying riser pipe and further compressing the pipe can functionally replace the pipe with a restraint and mitigate fatigue crack growth by maintaining the riser pipe in the required compression.

[0029] The exemplary method allows for the upper clamp member 102 and the lower clamp member 101 to be independently secured to the restraint fitting 5 ( FIG. 1B ), regardless of the vertical positioning of the restraint fitting 5 and the exemplary embodiment clamp 100. Such securing can be performed at any time, before or after the clamp members are vertically secured to the riser pipe. Vertical compression or biasing of the upper clamp member 102 and the lower clamp member 101 can be performed after the members 101 and 102 are joined to the riser pipe, applying a compressive vertical force to the riser pipe. Additionally, joining to the restraint fitting 5 can be performed independently of such vertical compression or biasing of the riser pipe.

[0030] As shown in FIG. 4 , the jet pump clamp 100 of the exemplary embodiment includes a restraint fitting restraint 150 configured to secure a restraint fitting 5 ( FIG. 1B ) with the clamp 100. Any number of restraint fitting restraints 150 can be used with the clamp 100, and in the example of FIG. 4 , two restraints 150 are used on opposite sides to match two separate restraint fittings 5 ​​on opposite sides of the riser pipe 3 ( FIG. 1A ). The restraints 150 pass through clamp holes 502 and / or 504 in the restraint fitting 5 ( FIG. 3 ), and the location of the restraints 150 matches the location of any holes formed by the exemplary method in the restraint fitting 5 (or vice versa). In this way, the restraints 150 prevent the restraint fitting from disengaging or moving relative to the clamp 100 and any riser pipe to which the clamp 100 is secured.

[0031] Restraint 150 can take any form that secures to the restraint fitting, including clamps, screws, harnesses, augers, tongue locks, and the like. For example, as shown in FIG. 5, restraint 150 can include a draw bolt 154 having a nut on one end and a threaded end on the other end that passes completely through corresponding holes in members 101 and 102 and holes 502 or 504 in restraint fitting 5. A crimp nut 151 with opposing internal threads can ride on the threaded end and laterally tighten bolt 154. In an exemplary manner, once the desired tightening is reached, crimp nut 151 can deform onto draw bolt 154, preventing further rotation and loosening.

[0032] The threaded bushing 152 seats on threads within a bore in the member 102 of the arresting portion 150 and can be rotated to vertically displace around the draw bolt 154. The retainer 152 can be paired with a washer that matches the seating surface 501 or 503 ( FIG. 3 ). For example, the washer on the retainer 152 can have a spherical cross-sectional surface or other shape that matches the seating surface 501 or 503 to increase and / or match the surface area between the vertical connector and the clamping member. The threaded bushing 152 can be rotated on the internal threads to raise or lower the washer-equipped retainer 153 vertically. This can provide any desired vertical displacement of the retainer 153, and therefore the arresting bracket 5, which presses against the retainer 153. The matching pair of bushing-with-washer and retainer can be on different sides of the draw bolt 154 of the clamping member 101. These bushing, retainer, and washer sets can therefore hold the restraining bracket 5 (FIG. 3) in any vertical position and secure it with the clamp 100.

[0033] An exemplary method can install and tighten the restraint 150 at any time to provide the desired positioning and / or tension to the restraint fitting. For example, after the exemplary embodiment clamp 100 secures both the lower clamp member 101 and the upper clamp member 102 to the riser pipe relative to the restraint fitting, the restraint 150 can be installed through the clamp 100 and the restraint fitting by threading a draw bolt 154 through holes in all of the members 101 and 102 and the restraint fitting. The draw bolt 154 can be tightened by rotating the crimp nut 151, which deforms and locks the draw bolt 154. The bushing 152 of member 101 can be rotated until the retainer 153 and the washer thereon are seated against the restraint fitting, and the bushing of member 102 can be similarly rotated to capture and secure the restraint fitting in any orientation with the clamp 100 and its connected riser pipe. In this manner, the RS-6 / 7 weld of the restraint fitting can be relaxed, preventing crack growth in the restraint fitting where it joins the riser pipe.

[0034] 7 is an illustration of another exemplary embodiment clamp 200 joined to a riser pipe 3 in accordance with an exemplary method of forming and installing a clamp. As can be seen in FIG. 7, the clamp 200 may use slightly different closure mechanisms for the lower clamp member 101 and the upper clamp member 102, and almost any closure or joining configuration may be used in exemplary embodiments.

[0035] Exemplary embodiment clamp components are fabricated from materials compatible with the operating reactor environment, including materials that maintain their physical properties when exposed to high-temperature fluids and radiation. Direct contact points can be lubricated and fabricated from alternative or other compatible materials to prevent seizure, fouling, and metal-to-metal reactions. Neutron poisons and highly reactive materials, such as halides and cobalt, can be eliminated or reduced. For example, the draw bolts and washers can be fabricated from XM-19, while the clamp members and restraining elements can be fabricated from 316-nuclear-grade stainless steel. Other stainless steels and other metals, such as iron alloys, nickel alloys, and zirconium alloys, can also be used for similar components.

[0036] Having thus described exemplary embodiments and methods, those skilled in the art will recognize that the exemplary embodiments may be varied or substituted by routine experimentation while remaining within the scope of the following claims. For example, any number of different leakage reduction structures and shapes other than Torii may be used with the clamps of the exemplary embodiments, simply by providing the appropriate dimensions and positioning. Such variations are not considered a departure from the scope of these claims.

Claims

1. 1. A clamp for a jet pump assembly of a nuclear reactor, comprising: an upper clamp member having an inner surface formed to fit around a riser pipe of the jet pump assembly, the inner surface of the upper clamp member including a tongue extending from the inner surface of the upper clamp member and configured to fit into a first groove in the riser pipe to prevent vertical movement of the upper clamp member relative to the riser pipe; a lower clamp member having an inner surface formed to fit around the riser pipe of the jet pump assembly, the inner surface of the lower clamp member including a tongue extending from the inner surface of the lower clamp member and configured to fit into a second groove in the riser pipe to prevent vertical movement of the lower clamp member relative to the riser pipe; a vertical connection between the upper clamp member and the lower clamp member configured to vertically draw the upper clamp member and the lower clamp member together; A clamp comprising:

2. 2. The clamp of claim 1, wherein the upper clamp member and the lower clamp member form a restraint configured to vertically pass a restraint fitting of the jet pump assembly between the upper clamp member and the lower clamp member.

3. The clamp of claim 2 , wherein the restraint includes a draw bolt that extends vertically and entirely through the upper and lower clamp members.

4. 4. The clamp of claim 3, wherein the restraint includes two vertically adjustable bushings on the draw bolt between the upper and lower clamp members, the bushings configured to seat on opposite sides of a restraint bracket.

5. 3. The clamp of claim 2, wherein the restraining portion includes a crimp nut on the draw bolt configured to vertically clamp the draw bolt and, upon deformation, lock the draw bolt relative to the upper and lower clamp members.

6. The clamp of claim 1 , wherein the vertical connection includes a draw bolt that passes vertically and entirely through the upper clamp member and the lower clamp member.

7. 7. The clamp of claim 6, wherein the vertical connection includes a crimp nut on the draw bolt configured to vertically clamp the draw bolt and, upon deformation, lock the draw bolt relative to the upper and lower clamp members.

8. The clamp of claim 1 further comprising three of said vertical connections, said four vertical connections being equally spaced from one another about the circumference of said clamp.

9. The clamp of claim 1 , wherein the upper clamp member, the lower clamp member, and the vertical connector are fabricated entirely from at least one of a stainless steel alloy, a zirconium alloy, and an aluminum alloy.

10. 1. A nuclear reactor repair jet pump assembly, comprising: a riser pipe configured to convey a fluid coolant vertically upward; two inlet mixers on different sides of the riser pipe configured to convey the fluid coolant vertically downward; a restraint fitting connected to the riser pipe and one of the two inlet mixers; a clamp attached to the riser pipe and passing through the restraint fitting to prevent relative movement between the riser pipe and the restraint fitting, the clamp vertically compressing the riser pipe only within the clamp; and A repair jet pump assembly comprising:

11. The repair jet pump assembly of claim 10 , wherein the clamp seats in two grooves in the outer surface of the riser pipe, and the clamp compresses the riser pipe by vertically compressing the two grooves together.

12. The repair jet pump assembly of claim 10 , wherein the clamp passes through two distinct holes in the restraint bracket.

13. 11. The repair jet pump assembly of claim 10, wherein the clamp includes a restraint configured to pass through the restraint fitting, the restraint including a draw bolt that passes vertically and entirely through the restraint fitting and a body of the clamp that passes vertically and entirely above and below the restraint fitting.

14. 14. The repair jet pump assembly of claim 13, wherein the restraint includes a crimp nut on the draw bolt configured to vertically clamp the draw bolt and, upon deformation, lock the draw bolt relative to the upper and lower clamp members.

15. 14. The repair jet pump assembly of claim 13, wherein the restraint includes two vertically adjustable bushings on the draw bolt between the upper and lower ends of the clamp, the bushings seating against opposite vertical sides of the restraint bracket.

16. 1. A method of preparing a jet pump assembly for use in a nuclear reactor having a jet pump clamp, comprising: forming at least one groove in an outer surface of a riser pipe of the jet pump assembly above a junction between the restraint and the riser pipe; forming at least one groove in an outer surface of the riser pipe below a junction of the restraint fitting and the riser pipe; forming at least one aperture vertically through the restraint fitting of the jet pump assembly; A method comprising:

17. The method of claim 16 , wherein the forming step includes electrical discharge machining the grooves and the holes.

18. 20. The method of claim 17, wherein the forming step is performed during a maintenance outage of the nuclear reactor and after the nuclear reactor is commercially generating electricity.

19. 17. The method of claim 16, further comprising placing a clamp on the riser pipe and the restraint fitting to prevent relative movement between the riser pipe and the restraint fitting, the clamp compressing together at least one groove in the outer surface of the riser pipe below the restraint fitting and the at least one groove in the outer surface of the riser pipe above the restraint fitting.

20. 20. The method of claim 19, wherein the clamp installing step includes the step of threading a restraining portion of the clamp through at least one aperture in the restraining bracket.

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