WO2013192503A2 - Thermally compliant pump interfaces - Google Patents

Abstract

A thermally compliant interface between mechanically coupled components. In one form, there is more than one register fit between joined components such that a primary register fit maintains the desired fit during certain distortion-inducing operating conditions, while a secondary register fit maintains the desired fit during other operating conditions. In a more particular form, the operating conditions may correspond to times when the joined components are in thermal steady state and thermal transition relative to one another, respectively. Other operating conditions may include periods of where the joined components may be exposed to pressure differentials. In an even more particular form, such a thermally compliant interface may be formed between concentrically coupled shafts in a pump, such as a nuclear safety pump.

Description

THERMALLY COMPLIANT PUMP INTERFACES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 61/662,436 filed on June 21, 2012 the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

[0002] The embodiments described herein relate generally to alignment of joined components, and more particularly to the use of thermally compliant interfaces to accommodate different rates of thermal expansion and contraction of components used in fluid pumping systems in order to maintain such alignment.

[0003] Register fits (or interfaces) are commonly used to maintain rotating components (such as shafts, rotors, bearing surfaces or the like) in alignment with one another, as well as between rotating and stationary components and also between adjacent stationary components. In one conventional register fit form, such components are coupled to one another through a concentric (i.e., "male/female") connection such that significant portions of the respective surfaces are in facing cooperation with one another. The desired register between the outer diameter of the inner (male) part and the inner diameter of the outer (female) part is typically maintained by tight connections or very small clearances (as small as .0005 inch per side) between the facing components.

[0004] Certain pump configurations necessitate that dissimilar materials are used to form the concentric connection interface; one example is a pump used in environments with a high degree of thermal cycling (such as in the power generation industry in general, and in the nuclear variant in particular). The singular register fits formed by these connections are susceptible to becoming misaligned during thermal transients (as well as during steady state conditions where a temperature difference across the connection may persist), as differences in thickness and materials (as well as coefficients of thermal expansion (CTE)) can cause normally close-tolerance fits to become loose. In general, if the male component was to heat up and grow faster than the female component (or conversely the female component was to cool and shrink faster than the male component) misalignment problems would not typically arise because the joint between the connected components becomes tighter. However, if the opposite happens, and the female component heats up and grows faster than the male component (or the male component cools and shrinks faster than the female component) there is a potential for misalignment because the clearance at the joint has increased. Similar conditions may also arise from mechanical or pressure loading differences on the parts, as well as a combination of mechanical and pressure loading.

[0005] It is known to maintain a radial clearance for a rotating shaft so that differences in thermal expansion between the shaft and a concentrically-placed surrounding member (such as a bearing) do not impair shaft operability. While it is likewise known that multiple support structures may be used, there is no indication that such structures may be used as multiple register fits in a cooperative way such that one provides secure connection backup in the event the other slips, fails or otherwise becomes loose during operational transients to keep a pair of coupled shafts in secure aligned movement with one another. While it likewise may be possible to employ multiple bearing supports as a way to overcome thermal mismatch and distortion in a shaft, the present inventors are unaware of any attempt at using such supports as part of a concentric relationship between cooperating shaft components to keep them aligned during such thermal events.

BRIEF SUMMARY

[0006] According to one embodiment, a pump having a thermally compliant interface can include a rotatable shaft and a housing. The rotatable shaft can include at least one impeller disposed thereon. The housing can be cooperative with the rotatable shaft and the at least one impeller to provide rotational support thereto. The housing can include a plurality of components joined to one another such that at least two of the components form at least one thermally compliant interface. The thermally compliant interface can include a primary close tolerance register fit having a primary register distance, and a secondary close tolerance register fit having a secondary register distance. When the thermally compliant interface is below a threshold temperature, the primary register distance can be less than the secondary register distance. When the thermally compliant interface is above the threshold temperature, the primary register distance can be greater than the secondary register distance. [0007] According to another embodiment, a residual heat removal system can include a fluid source, a heat exchanger, and a low head safety injection pump. The fluid source can supply cooling fluid to a power plant. The heat exchanger can be in thermal communication with the power plant and configured to exchange thermal energy between the cooling fluid and the power plant. The low head safety injection pump can be in fluid communication with the fluid source and the heat exchanger and configured to transfer the cooling fluid from the fluid source to the heat exchanger. The low head safety injection pump can include a rotatable shaft and a housing. The rotatable shaft can include at least one impeller disposed thereon. The housing can be cooperative with the rotatable shaft and the at least one impeller to provide rotational support thereto. The housing can include a plurality of components joined to one another such that at least two of the components form at least one thermally compliant interface. The thermally compliant interface can include a primary close tolerance register fit having a primary register distance, and a secondary close tolerance register fit having a secondary register distance. When the thermally compliant interface is below a threshold temperature, the primary register distance can be less than the secondary register distance. When the thermally compliant interface is above the threshold temperature, the primary register distance can be greater than the secondary register distance.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0008] The following detailed description of the preferred embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

FIG. 1 shows a register fit between concentrically connected parts in the form of a discharge cover and a balance sleeve in the last stage of a pump according to an aspect of the prior art;

FIG. 2 shows a suction end and bearing brackets of the pump of FIG. 1 according to an aspect of the prior art;

FIG. 3 shows an emergency core cooling system for a pressurized water reactor power plant, including residual heat removal system for use in event of a loss of coolant accident; FIG. 4 shows details of a low head safety injection pump that makes up a portion of the residual heat removal system according to an aspect of the present disclosure are employed;

FIG. 5 shows a dual register fit between concentrically connected discharge cover and balance sleeve parts in the last stage of the low head safety injection pump of FIG. 4 according to an aspect of the present disclosure; and

FIG. 6 shows a suction end and bearing brackets of the low head safety injection pump of FIG. 4 with a dual register fit between concentrically connected features, the register fits including a primary fit between the suction cover and suction guide and a secondary fit between the suction cover and bearing bracket, all according to an aspect of the present disclosure.

DETAILED DESCRIPTION

[0009] According to a first aspect of the present disclosure, the limitations inherent in a singular register fit are overcome by modifying the interface between concentric shafts to include a multi-register configuration. In a preferred form, the register includes a primary interface and a secondary interface spaced apart from one another. In this way, the primary interface maintains the joined components in alignment with one another during normal operating conditions of the pump or related underlying component, while the secondary interface maintains such alignment in significant thermal or pressure transient events that would otherwise lead to primary interface looseness, slippage or related loss of function. As used herein, the phrase "register fit" generally means that concentric surfaces cooperate with one another to limit the motion of at least one of the concentric surfaces within a tolerance and to center at least one of the concentric surfaces. For example, objects having substantially cylindrical surfaces can share a common central axis. Each of the substantially cylindrical surfaces can be controlled (e.g., runout) such that an initial alignment of the substantially cylindrical surfaces centers at least one of the objects with respect to the common central axis during operation of the objects.

[0010] Each of the primary close tolerance register fit and the close tolerance register fit can be precisely designed to mechanically lock components together at different thermal states. For example, the primary close tolerance register fit can be configured to operate a low temperature range that is below a threshold temperature and the secondary close tolerance register fit can be configured to operate a high temperature range that is above a threshold temperature. The close tolerance register fit defines a primary register distance (or gap), i.e., distance between cooperating surfaces, that can vary with temperature. Similarly, the secondary close tolerance register fit defines a secondary register distance (or gap) that can vary with temperature. In some embodiments, the primary register distance can increase with increasing temperature and the secondary register distance can decrease with increasing temperature.

[0011] In one form, the primary close tolerance register fit can be designed to provide proper fit and alignment of the components during assembly or a related undistorted state, while the secondary close tolerance register fit can be designed such that during a distortion-inducing state (such as a thermal transient, high pressure condition or the like), as the primary close tolerance register fit falters (due, for example, to differences in thermal properties of the metals, external loading or the like) the secondary close tolerance register fit can be improved as one component reacts faster or more dramatically than the other to the distortion-inducing event. Under this latter situation, the secondary close tolerance register fit maintains the alignment in the distorted state. For example, below a threshold temperature, the primary register distance of the primary close tolerance register fit can be less than the secondary register distance of the secondary close tolerance register fit. Additionally, above the threshold temperature, the primary register distance can be greater than the secondary register distance. Even though the present disclosure is applied to stationary components, its presence helps ensure that the shafts, impellers and related rotating components maintain their proper alignment and clearance with their stationary component counterparts. Additionally, it is noted that the terms "primary" and "secondary" are utilized for clarity, and that the primary and secondary objects may be interchanged without deviating from the scope of the present disclosure.

[0012] Referring first to FIG. 1, a singular register fit 20 according to the prior art between a balance sleeve 14 and a discharge cover 12 of a pump outlet is depicted. The balance sleeve 14 can be configured to provide structural support for components that rotate about a central axis C of the pump. Specifically, the balance sleeve 14 can be a stationary component that, in conjunction with the balance drum (not shown), breaks down high pressure to low pressure and works to counter the axial thrust developed by the pump's impellers. The discharge cover 12 can form at least a portion of the pressure vessel of the pump. Accordingly, during operation of the pump, the balance sleeve 14 and the discharge cover 12 can be subject to transient loads due pressure, vibration, and temperature. Transient loading can act to cause misalignment or inoperability of the singular register fit 20. Specifically, the singular register fit 20 can be formed by a first register surface 22 of the discharge cover 12 and the second register surface 24 of the balance sleeve 14. The first register surface 22 and the second register surface 24 can define a register distance (not depicted) there between. When the discharge cover 12 is formed from material having a relatively high CTE, i.e., grows volumetrically in proportion to temperature, the singular register fit 20 can be susceptible to thermally-induced misalignment. Thus, during high temperature and high load conditions, the register distance can grow to a dimension large enough to allow the singular register fit 20 to be overcome by the mechanical loads and cause the discharge cover 12 and the balance sleeve 14 to become misaligned.

[0013] Additionally, when the discharge cover 12 is formed from material having a relatively high CTE and the last stage diffuser 10, which can be utilized to define a portion of a flow path of the pump, is formed from a different material, a mixed metallurgical interface 30 can be formed there between. Accordingly, a seal 18 can be located within the mixed metallurgical interface 30. During transient loading, the discharge cover 12 can grow towards the last stage diffuser 10 and affect the geometry of the mixed metallurgical interface 30.

[0014] Referring now to FIG. 2, in a manner generally similar to that of the singular register fit 20 between the discharge cover 12 and the balance sleeve 14 (FIG.l), a singular register fit 48 can be formed between a barrel 40 and a bearing bracket 46. The barrel 40 can be the main pressure vessel component of a pump. The bearing bracket 46 can be a stationary structural component that attaches to the respective suction cover 44 or discharge cover 12 and provide an attachment point for a bearing housing. The suction cover 44 and discharge cover 12 can attach to the barrel 40 to form a sealed pressure vessel. The suction guide 42 is stationary and can direct incoming flow (from the piping) into a first stage rotating impeller. When the suction cover 44 is formed from material having a relatively high CTE, the singular register fit 48 can be susceptible to thermally-induced misalignment.

[0015] Referring FIGS. 1 and 2, the singular nature of the singular register fit 20 and the singular register fit 48 are such that in the event of certain thermal activities, the register fit may become loose; this loosening may be tantamount to "slop" in the fit to the point that precise alignment along their common axial dimension becomes upset. This misalignment is particularly disadvantageous with high rotational speed components, as imbalance arising out of such misalignment speeds up wear on the components or bearings or related structure used to support such components. Such misalignment is also undesirable for emergency systems such as, for example, low head safety injection (LHSI) pumps used in a nuclear reactor or related system.

[0016] Referring now to FIG. 3, an embodiment of an emergency core cooling system (ECCS) 200 for a pressurized water reactor (PWR) power plant 202, including a residual heat removal (RHR) system 204 for use in event of a loss of coolant accident is schematically depicted. The RHR system 204 for use with the PWR power plant 202 can include numerous redundant ECCS components. In some embodiments, the RHR system 204 can comprise one or more LHSI pumps 100. In event of a loss of coolant accident, the LHSI pumps 100 can be configured to receive suction from a refueling water storage tank 206. Alternatively or additionally, in situations where the water level in the refueling water storage tank 206 is too low, the LHSI pumps 100 can be configured to receive suction from the containment sump 208. Accordingly, the LHSI pumps 100 can discharge makeup water into a portion of the RHR system 204 through one or more heat exchangers 210. Accordingly, the LHSI pumps 100 can supplement cooling which can be provided by containment spray pumps 212 that supply coolant spray 214 within a containment boundary 216.

[0017] Referring next to FIG. 4, an embodiment of an LHSI pump 100 is schematically depicted. The LHSI pump 100 comprises a housing 102 that can be formed from a plurality of stationary components to define a flow path 103 for guiding through the housing 102 from an inlet 107 to an outlet 108. The housing 102 can surround a shaft 104 that is configured to rotate with respect to the housing 102 and interact with the flow path 103. Specifically, the shaft 104 can be configured to rotate about a central axis C. For example, bearings can be coupled to the housing 102 and be in rotatable engagement with the shaft 104 to enable the relative motion of the shaft 104 with respect to housing 102. In some embodiments, the shaft 104 can be in operable engagement with a motor (not depicted) that is configured to urge the shaft 104 into rotation.

[0018] The shaft 104 can be coupled to one or more impellers 105. In some embodiments, the one or more impellers can be coupled to the shaft 104 and extend radially away from the shaft 104 such that the impellers 105 interact with any fluids present in the flow path 103. The one or more impellers 105 can be arranged in a plurality of stages axially along the shaft 104 (three stages are in the depicted embodiment). Accordingly, the shaft 104 can rotate the impellers 105 about the central axis C and with respect to the stationary flow path components 106 of the flow path 103. The one or more impellers 105 can compress fluids as the fluids are pulled into the inlet 107 (i.e., suction) and discharged from the outlet 108. In the present view, the left side of the LHSI pump 100 corresponds to the discharge side, while the right side corresponds to the suction side. It is noted that the term "axial" generally refers to a direction along the central axis C, and the term "radial" generally refers to a direction substantially perpendicular to the central axis that runs from the central axis C towards the exterior of the housing 102.

[0019] Referring collectively to FIGS. 4 and 5, the LHSI pump 100 can comprise a thermally compliant interface 120 formed by the balance sleeve 114 and the discharge cover 112. The thermally compliant interface 120 can orient and secure various components with respect to one another. The balance sleeve 114 can be located radially outward of the shaft 104, and the last stage diffuser 110 can be located radially outward of the balance sleeve 114. A stationary flow path component 106 can be located radially outward of the discharge cover 112, the balance sleeve 114, and last stage diffuser 110. The thermally compliant interface 120 can comprise a primary close tolerance register fit 122 and a secondary close tolerance register fit 130 for maintaining engagement between the balance sleeve 114 and the discharge cover 112.

[0020] In some embodiments, the primary close tolerance register fit 122 can be configured for engagement at relatively low temperatures and the secondary close tolerance register fit 130 can be configured for engagement at relatively high temperatures. Specifically, the primary close tolerance register fit 122 can have a primary register distance (not depicted) located between an inward cold register surface 124 that faces radially inward and an outward cold register surface 126 that faces radially outward. The secondary close tolerance register fit 130 can have a secondary register distance (not depicted) located between an inward hot register surface 132 that faces radially inward and an outward hot register surface 134 that faces radially outward.

[0021] In some embodiments, the inward cold register surface 124 and the outward hot register surface 134 can be concentric faces formed on the discharge cover 112. The inward cold register surface 124 and the outward hot register surface 134 can be radially offset and at least partially in axial alignment. The outward cold register surface 126 and the inward hot register surface 132 can be concentric faces formed on the balance sleeve 114. The inward cold register surface 124 of the discharge cover 112 can be concentric and axially aligned with the outward cold register surface 126 of the balance sleeve 114. Additionally, the inward hot register surface 132 of the balance sleeve 114 can be concentric and radially aligned with the outward hot register surface 134 of the discharge cover 112. Accordingly, the primary close tolerance register fit 122 and the secondary close tolerance register fit 130 can be radially offset and at least partially in axial alignment.

[0022] In one form, the discharge cover 112 may be made from a 300-series stainless steel. Because nuclear-compliant equipment is often required to pass through additional (i.e., more stringent) inspection criteria, they are often made with forged (rather than cast) parts to increase the likelihood they will pass quality inspections without multiple re-work cycles. Likewise, cast 400-series martensitic steels may be valuable where severe temperature cycles or shocking are expected to be encountered; in a pump embodiment, such materials may be used to form pump internals. Furthermore, other components (such as the balance sleeve 114) require superior hardness. In one form, this may include a laser cladding, where a 400-series martensitic steel base material could be advantageously employed. Thus, multiple locations in the pump can be made from joints of dissimilar metals that, in combination with the thermally compliant interfaces of the present disclosure, help promote alignment of the components at all expected pump operating conditions and temperatures. [0023] In some embodiments, the pressure boundary components of the LHSI pump 100 can be made from ASTM A304L, while the internal components can be made from ASTM A487. Because ASTM A304L has a CTE that is about 1.5 times that of ASTM A487, high temperature gradients may significantly impact how these components interface. Accordingly, some components can be expanding members that grow volumetrically with increasing temperatures (relatively low CTE), and some components can be rapidly expanding members that grow relatively fast volumetrically with increasing temperatures (relatively high CTE).

[0024] Referring still to FIGS. 4 and 5, the discharge cover 112 can be a rapidly expanding member, and the balance sleeve 114 can be an expanding member. For example, and not by way of limitation, the discharge cover 112 can be made from ASTM A304L, the last stage diffuser 110 can be made from ASTM A497, and the balance sleeve 114 can be formed from ASTM A743. Accordingly, at relatively low temperatures, the primary register distance between the inward cold register surface 124 and the outward cold register surface 126 can be smaller than the secondary register distance located between the inward hot register surface 132 the outward hot register surface 134. As the temperature of the thermally compliant interface 120 increases, the primary register distance can increase, i.e., the inward cold register surface 124 and the outward cold register surface 126 can separate radially. Contemporaneously, as the temperature of the thermally compliant interface 120 increases, the secondary register distance can decrease, i.e., the inward hot register surface 132 and the outward hot register surface 134 can converge radially. At relatively high temperatures, the primary register distance between the inward cold register surface 124 and the outward cold register surface 126 can be larger than the secondary register distance located between the inward hot register surface 132 the outward hot register surface 134. In some embodiments, the relatively high temperature can be greater than a threshold temperature, while the relatively low temperature can be less than the threshold temperature.

[0025] Accordingly, at temperatures below the threshold temperature, the primary register distance can be set to a small distance. For example, the primary register distance can be set to hold the primary register distance to an interference fit, i.e., at the interface the rapidly expanding member can be held in compression. Moreover, at temperatures above the threshold temperature, the secondary register distance can be set to a small distance. For example, the secondary register distance can be set to hold the secondary register distance to an interference fit.

[0026] In some embodiments, a seal interface 116 can be formed at the interface between the last stage diffuser 110 and the balance sleeve 114. As is noted above, each of the last stage diffuser 110 and the balance sleeve 114 can be formed from material having a substantially similar CTE, i.e., a relatively tight tolerance can be maintained at the seal interface 116 throughout the operating temperature range of the LHSI pump 100. Additionally, a seal 118 can be disposed between the last stage diffuser 110 and the balance sleeve 114 to mitigate fluid escaping from the flow path 103. The discharge cover 112 can cooperate with the last stage diffuser 110 and the balance sleeve 114 to compress the seal 118 axially to expand the seal 118 radially and mitigate undesired fluid flow between the discharge cover 112, the last stage diffuser 110 and the balance sleeve 114.

[0027] A mixed metallurgical offset 136 can be formed between the discharge cover 112 and the last stage diffuser 110 and the balance sleeve 114. When the discharge cover 112 is a rapidly expanding member and each of the last stage diffuser 110 and the balance sleeve 114 is an expanding member, the discharge cover 112 can be radially offset from each of the last stage diffuser 110 and the balance sleeve 114 throughout an operating temperature range. Specifically, the radial offset between the discharge cover 112 and the balance sleeve 114 can be set to provide radial clearance between the discharge cover 112 and the balance sleeve 114 at the mixed metallurgical offset 136 throughout the operating temperature range. Moreover, the radial offset between the discharge cover 112 and the last stage diffuser 110 can be set to provide radial clearance between the discharge cover 112 and the last stage diffuser 110 at the mixed metallurgical offset 136 throughout the operating temperature range. Accordingly, mating surfaces of differing metallurgy can be eliminated at the mixed metallurgical offset 136.

[0028] Referring collectively to FIGS. 4 and 6, the LHSI pump 100 can comprise a thermally compliant interface 150 formed by a suction cover 144 that cooperates with the barrel 140 to form a pressure vessel, and a bearing bracket 146 that is configured to secure bearings with respect to the housing 102 to allow for the rotation of the shaft 104. The suction cover 144 can be integral or can comprise a thermal ring 156. For example, the thermal ring 156 can be coupled to the suction cover 144, i.e., the thermal ring 156 can be received within a groove of the suction cover 144 such that a small tolerance or interference fit is maintained. The thermal ring 156 can be formed of the same material or a material with a substantially similar CTE as the CTE of the suction cover 144. The thermally compliant interface 150 can comprise a primary close tolerance register fit 148 and a secondary close tolerance register fit 158 for maintaining engagement between the suction cover 144 and the bearing bracket 146.

[0029] The suction cover 144 can be a rapidly expanding member, and the bearing bracket 146 can be an expanding member. For example, and not by way of limitation, the suction cover 144 can be made from ASTM A304L, the bearing bracket 146 can be made from ASTM A216, and the thermal ring 156 can be formed from ASTM A304L. In one form ASTM A216 which, although not the same as ASTM A487, exhibits negligible differences in CTE as ASTM A487. Accordingly, the primary close tolerance register fit 148 can be configured for engagement at relatively low temperatures and the secondary close tolerance register fit 158 can be configured for engagement at relatively high temperatures. Specifically, the primary close tolerance register fit 148 can be defined by a primary register distance disposed between an inward cold register surface 152 that faces radially inward and is formed on the suction cover 144 and an outward cold register surface 154 that faces radially outward and is formed on the bearing bracket 146. The secondary close tolerance register fit 158 can be defined by a secondary register distance disposed between an inward hot register surface 160 that faces radially inward and is formed on the bearing bracket 146 and an outward cold register surface 162 that faces radially outward and is formed on the thermal ring 156. In some embodiments, the primary close tolerance register fit 148 and the secondary close tolerance register fit 158 can be radially offset and at least partially in axial alignment. For example, the primary close tolerance register fit 148 can be radially outward from the secondary close tolerance register fit 158.

[0030] The thermally compliant interface 150 can operate thermally in a manner substantially similar to the thermally compliant interface 120, described herein above. Specifically, at relatively low temperatures, the primary register distance between the inward cold register surface 152 and the outward cold register surface 154 can be smaller than the secondary register distance located between the inward hot register surface 160 and the outward hot register surface 162. As the temperature of the thermally compliant interface 150 increases, the primary register distance can increase, i.e., expand radially, and the secondary register distance can decrease, i.e., contract radially. At relatively high temperatures, the primary register distance can be larger than the secondary register distance.

[0031] Referring collectively to FIGS. 4-6, the discharge end of the LHSI pump 100 can comprise a thermally compliant interface 250 that is structurally similar to the thermally compliant interface 150 at the suction end of the LHSI pump 100. The thermally compliant interface 250 can be formed between the discharge cover 112 and the bearing bracket 246 that is axially offset from the bearing bracket 146. The discharge cover 112 can be configured as a rapidly expanding member and the bearing bracket 246 can be configured as an expanding member. The discharge cover 112 can be integral with or can comprise a thermal ring 256. For example, the thermal ring 256 can be coupled to the discharge cover 112 in a manner similar to that described above with respect to the thermal ring 156. The thermal ring 256 can be formed of the same material or a material with the substantially similar CTE as the discharge cover 112.

[0032] The primary close tolerance register fit 248 can be configured for engagement at relatively low temperatures and the secondary close tolerance register fit 258 can be configured for engagement at relatively high temperatures. Specifically, the primary close tolerance register fit 248 can have a primary register distance (not depicted) located between an inward cold register surface 252 of the discharge cover 112 that faces radially inward and an outward cold register surface 254 of the bearing bracket 246 that faces radially outward. The secondary close tolerance register fit 258 can have a secondary register distance (not depicted) located between an inward hot register surface 260 of the bearing bracket 246 that faces radially inward and an outward hot register surface 262 of the thermal ring 256 that faces radially outward. In some embodiments, the primary register distance can increase with increasing temperature and the secondary register distance can decrease with increasing temperature. Additionally, it is noted that when the thermally compliant interface 250 is below a threshold temperature, the primary register distance can be less than the secondary register distance, and when the thermally compliant interface is above the threshold temperature, the primary register distance can be greater than the secondary register distance.

[0033] Referring collectively to FIGS. 4 and 6, the LHSI pump 100 can comprise a thermally compliant interface 170 formed by a suction cover 144 and a suction guide 142 that cooperate to define a portion of the flow path 103. The suction guide 142 can be integral or can comprise a thermal ring 176, which can be coupled to the suction guide 142 in a manner substantially similar to the coupling between the suction cover 144 and the thermal ring 156. The thermal ring 176 can be formed of the same material or a material with the substantially similar CTE as the suction cover 144. The thermally compliant interface 170 can comprise a primary close tolerance register fit 168 and a secondary close tolerance register fit 178 for maintaining engagement between the suction cover 144 and the suction guide 142.

[0034] The suction cover 144 can be a rapidly expanding member, and suction guide 142 can be an expanding member. For example, and not by way of limitation, the suction cover 144 can be made from ASTM A304L, suction guide 142 can be made from ASTM A487, and the thermal ring 176 can be formed from ASTM A304L. Accordingly, the primary close tolerance register fit 168 can be configured for engagement at relatively low temperatures and the secondary close tolerance register fit 178 can be configured for engagement at relatively high temperatures, as is described in greater detail herein above.

[0035] The primary close tolerance register fit 168 can be defined by a primary register distance disposed between an inward cold register surface 172 that faces radially inward and is formed on the thermal ring 176 and an outward cold register surface 174 that faces radially outward and is formed on the suction guide 142. The secondary close tolerance register fit 178 can be defined by a secondary register distance disposed between an inward hot register surface 180 that faces radially inward and is formed on the suction guide 142 and an outward cold register surface 182 that faces radially outward and is formed on the thermal ring 176. In some embodiments, the primary register distance can increase with increasing temperature and the secondary register distance can decrease with increasing temperature. Additionally, it is noted that when the thermally compliant interface 170 is below a threshold temperature, the primary register distance can be less than the secondary register distance, and when the thermally compliant interface is above the threshold temperature, the primary register distance can be greater than the secondary register distance. In some embodiments, the primary close tolerance register fit 168 and the secondary close tolerance register fit 178 can be radially offset and at least partially in axial alignment. For example, the primary close tolerance register fit 168 can be radially inward from the secondary close tolerance register fit 178.

[0036] It should now be understood that the thermally compliant interface described herein can include a primary close tolerance register fit and a secondary close tolerance register fit that complement one another and interact during a thermal transient to maintain the alignment of components in a manner not possible with a singular register fit. Specifically, the thermally compliant interface can mate such that the change in dimensions due to thermal growth will not be detrimental to the pump. The primary close tolerance register fit can be designed to provide proper fit and alignment of the components during assembly, while the secondary close tolerance register fit can be custom designed such that, during a thermal transient, as the primary fit is "lost" (due to the difference in CTEs of the metals) the secondary fit is actually improved as one component reacts faster than the other to temperature differences. As such, the secondary close tolerance register fit maintains component alignment during periods of primary close tolerance register fit compromise.

[0037] Although shown with particularity for LHSI pumps, it will be appreciated by those skilled in the art that the thermally compliant interface made possible by the present dual register fit may be used in any pump design where significant temperatures differences exist and the use of dissimilar metals (or other structural materials) would be preferred, as well as in situations where significant distortions might occur from other loading. In the LHSI-specific example, the thermally compliant interface may be employed where various parts of the pump may be made from different materials than their adjacent or cooperating neighboring parts.

[0038] It is noted that the terms "substantially" and "about" may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0039] Having described the various embodiments in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these preferred aspects of the disclosure.

Claims

1. A pump having a thermally compliant interface, the pump comprising:

a rotatable shaft with at least one impeller disposed thereon; and

a housing cooperative with the rotatable shaft and the at least one impeller to provide rotational support thereto, the housing comprising a plurality of components joined to one another such that at least two of the components form at least one thermally compliant interface, and wherein the at least one thermally compliant interface comprises:

a primary close tolerance register fit having a primary register distance; and

a secondary close tolerance register fit having a secondary register distance, wherein:

when the thermally compliant interface is below a threshold temperature, the primary register distance is less than the secondary register distance; and

when the thermally compliant interface is above the threshold temperature, the primary register distance is greater than the secondary register distance.

2. The pump of claim 1, wherein:

the primary register distance is disposed between an inward cold register surface that faces radially inward of a rapidly expanding member and an outward cold register surface that faces radially outward of an expanding member;

the secondary register distance is disposed between an inward hot register surface that faces radially inward of the expanding member and an outward hot register surface that faces radially outward of the rapidly expanding member; and

the expanding member has a lower coefficient of thermal expansion than the rapidly expanding member.

3. The pump of claim 2, wherein the rapidly expanding member comprises a thermal ring.

4. The pump of claim 2, wherein the rapidly expanding member is a discharge cover and the expanding member is a balance sleeve.

5. The pump of claim 5, further comprising a last stage diffuser disposed radially outward from the balance sleeve and adjacent to the discharge cover, wherein a mixed metallurgical offset is disposed between the last stage diffuser and the discharge cover such that the last stage diffuser and the discharge cover are radially offset.

6. The pump of claim 2, wherein the rapidly expanding member is a discharge cover and the expanding member is a bearing bracket.

7. The pump of claim 2, wherein the rapidly expanding member is a suction cover and the expanding member is a balance sleeve.

8. The pump of claim 2, wherein the rapidly expanding member is a suction cover and the expanding member is a suction guide.

9. The pump of claim 2, wherein the inward cold register surface, the outward cold register surface, the inward hot register surface, and the outward hot register surface are concentric.

10. The pump of claim 2, wherein the rapidly expanding member is formed from ASTM A304L.

11. The pump of claim 2, wherein the rapidly expanding member is forged.

12. The pump of claim 11, wherein the expanding member is cast.

13. The pump of claim 2, wherein a relatively high coefficient of thermal expansion of the rapidly expanding member is about 1.5 times a relatively low coefficient of thermal expansion of the expanding member.

14. The pump of claim 1, wherein the primary close tolerance register fit is concentric with and at least partially axially aligned with the secondary close tolerance register fit.

15. The pump of claim 1, wherein the primary close tolerance register fit is radially outward from the secondary close tolerance register fit.

16. The pump of claim 1, wherein the primary close tolerance register fit is radially inward from the secondary close tolerance register fit.

17. The pump of claim 1, wherein when the thermally compliant interface is below the threshold temperature, the primary close tolerance register fit is an interference fit.

18. The pump of claim 1, wherein when the thermally compliant interface is above the threshold temperature, the secondary close tolerance register fit is an interference fit.

19. The pump of claim 1, wherein the at least one impeller is arranged in multiple axial stages.

20. A residual heat removal system comprising:

a fluid source for supplying cooling fluid to a power plant;

a heat exchanger in thermal communication with the power plant and configured to exchange thermal energy between the cooling fluid and the power plant; and

a low head safety injection pump in fluid communication with the fluid source and the heat exchanger and configured to transfer the cooling fluid from the fluid source to the heat exchanger, the low head safety injection pump comprising:

a rotatable shaft with at least one impeller disposed thereon; and a housing cooperative with the rotatable shaft and the at least one impeller to provide rotational support thereto, the housing comprising a plurality of components joined to one another such that at least two of the components form at least one thermally compliant interface, and wherein the at least one thermally compliant interface comprises:

a primary close tolerance register fit having a primary register distance; and

a secondary close tolerance register fit having a secondary register distance, wherein:

when the thermally compliant interface is below a threshold temperature, the primary register distance is less than the secondary register distance; and

when the thermally compliant interface is above the threshold temperature, the primary register distance is greater than the secondary register distance.