Nuclear coolant pump seal and sealing method

Abstract

A seal assembly for a pump includes a gland housing mounted to a pump housing. A stepped flow path is defined within the gland housing, the stepped flow path having a plurality of seal chambers. A sealing stage is located within each seal chamber, each sealing stage having a static sealing element and a rotating sealing element, the sealing elements engaging one another to form a fluid-tight seal. A rotor assembly pumps coolant through the gland housing. Fluid introduced through the stepped flow path is accelerated by an accelerating surface of the rotor assembly. An inlet passage supplies coolant fluid to the stepped flow path and past the accelerating surface.

Description

[0001] Cross-reference to related applications

[0002] This application claims all benefits, including priority, of U.S. Provisional Patent Application No. 62 / 633,578, filed on February 21, 2018, entitled "NUCLEAR COOLANT PUMP SEAL AND SEALING METHOD," which is hereby incorporated by reference in its entirety into this application. Technical Field

[0003] The present application relates to nuclear power generation, and more particularly to coolant pumps for nuclear power generation facilities. Technical Background

[0004] In nuclear power generation facilities, pumps are used to circulate fluid coolants such as water to control reactor temperature and reaction rates. Pump seals are critical to performance. In addition, effective seals are important to meet regulatory requirements, such as preventing the leakage of radioactive materials.

[0005] In rotating machinery, such as pumps, seals may be installed between stationary and rotating components. In this case, the pressure differential that can be maintained from one side of the seal to the other may be proportional to the pressure that pushes the sealing elements together. However, increased sealing pressure may lead to increased wear on the sealing elements.

[0006] The effective pressure drop from one side of the seal to the other side may depend on the fluid conditions, such as pressure and fluid velocity, closest to the seal. Accordingly, the balance of seal effectiveness and life may also depend on the fluid conditions. Summary of the invention

[0007] A coolant pump for a nuclear power generation facility comprises: a housing assembly having a sealing gland housing; a sealing assembly having a stepped flow passage, the stepped flow passage defining first and second sealed chambers; a rotor assembly for pumping coolant fluid through the sealing gland housing, the rotor assembly having an acceleration surface, wherein the fluid flowing through the stepped flow passage is accelerated by the acceleration surface; first and second sealing stages within the first and second sealed chambers, each sealing stage having a static sealing element and a rotating sealing element, the sealing elements being engaged with each other to form a fluid-tight seal; and an inlet channel for supplying coolant fluid to the stepped flow passage and passing it through the acceleration surface.

[0008] An example sealing method for a pump in a nuclear power generation facility includes: directing a pressurized fluid to flow through a first section of a graded flow path toward a first seal; increasing the angular velocity of the pressurized fluid as it passes through the graded flow path by movement of a rotor assembly of the pump; and directing the pressurized fluid to flow through a second section of the graded flow path toward a second seal.

[0009] A sealing assembly for a pump comprises: a sealing gland housing mounted to a pump housing; a stepped flow passage within the sealing gland housing, the stepped flow passage defining first and second sealing chambers; a rotor assembly for pumping a coolant fluid through the sealing gland housing, the rotor assembly having an acceleration surface, wherein the fluid flowing through the stepped flow passage is accelerated by the acceleration surface; first and second sealing stages within the first and second sealing chambers, each sealing stage having a static sealing element and a rotating sealing element, the sealing elements engaging with each other to form a fluid-tight seal; and an inlet channel for supplying coolant fluid to the stepped flow passage and passing it through the acceleration surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings illustrate example implementations, in which:

[0011] Figure 1 is a schematic diagram of a coolant pump;

[0012] Figure 2A yes Figure 1 A cross-sectional view of the pump in FIG.

[0013] Figure 2B yes Figure 2A A partial enlarged view of the middle area II showing the rotor subassembly;

[0014] Figure 2C yes Figure 2A A partial enlarged view of the middle area II showing the stator subassembly;

[0015] Figure 3 yes Figure 2A an enlarged view of region II showing the flow path of water through the coolant pump; and

[0016] Figure 4 yes Figure 3 A magnified view of region IV showing the sealing stage in detail. DETAILED DESCRIPTION

[0017] Figure 1 A coolant pump 100 for use in a nuclear power generation facility is illustrated. The coolant pump 100 has a housing 102.

[0018] The pump 100 includes a pump rotating assembly including a drive shaft 108 coupled to a pump impeller 110 (e.g., an impeller) for circulation of a working fluid. The drive shaft 108 is mounted to a housing 102 via a hydrostatic bearing 101. The working fluid may be a reactor coolant, such as water. The pump impeller 110 draws the working fluid into the pump 100 through an inlet 112, forcing the working fluid out of the pump through an outlet 114 with pressure.

[0019] A gland 113 is mounted atop the housing 102 around the hydrostatic bearing 101 and houses the shaft 108. The gland 113 contains a seal assembly 116 for preventing fluid leakage from the pump 100. The seal assembly 116 is provided with seals between a rotating component mounted to the drive shaft 108, also known as the pump rotating assembly 104, and a stationary component mounted to or formed as part of the gland 113, also known as the stator assembly 106. The gland 113 defines an internal fluid chamber 118. The fluid chamber 118 holds fluid at a high pressure, which holds the working fluid in the main impeller housing of the pump 100.

[0020] The fluid circulates through the fluid chamber 118 along the staging circuit 117 and the recirculation loop 119. The staging circuit 117 directs the working fluid through a series of chambers for staging seals. The recirculation loop 119 provides a flow of working fluid within the fluid chamber 118 and the cooling groove 121. The circulation through the cooling groove 121 provides a supply of low temperature working fluid for the circulation through the staging circuit 117, so that the fluid passing through the staging circuit 117 cools the components of the seal assembly 116. The fluid passing through the recirculation loop 119 can be driven by the auxiliary rotor 123. The auxiliary rotor also creates a flow of pressurized fluid in the fluid chamber 118 to the hydrostatic bearing 101 to ensure that the fluid flowing through the hydrostatic bearing 101 flows from the chamber 118 to the main impeller housing of the pump 100.

[0021] The working fluid may be admitted under pressure from chamber 118 into staging circuit 117, passing through components of seal assembly 116, gradually reducing pressure in one or more sealing stages. The flow through staging circuit 117 may also cool and lubricate the seal interface and other components. In particular, each sealing stage may include an interface between a rotating seal element and a stationary seal element, which may be pushed together for a tight seal. While being pushed together, the relative movement of these seal components may cause wear of the seal components and heat accumulation from friction.

[0022] The forces acting on a seal can be expressed as a balance ratio, that is, the ratio of the forces tending to close the seal to the forces tending to open the seal. The balance ratio of a seal can be correlated to the seal's propensity to leak or fail, with a higher balance ratio corresponding to a tighter (more leak-proof) seal and a lower balance ratio corresponding to a looser (less leak-proof) seal.

[0023] Pushing the seal elements together tends to increase the seal's leak resistance. But it also tends to increase the seal's wear rate and the heat generated as the seal elements move relative to each other. Typically, seals are designed to a specific balance ratio target to achieve a compromise between leak resistance and life. The balance ratio selected for a particular seal application can depend on the pressure differential that will be created from one side of the seal to the other and the desired service life of the seal.

[0024] The balance ratio of a seal can be affected by factors such as seal geometry (such as the inner and outer diameters of the stator rings), fluid pressures on the high- and low-pressure sides of the seal, and any mechanical forces applied to push the seal elements together.

[0025] Figure 2A , 2B 2C illustrate the seal assembly 116 in greater detail. Figure 2A is a cross-sectional view of the completed seal assembly 116 . Figure 2B yes Figure 2A An enlarged view of region II in FIG. 2 shows components of the pump rotation assembly 104 mounted for rotation with the drive shaft 208 . Figure 2C yes Figure 2A An enlarged view of area II in the figure shows the components of the stator assembly 106 , which stationary components are mounted to the gland 113 .

[0026] In the illustrated embodiment, the seal assembly 116 has two seal stages 120, which are individually referred to as seal stages 120-1 and 120-2. The seal stages 120-1 and 120-2 form first and second seal stages. The seal stages 120-1 and 120-2 have respective rotor seal members 126-1, 126-2 (collectively, rotor seal members 126). The seal stages 120-1 and 120-2 have respective stator seal members 128-1, 128-2 (collectively, seal members 128).

[0027] like Figure 2A and Figure 3 As is clearly shown, the rotating assembly 142 is housed within the primary classification chamber 130 and the secondary classification chamber 132 which form part of the classification flow circuit 117 .

[0028] The stator seal member 128 is mounted in a seat structure 150, which is mounted in the chamber 118. The seat structure 150 securely stores the stator seal member 128 in a fixed position. The seat structure 150 defines a plurality of internal classification chambers. As shown, the seat structure 150 defines two classification chambers, namely a primary classification chamber 130 and a secondary classification chamber 132. Each classification chamber corresponds to a sealing stage of the seal assembly 116. In other embodiments, more or less than two classification chambers may be defined, such as one chamber for each sealing stage 120.

[0029] In the illustrated embodiment, the rotating assemblies 142 of the sealing stages 120 - 1 and 120 - 2 are identical. This design allows the rotating assemblies 142 to be interchangeable, thereby limiting the number of individual parts and components in the pump 100 .

[0030] Figure 3 is a simplified schematic diagram of the sealing stages 120 - 1 , 120 - 2 of the seal assembly 116 showing the staged flow of the cooling fluid.

[0031] The primary classification chamber 130 and the secondary classification chamber 132 are in communication via a classification flow channel 134. The classification flow channel 134 receives flow from the primary classification chamber 130 and includes a convoluted flow conduit, such as a conduit disk. The convoluted flow path cooperates to restrict the flow through the flow channel 134 so that the cooling fluid passes through the flow channel at a defined rate and a specific pressure drop. In some embodiments, the convoluted flow path may have an orifice, the size of which is set according to the application of the pressure drop.

[0032] The secondary classification chamber 132 receives fluid from the classification flow channel 134, and the secondary classification chamber 132 discharges the classification fluid through the discharge channel 138. As shown, the discharge channel 138 extends through the stator seat 150. The flow leaving through the discharge channel 138 is further restricted, and the pressure drops to approximately atmospheric pressure. The discharge channel 138 can be configured to impose a flow restriction similar to the channel 134. For example, the discharge channel 138 may include a conduit with a convolution to impose a flow restriction, or may include an orifice of a small cross section to restrict the flow at the inlet or another part. Alternatively, this flow restriction can be applied outside the discharge channel 138. Additional classification and cooling flow can flow through the collection pipe 139, and the collection pipe 139 can be communicated with the discharge channel 138 by means of the air chamber 136.

[0033] Hydraulic chambers 147 and 149 are defined behind sealing stages 120-1 and 120-2, respectively. Each sealing stage 120 is designed to allow a small amount of fluid to flow into the respective hydraulic chambers. That is, sealing stage 120-1 allows a slight leakage of fluid to hydraulic chamber 147, and sealing stage 120-2 allows a slight leakage of fluid to hydraulic chamber 149. Hydraulic chamber 147 flows out into sub-classification chamber 132. Hydraulic chamber 149 flows out to outlet 140.

[0034] The hydraulic chambers 147, 149 are located on the low pressure side of the sealing stages 120-1, 120-2. The pressure differential from one side of the sealing stage 120-1 to the other side is approximately equal to the pressure drop occurring from one end of the stepped flow passages 134a, 134b to the other end. The pressure differential from one side of the sealing stage 120-2 to the other side is approximately equal to the pressure drop (e.g., atmospheric pressure) at the inlet and outlet 140 of the exhaust passages 138a, 138b.

[0035] The fractionation flow circuit 117 defines a flow path from the chamber 118 into the primary fractionation chamber 130, then through the fractionation flow passage 134 into the secondary fractionation chamber 132, through the outlet passage 138, and finally through the discharge outlet 140. The flow path of the fractionation flow circuit 117 extends generally axially, i.e., in a direction parallel to the axis of the drive shaft of the pump 100.

[0036] The fluid in chamber 118 is pressurized with a high pressure, typically exceeding the discharge pressure of pump 100. The pressure of the fluid discharged to outlet 138 is a low pressure, which may be approximately atmospheric pressure. In one example, the pressure drop from one end of the stepped flow path 117 to the other end is about 1000 psi. In other embodiments, the pressure drop can be higher, such as 1500 psi, or lower, such as 200 psi.

[0037] The sealing stages 120-1, 120-2 and the graded flow circuit 117 are configured to share the pressure drop. In other words, the plurality of sealing stages 120 may be configured so that each stage bears only a portion of the total pressure drop from one side of the sealing assembly 116 to the other side. The first pressure drop occurs from one side of the sealing stage 120-1 to the other side and from one end of the graded flow channel 134 to the other end, and the second pressure drop occurs from one side of the sealing stage 120-2 to the other side and from one end of the exhaust channels 138a, 138b to the other end. The total stagnation pressure of the fluid at the inlet of the main graded chamber 130 is approximately equal to the pressure drop at the sealing interface of the sealing stage 120-1 ( Figure 3 The total stagnation pressure at the entrance of the primary classification chamber 130 is higher than the total stagnation pressure at the entrance of the secondary classification chamber 132 by about the pressure drop from one end of the classification flow channel 134 to the other end. Figure 3 The atmospheric pressure at point D in the sealing stage 120-2 is lower than that at the sealing interface ( Figure 3 138a, 138b from one end to the other. As shown, the stepped flow channel 134 and the outlet channel 140 apply approximately equal pressure drops, i.e., about 500 psi. As used herein, the term "stagnation pressure" refers to the sum of the static pressure and the dynamic pressure of a fluid flow, that is, the pressure resulting from decelerating the fluid flow to stagnation without incurring losses.

[0038] Although the exemplary embodiments described herein show two stages 120-1, 120-2, other embodiments include three or more stages. A third stage and / or additional stages are disposed in series with the first two stages in the flow path. In some embodiments, components in or engaged with a third section or stage of the flow path may be configured such that each stage receives a desired portion of the total pressure drop from one side of the assembly to the other. These components and interfaces may include chamber geometry, staged flow values, sealing element configurations, surface features, flow path lengths, etc., and / or any other features described herein for a two-stage design.

[0039] In some implementations, reference to a component with a first level and a second level may refer to a component with more than two levels.

[0040] Figure 4 An enlarged schematic diagram of the sealing elements of the sealing stage 120 is shown. As described above, the sealing stage 120 is designed to be slightly leaky. Accordingly, there is generally a thin leakage layer 127 of fluid between the sealing elements. The sealing elements are pushed to separate by the fluid pressure of the leakage layer and are pushed by the fluid pressure on the high pressure side of the sealing stage, which is achieved by pushing the rotor assembly 142 toward the seat structure 150. The fluid flow around the sealing elements 126, 128 and the fluid flow between the sealing elements 126, 128 through the leakage layer 127 provides cooling of the sealing elements, which tends to improve the constant and / or predictable temperature of the sealing elements 126, 128.

[0041] The rotor assembly 142 is free to move axially such that the position of the rotor assembly 142 and the pressure with which the rotor assembly 142 urges the sealing elements together are dependent upon the pressure of the fluid acting on the rotor assembly 142 .

[0042] like Figure 4 As shown, the seal members 126, 128 have opposing faces 126a, 128a, high pressure faces 126b, 128b, and low pressure faces 126a, 128a. The high pressure faces taper and move away from each other (radially outward in the illustrated embodiment) in a direction extending into the classification chamber 130 / 132.

[0043] Generally speaking, the pressure acting on the opposing faces 126a, 128a and the high pressure faces 126b, 128b tends to push the sealing members 126, 128 apart. Load conditions may cause the sealing members 126, 128 to deform, which may change the outer profile of the sealing members and thus change the forces acting on their faces. Therefore, the balance ratio of the sealing stage 120 is affected by the fluid pressure near the sealing element, the fluid pressure acting on the rotor assembly 142, and the pressure acting on the stationary components (e.g., the stator 128).

[0044] During operation, the leak tendency of the sealing stage 120 may be related to the balance ratio of the sealing stage 120. A seal with a lower balance ratio may have a higher likelihood of leaking, while a seal with a higher balance ratio may have a lower likelihood of leaking.

[0045] On the other hand, the wear rate of the sealing components may also be related to the balance ratio. Specifically, the higher the balance ratio, the faster the seal may wear. The rotor sealing component 126 and the stator sealing component 128 of each sealing stage 120 move relative to each other, resulting in wear that is proportional to the balance ratio of the sealing stage.

[0046] Therefore, effective seal design may rely on accurate calculation of the balance ratio. Underestimating the balance ratio of the seal can lead to a design that is prone to leakage, while overestimating the balance ratio of the seal can lead to a design that wears prematurely. In a multi-stage configuration, the sealing performance and life of the seal of each stage may depend on the pressure drop of that stage. In some embodiments, it may be necessary to balance the pressure drop and balance ratio of each stage so that the sealing elements wear evenly and provide the same sealing performance. For example, for a seal with two stages, when each stage is subjected to approximately half the pressure drop and the stages have approximately equal balance ratios, the stage wear tends to be uniform. Conversely, if one stage is subjected to a larger pressure drop and a larger balance ratio, that stage may tend to wear and fail faster than the other stage, and the other stage may be more prone to leakage.

[0047] Typically, seal parameters are selected based on static analysis. That is, the calculation of pressure and balance ratio is usually based on the assumption that dynamic pressure can be neglected.

[0048] However, the inventors observed that the previously designed sealing stages tended to wear unevenly and leak more than expected. That is, it was observed that the single seal sealing stages 120 that were expected to have the same balance ratio wore unevenly with each other. In addition, it was observed that some sealing stages 120 behaved as if their balance ratio was lower than expected.

[0049] The inventors have discovered that in pump 100, dynamic effects may be critical. Specifically, the static pressure may vary due to dynamic effects within the staged flow circuit. For example, the pressure applied to sealing stage 120-1 depends on Figure 3 The stagnation pressure of the fluid at point B in , and the velocity of the fluid at point B, such as the velocity of the average fluid streamline. Similarly, the pressure applied to the sealing stage 120-2 depends on Figure 3=The stagnation pressure at point C in the figure, and the fluid velocity at point C, such as the velocity of the average fluid streamline. Thus, the balance ratio of each sealing stage 120 may depend on the pressure drop from one side of the sealing stage to the other, the pressure loss from one end of the flow channel 134 to the other, and the static pressure acting on the sealing element (which in turn depends on the fluid velocity). Generally, the high fluid velocity on the high pressure side of the sealing stage 120 reduces the force acting on the high pressure surfaces 126b, 128b. In addition, the bottom ( Figure 3 The velocity (and pressure) of point A in the sealing stage is relatively close to 120-1 ( Figure 3 The speed and pressure of the rotor assembly and the stator assembly (point B in FIG. 1 ) may affect the balance ratio and sealing effectiveness of the sealing stage 120 - 1 . Specifically, the rotor assembly and the stator assembly ( Figure 3 The lower velocity and higher pressure between point B in the figure may tend to push the rotor assembly away from the stator assembly, while the inlet of the classification chamber 130 ( Figure 3 The lower speed and higher pressure at point A in the figure may tend to push the rotor assembly toward the stator assembly.

[0050] Each rotor seal element 126 forms part of a rotating assembly 142. The fluid flow in the chambers 130, 132 passes through the rotating assembly 142 and is accelerated. Therefore, the flow entering the chambers 130, 132 has a lower velocity and a greater static pressure than the flow leaving the chambers 130, 132.

[0051] While a static analysis would balance the sealing stages 120-1, 120-2 based on the expected losses from one end of the channels 134, 138 to the other, the design shown compensates for the losses and dynamic effects from one end of the channels 134, 138 to the other. For example, based on simulations of flow conditions, the chambers 130, 132 and flow channels 134, 138 are designed to balance the effects of fluid acceleration at the stages 120-1, 120-2. Specifically, the shapes of the chambers 130, 132 and the flow resistances in the channels 134, 138 are designed so that the fluid flows in a consistent direction—on average along the Figure 3 Flows in the direction indicated by arrow F.

[0052] As the fluid flows through the primary classification chamber 130, the fluid passes through a path adjacent to the rotating assembly 142 and is therefore accelerated by the movement of the rotating assembly 142, thereby increasing its average velocity. As the fluid accelerates, its dynamic pressure increases and its static pressure decreases accordingly. Accordingly, the static pressure at the entrance ( Figure 3 Point A in the middle) and the area closest to the sealing stage 120-1 ( Figure 3Similarly, as the fluid flows through the secondary classification chamber 132, the fluid is accelerated by the movement of the rotating assembly 142, thereby increasing the velocity, and the static pressure at the outlet of the classification flow channel 134 and the area closest to the sealing stage 120-2 ( Figure 3 The value of the curve decreases between point C in the figure.

[0053] It is obvious that the tangential velocity at any point on the surface of the rotating component 142 depends on the rotation speed and the radius from the rotation axis. In the illustrated embodiment, the rotating component 142 has an outer cylindrical surface 143 at a relatively large radius. In operation, the tangential velocity of the rotating component at a point on the cylindrical surface 143 is relatively high, so the cylindrical surface 143 causes a relatively significant acceleration of the surrounding fluid. Therefore, the cylindrical surface 143 can be referred to as an acceleration surface.

[0054] In some embodiments, the chambers 130, 132 and the rotating assembly 142 can be configured to control the velocity (and thus the static pressure) of the fluid proximate the sealing stage 120. In particular, the fluid can be accelerated as it passes through a path adjacent to one or more acceleration surfaces 143. Accordingly, the chambers 130, 132 can be configured to control the cumulative acceleration caused by the acceleration surfaces 143, 146. In some embodiments, the fluid proximate the sealing stages 120-1, 120-2 can be accelerated to approximately equal velocities. In other words, the velocity and dynamic pressure of the fluid proximate the sealing stages 120-1, 120-2 may be approximately equal. For example, the chambers 130, 132 can have equal cross-sectional areas proximate the sealing stages 120-1, 120-2, respectively.

[0055] In some embodiments, one or more of the acceleration surfaces 143, 146 include surface features configured to increase fluid velocity. In some embodiments, these features maintain cooling flow in and around the rotating component. In some embodiments, the surface features may include wedges, grooves, and / or any other suitable protrusions, indentations, or other surface features. In some embodiments, the surface features may include machined slots and / or windows. In some embodiments, the acceleration surface 143 includes a window and the acceleration surface 146 includes a machined slot.

[0056] In some embodiments, one or more accelerating surfaces 143, 146 provide recirculation of fluid to control the temperature of the surface. In some embodiments, additionally or alternatively, one or more accelerating surfaces 143, 146 may be used to generate a velocity required for force balance.

[0057] In some embodiments, the length of the flow path through chambers 130, 132 and the length of the flow path adjacent to rotating assembly 142 may be equal, so that the fluid spends a similar length of time in chambers 130, 132 and is therefore accelerated to a similar velocity by rotating assembly 142. The length of the flow path may depend on the shape of chambers 130, 132 and rotating assembly 142, as well as the location at which the fluid flow enters each respective chamber 130, 132.

[0058] In some embodiments, one or more of the components described herein provide a velocity based on an absolute velocity and / or a relative velocity. Absolute velocity can be targeted to adjust pressure, and relative velocity can be targeted to adjust heat transfer.

[0059] In some cases, fractional flow is a parameter that can be adjusted in a new design or installation. In other cases, such as retrofits, fractional flow parameters may be predefined by the system in place.

[0060] Reference again Figure 3 , the primary classification chamber 130 has an inlet passage 145 through which fluid is drawn from chamber 118 into chamber 130. The inlet passage 145 extends generally radially through the seat structure 150. Some of the fluid drawn through the passage 145 flows toward the sealing stage 120-1 generally in the direction indicated by arrow F. Some of the fluid drawn through the passage 145 may flow out through the classification chamber throat 148 located in the axial plane generally in the reverse flow direction indicated by arrow R. In some embodiments, this may be driven by an auxiliary impeller.

[0061] As shown, the inlet passage 145 is located at an axial position between the classification chamber throat 148 and the acceleration surface 143. The acceleration experienced by the fluid flowing to the sealing stage 120-1 may depend on the position of the passage 145. For example, if the passage 145 is moved in the direction F relative to the position shown, the acceleration of the fluid caused by the rotating assembly 142 may be reduced if the fluid traverses a shorter path adjacent to the acceleration surface 143. Conversely, if the passage 145 is moved in the direction R, more fluid may flow out generally in the direction R, and the acceleration of the fluid flowing to the sealing stage 120-1 may be increased.

[0062] The graded flow circuit 117 is configured so that the sealing stages 120-1, 120-2 are approximately at their desired balance ratio during operation. That is, the flow and pressure conditions within the graded chambers 130, 132 cause the mechanical loads of the sealing stages 120-1, 120-2 to reach their desired balance ratio. The flow and pressure conditions are in turn affected by the location of the inlet passage 145. For example, the location of the inlet passage 145 affects the static pressure distribution within the main graded chamber 130. The high pressure closest to the throat 148 pushes the rotating assembly 142 toward the blocking assembly 150, tending to improve the balance ratio of the sealing stage. Conversely, the low pressure closest to the throat 148 exerts less force on the rotating assembly 142. In some embodiments, by balancing the dynamic pressure, as well as the loss from one end of the passages 134, 138 to the other end, the load of the sealing element is also balanced. In other words, the design for loss and dynamic effects provides a consistent balance ratio for the sealing stages 120-1, 120-2. Similarly, the performance and life of the sealing stages are balanced. Accordingly, the seal stages 120-1, 120-2 wear at similar rates and can be repaired or replaced at the same maintenance interval. Conversely, uneven wear between the stages 120-1, 120-2 can lead to premature failure or may require a shorter replacement interval for the seal stages 120. In some cases, when one stage is replaced, both stages must be replaced, so uneven wear may cause the less worn seal to be replaced before it is fully utilized.

[0063] Figures 2a-2c, 3 and 4 are cross-sectional views of the sealing assembly 116. For simplicity, some components of the sealing assembly 116 are schematically shown in a planar direction. However, it is obvious that such structures can extend radially, for example, in a direction that is normal or inclined relative to the cross-sectional plane shown. Similarly, the flow path shown as a plane in Figures 2a-2c, 3 and 4 can extend around the radius of the sealing assembly 116. For example, chambers 130, 132 and fluid channels 147, 149 and 136 can be roughly annular. Additionally or alternatively, the structure shown as a plane and described as a singular can be, for example, a series of radially extending channels spaced apart in different angular directions. For example, channel 145 can extend radially. There can be a single channel 145, or there can be multiple channels 145, which are spaced apart at uniform intervals around the sealing assembly 116.

[0064] During operation of the pump 100, the temperature within the seal assembly 116 may increase, causing expansion of the components. The rate and direction of expansion may depend on factors such as part shape and material properties.

[0065] Differential expansion of the components may result in changes in the seal geometry. Such changes may result in an increase in the gap or a decrease in pressure between the sealing elements 126, 128, thereby reducing the stability or sealing effectiveness of the sealing stage 120.

[0066] Therefore, in order to ensure sealing performance and deal with component wear, the components of the sealing assembly 116 can be configured to promote or maintain the dimensional stability of the sealing stages 120-1, 120-2 and their respective sealing elements 126, 128 within the typical temperature range that will occur during normal operation of the pump 100. In some examples, during normal operation, the components of the sealing assembly 116 may generally experience temperatures between about 90° F and 200° F. The sealing components can be made of materials such as silicon carbide or titanium carbide, which have a relatively low coefficient of thermal expansion within the expected operating thermal energy zone. Obviously, the operating temperature may vary depending on the reactor design, and similarly, the choice of material may also vary. Suitable materials refer to materials that have acceptable sealing and wear performance, and have sufficiently low thermal expansion so that the sealing performance is not excessively degraded by normal operating temperatures. For example, if the sealing elements 126, 128 are designed to be self-depressurized, the part geometry and material can be designed so that the self-depressurization feature is maintained throughout the normal operating temperature range.

[0067] In some embodiments, one or both of the sealing elements 126, 128 may be constrained by one or more expansion control rings 160. The expansion control ring 160 may be a high-strength metal component mounted around the sealing element 126 or 128. The expansion control ring 160 may be sized with a nominal inner diameter that is sized to radially constrain the sealing element 126, 128 around which the expansion control ring 160 is mounted. The expansion control ring 160 may be made of a material having a low coefficient of expansion at the normal operating temperature of the pump 100. At such temperatures, the expansion control ring 160 mechanically resists thermal expansion of the sealing elements 126, 128 to maintain the shape of the sealing elements 126, 128. For example, in the illustrated embodiment, the sealing elements 126, 128 taper at the radially outermost portions of their interfaces and slightly away from each other. Pressure acting on the tapered portions of the sealing elements tends to push the sealing elements away from each other. Thus, the shape of the sealing elements may act as a self-decompression device.

[0068] In some embodiments, as the temperature increases, the sealing surface is configured to deflect, causing it to open more, allowing more leakage. This leakage has the effect of cooling the friction surface, thereby reducing the heat passing through the sealing parts.

[0069] Certain operating conditions of a nuclear power generation facility may result in a loss of coolant flow. In such an event, the coolant pump 100 may stop operating. The temperature of the fluid in the pump 100 may rise sharply and may significantly exceed the normal operating range. For safety and regulatory considerations, leakage prevention may be required in such events. In some examples, in a coolant flow loss event (such as a power outage), fluid temperatures up to or exceeding 500° F may be encountered. The expansion control ring 160 may have a greater thermal expansion coefficient than the sealing element 126 and the rotor assembly 142. Therefore, as the temperature rises, the gap between the sealing element 126 and the expansion control ring 160 may increase. Alternatively, the expansion control ring 160 may be configured to have an increased thermal expansion coefficient above a threshold temperature, which is within the expected range of the coolant flow loss event and is higher than the normal operating temperature. In the coolant flow loss event, the expansion control ring 160 expands, creating a gap between the sealing element 126 and the expansion control ring 160. This in turn allows the sealing elements 126, 128 to expand into each other. The expansion of the sealing elements 126, 128 may be sufficient to eliminate leakage past the sealing stage 120. Further temperature increases may strengthen the seal by causing the sealing elements 126, 128 to continue to expand together.

[0070] In some embodiments, the materials of these components are selected based on material properties. In some cases, selecting different materials can allow selective ring disengagement, so that when a given threshold is exceeded, the overall behavior of the rotating assembly will change.

[0071] In the illustrated embodiment, the expansion control rings 160 mounted around a particular sealing element 126 may be made of different materials having different thermal expansion rates. For example, one ring 160 may be made of high strength stainless steel 50 while the other ring is made of stainless steel. The differential expansion rates of the expansion control rings 160 may cause one ring 160 to detach from the sealing element 126 earlier than the other ring 160. This in turn causes the sealing element 126 to deform when it expands above the normal operating temperature. For example, the sealing element 126 may deflect toward the sealing element 128, thereby eliminating any self-decompression characteristics of the seal.

[0072] In other embodiments, the expansion control rings 160 may be made of the same material, but may be sized for different nominal clearances (or interferences) with the sealing element 126. In such a design, one expansion control ring 160 may expand away from the sealing element 126 before the other expansion control ring 160. Additionally or alternatively, the sealing element 126 may be shaped such that its diameter varies, and the nominal inner diameters of the expansion control rings 160 are different. In such a configuration, an equal percentage change in the expansion control rings 160 may correspond to a larger absolute change in the diameter of the larger of the two rings. Accordingly, the expansion control rings 160 may be sized for an equal amount of nominal clearance or interference with the sealing element 126, and the expansion control rings 160 may be made of the same material, but the larger ring may release the sealing element 126 at a lower temperature than the smaller ring.

[0073] In some embodiments, the geometry of the sealing elements 126, 128 is configured to allow the use of a single expansion control ring, or to allow the use of multiple rings configured to release the sealing element 126 at the same temperature. Specifically, the design and expansion constraints of the sealing elements 126, 128 can be configured so that the sealing elements 126, 128 allow a small amount of leakage at normal operating temperatures, self-depressurize under thermal expansion, or both, and when the temperature is above the normal operating range, one or more expansion control rings 160 release and the sealing element 126 is allowed to expand toward the sealing element 128, thereby reducing or eliminating leakage or self-depressurization characteristics.

[0074] Thus, the seal assembly 116 provides fail-safe protection against leakage. However, due to the relatively low coefficient of expansion of the components, the seal balance ratio is not substantially affected during normal operation, nor is the wear rate or sealing performance affected under normal operating conditions.

[0075] As described above, the fluid flow enters the respective primary classification chamber 130 and secondary classification chamber 132 at the inlet end, while the sealing stages 120-1, 120-2 are located closest to the outlet end of the classification chamber 130', 132'. The fluid flow passes through the chamber 130 or chamber 132 before reaching the respective sealing stage 120, and is accelerated during this passage. The effect of acceleration, that is, the reduced static pressure, is balanced between the stages. In addition, the amount of acceleration can be controlled by changing the length of the fluid flow path closest to the acceleration surface 143, 146, thereby controlling the static pressure change at the sealing stage 120. As described in the present invention, in some embodiments, this is also controlled by the shape of the chamber 130, 132 and the characteristics of the surface 143, 146.

[0076] Although the embodiments have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto.

[0077] Furthermore, the scope of the present application is not intended to be limited to the particular embodiments of the processes, machines, manufactures, compositions of matter, means, methods, and steps described in the specification. As will be readily appreciated by one of ordinary skill in the art from the disclosure of the present invention, processes, machines, manufactures, compositions of matter, means methods, or steps currently existing or to be developed in the future that perform substantially the same functions as the corresponding embodiments described herein or achieve substantially the same results as those described herein may be utilized. Therefore, the appended claims are intended to fall within the scope of the processes, machines, manufactures, compositions of matter, means, methods, or steps.

[0078] It will be appreciated that the detailed embodiments described above and illustrated are by way of example only. The present invention is defined by the appended claims.

Claims

1. A coolant pump for a nuclear power generation facility, comprising: A housing assembly having a sealing gland housing; a seal assembly having a staged flow path defining first and second seal chambers; a rotor assembly for pumping coolant fluid through the gland housing, the rotor assembly having at least one accelerating surface, wherein fluid flowing through the graded flow path is accelerated by the at least one accelerating surface; a first sealing stage and a second sealing stage within the first and second sealing chambers, each of the sealing stages having a stator sealing element and a rotor sealing element, respectively, the stator sealing element and the rotor sealing element engaging with each other to form a seal at a sealing interface defined between the stator sealing element and the rotor sealing element; an inlet passage for supplying coolant fluid to the stepped flow path and across the accelerating surface; wherein the stator sealing element and the rotor sealing element are configured to expand upon heating; wherein a first expansion control ring and a second expansion control ring constrain the expansion of the rotor sealing element, and wherein the first expansion control ring and the second expansion control ring are configured to limit thermal expansion of the rotor sealing element below a threshold temperature, The first expansion control ring is configured to expand at a lower temperature than the second expansion control ring without contacting the rotor sealing element.

2. The coolant pump according to claim 1, characterized in that The first and second sealed chambers define flow paths each adjacent a component of the rotor assembly, wherein the flow paths have the same length.

3. The coolant pump of claim 2, comprising rotor assemblies respectively located in the first and second sealed chambers, each of the rotor assemblies having at least one acceleration surface.

4. The coolant pump according to claim 3, characterized in that Each of the rotor assemblies has a plurality of accelerating surfaces with a plurality of surface features for accelerating a fluid velocity.

5. The coolant pump according to claim 4, characterized in that The inlet passage extends radially.

6. The coolant pump according to claim 4, characterized in that The stepped flow path extends axially parallel to the shaft of the pump.

7. The coolant pump according to claim 4, characterized in that The pressure drop from one side of the first sealing stage to the other side is substantially the same as the pressure drop from one side of the second sealing stage to the other side.

8. The coolant pump according to claim 1, characterized in that The threshold temperature is above an operating temperature range.

9. The coolant pump according to any one of claims 1 to 8, characterized in that: The seal assembly defines a third seal chamber having a stator seal element and a rotor seal element.

10. The coolant pump according to any one of claims 1 to 8, characterized in that The first and second seal chambers have respective geometries to control fluid velocity and dynamic pressure proximate their respective sealing stages, wherein the geometries include at least one of at least one accelerating surface, a stator sealing element, a rotor sealing element, an inlet passage, and a stepped flow channel geometry.

11. The coolant pump according to any one of claims 1 to 8, characterized in that: The at least one accelerating surface and the first and second sealing chambers are configured to generate a desired velocity of the coolant fluid to provide a consistent force balance ratio of the first sealing stage and the second sealing stage, and wherein the force balance ratio of each of the first sealing stage and the second sealing stage is a ratio of a force pushing the rotor sealing element toward the stator sealing element to a force pushing the rotor sealing element away from the stator sealing element in each of the first sealing stage and the second sealing stage.

12. A method for sealing a pump in a nuclear power generation facility, comprising: directing the pressurized fluid through the first segment of the graded flow path toward the first seal; increasing the velocity of the pressurized fluid as it passes through the graded flow path by movement of a rotor assembly of the pump; directing the pressurized fluid through the second section of the graded flow path to flow toward the second seal, wherein the first seal and the second seal each have a stator seal element and a rotor seal element, the rotor seal element including a first expansion control ring and a second expansion control ring for limiting expansion of the rotor seal element, the first expansion control ring being configured to expand out of contact with the rotor seal when the temperature is lower than that of the second expansion control ring; limiting thermal expansion of the rotor seal below a threshold temperature using a first expansion control ring and a second expansion control ring; Since the expansion rates of the first expansion control ring and the second expansion control ring are different, when the temperature of the fluid rises above the threshold temperature, the first expansion control ring is separated from the rotor sealing element before the second expansion control ring.

13. The method according to claim 12, characterized in that Increasing the speed includes directing the pressurized fluid over at least one acceleration surface of the rotor assembly.

14. The method of claim 13, comprising increasing the velocity of the second section of the graded flow path by directing the pressurized fluid over the at least one accelerating surface of the rotor assembly.

15. The method according to claim 13, characterized in that The stepped flow path extends generally parallel to the axis of the pump shaft.

16. The method of claim 14, comprising directing the pressurized fluid into the stepped flow path through a radially extending inlet passage.

17. The method according to claim 12, characterized in that The threshold temperature is above an operating temperature range.

18. The method according to any one of claims 12 to 17, comprising: The pressurized fluid is directed through the third section of the stepped flow path toward a third seal.

19. The method according to any one of claims 12 to 17, characterized in that: Increasing the velocity includes directing the pressurized fluid through at least one acceleration surface of the rotor assembly, and wherein the at least one acceleration surface and the first and second sections of the stepped flow path are configured to generate a desired velocity of the pressurized fluid to provide a consistent force balance ratio for a first sealing stage and a second sealing stage, and wherein the force balance ratio for each of the first sealing stage and the second sealing stage is a ratio of a force pushing the rotor sealing element toward the stator sealing element to a force pushing the rotor sealing element away from the stator sealing element for each of the first sealing stage and the second sealing stage.

20. A sealing assembly for a pump of a nuclear power generation facility, comprising: a gland housing mounted to the pump housing; The seal gland covers a graded flow path within the housing, the graded flow path defining first and second sealed chambers; a rotor assembly for pumping coolant fluid through the gland housing, the rotor assembly having at least one accelerating surface, wherein fluid flowing through the graded flow path is accelerated by the at least one accelerating surface; a first sealing stage and a second sealing stage within the first and second sealing chambers, each of the sealing stages having a stator sealing element and a rotor sealing element, respectively, the stator sealing element and the rotor sealing element engaging with each other to form a seal at a sealing interface defined between the stator sealing element and the rotor sealing element; an inlet passage for supplying coolant fluid to the stepped flow path and past the at least one accelerating surface, wherein the stator seal element and the rotor seal element are configured to expand upon thermal expansion, wherein a first expansion control ring and a second expansion control ring limit expansion of the rotor seal element, and wherein the first expansion control ring and the second expansion control ring are configured to limit thermal expansion of the rotor seal below a threshold temperature, The first expansion control ring is configured to expand when the temperature of the first expansion control ring is lower than that of the second expansion control ring and is out of contact with the rotor sealing element.

21. The sealing assembly according to claim 20, characterized in that The first and second sealed chambers define flow paths each adjacent a component of the rotor assembly, wherein the flow paths have the same length.

22. The seal assembly of claim 21 including rotor assemblies positioned in said first and second seal chambers, respectively, each of said rotor assemblies having at least one acceleration surface.

23. The sealing assembly according to claim 22, characterized in that Each of the rotor assemblies has a plurality of accelerating surfaces with a plurality of surface features for accelerating a fluid velocity.

24. The sealing assembly according to claim 23, characterized in that The inlet passage extends radially.

25. The seal assembly according to claim 24, characterized in that The stepped flow path extends axially parallel to the shaft of the pump.

26. The seal assembly according to claim 25, characterized in that The pressure drop from one side of the first sealing stage to the other side is the same as the pressure drop from one side of the second sealing stage to the other side.

27. The seal assembly of claim 20, wherein: The threshold temperature is above an operating temperature range.

28. The sealing assembly according to any one of claims 20 to 27, characterized in that The stepped flow path in the sealing gland housing defines a third sealing chamber, and the sealing assembly includes a third sealing stage in the third sealing chamber, wherein the third sealing stage has a stator sealing element and a rotor sealing element.

29. The sealing assembly according to any one of claims 20 to 27, characterized in that The first and second sealing chambers have respective geometries to control fluid velocity and dynamic pressure proximate their respective sealing stages.

30. The sealing assembly of any one of claims 20 to 27, wherein the at least one accelerating surface and the first and second sealing chambers are configured to generate a desired velocity of the coolant fluid to provide a consistent force balance ratio for the first sealing stage and the second sealing stage, and wherein the force balance ratio for each of the first sealing stage and the second sealing stage is a ratio of a force pushing the rotor sealing element toward the stator sealing element to a force pushing the rotor sealing element away from the stator sealing element for each of the first sealing stage and the second sealing stage.

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