Intrinsically safe parking seal of nuclear main pump

Abstract

The intrinsically safe parking seal comprises a sealing pair, a corrugated pipe assembly and a fluid pressurizing device, the sealing pair comprises a plane upper ring and a convex lower ring which are arranged on a main shaft of the nuclear main pump in a sleeving mode, and the plane upper ring is fixed to the main shaft in a sealed mode; the convex lower ring is composed of a convex soft ring and a plane metal ring base which are connected together, the corrugated pipe assembly comprises an inner corrugated pipe and an outer corrugated pipe which are coaxially arranged together in a sleeved mode, and the two ends of the inner corrugated pipe and the two ends of the outer corrugated pipe are welded to the plane metal ring base of the convex lower ring and a bottom plate of the sealing box in a sealed mode respectively. A pressure cavity is formed by the space defined by the inner corrugated pipe, the outer corrugated pipe, the convex lower ring and the bottom plate. When fluid is filled into the pressure cavity by the pressurizer, the corrugated pipe assembly can be extended, so that the convex lower ring and the plane upper ring are sealed; and after the fluid in the pressure cavity is discharged, sealing is removed. The service life of the parking seal can be effectively prolonged, and the safety coefficient of operation of the nuclear main pump is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sealing, and in particular relates to an intrinsically safe shutdown seal for a nuclear main pump. Background Art

[0002] As an important clean energy, nuclear power is in line with the development trend of a low-carbon society. The nuclear main pump located in the core and steam generator loop (main loop) is the "heart" of the nuclear power plant, circulating the coolant to absorb the fission reaction heat in the core and release the heat in the steam generator. Mechanical seals are generally used between the main shaft and the shell of the nuclear main pump to control the leakage of the core coolant. Once the coolant containing radioactive substances leaks, it will endanger the operators and even cause the nuclear main pump to shut down, resulting in the inability to cool the reactor and the core melting, causing catastrophic damage to humans and the environment.

[0003] Typical reactors that use nuclear main pumps as main loop coolant delivery equipment include pressurized water reactors, molten salt reactors, and sodium-cooled fast reactors. The nuclear main pumps of pressurized water reactors use three-stage series non-contact mechanical seals, while the nuclear main pumps of molten salt reactors and sodium-cooled fast reactors use single-stage contact mechanical seals. Due to the wear of the end faces of the dynamic and static rings of the mechanical seals, and the aging of the auxiliary O-rings due to long-term exposure to high-radioactivity environments, the mechanical seals need to be replaced and maintained regularly. In order to avoid the leakage of coolant during the replacement process, people invented the parking seal to ensure that the nuclear main pump is still in a sealed state after the mechanical seal fails, so as to create conditions for maintenance or replacement.

[0004] At present, there are three main types of parking seals for existing nuclear main pumps, namely, flat seals, O-ring seals and conical seals. Regarding flat seals, flat seals include two flat upper rings and a flat lower ring, where the flat upper ring is sealed and connected to the housing and can move axially, and the flat lower ring is sealed and fixed on the main shaft. When the flat upper ring and the flat lower ring are pressed together, a sealing contact is formed; considering the redundant design, the sealing end faces of the flat upper ring and the flat lower ring are set larger, resulting in a larger axial force required to complete the sealing, which adds uncertainty to the sealing performance of the parking seal.

[0005] Among them, the O-ring seal is an improvement based on the flat seal. Specifically, a rubber O-ring is fixed on the flat ring, and the O-ring is deformed when squeezed to achieve sealing. Since the O-ring used for parking seals is exposed to a high radioactive environment for a long time, it is prone to aging and failure, and it is difficult to operate safely and stably for a long period of time.

[0006] Conical seals include a conical ring fixed on the main shaft, and a flat upper ring connected to the housing and movable in the axial direction. When the flat upper ring presses against the conical ring, the two form a line seal. However, the formed line seal is easy to leave grooves on the soft sealing surface, which makes it difficult to achieve the next parking seal.

[0007] In the above three types of parking seals, a flat upper ring is provided, and the movement of the flat upper ring is utilized to achieve mutual extrusion with another seal to achieve a sealing effect. Since the flat upper ring is directly installed on the inner wall of the sealing cavity, it is necessary to first ensure the sealing between the flat upper ring and the inner wall of the sealing cavity. Since the flat upper ring is a moving part, it will inevitably produce certain wear after multiple movements, resulting in reduced sealing between the flat upper ring and the inner wall of the sealing cavity, affecting the sealing performance of the parking seal itself and the sealing performance of the entire sealing structure.

[0008] In view of the various problems of the existing parking seals mentioned above, how to improve the service life of the parking seals is still a problem that needs to be solved for the safe operation of the nuclear main pump. Summary of the invention

[0009] In order to increase the service life of the parking seal and improve the safety factor of the operation of the nuclear main pump, the present application proposes an intrinsically safe parking seal for the nuclear main pump, which is arranged in a sealing box and located between the main seal of the nuclear main pump and the impeller. The intrinsically safe parking seal includes a sealing pair, a bellows assembly and a fluid pressure charging device. The sealing pair includes a plane upper ring and a convex lower ring sleeved on the main shaft of the nuclear main pump, wherein the plane upper ring is sealingly fixed on the main shaft, the convex lower ring is located on the side of the plane upper ring facing the impeller, and the convex lower ring is composed of a convex soft ring and a plane metal ring seat connected together, wherein the convex soft ring is located on the side of the plane metal ring seat facing the plane upper ring; the bellows assembly is located on the side of the convex lower ring facing the impeller, and the bellows assembly includes an inner bellows and an outer bellows coaxially sleeved together, and the inner bellows and the outer bellows are both sleeved on the main shaft;

[0010] Both ends of the inner bellows and the outer bellows are respectively welded to the plane metal ring seat of the convex lower ring and the bottom plate of the sealing box in a sealing manner, and the space enclosed by the inner bellows, the outer bellows, the convex lower ring and the bottom plate forms a pressure chamber;

[0011] The fluid charging device comprises a pressurizer and a storage tank, the inlet of the pressurizer is connected to the storage tank, the outlet of the pressurizer is connected to the pressure chamber, the pressurizer is used to charge the fluid in the storage tank into the pressure chamber, and a regulating valve is installed at the outlet of the pressurizer;

[0012] When the inflator fills the pressure chamber with fluid, the bellows assembly can stretch, push the convex lower ring to move toward the planar upper ring, and seal against the planar upper ring. When the fluid pressure in the pressure chamber reaches the set pressure value, stop filling the pressure chamber with fluid, and form a non-percolation contact interface between the planar upper ring and the convex lower ring. When the fluid in the pressure chamber is discharged, the bellows assembly can move away from the planar upper ring and return to its original state. In the bellows assembly, the outer bellows is sleeved on the outside of the inner bellows. The fluid can be a liquid or a gas. When the fluid is a liquid, it can be water or hydraulic oil. When the fluid is a gas, it can be air, nitrogen or other gases.

[0013] The sealing pair in the present application is composed of a flat upper ring and a convex lower ring, and uses a pressure chamber to extend the bellows assembly to push the convex lower ring against the flat upper ring to form a seal. The convex lower ring and the flat upper ring adopt a flat sealing form. The present application eliminates the O-ring seal and conical seal used in the prior art, avoiding the problem of easy aging of the O-ring and the problem of easy grooves left by the conical seal. The flat upper ring in the present application is connected to the main shaft seal, and the convex lower ring is connected to the bottom plate of the sealing box through a bellows. In the normal operation of the nuclear main pump, the flat upper ring and the convex lower ring are separated and have no contact, which will not cause wear of the flat upper ring or the convex lower ring. When the parking seal is working, the flat upper ring and the convex lower ring are in contact to form a static seal. There is no friction, and no wear will be caused, thereby increasing the service life of the sealing pair.

[0014] The present application can push the convex lower ring to squeeze the flat upper ring by adjusting the pressure in the pressure chamber, thereby generating sufficient sealing contact pressure ratio between the convex lower ring and the flat upper ring. In order to smoothly weld the inner bellows and the outer bellows to the flat metal ring seat of the convex lower ring and the bottom plate of the sealing box, in the present application, the cylinder and the bottom plate of the sealing box are processed separately, and after the welding of the inner and outer bellows to the bottom plate and the flat metal ring seat, and the pressure test of the pressure chamber, the cylinder and the bottom plate are welded together.

[0015] Specifically, when the nuclear main pump is stopped, when the fluid pressure in the pressure chamber reaches the set pressure value, the porosity of the contact interface between the plane upper ring and the convex lower ring is less than 0.3116. When the porosity between the sealing interfaces reaches 0.3116, the surface micro-convex bodies on the sealing interfaces of the plane upper ring and the convex lower ring are squeezed and deformed, and there is only one channel connected by gaps and penetrating the sealing surface in the sealing interface; when the sealing contact specific pressure increases and the porosity of the sealing interface is less than 0.3116, the surface micro-convex bodies on the sealing interface of the plane upper ring and the convex lower ring continue to squeeze each other and deform more, which has a high probability of blocking the possibility of the gap in the sealing interface to form a channel through the sealing surface, and realizing the sealing between the plane upper ring and the convex lower ring of the sealing pair.

[0016] Furthermore, the hardness of the flat upper ring is greater than that of the convex soft ring. If the hardness of the convex soft ring is greater than that of the flat upper ring, the convex upper ring will move upward to squeeze the flat upper ring, and the flat upper ring will be slightly deformed, forming a cutting effect, which may damage the flat upper ring. However, if the hardness of the flat upper ring is greater than that of the convex soft ring, this problem can be avoided and the service life of the parking seal can be increased.

[0017] The axial cross section of the first ring body of the plane upper ring is rectangular; the axial cross section of the second ring body of the convex soft ring is T-shaped, and the second ring body includes an integrally formed flat plate portion and a protrusion, the protrusion is located on the side of the flat plate portion facing the plane upper ring, the end face of the protrusion facing the plane upper ring is annular, and the plane metal ring seat is connected to the side of the flat plate portion away from the protrusion; observed along the axial direction, the first ring body of the plane upper ring completely covers the end face of the protrusion facing the plane upper ring. Preferably, in the radial direction, when the convex lower ring is pressed against the plane upper ring, the inner circumference of the plane upper ring outwardly exceeds the inner edge of the protrusion, and the outer circumference of the plane upper ring outwardly exceeds the outer edge of the protrusion, so as to reduce the contact area of ​​the sealing interface, so as to form a larger sealing contact pressure ratio when a smaller fluid pressure is loaded in the pressure chamber, and achieve zero leakage of the parking seal.

[0018] Specifically, the plane upper ring is made of a hard material that is resistant to corrosion, oxidation, high temperature and pressure, and radiation, and the convex soft ring is made of a soft material that is resistant to corrosion, oxidation, high temperature and pressure, and radiation. The plane upper ring can be made of stainless steel, and the convex lower ring can be made of graphite ring, polytetrafluoroethylene, polyetheretherketone and other materials. The plane metal ring seat is used to support the convex soft ring and can be made of hard and corrosion-resistant materials such as stainless steel.

[0019] Furthermore, the sealing box includes a cylinder extending along the axial direction of the main shaft and a bottom plate arranged at one end of the cylinder facing the impeller, a fluid channel is arranged on the bottom plate, one end of the fluid channel is connected to the pressure chamber, and the other end of the fluid channel passes through the outer peripheral surface of the sealing box; the outlet of the inflator is connected to the fluid channel. This design avoids the need to open a fluid channel on the pump housing and the resulting difficulty in connecting the fluid channel with the pressure chamber.

[0020] Furthermore, for the convenience of control, a pressure control system is also included, which includes a central processing unit, a pressure detection unit connected to the central processing unit, a valve adjustment unit, and a pressure inflator control unit, wherein:

[0021] The central processing unit is used to receive information from the pressure detection unit, compare the information with the set pressure value, and issue control instructions according to the comparison result to coordinate the work of the valve adjustment unit and the inflator control unit;

[0022] A pressure detection unit, used for detecting the pressure in the pressure chamber and transmitting the detection data to the central processing unit;

[0023] The valve regulating unit receives control from the central processing unit and opens the regulating valve to keep the pressure in the pressure chamber at a set pressure value;

[0024] The charger control unit receives control from the central processing unit and controls the start and stop of the charger.

[0025] Specifically, the set pressure value of the fluid pressure in the pressure chamber is calculated using the following steps:

[0026] S1. Obtaining the fractal dimension, scale coefficient and elastic modulus of the sealing surface including the plane upper ring and the convex soft ring;

[0027] S2, obtain the fractal parameters and elastic modulus of the equivalent rough surface as well as the maximum micro-convexity height and initial porosity;

[0028] S3. Determine the compression required for the sealing interface according to the no percolation contact interface condition;

[0029] S4. Determine the contact specific pressure required for the sealing interface;

[0030] S5. Determine a set pressure value of the fluid pressure in the pressure chamber.

[0031] The calculation steps for setting the pressure value above adopt a design method for the fluid pressure in the pressure chamber under the contact interface without percolation, which solves the problem that the contact pressure of the parking seals of the three existing sealing forms is designed only based on experience. In addition, the contact area between the convex lower ring and the flat upper ring in the present invention is designed to be small, which can make the fluid pressure in the pressure chamber form a larger sealing contact pressure ratio under a lower condition and achieve zero leakage of the parking seal.

[0032] Specifically, the set pressure value of the fluid pressure in the pressure chamber is expressed by the base length of the largest micro-convex body on the equivalent rough surface that affects the compression required for the sealing interface, and the expression is as follows:

[0033]

[0034] In the formula, p b is the pressure of the fluid in the pressure chamber, p c is the contact pressure of the sealing interface, A c A is the nominal contact area formed when the convex lower ring and the flat upper ring are in contact. b is the cross-sectional area of ​​the pressure chamber, A b =(φ2 2 -φ1 2)π / 4, φ1 is the outer diameter of the welding point between the inner bellows and the plane metal ring seat, φ2 is the inner diameter of the welding point between the outer bellows and the plane metal ring seat, h is the height of the largest micro-convex body on the equivalent rough surface, D is the fractal dimension of the equivalent rough surface, l is the base length of the largest micro-convex body on the equivalent rough surface, G is the scale factor of the equivalent rough surface, S m is the average peak spacing of the equivalent rough surface.

[0035] The specific calculation steps of the set pressure value of the fluid pressure in the pressure chamber are as follows:

[0036] S1. Obtaining the fractal dimension, scale coefficient and elastic modulus of the sealing surface of the plane ring and the sealing surface of the convex soft ring;

[0037] S2, obtain the fractal parameters and elastic modulus of the equivalent rough surface as well as the maximum micro-convexity height and initial porosity;

[0038] To simplify the calculation steps, the contact between the convex lower ring and the plane upper ring is regarded as the contact between an equivalent rough surface and a rigid smooth plane.

[0039] The equivalent rough surface parameters include fractal parameters, scale coefficients and elastic modulus, which are calculated from the corresponding parameters of the convex soft ring of the convex lower ring and the plane upper ring. The specific calculation is based on formula (1):

[0040]

[0041] In formula (1), D is the fractal dimension of the equivalent rough surface, D1 and D2 are the fractal dimensions of the convex soft ring and the ring on the plane, respectively, G is the scale factor of the equivalent rough surface, G1 and G2 are the scale factors of the convex soft ring and the ring on the plane, respectively, E is the elastic modulus of the equivalent rough surface, E1 and υ1 are the elastic modulus and Poisson's ratio of the convex soft ring, respectively, and E2 and υ2 are the elastic modulus and Poisson's ratio of the ring on the plane, respectively.

[0042] The height h and base length l of the maximum micro-convexity on the equivalent rough surface are calculated using formula (2):

[0043]

[0044] In formula (2), S m is the average peak spacing of the equivalent rough surface.

[0045] The initial porosity is calculated using formula (3):

[0046]

[0047] In formula (3), φ0 is the initial porosity, a Lm is the base area of ​​the largest microconvex body, A nis the nominal contact area of ​​the sealing interface, ψ is the domain expansion factor, and its specific value can be obtained by looking up Table 5-1 on page 176 of Fractals in Tribology, and a is the contact area of ​​the micro-convex body.

[0048] S3. According to the non-percolation contact interface condition, the actual compression of the sealing interface is solved:

[0049] The non-percolation contact interface condition is shown in formula (4):

[0050] δ>2.17h(φ0-0.3116) Formula (4)

[0051] In formula (4), δ is the compression of the sealing interface when the interaction between the micro-protrusions and the deformation of the substrate are not considered.

[0052] The actual compression of the sealing interface is expressed as follows:

[0053]

[0054] In formula (5), δ r is the actual compression of the sealing interface, δ ec is the critical deformation of the micro-convex body in the elastic stage, δ pc is the critical deformation of the micro-convex body in the elastic-plastic stage; k1, k2, k3 are the surface material characteristic parameters, ξ1, ξ2, ξ3 are the geometric parameters of the largest micro-convex body, α1, α2 are the hardness coefficients k v , g1 is an expression that includes the sealing interface compression δ.

[0055] g1、δ ec With δ pc The expressions are respectively:

[0056]

[0057]

[0058] In formula (6) and formula (7), H is the hardness of the convex soft ring, H = 2.8σ y , σ y is the yield limit of the convex soft ring, k v is the hardness coefficient of the convex soft ring, k v =0.454+0.41υ1, R is the peak curvature radius of the largest micro-convex body, R=l D / π 2 G D-1 .

[0059] The expressions of α1, α2, k1, k2, k3, ξ1, ξ2, and ξ3 are respectively:

[0060]

[0061]

[0062]

[0063] The steps to solve the actual compression of the sealing interface are as follows:

[0064] According to the non-percolation contact interface condition, the compression amount without considering the asperity interaction and substrate deformation is obtained.

[0065] Use the assumption method to find the actual compression of the sealing interface. For example, assuming δ r <δ ec , substitute the obtained compression δ into the δ of the elastic stage r , and find δ r If δ r <δ ec , it means the hypothesis is correct, otherwise it means the hypothesis is incorrect, and we need to assume δ ec ≤δ r ≤δ pc or δ pc <δ r Further calculation.

[0066] S4. Determine the deformation stage of the micro-convex body of the sealing interface and determine the contact pressure ratio required for the sealing interface:

[0067] According to the actual compression of the sealing interface, the maximum deformation area of ​​the micro-convex body is obtained using formula (11):

[0068]

[0069] In formula (11), a max is the maximum deformation area of ​​the micro-convex body.

[0070] The deformation stage of the micro-convex body of the sealing interface is determined according to the maximum deformation area of ​​the micro-convex body, and the formula (12) and formula (13) are used specifically:

[0071]

[0072]

[0073] In formula (12) and formula (13), a ec 、a epc 、a pc are the critical deformation areas of the micro-convex body in the elastic deformation stage, the first elastic-plastic deformation stage and the second elastic-plastic deformation stage respectively.

[0074] According to the different deformation stages of the micro-convex body of the sealing interface, there are different expressions of contact pressure ratio of the sealing interface.

[0075] When the sealing interface micro-convex body is in the elastic deformation stage, the contact pressure of the sealing interface is solved by equations (14), (15) and (16):

[0076]

[0077]

[0078]

[0079] In formula (14), formula (15) and formula (16), p c is the contact pressure of the sealing interface, f ec is the contact load expression of the micro-asperity in the elastic stage, and n(a) is the contact area distribution function of the micro-asperity.

[0080] When the sealing interface micro-convex body is in the first elastic-plastic deformation stage, the contact pressure of the sealing interface is solved by equations (17) and (18):

[0081]

[0082]

[0083] In formula (17) and formula (18), f epc1 It is the contact load expression of the micro asperity in the first elastic-plastic stage.

[0084] When the sealing interface micro-convex body is in the second elastic-plastic deformation stage, the contact pressure of the sealing interface is solved by equations (19) and (20):

[0085]

[0086]

[0087] In formula (19) and formula (20), f epc2 It is the contact load expression of the asperity in the second elastic-plastic stage.

[0088] When the sealing interface micro-convex body is in the stage of complete plastic deformation, the formula for solving the contact pressure ratio of the sealing interface is formula (21) and formula (22):

[0089]

[0090] f pc =Ha Formula (22)

[0091] In formula (21) and formula (22), fpc The contact load expression of the micro-asperity when it is in the complete plastic deformation stage.

[0092] S5. Determine the set pressure value of the fluid pressure in the pressure chamber:

[0093] The fluid pressure in the double-layer bellows is calculated according to the required contact pressure ratio, using formula (23):

[0094]

[0095] In formula (23), p b is the pressure of the fluid in the pressure chamber, A c A is the nominal contact area formed when the convex soft ring and the flat surface ring seal contact. b is the cross-sectional area of ​​the pressure chamber, A b =(φ2 2 -φ1 2 )π / 4, φ1 is the outer diameter of the welding point between the inner bellows and the flat metal ring seat, and φ2 is the inner diameter of the welding point between the outer bellows and the flat metal ring seat. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 It is a schematic diagram of the structure of an embodiment of the present invention, specifically a diagram of a non-working state of an intrinsically safe parking seal.

[0097] Figure 2 yes Figure 1 The working state diagram of the intrinsically safe parking seal is shown in the accompanying drawing.

[0098] Figure 3 It is a structural diagram of the sealing pair.

[0099] Figure 4 It is the installation diagram of the bellows assembly.

[0100] Figure 5 It is a flow chart for determining the set pressure value of the fluid pressure in the pressure chamber of the intrinsically safe parking. DETAILED DESCRIPTION

[0101] See also Figure 1-Figure 3, an intrinsically safe shutdown seal for a nuclear main pump, the nuclear main pump comprises a pump casing 11 and a sealing box 20 which are axially mounted together, an impeller 13 is rotatably mounted in the pump casing 11, a pump inlet 12 is provided at the end of the pump casing 11 away from the sealing box, and a pump outlet 14 is provided on one side of the pump casing 11 in the radial direction. One end of the main shaft 18 extends into the pump casing and is fixedly connected to the impeller, and the other end of the main shaft extends outwardly from the sealing box 20. In this application, unless otherwise specified, the axial direction refers to the extension direction of the main shaft. In this embodiment, the sealing box 20 comprises a cylinder 21 extending axially and a bottom plate 22 arranged at one end of the cylinder facing the impeller, and the bottom plate is sealed and fixed to the pump casing by bolts so that the sealing box is sealingly mounted on the pump casing.

[0102] The intrinsically safe parking seal is arranged in the sealing box 20 and is located between the main seal 30 of the nuclear main pump and the impeller 13. The main seal includes a static ring 32 fixedly set on the inner wall of the cylinder and a dynamic ring 31 sealingly fixedly installed on the main shaft 18, and the dynamic ring and the static ring form a mechanical seal pair. A sealing ring 33 is provided between the static ring and the cylinder, and the end cover 25 is fixed to the side of the cylinder away from the bottom plate by bolts to keep the main seal in the sealing box. In order to simplify the drawings, in the drawings, only some parts of the structure of the main seal 30 are shown, and not all of its parts are shown. The detailed structure and installation method of the main seal are existing mature technologies and will not be repeated.

[0103] The intrinsically safe parking seal arrangement specifically includes a sealing pair, a bellows assembly 40 and a fluid pressurizing device 60, wherein the sealing pair includes a planar upper ring 56 and a convex lower ring 51 which are sleeved on the main shaft, wherein the planar upper ring 56 is sealingly fixed on the main shaft, and the convex lower ring is located on the side of the planar upper ring facing the impeller.

[0104] In this embodiment, the planar upper ring has an upper petal ring 561 and a lower petal ring 562 fixed on the main shaft 18, and an upper ring groove 181 and a lower ring groove 182 are provided on the outer peripheral surface of the main shaft 18, and the upper ring groove 181 and the lower ring groove 182 both extend around the outer peripheral surface of the main shaft. The upper petal ring 561 is tightly clamped in the upper ring groove, and the lower petal ring 562 is tightly clamped in the lower ring groove. The upper petal ring 561 and the lower petal ring 562 are respectively tightly pressed on both sides of the planar upper ring to fix the planar upper ring on the main shaft. The upper petal ring 561 and the lower petal ring 562 each have two ring petals. It can be understood that in other embodiments, the number of ring petals of the upper petal ring 561 and the lower petal ring 562 can be set according to specific needs.

[0105] The axial cross section of the first ring body 57 of the planar upper ring 56 is rectangular. Specifically in this embodiment, the planar upper ring is made of 304 stainless steel.

[0106] The convex lower ring 51 is composed of a convex soft ring 54 and a plane metal ring seat 55 connected together, wherein the axial section of the second ring body of the convex soft ring 54 is T-shaped, and the second ring body includes an integrally formed flat plate portion 52 and a protrusion 53, the protrusion is located on the side of the flat plate portion facing the plane upper ring, the end face of the protrusion facing the plane upper ring is annular, and the plane metal ring seat is connected to the side of the flat plate portion away from the protrusion; observed along the axial direction, the first ring body of the plane upper ring completely covers the end face of the protrusion facing the plane upper ring. And in this embodiment, in the radial direction, when the convex lower ring is pressed against the plane upper ring, the inner circumference of the plane upper ring outwardly exceeds the inner edge of the protrusion, and the outer circumference of the plane upper ring outwardly exceeds the outer edge of the protrusion, so as to reduce the contact area of ​​the sealing interface, so that a larger sealing contact pressure ratio can be formed when a smaller fluid pressure is loaded in the pressure chamber, and zero leakage of the parking seal is achieved.

[0107] The convex soft ring is made of M106F graphite material. It can be understood that in another embodiment, the convex soft ring can also be made of polytetrafluoroethylene material, so that the hardness of the plane upper ring is greater than the hardness of the convex lower ring. The plane metal ring seat is made of 304 stainless steel, and the convex soft ring 54 is bonded to the plane metal ring seat 55 using silicone modified epoxy resin.

[0108] The bellows assembly 40 is located on the side of the convex lower ring 51 facing the impeller 13. The bellows assembly 40 includes an inner bellows 41 and an outer bellows 42 coaxially sleeved together. The inner bellows and the outer bellows are sleeved on the main shaft, and the outer bellows are sleeved on the outer side of the inner bellows. One end of the inner bellows is sealed and welded to the bottom plate of the sealing box, and the other end of the inner bellows is sealed and connected to the plane metal ring seat 55 of the convex lower ring; one end of the outer bellows is sealed and welded to the bottom plate of the sealing box, and the other end of the outer bellows is sealed and connected to the plane metal ring seat 55 of the convex lower ring, that is, both ends of the inner bellows and the outer bellows are sealed and welded to the plane metal ring seat of the convex lower ring and the bottom plate of the sealing box respectively. The space enclosed by the inner bellows, the outer bellows, the plane metal ring seat and the bottom plate forms a pressure chamber 43. To facilitate the welding of the inner and outer bellows to the bottom plate and the flat metal ring seat, in this embodiment, the cylinder 21 and the bottom plate 22 of the sealing box are processed separately, and after the welding of the inner and outer bellows to the bottom plate and the flat metal ring seat, and the pressure test of the pressure chamber 43 are completed, the cylinder 21 and the bottom plate 22 are welded together.

[0109] A fluid channel 23 is provided on the bottom plate 22 , one end of the fluid channel 23 is connected to the pressure chamber 43 , and the other end of the fluid channel 23 penetrates the outer peripheral surface of the sealing box to form a fluid inlet 24 .

[0110] The fluid charging device 60 includes a pressurizer 62 and a storage tank 61. The inlet of the pressurizer 62 is connected to the storage tank 61, and the outlet of the pressurizer is connected to the fluid inlet 24 via a delivery pipe 63. A regulating valve 64 is installed at the outlet of the pressurizer. The pressurizer is used to charge the fluid in the storage tank into the pressure chamber. A pressure detection unit 72 and a vent pipe 65 are installed on the delivery pipe. The connection point between the pressure detection unit and the delivery pipe is located between the regulating valve and the fluid inlet 24, and the connection point between the vent pipe 65 and the delivery pipe is also located between the regulating valve and the fluid inlet 24. A vent valve 66 is installed on the vent pipe 65. Specifically in this embodiment, the storage tank 61 is used to store nitrogen. The pressurizer 62 specifically adopts a gas compressor.

[0111] When the inflator fills the pressure chamber with fluid, the bellows assembly can be extended, pushing the convex lower ring to move toward the plane upper ring and sealing against the plane upper ring. When the pressure in the pressure chamber reaches the set pressure value, the fluid is stopped from being filled into the pressure chamber, and a non-percolation contact interface is formed between the plane upper ring and the convex lower ring. When the fluid in the pressure chamber is discharged, the bellows assembly can move away from the plane upper ring and return to its original state. When the pressure in the pressure chamber reaches the set pressure value, the porosity of the contact interface between the plane upper ring and the convex lower ring is less than 0.3116.

[0112] In order to better control the pressure in the pressure chamber, the present embodiment is further provided with a pressure control system 70, which includes a central processing unit 71, a pressure detection unit 72 connected to the central processing unit 71, a valve adjustment unit 73, and a pressure inflator control unit 74, wherein:

[0113] The central processing unit is used to receive information from the pressure detection unit, compare the information with the set pressure value, and issue control instructions according to the comparison result to coordinate the work of the valve adjustment unit and the inflator control unit;

[0114] A pressure detection unit, used for detecting the pressure in the pressure chamber and transmitting the detection data to the central processing unit;

[0115] The valve regulating unit receives control from the central processing unit and opens the regulating valve to keep the pressure in the pressure chamber at a set pressure value;

[0116] The charger control unit receives control from the central processing unit and controls the start and stop of the charger.

[0117] Specifically in this embodiment, the central processing unit 71 specifically adopts a 32-bit PLC programmable controller; the pressure detection unit is a pressure sensor with model BA5803; the regulating valve adopts a pneumatic regulating valve with a valve regulating unit, and it only needs to connect its valve regulating unit to the central processing unit; the charging device control unit specifically adopts an AC contactor.

[0118] The following is an explanation of the process of determining the set pressure value of the fluid pressure in the pressure chamber for intrinsically safe parking. Figure 5 , the determination process specifically includes the following steps:

[0119] S1. Obtaining raw data including equivalent rough surface parameters, sealing gap height and initial porosity:

[0120] S2. Obtain fractal parameters and elastic modulus of equivalent rough surface, as well as maximum micro-convex height and initial porosity

[0121] To simplify the calculation steps, the contact between the convex lower ring and the plane upper ring is regarded as the contact between an equivalent rough surface and a rigid smooth plane.

[0122] The equivalent rough surface parameters include fractal parameters, scale coefficients and elastic modulus, which are calculated from the corresponding parameters of the convex soft ring of the convex lower ring and the plane upper ring. The specific calculation is based on formula (1):

[0123]

[0124] In formula (1), D is the fractal dimension of the equivalent rough surface, D1 and D2 are the fractal dimensions of the convex soft ring and the ring on the plane, respectively, G is the scale factor of the equivalent rough surface, G1 and G2 are the scale factors of the convex soft ring and the ring on the plane, respectively, E is the elastic modulus of the equivalent rough surface, E1 and υ1 are the elastic modulus and Poisson's ratio of the convex soft ring, respectively, and E2 and υ2 are the elastic modulus and Poisson's ratio of the ring on the plane, respectively.

[0125] The maximum micro-convex height h and base length l of the equivalent rough surface are calculated using formula (2):

[0126]

[0127] In formula (2), S m is the average peak spacing of the equivalent rough surface.

[0128] The initial porosity is calculated using formula (3):

[0129]

[0130] In formula (3), φ0 is the initial porosity, a Lmis the base area of ​​the largest microconvex body, A n is the nominal contact area of ​​the sealing interface, ψ is the domain expansion factor, and its specific value can be obtained by looking up Table 5-1 on page 176 of Fractals in Tribology, and a is the contact area of ​​the micro-convex body.

[0131] S3. According to the non-percolation contact interface condition, the actual compression of the sealing interface is solved:

[0132] The non-percolation contact interface condition is shown in formula (4):

[0133] δ>2.17h(φ0-0.3116) Formula (4)

[0134] In formula (4), δ is the compression of the sealing interface when the interaction between the micro-protrusions and the deformation of the substrate are not considered.

[0135] The actual compression of the sealing interface is expressed as follows:

[0136]

[0137] In formula (5), δ r is the actual compression of the sealing interface, δ ec is the critical deformation of the micro-convex body in the elastic stage, δ pc is the critical deformation of the micro-convex body in the elastic-plastic stage; k1, k2, k3 are the surface material characteristic parameters, ξ1, ξ2, ξ3 are the geometric parameters of the largest micro-convex body, α1, α2 are the hardness coefficients k v , g1 is an expression that includes the sealing interface compression δ.

[0138] g1、δ ec With δ pc The expressions are respectively:

[0139]

[0140]

[0141] In formula (6) and formula (7), H is the hardness of the convex soft ring, H = 2.8σ y , σ y is the yield limit of the convex soft ring, k v is the hardness coefficient of the convex soft ring, k v =0.454+0.41υ1, R is the peak curvature radius of the largest micro-convex body, R=l D / π 2 G D-1 The expressions of α1, α2, k1, k2, k3, ξ1, ξ2, and ξ3 are respectively:

[0142]

[0143]

[0144]

[0145] The steps to solve the actual compression of the sealing interface are as follows:

[0146] According to the non-percolation contact interface condition, the compression amount without considering the asperity interaction and substrate deformation is obtained.

[0147] The actual compression of the sealing interface is obtained by trial and error method. For example, assuming δ r <δ ec , substitute the obtained compression δ into δ in the elastic stage a2 , and find δ r If δ r <δ ec , it means the hypothesis is correct, otherwise it means the hypothesis is incorrect, and we need to assume δ ec ≤δ r ≤δ pc or δ pc <δ r Further calculation.

[0148] S4. Determine the contact pressure ratio required for the sealing interface:

[0149] According to the actual compression of the sealing interface, the maximum deformation area of ​​the micro-convex body is obtained using formula (11):

[0150]

[0151] In formula (11), a max is the maximum deformation area of ​​the micro-convex body.

[0152] The deformation stage of the micro-convex body of the sealing interface is determined according to the maximum deformation area of ​​the micro-convex body, and the formula (12) and formula (13) are used specifically:

[0153]

[0154]

[0155] In formula (12) and formula (13), a ec 、a epc 、a pc are the critical deformation areas of the micro-convex body in the elastic deformation stage, the first elastic-plastic deformation stage and the second elastic-plastic deformation stage respectively.

[0156] According to the different deformation stages of the micro-convex body of the sealing interface, there are different expressions of contact pressure ratio of the sealing interface.

[0157] When the sealing interface micro-convex body is in the elastic deformation stage, the contact pressure of the sealing interface is solved by equations (14), (15) and (16):

[0158]

[0159]

[0160]

[0161] In formula (14), formula (15) and formula (16), p c is the contact pressure of the sealing interface, f ec is the contact load expression of the micro-asperity in the elastic stage, and n(a) is the contact area distribution function of the micro-asperity.

[0162] When the sealing interface micro-convex body is in the first elastic-plastic deformation stage, the contact pressure of the sealing interface is solved by equations (17) and (18):

[0163]

[0164]

[0165] In formula (17) and formula (18), f epc1 It is the contact load expression of the micro asperity in the first elastic-plastic stage.

[0166] When the sealing interface micro-convex body is in the second elastic-plastic deformation stage, the contact pressure of the sealing interface is solved by equations (19) and (20):

[0167]

[0168]

[0169] In formula (19) and formula (20), f epc2 It is the contact load expression of the asperity in the second elastic-plastic stage.

[0170] When the sealing interface micro-convex body is in the stage of complete plastic deformation, the formula for solving the contact pressure ratio of the sealing interface is formula (21) and formula (22):

[0171]

[0172] f pc =Ha Formula (22)

[0173] In formula (21) and formula (22), fpc The contact load expression of the micro-asperity when it is in the complete plastic deformation stage.

[0174] S5. Determine the set pressure value of the fluid pressure in the pressure chamber:

[0175] The fluid pressure in the double-layer bellows is calculated according to the required contact pressure ratio, using formula (23):

[0176]

[0177] In formula (23), p b is the pressure of the fluid in the pressure chamber, A c A is the nominal contact area formed when the convex lower ring and the flat upper ring are in contact. b is the cross-sectional area of ​​the pressure chamber, A b =(φ2 2 -φ1 2 )π / 4, φ1 is the outer diameter of the welding point between the inner bellows and the flat metal ring seat, and φ2 is the inner diameter of the welding point between the outer bellows and the flat metal ring seat. For the specific positions of φ1 and φ2, please refer to Figure 4 . Specific embodiment:

[0179] Taking the sodium-cooled fast reactor nuclear main pump as an example, when the shutdown seal is started, the convex lower ring and the flat upper ring must be able to withstand a pressure difference of 0.5MPa.

[0180] The convex soft ring and the flat upper ring are both ground, with a surface roughness between 0.1 and 0.2 μm. The material properties and fractal parameters are shown in Table 1.

[0181] Table 1 Material properties of convex soft ring and plane ring

[0182] Convex soft ring (M106K) Flat top ring (304 stainless steel) Elastic modulus E / GPa 16 193 <![CDATA[Yield strength σ y / MPa]]> 50 / Poisson's ratio 0.29 0.3 Fractal dimension D 1.426 1.607 Scale factor G / m <![CDATA[2.48×10 -10 ]]> <![CDATA[2.27×10 -11 ]]>

[0183] The cross-sectional area of ​​the pressure chamber is A b The calculation of the nominal contact area A formed by the convex lower ring and the flat upper ring when the seal contacts c Calculation of nominal contact area A c It is the area of ​​the end surface of the protrusion 53 facing the ring 56 on the plane. The relevant data are listed in Table 2. In Table 2, the end surface of the protrusion refers to the end surface of the protrusion 53 facing the ring 56 on the plane.

[0184] Table 2

[0185] <![CDATA[φ1 / m]]> 0.21 <![CDATA[φ2 / m]]> 0.27 Inner diameter of the protruding end surface / m 0.23 Outer diameter of the protruding end surface / m 0.25

[0186] The elastic modulus of the equivalent rough surface is calculated to be 1.614×10 10 GPa, fractal dimension is 1.424, and scale factor is 2.49×10-10 m, and the base length of the largest micro-convex body on the sealing interface is 9.33×10 -5 m, the sealing gap height is 4.04×10 -7 m, the domain expansion factor is 2.063, and the base area of ​​the largest microconvex body is 6.84×10 -9 m 2 , the nominal contact area of ​​the sealing interface is 2.08×10 -8 m 2 , the initial porosity is 0.824.

[0187] According to the no-percolation interface condition, the compression of the sealing interface without considering the interaction between micro-asperities and the deformation of the substrate should be greater than 4.5×10 -7 m. The critical deformation of the micro-convex body in the elastic stage is 1.32×10 -7 m, and the critical deformation in the elastic-plastic stage is 1.45×10 -5 m. According to the trial and error method, the actual compression of the sealing interface should be greater than 1.46×10 -7 m.

[0188] The critical deformation area of ​​the micro-convex body in the elastic deformation stage is 9.06×10 -10 m 2 , the critical deformation area of ​​the micro-convex body in the first elastic-plastic deformation stage is 6.45×10 -9 m 2 The critical deformation area of ​​the micro-convex body in the second elastic-plastic deformation stage is 1.86×10 -7 m 2 According to the calculation, the maximum deformation area of ​​the micro-convex body should be greater than 2.72×10 -9 m 2 It is judged that the sealing interface is in the first elastic-plastic deformation stage, and the contact pressure of the sealing interface is calculated to be greater than 4.92MPa.

[0189] The cross-sectional area of ​​the pressure chamber is 0.02262m 2 The nominal contact area formed by the convex lower ring and the flat upper ring seal contact is 0.00754m 2 , it is calculated that when the sealing interface is under non-percolation contact conditions, the fluid pressure in the pressure chamber should be greater than 1.64MPa.

Claims

1. An intrinsically safe shutdown seal for a nuclear main pump, which is arranged in a sealing box and located between the main seal and the impeller of the nuclear main pump, characterized in that: It comprises a sealing pair, a bellows assembly and a fluid pressure charging device, wherein the sealing pair comprises a plane upper ring and a convex lower ring sleeved on the main shaft of the nuclear main pump, wherein the plane upper ring is sealingly fixed on the main shaft, the convex lower ring is located on the side of the plane upper ring facing the impeller, and the convex lower ring is composed of a convex soft ring and a plane metal ring seat connected together, wherein the convex soft ring is located on the side of the plane metal ring seat facing the plane upper ring; the bellows assembly is located on the side of the convex lower ring facing the impeller, and the bellows assembly comprises an inner bellows and an outer bellows coaxially sleeved together, and both the inner bellows and the outer bellows are sleeved on the main shaft; Both ends of the inner bellows and the outer bellows are respectively welded to the plane metal ring seat of the convex lower ring and the bottom plate of the sealing box in a sealing manner, and the space enclosed by the inner bellows, the outer bellows, the convex lower ring and the bottom plate forms a pressure chamber; The fluid charging device comprises a pressurizer and a storage tank, the inlet of the pressurizer is connected to the storage tank, the outlet of the pressurizer is connected to the pressure chamber, the pressurizer is used to charge the fluid in the storage tank into the pressure chamber, and a regulating valve is installed at the outlet of the pressurizer; When the inflator fills the pressure chamber with fluid, the bellows assembly can stretch, push the convex lower ring to move toward the planar upper ring, and seal against the planar upper ring. When the fluid pressure in the pressure chamber reaches the set pressure value, stop filling the pressure chamber with fluid, and form a non-percolation contact interface between the planar upper ring and the convex lower ring. When the fluid in the pressure chamber is discharged, the bellows assembly can move away from the planar upper ring and return to its original state.

2. The intrinsically safe parking seal according to claim 1, characterized in that: When the fluid pressure in the pressure chamber reaches a set pressure value, the porosity of the contact interface between the plane upper ring and the convex lower ring is less than 0.3116.

3. The intrinsically safe parking seal according to claim 1, characterized in that: The hardness of the ring on the plane is greater than the hardness of the convex soft ring.

4. The intrinsically safe parking seal according to claim 1, characterized in that: The axial cross-section of the first ring body of the ring on the plane is rectangular; The axial cross-section of the second ring body of the convex soft ring is T-shaped. The second ring body includes an integrally formed flat plate portion and a protrusion. The protrusion is located on the side of the flat plate portion facing the planar upper ring. The end face of the protrusion facing the planar upper ring is in a circular ring shape. The planar metal ring seat is connected to the side of the flat plate portion away from the protrusion. When viewed along the axial direction, the first ring body of the planar upper ring completely covers the end face of the protrusion facing the planar upper ring.

5. The intrinsically safe parking seal according to claim 1, characterized in that: The plane upper ring is made of a hard material that is resistant to corrosion, oxidation, high temperature and pressure, and radiation, and the convex soft ring is made of a soft material that is resistant to corrosion, oxidation, high temperature and pressure, and radiation.

6. The intrinsically safe parking seal according to claim 1, characterized in that: The sealing box includes a cylinder extending along the axial direction of the main shaft and a bottom plate arranged at one end of the cylinder facing the impeller, a fluid channel is arranged on the bottom plate, one end of the fluid channel is connected to the pressure chamber, and the other end of the fluid channel penetrates the outer peripheral surface of the sealing box outwardly; The outlet of the inflator is connected to the fluid passage.

7. The intrinsically safe parking seal according to claim 1, characterized in that: It also includes a pressure control system, which includes a central processing unit, a pressure detection unit connected to the central processing unit, a valve adjustment unit, and a pressure inflator control unit, wherein: The central processing unit is used to receive information from the pressure detection unit, compare the information with the set pressure value, and issue control instructions according to the comparison result to coordinate the work of the valve adjustment unit and the inflator control unit; A pressure detection unit, used for detecting the pressure in the pressure chamber and transmitting the detection data to the central processing unit; The valve regulating unit receives control from the central processing unit and opens the regulating valve to keep the pressure in the pressure chamber at a set pressure value; The charger control unit receives control from the central processing unit and controls the start and stop of the charger.

8. The intrinsically safe parking seal according to claim 1, characterized in that: The set pressure value of the fluid pressure in the pressure chamber is calculated using the following steps: S1. Obtaining the fractal dimension, scale coefficient and elastic modulus of the sealing surface including the plane upper ring and the convex soft ring; S2, obtain the fractal parameters and elastic modulus of the equivalent rough surface as well as the maximum micro-convexity height and initial porosity; S3. Determine the compression required for the sealing interface according to the no percolation contact interface condition; S4. Determine the contact specific pressure required for the sealing interface; S5. Determine a set pressure value of the fluid pressure in the pressure chamber.

9. The intrinsically safe parking seal according to claim 8, characterized in that: The set pressure value of the fluid pressure in the pressure chamber is expressed by the base length of the largest micro-convex body on the equivalent rough surface that affects the compression required for the sealing interface, and the expression is as follows: In the formula, p b is the pressure of the fluid in the pressure chamber, p c is the contact pressure of the sealing interface, A c A is the nominal contact area formed when the convex lower ring and the flat upper ring are in contact. b is the cross-sectional area of ​​the pressure chamber, A b =(φ2 2 -φ1 2 )π / 4, φ1 is the outer diameter of the welding point between the inner bellows and the plane metal ring seat, φ2 is the inner diameter of the welding point between the outer bellows and the plane metal ring seat, h is the height of the largest micro-convex body on the equivalent rough surface, D is the fractal dimension of the equivalent rough surface, l is the base length of the largest micro-convex body on the equivalent rough surface, G is the scale factor of the equivalent rough surface, S m is the average peak spacing of the equivalent rough surface.

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