Intrinsic safety parking seal for a nuclear primary pump

Abstract

The application provides an intrinsically safe parking seal of a nuclear main pump, which comprises a sealing pair, a bellows assembly and a fluid pressure charging device, the sealing pair comprises a flat upper ring and a convex lower ring which are sleeved on a main shaft of the nuclear main pump, the flat upper ring is sealingly fixed on the main shaft, and the convex lower ring is composed of a convex soft ring and a flat metal ring seat which are connected together, the bellows assembly comprises an inner bellows and an outer bellows which are coaxially sleeved together, the two ends of the inner bellows and the outer bellows are sealingly welded on the flat metal ring seat of the convex lower ring and a bottom plate of a sealing box respectively, and a space surrounded by the inner bellows, the outer bellows, the convex lower ring and the bottom plate is formed as a pressure cavity; when the pressure charger charges fluid into the pressure cavity, the bellows assembly can be elongated, the convex lower ring and the flat upper ring form a seal, and the seal is cancelled after the fluid in the pressure cavity is discharged. The application can effectively prolong the service life of the parking seal and improve the safety coefficient of the nuclear main pump operation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sealing, and particularly relates to an intrinsically safe parking seal for a nuclear main pump. BACKGROUND

[0002] Nuclear power, as an important clean energy, meets the development trend of a low-carbon society. The nuclear main pump, located on the reactor core and the steam generator loop (main loop), is the "heart" of a nuclear power plant, circulating the coolant to absorb the heat of the fission reaction at the reactor core and release the heat in the steam generator. The mechanical seal is generally used between the main shaft and the casing of the nuclear main pump to control the leakage of the coolant in the reactor core. 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 of the reactor to be cooled, the melting of the reactor core, and catastrophic damage to humans and the environment.

[0003] The typical reactors using the nuclear main pump as the main loop coolant delivery device include the pressurized water reactor, the molten salt reactor, and the sodium-cooled fast reactor. The nuclear main pump of the pressurized water reactor uses a three-stage series non-contact mechanical seal, and the nuclear main pumps of the molten salt reactor and the sodium-cooled fast reactor use a single-stage contact mechanical seal. Due to the wear of the dynamic and static ring end faces of the mechanical seal and the aging of the auxiliary O-ring exposed to the high radioactive environment for a long time, the mechanical seal needs to be replaced and maintained regularly. To avoid the leakage of the coolant outside during the replacement process, a parking seal is invented to ensure that the nuclear main pump remains in a sealed state after the mechanical seal fails, creating conditions for maintenance or replacement.

[0004] Currently, there are mainly three forms of parking seals for the existing nuclear main pumps, namely, the plane seal, the O-ring seal, and the conical seal. Regarding the plane seal, the plane seal includes an upper plane ring and a lower plane ring, wherein the upper plane ring is sealingly connected with the outer shell and can move axially, and the lower plane ring is sealingly fixed on the main shaft, and when the upper plane ring and the lower plane ring are pressed together, a sealing contact is formed; considering the redundancy design, the sealing end faces of the upper plane ring and the lower plane ring are designed to be relatively large, which requires a relatively large axial force to complete the sealing, which increases the uncertainty of the sealing performance of the parking seal.

[0005] The O-ring type seal is an improvement based on the plane seal, specifically a rubber O-ring is fixed on the upper plane ring, and the O-ring is deformed to achieve sealing under pressure; since the O-ring of the parking seal is exposed to a high radioactive environment for a long time, it is prone to aging and failure, and it is difficult to run safely and stably for a long period.

[0006] Regarding the conical seal, the conical seal includes a conical ring sealingly fixed on the main shaft, and an upper plane ring sealingly connected with the outer shell and capable of moving axially, and when the upper plane ring is pressed against the conical ring, a linear seal is formed between the two. However, the linear seal is prone to leaving grooves on the soft sealing surface, which brings difficulties to the implementation of the next parking seal.

[0007] Among the above three parking seals, a flat upper ring is provided, and the flat upper ring is moved to be pressed against another sealing member to achieve sealing effect. Since the flat upper ring is directly installed on the inner wall of the sealing cavity, the sealing between the flat upper ring and the inner wall of the sealing cavity needs to be ensured first. Since the flat upper ring is a moving part, it will inevitably be worn after being moved for many times, which will reduce the sealing between the flat upper ring and the inner wall of the sealing cavity, and affect 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 seal, how to improve the service life of the parking seal is still a problem to be solved for the safe operation of the nuclear main pump. SUMMARY

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

[0010] Both ends of the inner bellows and the outer bellows are sealingly welded on the flat metal ring seat of the convex lower ring and a bottom plate of the sealing pot respectively. A space enclosed by the inner bellows, the outer bellows, the convex lower ring and the bottom plate forms a pressure cavity.

[0011] The fluid pressure charging device comprises a pressure charger and a storage tank. The inlet of the pressure charger is communicated with the storage tank, and the outlet of the pressure charger is communicated with the pressure cavity. The pressure charger is used for charging the fluid in the storage tank into the pressure cavity, and an adjusting valve is installed on the outlet of the pressure charger.

[0012] When the pressure chamber is filled with fluid, the bellows assembly is elongated, the convex lower ring is pushed to move towards the flat upper ring and tightly presses against the flat upper ring. When the fluid pressure in the pressure chamber reaches a set pressure value, the fluid filling into the pressure chamber is stopped, and the flat upper ring and the convex lower ring form a non-permeable contact interface. When the fluid in the pressure chamber is discharged, the bellows assembly can move away from the flat upper ring and restore to the original state. In the bellows assembly, the outer bellows is sleeved outside the inner bellows. The fluid can be liquid or gas. When the fluid is liquid, it can be water or hydraulic oil. When the fluid is gas, it can be air, nitrogen or other gas.

[0013] The sealing pair in the application is composed of the flat upper ring and the convex lower ring, and the bellows assembly is elongated by the pressure chamber to push the convex lower ring to press against the flat upper ring to form a seal. The flat upper ring and the convex lower ring adopt a flat sealing form. The application cancels the O-ring seal and the taper seal in the prior art, avoiding the aging of the O-ring and the problem of leaving grooves in the taper seal. In the application, the flat upper ring is connected with the main shaft seal, and the convex lower ring is connected with the bottom plate of the seal housing through the bellows. In the normal operation of the nuclear main pump, the flat upper ring and the convex lower ring are in a separated state without contact, which will not cause wear of the flat upper ring or the convex lower ring. When the parking seal works, the flat upper ring and the convex lower ring are in contact to form a static seal without friction, which will not cause wear. Therefore, the service life of the sealing pair can be improved.

[0014] The application can adjust the pressure in the pressure chamber to push the convex lower ring to extrude the flat upper ring to generate sufficient sealing contact specific pressure between the convex lower ring and the flat upper ring. In the application, the cylinder and the bottom plate of the seal housing are machined separately, and then the cylinder and the bottom plate are welded together after the welding of the inner and outer bellows with the bottom plate and the flat metal ring seat of the convex lower ring and the pressure test of the pressure chamber are completed.

[0015] Specifically, when the fluid pressure in the pressure chamber reaches a set pressure value during parking of the nuclear main pump, the porosity of the contact interface between the flat upper ring and the convex lower ring is less than 0.3116. When the porosity between the sealing interfaces reaches 0.3116, the surface microconvex bodies on the sealing interfaces of the flat upper ring and the convex lower ring are deformed by mutual extrusion, and only one channel through the sealing surface connected by gaps exists in the sealing interface. When the sealing contact specific pressure increases to make the porosity of the sealing interface less than 0.3116, the surface microconvex bodies on the sealing interfaces of the flat upper ring and the convex lower ring continue to deform by mutual extrusion, which greatly blocks the possibility of the channel through the sealing surface connected by gaps in the sealing interface, and realizes the sealing between the flat upper ring and the convex lower ring of the sealing pair.

[0016] Further, 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 press the flat upper ring, and the flat upper ring will be slightly deformed to form a cutting effect, which may damage the flat upper ring. If the hardness of the flat upper ring is greater than that of the convex soft ring, the problem can be avoided, and the service life of the parking seal can be improved.

[0017] The axial section of the first ring body of the flat upper ring is rectangular, and the axial section of the second ring body of the convex soft ring is T-shaped. The second ring body includes an integral flat plate portion and a protruding portion. The protruding portion is located on the side of the flat plate portion facing the flat upper ring. The end surface of the protruding portion facing the flat upper ring is annular. The flat metal ring seat is connected to the side of the flat plate portion away from the protruding portion. When viewed in the axial direction, the first ring body of the flat upper ring completely covers the end surface of the protruding portion facing the flat upper ring. Preferably, when the convex lower ring is pressed against the flat upper ring in the radial direction, the inner circumferential surface of the flat upper ring outwardly exceeds the inner side edge of the protruding portion, and the outer circumferential surface of the flat upper ring outwardly exceeds the outer side edge of the protruding portion, so as to reduce the contact area of the sealing interface, thereby being able to form a larger sealing contact specific pressure under a smaller fluid pressure loaded in the pressure cavity, and realizing zero leakage of the parking seal.

[0018] Specifically, the flat upper ring is made of a hard material resistant to corrosion, oxidation, high temperature and pressure, and radiation. The convex soft ring is made of a soft material resistant to corrosion, oxidation, high temperature and pressure, and radiation. The flat upper ring can be made of stainless steel, and the convex lower ring can be made of graphite ring, polytetrafluoroethylene, polyether ether ketone, etc. The flat 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] Further, the seal housing includes a cylinder body extending in the axial direction of the main shaft and a bottom plate provided at one end of the cylinder body in the direction of the impeller. A fluid passage is provided on the bottom plate. One end of the fluid passage communicates with the pressure cavity, and the other end of the fluid passage penetrates the outer circumferential surface of the seal housing outwardly. The outlet of the pressure charger communicates with the fluid passage. This design avoids opening a fluid passage on the pump shell and the difficulty of connecting the fluid passage with the pressure cavity.

[0020] Further, for easy control, a pressure control system is further included. The pressure control system includes a central processing unit, a pressure detection unit connected to the central processing unit, a valve adjusting unit, and a pressure charger control unit. Wherein:

[0021] The central processing unit is used to receive information from the pressure detection unit and compare the information with a set pressure value. According to the comparison result, a control instruction is issued to coordinate the work of the valve adjusting unit and the pressure charger control unit.

[0022] a pressure detection unit for detecting the pressure in the pressure chamber and sending the detection data to the central processing unit;

[0023] a valve adjustment unit receiving the control of the central processing unit and opening the regulating valve to keep the pressure in the pressure chamber at the set pressure value;

[0024] a pressure charger control unit receiving the control of the central processing unit and controlling the start and stop of the pressure charger.

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

[0026] S1, obtaining the fractal dimension, scale factor and elastic modulus of the sealing surface including the upper flat ring and the lower convex soft ring;

[0027] S2, obtaining the fractal parameters and elastic modulus of the equivalent rough surface, and the maximum asperity height and initial porosity;

[0028] S3, determining the compression amount required by the sealing interface according to the non-percolation contact interface condition;

[0029] S4, determining the contact specific pressure required by the sealing interface;

[0030] S5, determining the set pressure value of the fluid pressure in the pressure chamber.

[0031] The calculation steps of the above set pressure value adopt the design method of the fluid pressure in the pressure chamber under the non-percolation contact interface, which solves the problem that the parking sealing contact pressure of the existing three sealing forms is only designed by experience, and the contact area design of the lower convex ring and the upper flat ring in the application is smaller, which can form larger sealing contact specific pressure and realize zero leakage of parking sealing under lower fluid pressure in the pressure chamber.

[0032] Specifically, the set pressure value of the fluid pressure in the pressure chamber is expressed by the base length of the maximum asperity on the equivalent rough surface affecting the compression amount required by 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 specific pressure of the sealing interface, A c is the nominal contact area formed when the lower convex ring and the upper flat ring sealing contact, A 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, φ2 is the inner diameter of the welding point between the outer bellows and the flat 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 for 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. Calculate the fractal parameters and elastic modulus of the equivalent rough surface as well as the maximum asperity height and initial porosity;

[0038] To simplify the calculation steps, the contact between the convex lower ring and the flat 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 moduli, which are calculated from the corresponding parameters of the convex soft ring of the convex lower ring and the flat 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 asperity 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 asperity, 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 no-percolation contact interface condition, solve the actual compression of the sealing interface:

[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-asperities 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 asperity 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 The coefficient of g1 is the expression including the sealing interface compression δ.

[0055] g1、δ ec and δ pc The expressions are respectively as formula (6) and formula (7):

[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 solving steps of the actual compression of the sealing interface are as follows:

[0064] According to the condition of no percolation contact interface, the compression amount when not considering the interaction of microconvex bodies and the deformation of the base is obtained.

[0065] The actual compression of the sealing interface is obtained by the assumption method. For example, it is assumed that δ r <δ ec The obtained compression amount δ is substituted into the δ r of the elastic stage to obtain δ r . If δ r <δ ec , it represents that the assumption is correct, otherwise, it represents that the assumption is incorrect, then δ ec ≤δ r ≤δ pc or δ pc <δ r is assumed and further calculation is performed.

[0066] S4, determining the deformation stage of the microconvex body of the sealing interface, and determining the required contact specific pressure of the sealing interface:

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

[0068]

[0069] In formula (11), a max is the maximum deformation area of the microconvex body.

[0070] According to the obtained maximum deformation area of the microconvex body, the deformation stage of the microconvex body of the sealing interface is determined, and formula (12) and formula (13) are specifically used:

[0071]

[0072]

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

[0074] According to different deformation stages of the micro asperity on the sealing interface, different contact pressure expressions of the sealing interface are obtained.

[0075] When the micro asperity on the sealing interface is in the elastic deformation stage, the contact pressure solving formula of the sealing interface is formula (14), formula (15) and formula (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 micro asperity on the sealing interface is in the first elastic-plastic deformation stage, the contact pressure solving formula of the sealing interface is formula (17) and formula (18):

[0081]

[0082]

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

[0084] When the micro asperity on the sealing interface is in the second elastic-plastic deformation stage, the contact pressure solving formula of the sealing interface is formula (19) and formula (20):

[0085]

[0086]

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

[0088] When the micro asperity on the sealing interface is in the complete plastic deformation stage, the contact pressure solving formula 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 based on the required contact pressure ratio, specifically 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 structural schematic diagram 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 drawings.

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

[0099] Figure 4 This is a schematic diagram of the installation of the bellows assembly.

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

[0101] See also Figures 1-3The essential safety parking seal of the nuclear main pump comprises a pump shell 11 and a sealing case 20 which are installed together in an axial direction, an impeller 13 which is rotatably installed in the pump shell 11, a pump inlet 12 which is formed at one end of the pump shell 11 away from the sealing case, and a pump outlet 14 which is formed at one side of the pump shell 11 in a radial direction. One end of a main shaft 18 extends into the pump shell and is fixedly connected to the impeller, and the other end of the main shaft extends out of the sealing case 20. In the present application, the axial direction refers to the extending direction of the main shaft unless otherwise specified. In the present embodiment, the sealing case 20 comprises a cylinder 21 which extends in the axial direction and a bottom plate 22 which is arranged at one end of the cylinder 21 which is directed towards the impeller, and the bottom plate is fixedly sealed to the pump shell by means of bolts, so that the sealing case is sealingly installed on the pump shell.

[0102] The essential safety parking seal is arranged in the sealing case 20 and is located between a main seal 30 of the nuclear main pump and the impeller 13. The main seal comprises a static ring 32 which is fixedly arranged on the inner wall of the cylinder and a dynamic ring 31 which is sealingly and 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 arranged between the static ring and the cylinder, and an end cover 25 is fixedly arranged on one side of the cylinder which is away from the bottom plate by means of bolts, so as to keep the main seal in the sealing case. In order to simplify the drawing, only part of the components of the main seal 30 are shown in the drawing, and the whole components of the main seal are not shown. The detailed structure and installation mode of the main seal are both mature technologies and will not be described herein.

[0103] The essential safety parking seal specifically comprises a seal pair, a bellows assembly 40 and a fluid pressure charging device 60. The seal pair comprises a flat upper ring 56 which is sealingly fixed on the main shaft and a convex lower ring 51 which is located on the side of the flat upper ring which is directed towards the impeller.

[0104] In the present embodiment, the flat upper ring has an upper split ring 561 and a lower split ring 562 which are fixed on the main shaft 18, and an upper ring groove 181 and a lower ring groove 182 are arranged on the outer circumferential surface of the main shaft 18, and the upper ring groove 181 and the lower ring groove 182 both extend around the outer circumferential surface of the main shaft. The upper split ring 561 is tightly clamped in the upper ring groove, and the lower split ring 562 is tightly clamped in the lower ring groove, and the upper split ring 561 and the lower split ring 562 are tightly pressed on the two sides of the flat upper ring respectively, so as to fix the flat upper ring on the main shaft. The upper split ring 561 and the lower split ring 562 both have two ring segments. It can be understood that in other embodiments, the number of ring segments of the upper split ring 561 and the lower split ring 562 can be arranged according to specific needs.

[0105] The axial section of the first ring body 57 of the flat upper ring 56 is rectangular, and in the present embodiment, the flat upper ring is made of 304 stainless steel.

[0106] The convex lower ring 51 is composed of a convex soft ring 54 and a flat metal ring seat 55 connected together, wherein the axial section of the second ring body of the convex soft ring 54 is T-shaped, the second ring body comprises an integral flat plate part 52 and a protruding part 53 located on the side of the flat plate part facing the flat upper ring, the end face of the protruding part facing the flat upper ring is annular, and the flat metal ring seat is connected on the side of the flat plate part away from the protruding part; the first ring body of the flat upper ring completely covers the end face of the protruding part facing the flat upper ring when viewed in the axial direction. In this embodiment, when the convex lower ring is pressed on the flat upper ring in the radial direction, the inner circumferential surface of the flat upper ring outwardly exceeds the inner side edge of the protruding part, and the outer circumferential surface of the flat upper ring outwardly exceeds the outer side edge of the protruding part, so as to reduce the contact area of the sealing interface, thereby being able to form a larger sealing contact specific pressure under a smaller fluid pressure loaded in the pressure cavity, and realizing zero leakage of the parking seal.

[0107] The convex soft ring is made of M106F graphite material, and 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 flat upper ring is greater than that of the convex lower ring. The flat metal ring seat is made of 304 stainless steel, and the convex soft ring 54 is bonded on the flat metal ring seat 55 by 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, and the bellows assembly 40 comprises an inner bellows 41 and an outer bellows 42 coaxially sleeved together, both the inner bellows and the outer bellows are sleeved on the main shaft, and the outer bellows is sleeved on the outer side of the inner bellows. One end of the inner bellows is sealingly welded on the bottom plate of the seal housing, and the other end of the inner bellows is sealingly connected on the flat metal ring seat 55 of the convex lower ring; one end of the outer bellows is sealingly welded on the bottom plate of the seal housing, and the other end of the outer bellows is sealingly connected on the flat metal ring seat 55 of the convex lower ring, that is, both ends of the inner bellows and the outer bellows are respectively sealingly welded on the flat metal ring seat of the convex lower ring and the bottom plate of the seal housing. The space enclosed by the inner bellows, the outer bellows, the flat metal ring seat and the bottom plate forms a pressure cavity 43. In order to facilitate the welding of the inner and outer bellows with the bottom plate and the flat metal ring seat, in this embodiment, the cylinder 21 and the bottom plate 22 of the seal housing are machined respectively, and after the welding of the inner and outer bellows with the bottom plate and the flat metal ring seat and the pressure test of the pressure cavity 43 are completed, the cylinder 21 and the bottom plate 22 are welded together.

[0109] The fluid passage 23 is provided on the bottom plate 22, one end of the fluid passage 23 communicates with the pressure cavity 43, and the other end of the fluid passage penetrates outwardly through the outer circumferential surface of the seal housing to form a fluid inlet 24.

[0110] The fluid pressurizing device 60 comprises a pressurizer 62 and a storage tank 61, the inlet of the pressurizer 62 is communicated with the storage tank 61, the outlet of the pressurizer is communicated with the fluid inlet 24 through a delivery pipe 63, and an adjusting valve 64 is installed at the outlet of the pressurizer, and the pressurizer is used to pressurize 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 of the pressure detection unit with the delivery pipe is located between the adjusting valve and the fluid inlet 24, and the connection point of the vent pipe 65 with the delivery pipe is also located between the adjusting valve and the fluid inlet 24, and a vent valve 66 is installed on the vent pipe 65. Specifically, in the embodiment, the storage tank 61 is used to store nitrogen. The pressurizer 62 specifically adopts a gas compressor.

[0111] When the pressurizer pressurizes the fluid into the pressure chamber, the bellows assembly can be elongated to push the convex lower ring to move towards the planar upper ring and sealingly abut against the planar upper ring, when the pressure in the pressure chamber reaches the set pressure value, the pressurization of the fluid into the pressure chamber is stopped, and the planar upper ring and the convex lower ring form a non-permeable contact interface; when the fluid in the pressure chamber is discharged, the bellows assembly can move away from the planar upper ring and restore to the original state. When the pressure in the pressure chamber reaches the set pressure value, the porosity of the contact interface between the planar 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 embodiment also provides a pressure control system 70, which comprises a central processing unit 71, a pressure detection unit 72 connected with the central processing unit 71, a valve adjusting unit 73, and a pressurizer control unit 74, wherein:

[0113] The central processing unit is used to receive information of the pressure detection unit, compare the information with a set pressure value, and send a control instruction according to a comparison result to coordinate the work of the valve adjusting unit and the pressurizer control unit;

[0114] The pressure detection unit is used to detect the pressure in the pressure chamber and transmit detection data to the central processing unit;

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

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

[0117] Specifically in the embodiment, the central processing unit 71 specifically adopts a 32-bit PLC programmable controller; the pressure detection unit is a pressure sensor with a model of BA5803; the regulating valve adopts a pneumatic regulating valve, which is provided with a valve adjusting unit, and only needs to be connected to the central processor; and the pressure charger control unit specifically adopts an AC contactor.

[0118] The determination process of the set pressure value of the fluid pressure in the intrinsically safe parking pressure chamber is described below. Please refer to Figure 5 , which specifically includes the following steps:

[0119] S1, obtaining original data including equivalent rough surface parameters, sealing gap height and initial porosity:

[0120] S2, obtaining the fractal parameters of the equivalent rough surface, the elastic modulus, and the maximum micro-convex body height and the initial porosity

[0121] In order to simplify the calculation steps, the contact between the convex lower ring and the flat upper ring is regarded as the contact between the equivalent rough surface and the 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 flat upper ring, and are specifically calculated by 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 flat upper ring respectively, G is the scale coefficient of the equivalent rough surface, G1 and G2 are the scale coefficients of the convex soft ring and the flat upper ring 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 flat upper ring respectively.

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

[0126]

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

[0128] The calculation of the initial porosity is carried out by formula (3):

[0129]

[0130] In formula (3), φ0 is the initial porosity, a LmA is the base area of the asperity n is the nominal contact area of the sealing interface, ψ is the domain extension factor, which can be found in Friction and Traction: A

[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 equation (4):

[0133] δ>2.17h(φ0-0.3116) equation (4)

[0134] In equation (4), δ is the compression of the sealing interface without considering the interaction of asperities and the deformation of the base.

[0135] The actual compression of the sealing interface is expressed as equation (5):

[0136]

[0137] In equation (5), δ r is the actual compression of the sealing interface, δ ec is the critical deformation of the asperity in the elastic stage, δ pc is the critical deformation of the asperity in the elastic-plastic stage; k1, k2, k3 are surface material properties parameters, ξ1, ξ2, ξ3 are geometric parameters related to the largest asperity, α1, α2 are coefficients related to the hardness coefficient k v of the surface, g1 is an expression containing the compression of the sealing interface δ.

[0138] The expressions of g1, δ ec and δ pc are equations (6) and (7) respectively:

[0139]

[0140]

[0141] In equations (6) and (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 asperity, R=l D / π 2 G D-1 . The expressions of α1, α2, k1, k2, k3, ξ1, ξ2, ξ3 are equations (8), (9) and (10) respectively:

[0142]

[0143]

[0144]

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

[0146] According to the condition of no percolation contact interface, the compression amount when not considering the interaction of microconvexes and the deformation of the base is obtained.

[0147] The actual compression of the sealing interface is obtained by using the trial method. For example, it is assumed that δ r <δ ec The obtained compression δ is substituted into the δ a2 of the elastic stage to obtain δ r . If δ r <δ ec , it represents that the assumption is correct, otherwise, it represents that the assumption is incorrect, then it is needed to assume δ ec ≤δ r ≤δ pc or δ pc <δ r for further calculation.

[0148] S4, determining the contact specific pressure required by the sealing interface, determining the contact specific pressure required by the sealing interface:

[0149] According to the obtained actual compression of the sealing interface, the maximum deformation area of the microconvex is obtained by using formula (11):

[0150]

[0151] In formula (11), a max is the maximum deformation area of the microconvex.

[0152] According to the obtained maximum deformation area of the microconvex, it is judged that the deformation stage of the microconvex of the sealing interface, and specifically formula (12) and formula (13) are used:

[0153]

[0154]

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

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

[0157] When the micro-convex body at the sealing interface is in the elastic deformation stage, the contact pressure solving formula of the sealing interface is formula (14), formula (15) and formula (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-convex body in the elastic stage, and n(a) is the contact area distribution function of the micro-convex body.

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

[0163]

[0164]

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

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

[0167]

[0168]

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

[0170] When the micro-convex body at the sealing interface is in the complete plastic deformation stage, the contact pressure solving formula 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 For the fully plastic deformation stage, the contact load expression of the micro-convex body.

[0174] S5, determining the set pressure value of the fluid pressure in the pressure cavity:

[0175] According to the calculated contact specific pressure, the fluid pressure in the double-layer corrugated pipe is calculated, specifically using formula (23):

[0176]

[0177] In formula (23), p b is the pressure of the fluid in the pressure cavity, A c is the nominal contact area formed when the convex lower ring and the flat upper ring are in sealing contact, A b is the cross-sectional area of the pressure cavity, A b =(φ2 2 -φ1 2 )π / 4, φ1 is the outer diameter of the welding position of the inner corrugated pipe and the flat metal ring seat, and φ2 is the inner diameter of the welding position of the outer corrugated pipe and the flat metal ring seat. The specific positions of φ1 and φ2 are described in Figure 4 . Specific embodiments:

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

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

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

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

[0183] The calculation of the cross-sectional area A b of the pressure cavity and the calculation of the nominal contact area A c formed when the convex lower ring and the flat upper ring are in sealing contact. The nominal contact area A c is the area of the end face of the protrusion 53 facing the flat upper ring 56. The relevant data are listed in Table 2, in which the protrusion end face refers to the end face of the protrusion 53 facing the flat upper ring 56.

[0184] Table 2

[0185] [phi]1 / m 0.21 [phi]2 / m 0.27 Inner diameter of the protrusion end face / m 0.23 Outer diameter of the protrusion end face / m 0.25

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

[0187] According to the non-percolation interface condition, the sealing interface compression when the micro-asperity interaction and base deformation are not considered should be greater than 4.5 x 10 -7 m. The critical deformation of the micro-asperity elastic stage is 1.32 x 10 -7 m, and the critical deformation of the elastic-plastic stage is 1.45 x 10 -5 m. According to the trial method, the actual compression of the sealing interface should be greater than 1.46 x 10 -7 m.

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

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

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, is characterized in that: It includes a sealing pair, a bellows assembly and a fluid pressure charging device. The sealing pair includes a flat upper ring and a convex lower ring sleeved on the main shaft of the nuclear main pump, wherein the flat upper ring is sealingly fixed to the main shaft, the convex lower ring is located on the side of the flat upper ring facing the impeller, and the convex lower ring is composed of a convex soft ring and a flat metal ring seat connected together, wherein the convex soft ring is located on the side of the flat metal ring seat facing the flat 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 sleeved together coaxially, and the inner bellows and the outer bellows are both sleeved on the main shaft; Both ends of the inner bellows and the outer bellows are sealed and welded to the flat 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 convex lower ring and the bottom plate forms a pressure chamber. The fluid charging device includes a pressurizer and a storage tank. The inlet of the pressurizer is connected to the storage tank, and 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 extend, pushing the convex lower ring to move toward the planar upper ring and sealingly pressing against the planar upper ring. When the fluid 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 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 planar 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 flat ring is greater than that 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, and 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 flat upper ring is made of a hard material that is resistant to corrosion, oxidation, high temperature and high pressure, and radiation, and the convex soft ring is made of a soft material that is resistant to corrosion, oxidation, high temperature and high pressure, and radiation.

6. The intrinsically safe parking seal according to claim 1, characterized in that: The sealing box includes a cylindrical body extending along the axial direction of the main shaft and a bottom plate provided at one end of the cylindrical body facing the impeller. A fluid channel is provided on the bottom plate. One end of the fluid channel communicates with the pressure chamber, and the other end of the fluid channel extends outwardly through the outer peripheral surface of the sealing box. The outlet of the inflator is connected to the fluid channel.

7. The intrinsically safe parking seal according to claim 1, characterized in that: The system 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 an 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 based on the comparison result to coordinate the work of the valve adjustment unit and the inflator control unit; A pressure detection unit is used to detect the pressure in the pressure chamber and transmit 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 the 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. Calculate the fractal parameters and elastic modulus of the equivalent rough surface as well as the maximum asperity height and initial porosity; S3. Determine the compression required for the sealing interface based on the no-percolation contact interface condition; S4. Determine the contact pressure required for the sealing interface; S5. Determine a set pressure value of the fluid pressure in the pressure chamber.

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