RU2296380C1 - Device for securing pressurized-water reactor core - Google Patents

Abstract

FIELD: pressurized-water reactor equipment.

SUBSTANCE: proposed device for securing pressurized-water reactor core with coolant flowing over it has supporting cylinder and flexible member. Supporting cylinder is mounted on pressurized tank flange. Flexible member has a number of adjacent circular segments disposed between and engageable with supporting cylinder flange and pressurized tank cover flange. Each circular segment of flexible member has segmental supporting plate. The latter mounts hold-down devices secured thereon by means of locking devices. Each hold-down device has supporting sleeve accommodating working element of precompressed thermally expanded graphite which is locked therein by means of locking device, as well as hold-down bushing. The latter is in contact with working element or with locking device.

EFFECT: reduced vibration of reactor core when changed over to fuel load incorporating zirconium-can fuel assemblies.

7 cl, 10 dwg

Description

Technical field

The invention relates to devices for fixing the internal equipment of a nuclear reactor, and in particular to devices for fixing the core installed in a reactor with water under pressure and washed by a cooling coolant.

State of the art

The device / 1 / is known (Drawing 1135.01.04.000. Mine with a screen. Izhora plant. 1972). for fixing the core containing a support cylinder mounted on a flange in a vessel under pressure of a nuclear reactor, an elastic element comprising a series of adjacent annular segments located between the flange of the support cylinder and the flange of the pressure vessel lid. The annular segments of the elastic element are made of pipes. Compression of the elastic element is carried out by the pressure vessel cover when sealing the main connector of the pressure vessel. This creates a clamping force on the flange of the support cylinder, which, along with the force from the spring blocks of the fuel assemblies pressed by the pressure cylinder, and the force of the weight of the support cylinder with fuel loading, presses the support cylinder against the flange of the pressure vessel and prevents it from floating and vibration when exposed pressure drop of the coolant circulating in the reactor.

A disadvantage of the known device is that when switching to reactor loading with fuel assemblies with a zirconium alloy frame instead of fuel assemblies with a stainless steel frame, there is a significant reduction in the force created by the pressure cylinder when the springs are compressed in the heads of the fuel assemblies, since when the operating temperature is reached the heat carrier, the zirconium frame of the fuel assembly expands 12-15 mm less than the corresponding channel formed by the internals the joints made of 08Kh18N10T stainless steel (the elongation value was taken for the VVER-1000 reactor with a fuel part length of 3.5 m).

With a decrease in the clamping force from the spring blocks of the fuel assemblies, the pressure of the support cylinder against the pressure vessel flange and the pressure of the pressure cylinder against the pressure vessel cover decrease, therefore, it becomes necessary to compensate for the decrease in the pressure force of the support cylinder against the pressure vessel flange by increasing the pressure from elastic element. Otherwise, the inner shell devices will come off the supports, which will lead to vibration of both themselves and the fuel assemblies and regulatory bodies, that is, the reliability and safety of the reactor will be significantly reduced.

The weakening of the pressing of the internal devices to the supports can also occur due to relaxation of stresses in the springs of the heads of the fuel assemblies and the known elastic element under the action of high temperature and radiation.

Under conditions of limited space allocated to the placement of an elastic element in a nuclear reactor, an increase in its pressing force (bearing capacity) can be achieved, for example, by increasing the pipe wall thickness of the toroidal ring segment. In this case, simultaneously with an increase in the linear load on the pipe, its elastic deformation (both relative and absolute) decreases, and the relaxation resistance of such pipes decreases.

It is also known a device / 2 / (RF Patent No. 2061263) for fixing the core containing a support cylinder mounted on a flange in a vessel under pressure of a nuclear reactor, an elastic element comprising a series of adjacent annular segments located between the flanges of the support and pressure cylinders and pressed by the lid of the pressure vessel. The annular segments of the elastic element are made in the form of a helical coil spring on which cylindrical rings are tightened. Compression of the elastic element is carried out by sealing the main connector of the pressure vessel. This creates a clamping force on the flange of the support cylinder, which, along with the force from the spring blocks of the fuel assemblies pressed by the pressure cylinder, and the force of the weight of the support cylinder with fuel loading, presses the support cylinder against the flange of the pressure vessel and prevents it from floating and vibration when exposed pressure drop of the coolant circulating in the reactor. A pressing force is also created on the flange of the pressure cylinder, which, along with the force from the spring blocks of the fuel assemblies and the buoyancy force of the pressure cylinder from the pressure drop during circulation of the coolant in the reactor, presses the pressure cylinder against the flange of the pressure vessel cap.

The known device / 2 / in comparison with the known device / 1 / can provide a more significant linear load and elastic deformation, since the elasticity of the device / 2 / is summed from the elasticity of the cylindrical rings and the elasticity of the coil spring made of a stronger spring compared to / 1 / stainless steel. However, under conditions of transition to loading the reactor with fuel assemblies with a zirconium alloy frame instead of stainless steel fuel assemblies, relaxation of the springs of the fuel assemblies and components of the elastic element, as well as in conditions of limited space allocated to the placement of the elastic element in the nuclear reactor, this increase downforce may not be enough.

Similarly to / 1 / in the device / 2 /, with an increase in the diameter of the spring wire, at the same time as the linear load on the spring increases, its elastic deformation (both relative and absolute) decreases, as well as the relaxation resistance of the spring.

Both known devices / 1, 2 / during initial transverse compression (when sealing the main connector of the reactor) are deformed plastically. With an increase in initial compression, the plastic deformation of these devices increases, and the values of elastic deformation change slightly, which, in combination with small values of residual elastic deformation, is a disadvantage of these known devices.

It should be noted that the main criterion for the operability of the elastic element in the known devices / 1 / and / 2 / is the sufficient force on it (sufficient bearing capacity), which ensures guaranteed pressing of the support cylinder to the pressure vessel flange. The measurable criterion for the operability of the elastic element is the minimum allowable residual elastic deformation corresponding to the minimum allowable residual force on it, which is measured in the cold state of the reactor. That is, the necessary conditions for the operability of the elastic element are both a sufficient residual linear load on the pipe / 1 / or spring / 2 /, and a sufficient residual elastic deformation, which could be measured with a certain accuracy on the reactor after its cooling and dismantling of the pressure vessel cover .

Also known is a device / 3 / (RF Patent No. 2124237) for fixing the core, different from / 1 / and / 2 / in that each of the annular segments of the elastic element is made in the form of a multilayer package of plates supported uniformly around the perimeter of the segment from the bottom and top and the places of the lower and upper bearing are offset in plan relative to each other by half a step. In this device, it was supposed to increase the bearing capacity of the elastic element by increasing the mass of the metal of its elastic components filling the cross section of the annular groove, and increasing the life of the elastic element by significantly reducing relaxation when loading it in the region of elastic deformations. The studies of single-span models of this device when modeling design linear loads and temperatures showed that the elastic deformation region of the models of this device is limited to 2 mm, that is, when the total deformation is more than 2 mm, the device is subject to plastic deformation. For the reactor, the total deformations of the elastic element less than 2 mm are insufficient, since taking into account the tolerances on the axial dimensions of the elements of the VVER-1000 reactor, the maximum difference in the total deformations of the elastic element is 1 mm. The relative relaxation of the tested models of this device has almost the same values in comparison with the tested models of the device / 1 /. An analysis of the influence of the loading scheme for the single-span tested model of the device and the multi-span device (as stated in / 3 /) showed that the stiffness of the multi-span device is four times higher than the stiffness of the single-span model of the device, therefore, with the same linear load, the elastic deformation of the multi-span device will decrease by four times. That is, this device may not provide the minimum permissible residual elastic deformation required by the project.

In the description / 3 / two layouts of an elastic element in a nuclear reactor are considered:

Scheme 1 - an elastic element is mounted on the flange of the support cylinder and interacts with the flange of the support cylinder and the flange of the pressure cylinder;

Scheme 2 - the elastic element is mounted on the flange of the pressure cylinder and interacts with the flange of the pressure cylinder and the flange of the pressure vessel cover.

The first scheme of fixing the elastic element was also considered in / 2 / and its advantage is the ability to measure the residual elastic deformation of the elastic element in the cold state without unloading the fuel assemblies from the support cylinder.

A feature of the second elastic element fixing scheme is that the force from the spring blocks of the fuel assemblies pressed by the pressure cylinder presses the pressure cylinder against the pressure vessel lid and does not affect the pressure of the support cylinder against the pressure vessel flange.

The advantage of the second scheme is more convenient access to the elastic element during its installation and dismantling. However, it is significantly difficult to measure the residual elastic deformation of the elastic element without unloading the fuel assemblies, since the residual force on their spring blocks can raise the pressure cylinder together with the elastic element relative to the flange of the main connector of the pressure vessel.

In addition, in both of these schemes / 3 /, the temperature deformation of the elastic element is 1.5 times greater than in the fastening scheme of the elastic element / 1 /, that is, after the temperature loading of the elastic element, the residual linear load and residual elastic deformation decrease in these schemes in to a greater extent, since the stiffness of the elastic element during elastic unloading is significantly higher than under elastic-plastic loading.

In / 1 / the elastic element is mounted on the flange of the support cylinder and interacts with the flange of the support cylinder and the flange of the pressure vessel cap. In this fixing option, the elastic element does not press the pressure cylinder against the flange of the pressure vessel cover (the pressure cylinder is pressed against the pressure vessel flange of the vessel cover only due to the force from the spring blocks of the fuel assemblies), which is a drawback of this fixing scheme.

The closest technical solution of the known is / 3 /.

Disclosure of invention

The aim of the invention is to increase the reliability and safety of a nuclear reactor.

The objective of the invention is to increase the bearing capacity, the field of elastic deformation and the damping properties of the elastic element.

EFFECT: reduced vibration of internal shell devices and the core of a nuclear reactor when switching to a fuel charge, which includes fuel assemblies with a zirconium frame.

The proposed device for fixing the core of a nuclear reactor with water under pressure contains a support cylinder mounted on a flange in a pressure vessel, an elastic element comprising a series of adjacent annular segments located between the flange of the support cylinder and the flange of the pressure vessel lid and interacting with them .

What is new is that each of the annular segments of the elastic element contains a segment support plate on which pressure devices are placed and fixed using fixing devices, each of which contains a support cup with a working element made of pre-pressed heat-expanded and placed in it with a locking device. graphite, and a pressure sleeve in contact with the working element or locking device.

A locking device designed to prevent the penetration of thermally expanded graphite into the cylindrical gap between the outer surface of the pressure sleeve and the inner surface of the support cup can be made in the following variants:

option 1 - The locking device is made in the form of a ring having a thin-walled cylindrical collar around the periphery in contact with the outer diameter with the inner cylindrical surface of the support cup and with the inner diameter of the working element of thermally expanded graphite, while the locking device is located between the pressure sleeve and the working element of thermally expanded graphite;

option 2 - The locking device contains two identical locking split rings in contact with each other on the end surfaces and in outer diameters in contact with the inner cylindrical surface of the support cup, while the upper locking ring is in contact with the pressure sleeve, and the ring cuts are in different vertical planes;

option 3 - The locking device contains three locking rings: two rings of option 2 and a third split ring of smaller diameter, which in outer diameter is in contact with two rings of option 2 and on the upper end with a pressure sleeve, while the height of the third ring is greater than the height of the rings according to option 2, and the cuts of all three rings are in different vertical planes.

Locking devices are designed to fix and fix the clamping devices on the segment plate. Each locking device contains two clamps mounted on a segment plate having cylindrical protrusions extending into reciprocal stepped bayonet grooves made on the outer side surface of the cup of the pressing device.

These fixing devices can reduce the time of mounting and dismounting of clamping devices on segment plates and, as a result, reduce the radiation dose of personnel during these operations.

In order to prevent slipping of the cup of the pressing device relative to the segment plate, a cylindrical protrusion is made at the lower end of the support cup, which extends into the mating coaxial hole made in the segment plate. At the same time, breakage (shaping) of the clips is prevented. Sliding the cup of the clamping device relative to the segment plate during the implementation of the first scheme for securing the elastic element would be possible due to different linear expansion coefficients of the materials of the supporting cylinder on which the segment plates are fixed and the pressure vessel covers, and when implementing the second scheme for securing the elastic element, due to different linear expansion coefficients of the materials of the pressure cylinder, on the flange of which segment plates are fixed, and the covers of the pressure vessel eat.

In order to prevent the pressure sleeve from escaping from the support cup of the pressure device when mounting and removing this device on the segment plate or when lifting the pressure vessel cover, at least one flange is made on the pressure sleeve of the pressure device and at least one is fixed on the upper end of the support glass reciprocal locking strip.

A brief description of the drawings.

Figure 1 shows a diagram of a nuclear reactor, a longitudinal section.

Figure 2 shows the node And figure 1 is a diagram of the fastening of the elastic element on the flange of the pressure cylinder, in which the elastic element is in contact with the flange of the pressure cylinder and the flange of the pressure vessel.

Figure 3 shows the node And figure 1 is a diagram of the fastening of the elastic element on the flange of the supporting cylinder, in which the elastic element is in contact with the flanges of the supporting and pressure cylinders.

Figure 4 shows a section bB in figure 2.

Figure 5 shows the node In figure 2 in an enlarged scale.

Figure 6 shows a view of figure 5.

In Fig.7 shows a section DD in Fig.5.

On Fig shows a view of E in figure 5.

In Fig.9 shows the node W in Fig.5 - options 1-3 of the locking device.

Figure 10 shows a perspective view of the fixing circuit of the clamping device.

The reactor with a device for securing the support cylinder with an active zone is a pressure vessel 1 sealed by a cover 2. In the vessel 1, a support cylinder 4 with an active zone containing fuel assemblies 5 is installed on the flange 3. According to figure 2 (scheme 2) between the end face a cover 2 and a flange 6 of the pressure cylinder interacting with the flange 3 of the support cylinder, an elastic element is installed comprising a series of segments 7 (FIG. 4) mounted on the flange 6. According to FIG. 3 (diagram 1) between the flange 3 of the support cylinder and the flange 6 of the pressure cylinder operating with the end face of the cover 2, an elastic element is installed containing a number of segments 7, mounted on the flange 3 of the supporting cylinder. Each of the segments 7 contains a support segment plate 8, on which the pressing devices are placed and fixed, each of which (Fig. 5) contains a support cup 9, in which the working element 11 of pre-pressed thermally expanded graphite is placed and locked using the locking device 10, and a push sleeve 12 in contact with the working element or the locking device. The locking device designed to fix and fix the clamping device on the segment plate contains two locks 13 (Fig. 7), mounted on the segment plate 8, having cylindrical protrusions 14 that extend into the mating step bayonet grooves 15, made on the outer side surface of the support cup 9 clamping device (6, 7). A cylindrical protrusion 16 (Fig. 5, 7) is made at the lower end of the support cup, which enters the mating coaxial hole 17 made in the segment plate. At least one flange 18 is made on the pressing sleeve 12 of the pressing device (Figs. 7, 8), and at least one reciprocal locking strip 19 is fixed on the upper end of the support cup.

The vessel 1 (Fig. 1) is equipped with an inlet pipe 20 and an outlet pipe 21 and forms with the wall of the reference cylinder 4 a lowering channel 22 of the coolant circulation circuit in the reactor.

The implementation of the invention

The device operates as follows.

Cold coolant enters the nozzle 20, passing the lower channel 22 through the holes in the bottom of the supporting cylinder 4 enters the active zone, removes heat from the fuel assemblies 5 and the heated leaves through the nozzle 21 from the reactor. When the coolant flows through the reactor, its pressure decreases, and the pressure difference at the inlet and outlet is the force that pushes the support cylinder 4 up if the weight of the support cylinder with an active zone is less than the buoyancy force. The pressing of the support cylinder to the support is a necessary condition for holding the support cylinder and fuel assemblies from vibrational movements (causing wear and tear) that may occur under the influence of a flowing coolant. When sealing the main connector, the cover 2 compresses the working elements 11 of the clamping devices of the elastic element 7, which creates the necessary force to press the flange of the supporting cylinder to the support. Since the working elements of the clamping devices are made of pre-pressed and locked thermally expanded graphite with high elastic properties and bearing capacity, several clamping devices are able to withstand the load required by the project, while the residual elastic deformation will be 5-10 times higher than in the prototypes considered / 1-3 /. Studies of the models of clamping devices showed that with sufficient residual elastic deformation of the clamping devices (at least 2 mm), the required load-bearing capacity of the elastic element is achieved by their number (for the VVER-1000 reactor, no more than 24 pieces). That is, for the proposed device of the elastic element, the performance criteria (the bearing capacity of the elastic element and its residual elastic deformation) do not contradict each other (with an increase in the bearing capacity of the elastic element, its residual elastic deformation does not decrease, as in / 1-3 /). In addition, the proposed design of the clamping devices has good damping properties due to internal friction in thermally expanded graphite and the friction of the locking elements on the inner cylindrical surface of the support cup in the region of elastic deformation of the clamping device.

Thus, the proposed design of the elastic element makes it possible to increase the pressing force of the support cylinder to the required value without increasing its dimensions, to increase the elastic and damping properties, while increasing its service life under conditions of prolonged thermal cyclic loading.

Information sources

1. Drawing 1135.01.04.000. Mine with a screen. Izhora plant, 1972.

2. Patent of the Russian Federation No. 2061263.

3. Patent of the Russian Federation No. 2124237.

Claims (7)

1. Device for fixing the core of a nuclear reactor with water under pressure, comprising a support cylinder mounted on a flange in a pressure vessel, an elastic element including a series of adjacent annular segments located between the support cylinder flange and the pressure vessel lid flange and interacting with them, characterized in that each of the annular segments of the elastic element comprises a segment support plate, on which the pressing devices are placed and fixed using fixing devices, DOE of which comprises a supporting glass placed into it and locked with a locking device the operation member from a pre-compressed expanded graphite and a pressure sleeve, in contact with the operation member or a locking device. 2. The device for fixing the active zone according to claim 1, characterized in that the locking device is made in the form of a ring having a thin-walled cylindrical collar around the periphery in contact with the inner diameter of the support cup and the inner diameter of the working element of thermally expanded graphite while the locking device is located between the pressure sleeve and the working element of thermally expanded graphite. 3. The device for fixing the active zone according to claim 1, characterized in that the locking device contains two identical locking split rings in contact with each other along the end surfaces and in external diameters in contact with the inner cylindrical surface of the support cup, while the upper locking ring is in contact with push sleeve, and the cuts of the rings are in different vertical planes. 4. The device for fixing the core according to claim 1, characterized in that each fixing device contains two clamps mounted on a segment plate having cylindrical protrusions extending into mating stepped bayonet grooves made on the outer side surface of the support cup of the pressing device. 5. The device for fixing the active zone according to claim 1, characterized in that a cylindrical protrusion is made at the lower end of the support cup, which extends into the mating coaxial hole made in the segment plate. 6. The device for fixing the core according to claim 1, characterized in that at least one flange is made on the pressure sleeve of the pressure device, and at least one reciprocal locking plate is fixed on the upper end of the support cup. 7. A device for fixing the active zone according to claim 3, characterized in that the locking device comprises a third split ring of smaller diameter, which in outer diameter contacts two rings specified in claim 3 and at the upper end with a pressure sleeve, the height the third ring is greater than the height of the rings according to claim 3, and the cuts of all three rings are in different vertical planes.

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