RU2124237C1 - Core fixing device for pressurized-water reactor - Google Patents

Abstract

FIELD: fixation of equipment in pressurized-water vessel of reactor incorporating flexible member segments. SUBSTANCE: each segment of flexible member is made in the form of multilayer stack of plates uniformly supported on segment perimeter at bottom and on top. Top and bottom supporting points are spaced apart through half-pitch. EFFECT: improved reliability and safety of nuclear reactor. 7 dwg

Description

 The invention relates to devices for securing the internal equipment of a nuclear reactor, and in particular to devices for securing an active zone installed in a reactor with pressurized water and washed by a coolant.

 A device / 1 / for fixing the core, comprising 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 interacting with the flange of the support cylinder and the lid of the pressure vessel. The annular segments of the elastic element are made of pipes placed between the flange of the support cylinder and the flange of the pressure vessel lid. 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 supporting 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 supporting cylinder with fuel loading, presses the supporting cylinder against the flange of the pressure vessel and prevents it from floating and vibration when exposed to the 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 compressing the springs 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 by means of stainless steel 08Kh18N10T (the elongation was taken for the VVER-1000 reactor with a fuel part length of 3.5 m).

 When decreasing the pressing force (the pressing force of the support and pressure cylinders) from the spring blocks of the fuel assemblies, it becomes necessary to compensate for this decrease by increasing the force from the elastic element. Otherwise, the internal housing devices will come off the supports, which will lead to vibration of both themselves and the fuel assemblies and regulatory bodies, i.e. 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 the relaxation of the springs of the heads of the fuel assemblies and the known elastic element under the action of stresses, high temperature and radiation.

 In conditions of limited space allocated to the placement of an elastic element in a nuclear reactor, an increase in clamping force 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, the value of elastic deformation (both relative and absolute) decreases, and the relaxation resistance of such pipes decreases, which necessitates an early (before the end of the fuel campaign) replacement of the elastic element.

 If we follow the path of further increasing the initial compression (when sealing the main connector of the reactor) of the pipe of the annular segment of a known elastic element, then in this case the plastic deformation of the pipe increases, and the value of the residual elastic deformation practically remains unchanged. The loading of pipes by transverse forces until plastic deformation of the pipe walls is achieved is one of the main disadvantages of the known device / 1 /, since the cyclic and relaxation resistance of such pipes is very low, which necessitates frequent periodic replacement of them.

 It is also known a device / 2 / 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 interacting with the flange of the support cylinder and the lid of the pressure vessel. The elastic element includes a number of adjacent annular segments, 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 supporting 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 supporting cylinder with fuel loading, presses the supporting cylinder against the flange of the pressure vessel and prevents it from floating and vibration when exposed to the pressure drop of the coolant circulating in the reactor.

 The known device / 2 / in comparison with the known device / 1 / can withstand a more significant linear load, since its elasticity is summed up from the elasticity of the cylindrical rings and the elasticity of the coil spring. However, under conditions of transition to loading the reactor with fuel assemblies with a zirconium alloy framework instead of stainless steel 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.

 Both known devices / 1, 2 / have small coefficients of the useful use of the cross section of the annular groove, since the filling of the cross section of the annular groove with the metal of the components of the known devices occurs only along the outer perimeter, and substantially larger cross sections of the annular grooves for accommodating the elastic element in the reactor can only be realized by increasing the size of pressure vessels in the region of the main connector, which reduces the reliability of the vessel.

 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 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 field of elastic deformations.

 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 the 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 .

 New is that each of the ring segments is made in the form of a multilayer package of plates supported uniformly along the perimeter of the segment from the bottom and from the top, and the places of the lower and upper abutment are offset halfway from each other in relation to each other.

 In FIG. 1 shows a diagram of a nuclear reactor, a hem section (the elastic element is mounted on the flange of the pressure cylinder).

 In FIG. 2 shows a diagram of a nuclear reactor, a hem section (an elastic element is mounted on a flange of a support cylinder).

 In FIG. 3 shows a section AA in FIG. one.

 In FIG. 4 shows a section BB in FIG. 1 (when the pack of plates of the elastic element is supported on the flanges of the cover and pressure cylinder through the support plates).

 In FIG. 5 shows a section BB in FIG. 1 (when the pack of plates of the elastic element is supported directly on the flanges of the cap and pressure cylinder).

 In FIG. 6 and 7 show sections BB in FIG. 4 and in FIG. 5 respectively.

 A reactor with a device for securing a 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 mounted on a flange 3. According to FIG. 1 (option 1) between the end face of the cover 2 and the flange 6 of the pressure cylinder interacting with the flange 3 of the support cylinder, an elastic element is installed containing a series of segments 7, mounted on the flange 6. According to FIG. 2 (option 2) between the flange 3 of the support cylinder and the flange 6 of the pressure cylinder interacting with the end face of the cover 2, an elastic element is installed containing a series of segments 7 mounted on the flange 3. Each of the segments 7 contains a multilayer package of plates supported uniformly around the perimeter of the segment bottom and top, and the places of the lower 8 and upper 9 bearings are offset in plan relative to each other by half a step. The vessel 1 is equipped with an inlet pipe 10 and an outlet pipe 11 and forms with the wall of the supporting cylinder 4 a lowering channel 12 of the coolant circulation circuit in the reactor.

 The device operates as follows.

 Cold coolant enters the nozzle 10, passing the lowering channel 12 through the holes in the bottom of the supporting cylinder, enters the active zone, removes heat from the fuel assemblies 5 and the heated leaves through the nozzle 11 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 up if the weight of the support cylinder with the core is less than the buoyancy force. Pressing the support cylinder to the support is a necessary condition for holding the support cylinder and fuel assemblies from vibration movements (causing wear and tear) that can occur under the influence of a flowing coolant. When sealing the main connector, the cover 2 compresses the multilayer package of plates of the elastic element 7, which creates the necessary force to press the flange of the support cylinder to the support.

 Since the plates of segments 7 are made of high-strength spring material (for example, from heat-resistant corrosion-resistant steel 14X17H2), and the package of such plates is in the same dimensions of the allotted annular gap as the pipe in the prototype (for example, a pipe made of steel ОХ18Н10Т mastered in industrial production) , has a significantly higher fill factor of the allotted gap for the metal, the proposed elastic element can withstand a much more significant linear load than the prototype (4-5 times), while the working life of the elastic lementa increases by an order.

When determining the structural characteristics of a package of plates of an elastic element loaded as a multilayer and multi-span beam, the following values should be taken as the initial criteria:
- stresses in each layer of the plate should not be higher than allowable in terms of yield strength so that it is possible to operate an elastic element taking into account long-term thermocyclic loading during the calculated service life;
- the total linear load of the segments should provide the necessary retention force of the internal devices with a given safety factor for ascent during the estimated life of the work.

 Such structural characteristics of the elastic element as the distance between the points of support L, the deformation of the plates f and the number of plates in the package are interdependent quantities and should be determined by a specific calculation.

 Thus, the proposed design of the elastic element makes it possible to increase the pressing force of the support cylinder to the required size without increasing its dimensions, and to increase its service life under conditions of prolonged thermocyclic loading.

Sources of information:
1. Drawing 1135.01.04.000, Mine with a screen. Izhora plant, 1972;
2. Patent of the Russian Federation N 2061263.

Claims (1)

 A 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 flange of the support cylinder and the flange of the pressure vessel lid and interacting with them characterized in that each of the annular segments is made in the form of a multilayer package of plates supported uniformly along the perimeter of the segment from the bottom and from the top, and the places of the lower and upper bearing s in terms relative to each other by half a pitch.

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