Group pipe penetration of steel containment shell of low-power reactor

Abstract

FIELD: nuclear power engineering.SUBSTANCE: invention relates to a group pipe penetration of a steel protective shell of a low-power reactor and can be used in nuclear power engineering. The technical result is to increase the strength of the steel protective shell of a low-power nuclear power plant and to ensure the localization of radioactive fission products inside the steel protective shell at pressures up to 1 MPa and temperatures up to 350°C with different states of the reactor installation under seismic and external influences. The passage comprises a cylinder, an adapter, a flange, sleeves connected by end surfaces, wherein the inner front surface of the cylinder is made cylindrical, the inner front surface of the adapter is made in the form of two truncated cones intersecting at an angleα from 90 to 180°. Moreover, the inner face surface of the flange has an incomplete elliptical shape, and the outer face surface of the flange has a conical shape, while the adapter and the flange are connected in such a way that they form a first cavity and a second cavity, which are intended to accommodate the pipes. The flange and sleeve are connected in such a way that they form a third cavity and a fourth cavity, intended to accommodate the pipes.EFFECT: increased strength of the steel protective shell and localization of radioactive fission products inside the steel protective shell.4 cl, 7 dwg

Description

[0001] The invention relates to the field of nuclear energy, in particular to systems ensuring the safety of nuclear power plants (NPPs) with low-power nuclear reactors, and can be used during nuclear reactor operation in the following modes: during normal operation, during abnormal operation, during design basis accidents, during beyond-design basis accidents without destruction of the nuclear reactor core, and during severe beyond-design basis accidents leading to destruction of the nuclear reactor core. In all these modes, the group pipe penetration, acting as a hermetic barrier between the steel protective shell and the NPP premises, ensures the localization of solid, liquid, and gaseous radioactive fission products within the steel protective shell for the time required to implement emergency response measures at the NPP.During normal operation, the group pipe penetration and the steel containment shell ensure the maintenance of a slight vacuum inside the steel containment shell in which the reactor installation is located, together preventing the ingress of low-level radioactive condensate, aerosols, gases and vapors into the SNPP premises.

[0002] The greatest radiation hazard is posed by design basis accidents associated with the destruction of the pipelines of the first or second circuit of the reactor plant, beyond design basis accidents without destruction of the core associated with non-design basis multiple failures of equipment, as well as severe beyond design basis accidents with meltdown of the core, which can occur with multiple failures of the core cooling systems.

[0003] In such accidents, solid, liquid and gaseous radioactive fission products are released from the reactor facility into the interior of the SNPP and then beyond the SNPP into the environment.

[0004] To prevent this phenomenon and minimize the spread of radioactive fission products throughout the SNPP premises, it is necessary to localize solid, liquid, and gaseous radioactive fission products in a concentrated volume located around the small nuclear reactor until the completion of emergency response measures. This ensures the containment, gradual cooling, and condensation of radioactive fission products in the gas and vapor phases, as aerosols, and in liquid and solid form. This function is performed by grouped pipe penetrations in conjunction with the steel containment shell of the small nuclear reactor, preventing (minimizing) the entry of radioactive fission products into the SNPP premises, thereby protecting the population and the environment from radiation exposure during accidents involving the small nuclear reactor.

[0005] The primary factor ensuring the operational reliability of a small-power reactor is the strength and stability of the steel containment pipe penetrations to resist seismic and external impacts during normal operation, operational disturbances, design-basis accidents, beyond-design-basis accidents without core destruction, and severe beyond-design-basis accidents. In all these situations, loss of strength and stability of the steel containment pipe penetrations can lead to a breach of the containment seal and the release of radioactive fission products into the internal volumes of the SNPP building structures and the environment.

[0006] The second factor ensuring the operational reliability of a small-power reactor is the strength and stability of the steel containment pipe penetration group to withstand internal pressures of up to 1 MPa and temperatures of up to 350°C, during design-basis accidents, beyond-design-basis accidents without destruction of the nuclear reactor core, and during severe beyond-design-basis accidents. These parameters are necessary to reduce and seal leaks in the reactor facility's primary and secondary circuit pipelines located within the steel containment (within the accident containment zone). In all these processes, loss of strength and stability of the pipe penetration group can lead to a breach of the steel containment seal and the release of radioactive fission products into the internal volumes of the SNPP building structures and the environment.

[0007] A unit [1] for sealing a pipeline passage is known, comprising a shell secured in a protective shell, coaxially installed on the pipeline and rigidly connected to it by means of a transition flange made in the form of a shell that transitions into a truncated cone, the apex of which is directed towards the outlet of the installation end of the pipeline.

[0008] A disadvantage of this invention is the lack of compensatory capabilities of the penetration, associated with the rigid fixation of the truncated cone to the pipeline using a welded joint with a design that abuts the truncated cone to the shell without the use of compensatory mechanisms for reducing internal stresses in the welded joints and in the transition flange. This invention is not designed for use under conditions of continuous or periodic mechanical alternating (vibrational) loads applied to the pipeline, is not designed for use under conditions of large variable thermal loads associated with changes in the temperature of the medium in the pipeline, and is not designed for use under conditions of mechanical loads acting on the pipeline perpendicular to its axis.The specified loads lead to the destruction of the welded joint, which does not have compensatory capabilities due to the small area of ​​contact with the pipeline, and lead to the formation of cracks in the welded joint with the risk of destruction of the entire sealing unit and loss of tightness of the protective shell due to the lack of conditions for compensating for internal stresses.

[0009] A sealed penetration [2] is known, comprising two shells installed in inner and outer protective shells, in which a pipeline is coaxially installed. The gap between the shell and the pipeline is sealed by a transition flange.

[0010] A disadvantage of this invention is the lack of expansion joint capabilities due to the use of a welded transition flange, which does not ensure the tightness, strength, and density of the internal protective shell under constant or periodic mechanical alternating (vibrational) loads applied to the pipeline. It is not designed for use under conditions of high variable thermal loads associated with changes in the temperature of the medium in the pipeline, and is not designed for use under mechanical loads acting on the pipeline perpendicular to its axis. These loads lead to the destruction of the transition flange, which does not have expansion joint capabilities due to the small contact area with the pipeline. This leads to the destruction of the transition flange and to the loss of tightness of the protective shell due to the lack of conditions for compensating for internal stresses.

[0011] A known unit [3] for sealing a pipeline penetration comprises a cylindrical shell secured in a protective shell, coaxially mounted on the pipeline and rigidly connected to it by means of a flange formed in the form of an annular shell with a section in the form of a truncated cone directed inward of the annular shell. The truncated cone of the transition flange is formed with at least one annular section perpendicular to the pipeline axis, connecting it to the surface of the pipeline.

[0012] A disadvantage of the utility model is the lack of compensatory capabilities for penetration, associated with the rigid fixation of the truncated cone on the pipeline using an annular section installed perpendicular to the pipeline axis by means of a welded joint without the use of compensatory mechanisms for reducing internal stresses in the welded joint, in the annular shell, in the truncated cone section. This invention is not intended for use under conditions of constant or periodic mechanical alternating (vibrational) loads applied to the pipeline, is not intended for use under conditions of high variable thermal loads associated with changes in the temperature of the medium in the pipeline, and is not intended for use under conditions of mechanical loads acting on the pipeline perpendicular to its axis.The specified loads lead to the destruction of the welded joint, which does not have compensatory capabilities due to the small area of ​​contact with the pipeline, and lead to the formation of cracks in the welded joint with the risk of destruction of the entire sealing unit and loss of tightness of the protective shell due to the lack of conditions for compensating for internal stresses.

[0013] The technical result of the invention consists in increasing the strength of the steel protective shell of the SNPP and ensuring the localization of radioactive fission products inside the steel protective shell at pressures of up to 1 MPa and temperatures of up to 350°C (which is 2 times higher than the pressure and temperature of localization inside sealed shells for high-power reactors) under various states of the reactor installation under conditions of seismic and external impacts on the building structures of the SNPP.

[0014] The problem that the invention is aimed at solving is the creation of a design for a group pipe penetration of a steel protective shell of a low-power reactor that ensures compensation for internal stresses acting at pressures of up to 1 MPa and temperatures of up to 350°C.

[0015] The set tasks are solved due to the fact that the group pipe penetration (1) of the steel protective shell (2) of a low-power reactor, according to the invention, contains a cylinder (3), an adapter (4), a flange (5), sleeves (6), connected by end surfaces, wherein the inner front surface (3a) of the cylinder (3) is made cylindrical, the inner front surface (4a) of the adapter (4) is made in the form of two intersecting truncated cones (4b), which are intersected at an angle α from 90 to 180 degrees, the inner front surface (5a) of the flange (5) has an incomplete elliptical shape, and the outer front surface (5b) of the flange (5) has a conical shape, the adapter (4) and the flange (5) are connected in such a way that they form the first cavity (7) and the second cavity (8), which are intended to accommodate the pipes (9), the flange (5) and the sleeve (6) are connected in such a way that they form a third cavity (10) and a fourth cavity (11), intended for accommodating pipes (9).

[0016] One essential feature of the claimed invention is the presence of an internal front surface (4a) of the adapter (4), made in the form of two intersecting truncated cones (4b), which are intersected at an angle α from 90 to 180 degrees, which makes it possible to reduce the maximum stresses arising in the group pipe penetration (1) when exposed to loads from the steel protective shell (2) or when transferring loads to the steel protective shell (2) from the flange (5).

[0017] Another essential feature of the claimed invention is the presence of an internal front surface (5a) of the flange (5) having an incomplete elliptical shape, providing compensation for thermomechanical stresses acting on the flange (5) from the side of the adapter (4) or acting on the flange (5) from the side of several sleeves (6) having different-profile thermomechanical loads of their own from the side of the pipes (9), which makes it possible to ensure the redistribution and averaging of internal stresses.

[0018] Another essential feature of the claimed invention is the presence of an outer front surface (5b) of the flange (5), having a conical shape, providing compensation for thermomechanical stresses acting on the flange (5) from several sleeves (6), having different-profile thermomechanical loads of their own from the pipes (9) or being under the influence of alternating vibration loads.

[0019] Another essential feature of the claimed invention is the presence of a third cavity (10) and a fourth (radial) cavity (11), formed by the connection of the flange (5) and the sleeve (6), which ensure the installation of the pipes (9) in such a way that the forces influencing the mechanical and thermal changes in the shape of the pipes (9) are not transmitted directly to the flange (5), adapter (4) and cylinder (3), ensuring the transmission of loads only through the sleeves (6).

[0020] Another essential feature of the claimed invention is the presence of sleeves (6) connected by the first external coupling (6a) with the flange coupling (5b) of the flange (5), ensuring the transfer of thermomechanical loads from the pipes (9) to the flange (5), in which mechanical and thermal changes in the shape of the pipes (9) are damped by the toroidal internal surface (10a) of the third cavity (10), reducing the maximum stresses in the sleeves (6) and their external couplings (6a).

[0021] Additionally, in the group pipe penetration (1) of the steel protective shell (2) of the low-power reactor, according to the invention, on one side of the sleeve (6) a first external coupling (6a) is made, intended for connection with the flange coupling (5c) of the flange (5), as well as a second internal coupling (6b), intended for connection with the branch pipe (9), on the other side of the sleeve (6) a third end coupling (6c) is made, between the couplings (6a), (6b), (6c) a connecting section (6 d) with a conical surface (6d) is made, wherein the first external coupling (6a) and the second internal coupling (6b) of the sleeve (6) are made in such a way that they form a third cavity (10) with a toroidal inner surface (10a). The presence of couplings (6a), (6b), (6c) at the sleeve (6) allows for the redistribution and averaging of internal stresses of the group pipe passage (1).

[0022] Additionally, in the group pipe penetration (1) of the steel protective shell (2) of the low-power reactor, according to the invention, the fourth cavity (11), the first cavity (7), the second cavity (8) are made in such a way that their total volume exceeds the volume of the third cavities (10) on the side of the sleeves (6), which makes it possible to ensure uniform mixing of the gas medium in the fourth cavity (11), in the first cavity (7) and in the second cavity (8), ensuring a more uniform distribution of the heat flows acting on the flange (5), on the adapter (4) and on the cylinder (3) installed in the steel protective shell (2).

[0023] Additionally, in the group pipe penetration (1) of the steel protective shell (2) of the low-power reactor, according to the invention, the size in the radial direction of the fourth cavity (11) is larger than the size in the radial direction of the second cavity (8), which makes it possible to redistribute over a larger area the heat coming from the heated gas medium to the flange (5), thereby reducing the uneven heating of the flange (5) in the azimuthal and radial directions.

[0024] Figure 1 shows a steel protective shell (2) with group pipe penetrations (1), made in accordance with the claimed invention.

[0025] Fig. 2 shows a group pipe penetration (1) with a view from the inside of the steel protective shell (2).

[0026] Fig. 3 shows a group pipe penetration (1) with a view from the outside of the steel protective shell (2).

[0027] Fig. 4 shows a sectional view of a group pipe penetration (1) made in accordance with the claimed invention.

[0028] Fig. 5 shows a sectional view of a part of a group pipe penetration (1) made in accordance with the claimed invention.

[0029] Fig. 6 shows a sectional view of a part of a group pipe penetration (1) made in accordance with the claimed invention.

[0030] Fig. 7 shows a sectional view of a sleeve (6) made in accordance with the claimed invention.

[0031] The group pipe penetration (1) works as follows.

[0032] Mechanical and thermal loads from the steel protective shell (2) are transferred to the group pipe passage (1) through the cylinder (3), from which, through the adapter (4), the loads are transferred to the flange (5), along which they are redistributed through the sleeves (6) to the nozzles (9).

[0033] To reduce the maximum stresses arising in the group pipe penetration (1), when exposed to loads from the steel protective shell (2) or when transferring loads to the steel protective shell (2) from the flange (5), the adapter (4) has an internal front surface (4a) made in the form of two intersecting truncated cones (4b), which intersect at an angle α from 90 to 180 degrees.

[0034] Mechanical and thermal loads from the nozzles (9) are transferred to the steel protective shell (2) along the chain from the sleeves (6) to the flange (5), then through the adapter (4) to the cylinder (3) and from the cylinder (3) into the steel protective shell (2). Each element of the group pipe penetration (1) provides for a reduction in the maximum internal stresses, ensures the redistribution and averaging of internal stresses. This is achieved by increasing the interaction area during load transfer between the elements of the group pipe penetration (1) and by leveling out axial and radial unevennesses by using couplings (6a), (6b), (6c), using a conical surface (6d), truncated cones (4b) and using toroidal surfaces (5a), (10a), providing a consistent weakening of the maximum internal stresses in the group pipe penetration (1).

[0035] When exposed to excess pressure acting from inside the steel protective shell (2) on the group pipe penetration (1), namely on the cylinder (3), adapter (4), inner surfaces of the flange (5), inner surfaces of the sleeves (6) and the outer surface of the pipes (9), the tightness of the group pipe penetration (1) is ensured by the strength of the connection of the adapter (4) with the flange (5), the strength of the connection of the first outer union (6a) of the sleeve (6) with the flange union (5c) of the flange (5), the strength of the connection of the second inner union (6b) of the sleeve (6) with the pipe (9).

[0036] When exposed to thermal loads acting from inside the steel protective shell (2) on the group pipe penetration (1), the tightness of the group pipe penetration (1) is ensured by the strength and compensating capabilities of the sleeve (6) with the connecting section (6 g), with the conical surface (6d), with the toroidal inner surface (10a) of the third cavity (10), with the first outer coupling (6a) connected to the flange coupling (5c) of the flange (5); ensured by the second inner coupling (6b) of the sleeve (6) connected to the branch pipe (9); ensured by the third end coupling (6c) of the sleeve (6); ensured by the inner front surface (5a) of the flange (5), which has an incomplete elliptical shape, and the outer front surface (5b) of the flange (5), which has a conical shape; is provided by the inner front surface (4a) of the adapter (4), made in the form of two intersecting truncated cones (4b), which are intersected at an angle α from 90 to 180 degrees., which ensures a consistent weakening of the maximum internal stresses in the group pipe penetration (1).

[0037] When temperature disturbances occur, the steel protective shell (2) expands in the radial and axial directions. The group pipe penetration (1) moves axially together with the steel protective shell (2). Moreover, in the axial direction, the steel protective shell (2) experiences the greatest deformations with an increase in temperature, and the performed fastening of the group pipe penetration (1) in the steel protective shell (2) ensures the free movement of the group pipe penetration (1) under these conditions, without exerting additional mechanical impact on the steel protective shell (2).

[0038] When the temperature of the medium inside the pipes (9) changes simultaneously, the uneven thermomechanical effects from the sleeves (6) are transmitted through the couplings (6a), (6b), and the conical surface (6d) along the connecting section (6g) to the flange (5), which ensures the alignment and redistribution of the internal stresses on the flange (5), which transfers the average loads from the sleeves (6) further to the adapter (4), from which these loads are transmitted through the cylinder (3) to the steel protective shell (2). In this way, the possible maximum peak values ​​of the internal stresses acting from the pipes (9) on the sleeves (6) are reduced and aligned, being distributed throughout the entire volume of the group pipe passage (1).

[0039] High heterogeneous thermal loads acting from the nozzles (9) on the sleeves (6) during normal operation are supplemented by heat and mass transfer processes inside the group pipe penetration (1). When the medium inside different nozzles (9) is heated unevenly, uneven heat and mass transfer of the gas medium inside the group pipe penetration (1) occurs. This phenomenon leads to uneven and non-axisymmetric heating of the gas medium in the fourth cavity (11), in the first cavity (7) and in the second cavity (8), in which high-temperature areas can be formed, acting on the flange (5), adapter (4), cylinder (3), reducing their thermal strength and mechanical stability. To reduce (eliminate) uneven heating of the flange (5), adapter (4), cylinder (3), the following is done:

[0040] - the fourth cavity (11) is made larger in the radial direction than the second cavity (8), which allows for the heat coming from the heated gas medium to the flange (5) to be redistributed over a larger area, thereby reducing the uneven heating of the flange (5) in the azimuthal and radial directions; and the smaller size of the second cavity (8) in the radial direction allows for an increase in the thickness of the cylinder (3) and, as a consequence, a reduction in the thermal impact on the connection of the cylinder (3) with the steel protective shell (2), ensuring that isotherms with the maximum temperature are carried beyond this connection;

[0041] - in addition, the fourth cavity (11) provides conditions for mixing the gaseous media coming from the third cavities (10) from the side of the sleeves (6), which are at different temperatures associated with different heating of the media inside the pipes (9). Thus, the larger volume of the fourth cavity (11) ensures better mixing and better equalization of the temperatures of the gaseous medium located in the fourth cavity (11);

[0042] - between the second cavity (8) and the fourth cavity (11) there is a first cavity (7), which is a transition region in which the heat flows acting from the pipes (9) onto the adapter (4) and the cylinder (3) decrease as the thickness of the adapter (4) increases;

[0043] - the fourth cavity (11), the first cavity (7), the second cavity (8) are made significantly larger than the set of third cavities (10) on the side of the sleeves (6), which ensures sufficiently uniform mixing of the gas medium in the fourth cavity (11), in the first cavity (7) and in the second cavity (8), ensuring a more uniform distribution of heat flows acting on the flange (5), on the adapter (4) and on the cylinder (3) installed in the steel protective shell (2).

[0044] The equalization of the average temperatures of the gas medium located in the cavities (11), (7), (8), when it is heated from the side of the pipes (9) occurs in the radial, axial and azimuthal directions inside the pipe passage (I).

[0045] High mechanical heterogeneous loads acting from the nozzles (9) on the sleeves (6) during normal operation and in emergency modes lead to various changes in the shape of the nozzles (9), and mechanical and thermal loads affect the position of the nozzles (9) inside the third cavities (10), the fourth cavity (11), the first cavity (7) and the second cavity (8). Taking into account the peculiarities of thermomechanical stresses in the nozzles (9), the absence of mechanical contact between the nozzles (9) and the elements of the group pipe penetration (1), namely, the sleeves (6), flange (5), adapter (4) and cylinder (3), is ensured by selecting the geometric parameters of the third cavities (10), the fourth cavity

[0046] (II), the first cavity (7) and the second cavity (8).

[0047] Thus, the use of group pipe penetration of the steel protective shell allows increasing the strength of the steel protective shell of the SNPP and ensuring the localization of radioactive fission products inside the steel protective shell at pressures up to 1 MPa and temperatures up to 350°C (which is 2 times higher than the pressure and temperature of localization inside sealed shells for high-power reactors) under various states of the reactor facility under conditions of seismic and external impacts on the building structures of the SNPP.

[0048] Sources of information

[0049] 1. Russian Federation Patent RU2300042, IPC F16L5 / 00, priority dated June 20, 2005.

[0050] 2. Russian Federation Patent RU2304738, IPC F16L5 / 00, priority dated June 29, 2005.

[0051] 3. Russian Federation Patent RU184293, IPC F16L5 / 00, priority dated 06 / 08 / 2018.

Claims

1. A group pipe penetration (1) of a steel protective shell (2) of a low-power reactor, characterized in that it contains a cylinder (3), an adapter (4), a flange (5), sleeves (6) connected by end surfaces, wherein the inner front surface (3a) of the cylinder (3) is made cylindrical, the inner front surface (4a) of the adapter (4) is made in the form of two intersecting truncated cones (4b), which are intersected at an angle α from 90 to 180 degrees, the inner front surface (5a) of the flange (5) has an incomplete elliptical shape, and the outer front surface (5b) of the flange (5) has a conical shape, the adapter (4) and the flange (5) are connected in such a way that they form a first cavity (7) and a second cavity (8), which are intended to accommodate pipes (9), the flange (5) and the sleeve (6) are connected in such a way that they form a third cavity (10) and the fourth cavity (11), designed to accommodate the pipes (9).

2. A group pipe penetration (1) of a steel protective shell (2) of a low-power reactor according to claim 1, characterized in that on one side of the sleeve (6) a first external coupling (6a) is made, intended for connection with a flange coupling (5c) of a flange (5), as well as a second internal coupling (6b), intended for connection with a branch pipe (9), on the other side of the sleeve (6) a third end coupling (6c) is made, between couplings (6a), (6b), (6c) a connecting section (6g) with a conical surface (6d) is made, wherein the first external coupling (6a) and the second internal coupling (6b) of the sleeve (6) are made in such a way that they form a third cavity (10) with a toroidal internal surface (10a).

3. A group pipe penetration (1) of a steel protective shell (2) of a low-power reactor according to paragraph 1, characterized in that the fourth cavity (11), the first cavity (7), and the second cavity (8) are made in such a way that their total volume exceeds the volume of the third cavities (10) on the side of the sleeves (6).

4. A group pipe penetration (1) of a steel protective shell (2) of a low-power reactor according to paragraph 1, characterized in that the size in the radial direction of the fourth cavity (11) is larger than the size in the radial direction of the second cavity (8).

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