Integral nuclear reactor with heavy liquid metal coolantTechnical Field
The present invention relates to the field of nuclear energy, and in particular to a nuclear reactor with a heavy liquid metal coolant. More particularly, the present invention relates to a containment device for a monolithic nuclear reactor having a heavy liquid metal coolant.
Background
The monolithic nuclear reactor is characterized primarily by the absence of primary loop coolant piping. In addition to the core, all primary devices are located within the reactor housing that discharge core heat to the secondary loop coolant. In addition, the integral nuclear reactor includes a reactivity control mechanism required to control power and system equipment for monitoring coolant temperature and flow at various points in the loop. All of these devices are located substantially on or in connection with the reactor housing. The chain fission reaction, which holds and accompanies neutron and radiation migration, accompanies heat release both in the core and in the reflector and its surrounding structural components. The heat removal of the core element and the structural element disposed within the nuclear reactor housing requires a tissue cycle and a distribution of coolant flow so that the temperature of the structural element does not exceed an allowable value. For this purpose, pipes, channels, and flow-restricting devices are provided in the reactor structure to ensure distribution of the coolant flow required for cooling.
Important devices provided in the reactor shell include elements surrounding the core and performing the function of neutron reflectors, radiation protection devices that provide neutron and radiation absorption, which also reduce the negative effects of neutron and radiation absorption on all adverse factors in the reactor for some elements that must ensure structural integrity and operational performance.
All devices and metal structural members within the housing should be reliably secured. At the same time, nuclear reactor plants with heavy liquid metal coolants operate with temperature gradients up to hundreds of degrees. The structural elements may have different elongation or change in size at different temperatures, and the temperature variation differences associated therewith may be very large. Without special constructional solutions to ensure freedom of movement of the different elements when heated and cooled, very high stresses may occur, limiting the service life of the structural member or causing it to be damaged.
Thus, there is a need to develop structural members that prevent or reduce the mechanical effects of the components relative to each other when the temperature gradient is large, and also to eliminate uncontrolled or accidental spillage of coolant through the gap that is necessary to ensure the freedom of thermal expansion of the structural members relative to each other. The latter important task is complicated because the reactor is a large-scale apparatus with the clearances required to compensate for production errors even when cold assembled.
A reactor with a heavy liquid metal coolant has the further important feature that the density of all structural materials and radiation protective materials is substantially lower than the density of the coolant. Thus, when the apparatus is used to secure structural elements and the reactor internals associated therewith to the bottom or side walls of the housing, tensile stresses can occur due to buoyancy effects on such elements. Tensile stresses within the structural member and weld are most dangerous from the point of view of stress corrosion development.
It is also an important technical task to prioritize the compressive stress testing of the removable and non-removable joints of structural elements in the manufacture of reactor shell structures and the connection of reactor internals to the shell.
An integral nuclear reactor with heavy liquid metal coolant (US 10699816, international patent numbers G21C 1/03, G21C 1/32, G21C 5/02, G21C 15/06, published 30/2020) has been disclosed, comprising a reactor housing, a hot trap above the core, and a cold trap surrounding the hot trap and separated by an isolation structure, the cold trap having a single fluid circulation therein, in particular heavy liquid metal coolant. The reactor comprises at least one heat exchanger, in particular a steam generator, for removing heat from the heavy liquid metal coolant by means of a secondary fluid, in particular water. The isolation structure includes a bottom member disposed about the core and a top member disposed above the core. The top element has a smaller radial distance relative to the bottom element, and is connected to the bottom element by a connecting element. The connecting element is provided with an opening through which the vertical channel passes for connection to one or more heat exchangers provided between the top region of the isolation structure and the reactor shell for receiving heavy liquid metal coolant from the core. The connecting elements and the top elements of the isolation structure form a core limiter, in particular a radial limiter in the inactive top region of the fuel unit.
The insulating structure is also provided with a complex-shaped casing, which is fixed to the cover of the reactor by means of brackets. However, in this case, the bottom of the case is not fixed, which is a significant disadvantage. This arrangement results in increased loading of the support mounting area if the core installed in the enclosure is large in size and heavy in weight, and is particularly dangerous when subjected to seismic loads.
Also disclosed is a monolithic nuclear reactor (RU 2756231, international patent number G21C1/00, published at 2021, 9, 28) with heavy liquid metal coolant, comprising a reactor housing with a bottom cavity, a core, a hot cavity, a top cavity, and a heat exchanger. The hot cavity is disposed above the core and includes a hot cavity housing that is substantially cylindrical with a heat rejection pipe that discharges hot coolant from the core to the heat exchanger, and a plug, wherein the heat rejection pipe is rinsed from outside with cold coolant from the heat exchanger outlet. The thermal chamber housing comprises an inner housing and at least one auxiliary housing, the auxiliary housing being provided with a gap on the outside, concentric with the inner housing and forming at least one thermal chamber channel. Each heat extraction tube comprises an inner shell and at least one auxiliary shell provided with a gap on the outside, concentric with the inner shell and forming at least one tube channel, at least one hot cavity channel and at least one tube channel communicating with the outlet of the heat exchanger for guiding cold coolant to the channels.
The invention reduces the thermal load on the components of the thermal chamber, mainly the entire housing of the thermal chamber and the thermal coolant heat pipes, including adjusting and reducing the temperature gradients generated in the components, thus increasing the useful life of the components. However, the design and production process of the heat discharging pipe and the heat cavity are complex, and the achievement of the above results is difficult.
Also disclosed is a reactor with heavy liquid metal coolant (JP 2022097583, international patent numbers G21D1/02, G21C13/00, G21C15/02, published on 30 months 2022) comprising a housing closed with a cover, a core disposed within the housing, a hot trap above the core, a cold trap surrounding the hot trap and separated by a separating structure, the cold trap having a primary fluid therein for cooling the core. The reactor is also provided with a heat exchanger, a primary fluid inlet being provided at the bottom of the heat exchanger, and a surrounding drain being provided in the cold trap near the free level of primary fluid. The discharge orifice is positioned in a central position relative to the tube bundle, partially protruding above the free liquid level in the cold trap, and is filled with primary fluid by means of auxiliary equipment, so as to establish a negative pressure in the gas of the heat exchanger relative to the gas in the container. The heat exchanger is arranged in a protruding manner, and the discharge hole of the heat exchanger is arranged near the free liquid level of the primary fluid, so that the movement of the primary fluid is reduced to the greatest extent when the secondary fluid in the heat exchanger is discharged accidentally.
The lack of structural solutions that ensure freedom of movement of the different elements of the reactor when heated and cooled results in very high stresses on these elements of the reactor, limiting the service life of the structure or causing it to be damaged, making the reliability of the disclosed nuclear reactor not high.
A reactor with a heavy liquid metal coolant is also disclosed (US 20180061513, international patent numbers: G21C1/03, G21C15/14, G21C1/32, G21C5/02, published 30/6/2020), which is considered as a prototype, in terms of the maximum number of essential features, consistent with the technical solution of the present invention. The nuclear reactor prototype includes a reactor shell closed with a cover, in which a core well, a thermal catcher located above the core and a bottom cavity separated by an isolation structure are provided, in which a primary fluid circulation is provided for cooling the core. The reactor also comprises at least one heat exchanger, in particular a steam generator, secured to its cover for rejecting heat from the primary fluid by the secondary fluid. The isolation structure includes a bottom member disposed about the core and a top member disposed above the core. The top element has a smaller radial distance relative to the bottom element and is connected to the bottom element by means of a connecting element, which is manufactured from plastic or the like. The connecting element is provided with an opening through which the vertical channel passes for connection to one or more heat exchangers provided between the top region of the isolation structure and the reactor shell for receiving primary hot fluid from the core. The connecting elements and the top elements of the isolation structure form a core limiter, in particular a radial limiter in the inactive top region of the fuel unit.
The reliability of the known nuclear reactor prototype is inadequate because, due to the fact that the different elements of the reactor structure have no freedom of movement when heated and cooled, under the action of buoyancy, tensile stresses are generated in the structural elements having a density lower than that of the liquid metal coolant, and, due to the presence of the coolant cavity inside the reactor shell, the velocity of the coolant is extremely low, resulting in areas of poor movement of the coolant, which, due to insufficient monitoring of the quality of the coolant, produce corrosion damage.
Disclosure of Invention
The object of the present invention is to develop a nuclear reactor, in particular a nuclear reactor with a heavy liquid metal coolant, which increases the operational safety and reliability of the nuclear reactor by ensuring the freedom of longitudinal and radial movements of the structural elements of the nuclear reactor with respect to each other during assembly, heating and cooling, improving the corrosion resistance and the required friction properties of the contact materials, equalizing the velocity of the coolant at the bottom cavity and at the core inlet, and ensuring a reliable fixation of the fuel assembly during abnormal floating without affecting the controlled limiting compression forces of the temperature expansion.
By solving the above problems, the present invention can achieve the following technical effects:
Providing freedom of longitudinal and radial movement of the different elements with respect to each other during heating and cooling, without which the coolant may escape uncontrollably or accidentally via the gaps, thereby reducing the cooling reliability of the reactor installation and creating very large stresses, which in turn limit the service life of the structural member or cause its destruction;
-improving the corrosion resistance and the desired friction properties of the material;
Equalizing the velocity of the coolant at the bottom cavity and at the core inlet, which is very important to ensure reliable cooling and safety of the elements;
by limiting the compression force, ensuring a reliable fixation of the fuel assembly in abnormal floating without affecting the temperature expansion;
-improving the operational safety and reliability of the reactor.
In order to solve the above problems, the present invention provides a nuclear reactor having a heavy liquid metal coolant, comprising a reactor housing, a core, at least one primary loop circulation pump, at least one heat exchanger, and a plug, wherein the reactor housing is closed with a cover and has a bottom cavity formed by an isolation structure connected to the cover, the primary loop circulation pump is located in a circulation pump housing and the circulation pump housing is connected to the cover, the heat exchanger is located in a heat exchanger housing and the heat exchanger housing is connected to the cover, the heat exchanger is used for exhausting heat from the heavy liquid metal coolant to a secondary loop coolant. The novelty is that the isolation structure employs an annular element fixed to the reactor shell, the core shell is inserted on a guide shell of the annular element and connected to a cover of the reactor, the reactor internal device includes a plurality of channels limiting coolant circulation, the plurality of channels are connected to each other and fixed to the periphery of the cover of the reactor, the bottom end of the heat exchanger shell is disposed above the annular element, and the bottom end of the circulation pump shell penetrates into the bottom cavity through an opening in the annular element.
The bottom of the core housing may be provided with a support plate within which are secured Fuel Assemblies (FA) with Control and Protection System (CPS) channels and reflector units.
The ends of the control and protection system channels may be tapered within the plug of the reactor and have inner surfaces that contact the head of the fuel assembly.
A diaphragm may be provided below the top within the plug to which the control and protection system passage is connected using a resilient bellows joint and which limits the stress transmitted to the head of the fuel assembly.
An auxiliary annular element of smaller diameter can be provided below the annular element, in which auxiliary annular element at least one opening is provided, between which an annular trap is formed, the inlet of which is connected to the outlet of the circulation pump and the outlet of which is connected to the bottom chamber.
Below the auxiliary annular element may be provided a fin fixed to the bottom of the reactor shell for guiding coolant from the periphery of the bottom cavity to its centre. Preferably, in order to equalize the azimuthal distribution of the flow, an aperture is provided in the fin to ensure azimuthal direction.
An annular groove may be provided in the circulation pump casing, at least one piston seal being provided in the annular groove, the seal being radially movable and covering the gap between the circulation pump casing and the annular element when the circulation pump casing is radially moved.
An annular groove may be provided in the core housing, at least one piston seal ring being provided in the annular groove, the seal ring being radially movable and covering the gap between the core housing and the annular element when the core housing is radially moved.
The piston sealing ring can be made of high-strength gray cast iron or corrosion-resistant stainless steel containing lamellar graphite and silicon content of not less than 1%.
The housings are rigidly connected to the reactor cover by means of removable or non-removable joints, and the most important equipment is provided in these housings, which allow the reactor to be inspected, repaired or replaced during operation of the reactor. Openings are provided in the housing as needed to allow for coolant circulation. When heated or cooled, the housing is free to move longitudinally, and a special sliding seal is provided at the location of engagement with other components of the structure, which does not interfere with such movement.
Thus, for example, the circulating pump, steam generator, or heat exchanger between the primary and secondary circuits, the core support structure, the extractable portion of the core and radial reflectors, and the plugs above the core may all be extractable elements of the reactor structure.
The main parts of the internal devices of the reactor, including the pipes and the coolant guiding channels, are combined into one assembly structure and connected to the cover of the reactor. In this case, all stresses generated by the buoyancy of the coolant having a density higher than that of the structural members are guided from bottom to top and eventually transferred to the cover of the reactor. Considering that the majority of the internal devices of the reactor are located and fixed on the reactor cover, including the circulation pump with transmission, the adjustment mechanism transmission, the inlet and outlet chambers, the steam or heat exchanger tubes, the external radiation protection devices and other elements, the stresses generated by the archimedes buoyancy effect are largely compensated by the weight of these devices, which contributes to the working performance of the cover. In this case, the internal elements not belonging to the core element are preferably fixed around the cover of the reactor, which is advantageous in reducing bending moment and improving the workability of the cover.
For the coolant flow guiding elements, it should be ensured that only the minimum number necessary is fixed at the bottom of the reactor and that interfaces with the housing are provided within the elements for routing the core and pumps. The interface is provided with a seal to ensure that the housing is free to move longitudinally and only to produce limited radial movement while maintaining tightness or significantly limiting flooding.
It is necessary to compensate for dimensional tolerances and temperature expansion during production to determine the allowable radial movement values within the seal. In this case, large radial movements of the reactor are not possible, since they can be dangerous when external conditions significantly affect the reactor, for example earthquakes. The seal may be selected from prior art solutions disclosed in the art, but most preferably a piston seal is used. In this case, gray cast iron grade material containing lamellar graphite is the most preferred material. The content of silicon and lamellar graphite inclusion in the grade cast iron is (1-3) weight percent, so that the corrosion resistance and the required friction performance of the sealing element material are improved, and a labyrinth sealing ring can be adopted when the pressure difference is not large. By hydraulic calculations using methods disclosed in the art, it can be determined whether labyrinth seals can be employed, but the calculated leakage value must be determined separately when the project is to be implemented.
Drawings
The invention is illustrated by the following figures:
FIG. 1 shows a projection view, including a partial cross-sectional view, of a nuclear reactor having a heavy liquid metal cooler;
FIG. 2 illustrates a cross-sectional view of the interface of the end of the control and protection system passage with the head of the fuel assembly;
FIG. 3 shows a cross-sectional view of the components securing the control and protection system channel to the plug intermediate support plate;
FIG. 4 shows a cross-sectional view of a seal unit with a self-mount;
FIG. 5 shows an enlarged view of the unit G shown in FIG. 4, and
Fig. 6 shows an embodiment in which the seal unit is provided in a detachable joint in the extractable and non-extractable element of the housing, for example, unit E as shown in fig. 1, embodiment a is a rectangular sealing ring, embodiment B is a wire sealing ring, and embodiment C is a labyrinth sealing ring.
The following labels are used in the drawings to indicate elements:
1, a reactor cover;
2, circulating pump shell;
3, end shell;
4, circulating a pump housing sealing unit;
5, a reactor core well sealing unit;
6, triangular iron;
7, coolant channels;
8, reactor internal device;
9, reactor shell;
10, the bottom part;
11, an annular element;
A core well housing;
13, a reactor core well sealing unit;
14, connecting the shell;
15, auxiliary ring element;
16, a bottom cavity;
17, guiding triangular iron;
18, a shell;
19, supporting the flange;
a housing for providing a steam generator or heat exchanger module between the primary circuit and the secondary circuit;
21, a primary loop circulating pump;
22a core well support plate;
23, fuel assembly;
a reflector 24;
A reactor plug;
26, a flange;
control and protection system transmission means;
28, an in-plug control and protection system;
29, controlling and protecting the end of the system channel;
30, fuel assembly head;
31 a plug intermediate support plate;
a bellows unit in the plug for controlling and protecting the system channels;
33, the sealing element unit is self-installed;
Assembling the joint;
35, the bottom of the mounting seat;
36, a mounting seat ring;
37, a pin;
38, sealing ring;
39, a pressing ring;
40, coolant overflow holes;
41, a piston sealing ring;
42, an iron wire sealing ring;
43, a circulating pump transmission device;
44, rectangular sealing rings.
Detailed Description
Fig. 1 schematically illustrates a nuclear reactor with a heavy liquid metal coolant.
The cover 1 of the reactor housing 9 includes a circulation pump 21 housing 2 and a core well housing 12 with an end shell 3 on which are located seal units 4 and 5 of the circulation pump housing 2 and the end shell 3. Also provided in the reactor cover 1 are fastening elements for connection, such as a set-angle 6 for the internal reactor arrangement 8. Wherein preferably a triangle 6 is connected to the periphery of the reactor cover 1. The elements of the in-housing device 8 are provided between the reactor cover 1 and the annular element 11, which are assembled as a unified structure, and may include heat or radiation protection means (not shown), coolant channels, for example, the coolant channels 7 connecting to a trap above the core housing for providing the heat exchanger housing 20 or other elements as disclosed in the art. The components of the reactor internals 8 are assembled to form an assembly unit, which is then assembled with the cover 1 to form an assembly unit and connected to the reactor housing 9. On the elements for supplying coolant from the primary loop circulation pump 21 of the belt drive 43 to the core, a bottom 10 is formed which cooperates with the other elements of the structure via sliding removable joints, subject to a main load comprising the weight of the coolant and the pressure difference between the different areas of the loop. The annular element 11 is sealingly connected to the bottom 10. A connection housing 14 is provided along the inner ring within the annular element 11, which comprises an end shell 3 within which a sealing unit 13 and a joint with the core well housing 12 are provided. In the annular element 11 there is provided an opening and sealing unit 4 for alignment with the housing 2 of the circulation pump 21. The auxiliary ring element 15 is connected to the ring element 11 using the connection housing 14, whereby a ring chamber is formed between the ring element 11 and the auxiliary ring element 15, into which ring chamber liquid from the circulation pump 21 flows, after being redistributed there through the circumference of the ring chamber and out to the bottom chamber 16. The coolant flowing out of the annular chamber may flow through an annular gap, as shown in fig. 1, for example, through a system of holes (not shown), so that the coolant flow is distributed more evenly in azimuth. To equalize the velocity field, a guide triangle 17 may be connected to the ring element 15. Thus, balancing the velocity of the coolant at the entrance of the bottom chamber 16 achieves an additional technical effect, which is important to ensure reliable cooling and safety of the components. In the triangle 17, an overflow aperture 40 may be provided in order to improve the speed balance. The assembly unit of the cover 1 is connected to the assembly unit of the reactor internal device and then to the outer shell 18 of the reactor shell 9, which is connected to the bottom 10 first, forming the reactor shell assembly. In this case, the reactor shell assembly is supported on the support structure of the reactor well by means of a bearing flange 19 provided on the reactor cover 1. A housing 20 for providing a steam generator or heat exchanger module between the primary circuit and the secondary circuit is provided in the reactor housing assembly, and a circulation pump 21 is fixed to the reactor cover 1. the heat exchange surfaces of the above-mentioned heat exchanger and the fixing units for fixing it to the reactor cover are not shown in the figures and may have different embodiments known in the art. The weight load and buoyancy of the part of the above elements immersed in the coolant are transmitted to the reactor cover 1 from a plurality of directions. A core support plate (shroud) 22 is secured to the end shell 3 in which a fuel assembly 23 and a reflector element 24 are in turn secured. Ultimately, stresses in multiple directions act on the elements 23, 24. To a large extent, the downward gravitational force and the upward buoyancy force compensate each other, and the resulting stresses are transmitted to the shells 3, 12 and the reactor cover 1. The insulating structure assembled from the housings 3 and 12 may be in the form of an assembly element or may be divided into additional assemblies along the height while maintaining the tightness of the connection. This solution can solve the technical problems associated with the selection of different materials according to the height of the insulating structure, for example when there is a great difference in the conditions of use of the materials. A reactor plug 25 with a flange 26 is provided on the reactor cover 1, on which plug a drive 27 of the control and protection system mechanism is provided. The resultant force formed is transmitted to the reactor cover 1, similarly to the previous case.
The invention thus eliminates in principle the transmission of stresses from the core elements, the reactor internals or the equipment on the bottom 10 of the reactor shell 9, and accordingly, the important equipment is not connected to the reactor bottom 10, and also prevents accidents from the rupture of such joints and uncontrolled floating of the respective equipment or reactor elements. The overall weight load of the core, the reactor internals 8, the plugs 25 and other components of the reactor is compensated by the archimedes buoyancy and transferred from bottom to top to the cover 1. The circulation pump 21 with the transmission 43, the control and protection system transmission 27 are provided on the reactor cover 1 and the plug 25, respectively, from which additional loads are correspondingly compensated by the preferential action of buoyancy. By compressing the fuel assemblies 23 with the control and protection system passages 28 in the plugs 25, when the fuel assemblies 23 are secured in the core well support plate 22 with the lower handle, it is important for safety to ensure that the fuel assemblies 23 are reliably secured in abnormal floating conditions. In this case, compression should be limited and temperature expansion cannot be affected.
The bottom of the control and protection system channel 28, located within the plug 25, is provided with a tip 29 with a tapered surface along which it cooperates with the head 30 of the fuel assembly 23 (fig. 2). The end 29 of the control and protection system channel 28 is fixed to the intermediate support plate 31 of the plug 25 by means of a bellows unit 32, so that the control and protection system channel 28 can move vertically within the range of movement of the bellows connected to the intermediate support plate 31 (fig. 3).
Coolant leakage in the seal units must be limited in order to reliably cool the core and the reactor internals 8. In this case, the degree of freedom of thermal expansion and convenience of assembly should be ensured, and this is also one of important tasks in view of the very large size of the nuclear reactor device. When the maximum load of the seal unit is high compared to the pressure difference between the pumping chamber of the circulation pump 21 and the rest of the circuit, a seal unit with self-mounting seat 33 is preferably used, as shown in fig. 4 and 5. The mount 33 has an assembly joint 34 connected to the bottom 35 of the mount 33 for assembling the mount 33 and the mount ring 36 and ensuring co-operation thereof, the mount and the mount ring mating along a spherical surface of radius R, the centre of which is located on the axis of the mount ring 36. To limit movement, four pins 37 are used to secure the mount ring 36 along mutually perpendicular axes. The entire unit assembly is secured within the annular member 11 against axial movement and leakage by means of a sealing ring 38 and a clamping ring 39 which are in turn welded to the annular member 11. The gap delta (fig. 5) ensures that the cell seal can move horizontally without being compromised. The size of the gap required is related to the process tolerances, production and assembly accuracy of the large and ultra-long equipment of the reactor, as determined by dimensional engineering calculations known in the art. The extractable housing 2 of the pump well is sealed along the inner surface of the mount ring 36 by a piston seal 41, preferably made of gray cast iron containing lamellar graphite.
For large diameter detachable joints, for example, joints between the annular housing 3 of the core well and the corresponding stationary seal units, a simplified embodiment (embodiment a) as shown in fig. 6 is preferably employed. In this case, preferably, a rectangular seal ring 44, an iron wire seal ring 42 (fig. 6, embodiment B), or a labyrinth seal ring 43 (fig. 6, embodiment C) similar to the piston seal ring 41 is used.
Finally, the metallic structural members of the reactor cover are mainly operated under compressive stress conditions, the bottom of the reactor shell is unloaded via the joint with the core support structural member, the reactor internal device and the detachable elements of the reactor are unloaded by temperature expansion, and can move longitudinally independently and freely, and meanwhile, the tightness of the matched area is maintained, so that the working performance and safety of the structural members are facilitated.