High temperature gas cooled reactor core structure

Abstract

The application belongs to the technical field of high temperature reactor, and discloses a high temperature gas cooled reactor core structure, wherein a graphite shell is arranged in a pressure container, fuel balls are filled in the graphite shell from top to bottom, the fuel balls are stacked to form a pebble bed core, the graphite shell cooperates with the inner wall of the pressure container to form a flow cavity, the flow cavity is communicated with the bottom of the graphite shell, a coolant inlet communicated with the flow cavity is arranged in the upper region of the pressure container, and a coolant outlet communicated with the outside is arranged in the upper region of the graphite shell; helium coolant flows into the flow cavity through the coolant inlet, flows downwards along the flow cavity to the bottom of the graphite shell, flows upwards in the graphite shell, and flows out through the coolant outlet after taking away the heat of the pebble bed core; the fuel balls flow from top to bottom, and the coolant flows from bottom to top, the neutron flux of the place where the upper fissile nuclides are accumulated more is reduced through temperature negative feedback, the axial power density distribution is flattened, the maximum temperature of the fuel after the accident is reduced, the safety margin of the pebble bed is released, and the economy of the reactor is improved.

Description

Technical Field

[0001] This invention relates to the field of high-temperature reactor technology, and in particular to a high-temperature gas-cooled reactor core structure. Background Technology

[0002] As an advanced representative of fourth-generation nuclear power technology, the pebble bed high-temperature gas-cooled reactor (PTC) boasts excellent safety, high power generation efficiency, strong environmental adaptability, and wide applicability, with broad prospects for commercial application in nuclear power generation, combined heat and power (CHP), and high-temperature process heat. The Pebble bed PTC uses helium coolant, graphite moderator, and coated particulate fuel elements. It consists of a cylindrical cavity formed by stacking graphite components, within which flowable spherical fuel elements are deposited—the "pebble bed" active region.

[0003] In the existing pebble bed high-temperature gas-cooled reactor scheme, the helium coolant inlet is located at the bottom of the pressure vessel. After flowing around the bottom of the reactor, it enters the cold helium rising channel in the graphite bricks and flows into the cold helium header above the active zone for mixing. Helium flows from the top through the pebble bed core to the bottom and is heated before flowing into the hot helium header below the active zone for mixing and reaching the hot helium outlet at the bottom of the pressure vessel. Both fuel spheres and coolant flow from top to bottom. The fuel elements with shallower burnout and the coolant with lower temperatures are located in the upper part of the reactor core. Due to the strong temperature negative feedback effect of the high-temperature gas-cooled reactor (lower power at higher temperatures, and vice versa), the upper part of the reactor core will have peak neutron flux and power density. The peak power density is strongly positively correlated with the safety limit after a loss of cooling and depressurization accident - the maximum fuel temperature. When the peak power density is high, the maximum fuel temperature after the accident will also rise accordingly. Once the limit is exceeded, it will endanger the safety of the reactor. Therefore, the reactor outlet temperature during normal operation is usually limited to 750°C to limit the peak power density and avoid the maximum fuel temperature from exceeding the limit after an accident, which would lead to a decrease in the economics of the reactor. Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature gas-cooled reactor core structure that fully releases the safety margin of the pebble bed reactor and improves the economics of the reactor.

[0005] To achieve this objective, the present invention adopts the following technical solution: A high-temperature gas-cooled reactor core structure includes a pressure vessel, an interior graphite shell, and fuel spheres flowing and filling the interior of the graphite shell from top to bottom. The fuel spheres are stacked to form a pebble bed core. The graphite shell and the inner wall of the pressure vessel form a flow cavity, which is connected to the bottom of the graphite shell. A coolant inlet connected to the flow cavity is provided in the upper region of the pressure vessel, and a coolant outlet connected to the outside is provided in the upper region of the graphite shell.

[0006] Preferably, the system also includes an inlet pipe and an outlet pipe, wherein the inlet pipe is installed in the pressure vessel and connected to the coolant inlet, and the outlet pipe passes through the pressure vessel and is connected to the coolant outlet.

[0007] Preferably, the outlet pipe is coaxially sleeved inside the inlet pipe.

[0008] Preferably, the pressure vessel has an installation hole in its upper region, and the inlet pipe is sealed and inserted into the installation hole.

[0009] Preferably, the bottom of the graphite shell has several channels pre-set, and the channels are connected to the flow cavity.

[0010] Preferably, the channels are evenly spaced.

[0011] Preferably, the system also includes an inlet tube and an outlet tube, wherein one end of the inlet tube is connected to the top of the graphite shell and the other end passes through the top of the pressure vessel, and one end of the outlet tube is connected to the bottom of the graphite shell and the other end passes through the bottom of the pressure vessel.

[0012] Preferably, the ball inlet pipe and the ball unloading pipe are centrally located at the upper and lower parts of the ball bed core, respectively.

[0013] The beneficial effects of this invention are: The high-temperature gas-cooled reactor core structure provided by the present invention includes a pressure vessel, a graphite shell disposed inside the pressure vessel, fuel balls flowing and filling the inside of the graphite shell from top to bottom, the fuel balls accumulating to form a pebble bed core, the graphite shell and the inner wall of the pressure vessel forming a flow cavity, the flow cavity connecting to the bottom of the graphite shell, a coolant inlet connected to the flow cavity being opened in the upper region of the pressure vessel, and a coolant outlet connected to the outside being opened in the upper region of the graphite shell. Fuel spheres are filled from the top of the graphite shell and move downwards under gravity, leaving the bottom of the shell. Helium coolant flows into the flow chamber through the coolant inlet and down to the bottom of the graphite shell, then flows upwards inside the shell, carrying away heat from the pebble bed core. The coolant exits through the coolant outlet. By setting the fuel spheres to flow downwards and the coolant to flow upwards, the coolant temperature is higher in the upper part of the core where burnup is shallow. This temperature negative feedback reduces the neutron flux in areas where fissile nuclides accumulate more, flattens the axial power density distribution, and lowers the peak power density. Consequently, the maximum fuel temperature after an accident is also lowered. This allows the reactor outlet coolant temperature to be raised to 900°C while meeting safety limits, improving reactor safety, fully utilizing the safety margin of the pebble bed reactor, and enhancing its economic efficiency. Attached Figure Description

[0014] Figure 1This is a schematic diagram of the high-temperature gas-cooled reactor core structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram (radial center) showing the flattened comparison of the axial power density distribution of the reactor core provided in an embodiment of the present invention. Figure 3 This is a comparison chart of the highest fuel temperature after an accident, provided in an embodiment of the present invention.

[0015] In the picture: 1. Pressure vessel; 2. Graphite shell; 21. Coolant outlet; 10. Flow chamber; 11. Coolant inlet; 3. Fuel ball; 4. Inlet pipe; 5. Outlet pipe; 6. Inlet pipe; 7. Outlet pipe. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0017] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0019] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0020] In the existing pebble bed high-temperature gas-cooled reactor scheme, the helium coolant inlet is located at the bottom of the pressure vessel. After flowing around the bottom of the reactor, it enters the cold helium rising channel in the graphite bricks and flows into the cold helium header above the active zone for mixing. Helium flows from the top through the pebble bed core to the bottom and is heated before flowing into the hot helium header below the active zone for mixing and reaching the hot helium outlet at the bottom of the pressure vessel. Both fuel spheres and coolant flow from top to bottom. The fuel elements with shallower burnout and the coolant with lower temperatures are located in the upper part of the reactor core. Due to the strong temperature negative feedback effect of the high-temperature gas-cooled reactor (lower power at higher temperatures, and vice versa), the upper part of the reactor core will have peak neutron flux and power density. The peak power density is strongly positively correlated with the safety limit after a loss of cooling and depressurization accident - the maximum fuel temperature. When the peak power density is high, the maximum fuel temperature after the accident will also rise accordingly. Once the limit is exceeded, it will endanger the safety of the reactor. Therefore, the reactor outlet temperature during normal operation is usually limited to 750°C to limit the peak power density and avoid the maximum fuel temperature from exceeding the limit after an accident, which would lead to a decrease in the economics of the reactor.

[0021] This embodiment provides a high-temperature gas-cooled reactor core structure that utilizes the temperature negative feedback effect to flatten the core power distribution, reduce the peak power density, and correspondingly reduce the highest fuel temperature after an accident. This allows the reactor outlet coolant temperature to be raised to 900°C while meeting safety limits, thereby improving reactor safety, fully releasing the safety margin of the pebble bed reactor, and improving reactor economics.

[0022] like Figure 1As shown, the high-temperature gas-cooled reactor core structure provided in this embodiment includes a pressure vessel 1. The interior of the pressure vessel 1 is formed by stacking graphite bricks in a ring to form a cylindrical cavity, which is a graphite shell 2. Fuel balls 3 flow and fill the interior of the graphite shell 2 from top to bottom. The fuel balls 3 are stacked to form a pebble bed core. That is, the fuel balls 3 are filled from the top of the graphite shell 2 and move downward by gravity. After reaching the bottom of the graphite shell 2, they leave. The graphite shell 2 and the inner wall of the pressure vessel 1 cooperate to form a flow cavity 10. The flow cavity 10 is connected to the bottom of the graphite shell 2. A coolant outlet 21 is opened in the upper region of the graphite shell 2 to connect to the outside. A coolant inlet 11 is opened in the upper region of the pressure vessel 1 to connect to the flow cavity 10. Helium coolant flows into the flow cavity 10 through the coolant inlet 11 and flows downward along the flow cavity 10 to the bottom of the graphite shell 2. Inside the graphite shell 2, it flows upward to carry away the heat of the pebble bed core and flows out through the coolant outlet 21.

[0023] With the above configuration, fuel spheres 3 flow from top to bottom, while coolant flows from bottom to top. This achieves a higher coolant temperature in the upper part of the pebble bed core where burnup is shallow, and reduces the neutron flux in the upper part where fissile nuclides accumulate more through temperature negative feedback. (See also...) Figure 2 In this scheme, the axial power density distribution is flattened, the peak power density is reduced, and the maximum fuel temperature after an accident is also reduced accordingly, which improves the safety of the reactor. It can increase the reactor outlet coolant temperature while meeting safety limits, release the safety margin of the pebble bed reactor, and improve the economics of the reactor.

[0024] Furthermore, this embodiment also includes an inlet pipe 4 and an outlet pipe 5. The inlet pipe 4 is installed on the pressure vessel 1 and connected to the coolant inlet 11. Preferably, one end of the inlet pipe 4 is sealed and connected to the coolant inlet 11. The outlet pipe 5 passes through the pressure vessel 1 and is connected to the coolant outlet 21. Preferably, one end of the outlet pipe 5 is sealed and connected to the coolant outlet 21.

[0025] For example, a mounting hole is provided in the upper region of the pressure vessel 1, and one end of the inlet pipe 4 is inserted into the mounting hole and sealed to the coolant outlet 21. Preferably, the outer wall of the inlet pipe 4 is circumferentially sealed to the wall of the mounting hole by a sealing structure. More preferably, the sealing structure can be a high-temperature resistant sealing ring.

[0026] In some feasible embodiments, the outlet pipe 5 is coaxially sleeved inside the inlet pipe 4, and the outlet pipe 5 and the inlet pipe 4 cooperate to form a sleeve structure.

[0027] In this embodiment, several channels are pre-set at the bottom of the graphite shell 2. These channels are connected to the flow cavity 10. Helium coolant flows into the flow cavity 10 through the coolant inlet 11 and flows downwards along the flow cavity 10 to the bottom of the graphite shell 2. Then, it flows into the interior of the graphite shell 2 through the channels. Preferably, the channels are evenly spaced to ensure that the helium coolant is evenly distributed inside the graphite shell 2, thereby further ensuring that the helium coolant can uniformly cool the pebble bed core and improve the temperature uniformity of the pebble bed core.

[0028] Furthermore, this embodiment also includes an inlet pipe 6 and an outlet pipe 7. One end of the inlet pipe 6 is connected to the top of the graphite shell 2, and the other end passes through the top of the pressure vessel 1. One end of the outlet pipe 7 is connected to the bottom of the graphite shell 2, and the other end passes through the bottom of the pressure vessel 1. The fuel balls 3 are filled from above the graphite shell 2 through the inlet pipe 6 and move downwards by gravity. After reaching the bottom of the graphite shell 2, they can leave through the outlet pipe 7.

[0029] Optionally, the infeed pipe 6 and the unfeed pipe 7 are respectively centrally located at the upper and lower parts of the pebble bed core to ensure that the fuel balls 3 that make up the pebble bed core are always evenly distributed.

[0030] Decooling and depressurization accidents, as envelope accidents in the core structural safety analysis of high-temperature gas-cooled reactors, typically use the post-accident maximum fuel temperature as one of the important indicators for evaluating reactor safety, with a design limit of 1620℃. The post-accident maximum fuel temperature exhibits a strong positive correlation with the reactor's peak power density; therefore, a lower peak power density provides a considerable margin for the maximum fuel element temperature, a key indicator after a decooling and depressurization accident.

[0031] like Figure 3 As shown: In the existing plan, the coolant outlet temperature is adjusted to 750°C, and the highest fuel temperature after the accident is 1535.8°C; The high-temperature gas-cooled reactor core structure provided in this embodiment adjusts the coolant outlet temperature to 750°C by regulating the flow rate of helium coolant, resulting in a maximum fuel temperature of 1360.1°C after an accident, which is a significant reduction in the maximum fuel temperature after an accident.

[0032] like Figure 3 As shown: The high-temperature gas-cooled reactor core structure provided in this embodiment, when the flow rate of helium coolant is further reduced until the coolant outlet temperature is raised to 900°C, the highest fuel temperature after the accident is 1401°C, which is still lower than the design limit of 1620°C.

[0033] Therefore, this embodiment achieves a higher coolant temperature in the upper part of the pebble bed reactor core where the burnup is shallow by setting the fuel spheres 3 to flow from top to bottom and the coolant to flow from bottom to top. This reduces the neutron flux in the upper part where fissile nuclides accumulate more, thereby flattening the axial power density distribution, reducing the peak power density, and correspondingly reducing the maximum fuel temperature after an accident. Under the premise of meeting safety limits, the reactor outlet coolant temperature can be raised to 900°C, improving reactor safety, fully releasing the safety margin of the pebble bed reactor, and improving the reactor's economics.

[0034] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A high-temperature gas-cooled reactor core structure, characterized in that, The device includes a pressure vessel (1), inside which is a graphite shell (2). Fuel balls (3) flow and fill the interior of the graphite shell (2) from top to bottom. The fuel balls (3) are stacked to form a pebble bed core. The graphite shell (2) and the inner wall of the pressure vessel (1) cooperate to form a flow cavity (10). The flow cavity (10) is connected to the bottom of the graphite shell (2). A coolant inlet (11) is opened in the upper region of the pressure vessel (1) to connect to the flow cavity (10). A coolant outlet (21) is opened in the upper region of the graphite shell (2) to connect to the outside.

2. The high-temperature gas-cooled reactor core structure according to claim 1, characterized in that, It also includes an inlet pipe (4) and an outlet pipe (5), the inlet pipe (4) being installed on the pressure vessel (1) and connected to the coolant inlet (11), and the outlet pipe (5) penetrating the pressure vessel (1) and connected to the coolant outlet (21).

3. The high-temperature gas-cooled reactor core structure according to claim 2, characterized in that, The outlet pipe (5) is coaxially sleeved inside the inlet pipe (4).

4. The high-temperature gas-cooled reactor core structure according to claim 2, characterized in that, An installation hole is provided in the upper region of the pressure vessel (1), and the inlet pipe (4) is sealed and inserted into the installation hole.

5. The high-temperature gas-cooled reactor core structure according to claim 1, characterized in that, The bottom of the graphite shell (2) has several channels pre-set, and the channels are connected to the flow cavity (10).

6. The high-temperature gas-cooled reactor core structure according to claim 5, characterized in that, The aforementioned channels are evenly spaced.

7. The high-temperature gas-cooled reactor core structure according to any one of claims 1-6, characterized in that, It also includes an inlet tube (6) and an outlet tube (7). One end of the inlet tube (6) is connected to the top of the graphite shell (2), and the other end passes through the top of the pressure vessel (1). One end of the outlet tube (7) is connected to the bottom of the graphite shell (2), and the other end passes through the bottom of the pressure vessel (1).

8. The high-temperature gas-cooled reactor core structure according to claim 7, characterized in that, The ball inlet pipe (6) and the ball unloading pipe (7) are respectively centrally located at the upper and lower parts of the ball bed core.

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