A method for simulating the flow circulation of fuel spheres applied to a pebble bed high temperature gas cooled reactor

Abstract

This invention discloses a method for simulating the flow and circulation of fuel spheres in a pebble bed type high-temperature gas-cooled reactor. First, a sphere flow simulation program is used to divide the fuel sphere flow into multiple streamline chains, determining the flow rate of each streamline chain. Then, based on the core structure, a sphere flow grid is divided within the fuel sphere flow range. After overlapping the streamline chains and grids, the grids traversed by the streamline chains are marked. Starting from the bottom, based on the flow velocity and grid width, the proportion of fuel spheres originating from the preceding grid in each grid is calculated. The fuel sphere composition is obtained layer by layer upwards, thus simulating the fuel sphere flow. This invention, by dividing the fuel sphere flow in the core into flow channels and grids, and obtaining the fuel sphere flow through parameters such as flow velocity, simulates the fuel sphere flow within the core, achieving the simulation of the fuel sphere flow and circulation within the core for subsequent physical and thermal calculations. This method changes the traditional laminar step-flow simulation method for high-temperature gas-cooled reactors, realizing the simulation of fuel circulation in high-temperature gas-cooled reactors.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor fuel cycle technology, and more specifically to a method for simulating the flow and circulation of fuel spheres in a pebble bed type high-temperature gas-cooled reactor. Background Technology

[0002] Pebble bed high-temperature gas-cooled reactors (such as HTR-PM) employ a continuous online refueling strategy. Newly added fuel pellets, along with those not yet at burnup depth, fall from the top central fuel loading pipe into the reactor core's pebble bed. The fuel pellets and graphite pellets mix randomly and flow downwards at different locations within the pebble bed, then are discharged through fuel discharge pipes at the bottom of the core. Each discharged fuel pellet passes through a burnup measurement device. When a fuel pellet reaches its designed burnup depth or breaks, it is discharged and transported to the spent fuel storage system, while other batches of fuel pellets are returned to the top of the core. Simultaneously, new fuel pellets are loaded onto the top of the core and recycled along with other batches to maintain a stable total number of fuel pellets in the mixed pebble bed.

[0003] Currently, most high-temperature gas-cooled reactor calculation programs (such as VSOP) use a laminar flow step method to simulate fuel flow inside the reactor core. This method divides the entire reactor core into flow channels in the radial direction and layers in the axial direction. Each fuel flow causes the fuel in the grid to move down one layer, and the flow velocity is defined manually. This method ignores the mixing and differential velocity phenomena of fuel flow inside the reactor core, and the manually defined flow velocity is far from the actual fuel flow situation, making it difficult to simulate the real spherical flow situation. Summary of the Invention

[0004] To overcome the problems existing in the prior art, the present invention aims to provide a method for simulating the flow and circulation of fuel spheres in a pebble bed high-temperature gas-cooled reactor. In simulating high-temperature gas-cooled reactors, the present invention simulates the flow and circulation of fuel within the reactor core. First, a sphere flow simulation program is used to divide the fuel sphere flow into multiple streamline chains, determining the flow rate of each streamline chain. Then, based on the reactor core structure, a sphere flow grid is divided within the fuel sphere flow range. After overlapping the streamline chains and the grid, the grids traversed by the streamline chains are marked. When the reactor core circulates fuel, starting from the bottom, the proportion of fuel spheres in each grid originating from the preceding grid is calculated based on the flow velocity and grid width. The fuel sphere composition is obtained layer by layer upwards, thus simulating the fuel sphere flow for subsequent physical and thermal calculations of the pebble bed high-temperature gas-cooled reactor.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for simulating fuel sphere flow and circulation in a pebble bed type high-temperature gas-cooled reactor includes the following steps:

[0007] Step 1: Model the core structure in discrete element particle simulation software and simulate the flow of fuel spheres. Based on the simulation results, divide the core model into multiple streamline chains and determine the flow velocity of each streamline chain.

[0008] Step 2: Based on the actual core structure of the pebble bed high-temperature gas-cooled reactor, divide the core model into axial and radial grids, overlap the streamline chains and grids, and mark the grids through which the streamline chains pass.

[0009] Step 3: The previous marked grid of each marked grid on the streamline chain is called the predecessor grid of that grid. Calculate the proportion of fuel balls in each grid that originate from its predecessor grid, according to formula (1).

[0010]

[0011] In the formula:

[0012] d—Target grid;

[0013] a — a predecessor mesh of the target mesh d;

[0014] v a —The velocity of the streamline chain containing grid a;

[0015] d a — Width of grid a;

[0016] n — all predecessor grids of grid a;

[0017] i — the i-th predecessor grid of grid a;

[0018] Step 4: When the fuel balls inside the reactor core are undergoing fuel circulation, the fuel balls in the bottom grid of the reactor core are discharged, and the grids from which the discharged fuel balls are discharged are filled with fuel balls from the preceding grids according to the proportion of fuel balls sourced from that grid;

[0019] Step 5: Starting from the bottom of the reactor core, proceed upwards layer by layer to fill the fuel spheres within the grid until the top layer is reached, realizing the simulation of fuel sphere flow and circulation for subsequent physical and thermal calculations.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] In this invention, the reactor core is divided into streamline chains and grids, and the leading grids on the streamline chains are determined. The process is carried out by advancing layer by layer from bottom to top to simulate the fuel flow and refueling of the high-temperature gas-cooled reactor. This method simulates the differential velocity and mixing of fuel flow, making the fuel flow simulation closer to the real spherical flow and improving the simulation accuracy. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the overall process of simulating the flow and circulation of fuel spheres in a pebble bed type high-temperature gas-cooled reactor, as described in this invention.

[0023] Figure 2 A schematic diagram illustrating the streamline chain division of a pebble bed type high-temperature gas-cooled reactor.

[0024] Figure 3 This is a schematic diagram showing the overlap of streamline chains and grids in a pebble bed type high-temperature gas-cooled reactor.

[0025] Figure 4 This is a schematic diagram showing the material sources and precursor meshes in the mesh. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0027] This invention relates to a method for simulating the flow and circulation of fuel spheres in a pebble bed high-temperature gas-cooled reactor. In high-temperature gas-cooled reactor simulations, the flow of fuel spheres within the reactor core is random, and due to the presence of the bottom cone, differential flow and mixing phenomena occur. This invention first uses discrete element method (DEM) software (e.g., EDEM) to divide the fuel sphere flow into multiple streamline chains, determining the mobility of each streamline chain. Then, based on the reactor core structure, a sphere flow grid is divided within the fuel sphere flow range. After overlapping the streamline chains and the grid, the grids traversed by the streamline chains are marked. When the reactor core circulates fuel, starting from the bottom, the proportion of fuel spheres originating from the preceding grid is calculated based on the flow velocity and grid width. The fuel sphere composition is obtained layer by layer upwards, thus simulating the fuel sphere flow for subsequent physical and thermal calculations of the pebble bed high-temperature gas-cooled reactor.

[0028] like Figure 1 As shown, the method specifically includes the following steps:

[0029] Step 1: Model the core structure in the sphere flow simulation program and simulate the flow of fuel spheres. Based on the simulation results, such as... Figure 2 In the core model, multiple streamline chains are divided, and the flow velocity of each streamline chain is determined;

[0030] Step 2: Based on the actual core structure of the pebble bed high-temperature gas-cooled reactor, the core model is meshed axially and radially, such as... Figure 3 Overlay the streamline chain and the mesh, and mark the mesh that the streamline chain passes through;

[0031] Step 3: The previous marked mesh on each marked mesh in the streamline chain is called the predecessor mesh of that mesh, such as... Figure 4 The proportion of fuel spheres in computational grid D that originate from its predecessor grid A;

[0032] The following formula is used to calculate the proportion of fuel spheres in grid D originating from grid A:

[0033]

[0034] In the formula:

[0035] d—Target grid;

[0036] a, b, c — the precursor meshes a, b, c of the target mesh d;

[0037] v a v b v c —The velocity of the streamline chains containing the preceding meshes a, b, and c;

[0038] d a d b d c —The width of the preceding meshes a, b, and c;

[0039] Step 4: When the fuel balls inside the reactor core are undergoing fuel circulation, the fuel balls in the bottom grid of the reactor core are discharged, and the grids from which the discharged fuel balls are discharged are filled with fuel balls from the preceding grids according to the proportion of fuel balls sourced from that grid.

[0040] Step 5: Starting from the bottom of the reactor core, proceed upwards layer by layer to fill the fuel spheres within the grid until the top layer is reached, realizing the simulation of fuel sphere flow and circulation for subsequent physical and thermal calculations.

[0041] The method of this invention divides the flow of fuel balls in the reactor core into flow channels and grids, and obtains the flow of fuel balls through parameters such as velocity, thereby simulating the flow of fuel balls in the reactor core and realizing the simulation of the flow and circulation of fuel balls in the reactor core for subsequent physical and thermal calculations. This invention changes the traditional laminar step-flow simulation method of high-temperature gas-cooled reactor balls and realizes the simulation of fuel circulation in high-temperature gas-cooled reactors.

[0042] The ingenuity of this invention lies in the fact that the method of this invention divides the reactor core into streamline chains and grids, and determines the leading grids on the streamline chains. It adopts a bottom-up, layer-by-layer approach to simulate the fuel flow and refueling of the high-temperature gas-cooled reactor, thereby simulating the differential velocity and mixing of fuel flow. This makes the fuel flow simulation closer to the real spherical flow situation and improves the simulation accuracy.

Claims

1. A method for simulating the flow and circulation of fuel spheres in a pebble bed type high-temperature gas-cooled reactor, characterized in that: Includes the following steps: Step 1: Model the core structure in discrete element particle simulation software and simulate the flow of fuel spheres. Based on the simulation results, divide the core model into multiple streamline chains and determine the flow velocity of each streamline chain. Step 2: Based on the actual core structure of the pebble bed high-temperature gas-cooled reactor, divide the core model into axial and radial grids, overlap the streamline chains and grids, and mark the grids through which the streamline chains pass. Step 3: The previous marked grid of each marked grid on the streamline chain is called the predecessor grid of that grid, and the proportion of fuel balls in each grid originating from its predecessor grid is calculated; Step 4: When the fuel balls inside the reactor core are undergoing fuel circulation, the fuel balls in the bottom grid of the reactor core are discharged, and the grids from which the discharged fuel balls are discharged are filled with fuel balls from the preceding grids according to the proportion of fuel balls sourced from that grid; Step 5: Starting from the bottom of the reactor core, proceed upwards layer by layer to fill the fuel spheres within the grid until the top layer is reached, thus simulating the flow and circulation of the fuel spheres. Calculate the proportion of fuel spheres in each grid that originate from their predecessor grid, according to formula (1); (1) In the formula: d — Target grid; a ——Target grid d A precursor grid; — The velocity of the streamline chain containing grid a; — Width of grid a; n — Grid a All precursor meshes; i — Grid a The i A precursor grid.

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