Simulation method for charging of pebble bed reactor

Abstract

The application relates to a simulation calculation method of a ball bed reactor, which comprises the following steps: dividing a whole ball bed area (10) of the ball bed reactor into a plurality of ball flow grids (60), each flow channel being divided into a plurality of layers (50) in the axial direction of the ball bed reactor, each layer of each flow channel having one ball flow grid, the batch number (M) of fuel balls in each ball flow grid being less than or equal to the number of fuel balls in the ball flow grid, and the batch number (M) of fuel balls in the ball flow grid of each flow channel being set according to the volume proportion of the ball flow grid of each flow channel; after each fuel loading time step, all fuel balls move down by one layer into the next layer ball flow grid along the flow channel and fuel consumption calculation is performed; fuel balls unloaded from the bottom of the reactor core are reloaded into each flow channel at the top of the reactor core in a random sampling manner according to the volume proportion of the ball flow grid of each flow channel, and before being reloaded into each flow channel, a part of the fuel balls unloaded from the bottom of the reactor core are replaced by new fuel balls according to the fuel consumption calculation result.

Description

Technical Field

[0001] This invention relates to a nuclear reactor physics calculation method, and more particularly to a simulation calculation method for pebble bed reactors, especially for high-temperature gas-cooled reactors. Background Technology

[0002] In a pebble bed high-temperature gas-cooled reactor, fuel spheres discharged from the bottom of the flow channel are poured back into the top of the core for the next fuel cycle. Before being poured back into the top of the core, the spent fuel in these fuel spheres that have reached the target burnup depth is discarded and replaced with new fuel spheres.

[0003] In burnup calculations for pressurized water reactors and most other types of reactors, the burnup history of fuel elements is deterministic, and the accuracy of theoretical calculations can be verified by measuring the nuclide density of spent fuel. However, for pebble-bed high-temperature gas-cooled reactors, the trajectory and burnup history of any fuel sphere within the reactor core are random, making it theoretically impossible to "accurately" predict the nuclide density of spent fuel. Therefore, the verification of burnup calculations for pebble-bed high-temperature gas-cooled reactors is not based on a comparison between specific calculated and experimental values, but rather on a comparison based on probability distributions or statistical significance.

[0004] To simulate the material dumping process of a pebble bed high-temperature gas-cooled reactor, existing deterministic physics calculation software, such as PANGU and VSOP, employs a combination of methods described below. Figures 1 to 3 The aforementioned material pouring calculation model.

[0005] like Figure 1 As shown, the entire pebble bed region is first divided radially into several channels, with channel boundaries that can be straight lines or curves. Each channel is then divided axially into several layers, resulting in several pebble flow grids of equal volume. The number of layers can vary between channels to simulate different pebble flow velocities. Within each pebble flow grid, the fuel spheres are divided into several batches, each batch containing the same material composition. The number of batches, N, is typically equal to the number of times the fuel spheres pass through.

[0006] like Figure 3As shown, at each refueling time step, all fuel balls move down one layer along the flow channel, entering the next layer of the spherical flow grid (the bottommost fuel balls are unloaded from the bottom of the flow channel), and burnup calculations are performed. The corresponding batches of fuel balls unloaded from the bottom of each flow channel are merged and averaged, meaning the nth batch in each flow channel is merged (1≤n≤N) and placed into one of the N independent spaces in the unloading staging box, ensuring that the unloaded fuel still has the same batch number N. Then, before the loading staging box (also with N independent spaces) receives these fuel balls, several batches undergo replacement and sorting operations, such as discarding the spent fuel with the deepest burnup and replacing it with new fuel. Finally, they are re-poured into the various flow channels at the top of the core, assuming that the spherical flow grid at the top of each flow channel has the same fuel ball composition, meaning each flow channel receives each batch of N batches of fuel balls. Here, the unloading staging box and the loading staging box are abstract concepts used to simulate the unloading and loading processes during the calculation.

[0007] In the above refueling model, batch N within the sphere flow grid represents fuel spheres with different burn-out depths, meaning the grid is assumed to contain N different types of fuel spheres with varying burn-out depths. However, the actual number of fuel spheres within the grid is far greater than the number of batches N, and using only N batches cannot accurately reflect the fine distribution of burn-out depths. Furthermore, the process of batch merging and averaging of fuel spheres discharged from the bottom of the reactor core, and the assumption that the sphere flow grids entering the top layer of each flow channel have the same fuel sphere composition, further smooths out the burn-out distribution information and fails to account for the randomness of the refueling process. Summary of the Invention

[0008] Therefore, based on the above-mentioned refueling model, this invention proposes a simulation calculation method for refueling in a pebble bed reactor. This simulation calculation method includes the following steps: dividing the entire pebble bed region of the pebble bed reactor into several pebble flow grids; wherein, the entire pebble bed region of the pebble bed reactor is divided into several channels radially in the pebble bed reactor; each channel is divided into several layers of equal volume axially in the pebble bed reactor; each layer of each channel has one pebble flow grid; wherein the number of batches of fuel spheres in each pebble flow grid is less than or equal to the number of spheres. The number of fuel balls in the flow grid and the batch number (M) of fuel balls in the flow grid of each channel are set according to the volume ratio of the flow grid of each channel; after each feeding time step, each fuel ball in each flow grid is moved down to other flow grids and burnup is calculated; fuel balls unloaded from the bottom of the core are randomly sampled and refilled into each flow channel at the top of the core according to the volume ratio of the flow grid of each channel. Before refilling into each flow channel, a portion of the fuel balls unloaded from the bottom of the core are replaced by new fuel balls according to the burnup calculation results.

[0009] Preferably, all fuel balls in each ball flow grid move down the flow channel to the ball flow grid below the current flow grid in that flow channel; or, alternatively or supplementarily, a portion of the fuel balls in each ball flow grid move down the flow channel to the current flow grid in that flow channel, while the remaining fuel balls move down to ball flow grids in adjacent flow channels. The second scenario is used to simulate the mixing of fuel balls from different flow channels.

[0010] Because the fuel balls discharged from the bottom of the reactor core are no longer subject to batch merging and averaging as in existing technologies, and after replacing some of the discharged spent fuel balls with new fuel balls based on burnup calculations, they are then randomly sampled and refilled into each channel according to the volume ratio of the fuel ball flow grid in each channel. Therefore, this method can fully simulate the randomness of the refilling process. Since the batch merging and averaging operation is eliminated, this invention allows different volumes of fuel ball flow grids in different channels, but still requires all fuel ball flow grids within the same channel to have the same volume. In this case, the number of batches for each channel's fuel ball flow grid is set according to the volume ratio of the fuel ball flow grid in each channel, and when the fuel balls reaching the bottom of the reactor core return to the top of the reactor core, a corresponding number of fuel balls are randomly sampled and refilled into each channel according to the volume ratio of the fuel ball flow grid in each channel.

[0011] For ease of description, it is preferred to assume that each ball flow grid in each channel of the pebble bed region, that is, all ball flow grids in the pebble bed region, has the same volume and therefore the same batch number. In this way, the fuel balls unloaded from the bottom of the core are randomly sampled and evenly distributed into each channel at the top of the core according to the volume ratio of the ball flow grids in each channel.

[0012] Meanwhile, since the number of batches (M) of fuel balls in each ball flow grid can be set to be greater than the maximum number of times any fuel ball in the entire ball bed region passes through the ball bed region, the number of batches of fuel balls can be used to reflect their actual burn-out depth distribution as much as possible, and retains the information of burn-out distribution in more detail than simply expressing the number of batches as the maximum number of times they pass through the ball bed region.

[0013] In a preferred embodiment of the simulation calculation method for pebble bed reactor refueling according to the present invention, the batch number (M) of the pebble flow grid is chosen to be sufficiently large to reflect the burnup distribution within the pebble flow grid as precisely as possible. For example, the batch number of the pebble flow grid is chosen to be greater than or equal to the number of fuel spheres with different non-repeating burnup depths within the pebble flow grid. Therefore, the batch number can at least reflect the distribution of different burnup depths within the pebble flow grid.

[0014] More preferably, the batch number of the ball flow grid is set to be equal to the actual number of fuel balls within the ball flow grid. This way, even if each fuel ball in the ball flow grid has a different burnup, the burnup distribution of these fuel balls can be accurately reflected in the batch number.

[0015] The random refueling model proposed in the simulation calculation method for pebble bed reactor refueling according to the present invention is applicable to any type of pebble bed reactor employing online refueling. Preferably, the pebble bed reactor in the simulation calculation method for pebble bed reactor refueling according to the present invention has a balanced core / in the initial loading setup process / in the transition process, realizing a full-process simulation of the pebble bed reactor. In another preferred embodiment of the simulation calculation method for pebble bed reactor refueling according to the present invention, some of the fuel spheres can be replaced with graphite spheres to, for example, simulate the initial loading setup process and the transition process of a pebble bed high-temperature gas-cooled reactor.

[0016] As one potential application area, the random refueling model proposed in the simulation calculation method for refueling in a pebble bed reactor according to the present invention can be used to support the verification of burnup calculations for pebble bed reactors. Through the new refueling model proposed in this invention, the random burnup history effect of a pebble bed reactor can be simulated with high fidelity, obtaining the probability distribution of the density of each nuclide. Based on this, a burnup calculation verification strategy suitable for pebble bed reactors can be developed. Preferably, the pebble bed reactor is a pebble bed high-temperature gas-cooled reactor. Attached Figure Description

[0017] Embodiments of the present invention are illustrated below with reference to the accompanying drawings. In the drawings:

[0018] Figure 1 This is a schematic diagram of the mesh generation for the pebble bed reactor feed model;

[0019] Figure 2 This is a schematic diagram of the mesh generation for a pebble bed reactor feed model (simulating flow channel mixing);

[0020] Figure 3 This is a schematic diagram of the existing pouring model;

[0021] Figure 4 This is a schematic diagram of the new random material pouring model proposed in this invention. Detailed Implementation

[0022] Figure 1 and Figure 2 The mesh generation method for the pebble bed reactor dumping model is illustrated schematically. Figure 1 In the diagram, the vertical direction of the paper represents the axial direction of the pebble bed region 10, and the horizontal direction represents the radial direction of the pebble bed region 10. A local material grid 70 is shown as a dashed line. The entire pebble bed region 10 of the pebble bed reactor is divided into several flow channels 40 in the radial direction of the pebble bed reactor. Therefore, in... Figure 1 and Figure 2 Each flow channel 40 extends approximately axially. Furthermore, each flow channel 40 is divided into several layers 50 along the axial direction of the pebble bed reactor, with each layer of each flow channel being a pebble flow grid 60. The pebble flow grids 60 in each flow channel 40 have equal volumes (but the number of pebble flow grids in each flow channel may differ, therefore the height of the pebble flow grids in each flow channel may differ along the axial direction, and thus they are not necessarily aligned in height; this is only schematically shown in the figure). Therefore, at each unloading time step, the number of fuel balls received from above and discharged downwards by each pebble flow grid 60 remains the same. As seen in the figure, adjacent channels i-1, i, i+1 have different degrees of curvature, and the layers k-1, k, k+1 of the pebble flow grids 60 within them do not completely coincide with the material grid 70. A batch of fuel balls j-1, j, j+1 is illustrated in one of the pebble flow grids 60 in the figure. Figure 1 and Figure 2 The different shades of color are used to indicate the different burn depths.

[0023] Figure 1 and Figure 2 The difference lies in the fact that it illustrates the different ways in which the fuel balls descend within the ball flow grid 60. Figure 1 In the illustrated implementation, all fuel balls in each ball flow grid 60 descend along their current flow path to the next layer of ball flow grid 60. Figure 2 In the embodiment shown, two sets of arrows indicate ball flow grids in each ball flow grid 60 where some fuel balls flow to adjacent other flow channels, and the ball flow grids of these other flow channels that receive fuel balls are located below the ball flow grid that emits fuel balls.

[0024] In the second embodiment of the present invention, taking the balanced core simulation process of the high-temperature gas-cooled reactor demonstration project HTR-PM as an example, the reactor core is fully loaded with 420,000 fuel balls. The core can be divided into 5 flow channels and 20 layers, i.e., 100 ball flow grids, with each ball flow grid containing 4,200 fuel balls. Here, the batch number M for each ball flow grid is set to 4,200.

[0025] Thus, at each unloading time step, all fuel balls move down one layer along the flow channel 40, entering the next layer of the fuel flow grid (the bottommost fuel balls are unloaded from the bottom of the flow channel), and fuel consumption is calculated. The fuel balls unloaded from the bottom of each flow channel are received by the unloading temporary storage box 20. The unloading temporary storage box 20 independently stores each batch of fuel balls from each flow channel. Figure 4As shown, with I flow channels and fuel balls in each channel divided into M batches, the unloading staging box 20 stores one batch of fuel balls from one flow channel in each of I x M independent spaces. Then, according to the pre-designed refueling strategy, it is determined whether the fuel balls in the I x M independent spaces of the unloading staging box 20 are replaced with new fuel balls or re-entered into the reactor core.

[0026] The loading storage box 30 also has 1×M independent spaces. During the refueling strategy described above, spent fuel in the 1×M independent spaces of the unloading storage box 20 is unloaded from the unloading storage box 20, and the fuel balls in the remaining independent spaces are respectively supplied to one of the 1×M independent spaces of the loading storage box 30. The remaining independent spaces of the loading storage box 30 are then filled with new fuel balls.

[0027] Then, the fuel balls in the 1 x M independent spaces of the fuel storage box 30 are randomly sampled and evenly distributed to the various flow channels at the top of the core, that is, the I flow channels randomly and evenly receive each of the M batches of fuel balls. In the balanced core simulation of the example high-temperature gas-cooled reactor demonstration project HTR-PM, each ball flow grid re-obtains 4200 batches of fuel balls at the top of the core (i.e., one fuel ball per batch).

[0028] In the second embodiment of the present invention, taking the initial reactor setup process of the high-temperature gas-cooled reactor demonstration project HTR-PM as an example, the initial core of HTR-PM is a mixed pellet bed composed of low-enrichment fuel pellets and graphite pellets. The specific simulation process is basically the same as the HTR-PM balanced core simulation steps described above, except that the refueling strategy is not to unload spent fuel and replace it with new fuel pellets based on the calculated burnup depth, but to replace the graphite pellets and low-enrichment fuel pellets with high-enrichment fuel pellets at the bottom of the core. These fuel pellets are randomly sampled and evenly distributed to each channel 40 at the top of the core.

[0029] The preferred embodiments of the present invention have been described above, but the spirit and scope of the present invention are not limited to the specific contents disclosed herein. Those skilled in the art can make many more implementations and applications based on the teachings of the present invention, including any combination of the various technical features of the above embodiments. These implementations and applications are all within the spirit and scope of the present invention. The spirit and scope of the present invention are not limited by the specific embodiments, but by the claims.

[0030] List of reference numerals

[0031] 10 ball court areas

[0032] 20 Unloading Temporary Storage Box

[0033] 30 Loading Temporary Storage Box

[0034] 40-channel

[0035] 50 floors

[0036] 60 spherical flow grid

[0037] 70 Material Mesh

Claims

1. A simulation calculation method for refueling in a pebble bed reactor, characterized in that, The simulation calculation method includes the following steps: The entire pebble bed region (10) of the pebble bed reactor is divided into several pebble flow grids (60), wherein the entire pebble bed region (10) of the pebble bed reactor is divided into several channels (40) in the radial direction of the pebble bed reactor, and each channel (40) is divided into several layers (50) of equal volume in the axial direction of the pebble bed reactor, and each layer of each channel (40) has one pebble flow grid (60), wherein the number of batches (M) of fuel balls in each pebble flow grid (60) is less than or equal to the number of fuel balls in that pebble flow grid (60), and the number of batches (M) of fuel balls in the pebble flow grid (60) of each channel is set according to the volume ratio of the pebble flow grid of each channel; After each feeding time step, each fuel ball in each ball flow grid (60) is moved down to other ball flow grids (60) and fuel consumption is calculated. The fuel balls unloaded from the bottom of the reactor core are randomly sampled and refilled into the top channels (40) of the reactor core according to the proportion of the ball flow grid volume of each channel. Before refilling into each channel (40), a portion of the fuel balls unloaded from the bottom of the reactor core are replaced by new fuel balls based on the burnup calculation results.

2. The simulation calculation method for pebble bed reactor refueling according to claim 1, characterized in that, All fuel balls in each ball flow grid (60) move down along the flow channel (40) to the ball flow grid (60) below the current ball flow grid (60) in the current flow channel (40), or a portion of the fuel balls in each ball flow grid (60) move down along the flow channel (40) to the ball flow grid (60) below the current ball flow grid (60) in the current flow channel (40) and the remaining fuel balls move down to the ball flow grid (60) of an adjacent other flow channel (40).

3. The simulation calculation method for pebble bed reactor refueling according to claim 1 or 2, characterized in that, Each ball flow grid (60) of each channel (40) in the ball bed region (10) has the same volume and batch number (M). The fuel balls unloaded from the bottom of the core are randomly sampled and evenly distributed into each channel (40) at the top of the core according to the volume ratio of the ball flow grid of each channel.

4. The simulation calculation method for pebble bed reactor refueling according to claim 3, characterized in that, The number of batches (M) of each ball flow grid (60) is equal to the actual number of fuel balls in the ball flow grid (60).

5. The simulation calculation method for pebble bed reactor refueling according to claim 1 or 2, characterized in that, The pebble bed reactor employs online refueling.

6. The simulation calculation method for pebble bed reactor refueling according to claim 5, characterized in that, The pebble bed reactor is a pebble bed high-temperature gas-cooled reactor, which is in the initial build-up process, transition process, or equilibrium core state.

7. The simulation calculation method for pebble bed reactor refueling according to claim 1 or 2, characterized in that, Some of the fuel balls were replaced with graphite balls.

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