JP4021519B2 - Method for supplying fuel to the reactor core - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to fuel bundle management in a nuclear reactor core, and more particularly to a method for managing fuel loading in a nuclear reactor core, the average exposure burnout per bundle compared to conventional designs. ), Increase thermal margins, reduce downtime work, reduce net purchases of fuel bundles purchased over the life of the reactor core, and thereby reduce reprocessing costs. The present invention also reduces the spectral mismatch between each fuel bundle.
[0002]
[Prior art]
In boiling water reactors and pressurized water reactors, the initial core load is conventionally formed of several batches of fuel, ie several groups of fuel bundles, each group operating over a different number of cycles. Thus, a certain percentage of fuel bundles for initial core loading are designed to satisfy a single operating cycle, and at the end of that single operating cycle, these particular fuel bundles It is removed from the core and reprocessed. Other groups of fuel bundles are designed to operate through two or more cycles, and at the end of each cycle, these groups are removed or relocated within the core. Needless to say, the removed group is reprocessed. Thus, the fissile loading of a group of fuel bundles has traditionally been set to meet its inherent residence time in the core, ie 1 cycle, 2 cycles, etc. The average fissile material loading is determined to satisfy the cycle length.
[0003]
[Problems to be solved by the invention]
However, the group of fuel bundles that have been removed after the first operation cycle conventionally stays in the core for a relatively short period of time, for example, about one year. This group of fuels has not generated enough energy and therefore has a lower burnup than other fuel bundles that stay in the core over further cycles. In this way, the average energy generated per unit mass of fuel bundles removed after the first conventional cycle is less than in other fuel bundle groups that stay in the core over further cycles. Also, as a result of the low removal burn-up of the group of fuel bundles that are removed at the end of the initial cycle, the power generation cost is on average higher for this initial core fuel than for the reload fuel. This is due in part to the relatively constant degree of expense associated with reprocessing the fuel removed from the reactor core. Fuel reprocessing costs per bundle are relatively constant and are substantially independent of residence time in the core. For fuel bundles that were previously removed from the initial core load after the first cycle, the reprocessing cost of those fuels is substantially the same as the cost of reprocessing the fuel used across multiple cycles. It is. Thus, the average cost per unit of power for reprocessing fuel bundles that are removed after the first cycle is substantially higher than the cost of the remaining fuel bundles. That is, for fuel bundles removed from the initial core load after the first cycle, the average cost per unit power generation, including initial purchase and reprocessing costs, is the average cost for fuel bundles used in multiple cycles. Substantially higher.
[0004]
In the conventional nuclear reactor fuel management system, the initial core is loaded with fuel bundles only in a part thereof, and the remaining fuel bundle positions in the core are plugged. After completion of the second cycle, the plug is removed, the fuel bundle in the core is repositioned, and the remaining position is filled with replacement loaded fuel. However, this method increases the power density of the core and increases nuclear waste such as plugs.
[0005]
Furthermore, in conventional nuclear fuel core management, the initial fuel loading pattern is the same for replacement loading, but low, medium and high enriched fuel bundles are placed at various locations in the core. is doing. Considerable consideration has been given to their placement in the core, but if low and medium enrichment fuel bundles are placed adjacent to high enrichment fuel bundles, the spectrum There was a problem of spectral mismatch. For example, if a low enrichment fuel bundle is located adjacent to a high enrichment fuel bundle and a neutron leaks into the high enrichment bundle, the output of the high enrichment bundle increases, Undesirable output peaking occurs. In standard fuel core loading, the fuel rods that are most exposed to this increased thermal neutron flux are marginal fuel rods adjacent to any low or medium enrichment bundle. Typically, a high enrichment fuel bundle is surrounded by low or medium enrichment fuel bundles on all four sides, so that the edges located on all four sides of each high enrichment bundle are The fuel rods are operated at high power, while the fuel rods inside the high enrichment bundle are constrained in power. Thus, the fuel rods inside the high enrichment bundle are essentially shielded from the increased thermal neutron flux, but the fuel rods at the edges of the high enrichment bundle were severely affected. This is also detrimental to meet thermal limit criteria for highly enriched fuel rods along the bundle edge. With a standard core design, it was difficult to solve this spectral mismatch problem.
[Patent Document 1]
JP 07-270562 A
[Patent Document 2]
JP 07-234293 A
[Patent Document 3]
JP 05-209980
[0006]
[Means for Solving the Problems]
In accordance with the present invention, a method of reactor core fuel management is provided that allows the core to be fully loaded at the beginning of the initial cycle without removing or relocating the fuel bundle. In addition, the operation can be performed through at least the end of the second cycle. The method of the present invention also reduces the number of outages, improves overall plant capacity, and substantially reduces overall costs over the life of the reactor. To achieve this, the reactor core is initially fully loaded with a fuel bundle having a fissile material loading commensurate with the core residence time of two or more cycles. That is, the average enrichment of the initial core charge is determined to support more than one cycle of operation, i.e., at least two cycles of operation, and the specific fuel design for that operation is determined. In this way, the fissionable material inventory in the initial core can operate in two or more cycles without having to load and reposition fuel between the first and second cycles. It will be like that. This extends the average residence time of the fuel in the initial core, and in response, the burn-up burnup of the initial core is the same as that for conventional loading that required partial replacement loading at the end of the first cycle. Increased in comparison with the burnout degree of the core. This also saves many in-container operations during the first scheduled outage.
[0007]
By using the core management method described above, the overall net operating cost is substantially reduced. The cost of initial core loading is increased because the enrichment has been increased due to the need to allow operation over two or more cycles without having to replace the fuel between the first and second cycles. Although increased, the reprocessing costs are reduced net because the required mass of uranium is reduced. For example, in a conventional core design, if approximately 800 fuel bundles are initially loaded into the core, typically 150 bundles are at the end of the first cycle depending on cycle length, enrichment, etc. Can be taken out. An additional 150 bundles with fresh fuel are then loaded into the core at the end of the first cycle. However, the reprocessing cost is a function of the fuel mass required for reactor operation over the life of the reactor. Thus, in a conventional core management design, the first 150 bundles removed after the first cycle must be reprocessed at a substantially constant cost per bundle. Reprocessing costs are also incurred after each cycle until equilibrium is reached. However, according to the core management design of the present invention, the fuel stays in the core through at least the second cycle, so there is no reprocessing cost at the end of the first cycle. Thus, reprocessing costs are reduced by the number of fuel bundles that would have been reprocessed if they were removed at the end of the first cycle as in the conventional design. This truncation of reprocessing costs additional expense for fuels with higher enrichment required for initial core loading to operate beyond the initial cycle, so the truncation is offset to some extent. However, the overall cost per unit generated energy is reduced. That is, the cost of the initial core fuel is high because higher initial enrichment levels are used, but the overall fuel cost, including initial fuel purchase and reprocessing costs, is substantially reduced.
[0008]
When creating a standard multi-enrichment initial core design, optimizing the core design for thermal limits, as changing the loading pattern can lead to new problems related to spectral mismatches It is difficult. The present invention also employs a control cell core system in which high enrichment fuel bundles and low enrichment fuel bundles are specifically arranged with respect to each other, which can potentially cause spectral mismatch. Potential locations within the core can be identified, and their location is limited to only one side of each high enrichment fuel bundle adjacent to a low enrichment fuel bundle. Once identified, the high enrichment bundle can be specially designed to minimize or eliminate spectral mismatches, thereby improving core performance. For this improved design scheme, the fuel rods affected by the spectral mismatch are always the same, and the bundle contents can be designed to optimize the thermal margin.
[0009]
In conventional control cell core systems, shim control rod movement is limited to a certain group of control rods surrounded by a low enrichment bundle. Each of the cross-shaped control rods and the four fuel bundles surrounding it constitute one control cell. The control cell core method suppresses the peaking of output, increases the thermal margin, and suppresses the tendency of pellet-coating interaction. Generally speaking, the reactor operating cycle is thus only controlled by the control rods of the control cell. Non-cotrol cells are typically withdrawn during operation. In accordance with the present invention, a low enrichment fuel bundle is disposed in the control cell, while all non-control cells except the peripheral bundle in which the low enrichment bundle is disposed have a high enrichment. A enrichment fuel bundle is disposed. It will be appreciated that by configuring the core in this manner, the control cells are separated from each other by at least one non-control cell. Further, the high enrichment fuel bundle of the non-control cell in the core is arranged so that only one side thereof is adjacent to the side of the low enrichment fuel bundle of the control cell. Therefore, the locations that could potentially cause a spectral mismatch in the core are the above-mentioned sides of the high-concentration bundle that are located on the sides or edges of the control cell low-concentration bundle. Is identified at an early stage. As a result, the number of bundles and the number of fuel rods within these bundles that are susceptible to problems associated with spectral mismatches are significantly reduced. That is, for high-concentration bundles adjacent to the low-concentration bundle of the control cell, conventionally two or more sides of this high-concentration bundle typically have high power as a result of increased neutron flux. Only one side has experienced the place that was experiencing.
[0010]
In addition, identifying the enrichment bundle edge that is prone to spectral mismatch in the core design reduces or eliminates the enrichment of individual fuel rods along that edge of the enrichment bundle. Selectively, while the enrichment of the remaining fuel rods in the bundle can be maintained at a relatively high enrichment level. That is, in each high enrichment fuel bundle having an edge adjacent to the low enrichment bundle that would otherwise have caused a spectral mismatch problem, By selectively reducing the degree of power, the effects of spectral mismatch in high-power generating fuel rods are minimized, while at the same time the enrichment of the fuel bundle is reduced to a level typical for fuel core loading, especially initial core loading. Can be maintained at a higher level. Thus, by identifying the location within the core where the spectral mismatch occurs and modifying the high enrichment fuel bundle adjacent to the low enrichment fuel bundle, the initial core load has on average higher enrichment, It is possible to operate without refueling after the first cycle.
[0011]
In a preferred embodiment according to the present invention, a method is provided for supplying fuel to a nuclear reactor core having a plurality of nuclear fuel cycles that exceeds the initial cycle without replacing and loading nuclear fuel at the end of the initial cycle. In order to assist in operating the reactor core over time, a step is provided for increasing the enrichment on average to the fuel bundles involved in the initial core fuel loading.
[0012]
In a further preferred embodiment according to the invention, a method is provided for supplying fuel to a reactor core having a plurality of nuclear fuel bundles, the method comprising a control cell and a non-control cell in the reactor core. Forming a control cell such that the control cells are separated from each other by at least one non-control cell, and disposing a fuel bundle of low overall enrichment in the control cell; Disposing an overall highly enriched fuel bundle in the non-control cell to substantially avoid spectral mismatches between the fuel bundles in the non-control cell; Only one side of the higher enrichment bundle is located adjacent to the side of the lower enrichment fuel bundle in the control cell Sea urchin, and a step of arranging adjacent the control cells and uncontrolled cell in the core.
[0013]
Accordingly, it is a primary object of the present invention to provide a new and improved method for reactor core bundle management, which increases the average burnup per bundle and increases thermal Improve margins, reduce downtime, reduce the amount of fuel bundles purchased over the life of the reactor core, reduce reprocessing costs, and minimize spectral mismatches between fuel bundles Or eliminated.
[0014]
【Example】
Referring now to the drawings, and specifically to FIG. 1, a nuclear reactor is schematically shown in FIG. The nuclear reactor 10 has a plurality of fuel bundles 12 arranged in its core. The fuel bundles 12 are all contained in a nuclear reactor vessel 14 having a detachable head (head) 16. ing. In accordance with the present invention, FIG. 1 (A) shows an initial fuel loaded nuclear reactor core, each fuel bundle having a nuclear fuel material loading corresponding to the core residence time of two or more cycles. have. Thus, the average enrichment of the initial core loading is to operate for at least two cycles or more without having to reload and reposition fuel between the first and second cycles. I support. The end of the first operating cycle is shown in FIG. 1B, where the container head has not been removed. However, as shown, none of the fuel bundles have been repositioned or loaded. FIG. 1 (C) shows the reactor at the end of the second or subsequent cycle, where the fuel bundle has been removed and a new fuel bundle used in the subsequent cycle is in the core. It is loaded.
[0015]
As a result of this configuration, higher enrichment results from the need to operate over two or more cycles, resulting in higher initial fuel loading costs but reduced uranium mass. Processing costs are reduced as a net. That is, the fuel stays in the reactor through the second cycle or further cycles, so there is no reprocessing cost at the end of the first cycle. Thus, the initial core loading is increased in enrichment on average to assist in operating the reactor core for a period beyond the initial cycle without replacing the nuclear fuel at the end of the initial cycle. For the purposes of definition, a “cycle” is the length of time between scheduled sequential shutdowns during the life of the reactor, Included refueling.
[0016]
Turning now to FIG. 2, the conventional multi-enrichment loading pattern is shown for a quarter section of the reactor core. The numbers along the vertical and horizontal axes define the position of the bundle within the core. For purposes of this drawing, the letter C indicates a control cell, the letter N indicates a non-control cell, and the fuel bundle numbered 1 indicates a peripheral fuel bundle. In addition, the number immediately following the letter C and letter N corresponds to the average enrichment level of the fuel bundle at the position where the number is shown. Accordingly, the numbers 2, 3, 4 and 5 indicate the low enrichment, intermediate enrichment, high enrichment / high gadolinium and high enrichment / low gadolinium fuel bundles, respectively. The number 1 indicates a peripheral fuel bundle having an average low enrichment. The diagonal lines in the drawing show the fuel bundles affected by the spectral mismatch in this conventional core loading. A typical example of enrichment for fuel bundles numbered 1-5 is as follows. “1” = 0.71, “2” = 1.2, “3” = 2.2, “4” = 3.7, “5” = 3.7. The enrichment ranges for the fuel bundles numbered 1-5 are typically as follows. "1" is 0.71 to 1.2, "2" is 1.00 to 1.5, "3" is 2.0 to 2.5, "4" and "5" In the case, it is 3.5 to 4.0.
[0017]
As can be seen by examining the core shown in FIG. 2, a significant number of high enrichment fuel bundles numbered 4 and 5 have sides adjacent to the low enrichment bundle. For example, the high enrichment bundle labeled N4 shown on the horizontal axis 14 and the vertical axis 8 is adjacent to the medium enrichment or low enrichment fuel bundle on all four sides at the edges. Therefore, the fuel bundle N4 in this position is subject to a spectral mismatch, that is, a spectral mismatch in which the neutron leakage from the adjacent low enrichment bundle is increased, resulting in a higher output, and reaches the critical thermal limit. There is a fear. Thus, the conventional core pattern shown in FIG. 2 has a considerable number of fuel bundles that suffer from spectral mismatches.
[0018]
According to the conventional control cell system, a low-concentration fuel bundle is disposed in the control cell, and these are consistently designated as C2 in FIG. The cross-shaped control rods that separate the four low enrichment bundles C2 within each control cell serve as reactor control rods. Control rods attached to non-control cells are typically pulled out during operation.
[0019]
As can be seen with reference to FIG. 3, in a conventional core in which a high enrichment fuel bundle (H) and a medium enrichment fuel bundle (M) are mixed in a non-control cell, a considerable number in the non-control cell. Of high enrichment bundles experience spectral mismatches. Thus, as can be seen in FIG. 3, for example, at the positions where (horizontal axis, vertical axis) are (12, 14), respectively, the high enrichment bundle has a lower enrichment bundle (L) on all four sides And (M), so the fuel rods located along each of the four sides or edges of this high enrichment bundle are subject to a spectral mismatch. Similarly, the high enrichment bundle located at (13,15) also suffers a spectral mismatch on its four sides. Similarly, high-concentration bundles other than those shown in FIG. 3 are also subject to spectral mismatches on all four sides. Therefore, output peaking problems occur in these highly concentrated bundles.
[0020]
Referring now to FIG. 4, a core configuration according to the present invention is shown. As can be seen in the figure, the control cell is provided with a low concentration bundle, and the non-control cells are provided with a high concentration bundle except for the surrounding cells. The latter is either a high enrichment / low gadolinium type bundle or a high enrichment / high gadolinium type bundle. All peripheral bundles numbered 1 are of low enrichment. In this configuration, because of their location adjacent to the low enrichment bundle at the edge, the number of high enrichment fuel bundles that experience spectral mismatch is substantially reduced to the number shown in FIG. It is about one third of. Also, highly enriched fuel bundles that experience spectral mismatch are clearly identified between each control cell along the horizontal and vertical axes of the core coordinate system. Furthermore, it should be noted that in the conventional configuration, the high-concentration bundle often suffers a spectral mismatch on four sides, but using the above configuration, only one side of the high-concentration bundle causes a spectral mismatch. I don't receive it. Thus, at positions (12, 13), (12, 14), (13, 15) and (14, 15), the fuel rod located on the side adjacent to the bundle of low enrichment control cells is It becomes easy to get a mismatch. There are no highly enriched fuel bundles in an uncontrolled cell where all four sides suffer from a spectral mismatch.
[0021]
Since the edges of the non-control cell that are subject to a spectral mismatch have been identified, according to the present invention, fuel rods in a high enrichment bundle adjacent to the low enrichment bundle at the edge, wherein the spectral mismatch is The enrichment of the fuel rods received can be reduced while at the same time the enrichment level of the high enrichment fuel bundle can be maintained at a high level. In this way, both the power peaking problem and the critical thermal limit problem are avoided, while at the same time the enrichment of the fuel bundle is maintained at a high level, and this high level of enrichment rearranges the fuel. A sufficient fissile material inventory can be provided for the initial core loading sufficient to operate over two or more cycles without having to be loaded or replaced.
[0022]
For example, if a high enrichment fuel bundle and the edges of the fuel bundle are identified as having fuel rods that undergo spectral mismatch, reducing the fuel enrichment of these fuel rods. Can do. For example, when a 9 × 9 fuel rod array is provided in the high enrichment bundle, the first and last fuel rods adjacent to the lower enrichment bundle in pairs The enrichment of the set can be reduced. For example, the enrichment of such fuel rods can be reduced by 15% to 20%, thereby reducing the power peaking problem along its edges. In order to maintain symmetry, adjacent one side is also composed of fuel rods having similar enrichment along the same side, and the fuel bundle is along the diagonal of the bundle, for example, from the upper left to the lower right of the drawing. Try to be symmetric.
[0023]
Refer to FIGS. 6 and 7 as representative examples. FIG. 6 shows the conventional fissile material loading for high enrichment / high gadolinium in a typical initial core. Note in particular the loading of fuel rods 1, 2 and 3. In FIG. 7, the high enrichment / high gadolinium fuel bundle at the same location in the core has a fissile material loading different from that shown in FIG. Specifically, the fissile material loading of the fuel rods bordering the low enrichment fuel bundle in the control cell will mitigate spectral mismatches that would otherwise have occurred. Has been reduced. Compare the fissile material loadings of fuel rods 1A, 2A and 3A with the loadings of fuel rods 1, 2 and 3 of FIG. These fuel rods 1A, 2A and 3A with reduced enrichment reduce or eliminate spectral mismatches, while maintaining the fuel bundle with a high overall enrichment and within the core. Maintain a sufficient fissile material inventory to provide reactivity for at least the initial operating cycle and one subsequent operating cycle.
[0024]
Although the invention has been described in connection with what is considered to be the most practical and preferred embodiment at the present time, the invention is not limited to the embodiment disclosed herein, and conversely, patents It should be understood that it covers various modifications and equivalent arrangements included in the gist of the claims.
[Brief description of the drawings]
FIG. 1 (A) -FIG. 1 (C) are schematic illustrations of a nuclear reactor operating over a number of cycles.
FIG. 2 is a schematic diagram showing a quarter of a nuclear reactor core, showing fuel bundle loading according to a conventional core loading design.
FIG. 3 is a schematic view of a portion of the core shown in FIG. 2, showing a spectral mismatch between the fuel bundles of FIG.
4 is a view similar to FIG. 2, showing a core constructed in accordance with the present invention.
5 is a view similar to FIG. 3 and showing a part of the core of FIG. 4;
FIG. 6 is a schematic view showing a fissile material loading of a fuel bundle for a conventional fuel bundle.
FIG. 7 is a schematic diagram showing the fissile material loading of a fuel bundle for a fuel bundle of the present invention that avoids spectral mismatch.
[Explanation of symbols]
10 Reactor
12 Fuel bundle
14 Reactor vessel
16 heads

Claims (10)

A method of supplying fuel to a nuclear reactor core having a plurality of nuclear fuel bundles,
Forming a pattern of control cells and non-control cells in the reactor core such that the control cells are separated from each other by at least one non-control cell;
Providing an overall low enrichment fuel bundle in the control cell;
Providing an overall high enrichment fuel bundle in the non-control cell to substantially avoid spectral mismatches between fuel bundles in the non-control cell;
The control cell and the non-control cell are placed in the core so that only one side of the high enrichment bundle in the non-control cell is located adjacent to the side of the low enrichment fuel bundle in the control cell. And arranging the cells adjacent to each other,
Each fuel bundle has a rectangular matrix of fuel rod arrays, each high enrichment in a non-control cell adjacent to one side of a low enrichment fuel bundle in an adjacent control cell. The enrichment of at least some of the fuel rods along the first side of the fuel bundle at a degree to the enrichment of the fuel rods along opposite sides of the high enrichment fuel bundle in the non-control cell. A method of supplying fuel to a nuclear reactor core that is reduced in comparison to minimize power peaking of the fuel rod along the first side due to spectral mismatch .   In the core, only two sides of each low enrichment fuel bundle in the control cell are located adjacent to each side of the high enrichment fuel bundle in the adjacent non-control cell. The method of supplying fuel to a nuclear reactor core according to claim 1, comprising the step of placing a control cell and a non-control cell adjacent to each other. Providing different fuel rod enrichments to several fuel rods in the high enrichment fuel bundle, and the fuel so that the high enrichment fuel bundle is symmetric about a diagonal of the fuel bundle. the method for supplying fuel to the reactor core according to claim 1, and a step of increasing the concentration of the bar. The nuclear reactor core has a plurality of nuclear fuel cycles and is configured to assist in operating the nuclear reactor core for a period exceeding the initial cycle without replacing nuclear fuel at the end of the initial cycle. The method of supplying fuel to a nuclear reactor core as recited in claim 1 , wherein the enrichment is provided on average to high enrichment fuel bundles involved in core fuel loading. Increasing the enrichment of the fuel bundles associated with the initial core fuel loading on average to assist in operating the reactor core for a period beyond the initial cycle without replacing nuclear fuel at the end of the initial cycle The method for supplying fuel to the reactor core according to claim 1, further comprising : 6. The method of supplying fuel to a nuclear reactor core according to claim 5 , comprising maintaining the fuel bundle in the core without rearranging the fuel bundle at the end of the initial cycle. The method of supplying fuel to a nuclear reactor core according to claim 6 , comprising supplying a fuel bundle for replacement loading at the end of one cycle following the initial cycle. A method of supplying a plurality of fuels to a nuclear reactor core having a plurality of nuclear fuel cycles in a vertical and horizontal grid arrangement,
Providing a plurality of control cells in the core;
Providing a first fuel bundle having fuel with a first average enrichment in both the control cell and the periphery of the core;
Providing a second fuel bundle having a second average enrichment in the remainder of the core of the lattice ,
The method for supplying fuel to the nuclear reactor core according to claim 5 , wherein the second fuel bundle has an average enrichment higher than an average enrichment of the first fuel bundle.   6. A method for supplying fuel to a nuclear reactor core according to claim 1 or 5, wherein the method is performed in a boiling water reactor.   6. A method for supplying fuel to a nuclear reactor core according to claim 1 or 5, wherein the method is performed in a pressurized water reactor.

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