JPH1062576A - Method for supplying reactor core with fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for supplying reactor core with fuel which is capable of increasing average take-out burnup per bundle, improving thermal margin, reducing work during shut down, reducing the amount of fuel bundle purchased for whole life of the reactor core and reprocessing cost and minimizing or eliminating the spectrum mismatch between fuel bundles. SOLUTION: Before shuffling of fuel bundles or refueling loading is required, fuel bundles having sufficient fissile material inventory for operating the core for full 2 cycles are supplied at initial loading of core. Low enrichment bundles are arranged in a control cells C and high enrichment bundles are arranged in non-control cells N so as to identify the side of high enrichment bundles suffering spectrum mismatch. As the results, fuel bundles are arranged so that the number of bundles encountering spectrum mismatch are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the management of fuel bundles in a nuclear reactor core, and more particularly, to a method of managing fuel loading in a nuclear reactor core. Average discharge burnup (discharge exposure)
To improve thermal margins, reduce downtime, reduce net fuel bundle purchase 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]

BACKGROUND OF THE INVENTION In boiling water reactors and pressurized water reactors, the initial core loading has traditionally been formed of several batches of fuel, i.e., several groups of fuel bundles, each group operating over a different number of cycles. Have been. Thus, a certain percentage of the fuel bundles for initial core loading are designed to fill 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 in the core. The removed group is, of course, reprocessed. Thus, the fissile loading of a group of fuel bundles is conventionally set to match its unique residence time in the core, ie, one cycle, two cycles, etc. The average fissile material loading has been determined to satisfy the cycle length.

[0003]

However, the group of fuel bundles which had been removed after the first operation cycle, has stayed 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 removal burn-up than other fuel bundles that remain in the core for additional cycles. Thus, the average energy generated per unit mass of fuel bundle removed after the first conventional cycle is less than other groups of fuel bundles staying in the core over additional cycles.
Also, as a result of the lower removal burn-up of the group of fuel bundles removed at the end of the initial cycle, the power generation costs are, on average, lower for this initial core fuel than for the replacement charge fuel (relo
ad fuel). This is due, in part, to a relatively constant cost associated with the reprocessing of fuel removed from the reactor core. The fuel reprocessing cost per bundle is relatively constant and substantially independent of residence time in the core. For fuel bundles that were conventionally removed from the initial core charge after the first cycle, the cost of reprocessing those fuels is substantially the same as the cost of reprocessing fuel used over multiple cycles. It is. Thus, the average cost per unit of power to reprocess the fuel bundles 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 loading after the first cycle, the average cost per unit generation, including initial purchase and reprocessing costs, is the average cost for fuel bundles used in multiple cycles. Substantially higher.

[0004] In the conventional fuel management system for a reactor core, the initial core only has a part loaded with the fuel bundle, and the remaining fuel bundle position in the core is plugged with a plug. After the completion of the second cycle, remove the plug,
The fuel bundle in the core is rearranged, and the remaining positions are replaced and filled with the loaded fuel. However, this method increases the power density of the core and increases nuclear waste such as plugs.

Further, in the conventional nuclear fuel core management, the loading pattern of the initial fuel loading is the same in the case of replacement loading, but the fuel bundles of low enrichment, medium enrichment, and high enrichment are variously packed in the core. Position. Considerable care has been taken in their placement within the reactor core, but where low and medium enrichment fuel bundles are located adjacent to high enrichment fuel bundles, spectral and There was a problem of a mismatch (spectral mismatch). For example, if a low-enrichment bundle is located adjacent to a high-enrichment bundle, and neutrons leak into the high-enrichment bundle, the output of the high-enrichment bundle will increase and these bundles will have: Undesirable output peaking occurs. In standard fuel core loading, the fuel rods most exposed to this increased thermal neutron flux are the marginal fuel rods adjacent to any low or medium enrichment bundles. Typically, the high enrichment fuel bundle is surrounded by low or medium enrichment fuel bundles on all four sides, so that the margins 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 throttled. Thus, while the fuel rods inside the high-enrichment bundle were essentially shielded from the increased thermal neutron flux, the fuel rods on the periphery of the high-enrichment bundle were severely affected. This is also detrimental to meeting thermal limits for high enrichment fuel rods along the bundle edge. It has been difficult to resolve this spectral mismatch problem with standard core designs.

[0006]

According to the present invention, there is provided a method of fuel management for a nuclear reactor core, which method allows a full loading of the core at the beginning of an initial cycle and provides a fuel bundle. Operation can be performed at least until the end of the second cycle without removal or rearrangement. 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 accomplish this, the reactor core is initially fully loaded with a fuel bundle having a fissile material loading commensurate with the core or 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, ie, at least two cycles of operation, and a unique fuel design for that operation is determined. In this manner, the fissile material inventory of the initial core can operate for two or more cycles without reloading and relocating fuel between the first and second cycles. It will be something like This increases the average residence time of the fuel in the initial core, and in response, the removal burn-up of the initial core increases the load of the conventional load that required a partial replacement load at the end of the first cycle. It increases compared to the burn-up of the core. This also saves a lot of scheduled work in the container during the first shutdown.

[0007] By using the core management method described above, the overall net operating cost is substantially reduced. Since the enrichment has been increased due to the need to allow operation over two or more cycles without reloading the fuel between the first and second cycles, the cost of the initial core loading is Although increased, the required mass of uranium is reduced, so that reprocessing costs are net reduced. For example, in a conventional core design, if about 800 fuel bundles are initially loaded into the core, typically 150 bundles will be placed at the end of the first cycle depending on cycle length, enrichment, etc. Can be taken out. Then, an additional 150 bundles with fresh fuel are loaded into the core at the end of the first cycle. However, reprocessing costs are a function of the mass of fuel required for reactor operation over the life of the reactor. Thus, in conventional core management designs, the first 150 bundles removed after the first cycle need to 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, reprocessing costs are not incurred at the end of the first cycle because fuel remains in the core at least through the second cycle. Thus, reprocessing costs are reduced by the number of fuel bundles that would have been reprocessed if removed at the end of the first cycle as in conventional designs. Even with such reduced reprocessing costs, the reduced amount will be offset to some extent by the additional cost of the fuel with the higher enrichment required for initial core loading to operate beyond the initial cycle. However, the overall cost per unit generated energy is reduced. That is, the cost of initial core fuel is higher due to the use of higher initial enrichment levels, 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, modifying the loading pattern can lead to new problems associated with spectral mismatches, so the core design should be optimized for thermal limitations. It is difficult to convert. The present invention also employs a control cell core scheme in which the high enrichment fuel bundle and the low enrichment fuel bundle are specifically positioned with respect to each other, thereby potentially causing a spectral mismatch. Potential locations within the core can be identified, and those locations are 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 specifically designed to minimize or eliminate spectral mismatches, thereby improving core performance. For this improved design approach,
The fuel rods affected by the mismatch are always the same, and the contents of the bundle can be designed to optimize thermal margin.

In conventional control cell core systems, movement of the shim control rods is limited to a group of control rods surrounded by a low enrichment bundle. Each of the cruciform control rods and the four fuel bundles surrounding it form a control cell. The control cell core scheme reduces power peaking, increases thermal margin, and reduces the tendency for pellet-coating interaction. Generally speaking, the operating cycle of the reactor is thus controlled only by the control rods of the control cell. Non-control
The cell (non-cotrolcell) is typically withdrawn during operation. In accordance with the present invention, the control cells are provided with a low-enrichment fuel bundle, while the non-control cells, except for the peripheral bundle in which the low-enrichment bundle is provided, have a high-enrichment bundle. An enrichment fuel bundle is provided. By configuring the core in this manner, it will be appreciated that the control cells are separated from each other by at least one non-control cell. In addition, only one side of the high-enrichment fuel bundle of the non-control cell in the core
The cells are arranged adjacent to the sides of the low enrichment fuel bundle. Therefore, locations that could potentially cause a spectral mismatch in the core are the above described edges of the high enrichment bundle located side or marginally adjacent to the low enrichment bundle of the control cell. At an early stage. As a result, the number of bundles and the number of fuel rods in those bundles that are susceptible to problems associated with spectral mismatch are significantly reduced. That is, for high enrichment bundles adjacent to the low enrichment bundle of the control cell, typically two or more sides of the high enrichment bundle typically have high power as a result of increased neutron flux. Only one side experiences what was experienced.

Further, by identifying the sides of the high enrichment bundle that are susceptible to spectral mismatch in the core design, the enrichment of individual fuel rods along that side of the high enrichment bundle is reduced, reducing the spectral mismatch. To be removed or eliminated, while 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, the enrichment of the fuel rods By selectively reducing the degree of enrichment, the effects of spectral mismatch on the high power generating fuel rods are minimized, while the enrichment of the fuel bundle is reduced by the fuel core loading,
In particular, they can be maintained at levels higher than those typical for initial core loading. Thus, by identifying the location in the core where the spectral mismatch occurs and modifying the high enrichment fuel bundle adjacent to the low enrichment fuel bundle, the initial core loading has, on average, a higher enrichment, Allows operation without refueling after the first cycle.

In a preferred embodiment according to the present invention, there is provided a method of supplying fuel to a reactor core having a plurality of nuclear fuel cycles, the method comprising the steps of: An average enrichment step is provided for the fuel bundles involved in the initial core fuel loading to assist in operating the reactor core for periods beyond the cycle.

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: forming a pattern of control cells and non-control cells in a reactor core; Forming at least one non-control cell so as to be spaced apart from each other; providing a generally low enrichment fuel bundle in the control cell; Placing an overall high enrichment fuel bundle in a non-control cell to substantially avoid spectral mismatch of the high enrichment bundle in only one side of the non-control cell The control cell in the core so that the fuel cell is located adjacent to the side of the low enrichment fuel bundle in the control cell. A Control cell and a step of arranging adjacent.

Accordingly, it is a primary object of the present invention to provide a new and improved method for managing reactor core bundles, which increases the average withdrawal burnup per bundle. Improved thermal margins, reduced downtime, reduced fuel bundle purchase over the life of the reactor core, reduced reprocessing costs, and spectral mismatch between fuel bundles. Are minimized or eliminated.

[0014]

Referring now to the drawings, and specifically to FIG.
FIG. 1 schematically shows a nuclear reactor, generally denoted by reference numeral 10. The reactor 10 has a plurality of fuel bundles 12 arranged in its core, all of which are contained in a reactor vessel 14 having a detachable head 16. ing. In accordance with the present invention, FIG. 1 (A) shows a reactor core with an initial fuel loading, wherein each fuel bundle has 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 at least 2 without reloading or relocating fuel between the first and second cycles.
Assists in driving for cycles or more. The end of the first operating cycle is shown in FIG. 1 (B), where the head of the container has not been removed.
However, as shown, none of the fuel bundles have been rearranged or replaced. FIG.
(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 to be used in a subsequent cycle is loaded into the core. ing.

As a result of this configuration, higher enrichment due to the need to operate over two or more cycles results in higher initial fuel loading costs, but reduced uranium mass. Thus, reprocessing costs are reduced net. That is, the fuel remains in the reactor through the second cycle or a further cycle, so that the first
No reprocessing costs at the end of the cycle. Therefore,
The initial core loading is, on average, enriched to assist in operating the reactor core for periods beyond the initial cycle without reloading nuclear fuel at the end of the initial cycle. To add for definition,
A "cycle" is the length of time between scheduled sequential outages during the life of the reactor, each outage conventionally including refueling.

Turning now to FIG. 2, a 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 the 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 numbers immediately following the letters C and N correspond to the average enrichment level of the fuel bundle at the location where the numbers are indicated. Thus, the numbers 2, 3, 4 and 5 indicate low enrichment, medium enrichment, high enrichment / high gadolinium, and high enrichment / low gadolinium fuel bundles, respectively. Numeral 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. Typical examples of enrichment for fuel bundles numbered 1-5 are as follows.
“1” = 0.71, “2” = 1.2, “3” = 2.2,
“4” = 3.7 and “5” = 3.7. The enrichment ranges for fuel bundles numbered 1-5 are typically as follows. In the case of “1”, 0.71 to 1.
2, 1.00 for 1.5 for "2", 2.0-2.5 for "3", 3.5 for "4" and "5"
4.0.

As can be seen from a consideration of the core shown in FIG. 2, a significant number of the high enrichment fuel bundles numbered 4 and 5 have sides adjacent to the low enrichment bundle. For example, the high enrichment bundle denoted by N4 shown on the horizontal axis 14 and the vertical axis 8 has all four sides adjacent to the middle or low enrichment fuel bundle at the periphery. Thus, the fuel bundle N4 at this location is susceptible to spectral mismatch, i.e., higher neutron leakage from adjacent low enrichment bundles, resulting in higher power and reaching the critical thermal limit. There is a risk. Thus, in the conventional core pattern shown in FIG. 2, there is a considerable number of fuel bundles suffering from spectral mismatch.

According to the conventional control cell system,
The control cells are provided with low enrichment fuel bundles, which are consistently labeled C2 in FIG. A cross-shaped control rod separating the four low-enrichment bundles C2 in each control cell serves as a control rod for the reactor. Control rods attached to non-control cells are typically withdrawn during operation.

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 significant number of high-enrichment bundles in non-control cells experience spectral mismatch. Thus, FIG.
As can be seen, for example, (horizontal axis, vertical axis)
2,14), the high-enrichment bundle is surrounded on all four sides by lower-enrichment bundles (L) and (M), and thus the four sides or Fuel rods located along each of the edges suffer from spectral mismatch. Similarly, (13,
The highly enriched bundle located at 15) also suffers spectral mismatch on its four sides. Similarly, high enrichment bundles other than those shown in FIG. 3 suffer spectral mismatches on all four sides. Therefore, in these high enrichment bundles, the problem of power peaking occurs.

Referring now to FIG. 4, a core configuration according to the present invention is shown. As can be seen from the figure, the control cells are provided with low-concentration bundles, and the non-control cells are provided with high-concentration bundles except for peripheral cells. The latter has high enrichment /
Bundles of either low gadolinium type or high enrichment / high gadolinium type. All of the peripheral bundles numbered 1 are of low enrichment. In this configuration, because of their location adjacent to the low enrichment bundle, the number of high enrichment fuel bundles suffering from spectral mismatch is substantially reduced to the number shown in FIG. About one third of the total. Also, highly enriched fuel bundles suffering from 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-enrichment bundle often suffered a spectral mismatch on four sides, but using the above-described configuration, only one side of the high-enrichment bundle had a spectral mismatch. I will not be affected. Therefore, the positions (12, 13), (12, 14),
In (13,15) and (14,15), fuel rods located on the side adjacent to the bundle of low enrichment control cells are susceptible to spectral mismatch.
There are no high-enrichment fuel bundles in non-control cells where all four sides suffer spectral mismatch.

According to the present invention, the fuel rods in the high enrichment bundle that are marginally adjacent to the low enrichment bundle, since the sides of the non-control cells that are subject to the spectral mismatch have been identified, The enrichment of the fuel rods suffering the mismatch can be reduced, while the enrichment level of the high enrichment fuel bundle can be maintained at a high level; In this way, both the problem of power peaking and the problem of critical thermal limits 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 relocates the fuel. Enough fissile material inventory can be provided for the initial core loading to perform operation over two or more cycles without dropping or replacement loading.

For example, if a high enrichment fuel bundle and the periphery of the fuel bundle are identified as having fuel rods subject to spectral mismatch, the fuel enrichment of these fuel rods may be reduced. Can be reduced. For example, when a 9 × 9 rod array is provided in the high enrichment bundle, the first and last fuel rods adjacent to the lower enrichment bundle are grouped in triplicate. Can be reduced. For example,
Such fuel rod enrichment can be reduced by 15% to 20%, thereby reducing the problem of power peaking along its periphery. To maintain symmetry, one adjacent side is also made up of fuel rods with similar enrichment along it so that the fuel bundle runs along the diagonal of the bundle, e.g., from top left to bottom right of the drawing. Make it symmetric.

As a representative example, reference is made to FIGS. FIG. 6 shows high enrichment /
Conventional fissile material loading for high gadolinium is shown. In particular, pay attention to the loading amounts of the 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 different fissile material loading than that shown in FIG. Specifically, the fissile material loading of the fuel rods marginally adjacent to the low-enrichment fuel bundle in the control cell will reduce the spectral mismatch that would otherwise have occurred. Has been reduced. Compare the fissile material loading of fuel rods 1A, 2A and 3A with the loading of fuel rods 1, 2 and 3 in FIG. These reduced enriched fuel rods 1A, 2A and 3A reduce or eliminate spectral mismatches, while maintaining the fuel bundle as having an overall high enrichment, while maintaining the fuel bundle in the core. Maintain and maintain a sufficient fissile material inventory to provide reactivity for at least the initial operating cycle and one subsequent operating cycle.

Although the present invention has been described in connection with what is considered to be the most practical and preferred embodiment at the present time, the present invention is not limited to the embodiments disclosed herein, but It is to be understood that the above covers all modifications and equivalents encompassed by the scope of the claims.

[Brief description of the drawings]

1A to 1C are schematic diagrams of a nuclear reactor operating over a number of cycles.

FIG. 2 is a schematic diagram illustrating a quarter of a reactor core,
FIG. 3 is a diagram showing fuel bundle loading by a conventional core loading design.

FIG. 3 is a schematic view of a part of the core shown in FIG. 2;
FIG. 4 shows a spectral mismatch between the fuel bundles of FIG.

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, but showing a part of the core of FIG. 4;

FIG. 6 is a schematic diagram showing a fissile material loading amount of a fuel bundle for a conventional fuel bundle.

FIG. 7 is a schematic diagram showing fissile material loading of a fuel bundle for a fuel bundle of the present invention that avoids spectral mismatch.

[Explanation of symbols]

 Reference Signs List 10 reactor 12 fuel bundle 14 reactor vessel 16 head

Continued on the front page (72) Inventor Stephen Joseph Peters United States, North Carolina, Wilmington, Hampshire, No. 3440 (72) Inventor Russell Morgan Fawset, United States of America, Wilmington, North Carolina Hollingsworth Drive, No. 609 (72) Inventor Gerald Dean Kvar, Jr. United States, California, San Jose, The Woods Drive, Apartment 183, No. 4300 (72) Inventor Lawrence Lee Chi, Los Pinos Place, Fremont, California, United States, number 691

Claims (13)

[Claims] 1. A method for supplying fuel to a reactor core having a plurality of nuclear fuel cycles, the reactor core being replaced for a period beyond the initial cycle without replacing nuclear fuel at the end of the initial cycle. Supplying fuel to a nuclear reactor core comprising: averaging and increasing the enrichment of fuel bundles associated with initial core fuel loading to assist in operating the reactor core. 2. Fueling the reactor core of claim 1 including maintaining the fuel bundles in the core without relocating the fuel bundles at the end of the initial cycle. how to. 3. The method of claim 2, further comprising the step of providing a replacement fuel bundle at the end of one cycle following the initial cycle. 4. A method for providing a plurality of control cells in the core, the first fuel comprising a fuel having a first average enrichment in both the control cells and the periphery of the core. Providing a bundle and providing a second fuel bundle having a second average enrichment to the remainder of the core, wherein the second fuel bundle comprises:
The method of providing fuel to a nuclear reactor core according to claim 1, wherein the reactor core has an average enrichment higher than an average enrichment of the first fuel bundle. 5. The method for supplying fuel to a nuclear reactor core according to claim 1, which is performed in a boiling water reactor. 6. The method of claim 1, wherein the method is performed in a pressurized water reactor. 7. A method for supplying fuel to a reactor core having a plurality of nuclear fuel bundles, comprising: forming a pattern comprising a control cell and a non-control cell in the reactor core. Forming control cells spaced apart 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 said non-control cell to substantially avoid spectral mismatch between said fuel bundles; and a high enrichment bundle in said non-control cell. So that only one side of the core is adjacent to the side of the low enrichment fuel bundle in the control cell. The method for supplying fuel to the reactor core that includes a step of arranging adjacent a control cell and non-control cells. 8. The method of claim 1, wherein only two sides of each low enrichment fuel bundle in the control cell are positioned adjacent to each side of the high enrichment fuel bundle in the adjacent non-control cell. The method of claim 7 including the step of positioning a control cell and a non-control cell adjacent to each other in the core. 9. Each fuel bundle has an array of fuel rods in the form of a square matrix, and adjacent fuel cells.
Enrichment of at least some of the fuel rods along a first side of each high enrichment fuel bundle in a non-control cell adjacent to one side of the low enrichment fuel bundle in the cell; The fuel along the first side due to a spectral mismatch due to a reduction in fuel rod enrichment along opposite sides of the high enrichment fuel bundle in the non-control cell. The method of claim 1 wherein rod peaking is minimized. 10. A method for providing different fuel rod enrichments to several fuel rods in the high enrichment fuel bundle, wherein the high enrichment fuel bundle is symmetric about a diagonal of the fuel bundle. And increasing the enrichment of the fuel rods. 11. The reactor core having a plurality of nuclear fuel cycles to assist in operating the nuclear reactor core over the initial cycle without reloading nuclear fuel at the end of the initial cycle. The method of claim 7, wherein the enrichment is provided on average to the high enrichment fuel bundles involved in the initial core fuel loading to provide fuel enrichment. 12. The method according to claim 7, which is performed in a boiling water reactor.
A method for supplying fuel to a nuclear reactor core according to the above. 13. The pressurized water nuclear reactor of claim 7.
A method for supplying fuel to a nuclear reactor core according to the above.