TWI816560B - Design method of lattice enrichment of nuclear fuel bundle of boiling water reactor - Google Patents

Abstract

A design method of lattice enrichment of a nuclear fuel bundle of a boiling water reactor is provided. The lattice has a preset average enrichment E and a preset number N of burnable poison rods. The design method includes the following steps: an initial calculation step, a setting step of burnable poison rods, a repeated calculation step, a enrichment adjustment step, a judgment step, an initial design enrichment determination step, a enrichment matching step and a design enrichment adjustment step. The design method of lattice enrichment of a nuclear fuel bundle of a boiling water reactor of the present invention provides a set of lattice enrichment design methods that can be automated.

Description

Design method of lattice concentration of nuclear fuel beam in boiling water reactor

The present invention relates to a lattice concentration of a nuclear fuel beam, and more particularly to a design method of a lattice concentration of a nuclear fuel beam in a boiling water reactor.

The nuclear fuel beam of the boiling water reactor is composed of dozens of fuel rods, and the cross section of the fuel beam is called a lattice. The specifications of the fuel bundles vary from large to small. Figure 1 shows a ten-by-ten lattice. The three-by-three part of the central area is the water area. Therefore, the ten-by-ten lattice has a total of 91 fuel rods for adjusting the concentration.

Since the cost of replacing the nuclear fuel bundle every time a nuclear power plant is shut down is extremely huge, the ideal state is that each fuel rod in the nuclear fuel bundle with a preset average enrichment E can produce a very close power and be synchronized at Consumption of fuel evenly over a specified period to coincide with each scheduled replacement stop. Too much fuel consumption or too little consumption at the scheduled shutdown time for replacement will be a thorny problem. The former will lead to uneven output power distribution, and the latter will lead to uneconomical fuel use. The enrichment of fuel rods affects fuel consumption, so it is necessary to adjust the enrichment of each fuel rod (numbered e1 to e91 in Figure 1) to achieve the goal.

The crux of this problem is that because nuclear fission is a chain reaction, under the same concentration, the outermost fuel rod has the highest initial power, and as the concentration gradually decreases, the power decreases; relatively, the fuel rods in the inner ring have the highest initial power. The initial power of the rod is low. However, even if the enrichment of the outer fuel rods is reduced, the output power of the other fuel rods will also change if only one fuel rod is adjusted. Therefore, the design of the concentration of fuel rods in the lattice is an extremely complex arrangement and combination. According to the past manual design methods, only limited designs can be tried based on experience. At most, local lattice optimization can be achieved, and it is often difficult to achieve the goal of overall lattice optimization.

On the other hand, the enrichment of fuel rods is not an arbitrary value and must be further limited by other considerations. The first is the restriction on the upper limit of concentration by regulations; the second is that the aforementioned preset lattice average concentration E must be met; the third is process considerations, that is, fuel rods with different concentrations must be manufactured and manufactured differently. The assembly process causes increased costs and difficulty in assembly. Therefore, the crystal lattice cannot have too many concentrations. Generally speaking, there are usually at most six concentrations in the crystal lattice. These specified concentrations are called design concentrations.

Therefore, in order to solve various problems with the lattice concentration of the nuclear fuel beam of the conventional boiling water reactor, the present invention proposes a method for designing the lattice concentration of the nuclear fuel beam of the boiling water reactor.

In order to achieve the above objects and other objects, the present invention proposes a method for designing the lattice concentration of a nuclear fuel beam in a boiling water reactor. The lattice has a preset average lattice concentration E and a preset number of combustible poison rods. N, the design method includes the following steps: an initial calculation step, using a lattice calculation program to calculate the concentration of all fuel rods in the lattice when it is equal to the preset lattice average concentration E. The initial power of the fuel rods; a step of setting the combustible poison rods, setting N combustible poison rods according to the initial power of each fuel rod; a repeated calculation step, using the lattice calculation program to recalculate the power of each fuel rod; a concentration The degree adjustment step is to adjust the concentration degree of each fuel rod, wherein the concentration degree of the fuel rod whose power is greater than the average value is reduced, the concentration degree of the fuel rod whose power is less than the average value is increased, and the adjusted concentration degree of each fuel rod is calculated. The power of the fuel rods, and calculate the ratio of the power of each fuel rod to the change in concentration; a judgment step, judge whether the power of each fuel rod is the same, if not, return to the concentration adjustment step, if they are the same, proceed An initial design enrichment determination step; the initial design enrichment determination step determines a plurality of initial design enrichments; a concentration matching step, based on the current enrichment of each fuel rod and the plurality of initial design enrichments, re-determines Adjust the concentration of each fuel rod so that the concentration of each fuel rod is one of the plurality of initial design concentrations; and a design concentration adjustment step to adjust the values of the plurality of initial design concentrations and A plurality of design concentrations are obtained so that the average concentration in the lattice is equal to the preset average concentration E of the lattice.

In one embodiment of the present invention, in the step of setting combustible poison rods and the recalculating step, each time a combustible poison rod is set, the power of each fuel rod is recalculated using the lattice calculation program until N combustible poison rods are set. The poison rods are set up and the power of each fuel rod is calculated.

In one embodiment of the present invention, in the enrichment adjustment step, the adjusted enrichment of each fuel rod is not higher than a regulatory upper limit or an upper limit specified by design requirements.

In one embodiment of the present invention, the enrichment matching step further includes a first prediction sub-step and a first determining sub-step. In the first prediction sub-step, predict the current enrichment of each fuel rod. The power change amount after changing to the initial design enrichment degree, in the first determining sub-step, determines the enrichment degree of each fuel rod to be one of the plurality of initial design enrichment degrees, and the absolute value of the power change amount reaches Minimum.

In one embodiment of the present invention, the design enrichment adjustment step further includes a second prediction sub-step and a second determination sub-step. In the second prediction sub-step, the fuel rods are predicted to start from the initial design. The amount of change in fuel rod power after the enrichment changes to the design concentration. In the second determination sub-step, an optimization algorithm is used to determine the plurality of design enrichments, so that the change in maximum fuel rod power reaches Minimum.

In one embodiment of the present invention, a normalization step is further included after the design enrichment adjustment step. In the normalization step, the power distribution of each fuel rod is calculated and normalized. The maximum normalized fuel Rod power is the local spike factor.

In one embodiment of the present invention, a re-judgment step is further included after the normalization step. In the re-judgment step, it is judged whether the local peak factor has converged. If there is no convergence, the design concentration adjustment step is re-executed.

In one embodiment of the present invention, in the determination step, the fuel rod whose concentration has reached the upper limit is not the target of determination.

Thereby, the method for designing the lattice concentration of the nuclear fuel beam in the boiling water reactor of the present invention provides a set of lattice concentration design methods that can be automatically executed. In addition to improving the design efficiency, it can also improve the quality of the lattice design. It is not affected by the design experience of engineers, that is, it reduces problems limited by manual experience. In addition, the focus of lattice design is the peak value of the power distribution of the fuel rods. The size of the peak value will affect the efficiency of nuclear fuel use and the safety margin during operation. The characteristics of this invention are: it can consider the manufacturing limit of the number of fuel rods and find out a set of most suitable fuel rod concentrations based on the average concentration of the lattice, and at the same time decide where to place each fuel rod in the lattice. A concentration that can obtain a better overall fuel rod power distribution; in addition, the position of the fuel rod where the combustible poison rod is located in the lattice can be designed at the same time, and its concentration in the fuel rod can be set to a design concentration of several values within the degree.

In order to fully understand the present invention, the present invention is described in detail through the following specific embodiments and the accompanying drawings. Those skilled in the art can understand the purpose, features and effects of the present invention from the contents disclosed in this specification. It should be noted that the present invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. The following embodiments will further describe the relevant technical content of the present invention in detail, but the disclosed content is not intended to limit the patentable scope of the present invention. The description is as follows:

The goal of the present invention is to determine the concentration of multiple fuel rods in the lattice (for example, 91 fuel rods in Figure 1, but the present invention does not limit the lattice specifications), so as to optimize the output power of the entire lattice, and The following conditions are met: (1) the regulations limit the upper limit of concentration; (2) the average concentration of the fuel rods in the lattice is equal to the preset average concentration E of the lattice; and (3) the concentration limit is There are only a few options for the value (i.e., design enrichment). The design enrichment is usually less than 6, and the number of fuel rods in the lattice is more than double the number of design enrichments.

As shown in Figure 2, a method for designing the lattice concentration of a nuclear fuel beam in a boiling water reactor according to an embodiment of the present invention is provided. The lattice has a preset average lattice concentration E and a preset number N of combustible poison rods. The design method includes the following steps:

First, in an initial calculation step S10, the present invention takes a ten times ten lattice as an example, and uses a lattice calculation program to calculate that the concentrations e1~e91 of all fuel rods in the lattice are equal to the preset average concentration of the lattice. The initial power of each fuel rod in case E. The lattice calculation program is, for example, the fuel beam cross-section processing program CASMO-4. However, the present invention is not limited thereto. Any program or software that can simulate and calculate the power of each fuel rod in the lattice based on the input concentration is covered by the lattice of the present invention. in the calculation program.

Next, in a step S11 of setting burnable poison rods, N burnable poison rods are set based on the initial power of each fuel rod calculated above. The burnable poison rod is a device with a large neutron absorption cross-section, which will have a negative impact on the chain reaction of nuclear fission. In this field, as a means of inhibiting nuclear fission, it is usually placed at the position of the most powerful fuel rod. N is a positive integer and is smaller than the number of fuel rods in the lattice. In this embodiment, N is 15 and the invention is not limited thereto. In this embodiment, the rules for setting up burnable poison rods must meet the following conditions: (a) Burnable poison rods are prohibited from being placed at the outermost periphery of the crystal lattice. If the fuel rod with the highest power in the lattice is located at the outermost periphery, select the position of the fuel rod adjacent to it in the inner circle. (b) Combustible poison rods are not allowed on part length rods. Some long fuel rods are fuel rods that occupy multiple lattice lengths but are shorter in length. Burnable poison rods cannot be applied there to avoid affecting other lattice structures. (c) Combustible poison rods are prohibited from being placed face to face adjacent to each other, but are allowed to be placed diagonally adjacent. Figure 3 shows a schematic diagram of the burnable poison rods arranged in the crystal lattice in this embodiment, in which the black area represents the arrangement of the burnable poison rods.

Next, in a recalculation step S12, after arranging the combustible poison rods, the power of each fuel rod is recalculated using a lattice calculation program.

It should be noted here that in this embodiment, in the step of setting the burnable poison rods S11 and the recalculation step S12, the power of each fuel rod is recalculated using the lattice calculation program each time a burnable poison rod is set. That is, first find the position of the maximum fuel rod power, set a position of a combustible poison rod under the premise of satisfying the conditions (a) to (c) above, then recalculate the power of each fuel rod, and then set the next The position of the combustible poison rods... This operation is repeated until N combustible poison rods are set and the power of each fuel rod is calculated. However, the present invention is not limited to this. In other embodiments, the recalculation step S12 may be performed after all N combustible poison rods are installed, or the recalculation step S12 may be performed every time several combustible poison rods are installed.

After the recalculation step S12, a concentration adjustment step S13 is performed. In the concentration adjustment step S13, the concentration of each fuel rod is adjusted. The method of adjusting the enrichment of each fuel rod is to reduce the enrichment of fuel rods with power greater than the average, and increase the enrichment of fuel rods with power less than the average, and the enrichment can only be adjusted to the upper limit specified by regulations at most. value or the upper limit specified by the design requirements. After the adjustment, the power of each fuel rod is further calculated, and the ratio q of the power of each fuel rod to the change in enrichment is calculated. The ratio q between the power of each fuel rod and the change in enrichment is calculated as: ΔP _i / Δe _i , where ΔP _i is the change in power of each fuel rod and Δe _i is the change in enrichment of each fuel rod. The ratio q between the power of each fuel rod and the change in enrichment is an important reference value for subsequent enrichment adjustments.

After the concentration adjustment step S13, a judgment step S14 is followed. In the judgment step S14, it is judged whether the power of each fuel rod is the same. If not, return to the concentration adjustment step S13 of the previous step, continue to adjust the concentration and recalculate the ratio q between the power of each fuel rod and the change in concentration; if If the power of each fuel rod is the same, an initial design enrichment determination step S15 is performed. In addition, fuel rods whose concentration has reached the upper limit are not included in the judgment target of this judgment step S14. The distribution of the number of each fuel rod and the concentration can be obtained, for example, the concentration distribution diagram in Figure 4.

Due to manufacturing cost considerations, the manufacture of nuclear fuel usually allows only a few different concentrations of fuel rods in a lattice, which is the design concentration. Generally speaking, there are no more than six design concentrations within a lattice. In this embodiment, it is taken as an example that the target is six design concentrations, but the invention is not limited thereto and may be more or less design concentrations.

In the initial design concentration determination step S15, a plurality of initial design concentrations E1, E2,...E6 are determined. The initial design concentrations E1, E2,...E6 can be determined empirically or mathematically based on the current concentration distribution, and the present invention does not limit the determination method.

Next, in a concentration matching step S16, with reference to Figure 5, the concentration of each fuel rod is re-adjusted based on the current concentration of each fuel rod and a plurality of initial design concentrations E1, E2,...E6, so that each The enrichment degree of the fuel rod is one of a plurality of initial design enrichment degrees E1, E2,...E6. That is to say, the enrichment degrees of the multiple fuel rods must be matched to one of the initial design enrichment degrees E1, E2, ... E6. In this case, except that the current enrichment of the fuel rod is exactly equal to one of the initial design enrichments E1, E2,...E6, or the current enrichment of the fuel rod is located at one of the initial design enrichments E1, E2,...E6 Outside the range (such as the two points with the highest concentration in Figure 5), most fuel rods have two adjustment options for the concentration: upward or downward.

As shown in FIG. 2B , the concentration matching step S16 of this embodiment further includes a first prediction sub-step S161 and a first determination sub-step S162. These two sub-steps are used to assist in determining whether the enrichment of the fuel rod should be adjusted upward to match a higher design enrichment or downward to match a lower design enrichment.

In the first prediction sub-step S161, the power change of each fuel rod from the current enrichment to matching the initial design enrichment is predicted. The prediction method is to multiply the current enrichment change by the previously calculated power and enrichment. The changing ratio q is used to obtain the power change. Adjusting the concentration of each fuel rod upward or downward will result in a power change.

In the first decision sub-step S162, the absolute value of each power change of each fuel rod is taken, and the one with the smallest value is selected as the selection for enrichment upward matching or downward matching. In other words, in this sub-step, the enrichment of each fuel rod is determined to be one of a plurality of initial design enrichments E1, E2,...E6 and the absolute value of the power change is minimized.

However, the above-mentioned method of determining whether the enrichment of each fuel rod should be adjusted up or down to match is only one embodiment of the present invention. In fact, other decision methods can be used to determine whether it should be adjusted up to match the higher initial design enrichment or down to match. Lower initial design concentration.

Then comes the design concentration adjustment step S17, which adjusts a plurality of initial design concentration values E1, E2,...E6 to obtain a plurality of design concentration E7, E8,...E12, so that the average concentration in the crystal lattice Equal to the preset average concentration E of the lattice. Since each initial design concentration E1, E2,...E6 may be adjusted in the direction of increase or decrease, the amount of adjustment may also be different, and there are many possible adjustment combinations. The present invention does not limit the adjustment method, which can be experience or other mathematical formulas. However, in the design concentration adjustment step S17 of this embodiment, as shown in Figure 2C, a second prediction sub-step S171 and a second determination sub-step are also provided. S172, to assist in determining how to determine the design concentration E7, E8,...E12.

In the second prediction sub-step S171, the fuel rod power change amount after each fuel rod changes from the initial design enrichment to the design enrichment is predicted. The prediction method is to use the aforementioned ratio q of power to enrichment change to calculate the adjusted fuel Rod power, and find the maximum fuel rod power among them, and then calculate the change in maximum fuel rod power before and after adjustment (maximum fuel rod power after adjustment minus the maximum fuel rod power before adjustment), which is referred to as the maximum power change. The quantity ΔP _MAX (may be negative). In principle, the adjustment direction and size of the fuel rod design enrichment are determined based on the predicted maximum power change ΔP _MAX . The goal is to minimize the maximum power change ΔP _MAX after the initial design enrichment changes to the design enrichment.

In the second decision sub-step S172, an optimization algorithm (such as simulated annealing method) is used to search for the best adjustment combination to determine the values of a plurality of design enrichment degrees E7, E8,...E12, thereby changing the maximum power The quantity ΔP _MAX reaches the minimum.

In summary, the method for designing the lattice concentration of the nuclear fuel beam in the boiling water reactor of the present invention provides a set of lattice concentration design methods that can be automatically executed. In addition to improving the design efficiency, it can also make the lattice The quality of the design can not be affected by the design experience of engineers, that is, problems limited by manual experience are reduced. In addition, the focus of lattice design is the peak value of the power distribution of the fuel rods. The size of the peak value will affect the efficiency of nuclear fuel use and the safety margin during operation. The characteristics of this invention are: it can consider the manufacturing limit of the number of fuel rods and find out a set of most suitable fuel rod concentrations based on the average concentration of the lattice, and at the same time decide where to place each fuel rod in the lattice. A concentration that can obtain a better overall fuel rod power distribution; in addition, the position of the fuel rod where the combustible poison rod is located in the lattice can be designed at the same time, and its concentration in the fuel rod can be set to a design concentration of several values within the degree.

Further, in this embodiment, as shown in Figure 2, the method for designing the lattice concentration of the nuclear fuel beam of the boiling water reactor of the present invention may further include a normalization step after the design concentration adjustment step S17. S18. In the normalization step S18, the power distribution of each fuel rod is calculated and normalized (that is, the average value of the fuel rod power is equal to 1.0), and the maximum normalized fuel rod power is set as the local peak factor.

Then, after the normalization step S18, a re-judgment step S19 is included. In the re-judgment step S19, it is judged whether the aforementioned local peak factor has converged. If there is no convergence, the design concentration adjustment step S17 is re-executed to determine another set of design concentration. The values of E13, E14,...E18 until the local peak factor converges. If the local peak factor has converged, the lattice design results can be output. Through the normalization step S18 and the re-judgment step S19, aiming to minimize the local peak factor can further help reduce the power peak of each fuel rod in the lattice.

The present invention has been disclosed in the above embodiments. However, those skilled in the art should understand that the embodiments are only used to illustrate the present invention and should not be interpreted as limiting the scope of the present invention. It should be noted that any changes and substitutions that are equivalent to this embodiment should be considered to be within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope of the patent application.

E1: Initial design concentration E2: Initial design concentration E3: Initial design concentration E4: Initial design concentration E5: Initial design concentration E6: Initial design concentration S10~S19: steps

Figure 1 shows a schematic diagram of a cross-section of a nuclear fuel bundle of a prior art boiling water reactor. FIG. 2A is a flow chart of a method for designing the lattice concentration of a nuclear fuel beam in a boiling water reactor according to an embodiment of the present invention. Figure 2B is a flow chart of the concentration matching step according to an embodiment of the present invention. Figure 2C is a flow chart of the design concentration adjustment steps according to an embodiment of the present invention. Figure 3 is a schematic diagram of a burnable poison rod disposed in a crystal lattice according to an embodiment of the present invention. Figure 4 is a concentration distribution diagram of each fuel rod after the concentration adjustment step according to the embodiment of the present invention. Figure 5 is a schematic diagram of the concentration matching step according to the embodiment of the present invention.

S10~S19: Steps

Claims (8)

A method for designing the lattice concentration of a nuclear fuel beam in a boiling water reactor. The lattice has a preset lattice average concentration E and a preset number of combustible poison rods N. The design method includes the following steps: An initial calculation step uses a lattice calculation program to calculate the initial power of each fuel rod when the concentration of all fuel rods in the lattice is equal to the preset average concentration of the lattice E; A step of setting burnable poison rods, setting N burnable poison rods according to the initial power of each fuel rod; Repeat the calculation step to recalculate the power of each fuel rod using the lattice calculation program; A concentration adjustment step, adjusting the concentration of each fuel rod, wherein the concentration of the fuel rod with a power greater than the average is reduced, the concentration of the fuel rod with a power less than the average is increased, and the adjusted The power of each fuel rod, and the calculation of the ratio of the power of each fuel rod to the change in enrichment; A judgment step to determine whether the power of each fuel rod is the same. If not, return to the concentration adjustment step. If they are the same, proceed to an initial design concentration determination step; The initial design concentration determination step determines a plurality of initial design concentrations; A concentration matching step, based on the current concentration of each fuel rod and the plurality of initial design concentrations, readjusting the concentration of each fuel rod so that the concentration of each fuel rod is the plurality of initial designs one of the concentrations; and A design concentration adjustment step is to adjust the values of the plurality of initial design concentrations to obtain a plurality of design concentrations so that the average concentration in the lattice is equal to the preset average concentration E of the lattice. The method for designing the lattice concentration of the nuclear fuel beam of the boiling water reactor as described in claim 1, wherein in the step of setting the combustible poison rod and the recalculation step, each combustible poison rod is calculated based on the lattice The program recalculates the power of each fuel rod until N combustible poison rods are installed and calculates the power of each fuel rod. The method for designing the lattice concentration of a nuclear fuel bundle in a boiling water reactor as described in claim 1, wherein in the concentration adjustment step, the adjusted concentration of each fuel rod is not higher than a regulatory upper limit or The upper limit specified by the design requirements. The method for designing the lattice concentration of the nuclear fuel beam in the boiling water reactor as described in claim 1, wherein the concentration matching step further includes a first prediction sub-step and a first determiner sub-step. The prediction sub-step predicts the power change amount of each fuel rod after the current enrichment changes to the initial design enrichment. In the first determining sub-step, the enrichment of each fuel rod is determined to be the plurality of initial designs. One of the concentrations and minimizing the absolute value of the power change. The method for designing the lattice concentration of the nuclear fuel beam of the boiling water reactor as described in claim 1, wherein the design concentration adjustment step further includes a second prediction sub-step and a second determination sub-step. The second prediction sub-step predicts the change in fuel rod power after each fuel rod changes from the initial design enrichment to the design enrichment. In the second determination sub-step, an optimization algorithm is used to determine the plurality of fuel rods. Design enrichment to minimize variation in maximum fuel rod power. The method for designing the lattice concentration of the nuclear fuel bundle of the boiling water reactor as described in claim 1, further including a normalization step after the design concentration adjustment step, and in the normalization step, each of the The fuel rod power is distributed and normalized, and the maximum normalized fuel rod power is the local peak factor. The method for designing the lattice concentration of a nuclear fuel beam in a boiling water reactor as described in claim 6, further comprising a re-judgment step after the normalization step, and in the re-judgment step, it is judged whether the local peak factor has converged. , if there is no convergence, re-execute the design concentration adjustment step. The method for designing the lattice concentration of a nuclear fuel bundle in a boiling water reactor as described in claim 1, wherein in the judgment step, the fuel rod whose concentration has reached the upper limit is not the target of judgment.