JP2006119004A - Method for operation of light water reactor and fuel loading - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cost of nuclear power by shortening an intermediate termination period. <P>SOLUTION: The method for operation of a light water reactor and fuel loading adopts long cycle operation determined by the period for receiving predetermined periodical inspection, and a part of burned fuel is removed out of the core in the middle of a long cycle operation and an intermediate termination period for loading new fuel in the core is set in place. The exchange of a part of burned fuel to new fuel in the intermediate termination period is conducted without rearranging fuel to be reused in the next operation in the particular fuel loading method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to fuel replacement in a nuclear power plant, and more particularly to performing only fuel replacement during the stop period in order to shorten the stop period of the reactor during cycle operation in a light water reactor.

  Nuclear fission (hereinafter referred to as “fuel” in principle) in a nuclear reactor (hereinafter also simply referred to as “reactor”) is a high neutron density at the center of the core, etc. Combustion is more intense in the place, newer fuel is more intense, fissile material such as plutonium 239 is newly generated with combustion, and daughter nuclei that affect the controllability of nuclear reactions are generated. It is essentially different from boilers and internal combustion engines that burn fossil fuels, such as the fact that neutron absorbers that suppress nuclear reactions are consumed, and that light-water reactors cannot be loaded and unloaded during operation. There are features.

For this reason, the supply of fuel into the furnace in nuclear power generation does not simply remove the burned fuel from the core and then load new fuel after it when the furnace is stopped by periodic inspection or the like. That is, in the burning and replacement of nuclear fuel in a light water reactor, the following operations are generally performed as a set (Patent Document 1).
First, the reactor is operated for a certain period in consideration of the periodic inspection of the reactor and the restrictions on the use of fuel assemblies, etc., which are determined based on the passage of a predetermined period and the total operating time. Continued cycle operation.

  Secondly, the nuclear fuel in the core is divided into several batches (grouped), and some batches of fuel that have been burned within the reactor shutdown period provided for each cycle or half cycle are Remove from the furnace so that it is not used in cycle operation. In some cases, certain batches of unburned fuel are also partially removed from the furnace. Instead, new batches and new (unused) fuel are loaded into the furnace.

  Thirdly, the fuel belonging to the other partially burned batch is changed in position in the core in conjunction with the replacement operation of the second fuel so that proper combustion is performed even in the next continuous operation ( Shuffling). For this reason, all of these other batches of fuel are once taken out into the fuel pit outside the furnace, inspected for abnormalities or damage in the pit, and removed depending on their degree. Therefore, the new fuel is not loaded as it is at the position where the spent fuel removed from the core exists because it is not used for the next operation.

  Fourth, in addition to the third operation, a new fuel is previously mixed with a substance that absorbs neutrons so that proper combustion is performed in the core. Specifically, the fuel pellet itself is gadolinia. Or a cluster containing a boron compound is inserted into the guide thimble position of the fuel assembly. Various other adjustments and controls such as adjusting the concentration of neutron-absorbing substances (such as boron 10) in the cooling water according to the operating state.

  Fifthly, the fuel is stored in a fuel assembly in which, for example, 17 × 17 bundles of Zircaloy cladding tubes packed with a large number of uranium dioxide pellets are stacked in the vertical direction. For this reason, the entire fuel assembly is carried into the furnace, carried out to the outside of the furnace, and the batch division, combustion control, and setting of the upper limit of the burnup are also managed.

  Next, spent fuel removed from the furnace is reprocessed in Japan. Unburned uranium 235, newly generated plutonium 239, etc. are separately sent to manufacture of new fuel. Accordingly, the nuclear fuel used in our light water reactors includes not only uranium 235 extracted and concentrated from the mine but also uranium 235 and plutonium 239 obtained by this reprocessing. However, in order to adopt this reprocessing, not only the original cost but also the storage of waste such as zircaloy pipes coated with uranium dioxide pellets, radiation exposure due to radioactivity and countermeasures against contamination, etc. There is also the following cost.

  By the way, the costs in nuclear power generation are comprised of capital costs such as amortization of expensive construction costs, fuel cycle costs including fuel costs, and operation and maintenance costs including costs for periodic inspections. The following relationship is approximately between each of these costs and the operation period of the cycle operation.

The longer the period of one cycle, the higher the operating rate of the reactor and the lower the capital cost. In addition, operation and maintenance costs are also reduced. However, since the take-off burnup decreases, the fuel cycle cost increases. Figure 1 shows the trend of how power generation cost, fuel cycle cost, and capital cost change with cycle length for each enrichment of fuel uranium 235 at 4.6, 4.8, and 5.0 wt%. Show. In FIG. 1, the three lines at the bottom are capital costs. However, this has little relation to the enrichment of uranium, so these lines are effectively one line. The three central lines are fuel cycle costs. The top three lines are the power generation costs.
Therefore, as is apparent from FIG. 1, there is a cycle length that minimizes the power generation cost.

However, this is only a principle, and the present situation is that various ideas have been made according to the fuel specifications, the period of periodic inspection, other circumstances specific to each country, the type of light water reactor, and the like.
(1) Case 1
Case 1 is mainly performed in the United States. In the United States, since reprocessing is not performed, the ratio of the fuel cycle cost to the power generation cost is small. Therefore, the period of one cycle is increased to 24 months to increase the operating rate and lower the capital cost. FIG. 2 shows the fuel configuration and replacement scheme in each cycle of this case, and FIG. 3 shows the fuel loading pattern. In FIG. 2, the amount of fuel loaded is shown by the number of fuel assemblies.
Moreover, 1ce of FIG. 2 shows the fuel used for one cycle (Once Burned, 1 time combustion). FIG. 3 shows a so-called quarter core. Moreover, each square of FIG. 3 shows a fuel assembly. These are also the same for each case diagram that comes later.

  In this case 1, as shown in FIG. 2, there is no intermediate shutdown period of the furnace, and each cycle starts at the beginning, that is, at the start of the operation of the cycle, about 2 / total of new fuel (157 fuel assemblies). 3. Partially burned fuel is used for about 1/3 of the total because it has been used for 1 or 2 cycles, ie only 100 and 57 are loaded in each fuel assembly. Then, an intermediate stop period is not provided in the middle of the cycle to change the fuel or change its arrangement. For this reason, the new fuel in the nth cycle becomes 1ce fuel in the next cycle. Also, since 1ce fuel is completely removed after the end of the cycle, it is not used in the next cycle.

  In FIG. 3, the left diagram shows the change in the burnup distribution of the fuel assembly at each position in the core, and the right diagram shows the B10 residual ratio (BPRs Fraction of BPRs) corresponding to this change. ) Distribution change. As you can see on the right, this pattern does not use flammable poison clusters.

  In the figures on the left and right, uppercase letters such as A and B written in the horizontal direction at the top of the figure and numbers such as 8, 9 written in the left and up and down directions indicate the fuel assembly in the core. Indicates the position (coordinates). Further, in the left figure, the character strings described in three stages in each rectangular lattice are the fuel assembly identification code, the beginning of cycle (BOC) burnup, and the end of cycle (End) from the top. Of Cycle: EOC). The figure on the right remains white because no flammable poison clusters are used in this case.

Further, N in the identification code stage of the fuel assembly and N in NG indicate new fuel, and 1 in 1 and 1G indicate fuel that has been used once in the preceding cycle, and thus partially burnt fuel. Furthermore, NG and G of 1G mean fuel with gadolinia. As a result, burnup is improved after the middle of the cycle when gadolinia is consumed.
Here, the use of gadolinia instead of boron is due to the fact that no waste is generated and that it can be placed at the control rod position.

(2) Case 2
Case 2 is being considered by a practitioner in Japan. Since reprocessing is performed in Japan, the ratio of the fuel cycle cost to the power generation cost is relatively large. For this reason, if a long cycle operation similar to that of the United States is adopted, the fuel cycle cost deteriorates and the power generation cost may increase. As a countermeasure against this, it is the same as Case 1 above that one cycle is set to 24 months, but in the middle of the cycle, the burned fuel is replaced with new fuel. An intermediate stop period is provided in which the fuel to be used is sequentially loaded into the furnace. For this reason, for example, a half-cycle operation of 12 months is performed twice as a set.

  FIG. 4 shows the fuel configuration and replacement scheme in each cycle in this case, and FIG. 5 shows the fuel loading pattern. In the case 2, as shown in FIG. 4, an intermediate furnace stop period is provided in each cycle. In FIG. 5, 1 ce, 2 ce and 3 ce 1, 2 and 3 are simplified representations for convenience, and indicate the number of half cycles used in the furnace up to the start of operation. Therefore, at the end of the operation, the 1ce and 2ce fuels become 2ce (Twice Burned, 2 times combustion) and 3ce (Thrice Burned, 3 times combustion) fuel, respectively, and the 3ce fuel becomes the burned fuel.

  As shown in FIG. 4 and FIG. 5, at the end of each cycle and at each intermediate stop period, the fuel assembly that is a little over 1/4 of the total (157 fuel assemblies) is burned at the end of the operation. A total of 40 fuel assemblies including 37 bodies and 3 bodies, which become 3ce at the end of the operation, are removed from the furnace. Instead, the same number of new fuel assemblies are loaded into the furnace. Furthermore, all the fuel assemblies that become 1 ce and 2 ce at the end of the operation, and 37 fuel assemblies other than the 3 removed fuel assemblies that also become 3 ce, that is, a total of 117 fuel assemblies corresponding to about 3/4 of the total. Since the body is used in the next operation, it is continuously loaded into the furnace. However, at the time of fuel exchange within the intermediate stop period, all are once taken out to the pit and rearranged.

  Also in FIG. 5, the left side shows the distribution of the combustion rate of the fuel assembly, and the right side shows the distribution of the fraction of BPRs. In addition, the meanings of uppercase alphabets and numbers, and the meanings of the characters described in three rows in each lattice in the left figure are the same as those in FIG. Further, N in the identification code stage of the fuel assembly indicates a new fuel, and the numerals 1, 2 and 3 mean the number of half cycles burned in each preceding operation. Also in this case, the figure on the right side remains white and no flammable poison cluster is used.

  By the way, in the case 2 method studied in Japan, one cycle is 12 months from the viewpoint of the fuel cycle. For this reason, the cost of the fuel cycle is the same as the case where one cycle is 12 months. However, since there is an intermediate shutdown period, the operating rate of the reactor is reduced and the capital cost is increased compared to the 24-month operation in Case 1. For this reason, in terms of reducing the power generation cost, it is important how to shorten the intermediate stop period. As means for shortening, in addition to Case 2, the following method has been further studied.

  a) Reduce the movement to the spent fuel pit as much as possible and change the arrangement in the furnace. This method is adopted in domestic and overseas boiling water reactors (BWR) and overseas pressurized water reactors (PWR).

  b) Only the new fuel and the two-time combustion fuel are subject to change of arrangement, and the one-time combustion fuel is not moved. In addition, this method is an example examined by overseas BWRs, and since one cycle is 18 to 24 months, there is no 3ce fuel.

On the other hand, the PWR is smaller in the core than the BWR, and the loaded fuel assembly is large. Therefore, the degree of freedom for creating the fuel assembly arrangement pattern is low. Therefore, unlike BWR, it has been considered that the above a) is very difficult and the above b) is impossible. Therefore, in the PWR, all the fuel assemblies are once taken out into the spent fuel pits, and the fuel to be continuously used in the next operation is loaded again in the core together with the new fuel. The so-called full shuffling is performed.
JP 2002-286887 A

However, demands for lowering power generation costs in recent years have become increasingly severe. This is especially true under the current liberalization of electricity. For this reason, the development or practical use of a method for shortening the intermediate stop period has been desired more than the case 2 and the cases a) and b) in addition thereto.
In addition, development of a method applicable not only to BWR but also to PWR has been desired.
Of course, development of a method that is lower in cost than the method of Case 1 has been desired.
In addition, it is not limited to an intermediate stop period in a strict sense, and even if it is a relatively long stop period for receiving periodic inspections, that is, a stop period between cycles, an intermediate stop period in a broad sense, There was also a desire to reduce the time required for costly fuel changes as much as possible.
In addition to the above, it has been desired to develop a technology that reduces the exposure amount of workers and jigs and reduces the risk of fuel damage.

  The present invention has been made for the purpose of solving the above problems, and an intermediate stop period is provided for fuel replacement in the middle of a long cycle operation. In this case, the burned fuel removed from the core is occupied. The intermediate stop period can be shortened by simply loading new fuel at the new position and leaving the arrangement of the fuel to be used continuously in the next operation as much as possible, preferably making the arrangement unnecessary. Is intended. For this reason, the cycles before and after the intermediate stop are regarded as a pair, and the fuel loading positions before and after the intermediate stop are optimized in advance so as to minimize the amount of fuel movement during the intermediate stop. Specifically, the invention is as follows.

  The invention according to claim 1 employs a long cycle operation determined from a period for which a predetermined periodic inspection is to be performed, and removes a part of the burned fuel from the furnace during the long cycle operation. The operation of a light water reactor with an intermediate stop period for loading new fuel into the reactor, and a fuel loading method, in which replacement of part of the burned fuel with new fuel during the intermediate stop period is performed in the next operation However, this is a light water reactor operation and fuel loading method characterized in that the fuel that is continuously used is made without rearranging in the reactor.

In the present invention, the fuel loading position before and after the intermediate stop is optimized in advance so as to minimize the amount of fuel movement during the intermediate stop.
Here, the period of the long cycle operation is a period determined by taking a predetermined inspection period or taking a periodic inspection or a restriction from nuclear fuel determined for each elapsed period from the previous inspection, and in principle more than 18 months. 24 months is normal. However, there may be some fluctuations (extended in January or shortened in February) due to power conditions. Also, the spent fuel is carried out from the furnace and new fuel is carried into the furnace for each fuel assembly. Furthermore, at the time of periodic inspections after the end of each cycle, there is sufficient time, so the fuel assemblies that will continue to be used in the next cycle are once transported to the pit and transported again into the furnace. Also made.

  The invention according to claim 2 is the operation of the light water reactor and the fuel loading method, wherein the replacement of a part of the burned fuel with the new fuel during the intermediate stop period removes the unburned fuel from the furnace. In addition, the present invention is a light water reactor operation and fuel loading method characterized in that no new fuel is loaded at a position where the fuel is present.

  However, in a stop period other than the intermediate stop period, it is possible to remove unburned fuel from the furnace and load new fuel thereafter.

  The invention according to claim 3 is the operation of the light water reactor and the fuel loading method, wherein the long cycle operation is set to one cycle of 24 months, and the intermediate stop period is provided at a central timing thereof. This is a light water reactor operation and fuel loading method characterized by the above.

  However, the 24 months may be shortened by a little (10%) or extended by about 1 month for various reasons. In addition, the intermediate stop period is basically provided in the center of the operation period such as 24 months, but it is carried out about a month ahead for measures such as when the power situation in midsummer peaks, etc. There may be some deviation.

  The invention according to claim 4 is the operation of the light water reactor and the fuel loading method, wherein the fuel in the reactor is batch-divided into several parts, and a part of the burned fuel is exchanged during the intermediate stop period. Is a light water reactor operation and fuel loading method characterized in that it is carried out only for one burned batch.

  Thus, each batch initially comprises the same number of fuel assemblies. However, at the end of the long cycle operation, the fuel that has not been completely burned, that is, part of the fuel that has become 2 ce is also removed, so the fuel that has been used for one cycle is not necessarily the same number of batches.

  The invention according to claim 5 is the operation of the light water reactor and the fuel loading method, wherein the number of batches of the fuel in the reactor is 4, and is continued in the next operation without replacement in the intermediate stop period. The fuel used is a three-batch operation, a light water reactor operation and fuel loading method.

  The invention according to claim 6 is an operation and fuel loading method of the light water reactor, wherein when the spent fuel is replaced with a new fuel during the intermediate stop period, the fuel that is continuously used in the next operation is the reactor. Therefore, the fuel to be used for the next operation is placed at a predetermined position in the furnace within the period to receive the predetermined periodic inspection, and the predetermined periodic inspection is performed. The light water reactor operation and fuel loading method are characterized in that predetermined measures are taken for the new fuel loaded in the power period and the new fuel loaded in the furnace during the intermediate stop period.

Therefore, in order to minimize the fuel movement in the latter half cycle (basically 0%), the fuel arrangement should be considered simultaneously by coupling the former half cycle and the latter half cycle together. It becomes. That is, after the previous half cycle is completed, the fuel arrangement of the subsequent half cycle should not be considered, but the fuel arrangement of the subsequent half cycle should be considered together when considering the fuel arrangement of the previous half cycle. become.
For this reason, in the previous half cycle, fuel that has been used twice in the half cycle is loaded in the center of the core, and fuel that has been used once may be disposed around the center.

  The invention according to claim 7 is an operation of the light water reactor and a fuel loading method, wherein fuel used for the next operation is arranged at a predetermined position in the furnace within a period of time to receive the predetermined periodic inspection. The fuel assembly located on the outermost periphery of the core is the new fuel and the fuel that will be burned during the next shutdown period, and the most burned fuel among the fuels that are only used for half a cycle. This is a light water reactor operation and fuel loading method characterized in that a part of the reactor is removed from the core and replaced with a new fuel.

  For this reason, in the latter half cycle, the fuel disposed on the outermost periphery of the core becomes the new fuel and the fuel used for the half cycle operation.

  The invention according to claim 8 is an operation method of the light water reactor and a fuel loading method, wherein the measures taken for the new fuel loaded during the period to receive the predetermined periodic inspection are defined in a non-peripheral portion of the core. The operation of the light water reactor is characterized in that the new fuel to be loaded is in a gadolinia or a flammable poison cluster, and the measures taken for the new fuel loaded in the furnace during the intermediate shutdown period are in a flammable poison cluster. This is a fuel loading method.

  In the case of BWR, as described above, the inner diameter of the furnace is large and the number of fuel assemblies loaded is also large. For this reason, the freedom degree of a loading pattern increases. Accordingly, the present invention that can be implemented in the PWR can naturally also be implemented in the BWR.

  The invention according to claim 9 is an operation of the light water reactor and a fuel loading method, wherein the operation of the light water reactor and the fuel loading method are for a pressurized water reactor. This is a fuel loading method.

  Thereby, the effect of this invention will be exhibited largely.

  The invention described in claim 10 is the light water reactor operation and fuel loading method, wherein the number of loops of the light water reactor is three.

If the number of loops is 4, the number of fuel assemblies loaded increases, so the degree of freedom of the loading pattern increases. Therefore, the degree of freedom regarding the replacement and arrangement of fuel is increased. Therefore, the present invention can naturally be implemented.
Of course, the present invention can be applied to a light water reactor having a small number of loops of two.

The invention according to claim 11 employs a long cycle operation, in order to remove a part of the burned fuel from the furnace during the long cycle operation and to load a new fuel into the furnace instead. An operation and fuel loading method of a light water reactor with an intermediate stop period, in which replacement of a part of burned fuel with new fuel in the intermediate stop period is performed by replacing the fuel in the reactor at the start of the operation of the previous half cycle. The arrangement of the new fuel to be loaded in the period of the periodic inspection provided before the start of the previous half cycle or the intermediate stop period is set in accordance with a specific rule in advance, and the subsequent half cycle The fuel that is continuously used in the operation of the fuel and needs to be relocated within the furnace is a replacement that is made within 8% of the total loaded fuel, and is determined according to the specific rules. What is Characterized by satisfying the bottom (a) the fine print (h),
(A) The new fuel placed inside during the previous half-cycle operation, when used as a twice-burning fuel, is placed at the outer periphery or at a position adjacent to the fuel at the outer periphery, with the exception of up to eight bodies. To
(B) In the first half cycle, the same number of three-time combustion fuel is arranged inside as the new fuel arranged inside in the latter half cycle operation.
(C) The new fuel placed inside during the subsequent half-cycle operation is placed at the outer periphery or at a position adjacent to the fuel at the outer periphery, except for up to eight exceptions, when used as a three-time combustion fuel. To
(D) Other than the fuel taken out in the previous half cycle, it is arranged at a position where the power distribution becomes flat.
(E) During the operation period of one cycle, the five bodies at the center of the furnace are not used as new fuel.
(F) New fuel, which is not located inside the furnace and will be placed in the surrounding eight locations, will not be adjacent to each other, except in a flammable poison cluster,
(G) Since the top of 1 is located on the outer periphery of the furnace, the new fuel in which fuel is to be placed in the surrounding seven locations, the one adjacent to the new fuel on the outer periphery of the furnace is the maximum With 4 exceptions, it will be in a flammable poison cluster,
(H) The new fuel on the outer perimeter does not enter the flammable poison cluster, with the exception of up to four bodies.
This is a light water reactor operation and fuel loading method characterized by being a thing.

  Here, the fuel that is continuously used in the subsequent half cycle operation and needs to be rearranged in the furnace is within 8% of the total loaded fuel, so that the total loaded fuel is 157%. If it is a body, the maximum number of fuels whose position in the furnace is changed is 12, and in the 1/4 core, there are 3 fuels. If the amount of fuel is changed to such a level, the position where the extracted burnt fuel was present can be used as a temporary place. For this reason, the fuel to be rearranged is often not required to be carried out into the fuel pit outside the furnace.

  In addition, the content determined in advance according to the specific rule is a fuel that is continuously used in the subsequent half-cycle operation, and the relocation in the furnace is required to be 8% of the total loaded fuel. It is the arrangement and fuel state that are within. This is a work or calculation for finding the arrangement, contents to be matched trial and error under the condition that all the detailed rules (items) of (a) to (h) are satisfied, but from (a) to ( As long as the detailed rules (items) of h) are followed, the arrangement of fuel and the state of the fuel, which are preferable results based on empirical rules, are roughly understood. In particular, the arrangement of the fuel in the furnace is basically symmetrical with respect to both the X axis and the Y axis from the viewpoint of achieving uniform combustion of each fuel, so if the 1/4 core is targeted. Well, it is convenient for examination from this aspect.

According to the detailed rules of (a), the new fuel loaded at the beginning of the previous half cycle becomes the fuel used for the second combustion at the end of the subsequent half cycle (in the half cycle) and is used in the next cycle Then, with the exception of up to eight bodies, it is arranged at the outer periphery or a position near the outer periphery.
A maximum of 8 exceptions is a maximum of 2 exceptions in the 1/4 core.
Here, the “position near the outer periphery” refers to a position where one side is adjacent to the fuel on the outer periphery.
In addition, these eight bodies do not contain fuel that is not used and removed in the next cycle.
The twice-burning fuel that is removed without being used in the next cycle is preferably the most burned fuel among them.
According to the detailed rules of (b), the fuel used for combustion three times at the start of the previous half cycle becomes fuel burned four times at the end of the previous half cycle and is removed from the furnace during the intermediate shutdown period. Then, new fuel is loaded at the removed position.
According to the bylaws of (c), new fuel loaded at the beginning of the latter half cycle is used as a combustion fuel three times (in a half cycle), with the exception of up to eight bodies, Placed in position.
A maximum of 8 exceptions is a maximum of 2 exceptions in the 1/4 core.

According to the detailed rules of (d), the fuel continuously used at the same position in the subsequent half cycle does not greatly lose the burn-up balance or burn excessively.
“Position where output distribution is flat” refers to an arrangement (checker board arrangement) or the like where fuel with high reactivity and fuel with low reactivity are arranged like a checkerboard pattern. However, this is not the case when the output distribution becomes flat even if it is not a checkerboard pattern. Ultimately, it is determined and determined by a case-by-case examination and confirmation by simulation calculation of the combustion state and neutron distribution.

By the detailed rules of (e), it can be avoided that the new fuel burns extremely and the distribution of neutrons in the most central part of the furnace becomes too high.
Further, in the previous half cycle, the combustion fuel is not disposed three times at the center of the furnace.
According to the detailed rules (e) to (h), the neutron distribution in the furnace is flattened and the specific fuel is prevented from being extremely burned.
The “exception” in the detailed rules of (a), (c), (g), and (h) is preferably not originally present, but is taken into consideration when it is unavoidable.

  The invention according to claim 12 is the operation of the light water reactor and the fuel loading method, wherein the replacement of a part of the burned fuel with the new fuel in the intermediate stop period is continued even in the later half cycle operation. This is a light water reactor operation and fuel loading method characterized in that the fuel that is used in the reactor and needs to be relocated within the furnace is within 6% of the total loaded fuel. .

The fuel that is continuously used in the subsequent half-cycle operation and needs to be relocated within the furnace is within 6% of the total loaded fuel, so if the total loaded fuel is 157 For example, the maximum number of fuels whose positions in the reactor are changed is nine, and two in the quarter core.
For this reason, the time required for fuel exchange is shortened more than the previous invention.
In addition, if the number of fuels to be rearranged is small, the empty space that is present until the new fuel is loaded in the space where the removed fuel was placed may be used primarily as a temporary storage place for the fuel to be rearranged. Since it is possible, it is not always necessary to carry out the fuel to be rearranged to the pit.

  The invention according to claim 13 is the operation of the light water reactor and the fuel loading method, wherein the replacement of a part of the burned fuel with the new fuel in the intermediate stop period is continued even in the later half cycle operation. This is a light water reactor operation and fuel loading method characterized in that there is no fuel to be used in the reactor and rearranged in the reactor.

Since there is no fuel that needs to be rearranged among fuels that are continuously used, the time required for fuel replacement is shortened more than in the previous invention.
However, when the operation is stopped after the end of the long cycle, it is possible to remove the fuel that has not been completely burned out from the furnace and load new fuel thereafter.

  With the above configuration, according to the present invention, regardless of BWR and PWR, in the long cycle operation of the light water reactor, an intermediate stop period is provided in the middle of the long cycle, and the fuel burned within this period is taken out of the furnace and thereafter In this intermediate stoppage period, the fuel used for the subsequent half cycle operation will not be reshuffled in the furnace (shuffling of course). There can be a fuel assembly and a very small number of fuel assemblies that are removed or removed for some sampling investigation or testing). For this reason, the intermediate stop period is shortened. As a result, the operating rate of the nuclear power plant is improved, and the power generation cost is reduced accordingly.

In addition, the amount of exposure to people and equipment is reduced by the reduction in handling of nuclear fuel.
Further, although the present invention itself is not premised on the reprocessing of the fuel, in reality, the reprocessing is performed in our country, and thus the cost of the reprocessing is reduced.

Hereinafter, the present invention will be described based on the best mode.
FIG. 6 shows the basics of this embodiment. In the present embodiment, one cycle is 24 months, and a stop period for fuel replacement is provided in the middle. This figure shows, from the left, the first (first) half cycle operation start (BOC), the same operation end (EOC), the second (second) half cycle operation start (BOC), The fuel loading pattern in the core at the end of operation (EOC) is shown. The figure consisting of three, two and one square in order from the top is a so-called 1/4 core diagram.

  Of the two upper and lower character strings in the square, the lower row is the identification number of the fuel loaded body. Similarly, A, B, C and D indicate groups of fuel assemblies, and 01 and 02 which follow thereafter are identification numbers of the fuel assemblies in each group. Upper 1 ce, 2 ce, 3 ce 1, 2, 3 indicate the number of half-cycle operations that have been combusted so far. New indicates new fuel.

As shown in the center of FIG. 6, after the operation of the previous half cycle is compared with the time of the operation of the latter half cycle, only the fuel of the group A that has been subjected to the half cycle operation shown by a bold square three times is shown. It is unloaded during the intermediate stop period (MS), after which new fuel of group D is loaded.
Further, the positions of the B and C group fuels that are continuously burned in the latter half cycle remain in the furnace. For this reason, these fuels are once carried out of the furnace and not carried in again during the intermediate stop period. Further, as can be seen by comparing the arrangement diagrams in the left and right ends of FIG. 6, after the end of the latter half cycle, the burned 3ce fuel is not only removed from the furnace, but also indicated by New. Rearrangement including new fuel has been made. In this embodiment, since the number of fuels loaded in the core is small, 2/3 of the total fuel is continuously used, and the fuel is replaced in 1.5 cycles (36 months).

(Experimental example)
An experimental example of the present invention will be described with reference to the drawings.
The experimental example of the present invention is an examination of the core characteristics and economics of the two cases described in the background section above under the following conditions.
・ Core type: 3 loop 17 × 17 type PWR
・ Fuel enrichment: 4.8wt%
・ Maximum burnup of assembly: 55 GWd / t or less ・ Output peaking coefficient: 1.52 or less ・ Moderator temperature coefficient: Negative ・ Reactor shutdown margin: 1.8 Δk / k or more

-Required cycle length: Case 1: 26.2 GWd / t (24 months)
: Case 2: 13.1 GWd / t (12 months)
: Case 3 (present invention): 13.1 GWd / t (12 months × 2)
Case 1 is a case where no intermediate stop period is provided in a long cycle operation in which one cycle is 24 months. However, in the comparative calculation of power generation costs, it is assumed that spent fuel is reprocessed, unlike the US case described in the background section.
Case 2 is the same as Case 2 described in the background art section, and in the intermediate stop period provided in the middle of the long cycle operation, all the fuel assemblies continuously used for the next operation are taken out to the pits. For this reason, the fuel configuration, replacement scheme, and fuel loading pattern of Case 1 and Case 2 are the same as those shown in FIGS. 2, 3, 4, and 5, respectively.

  Case 3 is an experimental example of the present invention, and it is the same as Case 2 to replace the burned fuel with the new fuel during the intermediate stop period. It is to be loaded at the position.

  FIG. 7 shows the fuel configuration and replacement scheme of the experimental example of the present invention. FIG. 8 shows a fuel loading pattern before the intermediate stop period, and FIG. 9 shows a fuel loading pattern after that. As shown in FIG. 7, in this experimental example, at the end of the previous half cycle, 40 burned fuel assemblies, which are a little over 1/4 of the whole, are removed from the furnace, and the same number of new fuel assemblies are loaded. Is done. In addition, when stopping after the long cycle operation is completed, 40 fuel assemblies are removed from the furnace in the same way, of which 37 fuel assemblies are already burned, and in addition to 2ce There are three fuel assemblies.

  The meanings of the three-stage character strings in the lattice in FIGS. 8 and 9 are the same as those in FIG. As can be seen by comparing the left diagrams of FIG. 8 and FIG. 9, the position of the fuel continuously used in the subsequent half cycle is not changed. For this reason, it is once carried out of a furnace and is not carried in again. As can be seen from the diagrams on the right side of FIGS. 8 and 9, the combustible poison clusters are consumed in the latter half cycle because the arrangement of the fuel to be continuously used is not changed. As a reminder, in periodic inspections at the end of each cycle, the fuel that is continuously used or burned in the next cycle can be taken out of the pit and rearranged. is there.

  Next, Table 1 shows the evaluation results of the core characteristics of each case. In addition, about the experimental example of this invention of case 3, it shows about each half cycle before and after. From this table, in the case of the experimental example of the present invention, the arrangement of the new fuel and the fuel to be used continuously (shuffling) is not performed at all, but the limitations on various core characteristics are sufficiently satisfied. I can see that.

Finally, the evaluation of the economic efficiency of the experimental example of the present invention and the conventional example will be described.
The intermediate stop period is 0 days in case 1. In case 2, the cooling period is 5 days and all (157 bodies) pits are taken out, so the period required for the work is 8 days. For this reason, the total stop period is 13 days. In case 3, the cooling period is also 5 days, and the number of fuel assemblies to be replaced is 40. Therefore, the period required for this is (8 × 40/157 =) 2.04 days. For this reason, a total of about 7 days is required for the intermediate suspension period.

  The alternative power generation cost during the intermediate stop period will be described. During the intermediate shutdown period, thermal power generation with high fuel costs will be performed instead of nuclear power generation. For this reason, the extra cost depends on the crude oil price in reality, but is assumed to be 100 million yen / day for simplicity of calculation. Based on Case 1, Case 2 will cost an extra 1.3 billion yen. In Case 3, it will cost an additional 700 million yen.

  Next, a decrease in fuel cost will be described. The fuel cost is calculated from the difference in the number of replacement units by calculating the amount per unit for each case. As can be seen from Table 1, in each case, at the end of the cycle or at the end of the previous half cycle, the boron concentration at which the core becomes critical (critical boron concentration) is higher than the target value. For this reason, it is reflected that the fuel enrichment is lowered so that the critical boron concentration becomes the target value, and the fuel cycle cost is lowered accordingly. The results are shown in Table 2. From this table, it can be seen that with Case 1 as a reference, Case 2 will cost 48.3 billion yen, and Case 3 will cost 45.8 billion yen.

  From the above results, in the experimental example of the present invention, the cost of the alternative fuel is increased by 700 million yen, but the cost of the fuel cycle is reduced by approximately 4.6 billion yen because there is an intermediate stop period as compared with case 1. Therefore, the total cost is reduced by 3.9 billion yen per cycle. Compared to Case 2, the cost of the fuel cycle will increase by 250 million yen, but the cost for alternative fuel during the intermediate stoppage will decrease by 600 million yen. Therefore, the cost is reduced by 350 million yen per cycle. Differences in capital costs can be ignored.

  In addition to the above, in this experimental example, it is not possible to convert it into a monetary amount, such as a decrease in exposure dose, but important matters are also improved.

As mentioned above, although this invention has been demonstrated based on the desirable embodiment, this invention is not limited to this. That is, for example, the following forms are also included.
Implement on BWR, not PWR.
The fuel is used by mixing not only uranium but also plutonium.
On the 7th day of the stoppage, a part of periodic inspection is performed.
A part of the fuel that is continuously used in the next half-cycle operation is changed in its position.

It is a figure which shows the relationship between the length of 1 cycle, and various costs for every enrichment. It is a figure which shows a fuel structure and exchange scheme when there is no stop period in the middle of the long (24 months) cycle (case 1). FIG. 4 is a view showing a fuel loading pattern in the case 1. It is a figure which shows a fuel structure and replacement | exchange scheme when an intermediate stop period is provided for the fuel replacement | exchange and shuffling in the middle of a long cycle (case 2). FIG. 6 is a view showing a fuel loading pattern in the case 2. It is a figure which shows the principle of the best embodiment of this invention. It is a figure which shows a fuel structure and replacement | exchange scheme when the stop period which performs only a fuel replacement | exchange in a long cycle and the middle is provided (case 3). It is a figure which shows the fuel loading pattern at the time of the front half cycle start in the said case 3, and the burnup in this half cycle. It is a figure which shows the fuel loading pattern at the time of the latter half cycle start in the said case 3, and the burnup and boron consumption in this half cycle.

Claims (13)

Adopting a long cycle operation determined from the period of time to undergo a predetermined periodic inspection, etc., partly burnt fuel is removed from the furnace during the long cycle operation, and new fuel is loaded into the furnace instead. In order to operate a light water reactor with an intermediate shutdown period, a fuel loading method,
The replacement of a part of the burned fuel with the new fuel during the intermediate stop period is performed without rearranging the fuel continuously used in the next operation in the furnace. Light water reactor operation, fuel loading method.   The replacement of a part of the burned fuel with the new fuel during the intermediate stop period means that the unburned fuel is removed from the furnace and the new fuel is not loaded at the position where the fuel was present. The light water reactor operation and fuel loading method according to claim 1.   3. The light water reactor according to claim 1, wherein the long cycle operation is one cycle of 24 months, and the intermediate stop period is provided at a central time. Operation, fuel loading method.   The in-furnace fuel is batch-divided into several batches, and replacement of a part of burned fuel in the intermediate stop period is performed only for one burned batch. The operation of a light water reactor according to any one of claims 3 to 4, and a fuel loading method.   5. The light water reactor according to claim 4, wherein the number of batches of the fuel in the reactor is 4, and the number of fuels that are continuously used in the next operation without replacement during the intermediate stop period is 3 batches. Operation, fuel loading method.   When replacing the spent fuel with new fuel during the intermediate stop period, it is necessary to undergo the predetermined periodic inspection in order to eliminate the need to rearrange the fuel to be used continuously in the next operation. The new fuel to be used for the next operation within the period is placed at a predetermined position in the furnace, and is loaded in the period to receive the predetermined periodic inspection, and the new fuel loaded into the furnace in the intermediate stop period 6. The operation of the light water reactor and the fuel loading method according to any one of claims 1 to 5, wherein predetermined measures are taken respectively.   The fact that the fuel used for the next operation is arranged at a predetermined position in the reactor within the period to receive the predetermined periodic inspection means that the fuel assembly arranged at the outermost periphery of the core is the new fuel and the next time. It is a fuel that has been burned during the shutdown period, and a part of the most burned fuel out of only half-cycle fuel is removed from the core and replaced with new fuel. The light water reactor operation and fuel loading method according to claim 6.   The measures taken for the new fuel loaded during the period to receive the predetermined periodic inspection are that the new fuel loaded in the non-periphery of the core is in a gadolinia or a flammable poison cluster, 8. The light water reactor operation and fuel loading method according to claim 6 or 7, wherein the measures taken for the new fuel loaded in the tank include a combustible poison cluster.   The light water reactor operation and fuel loading method according to any one of claims 1 to 8, wherein the light water reactor operation and fuel loading method are for a pressurized water reactor.   The light water reactor operation and fuel loading method according to any one of claims 1 to 9, wherein the number of loops of the light water reactor is three. Operation of a light water reactor that employs a long cycle operation and removes part of the burned fuel from the reactor during the long cycle operation, and instead provides an intermediate stop period to load new fuel into the reactor. A fuel loading method,
The replacement of a part of the burned fuel with new fuel during the intermediate stop period is the arrangement of the fuel in the furnace at the start of the operation of the previous half cycle and the periodic inspection provided before the start of the previous half cycle. By setting the state of the new fuel to be loaded during the period or the intermediate stop period in advance according to a specific rule, it is fuel that will be used continuously in the subsequent half-cycle operation and placed in the furnace The fuel that needs to be changed is a replacement that is made to be within 8% of the total loaded fuel,
Furthermore, the content determined according to the specific rule satisfies the following detailed rules (a) to (h):
(A) The new fuel placed inside during the previous half-cycle operation, when used as a twice-burning fuel, is placed at the outer periphery or at a position adjacent to the fuel at the outer periphery, with the exception of up to eight bodies. To
(B) In the first half cycle, the same number of three-time combustion fuel is arranged inside as the new fuel arranged inside in the latter half cycle operation.
(C) The new fuel placed inside during the subsequent half-cycle operation is placed at the outer periphery or at a position adjacent to the fuel at the outer periphery, except for up to eight exceptions, when used as a three-time combustion fuel. To
(D) Other than the fuel taken out in the previous half cycle, it is arranged at a position where the power distribution becomes flat. (E) Throughout the operation period of one cycle, the five bodies at the center of the furnace are not new fuel.
(F) New fuel, which is not located inside the furnace and will be placed in the surrounding eight locations, will not be adjacent to each other, except in a flammable poison cluster,
(G) Since the top of 1 is located on the outer periphery of the furnace, the new fuel in which fuel is to be placed in the surrounding seven locations, the one adjacent to the new fuel on the outer periphery of the furnace is the maximum With 4 exceptions, it will be in a flammable poison cluster,
(H) A light water reactor operation and fuel loading method characterized in that the new fuel in the outer peripheral portion does not enter the combustible poison cluster except for a maximum of four exceptions. The operation of a light water reactor according to claim 11, a fuel loading method,
The fuel that is continuously used in the subsequent half-cycle operation and needs to be rearranged in the furnace is within 6% of the total loaded fuel. Light water reactor operation, fuel loading method. The light water reactor operation and fuel loading method according to claim 12,
A light water reactor operation and fuel loading method, characterized in that there is no fuel that is continuously used in the operation of the latter half cycle and is not rearranged in the furnace.

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