JP2016109585A - Fast reactor core and fast reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with a wide range of TRU compositions in which an MA ratio is different, flexibly, and perform nuclear transformation of MA.SOLUTION: A fast reactor core 100 of an embodiment comprises plural first fuel assemblies 110, and plural second fuel assemblies 120. Each of the first fuel assemblies 110 comprises plural forst fuel elements having a minor actinide which occupies a first ratio in transuranic element which is acquired as a result of separation in re-processing, and plural neutron spectrum softening elements having a neutron spectrum softening material. Each of the second fuel assemblies 120 comprises plural second fuel elements having a minor actinide which occupies a second ratio higher than the first ratio in transuranic element which is acquired as a result of separation in re-processing, and plural neutron spectrum softening elements having a neutron spectrum softening material.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to a fast reactor core that converts a transuranium element (TRU) into an element other than TRU and a fast reactor having the same.

  FIG. 21 is a horizontal sectional view schematically showing a configuration example of a core of a conventional fast reactor. As shown in FIG. 21, the core 1 includes a core fuel assembly 11 containing a lot of fissile material, a blanket fuel assembly 13 containing a large amount of a fissile parent material that is converted into a fissile material by neutron absorption, a neutron A control rod guide tube 14 into which a control rod containing a large amount of absorbing material and controlling the fission reaction is inserted. The core fuel assembly 11 includes an inner core fuel assembly 11a and an outer core fuel assembly 11b. The difference between the inner core fuel assembly 11a and the outer core fuel assembly 11b is that the Pu (plutonium) enrichment degree of the outer core fuel assembly 11b loaded in the outer region in the core where neutron leakage is large is high. It is.

  FIG. 22 is an elevational sectional view showing a configuration example of a core fuel assembly of a conventional fast reactor. FIG. 23 is a horizontal sectional view thereof. A number of fuel elements 22 are loaded in the core fuel assembly 11 in a tubular tube 24 arranged in parallel and extending vertically. The fuel element 22 has a cladding tube 32 (FIG. 24) made of a metal material such as stainless steel. The fuel element 22 has an upper blanket fuel part 29, a core fuel part 28, and a lower blanket fuel part 27.

  An upper portion of the trumpet tube 24 is provided with a handling head 25 that serves as a grip when the core fuel assembly 11 is loaded into the core 1 or taken out of the core 1. On the other hand, an entrance nozzle 21 for fixing and supporting the core fuel assembly 11 is provided below the trumpet tube 24. A coolant inflow hole 21 a is formed in the side wall of the entrance nozzle 21. The coolant flowing in from the coolant inflow hole 21 a flows out from the uppermost coolant outflow hole 26 after cooling the core fuel assembly 11.

  FIG. 24 is a horizontal sectional view showing an example of a fuel element of a fuel assembly of a conventional fast reactor. As shown in FIG. 24, in the fuel element 22, a fuel 31 made of a mixed oxide of plutonium (Pu) and uranium (U) is loaded in a cladding tube 32. There is a gap between the fuel and the cladding.

  The core fuel and blanket fuel constituting the core 1 of the fast reactor are mixed oxide fuel from Pu extracted from the spent fuel reprocessing facility of the light water reactor (LWR) and depleted uranium produced as a by-product from the uranium enrichment facility Is manufactured and burned in the core before being reused.

  Spent fuel reprocessing wastes include minor actinides (MA) with half-lives on the order of tens of thousands of years and long half-life fission products (LLFP) with half-lives on the order of thousands to tens of thousands of years. ) Is included and is planned to be disposed of deep underground as high-level radioactive waste (HLW). However, the disposal and management of HLWs taking into account the fact that they have a half-life on the order of tens of thousands of years is an issue.

  In order to sustain the use of nuclear power, the HLW disposal problem needs to be resolved. While uranium elements (PRUs) containing Pu are burned and destroyed by fission, LLFP is stable or short-lived by neutron transmutation. Studies are underway to convert it to a phase nuclide.

  In order to greatly improve the efficiency of TRU transmutation, a U fuel-free core has been proposed. In a conventional nuclear reactor that uses a mixture of TRU and U as fuel, since a new TRU is generated from U, the net TRU conversion amount is small. On the other hand, by eliminating U (no uranium), generation of new TRUs is eliminated, and a significant improvement in TRU transmutation efficiency is achieved. However, this also creates new challenges.

  Generally, in the safety design of nuclear reactors, the Doppler effect is expected in which the rate of neutron absorption by the core fuel increases and the reactivity decreases as the prompt negative feedback reactivity associated with the core temperature rise. This Doppler effect is mainly due to an increase in the resonance absorption reaction due to U238 in the fuel. Therefore, a negative feedback reactivity based on the Doppler effect is greatly reduced in a U-core without TRU. Although there are examples for solving this problem, it cannot be said that the degree of the effect or the feasibility is sufficient.

TRU Burning Fast Reactor Cycle Using Uranium-free Metallic Fuel (ICAPP2014 paper) Arie et al .: “TRU Burning Fast Reactor Cycle Using Uranium-free Metallic Fuel”, Proceedings of ICAPP 2014, Charlotte, USA, April 6-9, 2014, Paper 14136 N. Messaoudi and J. Tommasi: “Fast Burner Reactor Devoted to Minor Actinide Incineration”, Nuclear Technology, Vol.137, Feb.2002.

  In the future, in order to solve the problem of high-level waste while focusing on power generation using light water reactors, when considering the introduction of fast reactors responsible for TRU combustion including MA, fast reactors can be made by introducing as few Pu as possible. It is desirable to reduce the cost of the entire system. Also, a new reprocessing system that collects and recycles the entire TRU is required by upgrading the conventional reprocessing that collects and recycles only U / Pu. However, until such a fast reactor and reprocessing system are put into practical use, it is considered that only U / Pu is collected by the conventional reprocessing system, and MA moves to a high level waste liquid.

  The recovered Pu may be used in light water reactors loaded with MOX fuel. Therefore, it is necessary not only to recover TRU by the new reprocessing method but also to recover and recycle TRU in the high level waste liquid by the conventional reprocessing method in order to solve the problem of high level waste. is there. As will be described later, 90% or more of the composition of TRU transferred to the high-level waste liquid is MA, which is greatly different from the composition of TRU extracted in a mixed state by the new reprocessing method (MA; 20% or less). Therefore, as a fast reactor core for transmuting TRU, a flexible ability to transmutate by loading a wide range of TRU compositions with different MA ratios is required.

  In an example known as a reprocessing technology, it is assumed that spent fuel TRU is recovered in a mixed state, and the MA in the TRU composition is as small as about 13%, for example, and the amount of MA transmutation per 1 GWe is light water reactor About 5 units.

  In another example, a composition in which the MA ratio is increased to about 25% based on TRU from spent fuel is used, so that the amount of MA transmutation per 1 GWe is about 10 Although it is relatively large for several units, the problem of reprocessing U-oxide-free fuel has not been solved, and the feasibility as a system cannot be foreseen.

  Therefore, an embodiment of the present invention aims to perform transmutation of MA while flexibly supporting a wide range of TRU compositions having different MA ratios in the core of a fast reactor.

  In order to achieve the above-described object, the present embodiment is a fast reactor core that converts a transuranium element into an element other than the transuranium element, and a plurality of first fuel assemblies that extend in the vertical direction and are arranged in parallel to each other. And a plurality of second fuel assemblies that extend in the vertical direction and are arranged in parallel with the first fuel assemblies, and each of the first fuel assemblies is obtained as a result of separation in reprocessing. A first fuel having a minor actinide occupying a first ratio in the transuranium element, and a plurality of cladding tubes that contain the first fuel and extend in the vertical direction and are closed at both ends. A fuel element and a plurality of neutron spectrum softening elements having a cylindrical tube extending in the vertical direction and containing a cladding tube closed at both ends, containing a neutron spectrum softening material that softens the neutron energy spectrum, Each of the fuel assemblies contains a second fuel having a minor actinide occupying a second ratio higher than the first ratio in the transuranium element obtained as a result of separation in reprocessing, and the second fuel And a plurality of second fuel elements having a cylindrical tube extending in the vertical direction and closed at both ends, and a cylindrical shape extending in the vertical direction containing a neutron spectrum softening material for softening the neutron energy spectrum And a plurality of neutron spectrum softening elements having a cladding tube closed.

  The present embodiment also includes a fast reactor core, a reactor vessel that houses the fast reactor core immersed in a reactor coolant, and a reactor containment vessel that houses the reactor vessel. The fast reactor core includes a plurality of first fuel assemblies extending in a vertical direction and arranged in parallel to each other, and a plurality of first fuel assemblies extending in a vertical direction and arranged in parallel with the first fuel assemblies. A first fuel having a minor actinide occupying a first proportion of the transuranium element obtained as a result of separation in reprocessing, and a second fuel assembly, A plurality of first fuel elements having a cylindrical shape extending in the vertical direction and containing a first fuel element and a cladding tube closed at both ends, and a neutron spectrum softening material that softens the neutron energy spectrum are accommodated and extend in the vertical direction. Cylindrical at both ends A plurality of neutron spectrum softening elements having a cladding that is stopped, wherein each of the second fuel assemblies is less than the first proportion in the transuranium element obtained as a result of separation in reprocessing A plurality of second fuel elements having a second fuel having a minor actinide occupying a higher second ratio, and a cladding tube containing the second fuel and extending vertically and closed at both ends; And a plurality of neutron spectrum softening elements having a cylindrical tube extending in the vertical direction and having a cladding tube closed at both ends, containing a neutron spectrum softening material for softening the neutron energy spectrum.

  According to the embodiment of the present invention, MA transmutation can be performed in a fast reactor core while flexibly supporting a wide range of TRU compositions having different MA ratios.

It is an elevation sectional view showing the composition of the fast reactor according to the first embodiment. It is a horizontal sectional view of a 1/6 core showing the composition of the fast reactor core by a 1st embodiment. It is a horizontal sectional view of the 1st fuel assembly in a 1st embodiment. FIG. 3 is an elevational sectional view of a first fuel assembly in the first embodiment. It is a horizontal sectional view showing the 1st fuel element of the 1st fuel assembly in a 1st embodiment. It is a table | surface which shows the example of a composition of TRU which is a main component of the 1st fuel element of the 1st fuel assembly in 1st Embodiment. It is a horizontal sectional view showing the neutron spectrum softening element of the first fuel assembly in the first embodiment. It is a horizontal sectional view of the 2nd fuel assembly in a 1st embodiment. FIG. 3 is an elevational sectional view of a second fuel assembly in the first embodiment. It is a horizontal sectional view showing the 2nd fuel element of the 2nd fuel assembly in a 1st embodiment. It is a table | surface which shows the example of the composition of TRU which is a main component of the 2nd fuel element of the 2nd fuel assembly in 1st Embodiment. It is a graph which shows the comparative example of the influence on the Doppler coefficient by the neutron spectrum softening element of 1st Embodiment and a prior art example. It is a graph which shows the comparative example of the transmutation amount in the fast reactor core of 1st Embodiment and a prior art example. It is a graph which shows the comparative example of the combustion defect reactivity in the fast reactor core which concerns on 1st Embodiment, and a comparative core. It is a graph which shows the comparative example of the Na void reactivity in the fast reactor core which concerns on 1st Embodiment, and a comparative core. It is a horizontal sectional view of the 2nd fuel assembly in a 2nd embodiment. It is a horizontal sectional view showing the 2nd fuel element of the 2nd fuel assembly in a 2nd embodiment. It is a table | surface which shows the example of the composition of TRU which is a main component of the 2nd fuel element of the 2nd fuel assembly in 2nd Embodiment. It is a graph which shows the comparative example of the transmutation amount in the fast reactor core of 2nd Embodiment and a prior art example. It is a graph which shows the comparative example of the combustion defect reactivity in the fast reactor core which concerns on this embodiment, and a comparative core. It is a horizontal sectional view which shows the structural example of the core of the conventional fast reactor. It is an elevational sectional view showing a configuration example of a fuel assembly of a conventional fast reactor. It is a horizontal sectional view which shows the structural example of the fuel assembly of the conventional fast reactor. It is a horizontal sectional view which shows the example of the fuel element of the fuel assembly of the conventional fast reactor.

  Hereinafter, a U-free fuel assembly and a U-free fuel core according to an embodiment of the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is an elevational sectional view showing the configuration of the fast reactor according to the first embodiment. The fast reactor 200 is provided so as to close the fast reactor core 100, the cylindrical reactor vessel 4 that includes the fast reactor core 100 and has a bottom portion and extends in the vertical direction, and the upper opening of the reactor vessel 4. It has a shielding plug 6 and a reactor containment vessel 10 for storing them.

  The fast reactor core 100 is supported by the core support plate 2. The fast reactor core 100 is formed with respective core portions such as a plurality of first fuel assemblies 110 and second fuel assemblies 120 described later as constituent elements. A control rod drive mechanism 5 is provided on the shielding plug 6 above the fast reactor core 100 so that a control rod (not shown) can be inserted into the fast reactor core 100. The coolant used for cooling the fast reactor core 100 in the reactor vessel 4 is, for example, liquid metal sodium, which flows into the reactor vessel 4 from the coolant inlet pipe 8 and from the coolant outlet pipe 9. leak.

  FIG. 2 is a horizontal sectional view of the 1/6 core showing the configuration of the fast reactor core according to the present embodiment. The fast reactor core 100 is composed of a first fuel assembly 110, a second fuel assembly 120, and a control rod guide tube 14 that are arranged in parallel to each other in the vertical direction. It has a body 15. The control rod guide tubes 14 are arranged to be scattered in the fast reactor core 100. The thermal power of the fast reactor core 100 in the case of FIG. 2 is, for example, about 700 MWth, and the electrical power is about 300 MWe. However, the size of the fast reactor core 100 is not limited to this, and may be smaller. It may be larger than this.

  FIG. 3 is a horizontal sectional view of the first fuel assembly. FIG. 4 is an elevational sectional view. The first fuel assembly 110 includes a first fuel element 111 and a neutron spectrum softening element 112 which are arranged in a triangular arrangement in parallel with each other, and a trumpet tube 113 which houses them. One neutron spectrum softening element 112 is arranged at the center of the array, and annular arrays of the first fuel element 111 and the neutron spectrum softening element 112 are alternately arranged in the radial direction around the neutron spectrum softening element 112. A hexagonal tube-shaped trumpet tube 113 is provided radially outward of the final annular row. A space between the first fuel element 111 and the neutron spectrum softening element 112 in the trumpet 113 serves as a coolant flow path.

  FIG. 3 shows a case where four rows of the first fuel elements 111 and four rows of the neutron spectrum softening elements 112 are alternately arranged around the central neutron spectrum softening element 112, but the present invention is not limited thereto. Not. The number of columns may be smaller or larger. Further, the arrangement method of the first fuel element 111 and the neutron spectrum softening element 112 is not limited to a form in which an annular row as shown in FIG. 3 is alternately repeated. For example, a method of alternately arranging the first fuel elements 111 and the neutron spectrum softening elements 112 in rows parallel to each other may be used. In addition, although the case of a triangular arrangement as a whole is shown, the arrangement may be a square lattice and the trumpet tube 113 may also be a square cylinder.

  As shown in the elevation cross-sectional view of FIG. 4, the first fuel assembly 110 has a core fuel portion 110a, but unlike the conventional fast reactor fuel assembly, it has an upper blanket and a lower blanket for plutonium breeding. Not done.

  FIG. 5 is a horizontal sectional view showing the first fuel element of the first fuel assembly. The first fuel element 111 includes a first fuel 111a extending in a columnar shape in the vertical direction, and a cladding tube 111b provided on the outer periphery in the radial direction of the first fuel 111a. The cladding tube 111b is cylindrical and closed at both ends.

  The first fuel 111a is mainly composed of mixed TRU recovered in a state where a part or all of elements of plutonium (Pu), neptunium (Np), americium (Am) and curium (Cm) are mixed in the nuclear fuel recycling process. As a metal fuel having a base material that is substantially the remainder. As the base material, for example, zirconium (Zr), molybdenum (Mo), niobium (Nb), tungsten (W), or the like can be used. In practice, a small amount of U transferred to the collected mixed TRU is also included, but the effect on the effect of the present embodiment is small.

  FIG. 6 is a table showing an example of the composition of TRU that is the main component of the first fuel element of the first fuel assembly. The mixed TRU used for the first fuel element 111 is the TRU composition of the spent fuel taken out from the light water reactor. FIG. 6 shows an example in which the burnup is 33 GWd / t and the cooling is performed for 10 years after taking out. Pu accounts for the majority of 87% of TRU, and the total composition ratio of Np, Am, Cm, which is MA (minor actinide) excluding Pu among the superuranium elements belonging to actinoids, is 13%. Hereinafter, the ratio of MA in the TRU with the spent fuel taken out from the light water reactor is referred to as a first ratio.

  In the example shown above, the ratio of MA to all TRUs is about 13%, but this value varies depending on the burnup and cooling period. However, in reality, even if the burnup, cooling period, etc. change, the first ratio of MA to all TRUs is usually 20% or more based on the TRU composition of spent fuel extracted from the light water reactor. It will never be.

  FIG. 7 is a horizontal sectional view showing the neutron spectrum softening element of the first fuel assembly. The neutron spectrum softening element 112 includes a neutron spectrum softening material 112a extending in a columnar shape in the vertical direction and a cladding tube 112b provided on the outer periphery in the radial direction of the neutron spectrum softening material 112a. The cladding tube 112b extends in a cylindrical shape in the vertical direction, and both ends are closed.

Examples of the neutron spectrum softening material 112a include Li ₂ O, B ₄ C, BeO, and ZrH ₂ that include elements having a small neutron capture cross section and a relatively small atomic number. Here, Li mainly includes the isotope ⁷ Li, B mainly includes the isotope ¹¹ B, and the like. Further, although the neutron moderating ability is reduced as compared with H and Be, carbon (C) may be used in the form of graphite or SiC as the neutron spectrum softening material 112a.

  The first fuel 111a and the neutron spectrum softening material 112a are cylindrical, and the cladding tube 111b and the cladding tube 112b are cylindrical. However, the present invention is not limited to this and may be a polygonal shape.

  FIG. 8 is a horizontal cross-sectional view of the second fuel assembly in the first embodiment. FIG. 9 is an elevational sectional view of the second fuel assembly. The second fuel assembly 120 includes a second fuel element 121 and a neutron spectrum softening element 122 arranged in a triangular arrangement parallel to each other, and a wrapper provided radially outside the second fuel element 121 and the neutron spectrum softening element 122. It has a tube 123. The neutron spectrum softening element 122 may be the same as the neutron spectrum softening element 112 of the first fuel assembly 110.

  As shown in the sectional elevation view of FIG. 9, the second fuel assembly 120 has a core fuel portion 120 a, similar to the first fuel assembly 110.

  FIG. 10 is a horizontal sectional view showing the second fuel element of the second fuel assembly. The second fuel element 121 includes a second fuel 121a extending in a columnar shape, and a cladding tube 121b provided around the radial direction of the second fuel 121a. The cladding tube 121b is cylindrical and has both ends closed. The second fuel 121a is obtained by recovering TRU from the remaining high-level waste from which Pu has been recovered in the nuclear fuel recycling process.

  FIG. 11 is a table showing an example of the composition of TRU that is the main component of the second fuel element 121 of the second fuel assembly in the first embodiment. Since the remaining Pu is recovered, Pu is about 3%, and 97% is occupied by minor actinides of Np, Am, and Cm. Thus, instead of the TRU collected by normal reprocessing, the ratio of MA with high concentration in TRU collected focusing on MA is also referred to as the second ratio in contrast to the first ratio. And That is, in the present embodiment, the second ratio of the concentrated MA in the second fuel element 121 to the TRU is higher than the first ratio of the MA in the first fuel element 111 to the TRU. It should be noted that the second fuel element 121 is a metal fuel in the form of a metal having a base material that is substantially the remainder, and that, for example, zirconium (Zr) is used as the base material, the first fuel assembly The same as for the body.

  In the present embodiment configured as described above, the number of assemblies of the first fuel assemblies 110 is 336, and the number of assemblies of the second fuel assemblies 120 is 91. As a result, the minor actinide weight fraction in the TRU for both fuel assemblies, ie, the second fraction, averages about 30%. Accordingly, the minor actinide weight ratio is about 2.4 times that in the case where the core is configured by only the first fuel assembly 110.

  FIG. 12 is a graph showing a comparative example of the influence of the neutron spectrum softening element on the Doppler coefficient between this embodiment and the conventional example. The left side of the horizontal axis shows a case where there is no neutron spectrum softening element, and the right side of the horizontal axis shows the case of the present embodiment having a neutron spectrum softening element. The vertical axis represents the ratio (relative value) of absolute values of Doppler coefficients based on the case where there is no neutron spectrum softening element. As shown in FIG. 12, by loading the neutron spectral element, the Doppler coefficient is greatly increased, and a Doppler coefficient having an absolute value more than twice that obtained when the neutron spectral softening element is not loaded is obtained.

  FIG. 13 is a graph showing a comparative example of the amount of transmutation in the fast reactor core between the present embodiment and the conventional example. The left side of the horizontal axis is for the present embodiment, and the right side of the horizontal axis is for the comparative core. The comparative core is a case of a fast core in which the core is composed of only the first fuel assembly. In addition, the three bars in each indicate Pu, MA, and the sum of Pu and MA from the left. The vertical axis represents the nuclear transmutation amount (kg / year).

  In the case of the comparative core, the amount of Pu transmutation is about 200 kg / year and the amount of MA transmutation is about 30 kg / year, whereas in the fast core 100 of this embodiment, the Pu transmutation amount. Is about 130 kg / year and MA transmutation is 110 kg / year. The total value is comparable. Thus, although the amount of Pu transmutation is decreasing, the amount of MA transmutation is increasing several times.

  When the amount of transmutation of 110 kg / year of MA in this embodiment is converted per 1 GWe, it becomes about 380 kg / year / GWe, and MA in spent fuel from about 19 large light water reactors can be transmuted. This is an MA transmutation amount that is about four times the transmutation amount of the comparative core, which is about 100 kg / year / GWe.

The reason for the decrease in the amount of Pu transmutation is that the contribution of conversion from MA to Pu has increased. That is, because Pu ²³⁸ is generated from the Np or Am of MA by nuclear transformation, the net amount of plutonium nuclear transformation is reduced. However, this Pu ²³⁸ can also be transmuted to fission products by recycling.

  FIG. 14 is a graph showing a comparative example of combustion deficiency reactivity in the fast reactor core and the comparative core according to the present embodiment. The left side of the horizontal axis in FIG. 14 shows the case of this embodiment, and the right side shows the case of the comparative core. The comparative core is a case of a fast core in which the core is composed of only the first fuel assembly. The vertical axis represents the combustion deficiency reactivity (relative value).

  In the core loaded with U-free fuel, the generation of fissile material is extremely small, and therefore the reactivity decrease due to combustion is larger than in the core loaded with U-containing (with uranium) fuel containing uranium. That is, the combustion deficiency reactivity (per unit time) is large. For this reason, the operation cycle length is as short as about half that of the conventional U core.

In the fast reactor core 100 of the present embodiment, the amount of MA loaded is large, and as a result, the amount of Pu ²³⁸ generated as a result of MA transmutation is larger than that of the comparative core as described above. Since this Pu ²³⁸ is fissionable, the reduction of fissile material is less than that of the comparative core, and the combustion defect reactivity is reduced to almost half. As a result, the operation cycle can be extended as compared with the comparative core.

  FIG. 15 is a graph showing a comparative example of the Na void reactivity in the fast reactor core and the comparative core of the present embodiment. The left side of the horizontal axis shows the case of this embodiment, and the right side shows the case of the second comparative core. The vertical axis represents Na void reactivity (relative value). The second comparative core has the TRU composition in which the TRU composition of the first fuel assembly 110 and the TRU composition of the second fuel assembly 120 are load-averaged by the number of assemblies in the shape of the core of the present embodiment. It is a reactor core loaded with one type of fuel assembly with approximately the same MA loading.

The MA nuclides, first, unlike ^{U 235} and ^{Pu 239} causing fission in a wide energy range from thermal neutrons to fast ^neutrons, fission like the ^{U 238} is a threshold response at high energy. As for the MA nuclide, secondly, the neutron capture reaction is large in the energy region other than the high energy region.

  When Na is in a void state, the neutron moderation effect is reduced, so that the energy spectrum of neutrons is hardened, that is, shifted to a higher energy side. As a result, the fission reaction of MA increases due to the first effect, and the neutron capture reaction decreases due to the second effect. That is, the positive reactivity effect is large. Thereby, it is known that the Na void reactivity increases to the positive side as the MA loading amount increases.

  When the Na void reactivity is compared between the case of this embodiment and the case of the second comparative core, in this embodiment, both the first fuel assembly 110 and the second fuel assembly 120 are in a void state. The reactivity at the time is slightly larger than the reactivity at the time of void of the second comparative core. However, it can be seen that the reactivity when only the first fuel assembly 110 is in the void state is considerably smaller than the reactivity when the second comparative core is voided.

In the second fuel assembly 120 of the fast reactor core 100 of the present embodiment, the fissile material is hardly contained in the early stage of combustion, but the output is increased because the fissile material (mainly, Pu ²³⁸ described above) increases with combustion. Will rise significantly. For this reason, in the 2nd fuel assembly 120 in the core of the equilibrium cycle in which the fuel of various burnups is mixed, the difference in the output of each fuel becomes large. This difference in output leads to a difference in coolant outlet temperature. For this reason, even in an accident in which the flow rate is abnormally decreased, a large time difference occurs in the voiding behavior of Na in each part of the second fuel assembly 120. This means the possibility of mitigating the influence of Na void reactivity.

  As described above, in the fast reactor core 100 according to the present embodiment, the amount of MA transmutation can be increased while flexibly supporting a wide range of TRU compositions having different MA ratios.

[Second Embodiment]
This embodiment is a modification of the first embodiment. In the second embodiment, the second fuel assembly 130 is different from the second fuel assembly 120 in the first embodiment.

  FIG. 16 is a horizontal sectional view of the second fuel assembly. The second fuel assembly 130 includes a second fuel element 131 and a neutron spectrum softening element 122 arranged in parallel to each other, and a trumpet tube 123 provided on the outer periphery in the radial direction thereof. Regarding the arrangement of the second fuel element 131 and the neutron spectrum softening element 122 in the wrapper tube 123, the arrangement of the second fuel element 121 and the neutron spectrum softening element 122 in the second fuel assembly 120 according to the first embodiment It is the same.

  FIG. 17 is a horizontal sectional view showing the second fuel element of the second fuel assembly. The second fuel element 131 includes a TRU fuel 131a extending in a columnar shape, and a cladding tube 131b provided around the radial direction of the TRU fuel 131a. The cladding tube 131b is cylindrical and has both ends closed.

  FIG. 18 is a table showing an example of the composition of TRU that is the main component of the second fuel element of the second fuel assembly in the second embodiment. The TRU composition of the second fuel element 131 of the second fuel assembly 130 includes the transuranium element recovered in a mixed state of the transuranium element contained in the spent fuel of the nuclear reactor by the nuclear fuel reprocessing process, and the nuclear fuel reprocessing process. Thus, the transuranium elements recovered from the remaining components obtained by recovering U and Pu contained in the spent fuel of the nuclear reactor are mixed at 50:50, respectively.

  Therefore, as shown in FIG. 18, the composition is the composition of each MA shown in FIGS. 6 and 11, that is, the average of the first ratio and the second ratio. Therefore, compared to the TRU composition of the second fuel assembly 120 in the first embodiment, the Pu isotope increases, while the concentrated MA composition, that is, the second ratio decreases to 55%. Yes. However, even in this case, it is sufficiently larger than the proportion of MA (20% or less) in the first fuel assembly 110. Here, the number of assemblies of the first fuel assembly 110 and the first fuel assembly 120 is 336 and 91, respectively, which is the same as in the first embodiment.

  In this embodiment, in this case, the weight ratio of MA in the TRU of both fuel assemblies is about 22%. Therefore, the MA weight ratio is about 1.7 times that of the conventional case in which the core is configured by only the first fuel assembly 110.

  FIG. 19 is a graph showing a comparative example of the amount of transmutation in the fast reactor core between the present embodiment and the conventional example. The left side of the horizontal axis is the case of this embodiment, and the right side of the horizontal axis is the case of the comparative core. The comparative core is a fast core in which the core is composed of only the first fuel assemblies as in the comparative core shown in FIG. In addition, the three bars in each indicate Pu, MA, and the sum of Pu and MA from the left. The vertical axis represents the nuclear transmutation amount (kg / year).

  As in the first embodiment shown in FIG. 13, the comparative core is about 200 kg / year of Pu transmutation and about 30 kg / year of MA transmutation. In the fast reactor core 100, Pu transmutation is about 200 kg / year and MA transmutation is about 75 kg / year. The total value is about the same as in the first embodiment.

  If the transmutation amount of MA is converted per 1 GWe, it is about 250 kg / year / GWe, and MA in spent fuel from about 13 large light water reactors can be transmuted.

  FIG. 20 is a graph showing a comparative example of the combustion defect reactivity in the fast reactor core and the comparative core according to the present embodiment. The left side of the horizontal axis in FIG. 20 shows the case of the second embodiment, and the right side shows the case of the comparative core. The comparative core is the case of a fast core in which the core is constituted by only the first fuel assembly, as in FIG. 14 in the first embodiment. The vertical axis represents the combustion deficiency reactivity (relative value).

  Therefore, in the case of the comparative core, the combustion deficiency reactivity (relative value) is about 5, whereas in the case of the second embodiment, it is about 3 in the case of the first embodiment. Is increased to about 4 which is an intermediate between the case of the comparative core and the case of the first embodiment.

  As described above, the present embodiment has intermediate characteristics between the first embodiment and the conventional example, and does not have a particularly unique state. In this way, MA transmutation can be performed while flexibly supporting a wide range of TRU compositions with different MA ratios.

[Other Embodiments]
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention.

  For example, in the embodiment, the case of metal fuel has been described as an example, but the present invention is not limited to this. For example, an oxide may be included. Further, it may be diluted with at least one of magnesium oxide, aluminum oxide, and zirconium oxide. Further, nitride fuel may be used. Further, it may be diluted with at least one of aluminum nitride and silicon nitride.

  Moreover, you may combine the characteristic of each embodiment. Furthermore, these embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Core support plate, 4 ... Reactor vessel, 5 ... Control rod drive mechanism, 6 ... Shield plug, 8 ... Coolant inlet piping, 9 ... Coolant outlet piping, 10 ... Reactor containment vessel, 11 ... core fuel assembly, 11a ... inner core fuel assembly, 11b ... outer core fuel assembly, 13 ... diameter blanket fuel assembly, 14 ... control rod guide tube, 15 ... shielding body, 21 ... entrance nozzle, 21a ... cooling Material inlet hole, 22 ... Fuel element, 24 ... Trumpet pipe, 25 ... Handling head, 26 ... Coolant outlet hole, 27 ... Lower blanket fuel part, 28 ... Core fuel part, 29 ... Upper blanket fuel part, 31 ... Fuel, 32 ... cladding tube, 100 ... fast reactor core, 110 ... first fuel assembly, 110a ... core fuel part, 111 ... first fuel element, 111a ... first fuel, 111b ... cladding tube, 112 ... neutron spectrum Softening element, 112a ... neutron spectrum softening material, 112b ... cladding tube, 113 ... trumpet tube, 120 ... second fuel assembly, 120a ... core fuel part, 121 ... second fuel element, 121a ... second fuel, 121b ... coating Tube 122, neutron spectrum softening element, 123 ... Trumpet tube, 130 ... Second fuel assembly, 131 ... Second fuel element, 131a ... TRU fuel, 131b ... Cladding tube, 200 ... Fast reactor

Claims (10)

A fast reactor core used in a fast reactor core that converts a transuranium element into an element other than the transuranium element,
A plurality of first fuel assemblies extending in a vertical direction and arranged in parallel to each other;
A plurality of second fuel assemblies extending in a vertical direction and arranged in parallel with the first fuel assemblies;
With
Each of the first fuel assemblies is
A first fuel having a minor actinide occupying a first ratio in the transuranium element obtained as a result of separation in reprocessing, and a cylindrical shape containing the first fuel and extending in the vertical direction are closed at both ends. A plurality of first fuel elements having a cladding tube;
A plurality of neutron spectrum softening elements having a cladding tube containing a neutron spectrum softening material that softens a neutron energy spectrum and extending vertically and closed at both ends;
Comprising
Each of the second fuel assemblies is
A second fuel having a minor actinide occupying a second ratio higher than the first ratio in the transuranium element obtained as a result of separation in reprocessing, and a cylinder containing the second fuel and extending in the vertical direction A plurality of second fuel elements having a cladding tube closed at both ends,
A plurality of neutron spectrum softening elements having a cladding tube containing a neutron spectrum softening material that softens a neutron energy spectrum and extending vertically and closed at both ends;
A fast reactor core characterized by comprising:   The fast reactor core according to claim 1, wherein the second fuel is obtained by reducing a ratio of plutonium in the transuranium element obtained as a result of separation in reprocessing.   The fast reactor core according to claim 1, wherein the second ratio is 20% by weight or more.   The fast reactor core according to any one of claims 1 to 3, wherein the transuranium element includes at least one of neptunium, americium, and curium.   The at least one of the first fuel and the second fuel includes a metal form in which a transuranium element is diluted with at least one of zirconium, molybdenum, niobium, and tungsten. 5. The fast reactor core according to any one of 4 above.   5. The fast reactor core according to claim 1, wherein at least one of the first fuel and the second fuel contains an oxide. 6.   The fast reactor core according to claim 6, wherein at least one of the first fuel and the second fuel is diluted with at least one of magnesium oxide, aluminum oxide, and zirconium oxide.   5. The method according to claim 1, wherein at least one of the first fuel and the second fuel is a nitride, and is diluted with at least one of aluminum nitride and silicon nitride. A fast reactor core according to claim 1.   9. The neutron spectrum softening material includes at least one of boron carbide, silicon carbide, graphite, beryllium, beryllia, lithium oxide, and zirconium hydride. The fast reactor core according to the item. A fast reactor core,
A reactor vessel that houses the fast reactor core immersed in a reactor coolant; and
A reactor containment vessel for housing the reactor vessel;
A fast reactor comprising
The fast reactor core is:
A plurality of first fuel assemblies extending in a vertical direction and arranged in parallel to each other;
A plurality of second fuel assemblies extending in a vertical direction and arranged in parallel with the first fuel assemblies;
With
Each of the first fuel assemblies is
A first fuel having a minor actinide occupying a first ratio in the transuranium element obtained as a result of separation in reprocessing, and a cylindrical shape containing the first fuel and extending in the vertical direction are closed at both ends. A plurality of first fuel elements having a cladding tube;
A plurality of neutron spectrum softening elements having a cladding tube containing a neutron spectrum softening material that softens a neutron energy spectrum and extending vertically and closed at both ends;
Comprising
Each of the second fuel assemblies is
A second fuel having a minor actinide occupying a second ratio higher than the first ratio in the transuranium element obtained as a result of separation in reprocessing, and a cylinder containing the second fuel and extending in the vertical direction A plurality of second fuel elements having a cladding tube closed at both ends,
A plurality of neutron spectrum softening elements having a cladding tube containing a neutron spectrum softening material that softens a neutron energy spectrum and extending vertically and closed at both ends;
A fast reactor comprising:

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