JP2015064261A - Nuclear transformation assembly and fast neutron reactor nuclear power plant system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear transformation assembly capable of improving nuclear transformation efficiency of long-lived radioactive wastes such as minor actinide (MA), and a fast neutron reactor nuclear power plant system using the nuclear transformation assembly.SOLUTION: Nuclear transformation assemblies 5 that are loaded into a reactor core 22 of a fast neutron reactor and in each of which a plurality of fuel pins 6, 7, and 8 containing long-lived elements and a plurality of moderator pins 9 containing a neutron moderator are bundled together and contained in a wrapper tube 11 are each configured so that the plurality of fuel pins 6, 7, and 8 is arranged such that a cross-sectional area of fuel elements of the long-lived elements loaded into the fuel pins 6, 7, and 8 are smaller as being closer to a center of the nuclear transformation assembly 5. The fuel pins 6, 7, and 8 are arranged so as to satisfy d1≤d2≤d3, where d1 is a bore diameter of a hollow portion of each of the fuel pins 6 arranged in an outer circumferential portion of the nuclear transformation assembly 5, d3 is a bore diameter of a hollow portion of each of the fuel pins 8 arranged generally in a central portion of the nuclear transformation assembly 5, and d2 is a bore diameter of a hollow portion of each of the fuel pins 7 arranged between the fuel pins 6 and the fuel pins 8.

Description

  The present invention relates to a transmutation assembly loaded in a fast reactor and transmuting long-lived waste, and a fast reactor nuclear power generation system using the assembly.

  The fuel assemblies and cores of fast reactors are described in Naohiro Hirakawa and Tomohiko Iwasaki, “Introduction to Reactor Physics” (Tohoku University Press, October 30, 2003, p 279-286). Generally, in a fast breeder reactor, a reactor core is disposed in a reactor vessel, and liquid sodium which is a coolant is filled in the reactor vessel. The fuel assembly loaded in the core includes a plurality of fuel rods encapsulating plutonium-enriched depleted uranium (U-238), a trumpet tube surrounding the bundled fuel rods, and lower ends of these fuel rods. , And an entrance nozzle that supports the neutron shield located below the fuel rod, and a coolant outlet that is located above the fuel rod.

  The fast breeder reactor core has a core fuel region having an inner core region and an outer core region surrounding the inner core region, a blanket fuel region surrounding the core fuel region, and a shield region surrounding the blanket region. In the case of a standard homogeneous core, the Pu enrichment of the fuel assemblies loaded in the outer core region is higher than the Pu enrichment of the fuel assemblies loaded in the inner core region. As a result, the power distribution in the radial direction of the core is flattened.

  Examples of the form of nuclear fuel material stored in each fuel rod of the fuel assembly include metal fuel, nitride fuel, and oxide fuel. Of these, oxide fuels have the greatest track record.

  A mixed oxide fuel obtained by mixing the oxides of Pu and depleted uranium, that is, a pellet of MOX fuel, is filled in a fuel rod at a height of about 80 to 100 cm in the center in the axial direction. Further, in the fuel rod, axial blanket regions filled with a plurality of uranium dioxide pellets made of deteriorated uranium are respectively arranged above and below the MOX fuel filling region. The inner core fuel assembly loaded in the inner core region and the outer core fuel assembly loaded in the outer core region thus have a plurality of fuel rods filled with a plurality of pellets of MOX fuel. The Pu enrichment of the outer core fuel assembly is higher than that of the inner core fuel assembly.

  A blanket fuel assembly having a plurality of fuel rods filled with a plurality of uranium dioxide pellets made of deteriorated uranium is loaded in the blanket fuel region surrounding the core fuel region. Among the neutrons generated by the fission reaction generated in the fuel assembly loaded in the core fuel region, the neutrons leaking from the core fuel region are U-238 in each fuel rod of the blanket fuel assembly loaded in the blanket fuel region. To be absorbed. As a result, Pu-239 which is a fissile nuclide is newly generated in each fuel rod of the blanket fuel assembly.

Control rods are used when the fast breeder reactor is started, stopped, and when the reactor power is adjusted. The control rod has a plurality of neutron absorber rods in which boron carbide (B ₄ C) pellets are sealed in a stainless steel cladding tube, and these neutron absorber rods are similar to the inner core fuel assembly and the outer core fuel assembly. The cross section is housed in a trumpet having a regular hexagonal shape. The control rod has two independent systems, the main reactor shutdown system and the after-furnace reactor shutdown system, and the fast breeder reactor can be stopped urgently by either one of the main reactor shutdown system or the after-furnace reactor shutdown system. .

  On the other hand, among high-level radioactive waste (HLW) generated by reprocessing spent fuel in the reactor, minor actinide (MA) has radioactivity for a very long period of time. Recycling this MA and transmuting it in a fast reactor reduces the harmfulness of HLW and increases the decay rate, thereby reducing the load on the geological repository and reducing the environmental burden. Among them, K. Fujimura, et al. Has proposed a core concept for improving transmutation efficiency by loading a target assembly for transmutation composed of fuel pins containing MA and neutron moderator pins into the core region of the fast reactor. al., “Fast Reactor Core Concepts for Minor Actinide Transmutation Using Solid Moderator”, Proceedings of GLOBAL 2011, (December 2011, Makuhari Messe).

Naohiro Hirakawa and Tomohiko Iwasaki, “Introduction to Reactor Physics”, Tohoku University Press, pp. 279-286, October 30, 2003.

K. Fujimura, et al., “Fast Reactor Core Concepts for Minor Actinide Transmutation Using Solid Moderator”, Proceedings of GLOBAL2011, Makuhari, Japan, Dec.11-16, 2011, Paper No. 357422.

  However, in Non-Patent Document 2, the neutron spectrum of the target assembly for MA transmutation becomes soft (the average energy of neutrons decreases), and the neutron absorption cross section at low energy is Np-237 several times larger than U-238. There is a possibility that the transmutation efficiency of MA may be reduced due to the manifestation of the self-shielding effect in which the neutron flux in the fuel pin containing MA such as Am or 241 rapidly attenuates.

  The present invention provides a transmutation assembly capable of improving the transmutation efficiency of long-lived radioactive waste such as minor actinides, and a fast reactor nuclear power generation system using the same.

  In order to solve the above-described problems, the present invention provides a transmutation assembly loaded in a trumpet tube, which is loaded on a core of a fast reactor and bundles a plurality of moderator pins including a fuel pin containing a long-life element and a neutron moderator. A plurality of fuel pins are arranged so that the cross-sectional area of the long-life element fuel element filled in the fuel pins decreases toward the center of the nuclear transmutation assembly.

  ADVANTAGE OF THE INVENTION According to this invention, the assembly for transmutation which can improve the transmutation efficiency of long-lived radioactive wastes, such as a minor actinide, and a fast reactor nuclear power generation system using the same can be provided.

  As a result, the transmutation rate of long-lived radioactive waste such as minor actinides (MA) can be improved, the harmfulness decay period of high-level waste disposed of in geological formation is shortened to several hundred years, and the environmental load can be reduced.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a transverse cross section of the core for transmutation concerning one example of the present invention, and the core of the fast reactor which loads it. 1 is an overall configuration diagram of a fast reactor nuclear power generation system using a nuclear transmutation assembly according to an embodiment of the present invention. It is a transverse cross section of the core for transmutation concerning one example of the present invention, and the core of the fast reactor which loads it. It is a cross-sectional view of the assembly for transmutation which concerns on one Example of this invention. FIG. 4 is a transverse cross-sectional view of a nuclear transmutation assembly in case 1 which is a comparative example, and a diagram showing a combustion change in the atomic number density of Am241 and Am243. It is a cross-sectional view of the assembly for transmutation of Case 2 as a comparative example, and a diagram showing the combustion change in the atomic number density of Am241 and Am243. FIG. 4 is a transverse cross-sectional view of the nuclear transmutation assembly in case 3 and a diagram showing combustion changes in the atomic number density of Am241 and Am243. It is a cross-sectional view of the assembly for transmutation concerning one Example of this invention, and the radial direction output distribution map of the assembly for transmutation. 1 is a cross-sectional view of a fast reactor core in which a transmutation assembly according to an embodiment of the present invention is loaded between a core fuel region and a radiation shield region.

  As shown in FIG. 2, the fast reactor nuclear power generation system of the present invention includes a reactor vessel 21, a core 22 containing a fissile material housed in the reactor vessel 21, and a primary cooling system pipe 23 from the reactor vessel 21. The intermediate heat exchanger 24 and the primary main circulation pump 25 connected in order via the intermediate heat exchanger 24, the steam generator 28 and the secondary main circulation pump 27 connected in order from the intermediate heat exchanger 24 via the secondary cooling system pipe 26 Have. Further, a main steam system pipe 29a that sends the steam generated by the steam generator 28 to the high-pressure turbine 30a and the low-pressure turbine 30b, a condenser that condenses the steam after passing through the high-pressure turbine 30a and the low-pressure turbine 30b and returns it to water. 32, a water supply condensate system pipe 29b for returning the water condensed in the condenser 32 to the steam generator 28, a generator 31 connected to the shafts of the high pressure turbine 30a and the low pressure turbine 30b, and a downstream side of the condenser 32 The feed water pump 33 and the feed water heater 34 are connected to the condensate system pipe 29b.

  In the fast reactor nuclear power generation system of the present invention, the primary system coolant (for example, liquid sodium) heated in the core 22 is passed through the intermediate heat exchanger 24 to provide the secondary system coolant (for example, liquid sodium). Then, the secondary system coolant is passed through the steam generator 28 to generate steam in the main steam system pipe 29a. The steam is guided to the high-pressure turbine 30a and the low-pressure turbine 30b, and the generator 31 generates power. The steam used for power generation is condensed in the condenser 32 to become water in the same manner as in the boiling water type (BWR) or pressurized water type (PWR) light water reactor nuclear power generation system, and then the feed water pump 33 and the feed water heater 34 are supplied. The water is heated and pressurized through the steam generator 28 and supplied to the steam generator 28.

  The core 22 accommodates a plurality of core fuel assemblies, control rods, and a transmutation assembly which will be described later. The reactor vessel 21 containing the core 22 is filled with the primary coolant, and the primary coolant enters the core 22 from the lower part of the core 22 and rises along the core fuel assembly and the transmutation assembly. The main circulation pump 25 flows into the intermediate heat exchanger 24 provided outside the reactor vessel 21 through the primary cooling pipe 23. This constitutes a loop type fast reactor. In this specification, a loop type fast reactor will be described as an example. However, the present invention is not limited to this, and a tank type fast reactor in which the reactor vessel 21, the primary main circulation pump 25, and the intermediate heat exchanger 24 are accommodated in one tank. It can also be applied to furnaces.

  The core 22 includes a radiation shield region surrounding the inner core region 1, the outer core region 2, and the outer core region 2, and is located between the inner core region 1 and the outer core region 2, or between the outer core region 2 and the radiation shield region. Are loaded with multiple transmutation assemblies.

  The transmutation assembly includes a fuel tube filled with a long-life element and a moderator pin filled with a neutron moderator bundled in a trumpet tube and is packed toward the center of the transmutation assembly. A plurality of fuel pins are arranged so that the cross-sectional area of the long-lived element fuel element is reduced. Here, long-lived fission products (FP) such as technetium 99 (Tc-99) and iodine 99 (I-99) extracted from the spent fuel of the nuclear reactor as long-life elements filled in the fuel pins. : Nationium (Np) and Americium (Am) separated and recovered by reprocessing among long-lived elements contained in high-level radioactive waste (HLW) generated by reprocessing spent fuel Minor Actinide (MA) such as curium (Cm) is used. Further, for example, zirconium hydride (Zr—H) is used as the neutron moderator.

  In the present invention, the fuel pin is arranged so that the cross-sectional area of the long-lived element fuel element filled becomes smaller toward the center of the transmutation assembly. A decrease in the nuclear conversion rate can be suppressed, and the nuclear conversion rate of long-lived elements such as MA can be improved. This makes it possible to shorten the harmfulness decay period of high-level radioactive waste to be disposed of from 2 million years to several hundred years.

  Hereinafter, the core of a fast reactor loaded with the nuclear transmutation assembly of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a core of a fast reactor in which a transmutation assembly according to an embodiment of the present invention is loaded. As shown in FIG. 1 (a), the core 22 of the fast reactor according to the present embodiment is disposed in the reactor vessel 22 of the fast reactor, and includes an inner core region 1 and an outer core region 2 surrounding the inner core region 1. It has a core fuel region, a first radiation shield region 3 and a second radiation shield region 4. In the radial direction of the core 22, the first radiation shield region 3 surrounds the core region and is adjacent to the core fuel region, and the second radiation shield region 4 surrounds the first radiation shield region 3. The core 22 has no blanket fuel disposed in the radial direction and the axial direction (the depth direction with respect to the drawing in FIG. 1A). The inner core region 1 is provided with control rods 10 that are used when the reactor is started, stopped, and when the output is adjusted. The control rod 10 has a plurality of neutron absorber rods in which boron carbide (B ₄ C) pellets are sealed in a stainless steel cladding tube, and these neutron absorber rods are accommodated in a trumpet tube having a regular hexagonal cross section. Composed. The control rod 10 has two independent systems of a main furnace stop system and a post-furnace stop system, but these are shown in FIG. 1A without distinction.

The fast reactor to which the core 22 is applied uses liquid sodium as a coolant. Liquid sodium is filled in the reactor vessel 21. In the core fuel region (including the inner core region 1 and the outer core region 2) of the core 22, a mixed oxide (hereinafter referred to as MOX (hereinafter referred to as MOX)) in which plutonium oxide (PuO ₂ ) and deteriorated uranium oxide (UO ₂ ) are mixed. A plurality of core fuel assemblies including a mixed oxide) are loaded.

  In this embodiment, a transmutation assembly 5 in which an MA pin containing the above-mentioned minor actinide (MA) is mixed is loaded. As shown in Non-Patent Document 2, an MA transmutation assembly comprising a pin containing MA and a pin containing zirconium hydride (Zr-H) as a neutron moderator is loaded in the core region of the fast reactor. As a result, the transmutation rate and transmutation amount of MA can be increased. In the present invention, in order to alleviate the self-shielding effect in the MA pin, which is particularly noticeable in the central portion of the transmutation assembly by loading the neutron moderator, a part of the fuel pin containing MA, which is a long-lived element, is used. The closer to the center of the nuclear transmutation assembly, the larger the hollow pin diameter, the greater the MA transmutation rate, and the transmutation rate of long-lived radioactive waste such as minor actinides (MA). It can be improved, and the harmfulness decay period of high-level waste to be disposed of from geological disposal is shortened from 2 million years to several hundred years, thereby reducing the environmental load.

  The transmutation assembly 5 includes cylindrical fuel pins 6, 7, 8 filled with MA as a long-life element, and a moderator pin 9 filled with a neutron moderator such as zirconium hydride (Zr—H). Are bundled and accommodated in the trumpet tube 11. A cylindrical hollow portion is formed inside the fuel pins 6, 7, and 8, and is disposed in the transmutation assembly 5 at a position close to the trumpet tube 11, that is, at the outer periphery of the transmutation assembly 5. The diameter of the hollow portion of the fuel pin 6 is d1, and the diameter of the hollow portion of the fuel pin 8 disposed at the substantially central portion in the nuclear conversion assembly 5 is d3. The fuel pins 6, 7, and 8 are arranged so that the relationship of d 1 ≦ d 2 ≦ d 3 is established, where d 2 is the diameter of the hollow portion of the fuel pin 7 that is disposed between the fuel pin 6 and the fuel pin 8. That is, the fuel pins are arranged so that the diameter of the hollow portion increases toward the center of the transmutation assembly 5.

The following three cases were analyzed using combustion calculation with a continuous energy Monte Carlo code. As shown in FIG. 5A (only the inner structure is omitted and only 1/3 is shown) as the transmutation assembly 45 of case 1, the composition of 10 wt% AmO ₂ -UO ₂ is formed in the trumpet 11. Only 91 MA oxide pins 41 having the same shape are arranged, and each MA oxide pin 41 has a solid cylindrical shape and the same outer diameter. Further, as the transmutation assembly 55 of case 2, as shown in FIG. 6A, the MA oxide pin 41 having a composition of 10 wt% AmO ₂ -UO ₂ and zirconium hydride (Zr) The moderator pins 9 filled with -H) are arranged, 43 pieces of each MA oxide pin 41 are arranged, and the moderator pins 9 are arranged in a solid cylindrical shape and 48 pieces are arranged. Further, as the transmutation assembly 65 of the case 3, as shown in FIG. 7 (a), MA oxide pins 61 and 62 having a composition of 10 wt% AmO ₂ -UO ₂ and zirconium hydride in the trumpet tube 11 A moderator pin 9 filled with (Zr-H) is disposed. The MA oxide pins 61 have a solid cylindrical shape and are arranged on the outer peripheral side of the nuclear transmutation assembly 65, and the MA oxide pins 62 have a cylindrical hollow portion therein and a core. Nineteen are arranged on the center side of the conversion assembly 65. The hollow area ratio of the pellets of the MA oxide pin 62 is 50%. That is, the cross-sectional area of the fuel element of the MA oxide pin 62 disposed on the center side with respect to the MA oxide pin 61 disposed on the outer peripheral side of the transmutation assembly 65 is 50%. The ratio of the number of isotope atoms of Am contained in the new fuel is Am-241 / Am-243 = 80/20 [%].

Among the analysis results of Case 1, FIG. 5B shows changes in the atomic number densities of Am-241 and Am-243 due to one cycle (600 days) combustion. In FIG. 5 (b), the vertical axis represents the atomic number density [× 10 ⁻²⁴ / cm ³ ], the horizontal axis represents the number of days of combustion, and the graphs 44 and 46 represent the center position and diameter from the center in the transmutation assembly 45, respectively. The atomic number density of Am-241 in the MA oxide pin 41 (solid pin) at the position of the fourth row facing the outer periphery in the direction is shown. Graphs 47 and 48 respectively show the atomic position density of Am-243 in the MA oxide pin 41 (solid pin) at the position of the fourth row from the center position to the radially outer peripheral side from the center in the transmutation assembly 45. Show. From FIG. 5 (b), it can be seen that there is no difference in the combustion change of the MA nuclide due to the difference in position in the nuclear transmutation assembly 45.

In addition, the transmutation rate of the MA nuclide associated with one cycle of combustion defined by the formula (1) is about 39% for Am-241 and about 32% for Am-243.
Nuclear conversion rate of MA nuclide = (atomic density of new fuel-atomic number density at 600 days combustion) / atomic density of new fuel x 100 [%] (1)
Moreover, the change by 1 cycle (600 days) combustion of the atomic number density of Am-241 and Am-243 among the analysis results of case 2 is shown in FIG.6 (b). In FIG. 6B, graphs 54 and 56 respectively show the center position in the transmutation assembly 55 and Am-241 in the MA oxide pin 41 (solid pin) in the fourth row from the center toward the radially outer peripheral side. The atomic number density of is shown. Graphs 57 and 58 respectively show the center position in the transmutation assembly 55 and the atomic density of Am-243 in the MA oxide pin 41 (solid pin) in the fourth row from the center toward the radially outer side. Is shown. The transmutation rate of Am-241 based on the formula (1) is 70% of the MA oxide pin 41 (solid pin) arranged in the center, and the MA arranged in the fourth row from the center to the radially outer side. The oxide pin 41 is 80%. Similarly, the transmutation rate of Am-243 is 57% for the oxide pin 41 disposed at the center and 63% for the MA oxide 41 disposed in the fourth row from the center toward the radially outer side. From the above, it can be seen that the nearer the center of the nuclear transmutation assembly 55, the smaller the transmutation rate of the MA nuclide. This is because the transmutation assembly 55 is loaded with about 50% of the moderator pins 9 filled with zirconium hydride (Zr—H), and the neutron spectrum becomes closer to the center of the transmutation assembly 55. Is caused by softening (the average energy of the neutron spectrum becomes small). That is, for example, the outer diameters of the MA oxide pins 41 arranged in the center of the transmutation assembly 55 and the MA oxide pins 41 arranged in the fourth row from the center toward the radially outer side are the same. However, since the average energy of the neutrons reaching the MA oxide pin 41 arranged at the center is small, the self-shielding effect of the MA oxide pin 41 arranged at the center becomes larger.

  Case 3 is an analysis model obtained by simplifying the transmutation assembly according to the present embodiment. Among the analysis results, changes in the atomic number densities of Am-241 and Am-243 due to one cycle (600 days) combustion are shown in FIG. In FIG. 7B, a graph 64 shows the atom number density of Am-241 in the MA oxide pin 62 (hollow pin) arranged at the center position in the transmutation assembly 65, and the graph 66 shows a radial direction from the center. The atomic number density of Am-241 in the MA oxide pin 61 (solid pin) arranged in the fourth row toward the outer peripheral side is shown. Graph 67 shows the atomic number density of Am-243 in the MA oxide pin 62 (hollow pin) arranged at the center position, and graph 68 shows the MA arranged in the fourth row from the center toward the radially outer peripheral side. The atomic number density of Am-243 in the oxide pin 61 (solid pin) is shown. The transmutation rate of Am-241 based on the formula (1) is 79% of the MA oxide pin 62 (hollow pin) arranged in the center, and the MA oxide arranged in the fourth row from the center to the radially outer side. The pin 61 (solid pin) is 82%. Similarly, the transmutation rate of Am-243 is 60% for the MA oxide pin 62 (hollow pin) disposed in the center, and the MA oxide pin 61 (in the fourth row from the center toward the radially outer side). Solid pin) is 64%. From the above, the difference in the transmutation rate of the MA nuclide due to the difference between the position near the center of the transmutation assembly 65 and the position near the periphery is smaller than that in the transmutation assembly 55 of Case 2, and Am. It can be seen that both -241 and Am-243 are increased. This is because the MA oxide pin 62 close to the center of the transmutation assembly 65 is a hollow pin, thereby reducing the self-shielding effect of the MA oxide pin 62.

  According to the present embodiment, the diameters of the hollow portions of the fuel pins 6, 7, 8, which are filled with a long-lived element such as MA and have a cylindrical hollow portion at the center, are set to the center of the transmutation assembly 5. By enlarging as it goes, the self-shielding effect is reduced, and the transmutation rate of long-lived elements such as MA can be improved. This makes it possible to shorten the harmfulness decay period of high-level radioactive waste to be disposed of from 2 million years to several hundred years.

  FIG. 3 shows the core of a fast reactor in which the transmutation assembly according to this embodiment is loaded. Constituent elements similar to those in FIG. In Example 1, a cylindrical hollow portion is formed inside columnar fuel pins 6, 7, 8 filled with MA as a long-life element, and the diameter of the hollow portion is changed to that of the transmutation assembly 5. In the present embodiment, the fuel pin has a solid cylindrical shape filled with a long-life element such as MA, and the fuel pin is disposed in the transmutation assembly 5. The difference from the first embodiment is that the outer diameter of the fuel pin is made different depending on the position.

  In the present embodiment, the fast reactor core 22 shown in FIG. 3 is the same as the fast reactor core 22 of the first embodiment.

  In this embodiment, the transmutation assembly 5 loaded on the core 22 is made of solid fuel pins 16, 17, 18 filled with MA as a long-life element and neutrons such as zirconium hydride (Zr-H). It is configured by bundling a plurality of moderator pins 9 filled with a moderator and accommodating them in a trumpet tube 11. The diameter (outer diameter) of the fuel pin 18 disposed substantially at the center in the transmutation assembly 5 is D3, and the fuel pin 16 disposed in the outer peripheral portion of the transmutation assembly 5 (position closest to the trumpet tube 11). The fuel pins 16, 17, and 18 are arranged so that the relationship of D 1 ≧ D 2 ≧ D 3 is established, where D 1 is the diameter of the fuel pin 17 and D 2 is the diameter of the fuel pin 17 disposed between them.

  According to the present embodiment, the fuel pin is arranged so that the diameter (outer diameter) of the fuel pin becomes smaller toward the center in the transmutation assembly 5, so that the center side of the transmutation assembly 5 is arranged. The self-shielding effect of the fuel pin can be reduced. As a result, the transmutation rate of long-lived elements such as MA can be improved, and the harmfulness decay period of high-level radioactive waste to be geologically disposed can be shortened from 2 million years to several hundred years.

  Further, in this embodiment, the process of making the fuel pin shown in the first embodiment hollow is not necessary, and the fuel manufacturing process can be simplified. However, in a normal fast reactor fuel assembly, it is difficult to use the wire spacers used to maintain the space between the fuel pins. Therefore, a grid spacer is used so that the space between the fuel pins having different outer diameters can be maintained. It is necessary to make the aggregate structure for transmutation.

  FIG. 4 shows a transmutation assembly according to the present embodiment. The same components as those in FIG. 3 are denoted by the same reference numerals. In the second embodiment, there is one fuel pin 18 arranged at the substantially central portion of the transmutation assembly 5, whereas in this embodiment, a plurality of fuel pins 18 are provided at the substantially central portion (central portion). Is different. That is, the second embodiment is different from the second embodiment in that the arrangement density of the fuel pins in the substantially central portion of the transmutation assembly 5 is increased.

  The relationship between the diameters (outer diameters) of the solid cylindrical fuel pins 16, 17, 18 filled with MA or the like as the long-life element shown in FIG. 4 is the same as that of the second embodiment. In the present embodiment, by arranging three fuel pins 18 at the substantially central portion of the nuclear transmutation assembly 5, the arrangement density at the approximate central portion in the transmutation assembly 5 can be determined in the vicinity of the outer peripheral portion and the outer peripheral portion. It is made higher than the arrangement density of the fuel pins 17 and 18 arrange | positioned in the area | region between the center part.

  According to the present embodiment, compared to the second embodiment, the weight of a nuclide such as MA as a long-life element that can be loaded on the nuclear transmutation assembly 5 can be increased, and the weight of the transmutable MA can be increased.

  Also in this embodiment, the self-shielding effect of the fuel pin on the center side of the transmutation assembly 5 can be reduced, and the harmfulness decay period of the high-level radioactive waste to be disposed of is shortened to several hundred years. It becomes possible.

  FIG. 8 shows the power density in the vicinity of the transmutation assembly and the transmutation assembly of this example. The present embodiment is different from the first embodiment in that only the fuel pin 6 is arranged near the outer periphery of the transmutation assembly 5.

FIG. 8 (a) shows a case where a single nuclear transmutation assembly 5 is arranged at the central position and three core fuel assemblies are arranged at positions surrounding it. Shows the output density [W / cm ³ ], the horizontal axis is the distance from the center in the radial direction, and the output density distribution according to the distance from the center is shown. In FIG. 8A, a graph 74 shows the distribution of the power density in the radial direction at the beginning of the equilibrium cycle, and a graph 75 shows the distribution of the power density in the radial direction at the end of the equilibrium cycle. In the core fuel assembly, the power density is locally increased at a position facing the transmutation assembly. This is because when neutrons decelerated by zirconium hydride (Zr-H) loaded in the transmutation assembly leak into the core fuel assembly, fission nuclides such as Pu-239 in the core fuel assembly This is the result of accelerated fission. That is, this is because the neutron beam in the region facing the nuclear transmutation assembly of the fuel assembly suddenly increases due to the neutrons decelerated from the transmutation assembly leaking into the fuel assembly.

  In order to suppress such a local output peak, in this embodiment, the structure of the nuclear transmutation assembly shown in FIG. That is, only the fuel pin 6 filled with MA or the like as a long-life element is disposed at the outermost peripheral position adjacent to the trumpet tube 11. The relationship between the hollow diameters of the fuel pins 6, 7, and 8 is the same as that in the first embodiment.

  According to the present embodiment, the transmutation assembly 5 can be loaded on the core of the fast reactor while avoiding the occurrence of local power peaks in the adjacent core fuel assemblies. Compared with the assembly for assembly, the degree of freedom of the loading position in the core is greater and can be loaded at the optimum position, so that the transmutation rate and the transmutation amount can be increased as compared with the first and second embodiments.

  In this embodiment, the fuel pins 6, 7, and 8 have the same hollow pin configuration as in the first embodiment. However, the present invention is not limited to this, and a solid cylindrical shape may be used as in the second embodiment.

  Also in the present embodiment, the self-shielding effect of the fuel pin on the center side of the transmutation assembly 5 can be reduced, and the harmfulness decay period of the high-level radioactive waste disposed in the geological layer is shortened to several hundred years. It becomes possible.

  FIG. 9 shows the core of a fast reactor in which the fuel assembly according to this embodiment is loaded. In the first to fourth embodiments, the transmutation assemblies are arranged in the inner fuel region 1 and the outer fuel region 2 of the fast reactor core. However, in this embodiment, the transmutation assembly 5 is disposed outside. The difference is that the fuel region 2 and the radiation shielding region are loaded.

  In the present embodiment, as shown in FIG. 9B, the transmutation assembly 5 similar to that of the first embodiment is loaded between the outer core region 2 and the radiation shield region 81. As a result, as compared with the case where the nuclear transmutation assembly 5 including the moderator pin 9 filled with the neutron moderator is loaded in the core fuel region, the influence on the core performance and power distribution is suppressed to a smaller level. The transmutation assembly 5 can be loaded.

  In this embodiment, the transmutation assembly 5 loaded between the outer core region 2 and the radiation shield region 81 has the same configuration as that of the first embodiment. However, the present invention is not limited to this. To any one of the transmutation assemblies 5 of the fourth embodiment.

  In Examples 1 to 5 described above, MA is assumed as a long-life element, but TRU in the case of a transuranium element (TRU; TRans-Uranium) transmutation reactor for the purpose of reducing excess Pu, The same effect can be obtained even if fission products (FP) such as Tc-99 (Technetium-99) and I-129 (Iodine-129), which are high-level radioactive wastes, are subjected to transmutation. It is done.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace the configurations of other embodiments with respect to a part of the configurations of the embodiments.

DESCRIPTION OF SYMBOLS 1 Inner core area | region 2 Outer core area | region 3 1st radiation shield body area | region 4 2nd radiation shield body area | region 5 Assembly for transmutation 6, 7, 8 Fuel pin 9 Moderator pin 10 Control rod 11 Trumpet tube 21 Reactor vessel 22 Core 23 Primary cooling system piping 24 Intermediate heat exchanger 25 Primary main circulation pump 26 Secondary cooling system piping 27 Secondary main circulation pump 28 Steam generator 29a Main steam system piping 29b Supply / condensation system piping 30a High pressure turbine 30b Low pressure turbine 31 Power generation Machine 32 condenser 33 feed water pump 34 feed water heater

Claims (10)

A nuclear transmutation assembly loaded in the core of a fast reactor and bundled with a plurality of moderator pins containing a long-life element and a neutron moderator, and contained in a trumpet tube,
The transmutation assembly, wherein the plurality of fuel pins are arranged so that a cross-sectional area of a long-life element fuel element filled in the fuel pin becomes smaller toward the center of the transmutation assembly. The assembly for transmutation according to claim 1,
The fuel pin is filled with a long-life element inside, and has a shape with a cylindrical hollow portion at the center thereof,
The transmutation assembly, wherein the plurality of fuel pins are arranged so that the diameter of the hollow portion increases toward the center of the transmutation assembly. The assembly for transmutation according to claim 1,
The fuel pin has a solid cylindrical shape filled with a long-life element inside,
The transmutation assembly, wherein the plurality of fuel pins are arranged so that an outer diameter of the fuel pin becomes smaller toward a center of the transmutation assembly. The assembly for transmutation according to claim 3,
A transmutation assembly characterized in that an arrangement density of the fuel pins in a central portion of the transmutation assembly is higher than an arrangement density of the fuel pins in an outer peripheral portion. The assembly for transmutation according to claim 2 or 3,
Only the fuel pins are arranged on the outermost peripheral portion of the nuclear transmutation assembly. The assembly for transmutation according to any one of claims 1 to 4,
The long-lived element contained in the fuel pin is technetium, iodine extracted from spent nuclear fuel, or a minor actinide recovered by reprocessing. A fast reactor core comprising an inner core region, an outer core region and a radiation shield region surrounding the outer core region,
A plurality of fuel pins containing long-life elements and moderator pins containing neutron moderators are bundled together in a predetermined position in the inner core region and the outer core region, or between the outer core region and the radiation shield region, and accommodated in a wrapper tube. Place a transmutation assembly
A core of a fast reactor, wherein the transmutation assembly accommodates the plurality of fuel pins such that a cross-sectional area of the fuel element decreases toward the center. A core of the fast reactor according to claim 7,
The fuel pin is filled with a long-life element inside, and has a shape with a cylindrical hollow portion at the center thereof,
A core of a fast reactor, wherein the plurality of fuel pins are arranged such that the diameter of the hollow portion increases toward the center of the transmutation assembly. A reactor vessel containing a nuclear reactor containing fission material and filled with a primary coolant;
An intermediate heat exchanger for passing the primary coolant heated in the reactor vessel and exchanging heat with the secondary coolant;
A steam generator for generating steam through the secondary coolant heated in the intermediate heat exchanger;
A main steam pipe for introducing the steam from the steam generator into a high pressure turbine and a low pressure turbine connected to a generator;
The core accommodated in the reactor vessel includes an inner core region, an outer core region, and a radiation shield region, and a predetermined position of the inner core region and the outer core region, or the outer core region and the radiation shield region. In between, arrange a nuclear transmutation assembly that bundles multiple fuel pins filled with long-life elements and moderator pins filled with neutron moderator and accommodates them in a trumpet tube,
The fast reactor nuclear power generation system characterized in that the transmutation assembly accommodates the plurality of fuel pins such that a cross-sectional area of the filled long-life element is reduced toward the center. The fast reactor nuclear power generation system according to claim 9,
The fuel pin is filled with a long-life element inside, and has a shape with a cylindrical hollow portion at the center thereof,
The fast reactor nuclear power generation system, wherein the plurality of fuel pins are arranged so that the diameter of the hollow portion increases toward the center of the nuclear transmutation assembly.

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