JP2012154861A - Core of hybrid type nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sharply simplify the whole fuel cycle and to reduce a power generation unit cost of nuclear power generation.SOLUTION: A hybrid type nuclear reactor comprises: a neutron source area which loads depleted uranium, receives charged particle beams applied from the external and generates neutrons; and two reactors, i.e. a subcritical reactor which surrounds the neutron source area, uses a nitride of natural uranium or recovered uranium as a fuel and uses heavy water as a coolant and a moderator, and a fast reactor arranged adjacently to the subcritical reactor and loaded with a core fuel assembly which seals a nitride fuel of natural uranium, recovered uranium or depleted uranium into cladding tubes, bundles the cladding tubes in a wrapper tube, and allows liquid Na to flow among the cladding tubes upward to remove heat generated by nuclear fission.

Description

  The present invention relates to the cores of subcritical reactors (ADS) and fast reactors (FRs) driven by particle beam accelerators, and in particular, only depleted uranium and natural uranium without using enriched uranium and plutonium as fuel. The present invention relates to a hybrid reactor concept that enables power generation to continue during the lifetime of the reactor.

Regarding the fuel assembly and core of the fast reactor (FR), Naohiro Hirakawa, Tomohiko Iwasaki, “Introduction to Reactor Physics” (Tohoku University Press, October 30, 2003, p279-286) (Non-patent Document 1), etc. It is described in. That is, generally, an FBR core fuel assembly includes a fuel rod bundle in which deteriorated uranium (U-238) enriched with plutonium (Pu) is enclosed in a fuel rod cladding tube, and a wrapper tube surrounding the fuel rod bundle. A coolant outlet portion above the fuel rod bundle, and a neutron shield and coolant inlet portion (entrance nozzle) below the fuel rod bundle. The core is formed by bundling a large number of the above fuel assemblies in a cylindrical shape. In the case of a standard homogeneous core, Pu enrichment is arranged in two regions in the radial direction, and the fuel assemblies loaded on the peripheral side of the core are The Pu enrichment is set higher than the Pu enrichment of the fuel assembly loaded closer to the center to flatten the power distribution in the radial direction. Up to now, metals, nitrides, oxides, etc. have been studied as fuel forms, but oxide fuels have the most extensive results. In this case, the fuel rod cladding tube is filled with a mixed oxide obtained by mixing Pu and deteriorated U oxide, that is, MOX fuel pellets in a height region of about 80 to 100 cm at the center position in the axial direction of the fuel rod cladding tube. Is provided with an axial blanket region filled with pellets of deteriorated U oxide UO ₂ fuel. In addition, a blanket fuel assembly consisting only of fuel rods filled only with depleted uranium oxide UO ₂ fuel pellets is loaded around the core region where fuel assemblies composed of fuel rods filled with MOX fuel are arranged. A radial blanket region is provided. In the blanket region, among the neutrons generated by the nuclear fission reaction in the core region, neutrons leaking from the core region are absorbed by U-238 to generate fissile nuclides Pu-239, and the proliferation of Pu in the entire core (growth ratio) > 1.0). Control rods are used when starting and stopping the furnace and when changing the output. The control rod is packed with boron carbide (B ₄ C) pellets enclosed in a stainless steel cladding tube and housed in a regular hexagonal trumpet tube in the same manner as the core fuel assembly. The system consists of two independent systems, a main furnace stop system and a post-furnace stop system, and is designed so that an emergency stop is possible only with one of them.

  Normally, a radial blanket made of deteriorated uranium (U) fuel is loaded at the boundary between the core fuel assembly and the outermost shield body. In this region, a part of the neutrons generated by the nuclear fission in the core fuel region leaks out, and Pu is generated by the (n, γ) reaction in which U-238 occupying most of the degradation U absorbs the neutrons. That is, the main function of the blanket region is fuel growth.

  On the other hand, a high-energy proton or deuteron accelerated by a particle beam accelerator is irradiated to a target made of heavy metal such as lead or tungsten to cause a spallation reaction, and the generated neutron is used as an external neutron source to generate a subcritical reactor. Accelerator driven transmutation system (ADS) has been proposed. For example, “Current Status and Prospects of Accelerator-driven Transmutation Technology as High-level Waste Disposal”, Hideki Takano (RIST News No. 35 (2003), pp. 4-6, Non-Patent Document 2) A design example of an ADS with a heat output of 800 MWt, in which N is MA 60% + Pu 40% nitride (N-15 concentration) and the coolant is Pb-Bi is shown. In this ADS, the fuel contains long-lived minor actinides (MA), which are part of high-level radioactive waste (HLW) in the current light water reactor cycle, and high concentrations of Pu nitride. Therefore, the effective multiplication factor keff is designed to be 0.95. Since the nuclear reactor is subcritical in ADS, the fission reaction stops when the accelerator is stopped. Therefore, it is said that a large amount of MA can be transmuted while maintaining safety. A subcritical furnace for transmutating a long-lived fission product (LLFP) using ADS is disclosed in Japanese Patent Application Laid-Open No. 2000-321390. In this invention, the coolant is Na, fuel Are assumed to be nitrides of U, Pu and MA.

On the other hand, with only a small amount of enriched uranium, which initially becomes a fire type, the fission chain reaction of the Na-cooled fast reactor using depleted U or natural U as fuel is generated and continued, and power generation is continued without changing the fuel throughout the life of the core. to TWR (Traveling Wave reactor) the idea of "a oNCE-tHROUGH fUEL cYCLE fOR fAST rEACTORS ( once-through fuel cycle for fast reactors)" (Kevan D. Weaver et ^{al., Proceedings of the 17 th International Conference} on Nuclear Engineering , ICONE17, July 12-16, 2009, paper number 75381, Non-Patent Document 3). As shown in Figure 2 of the same document, the TWR fuel rod and fuel assembly are the same as the fast reactor shown in Non-Patent Document 1, but the distance between the fuel rods with respect to the fuel rod diameter of 8.8 mm is 0.8 mm. This is characterized by the fact that the volume ratio of the fuel to the coolant is large and a dense grid is adopted. As shown in the horizontal cross section of Figure 3 in the same document, the reactor core has hexagonal fuel assemblies arranged in a rectangular parallelepiped shape, and the combustion region where the fission chain reaction occurs is shown in Figure 1 of the same document. , Proceeds from one end of the core to the other.

JP 2000-321390 A

Naohiro Hirakawa, Tomohiko Iwasaki, “Introduction to Reactor Physics”, Tohoku University Press, pp. 279-286, October 30, 2003. Hideki Takano “Current Status and Prospects of Accelerator Driven Transmutation Technology as High-level Waste Disposal”, RIST News, No. 35 (2003), pp. 2-18. Kevan D. Weaver et al. “A ONCE-THROUGH FUEL CYCLE FOR FAST REACTORS”, Proceedings of the 17th International Conference on Nuclear Engineering, ICONE17, July 12-16, 2009, paper number 75381 .

  In addition to light water reactors, fast reactors that have been constructed and proposed so far and accelerator-driven subcritical reactors ADS require fissionable materials such as enriched U and Pu in order to continue the fission chain reaction and thus power generation. In addition, TWR requires a fissile material that becomes a fire type only at the beginning of the core life. If a nuclear reactor capable of maintaining the fission chain reaction, that is, continuing power generation during the life of the reactor, without the need for fissile materials as shown on the left, reprocessing, uranium enrichment facilities, and uranium mining will be unnecessary. The whole fuel cycle can be greatly simplified.

  The purpose of the present invention is to realize a nuclear reactor that can supply power for a long time without the use of fissile nuclides, eliminating the need for reprocessing, uranium enrichment facilities, and uranium mining, greatly simplifying the entire fuel cycle, The purpose is to reduce the unit price of power generation.

  In order to solve the above problems, in the present invention, a depleted uranium is loaded, a neutron source region that generates neutrons by receiving a charged particle beam irradiated from the outside, and the neutron source region is surrounded, and natural uranium or recovered uranium is A subcritical reactor using nitride as fuel and heavy water as a coolant and moderator, and adjacent to the subcritical reactor, and using nitrided fuel of natural uranium, recovered uranium, or deteriorated uranium as cladding Two fast reactors loaded with a core fuel assembly that consists of the above clad tube bundled in a trumpet tube and flows liquid Na from the bottom to the top to gradually heat the heat generated by fission. It is composed of a nuclear reactor.

  In the present invention, it is possible to realize a nuclear reactor that does not require fissile nuclides and can supply power for a long period of time. The unit price of power generation can be reduced.

It is a figure which shows the structure of the vertical cross section of the hybrid type reactor which shows 1st Embodiment. It is a horizontal sectional view of a hybrid type reactor showing the 1st and 2nd embodiments. It is a figure which shows the structure of the vertical cross section of the hybrid nuclear reactor which shows 3rd Embodiment. It is a figure which shows the structure of the horizontal cross section of a subcritical reactor core and a fuel assembly among the hybrid type reactors which show 3rd Embodiment. It is a figure which shows the structure of the horizontal cross section of the core and fuel assembly of a fast reactor among the hybrid type reactors which show 3rd Embodiment. It is a figure which shows the structure of the vertical cross section of a fuel assembly among the hybrid type reactors which show 3rd Embodiment. It is a figure which shows the combustion change of the neutron effective multiplication factor of the fast reactor which uses nitride as a fuel among hybrid type | mold reactors. It is a figure which shows the dependence on the neutron effective magnification of the neutron multiplication factor in a subcritical reactor. It is a figure which shows the combustion change of the neutron effective multiplication factor of the fast reactor which uses nitride as a fuel which becomes 2nd Embodiment compared with the case of 1st Embodiment.

  The present invention automatically performs fission reactions in the core of a liquid metal fast reactor using depleted uranium as fuel, using fission neutrons generated in an accelerator-driven subcritical reactor system (ADS) as a fire. The present invention relates to a hybrid reactor of an ADS and a fast reactor that does not require the supply of fissile material from the outside during the life of the reactor.

A mode for carrying out the present invention will be described with reference to FIGS. 1, 2, 7 and 8. FIG. 1 is a diagram showing an axial structure of a hybrid nuclear reactor according to the present embodiment, and FIG. 2 is a diagram showing a horizontal section. In FIG. 1, 4 is a beam of charged particles generated by a high energy proton beam accelerator of about 1.5 GeV, 2 is a neutron source for generating a neutron by causing the above-mentioned beam to cause a spallation reaction, 3 is the neutron multiplication region of the subcritical reactor to multiply the neutron generated by the neutron source on the left and continue the prescribed fission reaction, 5 is the fission reaction using the neutron generated in the subcritical reactor as a fire type This is the core region of the fast reactor to continue the process. In FIG. 2, 2 is a neutron source as described above, but the material is deteriorated uranium (U-235 / U = 0.2 to 0.3 wt%) or natural uranium (U-235 / U = 0.7 wt%). ) And loaded in a square channel 27 provided in the vicinity of the center of the heavy water tank 24 filled with heavy water, and the heat is removed by a heavy water coolant that is driven by a pump from below to flow upward. Reference numeral 22 denotes a fuel assembly in which an oxide of natural uranium or recovered uranium (U-235 / U≈1 wt%) is enclosed in a fuel rod cladding tube and bundled, and the fuel assembly provided in the heavy water tank described above. The fuel channel 26 for body loading is also removed by heavy water coolant. Reference numeral 7 denotes a fast reactor using liquid metal Na as a coolant and fuel of deteriorated uranium or natural uranium nitride. As described above, the subcritical reactor 6 uses natural uranium or recovered uranium as a fuel, and uses heavy water that absorbs small neutrons as a coolant and a neutron moderator. Therefore, stainless steel is used for cladding tubes and other structural materials. Even so, the effective neutron multiplication factor keff is close to 1 and 0.985. While the subcritical reactor is continuously irradiated with the charged particle beam, the fuel rod in the region near the subcritical reactor in the adjacent fast reactor 7 is irradiated with neutrons, and the burnup is increased with time. Will improve. The burnup dependence of the effective neutron multiplication factor keff of the fast reactor 7 is as shown in FIG. In the figure, 73 is a neutron effective multiplication factor, 72 is a burnup degree, and 71 is a curve showing the burnup dependence of keff. The keff increases as the burnup increases, and when the burnup reaches a certain burnup of 74, it exceeds 1.0. The fission chain reaction is maintained even without neutrons from the subcritical reactor, and the thermal energy required for power generation. Will occur. The subcriticality of the subcritical reactor = 1−keff and the neutron multiplication factor S are given by the following equation (1).
S = 1 / (1-keff) (1)

  FIG. 8 is a graph showing the relationship between keff and the neutron multiplication coefficient. Here, 83 is a neutron multiplication coefficient, 82 is keff, and 81 is a curve showing the keff dependence of the neutron multiplication coefficient. In the existing ADS design, there is a design example in which the keff is 0.95 and the thermal output of the reactor is 800 MWt. In the present invention, the keff is designed to be 0.985, and assuming a proton beam accelerator of the same scale as the existing design example, a reactor thermal output of about 3300 MWt can be achieved from the graph of FIG. Can be achieved.

  When the subcritical reactor 6 generates electric power as described above and continues to operate, the fuel at the position close to the subcritical reactor 6 in the core fuel assembly 23 of the fast reactor 7 adjacent to the subcritical reactor 7. However, when irradiated with neutrons and keff increases with time as described above and the burnup reaches about 300 GWd / t, it exceeds 1.0 and the fission chain reaction can be maintained. At this time, even if the beam of charged particles to the subcritical reactor is stopped, the combustion region automatically moves to the opposite side of the subcritical reactor while continuing the rated operation at an electric power of 1000 MWe, and the core It is possible to continue the rated power operation without supplying new fissile materials such as enriched uranium and Pu by refueling for about 60 years.

  A second embodiment for carrying out the present invention will be described with reference to FIGS. The subcritical reactor and the adjacent fast reactor are substantially the same as those in the first embodiment. However, the volume ratio occupied by the deteriorated uranium nitride in the core fuel assembly 23 of the fast reactor is larger than that of the first embodiment and is about 50%. FIG. 9 shows the burnup dependence of the keff of the core of the fast reactor in the present embodiment in comparison with the first embodiment. In the figure, 91 is a curve showing the burn-in dependence of keff in the case of Embodiment 1 shown in FIG.

  The fast reactor of the present embodiment has a large fuel volume ratio and, conversely, a small volume ratio of Na, which is a coolant, as compared with the first embodiment. Therefore, the fast reactor in the second embodiment has a neutron spectrum that is harder (= higher average energy) than the first embodiment, so that the neutron economy is improved and keff is increased. . Furthermore, the critical burnup at keff of 1.0 is lower than that of the first embodiment (about 200 GWd / t). That is, the burnup required to achieve automatic generation of the fission chain reaction and automatic movement of the combustion region in the fast reactor is reduced, so the development problem of the fuel rod cladding tube is reduced. Moreover, since the volume fraction of the coolant is small, the Na void reactivity related to safety is small, and the safety is improved.

  A third embodiment for carrying out the present invention will be described with reference to FIGS. 3, 4, 5 and 6. The present embodiment is characterized in that the hybrid reactor 31 is configured by disposing the core of the fast reactor similarly shown in the first embodiment below the subcritical reactor shown in the first embodiment. Yes. The configuration of the subcritical reactor in the AA cross section of FIG. 3 is shown in FIG. In the present embodiment, the subcritical reactor indicated by 41 in FIG. 4 is configured by a hexagonal assembly similar to the horizontal section of the fast reactor shown in FIG. Reference numeral 43 denotes a neutron source region for irradiating a charged particle beam, and the Na cooling fuel assembly 45 has an internal duct 48 as shown in (c), and a nitride of recovered uranium or natural uranium is placed inside the internal duct. A heavy water moderator 46 is filled between the inner ducts of the trumpet pipes enclosed in the fuel rod cladding pipe. As shown in FIG. 6B, the liquid Na 47 that has flowed in from the lower end of the fast reactor is squeezed inside the internal duct at the inlet of the subcritical reactor 41. As shown in FIG. 5, the structure of the other assembly is the same as the fuel assembly of the fast reactor, and the liquid Na 47 that has flowed in from the lower end of the fast reactor is directly passed through the subcritical reactor from below. To pass through. In this embodiment, the fuel in the upper part of the fast reactor adjacent to the lower end of the subcritical reactor is irradiated with neutrons, and a fission chain reaction occurs from above the core of the fast reactor that is irradiated with the neutrons, Once a fission chain reaction occurs in the core fuel region of the fast reactor, the combustion region automatically moves below the core.

  In the present embodiment, the core of the fast reactor is disposed at the lower end of the subcritical reactor, and the area of the reactor building can be reduced.

  In the above embodiment, the fast reactor fuel is nitride, but the same effect can be obtained by using metal. Furthermore, although liquid Na was used as the coolant for the fast reactor, the same effect can be obtained with liquid lead or lead-bismuth.

1,21,31 Hybrid reactor 2 Neutron source 3 Neutron multiplication region 4 of subcritical reactor Charged beam 5 Core region of fast reactor 6, 41 Subcritical reactor 7 Fast reactor 22 Fuel assembly 23 Core fuel assembly 24 Heavy water tank 25 Heavy water moderator 26 Fuel channel 27 Channel 43 Neutron source region 44 irradiated with charged particle beam Na-cooled fuel assembly 45 Na-cooled fuel assembly 46 Heavy water moderator 47 Liquid Na
48 Internal duct 51 Fast reactor core 52 of subcritical reactor Fast reactor core fuel assembly 61 of subcritical reactor Axial cross-sectional structure of heavy water moderator inclusion fuel assembly of subcritical reactor 71, 91 keff Curves 72 and 74 showing burnup dependence Burnup 73 and 82 Neutron effective multiplication factor (keff)
81 Curve showing keff dependence of neutron multiplication factor 83 Neutron multiplication factor

Claims (5)

  Loading depleted uranium, enclosing the neutron source region that receives neutrons by receiving a charged particle beam irradiated from the outside, and surrounding the neutron source region, using natural uranium or recovered uranium nitride as fuel, heavy water as a coolant and deceleration A subcritical nuclear reactor that is used as a material, and adjacent to the subcritical nuclear reactor, in which a nitride fuel of natural uranium, recovered uranium, or deteriorated uranium is sealed in a cladding tube, and the cladding tube is bundled in a wrapper tube A hybrid comprising two reactors of a fast reactor loaded with a core fuel assembly for gradually heating the heat generated by fission by flowing liquid Na from below to above between the cladding tubes Type reactor core.   The hybrid nuclear reactor core according to claim 1, wherein a volume ratio of fuel in the fast reactor core is larger than 50%.   The hybrid reactor core according to claim 1, wherein the fast reactor is disposed adjacent to a lower part of the subcritical reactor.   4. The hybrid nuclear reactor according to claim 1, wherein a nuclear fuel material enclosed in a cladding tube constituting a hexagonal fuel assembly of the fast reactor is a metal fuel. 5. The core of the furnace.   5. The core of a hybrid nuclear reactor according to claim 1, wherein the coolant of the fast reactor is lead or lead-bismuth.

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