JP2018071997A - Fast reactor core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fast reactor core capable of improving the safety property by reducing the combustion reactivity while suppressing increase of void reactivity to thereby reduce reactivity applied to the reactor core during UTOP.SOLUTION: A fast reactor core 10 includes, in a radial direction of the reactor core: an inner core fuel area 21; and an outer core fuel area 22 enclosing the inner core fuel area 21. The inner core fuel area 21 and the outer core fuel area 22 are loaded with a fuel assembly which includes an MOX fuel in a wrapper tube. At least the fuel assembly which is loaded in the inner core fuel area 21 includes an internal blanket fuel 31, which includes degraded uranium oxide containing minor actinide as the fuel in generally central area in an axial direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fast reactor core for improving safety by avoiding core damage when a control rod erroneous pull-out accident is assumed in a fast reactor.

  Regarding the fuel assembly and core of the fast reactor, as described in Non-Patent Document 1, in the fast breeder reactor, the core is disposed in the reactor vessel, and liquid sodium as a coolant is placed in the reactor vessel. Is filled. 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 for supporting the neutron shield located below the fuel rod, and a coolant outflow portion located above the fuel rod.

The core of the fast breeder reactor has a core fuel region having an inner core fuel region and an outer core fuel region surrounding the inner core fuel region, a blanket fuel region surrounding the core fuel region, and a shield region surrounding the blanket fuel 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 fuel 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 fuel region and the outer core fuel assembly loaded in the outer core fuel 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. .

Now, the combustion reaction of the fast reactor is generally about 3% Δk / kk ′, and an accident (UTOP: Unprotected Transient) that overlaps the erroneous extraction of the control rod and the scram failure.
Assuming Over Power (hereinafter referred to as UTOP), the output density near the control rod may change, and the line output may exceed the design tolerance. If such an increase in line output during UTOP can be avoided, an increase in thermal margin and, in turn, an improvement in core safety can be realized. In order to avoid an increase in line output at the time of UTOP, it is effective to reduce the combustion reactivity and to reduce the control reactivity required per control rod for combustion compensation.
For example, Patent Document 1 includes a minor actinide (hereinafter referred to as MA) as a fuel material in a fuel element (fuel pin) housed in a fuel assembly loaded in the core of a fast reactor. A configuration is disclosed in which the TRU (transuranic element) enrichment is 5% to 30% and the fissile Pu enrichment is 9% to 12%. This makes it possible to realize a fast breeder reactor that can supply the specified electric power without changing the fuel throughout the life of the plant of the nuclear power plant, improving the operating rate and extending the fuel life. It is described that it is possible to improve significantly.

Japanese Patent Laid-Open No. 5-52981

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

Kazuaki Sugino, Tomoyuki God, Heihei Hama, Kazuyuki Numata: Creation of fast reactor constants UFLIB.J40 and JFS-3-J4.0 based on JENDL-4.0, JAEA-Data / Code 2011-017, Japan Japan Atomic Energy Agency (2011).

Hane-sama, et al., “SLAROM-UF: Ultra Fine Group Cell Calculation Code for Fast Reactor-Version 20090113-,” JAEA-Review 2009-003 (2009).

T.A. R. Fowler, D.C. R. Vody and G. W. Cunningham: Nuclear Reactor Code Analysis Code: CITATION: ORNL / TM-2469 Rev. 2 (1971).

However, in the configuration of Patent Document 1, the addition of MA to the core fuel of the fast reactor results in a significant increase in void reactivity. Further, in the core of the fast reactor, although it is necessary to reduce the combustion reactivity when UTOP is assumed, Patent Document 1 does not consider this point at all.
Therefore, the present invention provides a fast reactor core capable of improving safety by reducing combustion reactivity while suppressing increase in void reactivity and reducing reactivity applied to the core during UTOP.

  In order to solve the above problems, a core of a fast reactor according to the present invention has an inner core fuel region and an outer core fuel region surrounding the inner core fuel region in a radial direction of the core, and the inner core fuel region and A fuel assembly containing MOX fuel in a trumpet tube is loaded in the outer core fuel region, and at least the fuel assembly loaded in the inner core fuel region is fueled with depleted uranium oxide containing minor actinides. A blanket fuel is provided in a substantially central portion in the axial direction.

According to the present invention, there is provided a fast reactor core capable of improving safety by reducing combustion reactivity while suppressing increase in void reactivity and reducing reactivity applied to the core during UTOP. It becomes possible.
For example, the core configuration is an axially inhomogeneous core, MA is added to the internal blanket fuel, and the content ratio is optimized so that the absolute value of the combustion reactivity is 1 dollar ($) or less, and when UTOP is assumed The absolute value of the applied reactivity can be reduced, and the core safety can be improved.

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

It is a longitudinal cross-sectional view of the core of the fast reactor of Example 1 which concerns on one Example of this invention, Comprising: It is a figure which shows a 1/2 core. It is a cross-sectional view of the core of the fast reactor shown in FIG. 1 is an overall configuration diagram of a fast reactor nuclear power generation system having a fast reactor core according to an embodiment of the present invention. It is a figure which shows the MA content rate dependence of the internal blanket of a combustion reactivity in the core of the fast reactor which made MA contain the internal blanket fuel. It is a longitudinal cross-sectional view of the modification of the core of the fast reactor shown in FIG. 1, and is a diagram showing a ½ core. It is a longitudinal cross-sectional view of the core of the fast reactor of Example 2 which concerns on the other Example of this invention, Comprising: It is a figure which shows a 1/2 core. It is a cross-sectional view of the core of the fast reactor shown in FIG.

  FIG. 3 is an overall configuration diagram of a fast reactor nuclear power generation system having a fast reactor core according to an embodiment of the present invention. As shown in FIG. 3, a fast reactor nuclear power generation system 1 includes a reactor vessel 2, a core 3 containing a fissile material housed in the reactor vessel 2, and a primary cooling system pipe 4a from the reactor vessel 2. The intermediate heat exchanger 5 and the primary main circulation pump 7a are connected in order, and the steam generator 8 and the secondary main circulation pump 7b are connected in order from the intermediate heat exchanger 5 through the secondary cooling system pipe 4b. Further, a main steam system pipe 9a that sends the steam generated by the steam generator 8 to the high-pressure turbine 11a and the low-pressure turbine 11b, and a condenser that condenses the steam after passing through the high-pressure turbine 11a and the low-pressure turbine 11b and returns it to water. 13. Supply water condensate system pipe 9b for returning the water condensed in the condenser 13 to the steam generator 8, the generator 12 connected to the shafts of the high-pressure turbine 11a and the low-pressure turbine 11b, and the downstream side of the condenser 13 The feed water pump 14 and the feed water heater 15 are connected to the condensate system pipe 9b.

  In the fast reactor nuclear power generation system 1, the primary coolant (for example, liquid sodium) heated in the core 3 is passed through the intermediate heat exchanger 5 to heat the secondary coolant (for example, liquid sodium). Further, the secondary coolant is passed through the steam generator 8 to generate steam in the main steam system pipe 9a. The steam is guided to the high-pressure turbine 11a and the low-pressure turbine 11b, and the generator 12 generates power. The steam used for power generation is condensed in the condenser 13 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 14 and the feed water heater 15 are supplied. The water is heated and pressurized through the steam generator 8 and supplied to the steam generator 8.

The core 3 is loaded with a plurality of core fuel assemblies and control rods to be described later. The reactor vessel 2 that houses the reactor core 3 is filled with a primary coolant, and the primary coolant enters the reactor core 3 from the lower part of the reactor core 3 and rises along the reactor core fuel assembly, and is atomized by the primary main circulation pump 7a. It flows into the intermediate heat exchanger 5 provided outside the furnace vessel 2 through the primary cooling system pipe 4a. This constitutes a loop type fast reactor. In the present 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 2, the primary main circulation pump 7a, and the intermediate heat exchanger 5 are accommodated in one tank. It can also be applied to furnaces.
Hereinafter, the core of a fast reactor according to an embodiment of the present invention will be described with reference to the drawings.

1 is a longitudinal sectional view of a core of a fast reactor according to an embodiment 1 of the present invention, showing a 1/2 core, and FIG. 2 is a core of the fast reactor shown in FIG. 4 is a diagram showing a half core, and FIG. 4 is a diagram showing the dependence of the combustion reactivity on the MA content of the internal blanket in a fast reactor core containing MA in the internal blanket fuel. FIG.
In FIG. 2, only a half portion is shown because of vertical symmetry. The core 10 of the fast reactor in the present embodiment is disposed in the reactor vessel 2 (FIG. 3) of the fast reactor, and includes an inner core fuel region 21 and an outer core fuel region 22 surrounding the inner core fuel region 21 in the radial direction. Thus, the core fuel region is configured. A plurality of control rod assemblies 24 are arranged in the core fuel region. The fast reactor core 10 includes a radial blanket fuel region 23 so as to surround the outer core fuel region 22, and a reflector region 25 and a shield region 26 outside the radial blanket fuel region 23. In the radial direction of the core 10 of the fast reactor, the reflector region 25 surrounds the radial blanket fuel region 23 and is adjacent to the radial blanket fuel region 23, and the shield region 26 surrounds the reflector region 25. The fast reactor core 10 of the present embodiment is an axially heterogeneous core in which an internal blanket fuel, which will be described later, is disposed in an inner core fuel region 21 constituting the core fuel region.

As shown in FIG. 1, the core 10 of the fast reactor includes an upper core 32 and a lower fuel 33 in the inner core fuel region 21 (FIG. 2), and an outer core fuel 34 in the outer core fuel region 22 (FIG. 2). Is a MOX fuel in which plutonium oxide (PuOx) is mixed with deteriorated uranium oxide (UO2), and both have the same Pu enrichment. The fuel of the internal blanket fuel 31 is a mixture of deteriorated uranium oxide (UO2) and MA oxide (MAOx). Further, the axial upper blanket fuel 35, the axial lower blanket fuel 36, and the radial blanket fuel 37 are all deteriorated uranium oxide (UO2).
As shown in FIG. 1, in the inner core fuel region 21 (FIG. 2), from the lower part to the upper part in the axial direction (from the upstream side to the downstream side along the flow direction of the liquid sodium as the primary coolant). In this order, an axial lower blanket fuel 36, a lower fuel 33, an internal blanket fuel 31, an upper fuel 32, and an axial upper blanket fuel 35 are arranged. For example, the axial lower blanket fuel 36 has an axial height of about 30 cm (length along the axial direction), the lower fuel 33 is 40 cm, the inner blanket fuel 31 is 20 cm, the upper fuel 32 is 40 cm, and The axial upper blanket fuel 35 has a height of 30 cm (length along the axial direction). Therefore, the total height (total length along the axial direction) of the lower fuel 33, the inner blanket fuel 31, and the upper fuel 32 in the axial direction is about 100 cm. On the other hand, in the outer core fuel region 22 (FIG. 2), from the lower part to the upper part in the axial direction (from the upstream side to the downstream side along the flow direction of the liquid sodium as the primary coolant), in the axial direction A lower blanket fuel 36, an outer core fuel 34, and an axial upper blanket fuel 35 are disposed. The outer core fuel 34 has a height (length along the axial direction) of about 100 cm in the axial direction. Further, the radial blanket fuel 37 in the radial blanket fuel region 23 (FIG. 2) has, for example, a height of about 160 cm (a length along the axial direction) in the axial direction.

The electrical output of the reactor is 750,000 kWe, the continuous operation period is about 20 months, 6 batch fuel replacements, the core fuel removal average burnup is about 150 GWd / t. Using the MA content (wt%) contained in the internal blanket fuel 31 of the core 10 of this embodiment as a parameter, the MA content (wt%) of the combustion reactivity (% Δk / kk ′) was evaluated by calculation.
In the evaluation, the standard analysis method of the fast reactor is used as shown below. SLAROM is a program for calculating the effective cross section of fast reactors using 70 nuclear data sets for fast reactors based on JENDL-4.0, the latest nuclear data library in Japan (see Non-Patent Document 2). The effective area of 70 energy groups of neutrons was calculated with -UF (see Non-Patent Document 3). Using this effective cross-sectional area, the equilibrium cycle calculation is performed with the two-dimensional RZ core system model of the neutron diffusion calculation program CITATION (see Non-Patent Document 4), and the neutron effective multiplication factor (keff) is obtained. wt%), the inner core fuel assembly loaded in the inner core fuel 21 and the outer core fuel assembly loaded in the outer core fuel region 22 become critical at the end of the equilibrium cycle at a predetermined removal burnup. Find the Pu enrichment of. At this time, the combustion reactivity (% Δk / kk ′) is calculated using the effective neutron multiplication factor (keff) at the beginning and end of the equilibrium cycle. The above calculation is repeated for several MA contents to plot a curve of the MA reactivity (wt%) dependence of the combustion reactivity (% Δk / kk ′). In addition, the standard analysis method of the above-mentioned fast reactor has been sufficiently verified by a critical experiment simulating the fast reactor and an actual fast reactor.
FIG. 4 shows the evaluation results. FIG. 4 is a diagram showing the MA content rate dependence of the internal blanket fuel in the combustion reactivity in the core 10 of the fast reactor. In FIG. 4, the horizontal axis represents the MA content (wt%) in the internal blanket fuel, and the vertical axis represents the combustion reactivity (% Δk / kk ′). The dependence of the combustion reactivity on the MA content of the internal blanket fuel. Is shown. MA is Np, Am, and Cm contained in the spent fuel of the light water reactor having an extraction burnup of 60 GWd / t. As shown in FIG. 4, the combustion reactivity (% Δk / kk ′) decreases as the MA content (wt%) in the internal blanket fuel 31 increases, and the MA content becomes almost zero near 40 wt%. When the MA content (wt%) further increases, the value becomes negative. Here, when the MA content exceeds about 40 wt%, the combustion reactivity (% Δk / kk ′) becomes a negative value. This is a reaction at the end of the equilibrium cycle rather than the reactivity at the beginning of the equilibrium cycle. It depends on the degree. When the MA content (wt%) is 35 wt%, the combustion reactivity is 1 $, and when the MA content (wt%) is 45 wt%, the combustion reactivity is −1 $ or less. That is. When the MA content (wt%) of the internal blanket fuel 31 is in the range of 35 wt% to 45 wt%, the absolute value of the combustion reactivity becomes 1 $ or less, and an accident (UTOP: Unprotected) where control rod mispulling and scram failure are superimposed Even when Transient Over Power is assumed, the increase in line output in the fuel assembly in the vicinity of the control rod assembly 24 is small, and the soundness of the fuel is maintained. Here, the absolute value of the combustion reactivity of 1 $ means that the generation rate of execution delayed neutrons is about 0.3%.

  FIG. 5 is a longitudinal sectional view of a modified example of the core of the fast reactor shown in FIG. 1 and shows a 1/2 core. As shown in FIG. 5, the modified fast reactor core 10 a is an outer core fuel 34 in the outer core fuel region 22 (FIG. 2), and an inner blanket fuel 31 in the inner core fuel region 21 (FIG. 2). An internal blanket fuel 31a is provided at a predetermined length (distance) in the radial direction from an adjacent region and substantially in the center in the axial direction. The internal blanket fuel 31 a in the outer core fuel 34 in the outer core fuel region 22 is in the same manner as the inner blanket fuel 31 in the inner core fuel region 21, and deteriorated uranium oxide (UO 2) and minor actinide (MA) oxide (MAOx). Are mixed. Therefore, also in the internal blanket fuel 31a in the outer core fuel 34 in the outer core fuel region 22, the MA content (wt%) is preferably 35 wt% to 45 wt%, and the MA content (wt%) It is desirable that the internal bracket fuel 31 in the fuel region 22 and the internal blanket fuel 31 a in the outer core fuel 34 in the outer core fuel region 22 be the same.

As described above, according to the present embodiment, a fast reactor capable of improving safety by reducing combustion reactivity while suppressing increase in void reactivity and reducing reactivity applied to the core during UTOP. It is possible to provide a core of
More specifically, the absolute value of the combustion reactivity is set to 1 dollar ($) or less by making the core structure an axially inhomogeneous core, adding MA to the internal blanket fuel, and optimizing its content. When the UTOP is assumed, the absolute value of the applied reactivity can be reduced, and the core safety can be improved.

  6 is a longitudinal sectional view of the core of the fast reactor of the second embodiment according to another embodiment of the present invention, showing a half core, and FIG. 7 is a diagram of the fast reactor shown in FIG. It is a cross-sectional view of a core, and is a diagram showing a ½ core. In the first embodiment, as shown in FIG. 1, an axial upper blanket fuel 35 and an axial lower blanket fuel 36 are arranged in the inner core fuel region 21 and the outer core fuel region 22. On the other hand, in this embodiment, the sodium plenum region 45 is arranged in the axial upper part of the upper fuel 42 and the outer core fuel 44 without arranging the axial upper blanket fuel 35 and the axial lower blanket fuel 36. This is different from the first embodiment. Further, the second embodiment is different from the first embodiment in that a gas expansion module (GEM: Gas Expansion Module, hereinafter referred to as GEM) 46 is arranged between the outer core fuel 44 and the radial blanket fuel 47.

  In FIG. 7, only a half portion is shown because of vertical symmetry. The fast reactor core 20 in this embodiment is disposed in the reactor vessel 2 (FIG. 3) of the fast reactor, and includes an inner core fuel region 21 and an outer core fuel region 22 surrounding the inner core fuel region 21 in the radial direction. Thus, the core fuel region is configured. A plurality of control rod assemblies 24 are arranged in the core fuel region. Further, a gas expansion module (GEM) 38 is loaded in the fast reactor core 20 so as to surround the outer core fuel region 22, and the radial blanket fuel region 23, the reflection is provided outside the gas expansion module (GEM) 38. It has a body region 25 and a shield region 26. In the radial direction of the core 20 of the fast reactor, the radial blanket fuel region 23 surrounds the gas expansion module (GEM) 38 and is adjacent to the gas expansion module (GEM) 38, and the shield region 26 is the reflector region 25. Surrounding. Here, the gas expansion module (GEM) 38 is a hollow tubular structure whose one end is closed and the other end is opened, and its appearance is the fuel loaded in the inner core fuel region 21 and the outer core fuel region 22. It is the same as the trumpet tube of the assembly. The core 20 of the fast reactor of the present embodiment is an axially inhomogeneous core in which an internal blanket fuel, which will be described later, is disposed in an inner core fuel region 21 constituting the core fuel region.

As shown in FIG. 6, the core 20 of the fast reactor includes an upper core 42 and a lower fuel 43 in the inner core fuel region 21 (FIG. 7), and an outer core fuel 44 in the outer core fuel region 22 (FIG. 7). Is a MOX fuel in which plutonium oxide (PuOx) is mixed with deteriorated uranium oxide (UO2), and both have the same Pu enrichment. The internal blanket fuel 41 is a fuel in which 35 wt% of MA oxide (MAOx) is mixed with deteriorated uranium oxide (UO2). In addition, a sodium plenum region 45 is disposed on the upper portion in the axial direction of the upper core fuel 42 in the inner core fuel region 21 (FIG. 7) and the outer core fuel 44 in the outer core fuel region 22 (FIG. 7). Here, the sodium plenum region 45 is a space defined by the inner wall surface of the trumpet pipe above the core fuel (upper fuel 42, outer core fuel 44). In addition, a gas expansion module (GEM) 46 is disposed on the radially outer side of the outer core fuel 44, and a radial blanket fuel 47 is disposed on the radially outer side of the gas expansion module (GEM) 46.
When an accident (ULOF: Unprotected Loss of Flow Accident, hereinafter referred to as ULOF) is assumed in which the loss of the flow rate of the coolant accompanying the stoppage of the primary main circulation pump 7a (FIG. 3) due to power loss or the like is superimposed. Even if the void reactivity increases, the generated void is accommodated in the sodium plenum region 45 located above the core fuel (upper fuel 42, outer core fuel 44) and the internal blanket fuel 41, An increase in the line output of the fuel assembly in the vicinity of the control rod assembly 24 is suppressed. Therefore, by including the sodium plenum region 45, the gas expansion module (GEM) 46 is not necessarily included so as to be adjacent to the fuel assembly loaded on the outermost periphery of the outer core fuel region 22 (FIG. 7). Thus, the above-described effects that cannot be achieved in the first embodiment can be achieved.

  As shown in FIG. 6, in the inner core fuel region 21 (FIG. 7), from the lower part to the upper part in the axial direction (from the upstream side to the downstream side along the flow direction of the liquid sodium as the primary coolant). In this order, a lower fuel 43, an internal blanket fuel 41, an upper fuel 42, and a sodium plenum region 45 are arranged. For example, the lower fuel 43 has an axial height of about 35 cm (length along the axial direction), the inner blanket fuel 41 is 20 cm, the upper fuel 42 is 45 cm, and the sodium plenum region 45 is 40 cm high. (Length along the axial direction). Therefore, the total height (total length along the axial direction) of the lower fuel 43, the inner blanket fuel 41, and the upper fuel 42 in the axial direction is about 100 cm. On the other hand, in the outer core fuel region 22 (FIG. 7), the outer core is sequentially turned from the lower portion to the upper portion (from the upstream side to the downstream side along the flow direction of the liquid sodium as the primary coolant). A fuel 44 and a sodium plenum region 45 are disposed. The outer core fuel 44 has a height (length along the axial direction) of about 100 cm in the axial direction. The sodium plenum region 45 has a height (length along the axial direction) of about 40 cm in the axial direction, for example.

  As described above, the core 20 of the fast reactor in the present embodiment eliminates the axial blanket fuel (the axial upper blanket fuel 35 and the axial lower blanket fuel 36) in the core of the first embodiment, and instead, the core. A sodium plenum region 45 is installed in the upper part of the fuel, and the outer periphery of the core fuel region composed of the inner core fuel region 21 and the outer core fuel region 22, that is, among the fuel assemblies loaded in the outer core fuel region 22, A gas expansion module (GEM) 46 is arranged so as to be adjacent to and surround the fuel assembly loaded on the outer periphery.

  The core 20 of the fast reactor according to the present embodiment, as in the first embodiment, ensures the soundness of the core fuel at the time of UTOP, and is significantly smaller than the fast reactor having the same power scale as the void reactivity. It is about 2-3 $. Further, assuming an accident (ULOF) in which the loss of the flow rate of the primary system coolant (for example, liquid sodium) due to the stoppage of the primary main circulation pump 7a due to power loss or the like and the scram failure are superimposed, the inner core fuel region 21 and the outer core Due to the decrease in the flow rate of the primary system coolant (for example, liquid sodium) in the fuel assembly loaded in the fuel region 22, the output / flow rate (P / F) ratio of the fuel assembly becomes inconsistent, and the primary system coolant (for example, , Liquid sodium) increases in temperature. However, in the configuration of the fast reactor core 20 of this embodiment, the neutrons from the fuel assemblies loaded in the inner core fuel region 21 and the outer core fuel region 22 to the sodium plenum region 45 and the gas expansion module (GEM) 46 are used. Since the leakage amount is large and negative reactivity is applied, boiling of the primary coolant (for example, liquid sodium) can be avoided and increase in core power can be suppressed, and the integrity of the core fuel is maintained.

  It should be noted that a plutonium enrichment degree (Pu enrichment degree) of the MOX fuel of the fuel assembly that is arranged in the circumferential direction so as to be adjacent to the gas expansion module (GEM) 46 and is loaded on the outermost circumference of the outer core fuel region 22 May be the highest. That is, the fuel loaded in the outer core fuel region 22 and the fuel loaded in the inner core fuel region 21 excluding the fuel assembly loaded on the outermost periphery of the outer core fuel region 22 (outermost fuel assembly). The plutonium enrichment (Pu enrichment) of the MOX fuel in the assembly is the same, and the MOX of the fuel assembly loaded in the outer core fuel region 22 and the fuel assembly MOX loaded in the inner core fuel region 21 are the same. The plutonium enrichment (Pu enrichment) of the MOX fuel in the outermost fuel assembly is higher than the plutonium enrichment (Pu enrichment) of the fuel.

  As described above, according to the present embodiment, in addition to the effect at the time of assuming the UTOP of the first embodiment, the sodium plenum region 45 is arranged so that the primary main circulation pump 7a (FIG. 3) is stopped due to power loss or the like. Assuming an accident (ULOF) that superimposes the loss of coolant flow and the failure of the scram, the sodium plenum region 45 and the gas expansion module (GEM) 46 are arranged in the core of the fast reactor. The amount of neutron leakage from the fuel assemblies loaded in the core fuel region 21 and the outer core fuel region 22 to the sodium plenum region 45 and the gas expansion module (GEM) 46 is large, and negative reactivity is applied. Maintains soundness of core fuel by avoiding boiling of primary coolant (eg, liquid sodium) and suppressing increase in core power Theft is possible.

  In the first and second embodiments described above, the case where a mixed oxide (MOX) fuel in which deteriorated uranium oxide (UO2) and plutonium oxide (PuOx) are mixed is used as an example of the core fuel. Is not limited to this. For example, metal fuel or nitride fuel may be used, and the coolant (primary coolant) may be configured to use liquid heavy metal such as lead, lead / bismuth or the like instead of sodium.

  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.

DESCRIPTION OF SYMBOLS 1 ... Fast reactor nuclear power generation system 2 ... Reactor vessel 3 ... Core 4a ... Primary cooling system piping 4b ... Secondary cooling system piping 5 ... Intermediate heat exchanger 7a ... Primary main circulation pump 7b ... Secondary main circulation pump 8 ... Steam generator 9a ... Main steam system piping 9b ... Supply / condensation system piping 10, 10a, 20 ... Core 11a ... High pressure Turbine 11b ... Low pressure turbine 12 ... Generator 13 ... Condenser 14 ... Feed water pump 15 ... Feed water heater 21 ... Inner core fuel region 22 ... Outer core fuel region 23 ... radial blanket fuel area 24 ... control rod assembly 25 ... reflector area 26 ... shield areas 31, 31a ... internal blanket fuel 32 ... upper fuel 33 ... lower part Fuel 34 ... Outer core fuel 35 ... Axial upper blanket DOO fuel 36 ... axis direction lower blanket fuel 37 ... radial blanket fuel 38 ... gas expansion module (GEM)
41 ... Internal blanket fuel 42 ... Upper fuel 43 ... Lower fuel 44 ... Outer core fuel 45 ... Sodium plenum region 46 ... Gas expansion module (GEM)
47 ... Radial blanket fuel

Claims (9)

A fuel assembly having an inner core fuel region and an outer core fuel region surrounding the inner core fuel region in a radial direction of the core, and containing MOX fuel in a wrapper tube in the inner core fuel region and the outer core fuel region. Loaded,
At least the fuel assembly loaded in the inner core fuel region comprises an internal blanket fuel fueled by depleted uranium oxide containing minor actinides at a substantially central portion in the axial direction. . In the core of the fast reactor according to claim 1,
The core of a fast reactor, wherein the inner blanket fuel has a minor actinide content of 35 wt% to 45 wt%. In the core of the fast reactor according to claim 2,
The fuel assembly loaded in the inner core fuel region includes an upper fuel with MOX fuel and an axial upper blanket fuel with depleted uranium oxide as fuel above the inner blanket fuel, and the inner blanket fuel. A fast reactor core comprising a lower fuel having MOX fuel and an axial lower blanket fuel having deteriorated uranium oxide as a fuel below. In the core of the fast reactor according to claim 3,
The MOX fuel is a fuel in which plutonium oxide is mixed with deteriorated uranium oxide, and is loaded in the upper and lower fuels of the fuel assembly loaded in the inner core fuel region and in the outer core fuel region. A fast reactor core characterized in that the plutonium enrichment of the MOX fuel in the fuel assembly is the same. In the core of the fast reactor according to claim 1,
The fuel assembly loaded in the inner core fuel region and the outer core fuel region has a sodium plenum region defined by an inner wall surface of the trumpet tube at an upper portion in the axial direction of the MOX fuel. Core. In the core of the fast reactor according to claim 5,
A hollow tubular structure including a radial blanket region disposed so as to surround the outer core fuel region and having one end closed and the other end opened between the radial blanket region and the outer core fuel region. A core of a fast reactor characterized by arranging a gas expansion module. In the core of the fast reactor according to claim 6,
A core of a fast reactor, wherein a plurality of the gas expansion modules are arranged in a circumferential direction so as to be adjacent to a fuel assembly loaded on an outermost periphery of the outer core fuel region. In the core of the fast reactor according to claim 7,
The MOX fuel is a fuel in which plutonium oxide is mixed with deteriorated uranium oxide, and is loaded in the upper and lower fuels of the fuel assembly loaded in the inner core fuel region and in the outer core fuel region. A fast reactor core characterized in that the plutonium enrichment of the MOX fuel in the fuel assembly is the same. In the core of the fast reactor according to claim 7,
A fast reactor having a highest plutonium enrichment of MOX fuel in a fuel assembly arranged in a circumferential direction adjacent to the gas expansion module and loaded on the outermost periphery of the outer core fuel region. Core.

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