JP6430141B2 - Boiling water reactor core - Google Patents

Description

  The present invention relates to a core of a boiling water reactor that is a kind of light water reactor.

  The core of a boiling water reactor is formed by arranging a plurality of unit lattices with a cross-shaped control rod and four fuel assemblies surrounding it as a unit lattice. In general, such a nuclear reactor takes out a part of the fuel assembly in the core every time the continuous operation period (operation cycle) ends, and a new fuel assembly (unburned fuel assembly having a burnup of 0 GWd / t). ) And the operation cycle is repeated.

  As a technique related to the core of such a boiling water reactor, for example, Patent Document 1 (Japanese Patent Laid-Open No. 10-082879) discloses an initial loaded core (a core in which a fuel assembly is loaded for the first time after the reactor is constructed). In order to flatten the radial power distribution and improve the core characteristics in the operation cycle, each fuel assembly with a different average enrichment was considered as a fuel assembly with a different residence time in the equilibrium core. Initial loading with a core configuration that simulates an equilibrium core as the fuel configuration, and a fuel assembly that has the highest enrichment and a low number of fuel rods containing flammable poisons in the outermost and second outermost layers in the core radial direction. A reactor core is disclosed.

Japanese Patent Laid-Open No. 10-082879

  By the way, in order to improve the operation rate of the nuclear power plant, that is, the ratio of the operating time to the whole period and improve the economic efficiency of the nuclear power plant, it is necessary to extend the operation cycle of the nuclear reactor (long-term cycle operation). It is valid. As a method of extending the operation cycle of the nuclear reactor, it is conceivable to increase the amount of nuclear fuel material in the fuel assembly unit so that high reactivity can be maintained for a long time.

The following methods can be used to increase the amount of nuclear fuel material loaded.
That is, for example, the amount of nuclear fuel material loaded can be increased by increasing the amount of fuel pellets per fuel assembly, but the design of the fuel assembly needs to be changed, which is not easy. In addition, for example, by increasing the proportion of fissile material in the fuel pellet, that is, increasing the enrichment, it is possible to increase the amount of nuclear fuel material loaded without changing the design. There are limitations. Further, when the enrichment of the fissile material is increased, it is difficult to satisfy the thermal limit operation limit value such as the maximum linear power density and the minimum limit power ratio and the operation limit value of the reactor shutdown margin.

  The present invention has been made in view of the above, and the operation cycle can be extended while satisfying the restrictions on the maximum uranium enrichment, the maximum linear power density, the minimum critical power ratio, the furnace shutdown margin, etc. An object of the present invention is to provide a boiling water reactor core capable of improving the economic efficiency of the reactor.

In order to achieve the above object, the present invention provides a core of a boiling water reactor that is composed only of unburned fuel assemblies and has an average enrichment of fissile material of 4.0 wt% or more. When the radius of the circumscribed circle of the core is R, an area inside the circle having a radius of 0.75R having the same center as the circumscribed circle is defined as an inner area of the core and an outer area is defined as an outer peripheral area of the core. Is defined as belonging to the core inner region and the fuel assembly located outside belongs to the outer peripheral region of the core. An average number of the flammable poison-containing fuel rods in the fuel assembly including the toxic poison-containing fuel rods is defined as a, and the outermost peripheral region of the core includes the flammable poison-containing fuel rods. Placed on the perimeter The average number of burnable poison-containing fuel rods in serial the fuel assembly excluding the fuel assembly defined is b, in the core inner region, the burnable poison in the fuel assembly comprising a burnable poison-containing fuel rods An average concentration of combustible poisons in the containing fuel rods is defined as A, and the fuel assemblies including the combustible poison-containing fuel rods in the outer peripheral region of the core are excluded from the fuel assemblies arranged on the outermost periphery. Further, when the average of the concentration of the flammable poison of the burnable poison-containing fuel rod in the fuel assembly is defined as B, 0.6 ≦ (bB) / (aA) ≦ 0.9 is satisfied.

  While satisfying restrictions on maximum uranium enrichment, maximum linear power density, minimum critical power ratio, etc., the operating cycle can be extended and the economics of nuclear power plants can be improved.

It is a figure which shows roughly the whole structure of the boiling water reactor which concerns on this Embodiment. It is a longitudinal cross-sectional view which shows roughly the structure of the fuel assembly which concerns on this Embodiment. It is a horizontal sectional view which shows roughly the structure of the fuel assembly which concerns on this Embodiment. It is a figure which shows typically the arrangement | sequence of the fuel assembly in the horizontal cross section of a core. It is a figure which shows an example of the power distribution with respect to the distance from the center of a core. It is a figure which shows the relationship between the ratio of the defined average a and average b, and the thermal margin (relative value) in the operation cycle initial stage. It is a figure which shows the relationship between the ratio of the defined average a and average b, and the core stop margin (relative value) in the initial stage of an operation cycle. Relationship between the defined number a and the product of the concentration average A aA, the ratio of the product BB of the number B and the concentration average B (bB / aA), and the neutron multiplication factor (relative value) which is the reactivity at the end of the operation cycle FIG. The relationship between the defined number a and the product of the concentration average A aA, the ratio of the product BB of the number B and the concentration average B (bB / aA), and the core shutdown margin (relative value) from the middle to the end of the operation cycle is shown. FIG. It is a figure which illustrates the relationship between the average uranium enrichment and the continuous operation period in the core comprised of only one type of fuel assembly. 2 is a diagram illustrating an example of an arrangement of fuel assemblies in a core of a boiling water reactor according to Embodiment 1. FIG. 5 is a diagram illustrating an example of the arrangement of fuel assemblies in the core of a boiling water reactor according to Embodiment 2. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing an overall configuration of a boiling water reactor according to the present embodiment.

  In FIG. 1, a boiling water reactor 100 includes a reactor pressure vessel 101, a core shroud 103 installed in the reactor pressure vessel 101, a core 105 installed in the core shroud 103, a reactor A simple steam dryer 107 installed above the inside of the pressure vessel 101, a water supply pipe 102 for supplying light water into the reactor pressure vessel 101, and a main steam pipe for sending steam generated in the reactor pressure vessel 101 to the outside 108.

The water supplied into the reactor pressure vessel 101 through the water supply pipe 102 descends in the downcomer 109 that is a region surrounded by the reactor pressure vessel 101 and the core shroud 103 and flows to the core 105 from below. The water flowing into the core 105 is heated by obtaining thermal energy from a plurality of fuel assemblies 116 (see FIG. 2 and the like) loaded in the core 105, and a part of the water boils to become steam. Steam generated in the reactor core 105 is rectified by the chimney 106 was placed on top of the core 105, it is guided to a simple steam dryer 107. The steam whose moisture has been separated by the simple steam dryer 107 is sent to the outside of the reactor pressure vessel 101 through the main steam pipe 108. Further, the water that has passed through the chimney 106 flows again into the downcomer 109 as recirculated water, and is mixed with the water supply.

  The thermal energy of the steam sent to the outside of the reactor pressure vessel 101 is used to turn a turbine (not shown), and power is generated by a generator (not shown) connected to the turbine. The steam that has lost energy in the turbine is condensed in a condenser (not shown), heated by a feed water heater (not shown), and then again through the feed water pipe 102 to the reactor pressure vessel 101. Water is supplied inside.

  The boiling water reactor 100 exemplified in the present embodiment is a natural circulation reactor, and feeds water and recirculation water from the downcomer 109 to the core 105 without using a recirculation pump. This is performed only by the natural circulation force generated by the density difference between the inside and outside of 103. In addition, the boiling water reactor 100 separates the steam heated by the core 105 and boiled from water, in addition to the simple steam dryer 107, and separates only by the difference in gravity generated between the steam and water. A phenomenon called air-water separation is used. If the speed of steam and water is high, the effect of gravity-water separation becomes low. Therefore, in the boiling water reactor in the present embodiment, the power density of the core 105 is reduced and the speed of generated steam and water is reduced. I am letting.

  FIG. 2 is a longitudinal sectional view schematically showing the configuration of the fuel assembly according to the present embodiment, and FIG. 3 is a horizontal sectional view of the fuel assembly.

  2 and 3, the fuel assembly 116 includes a plurality of fuel rods 111 enclosing a plurality of fuel pellets containing uranium dioxide, an upper tie plate 119 that supports the upper end portion of the fuel rod, and a lower end of the fuel rod 111. A lower tie plate 118 that supports the fuel cell, a plurality of fuel spacers 117 that maintain a space between the fuel rods 111, a water rod 113 that circulates cooling water, and a channel box 110 that bundles and stores the fuel rods 111. ing.

  The channel box 110 has an upper end attached to the upper tie plate 119 and extends toward the lower tie plate 118, and surrounds the plurality of fuel rods 111 bundled by the plurality of fuel spacers 117.

  The fuel rod 111 includes a partial-length fuel rod 112 in which the length (effective fuel length) of a region loaded with fuel pellets containing fissile material is shorter than the other fuel rods 111. The effective fuel length of the fuel rod 111 in the core of the present embodiment is about 2 m. In the horizontal sectional view shown in FIG. 3, the horizontal cross section at the height position where the standard fuel rod 111 and the partial length fuel rod 112 are present is shown.

  Further, the fuel rod 111 includes a combustible poison-containing fuel rod 114 containing gadolinia (gadolinium oxide) which is a combustible poison in the fuel pellet.

  As shown in FIG. 3, the fuel rods 111 (including the partial-length fuel rods 112 and the combustible poison-containing fuel rods 114) are arranged in 10 rows and 10 columns in the horizontal section of the fuel assembly 116. Two water rods 113 are arranged at the center of the fuel assembly 116. The water rod 113 is a large-diameter water rod and has a cross-sectional area that occupies a region where at least two fuel rods 111 can be arranged.

  The outer width of the channel box 110 is about 15 cm, the outer diameter of the fuel rod 111 is about 1.0 cm, and the outer diameter of the water rod 113 is about 2.5 cm. The fuel pellet filled in each fuel rod 111 is manufactured using uranium dioxide, which is a nuclear fuel material, and contains uranium-235, which is a fissile material.

  When the fuel assemblies 116 are loaded on the core 105 of the boiling water reactor, the four side surfaces of the rectangular tubular channel box 110 are spaced apart from the side surfaces of the channel boxes 110 of the adjacent fuel assemblies 116 by a predetermined distance. They are arranged in a square lattice so as to face each other. In the gap between the fuel assemblies 116, control rods 115 having a cross-shaped cross section are disposed. When the fuel assembly 116 is loaded on the core 105 of the boiling water reactor, one of the four corners (four corners) of the rectangular cylindrical channel box 110 faces the cross-shaped intersection of the control rod 115. Are arranged as follows.

  Channel box 110 is attached to upper tie plate 119 by channel fasteners (not shown). The channel fastener maintains a gap corresponding to the predetermined distance between the fuel assemblies 116 so that the control rod 115 can be inserted between the fuel assemblies 116 when the fuel assemblies 116 are loaded on the core 105. It has a function. For this reason, the channel fastener is attached to the upper tie plate 119 so as to be positioned at a corner facing the control rod 115. That is, the corner of the fuel assembly 116 facing the control rod 115 is a corner to which a channel fastener is attached.

  FIG. 4 is a diagram schematically showing the arrangement of the fuel assemblies in the horizontal cross section of the core. FIG. 5 is a diagram showing an example of the power distribution with respect to the distance from the center of the core.

In FIG. 4, a coordinate system in which the center of the circumscribed circle of the substantially circular horizontal cross section of the core 105 is the origin O and two orthogonal coordinate axes (coordinate axis X and coordinate axis Y) along the direction in which the fuel assemblies 116 are arranged is set. Only one of these quadrants (ie, one quarter) is shown.

Further, in FIG. 5, as an example, the core equivalent half diameter shows the power distribution in the following core 2.2 m, the distance from the core center (the origin O) on the horizontal axis and the vertical axis shows the relative outputs ing. In addition, the distance from the core center O is shown with the radius of the circumscribed circle being 1.

  As shown in FIG. 5, as the distance from the core center increases, the distance from the core center O becomes 0.7 (ie, a distance of about 75% from the core center with respect to the outer diameter of the core). Gradually decreases. The inventor of the present application pays attention to this point, and when the radius of the circumscribed circle of the core 105 is R, the region inside the circle having the same center as the circumscribed circle and a radius of 0.75R is defined as the core inner region 41 and the outer region. Was defined as the core peripheral region 42.

  That is, the boundary 40 is set at a distance of 75% from the core center with respect to the core outer diameter, and a region corresponding to the position of the fuel assembly 116 inside the boundary 40 in the core 105 is defined as the core inner region 41 and the outer fuel. A region corresponding to the position of the assembly 116 is defined as a core outer peripheral region 42, and a region corresponding to the position of the fuel assembly 116 (fuel disposed on the outermost periphery of the core 105) in contact with the reflector is defined as a core outermost peripheral region 43. In the core 105 at the initial stage of the operation cycle, the fuel assemblies 116 having relatively fewer combustible poison-containing fuel rods 114 than the fuel assemblies 116 in the core inner region 41 are arranged in the core outer peripheral region 42. The output distribution on the outside in the radial direction was made higher. The fuel assembly 116 located in the core outermost peripheral region 43 in contact with the reflector has a particularly high neutron leakage effect, a particularly low reactivity, and a small output, so that the influence on the core characteristics is small.

  The position of the fuel assembly 116 in the coordinate system shown in FIG. 4 is defined as follows. That is, the distance between the centers of adjacent fuel assemblies 116 is the unit length of the coordinate axis, and the position of each fuel assembly 116 is the center coordinate. For example, the coordinates of the fuel assembly 116 at the position E closest to the core center are (0.5, 0.5), and the distance from the origin O is 0.71. Further, the coordinates of the angle farthest from the origin O of the fuel assembly 116 at the position E is (1, 1), and the distance from the origin O is 1.41. That is, it is determined whether the fuel assembly 116 belongs to the core inner region 41 or the core outer peripheral region 42 depending on whether the center of the fuel assembly 116 is inside or outside the boundary 40.

  By the way, in order to improve the operation rate of the nuclear power plant, that is, the ratio of the operation time to the whole period and improve the economic efficiency of the nuclear power plant, the operation cycle of the boiling water reactor 100 is extended (long-term Cycle operation) is effective. As a method of extending the operation cycle of the nuclear reactor, it is conceivable to increase the loading amount of the nuclear fuel material in the unit of the fuel assembly 116 so that high reactivity can be maintained for a long time. As a method of increasing the amount of nuclear fuel material loaded in the fuel assembly 116, there is a method of increasing the ratio of fissile material in the fuel pellet, that is, increasing the enrichment.

  FIG. 10 is a diagram illustrating the relationship between the average uranium enrichment and the continuous operation period in a core composed of only one type of fuel assembly.

  As shown in FIG. 10, it is necessary to set the average uranium enrichment to 4.0 wt% or more in order to make the operation cycle of the boiling water reactor 3 years or more.

Here, the core 105 of the present embodiment configured as described above is further defined as follows. That, is composed of only the fuel assemblies 11 6 unburned, in average enrichment is the core of a boiling water reactor 100 is at least 4.0 wt% of the fissile material in the reactor core region 41, burnable poison-containing The average number of the flammable poison-containing fuel rods 114 in the fuel assembly 116 including the fuel rods 114 is defined as a, and in the core outer peripheral region 42, the fuel assembly 116 including the flammable poison-containing fuel rods 114 is the most. The average number of the flammable poison-containing fuel rods 114 in the fuel assembly 116 excluding the fuel assembly arranged on the outer periphery is defined as b.

  FIG. 6 is a diagram showing the relationship between the ratio of the defined average a and average b and the thermal margin (relative value) at the beginning of the operation cycle. In FIG. 6, the horizontal axis represents the average ratio (b / a), and the vertical axis represents the thermal margin (relative value).

  When the value of the ratio (b / a) is large, the output of the core outer peripheral region 42 cannot be sufficiently increased in the initial stage of operation, and the output of the core inner region 41 becomes relatively high. There is a possibility of imminent limits such as the limit power ratio.

  As can be seen from FIG. 6, when the ratio (b / a) is a small value of about 0.6, the thermal margin is smaller than the legally defined thermal limit for the boiling water reactor 100. As the ratio (b / a) increases, the thermal margin increases. When the ratio (b / a) value becomes 0.9, the thermal margin reaches the thermal limit, and the ratio ( As b / a) increases, the thermal margin increases. Therefore, in the core 105 of the boiling water reactor 100 in the present embodiment, the ratio (b / a) ≦ 0.9.

  FIG. 7 is a diagram showing the relationship between the defined ratio of average a and average b and the core shutdown margin (relative value) at the beginning of the operation cycle. In FIG. 7, the horizontal axis represents the average ratio (b / a), and the vertical axis represents the core stop margin (relative value).

  When the value of b / a is small, that is, when the number of combustible fuel rods included in the fuel in the core outer peripheral region 42 is small, the fuel output in the core outer peripheral region 42 at the beginning of the operation cycle becomes high. In operation, neutron leakage is large because the core is in a boiling state. However, when it reaches a cold state, it is not in a boiling state, and the effect of neutron leakage decreases rapidly. That is, the relative output of fuel in the core outer peripheral region 42 is further increased.

In particular, the relatively small core core equivalent half diameter of less 2.2m for the effect of neutron leakage is larger than the major core of the core equivalent half diameter, large difference between the operating state and the cold state. Moreover, since the core average uranium enrichment is 4.0 wt% or more and has a high reactivity, there is a possibility that the limit value of the reactor shutdown margin is imminent in a cold state. This core equivalent half diameter is relatively small, the relatively high core average uranium enrichment is the problem that the present inventor has first found.

  As can be seen from FIG. 7, when the ratio (b / a) is a small value of about 0.6, the core shutdown margin is smaller than the legal core shutdown margin limit for the boiling water reactor 100. Although the value is extremely small, the thermal margin increases as the ratio (b / a) increases. When the ratio (b / a) is 0.7, the core stop margin reaches the core stop margin limit, Further, when the ratio (b / a) increases, the value changes beyond the core stop margin limit. Therefore, in the core 105 of the boiling water reactor 100 in the present embodiment, 0.7 ≦ (b / a).

Further, in the core 105 of the present embodiment, it is further defined as follows. That, is composed of only the fuel assemblies 11 6 unburned, in average enrichment is the core of a boiling water reactor 100 is at least 4.0 wt% of the fissile material in the reactor core region 41, burnable poison-containing The average of the concentration of the combustible poison in the fuel assembly 116 including the fuel rod 114 is defined as A, and the fuel assembly 116 including the combustible poison-containing fuel rod 114 is arranged on the outermost periphery in the core outer peripheral region 42. The average of the concentration of the flammable poison in the fuel assembly 116 excluding the fuel assembly 116 is defined as B.

  FIG. 8 shows the ratio (bB / aA) of the product aB of the defined number a and the concentration average A, the product bB of the number B and the concentration average B, and the neutron multiplication factor (relative) at the end of the operation cycle. It is a figure which shows the relationship of (value).

  As can be seen from FIG. 8, when the ratio (bB / aA) is a small value of about 0.6, the neutron multiplication factor is larger than the critical value for the boiling water reactor 100, but the ratio ( As bB / aA) increases, the neutron multiplication factor decreases. When the ratio (bB / aA) becomes 0.9, the neutron multiplication factor reaches a critical value, and when the ratio (bB / aA) further increases, neutrons increase. The multiplication factor becomes even smaller. Therefore, in the core 105 of the boiling water reactor 100 according to the present embodiment, (bB / aA) ≦ 0.9 is set so that the core can be maintained critical at the end of the operation cycle.

  FIG. 9 shows the ratio (bB / aA) between the product aB of the defined number a and the concentration average A, the product bB of the number B and the concentration average B, and the core shutdown margin (relative value) from the middle to the end of the operation cycle. It is a figure which shows the relationship.

  From the middle of the operation cycle to the end of the operation cycle, the reactivity changes depending not only on the number of the flammable poison-containing fuel rods 114 in the fuel assembly 116 but also on the concentration of the flammable poison. It depends on the total number multiplied by the number of 114 and the density.

  As can be seen from FIG. 9, when the ratio (bB / aA) is a small value of about 0.5, the core shutdown margin (relative value) is a legally defined limit value for the boiling water reactor 100. However, as the ratio (bB / aA) increases, the core stop margin increases, and when the ratio (bB / aA) becomes 0.6, the core stop margin reaches a limit value. When the ratio (bB / aA) increases, the core stop margin changes at a value exceeding the limit value. Therefore, in the core 105 of the boiling water reactor 100 in the present embodiment, 0.6 ≦ (bB / aA).

  Further, in the core 105 of the present embodiment, the following definition is made so that the output difference between the fuels does not further increase and the operation limit value is not locally exceeded. That is, when the average enrichment of the fission material in the core 105 is defined as C and the maximum value of the average enrichment of the fission material in the fuel assembly 116 unit is defined as D, 0.9 ≦ C / D.

  As described above, in the present embodiment, 0.7 ≦ b / a ≦ 0.9, 0.6 ≦ (bB) / (aA) ≦ 0.9, and 0.9 ≦ C / D. To do.

  In general, in a core composed of only one type of fuel assembly having an average uranium enrichment of 4.0 wt% or more, the fuel assembly (fuel in the core inner region) located inside the core radial direction at the beginning of the operation cycle. Output increases and combustion proceeds faster. On the other hand, at the end of the operation cycle, instead of the fuel in the core inner region where the combustion progresses faster and the reactivity decreases, the output of the fuel assembly (fuel in the core outer peripheral region) located outside the core radial direction where the combustion does not progress Will increase. However, the fuel in the outer periphery region of the core has a relatively low reactivity because the reflector is close and the rate of neutron leakage is higher than the fuel in the inner region of the core. For this reason, it was found that the criticality cannot be maintained at the end of the operation cycle in which the fuel in the outer periphery region of the core bears much of the reactivity. In view of this, the inventors have devised that the power distribution in the radial direction of the core is as follows during the operation cycle so that the criticality can be maintained even at the end of the operation cycle. That is, at the initial stage of the operation cycle when the reactivity of the fuel assembly is excessive, the reactivity of the fuel in the outer peripheral region of the core is improved so that these fuels take up much of the output, and the reactivity of the fuel assembly is reduced. At the end of the operation cycle, the effect of the neutron leakage is small and the reactivity of the fuel in the core internal region that can maintain a relatively high reactivity is improved, so that these take up much of the output.

  In order to increase the power outside the core radial direction at the beginning of the operation cycle, prepare two or more types of fuel assemblies to be loaded on the core, and select the fuel rods with less flammable poisons contained in the fuel. Part of the fuel. This is because the number of combustible poison-containing fuel rods can adjust the reactivity at the beginning of the operation cycle, and the smaller the number, the higher the reactivity at the beginning of the operation cycle. In addition, the duration of the neutron absorption effect can be adjusted by the concentration of the flammable poison. do it. As a result, the flammable poison of the fuel on the outer periphery of the core disappears quickly and the combustion proceeds faster, so the reactivity of the fuel on the outer periphery of the core decreases at the end of the operation cycle, and the fuel output in the inner region of the core relatively It is for improving.

  The effect of the present embodiment configured as described above will be described.

  Extending the operating cycle of a nuclear reactor (long-term cycle operation) is effective in improving the operating rate of a nuclear power plant, i.e., the ratio of operating time over the entire period, and improving the economic efficiency of the nuclear power plant. is there. As a method of extending the operation cycle of the nuclear reactor, it is conceivable to increase the amount of nuclear fuel material in the fuel assembly unit so that high reactivity can be maintained for a long time. The following methods can be used to increase the amount of nuclear fuel material loaded. That is, for example, the amount of nuclear fuel material loaded can be increased by increasing the amount of fuel pellets per fuel assembly, but the design of the fuel assembly needs to be changed, which is not easy. In addition, for example, by increasing the proportion of fissile material in the fuel pellet, that is, increasing the enrichment, it is possible to increase the amount of nuclear fuel material loaded without changing the design. There are limitations. Further, when the enrichment of the fissile material is increased, it is difficult to satisfy the thermal limit operation limit value such as the maximum linear power density and the minimum limit power ratio and the operation limit value of the reactor shutdown margin.

  On the other hand, the present invention is a boiling water reactor core composed of only unburned fuel assemblies and having an average enrichment of the fissile material of 4.0 wt% or more, and is a circumscribed circle of the core. When the radius of R is R, the region inside the circle of radius 0.75R having the same center as the circumscribed circle is defined as the core inner region, and the outer region is defined as the core outer peripheral region. The average number of combustible poison-containing fuel rods in a fuel assembly including poisonous-containing fuel rods is defined as a, and the fuel assembly including combustible poison-containing fuel rods is arranged on the outermost periphery in the core outer peripheral region. When the average number of flammable poison-containing fuel rods in the fuel assembly excluding the fuel assembly is defined as b, it is configured to satisfy 0.7 ≦ b / a ≦ 0.9. Concentration, maximum linear power density, minimum critical power ratio While satisfying the restrictions on such reactor shutdown margin, it is possible to extend the operating cycle, thereby improving the economics of nuclear power plants.

  In the present invention, the average concentration of the flammable poison in the fuel assembly including the flammable poison-containing fuel rod is defined as A in the core inner region, and the fuel including the flammable poison-containing fuel rod in the core outer peripheral region. When the average of the concentration of the flammable poison in the fuel assembly excluding the fuel assembly arranged on the outermost periphery among the assemblies is defined as B, 0.6 ≦ (bB) / (aA) ≦ Since it is configured to satisfy 0.9, the operation cycle can be extended while satisfying the restrictions on maximum uranium enrichment, maximum linear power density, minimum limit power ratio, reactor shutdown margin, etc. The economics of the plant can be improved.

  Embodiments of the present invention will be described with reference to the drawings.

FIG. 11 is a diagram illustrating an example of the arrangement of the fuel assemblies in the core of the boiling water reactor according to the present embodiment. In FIG. 11, the arrangement of the fuel assemblies in the core is schematically shown as the arrangement in the horizontal section. In FIG. 11, two orthogonal coordinate axes (coordinate axis X and coordinate axis Y) along the direction in which the fuel assemblies 116 ( 116 a to 116 c) are arranged with the center as the origin O in the substantially circular horizontal cross section of the core. Only the second quadrant (that is, a quarter) of the coordinate system in which is set is shown.

  As shown in FIG. 11, the core 105 is composed of 400 fuel assemblies 116 and 97 control rods 115 (see FIG. 3).

  The fuel assemblies 116 are all new fuel assemblies having a burnup of 0 GWd / t. Depending on the number of fuel assemblies 116 included, there are three types of fuel assemblies 116: a multi-Gd fuel 116a, a small Gd fuel 116b, and a low-enriched fuel 116c. It is configured. The multi-Gd fuel 116a has the arrangement described with reference to FIG. 2 and FIG. 3 and includes 12 combustible poison-containing fuel rods 114, and the average concentration of the combustible poison (gadolinia) is 11%. The low Gd fuel 116b has eight burnable poison-containing fuel rods 114, and the average concentration of the burnable poison is 9%. The low-enriched fuel 116c is configured without including a combustible poison-containing fuel rod. The average uranium enrichment of the fuel assembly 116 is 4.3 wt% for both the high Gd fuel 116a and the low Gd fuel 116b, and the low enriched fuel 116c is 0.71 wt%. The low-enriched fuel 116 c forms units (cells) in 2 rows and 2 columns in the core 105. This is a cell called a control cell into which a control rod is inserted for output control during an operation cycle.

In the core in the present embodiment, the arrangement of each fuel is as shown in FIG. 11, and the fuel assembly 116 in the outermost peripheral region 43 of the core is 60 multi-Gd fuels, 0 low Gd fuels 116b, low enriched fuel. 116c is 0 body, and 60 bodies in total. Further, the fuel assemblies 116 in the core outer peripheral region 42 include 28 bodies of the multi-Gd fuel 116a, 56 bodies of the small Gd fuel 116b, and 0 body of the low enriched fuel 116c, for a total of 84 bodies. The average number b of the flammable poison-containing fuel rods 114 in the fuel assembly 116 including the flammable poison-containing fuel rods 114 in the core peripheral region 42 is 9.33. The average of the product bB of the density B and the number b is 92.0. On the other hand, the fuel assemblies 116 in the core inner region 41 include 204 bodies of the multi-Gd fuel 116a, 16 bodies of the small Gd fuel 116b, and 36 bodies of the low enriched fuel 116c, for a total of 256 bodies. The average number a of the combustible poison-containing fuel rods 114 in the fuel assembly 116 including the combustible poison-containing fuel rods 114 in the core inner region 41 is 11.71. The average of the product aA of the density A and the number a is 127.64. Accordingly, the average ratio b / a between the fuel assemblies 116 in the core inner region 41 and the fuel assemblies 116 in the core outer peripheral region 42 is 0.79, and 0.7 ≦ b / Satisfies a ≦ 0.9. Further, the average ratio (bB) / (aA) of the product of the combustible poison-containing fuel rod 114 and the combustible poison concentration of the fuel assembly 116 in the core inner region 41 and the fuel assembly 116 in the core outer peripheral region 42 is 0. . 721 and satisfies 0.6 ≦ (bB) / (aA) ≦ 0.9. Further, the average uranium enrichment in the core 105 is 4.01 wt%, which is 4.0 wt% or more. Further, the ratio between the average enrichment of the core 105 and the highest average enrichment of the fuel assembly is 0.92, which is 0.9 or more.

  As described above, in this embodiment, the ratio of the small Gd fuel 116b in the core outer peripheral region 42 is increased, and the ratio of the multi Gd fuel 116a in the core inner region 41 is increased, so that the radial output is obtained at the initial stage of the operation cycle. Since the distribution is large outside the core and the radial power distribution at the end of the operation cycle is large inside the core, the criticality can be maintained during the operation cycle. The average ratio b / a between the fuel assemblies 116 in the core inner region 41 and the fuel assemblies 114 in the fuel assembly in the core outer peripheral region 42 is in the range of 0.7 ≦ b / a ≦ 0.9. In the operation cycle, the ratio (bB) / (aA) of the average of the burnable poison-containing fuel rods 114 and the concentration is in the range of 0.6 ≦ (bB) / (aA) ≦ 0.9. The criticality can be maintained and the operation limit values such as thermal margin and furnace shutdown margin can be satisfied. That is, in this example, when the restriction that the maximum uranium enrichment is 5 wt% or less is imposed, the criticality is maintained during the operation cycle, and the operation limit value related to the thermal margin such as the maximum linear power density and the minimum critical power ratio and In addition, long-term cycle operation with an operation period of 3 years or more that satisfies the operation limit value of the furnace stop margin can be realized.

  In this embodiment, a control cell for control rod operation can be set.

  Therefore, in this example, when the restriction that the maximum uranium enrichment is 5 wt% or less is imposed, the criticality is maintained during the operation cycle, and the operation limit value relating to the thermal margin such as the maximum linear power density and the minimum critical power ratio, and In addition, a long-term cycle operation with an operation period of 3 years or more that satisfies the operation limit value of the furnace stop margin can be realized.

  In the embodiment and the actual examples 1 and 2, the case where the fuel rod array of the fuel assembly 116 is 10 rows and 10 columns has been described. However, the fuel assembly of 9 rows and 9 columns and the fuel assembly of 8 rows and 8 columns are described. The present invention can be applied to a fuel assembly of 11 rows and 11 columns, and the same effect can be obtained.

  Further, although the fuel assembly having a plurality of partial length fuel rods has been described, the same effect can be obtained for a fuel assembly that does not include partial length fuel rods.

  Further, the fuel assembly in which two water rods are arranged has been described, but the same effect can be obtained for a fuel assembly having one water rod and a fuel assembly in which a water rod having a square cross section is arranged. .

  Embodiments of the present invention will be described with reference to the drawings.

FIG. 12 is a diagram showing an example of the arrangement of the fuel assemblies in the core of the boiling water reactor according to this example. In FIG. 12, the arrangement of the fuel assemblies in the core is schematically shown as the arrangement in the horizontal section. In FIG. 12, two orthogonal coordinate axes (coordinate axis X, coordinate axis Y) along the direction in which the fuel assemblies 116 (116a, 116b) are arranged with the center being the origin O in the substantially circular horizontal cross section of the core. Only the second quadrant (that is, a quarter) of the coordinate system in which is set is shown.

  As shown in FIG. 12, the core 105 is composed of 400 fuel assemblies 116 and 97 control rods 115 (see FIG. 3).

  Each fuel assembly 116 is a new fuel assembly having a burnup of 0 GWd / t. Depending on the number of combustible poison-containing fuel rods 114 included, there are two types of fuel assemblies 116: a multi-Gd fuel 116a and a small Gd fuel 116b. ing. The multi-Gd fuel 116a has the arrangement described with reference to FIGS. 2 and 3 and includes twelve burnable poison-containing fuel rods 114, and the average concentration of the burnable poison (gadolinia) is 11%. The low Gd fuel 116b has eight burnable poison-containing fuel rods 114, and the average concentration of the burnable poison is 9%. The average uranium enrichment of the fuel assembly 116 is 4.3 wt% for both the high Gd fuel 116a and the low Gd fuel 116b. Therefore, the average uranium enrichment of the fuel assembly 116 loaded in the core 105 is 4.0 wt%. % Or more.

  In the present embodiment, all the fuel assemblies 116 included in the core 105 of the boiling water reactor 100 have the burnable poison-containing fuel rods 114 in order to suppress high reactivity in the initial operation. Thereby, a high core average enrichment can be realized, and the continuous operation period can be further extended.

  In the core 105 in this embodiment, the arrangement of each fuel is as shown in FIG. 12, and the fuel assemblies 116 in the outermost peripheral region 43 of the core are 60 multi-Gd fuels 116a and 0 low Gd fuels 116b. A total of 60 bodies. In addition, the fuel assemblies 116 in the core outer peripheral region 42 include 28 multi-Gd fuels 116a and 56 small Gd fuels 116b, for a total of 84. The average number b of the flammable poison-containing fuel rods 114 in the fuel assembly 116 in the core outer peripheral region 42 is 9.33. The average of the product bB of the density B and the number b is 92.0. On the other hand, the fuel assemblies 116 in the core inner region 41 include 240 multi-Gd fuels 116a and 16 small Gd fuels 116b, for a total of 256. The average number a of the burnable poison-containing fuel rods 114 in the fuel assembly 116 in the core inner region 41 is 11.75. The average of the product aA of the density A and the number a is 128.25. Accordingly, the average ratio b / a between the fuel assemblies 116 in the core inner region 41 and the fuel assemblies 116 in the core outer peripheral region 42 is 0.79, and 0.7 ≦ b / Satisfies a ≦ 0.9. The average ratio (bB) / (aA) of the product of the combustible poison-containing fuel rod 114 and the combustible poison concentration of the fuel assembly 116 in the core inner region 41 and the fuel assembly 116 in the core outer peripheral region 42 is 0. 717, and satisfies 0.6 ≦ (bB) / (aA) ≦ 0.9.

  As described above, in this embodiment, the ratio of the small Gd fuel 116b in the core outer peripheral region 42 is increased, and the ratio of the multi Gd fuel 116a in the core inner region 41 is increased, so that the radial output is obtained at the initial stage of the operation cycle. Since the distribution is large outside the core and the radial power distribution at the end of the operation cycle is large inside the core, the criticality can be maintained during the operation cycle. The average ratio b / a between the fuel assemblies 116 in the core inner region 41 and the fuel assemblies 114 in the fuel assembly in the core outer peripheral region 42 is in the range of 0.7 ≦ b / a ≦ 0.9. In the operation cycle, the ratio (bB) / (aA) of the average of the burnable poison-containing fuel rods 114 and the concentration is in the range of 0.6 ≦ (bB) / (aA) ≦ 0.9. The criticality can be maintained and the operation limit values such as thermal margin and furnace shutdown margin can be satisfied. That is, in this example, when the restriction that the maximum uranium enrichment is 5 wt% or less is imposed, the criticality is maintained during the operation cycle, and the operation limit value related to the thermal margin such as the maximum linear power density and the minimum critical power ratio and In addition, long-term cycle operation with an operation period of 3 years or more that satisfies the operation limit value of the furnace stop margin can be realized.

40 Boundary 41 Core inner region 42 Core outer peripheral region 43 Core outermost peripheral region 100 Boiling water reactor 101 Reactor pressure vessel 102 Water supply piping 103 Shroud 104 Control rod drive mechanism 105 Core 106 Chimney 107 Simplified steam dryer 108 Main steam piping 109 Downcomer 110 Channel box 111 Fuel rod 112 Partial length fuel rod 113 Water rod 114 Combustible poison-containing fuel rod 115 Control rod 116 Fuel assembly 116a Multiple Gd fuel 116b Low Gd fuel 116c Low enriched fuel 117 Spacer 118 Lower tie plate 119 Upper type rate

Claims (3)

A core of a boiling water reactor that is composed only of unburned fuel assemblies and has an average enrichment of fissile material of 4.0 wt% or more,
When the radius of the circumscribed circle of the core is R, a region inside a circle having a radius of 0.75R having the same center as the circumscribed circle is defined as a core inner region, and an outer region is defined as a core outer peripheral region. The fuel assembly whose center is inside the circle having the radius of 0.75R belongs to the core inner region, and the fuel assembly outside the core is defined to belong to the core outer peripheral region,
In the core inner region, a is defined as the average number of flammable poison-containing fuel rods in the fuel assembly including the flammable poison-containing fuel rods,
The average number of flammable poison-containing fuel rods in the fuel assembly excluding the fuel assemblies arranged on the outermost periphery among the fuel assemblies including the flammable poison-containing fuel rods in the core outer peripheral region. b and
In the core inner region, A is defined as the average concentration of flammable poisons of the flammable poison-containing fuel rods in the fuel assembly including the flammable poison-containing fuel rods ;
In the core periphery region, among the fuel assemblies containing the burnable poison-containing fuel rods, burnable poison burnable poison-containing fuel rods in the fuel assembly excluding the fuel assemblies disposed in the outermost periphery When the average density is defined as B,
A core of a boiling water reactor characterized by satisfying 0.6 ≦ (bB) / (aA) ≦ 0.9. In the core of the boiling water reactor according to claim 1,
The average enrichment of the fissile material in the core is C,
When the maximum value of the average enrichment of the fissile material in the fuel assembly unit is defined as D,
A core of a boiling water reactor characterized by satisfying 0.9 ≦ C / D. In the core of the boiling water reactor according to claim 1,
A core of a boiling water reactor, wherein all the fuel assemblies included in the core have the burnable poison-containing fuel rods.

Images