JP2001215290A - Light water reactor core and fuel assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light reactor water core and fuel assembly having economical efficiency and safety of the same degree as a BWR in operation at present, namely, directing Pu multi-recycle having a minimally changed reactor structure, maintaining a negative void coefficient, and having a breeding ratio near 1.0 or over 1.0. SOLUTION: This light water reactor core has an effective water-to-fuel volume ratio of 0.1-0.6, by combining together dense lattice fuel assembly comprising a fuel rod obtained by adding Pu to depleted uranium, natural uranium, or low enriched uranium, a coolant with a high void fraction of 45%-70%, and a large-sized control rod comprising one or more absorbing rods having a larger sectional area than the sectional area of a fuel rod unit lattice cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light water reactor core and a fuel assembly constituting the core, and more particularly to a boiling water reactor.
(BWR, Boiling Water Reactor) has the same economy and safety as the currently operating BWR, that is, minimizes changes in the furnace structure and maintains the negative void coefficient while maintaining a growth ratio of 1. The present invention relates to a light water reactor core and a fuel assembly for plutonium (Pu) multi-recycling, which is near zero or slightly more than 1.0.

[0002]

2. Description of the Related Art In a nuclear reactor, a nuclear fission reaction causes the depletion of fissile materials such as uranium-235 and plutonium-239, as well as uranium-238 and plutonium-2.
Conversion of fuel parent material, such as 40, to fissile material has occurred. The ratio of the amount of fissile material contained in the fuel taken out of the core to the amount of fissile material contained in the fuel loaded into the core is called the breeding ratio. In a conventional light water cooled reactor, the breeding ratio is about 0.5. It is. As a method of effectively utilizing uranium resources, it is considered to increase the breeding ratio.

[0003] JP-A-55-10591 and N.
uclear Technology, Vol. 59, pp. 212-227 shows that in a pressurized water reactor, the fuel rods can be densely arranged in a triangular lattice and the water to fuel volume ratio can be reduced to improve the breeding ratio. . However, the growth ratio is at most about 0.9, and it is necessary to replenish fissile material in order to continue operation without decreasing the output. In order to further increase the breeding ratio, it is conceivable to narrow the fuel rod gap and further reduce the water-to-fuel volume ratio.However, there are limitations in the production of fuel assemblies and securing thermal margins. It is difficult.

On the other hand, Japanese Patent Application Laid-Open No. 1-227993 discloses a method for effectively reducing the water-to-fuel volume ratio by utilizing a steam void generated in a reactor core, which is a feature of a boiling water reactor. Have been. However, in this conventional example, the plutonium multiplication ratio (the ratio of the amount of fissile plutonium contained in the fuel taken out of the core to the amount of fissile plutonium contained in the fuel loaded into the core; the proliferation ratio with respect to the fissile plutonium) is 1 Although it is shown to be near, the growth ratio (when natural uranium is enriched with plutonium, the value becomes about 4 to 5% smaller than the plutonium multiplication ratio)
Is not shown to be close to one or more than one. When the plutonium multiplication ratio is close to 1, plutonium must be enriched in natural uranium in order to continue the operation without decreasing the output, and the entire uranium resource cannot be used up. In the present invention, the growth ratio of around 1 is 0.98.
This means the above.

Further, Japanese Patent Application Laid-Open No. Hei 8-21890 discloses a reactor containing uranium containing at least one of depleted uranium, natural uranium, depleted uranium and low-enriched uranium and containing Pu or a fuel enriched with Pu and actinide nuclides. In the figure, a core having a breeding ratio of around 1.0 or 1.0 or more and a negative void coefficient is shown. However, this conventional example was not aimed at further improving the manufacturability and economy of the control rod.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reactor core and a fuel assembly which maintain the power generation cost, thermal margin and safety at the same level as those of a currently operating light water reactor and contribute to a long-term stable supply of energy. It is to be.

[0007]

According to the present invention which achieves the above objects, according to the present invention, depleted uranium, natural uranium, depleted uranium,
A uranium containing at least one of low-enriched uranium (hereinafter, referred to as depleted uranium) has a breeding ratio of around 1.0 in a core having a fuel enriched with Pu or Pu and an actinoid nuclide (hereinafter, referred to as Pu). Or 1.0 or more,
A core is provided, wherein the core has a negative void coefficient. ADVANTAGE OF THE INVENTION According to this invention, in order to contribute to the long-term stable supply of energy, it can implement | achieve a breeding ratio of 1.0 with the fuel which enriched the depleted uranium with Pu (henceforth 1st effect). According to the present invention, a fuel obtained by adding Pu to depleted uranium or the like achieves a breeding ratio of around 1.0 or 1.0 or more, so that the depleted uranium or the like is burned like Pu as a catalyst And contribute to long-term stable supply of energy.

In a first preferred embodiment, a fuel assembly having a fuel enriched with Pu or the like in uranium containing at least one of depleted uranium or the like has a fuel cell growth ratio of around 1.0 or less. 1.0 or more. First
According to the embodiment, the first effect can be obtained. First
According to the embodiment, a fuel obtained by adding Pu to depleted uranium or the like achieves a growth ratio of around 1.0 or 1.0 or more,
By using Pu as a catalyst, depleted uranium and the like can be burned, which can contribute to a long-term stable supply of energy.

In a preferred second embodiment, the light water reactor core comprises a fuel assembly in which fuel rods are arranged in a triangular lattice, and one or more fuel assemblies having a cross-sectional area larger than the cross-sectional area of the fuel rod unit lattice cell. A control rod having an absorption rod and being inserted into the fuel assembly. According to the second embodiment, the first effect can be obtained, and the water-to-fuel volume ratio is reduced to contribute to a long-term stable supply of energy. 1.
0 can be realized (hereinafter, referred to as a second effect). Also, the second
In the embodiment, by increasing the diameter of the control rod, the mechanical strength of the control rod is increased, and it is possible to suppress bending and buckling when the control rod is inserted and withdrawn. Further, by adopting the large-diameter control rods, the number of absorption rods per fuel assembly can be reduced, the control rods can be easily manufactured, and the manufacturing cost can be reduced.

In a third preferred embodiment, the light water reactor core is constituted by a fuel assembly having a water exclusion region made of a substance having a smaller speed reducing ability than light water on the surface of a guide tube into which a large diameter control rod is inserted. It is in. This third
According to the embodiment, the second effect can be obtained.

In a fourth preferred embodiment, the fuel assembly is a dense fuel assembly in which fuel rods are arranged in a triangular lattice, and the gap between the fuel rods is 0.7 to 2.0 mm. There is to be. A light water reactor core may be configured using this fuel assembly. According to the fourth embodiment, the second effect can be obtained.

In a fifth preferred embodiment, the effective water-to-fuel volume ratio of the fuel assembly is between 0.1 and 0.6. A light water reactor core may be configured using this fuel assembly. According to the fifth embodiment, the second effect can be obtained. According to the fifth embodiment, a dense fuel assembly made of a fuel obtained by adding Pu to depleted uranium or the like and a large-diameter control rod are combined so that the effective water-to-fuel volume ratio is 0.1 to 0.6.
As a result, a growth ratio of around 1.0 or 1.0 or more can be achieved, which can contribute to a long-term stable supply of energy.

Further, in a preferred sixth embodiment, the light water reactor core has an average enrichment of fissionable Pu of 6 in the core excluding the core outer peripheral portion and the upper and lower end blanket portions.
-20% by weight. According to the sixth embodiment, the second effect can be obtained.

[0014] In a preferred seventh embodiment, the average fissile Pu enrichment in the fuel assembly excluding the blanket portions at the upper and lower ends is 6 to 20 wt%. According to the seventh embodiment, the second effect can be obtained.

A preferred eighth embodiment is that the boiling water reactor core has an average void ratio of 45 to 70% when the core is operated at 50% or more of the rated output. According to the eighth embodiment, the second effect can be obtained. According to the eighth embodiment, the combination of the dense fuel assembly and the high void fraction coolant increases the proportion of neutrons in the resonance energy region, increases the Doppler effect, and reduces the absolute value of the negative void coefficient. Therefore, safety such as an output rise event, a pressurization event, and a coolant void ratio decrease event is improved.

In a ninth preferred embodiment, in the light water reactor core, all the large diameter control rods connected to one control rod drive mechanism are inserted into one fuel assembly, and the large diameter control rod is Is inserted into all the fuel assemblies loaded in the area except the outermost periphery of the core. According to the ninth embodiment, the second effect can be obtained without impairing the furnace stop margin.

Further, in a preferred tenth embodiment, in the light water reactor core, all the large diameter control rods connected to one control rod drive mechanism are inserted into one hexagonal or square fuel assembly, and The diameter control rod is to be inserted into all the fuel assemblies loaded in the region except the outermost periphery of the core. According to the ninth embodiment, the second effect can be obtained without impairing the furnace stop margin.

In a preferred eleventh embodiment, in a light water reactor core, a plurality of large diameter control rods connected to one control rod drive mechanism are inserted into three hexagonal fuel assemblies,
In addition, the large-diameter control rod is to be inserted into all the fuel assemblies loaded in the region except the outermost periphery of the core. According to the eleventh embodiment, the second effect can be obtained without impairing the furnace stop margin.

In a twelfth preferred embodiment, a plurality of large diameter control rods connected to one control rod drive mechanism are inserted into four square fuel assemblies in a light water reactor core,
In addition, the large-diameter control rod is to be inserted into all the fuel assemblies loaded in the region except the outermost periphery of the core. According to the twelfth embodiment, the second effect can be obtained without impairing the furnace stop margin.

In a preferred thirteenth embodiment, the light water reactor core is made of a material having a smaller moderating power than light water, such as carbon, deuterium, beryllium, beryllium, Zr alloy, stainless steel, etc., in order to remove the moderator at the tip of the control rod. Is provided with a control rod in which a follower portion is provided. According to the thirteenth embodiment, the second effect can be obtained.

A fourteenth preferred embodiment is characterized in that, in the fuel assembly, a fuel rod disposed in a region adjacent to the guide tube into which the large-diameter control rod is inserted, and a region farthest from the center of the fuel assembly. The average value of the fissionable plutonium enrichment of the fuel rods arranged in the other region is smaller than the average value of the fissionable plutonium enrichment of the fuel rods arranged in other regions. According to the fourteenth embodiment, the second effect can be obtained. According to the fourteenth embodiment,
Output peaking within the fuel assembly is reduced and thermal margin is increased.

In a preferred fifteenth embodiment, the light water reactor core has an average power density of 100 kW / l to 300 kW excluding the outer peripheral portion of the core and blanket portions at the upper and lower ends.
kW / l. According to the fifteenth embodiment, to contribute to long-term stable supply of energy,
To reduce the required Pu inventory per unit output, operate as many reactors for power generation as possible with a certain amount of Pu (hereinafter referred to as the third effect), and reduce the power generation cost to the same level as the current LWR, The same power and burnup can be achieved with the same material and the same pressure vessel size as the operating furnace with the same thermal margin (hereinafter referred to as the fourth effect),
Furthermore, in order to make the safety comparable to current LWRs, a negative void coefficient can be realized by increasing neutron leakage in the height of the core and swinging the power distribution in the height of the core when the power is increased (hereinafter, referred to as , The fifth effect).

According to the fifteenth embodiment, the operating conditions such as the diameter of the BWR and the pressure vessel, the output, and the like, and the materials used are substantially the same, so that the performance is greatly improved. Power generation cost can be suppressed to the same level as the current BWR. According to the fifteenth embodiment, by increasing the power density of the core to 100 to 300 kW / l, the amount of Pu inventories per unit power is reduced,
The capacity of the power generation facility of the present invention that can be operated for a constant Pu is increased, which can contribute to long-term stable supply of energy.

Further, in a preferred sixteenth embodiment, the light water reactor core has a portion in which the average fissionable Pu enrichment of the fuel assembly horizontal section is 6 wt% or more in the height direction excluding the blanket portions at the upper and lower ends of the core. Is between 40 cm and 140 cm. According to the sixteenth embodiment, the third, fourth, and fifth effects can be obtained. Sixteenth
According to the embodiment, the same output is produced by a pressure vessel having a diameter similar to that of the ABWR currently under construction, and the height of the core is set to 40-1.
By making the fuel assembly as short as 40 cm, the Pu inventory can be reduced and Pu generated from spent fuel in light water reactors under limited natural uranium reserves in the world
Therefore, many furnaces of the present invention can be operated, which can contribute to a long-term stable supply of energy.

Further, according to the sixteenth embodiment, the short fuel assembly can realize a core having a negative void coefficient by utilizing neutron leakage in the vertical direction of the core and swinging the power distribution in the vertical direction of the core. Therefore, it can have the same level of safety as the current fuel-burning type light water reactor. That is, in the height direction of the fuel assembly, the portion where the average enrichment of fissile Pu in the horizontal section is 6 wt% or more is 40 to 140.
cm, the amount of Pu inventory per unit output is reduced, the capacity of the power generation equipment of the present invention that can be operated for a constant Pu is increased, which contributes to the long-term stable supply of energy and the amount of generated steam. The neutron leakage effect in the height direction of the core when the value increases increases the negative void coefficient and contributes to safety.

In a preferred seventeenth embodiment, the fuel assembly has an average fissile Pu enrichment of 6 wt% or more in a horizontal section in the height direction of the fuel assembly excluding the upper and lower blanket portions. Some parts are between 40cm and 140cm. According to the seventeenth embodiment, the third, fourth, and fifth effects can be obtained. Seventeenth
According to the embodiment, the same output is produced by a pressure vessel having a diameter similar to that of the ABWR currently under construction, and the height of the core is set to 40-1.
By making the fuel assembly as short as 40 cm, the Pu inventory can be reduced and Pu generated from spent fuel in light water reactors under limited natural uranium reserves in the world
Therefore, many furnaces of the present invention can be operated, which can contribute to a long-term stable supply of energy.

According to the seventeenth embodiment, a short fuel assembly can realize a core having a negative void coefficient by increasing the neutron leakage in the vertical direction of the core and utilizing the swing of the power distribution in the vertical direction of the core. Therefore, it can have the same level of safety as the current fuel-burning type light water reactor. That is, in the height direction of the fuel assembly, the portion where the average enrichment of fissile Pu in the horizontal section is 6 wt% or more is 40 to 140.
cm, the amount of Pu inventory per unit output is reduced, the capacity of the power generation equipment of the present invention that can be operated for a constant Pu is increased, which contributes to the long-term stable supply of energy and the amount of generated steam. The neutron leakage effect in the height direction of the core when the value increases increases the negative void coefficient and contributes to safety.

In a preferred eighteenth embodiment, the light water reactor core is divided into two equal areas in the radial direction except for the outermost circumference of the core, and the average value of the number of fuel assembly core stay cycles in the core outer region is reduced. In other words, the fuel assembly is loaded so as to be smaller than that in the core inner region. According to the eighteenth embodiment, the fourth effect can be obtained. According to the eighteenth embodiment, the operating conditions such as the diameter of the currently operating BWR and the pressure vessel, the operating conditions such as the output, and the materials used are almost the same. It can be reduced to the same level as the current BWR.

A nineteenth preferred embodiment is such that the average value of the orifice pressure loss coefficients of the outermost periphery of the core and the fuel assembly adjacent thereto is larger than the average value of the orifice pressure loss coefficients of the other regions. According to the nineteenth embodiment, the fourth effect can be obtained. According to the nineteenth embodiment, the operating conditions such as the diameter and the output of the BWR and the pressure vessel that are currently operating and the materials used are substantially the same,
Despite the significant improvement in performance, power generation costs can be reduced to the same level as current BWRs.

Further, in a preferred twentieth embodiment, the fuel assembly has a fissile Pu enrichment having a lower half average value lower than the average value of the upper half portion, except for the blanket portions at the upper and lower ends. It is in. According to the twentieth embodiment, the fifth effect can be obtained. According to the twentieth embodiment, a core having a negative void coefficient can be realized by increasing the neutron leakage in the vertical direction of the core and utilizing the swing in the vertical direction of the core in the power distribution by the upper and lower two-zone fuel assembly, and It can have the same level of safety as the current type of light water reactor. That is, from the average value of the fissile Pu enrichment in the upper half of the fuel assembly using the blanket portions at the upper and lower ends,
The lower mean value in the lower part flattens the power distribution in the core height direction, increasing the thermal margin, and when the amount of steam generated increases, the swing of the power distribution in the core height direction works. , The negative void reactivity coefficient increases, which can contribute to safety.

Further, in a preferred twenty-first embodiment, the fuel assembly has a fissionable Pu enrichment of 6 wt% in the height direction of the fuel assembly excluding the upper and lower blanket portions.
The above portion is located above and below, and the fissionable Pu enrichment in the region near the center therebetween is 6 wt% or less. According to the twenty-first embodiment, the fifth effect can be obtained.
According to the twenty-first embodiment, a core having a negative void coefficient can be realized by utilizing an increase in neutron leakage in the vertical direction of the core, a swing in the vertical direction of the core in the power distribution, and the like, by the non-homogeneous fuel assembly in the axial direction. It can have the same level of safety as current burnable water reactors. That is, in the height direction excluding the blanket portions at the upper and lower ends of the fuel assembly, there are portions above and below the fissile Pu enrichment of 6 wt% or more, and the fissile Pu enrichment in the region near the center between the portions is 6 wt%. % Or less, the power of the furnace increases, and the negative void coefficient due to the power distribution swing in the vertical direction of the core when the amount of steam in the core increases increases safety. Further, due to the neutron absorption effect near the center in the axial direction of the core, the Pu inventory that can be loaded into the core increases, and the function as a Pu storage furnace improves.
Further, the core height is relatively high, and the overall length of the fuel rod is also long, so that the thermal margin for the maximum linear power density is also large.

In a preferred twenty-second embodiment, the boiling water LWR core has a steam weight ratio of 20 wt% at the outlet of the coolant core when the core is operated at 50% or more of the rated output.
% To 40 wt%. According to the twenty-second embodiment, in order to ensure the same level of safety as a current light water reactor, the distillation function by boiling can be maintained, and confinement of the activated material present in the reactor in the pressure vessel can be achieved (hereinafter, referred to as the following).
The sixth effect). According to the twenty-second embodiment, since the steam weight ratio at the core outlet of the coolant is suppressed to 40 wt% or less, radioactive substances such as corrosion products accumulated in the furnace are maintained in a distillation function by boiling by maintaining the function. The reactor can be confined in the furnace, the same level of radioactivity on the turbine side as that of the BWR currently in operation can be maintained, and the radioactivity level can be significantly reduced as compared with the steam-cooled fast reactor that is the concept of the conventional breeder reactor.

A twenty-third preferred embodiment is that the fuel assembly simultaneously loads Pu and uranium extracted from spent fuel. A light water reactor core may be configured using this fuel assembly. According to the twenty-third embodiment, in order to cope with nuclear non-proliferation, the single extraction of Pu is abolished,
Pu and U can be integrally recycled (hereinafter referred to as a seventh effect). According to the twenty-third embodiment, by simultaneously recycling Pu and uranium, the effect of preventing nuclear non-proliferation is increased.

A twenty-fourth preferred embodiment is that the fuel assembly simultaneously loads Pu extracted from spent fuel, uranium, and an actinoid. A light water reactor core may be configured using this fuel assembly. According to the twenty-fourth embodiment, actinoid nuclides can be kept in a furnace together with uranium and Pu and recycled so as not to leave long-lived radioactive waste in posterity (hereinafter, referred to as an eighth effect). According to the twenty-fourth embodiment, by simultaneously recycling Pu, uranium and actinoid nuclides, the amount of actinide nuclides generated and annihilated is balanced to reduce the amount of increase to zero, and the radioactive waste is particularly problematic. Long-lived actinoid nuclides can be confined only in nuclear reactors, reprocessing facilities, and fuel manufacturing facilities, improving environmental characteristics.

According to the study by the present inventors, the following has been found.

The world's natural uranium resource is estimated to be around 15 million tonnes, which corresponds to the capacity of 1,000 existing light water reactors with an electric output of 1 MW for about 100 years. As a result, less than 15 million tons of depleted uranium and 15,000 tons of fissile Pu remain. Therefore, a fuel in which Pu is enriched in depleted uranium has an electric output of 10
A fissionable Pu with a breeding ratio of 1.0 ton with an inventory of 10 tons per 100,000 kW including inside and outside the reactor (RB)
WR, Resource-Renewable Boiling Water Reactor)
Using Pu as a catalyst, it is possible to continue fission with depleted uranium, and uranium generates about 1 MWD of heat energy per gram, so that 1500 RBWRs can be operated for 10,000 years. Uranium resources can be used up. For this reason, the above-mentioned first effect, that is, long-term stable supply becomes possible.

The second effect described above is produced by the following operation. According to the study of the present inventors, regarding the relationship between the breeding ratio and the effective water to fuel volume ratio in the light water reactor core,
The following has been found: The effective water-to-fuel volume ratio (Vm / Vf) eff is a geometrical water-to-fuel volume ratio (Vm / Vf) in consideration of the occurrence of steam voids in the core.
It is an extension of geo (volume ratio of water to fuel without vapor voids). Assuming that the decrease rate of the hydrogen density due to the generation of the steam void is F, the two have the following relationship.

[0038]

(Vm / Vf) eff = F (Vm / Vf) geo (Equation 1) Further, F has the following relationship with the core average steam void fraction V (%).

F = (100−V) / 100 + fV / 100 where f is the ratio of the saturated vapor density to the saturated water density.

In general, f is a small value of about 1/20, and F can be approximated as follows.

F ≒ (100−V) / 100 FIG. 2 shows the conversion ratio defined by the effective water to fuel volume ratio and the neutron balance and the relationship between the three factors constituting the conversion ratio.

[0042]

Conversion ratio = α (1 + β) − (1 + γ) (Equation 2) where α: the number of new neutrons generated when neutrons are absorbed by fissile material and one fissile material is extinguished β: Additional portion due to fission in the fast energy region of the fuel parent material. Γ: Ratio of waste capture of neutrons (including neutron leakage) to neutron absorption by fissile material. Currently operating light water reactors have an effective water to fuel volume ratio of , About 2.0 and the growth ratio is about 0.5. In order to achieve a growth ratio of around 1, it is necessary to make the above conversion ratio close to 1. According to the study by the inventors of the present invention, fissile Pu within the range described below is used.
By increasing the enrichment and increasing the neutron leakage to the blanket, it was found that a multiplication ratio of about 1 can be realized at a conversion ratio of 0.85 or more. The effective water-to-fuel volume ratio for this is less than 0.6. On the other hand, in order to make the effective water-to-fuel volume ratio 0.1 or less, the average steam void fraction of the core must be set to a value exceeding 70%. Cannot be maintained.

The effective water to fuel volume ratio of 0.1 to 0.6 is:
This is achieved by arranging the fuel rods densely, utilizing a steam void generated in the reactor core, or inserting a follower at the control rod insertion position to eliminate the moderator when the control rod is not inserted. Alternatively, it is realized by combining the above three. FIG. 3 shows an example of the relationship between the fuel rod gap and the geometrical water to fuel volume ratio. In FIG. 3, the fuel rod diameter is in the range of about 9.5 to 12.3 mm currently used in light water reactors, and the fuel rod grid has an equilateral triangle. When the fuel rod gap is made 2 mm or less, the (Vm / Vf) geo of the fuel rod lattice becomes about 0.9 or less. In the case of a fuel assembly in which the fuel rods are densely arranged in a regular triangular lattice, considering the gap region between the fuel assemblies and the control rod insertion region, etc.
The value of m / Vf) geo is greater than the value of (Vm / Vf) geo of the fuel rod lattice by 0.1.
The value is larger than 1 by 0.2. Therefore, in order to realize an effective water-to-fuel volume ratio of 0.6 or less under this geometrical water-to-fuel volume ratio, the core average steam void ratio is set to 45% or more from Equation (1). According to the relationship diagram shown in FIG. 6, the steam weight ratio at the core outlet needs to be 20 wt% or more.
On the other hand, the fuel rod gap is 0.7 (minimum value of the fuel rod gap from the viewpoint of manufacturing a fuel assembly and securing a thermal margin) to 1.0 mm.
Range (1.0mm if fuel rod diameter is larger than 9.5mm)
Above), the steam void ratio is 0%,
(Vm / Vf) geo can be reduced to about 0.6 or less.

FIG. 4 shows the relationship between the average fissile Pu enrichment of the fuel assembly and the growth ratio. In order to maintain the core in a critical state throughout the operation, the fissile Pu enrichment is
It is necessary that the content be not less than wt%. On the other hand, the growth ratio
Although decreasing with the fissile Pu enrichment, as described above, by increasing the neutron leakage to the blanket by utilizing the increase in excess reactivity, it is possible to achieve a growth ratio of about 1 up to 20 wt% (wt%). I understood.

At this time, as means for controlling the reactivity of the furnace, a large-diameter control rod composed of an absorption rod having a cross-sectional area larger than the cross-sectional area of the fuel rod unit lattice cell is inserted into the fuel assembly. A method is conceivable. With the above combination, a core having a breeding ratio of 1.0 can be realized.

Further, the following operations are performed by the following operations.
5 effects are produced. According to the study by the present inventors, the output of the fuel assembly per unit horizontal cross section of the core is set to be approximately the same as that of the current boiling water light water reactor, thereby ensuring a thermal margin and the height of the fuel assembly. (Effective core length: length of the region where the average cross-section average fissile Pu enrichment is 6 wt% or more). Effective water to fuel volume ratio of 0.6
As a result, the number of fuel rods per unit horizontal cross section of the core becomes three to four times that of the current boiling water reactor. Therefore, the height (effective core length) of the fuel assembly having the same average linear power density is about 1/3 to 1/4 of that of the current boiling water reactor.

Further, as compared with the current boiling water type light water reactor, the moderator has a structure in which the moderator is uniformly dispersed, so that the local output peaking coefficient of the fuel rod is reduced by about 30% (if necessary, by employing the enrichment distribution). The above can be reduced. Further, the output peaking coefficient can be reduced by about 40% or more, in combination with the small change in the combustion reactivity and the change in the void reactivity, and the other means described below. Therefore, the height (effective core length) of the fuel assembly at which the average linear power density is equal to or more than 40 cm or more, which is about 1/10 of the current boiling water reactor.

On the other hand, by shortening the effective core length and increasing the neutron leakage in the axial direction, the effect of reducing the void coefficient can be utilized. According to the study by the present inventors, the effective core length is 1
It has been found that a negative void coefficient can be realized when the diameter is set to 40 cm or less, in combination with other means described below. Although the power generation ratio in the blanket portion increases due to the shortening, the average power density in the region excluding the blanket portion becomes about 100 to 300 kW / l because the effective core length is reduced.

As a result, the RBWR having the same output can be accommodated in a pressure vessel having substantially the same diameter as that of the current reactor, so that the power generation cost can be maintained at the same level as that of the current light water reactor, and the safety can be maintained at the same level as the current light water reactor. Level can be maintained. In addition, the Pu inventory can be reduced, so that a large number of power generating furnaces can be operated with a constant Pu amount, and a stable energy supply can be realized.

The above-described fifth effect is produced by the following operation. According to the study by the present inventors, by making the enrichment of fissile Pu in the upper part of the core higher than that in the lower part of the core, the axial power distribution of the core can be flattened, and as a result, the Pu inventory is reduced. Can be done. Further, when the power is increased or when the core coolant flow rate is decreased, the steam void fraction in the core is increased. At this time, as shown in FIG. 5, the enrichment of the fissionable Pu is relatively low. In addition, the power distribution swings below the core where the neutron importance is small, and the reactivity of the core can be reduced (with a negative void coefficient).

The second effect described above is produced by the following operation. According to the study of the present inventors, a core configuration in which fuel rods are densely arranged in a regular triangular lattice can be realized by inserting a large-diameter control rod into the fuel assembly. Further, according to the study of the present inventors, when a large-diameter control rod and a hexagonal fuel assembly are combined, all the large-diameter control rods connected to one control rod drive mechanism are connected to one hexagonal fuel rod. A core configuration that is inserted into a rectangular fuel assembly, and a large diameter control rod is inserted into all hexagonal fuel assemblies loaded in the area excluding the outermost periphery of the core, and connected to one control rod drive mechanism A core configuration is possible in which a plurality of large diameter control rods are inserted into three hexagonal fuel assemblies, and the large diameter control rods are inserted into all hexagonal fuel assemblies loaded in the area except the outermost periphery of the core. It is.

In any case, it is possible to secure a reactor stop margin. In the former case, the fuel assembly can be increased in size to reduce the number of loaded bodies to the core, and in the latter, the number of control rod drive mechanisms can be reduced. it can. Further, according to the study by the inventors of the present application, even when a square fuel assembly and a large diameter control rod are combined, a core configuration in which the fuel rods are densely arranged in a regular triangular lattice can be realized.

According to the study by the present inventors, in the combination of a fuel assembly having a hexagonal or square cross section and a large diameter control rod, the fuel rods in the fuel assembly have the same fissile plutonium enrichment. In this case, output peaking occurs in the fuel rods adjacent to the guide tube and in the fuel rods located farthest from the center of the fuel assembly. Therefore, by making the fissile plutonium enrichment of the fuel rods in these regions smaller than the fissile plutonium enrichment of the fuel rods in the other regions, the fuel assembly with a flat power distribution within the fuel assembly Can be realized.

The above-described fourth effect is produced by the following operation. According to the study by the inventors of the present application, by optimizing the arrangement of the fuel assemblies and the orifice configuration in the core, the output and the flow rate of the fuel assemblies in the core can be flattened, and the thermal margin can be improved. The area excluding the outermost periphery of the core is divided into two equal areas in the radial direction, and the fuel assemblies are loaded so that the average value of the number of cycles in which the fuel assembly stays in the core outside the core area is smaller than that in the core inside area. As a result, the neutron infinite multiplication factor in the outer region of the core can be made higher than that in the inner region, and the power distribution in the radial direction can be flattened. By loading a fuel assembly having a large number of stay cycles in the outermost peripheral region of the core having a low neutron importance, it is possible to realize a reduction in the required fissionable Pu enrichment.

According to the study by the present inventors, the effect of neutron leakage from the outer periphery of the core is particularly large in the outermost layer of the core and the fuel assemblies adjacent thereto, and as a result, the output of the fuel assemblies is reduced to other regions. As a result, the flow rate in the fuel assembly increases. Therefore, the flow rate distribution can be flattened by setting the average value of the orifice pressure loss coefficient of the outermost periphery of the core and the fuel assembly adjacent thereto to be larger than the average value of the orifice pressure loss coefficient of the other region. . This reduces the flow rate near the outermost circumference of the core,
The total core flow rate can be reduced. Also, the steam void ratio can be increased in the region where the orifice pressure loss coefficient is increased,
It can contribute to improvement of the void coefficient and increase of the growth ratio.

Further, the above-described sixth effect is produced by the following operation. According to the study of the present inventors, it is possible to increase the breeding ratio to 1.0 or more by light steam cooling. However, since the steam temperature exceeds the saturation temperature, the growth rate becomes higher than that used in the current BWR. It is necessary to develop a material having high temperature resistance, and radionuclides such as corrosion products flow out of the core together with the steam. In the present invention, the coolant keeps the steam weight ratio at the core outlet at 40 wt% or less, and the coolant keeps the two-phase flow state at the saturation temperature even when the output rises due to an abnormal transient change, and maintains the saturation temperature. ,
The same structural materials as the current light water reactor can be used, and the distillation function by boiling in the reactor prevents the radioactive nuclides such as corrosion products from being contained in the steam going to the turbine, and the core has a breeding ratio of 1.0 or more. Can be realized.

The above-described first and seventh effects are produced by the following operation. According to the study of the present inventors, in order to achieve a long-term stable supply of energy, an example will be examined with respect to a fuel in which Pu is enriched in depleted uranium generated as a residue during the production of enriched uranium used in current light water reactors. ,
When there is still a large amount of natural uranium and depleted uranium recovered from spent fuel as in the present case, natural uranium, depleted uranium and low-enriched uranium (0.71 wt% to 2.0 wt%) are substituted for depleted uranium. Also, by enriching Pu in fissionable Pu, the enrichment of fissile Pu is reduced by about 0.5 wt% or more as compared with the case of using depleted uranium. , Growth ratio,
A core having performance equal to or higher than the void coefficient can be realized.

The above-described eighth effect is produced by the following operation. According to the study of the present inventors, it is found that P
By not only enriching u but also recycling actinide nuclides at the same time, long-lived radionuclides equilibrate in the furnace and reach a certain amount. Therefore, in the reactor of the present invention, the amount of actinoid nuclide generated and annihilated is balanced, and the increase is zero, and the total amount of long half-life actinoid nuclide that is particularly problematic in radioactive waste is greatly increased. In addition to this, it is possible to realize a reactor system capable of confining actinide nuclides containing Pu only in a nuclear reactor, a reprocessing facility, and a fuel manufacturing facility.

[0059]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following embodiment, the electric output 13
Although the target was a 50,000 kW core, the power scale is not limited to this. By changing the number of fuel assemblies, it can be applied to other power scales. (First Embodiment) FIGS. 1 and 7 show a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 shows a horizontal cross section of the electric output 1356 MWe of the present embodiment. 504 fuel assemblies 1 and 157 control rod driving mechanisms 2 for operating a large-diameter control rod inserted into three fuel assemblies by one control rod driving mechanism are shown. FIG. 7 shows a cross section of the fuel assembly lattice. In the channel box 3, fuel rods 4 having a diameter of 10.1 mm are arranged in a regular triangle with a fuel rod gap of 1.3 mm, forming a regular hexagonal assembly of 12 fuel rod rows. In the center of the fuel assembly, a guide tube 6 in which the large-diameter control rods 5 enter three rows of fuel rod rows, that is, a region of 19 fuel rod unit lattice cells is arranged. The large-diameter control rod is composed of a stainless steel pipe absorption rod filled with B4C. The large diameter control rod has a follower at the tip end made of carbon, which is a substance having a smaller moderating power than light water.

FIG. 8 shows the fuel arrangement in the equilibrium core. The number written on the fuel assembly 1 indicates the period of staying in the core by the number of cycles. The fifth cycle fuel, which has the longest residence time in the reactor, is loaded on the outermost periphery of the core having a low neutron importance. The fuel inside the core outside region is loaded with fuel having the highest neutron infinite multiplication factor during the first stay period in the furnace, and the power distribution in the radial direction of the core is flattened. Fuel in the second to fourth cycles during the in-furnace stay period is loaded in the core inner region in a distributed manner, and the power distribution in the inner region is flattened. FIG. 9 shows the state of the orifice in the equilibrium core, and the number written on the fuel assembly indicates that the degree of opening and closing of the orifice installed in the fuel support portion is different, and there are two regions. . The orifice diameter in the outermost core region (No. 1) where the fuel assembly output is small is smaller than the orifice diameter in the inner region.

FIG. 10 shows the distribution in the height direction of the fissile Pu enrichment averaged in the horizontal section of the fuel assembly for the equilibrium core. The uranium enriched with Pu is depleted uranium. The height of the core is 70 cm, 20 cm from the lower end of the core,
At 49 cm, it is divided into three regions, and the fissile Pu enrichment is 19 wt%, 0 wt%, 19 wt%.
%, On average 11.1 wt%. Also, blankets of 20 cm and 25 cm of depleted uranium are provided above and below the core, respectively. Fig. 11 shows the fissile Pu enrichment of 19w.
FIG. 3 shows a horizontal cross-sectional view of a fuel assembly in a t% region. Fissile Pu
Of enrichment of 19.1 wt%, 18.5 wt%, 17.5 wt%
%, And the average enrichment is 19 wt%. FIG.
Figure 2 shows the power distribution and void fraction distribution in the height direction of the core average. The average core void ratio is 60%, and the steam weight ratio at the core outlet is 32% by weight.

Next, the operation of this embodiment will be described. A dense hexagonal fuel assembly with an equilateral triangular lattice with a 1.3 mm fuel rod gap,
The average core void ratio is 60% and the combination of large diameter control rods
An effective water-to-fuel volume ratio of 0.27 was achieved, and a breeding ratio of 0.87 and a blanket breeding ratio of 0.14 was achieved, for a total of 1.01. That is, in this embodiment, a light water reactor having a breeding ratio of 1.01 is realized by reducing the effective water to fuel volume ratio from about 2.0 of the current reactor to 0.27.

The power of this core is 1.35 million kWe, which is the same as that of the existing ABWR. The circumscribed radius of the core is 2.9 m.
It is almost the same as the value of BWR. The core height is 70 cm, with blankets of 20 cm and 25 cm above and below it, respectively, to form a short fuel assembly. However, because the fuel rods are dense, the total length of the fuel rods is not much different from that of ABWR, MCPR is 1.31 and thermal design standard value is 1.
24 is sufficiently satisfied. Core part 70 regardless of density
cm, the Pu inventory is 10
In terms of the amount of fissile Pu per 100,000 kWe output, 6.
It is as small as 0 tons, and it is 10 tons or less per 1 million kWe even if the period of stay of Pu outside the furnace such as reprocessing is considered.

For the above reasons, in this example having a growth ratio of 1.01, 1,000,000 tons of fissionable Pu and 15 million tons of depleted uranium generated from 15 million tons of uranium reserves worldwide are used. 1500 kWe furnaces can be operated for 10,000 years, realizing a long-term stable supply of energy.

In the present embodiment, in the height direction of the fuel assembly, the portion where the enrichment of fissile Pu is 19 wt% is located above and below, and the central region therebetween is depleted uranium containing no fissile Pu. I have. When the power is increased or the core coolant flow rate is decreased, the steam void fraction in the core is increased. At this time, the power distribution in the upper part of the core swings to a central region not containing fissile Pu. This results in a negative void reactivity result. Further, in this embodiment, the steam weight ratio at the core outlet is 32 wt%, and even during an abnormal transient change, all the coolant does not become steam,
A phase flow state is maintained, and radioactive substances such as corrosion products accumulated in the reactor core are confined in the reactor core by distillation by boiling, as in the current BWR, thereby preventing transfer to the turbine side.

For the above reasons, the present embodiment realizes a BWR capable of coping with a long-term stable supply of energy with the same level of safety as the currently operating fuel-fired light water reactor, while realizing the currently operating ABWR. With the same size of pressure vessel, the same output is obtained and 65 GWd / t is achieved.

The void coefficient (current value) of the currently operating BWR is −7.0 × 10 ⁻⁴ Δk / k /% void. The value of this embodiment is -0.5 * 10 < ^-4 > [Delta] k / k /% void, and the absolute value is designed to be smaller than the current value. As a result, the thermal margin in the event of an increase in pressure or the event of a decrease in the temperature of cooling water becomes relatively large. For the above reasons, in the present embodiment, a BWR core with a larger safety margin is realized in a considerable transient event than the BWR currently in operation.

In the present embodiment, a large-diameter control rod having an outer diameter larger than that of the fuel rod is employed as the absorption rod. By increasing the diameter of the control rod, the mechanical strength of the control rod is increased, and it is possible to suppress bending and buckling when the control rod is inserted and withdrawn. Further, by adopting the large-diameter control rods, the number of absorption rods per fuel assembly can be reduced, the control rods can be easily manufactured, and the manufacturing cost can be reduced.

According to the present embodiment, a fuel composed of depleted uranium with an average of 11.1 wt% of fissile Pu is provided by a combination of a dense hexagonal fuel assembly, a large-diameter control rod and an average core void rate of 60%. A breeding ratio of 1.01 has been achieved, and a 1 million kW reactor 1 with 15 million tons of natural uranium reserves worldwide
A BWR that can operate 500 units for 10,000 years can provide a long-term stable supply of energy. In addition, the operating conditions such as the diameter and output of the pressure vessel and the materials used are almost the same as those of the currently operating BWR, so that the power generation cost can be reduced to the same level as the current BWR despite the significant improvement in performance. it can. or,
The short fuel assembly, the maintenance of the negative void coefficient due to the axial fuel distribution, and the reduction of the steam weight ratio at the core outlet to about 32 wt% maintain the distillation function by boiling and keep the activated material in the pressure vessel. It is possible to keep the same safety margin as the current BWR such as confinement.

This embodiment describes the configuration, operation, and effects of a fuel in which depleted uranium generated as a residue is enriched with Pu in the production of enriched uranium used in current light water reactors for the purpose of long-term stable supply of energy. Was. But,
Instead of depleted uranium, natural uranium, depleted uranium recovered from spent fuel, and fuel enriched with Pu in low-enriched uranium can provide the same or better effects. In this case, by increasing the weight ratio of uranium-235 contained in the fuel,
The enrichment of fissile Pu can be reduced by 0.5 wt% or more as compared with the case of using depleted uranium. As a result, the multiplication ratio with respect to fissile Pu can be increased by about 3% or more, and the void coefficient can be made more negative.
Also, since the Pu inventory can be reduced, the RBWR
The number of operating bases can be further increased.

Although the void coefficient is negative in this embodiment, the output coefficient including the Doppler coefficient can be negative even if the void coefficient is 0 or slightly positive. According to the study by the inventors of the present application, the evaluation result of safety indicates that if the output coefficient is negative, the sign of the void coefficient is essentially no problem. Therefore, the core can be made longer, and the thermal margin can be further increased.
It is also possible to increase the breeding ratio by making the fuel rod gap narrower than 1.3 mm.

In this embodiment, the fuel in which uranium is enriched with only Pu is described, but other actinide nuclides can be enriched with Pu. In this case, RB
Since the WR has a high average energy of neutrons, it becomes difficult for Pu to move to actinoid nuclides with high mass numbers,
Actinoid nuclides can be extinguished by fission reactions. Further, in the present embodiment, in the height direction of the fuel assembly, there are upper and lower portions with the same fissile Pu enrichment, and a configuration of depleted uranium containing no fissile Pu therebetween. However, the enrichment of the upper and lower fissile Pus need not necessarily be equal. Further, in the present embodiment, the depleted uranium region is arranged slightly above the center of the core portion, but is not limited to this. By combining the upper and lower fissile Pu enrichment and the position of the depleted uranium region, it is possible to equalize the axial output peaking. (Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. The present embodiment is a reactor core having an electric output of 1356 MWe and a shorter fuel. The horizontal cross section of the core and the cross section of the fuel assembly lattice of the present embodiment are the same as those of FIGS. 1 and 7 of the first embodiment. FIG. 13 shows the height distribution of the fissile Pu enrichment averaged in the horizontal cross section of the fuel assembly for an equilibrium core.
The uranium enriched with Pu is depleted uranium. The core has a height of 45 cm and is divided into two regions at 8/12 from the lower end of the core. The enrichment of the upper portion is 13 wt% and the lower portion is 12 wt%. In addition, 25 each above and below the core
A blanket of depleted uranium of 20 cm and 20 cm is attached.

Next, the operation of the present embodiment will be described. The structure of the fuel assembly is the same as that of the first embodiment. The fuel assembly is a dense hexagonal fuel assembly having a regular triangular lattice with a fuel rod gap of 1.3 mm.
By the combination of the large diameter control rod and the core average void ratio of 60%,
An effective water to fuel volume ratio of 0.27 was achieved, with a growth ratio of 1.01.
Was realized.

In this embodiment, as compared with the first embodiment, in the height direction of the fuel assembly, there is no depleted uranium region containing no fissile Pu in the central region, and the core portion is even shorter at 45 cm. Has become. Further, at a position 15 cm from the upper end in the height direction of the fuel assembly, upper and lower two-region fuels with different enrichment of fissile Pu are obtained.
3 wt%, the lower enrichment is 12 wt%. On the other hand, when the amount of voids in the core increases, the relative increase in the void fraction is lower in the lower part of the core with a lower void fraction than in the upper part of the core that is already saturated, and as a result, the core with a higher neutron importance From the upper part, the neutron flux distribution swings to the lower part of the core with low neutron importance, and negative void reactivity is injected.

In this embodiment, a pressure vessel having the same size as that of the ABWR currently under construction produces the same output and has a capacity of 45 GW.
d / t is achieved. In this embodiment, natural uranium, depleted uranium and low-enriched uranium recovered from spent fuel are used in place of depleted uranium, and the same or higher effects can be obtained with a fuel enriched with Pu. In addition, other actinoid nuclides can be enriched with Pu. (Third Embodiment) FIGS. 14 to 1 show a third embodiment of the present invention.
7 will be described. The present embodiment is a core in which the number of fuel assemblies and the configuration of the fuel assemblies are changed at the same electric power as that of the first embodiment. FIG. 14 shows the electric output 1356 of this embodiment.
2 shows a horizontal section of MWe. 609 fuel assemblies 7,
193 control rod drive mechanisms 8 for operating a large diameter control rod inserted into three fuel assemblies by one control rod drive mechanism are shown.

FIG. 15 shows a cross section of the fuel assembly lattice. In the channel box 9, fuel rods 4 having a diameter of 10.1 mm
Are arranged in an equilateral triangle with a fuel rod gap of 1.3 mm, forming a regular hexagonal aggregate of 11 fuel rod rows. At two locations in the fuel assembly, guide tubes 11 in which the large-diameter control rods 10 enter two fuel rod rows, that is, areas corresponding to seven fuel rod unit lattice cells are arranged. The large-diameter control rod is composed of a stainless steel pipe absorption rod filled with B4C. The large diameter control rod has a follower at the tip end made of carbon, which is a substance having a smaller moderating power than light water.

FIG. 16 shows the fuel arrangement in the equilibrium core. The number written on the fuel assembly 1 indicates the period of staying in the core by the number of cycles. The fifth cycle fuel, which has the longest residence time in the reactor, is loaded on the outermost periphery of the core having a low neutron importance. The fuel inside the core outside region is loaded with fuel having the highest neutron infinite multiplication factor during the first stay period in the furnace, and the power distribution in the radial direction of the core is flattened. Fuel in the second to fourth cycles during the in-furnace stay period is loaded in the core inner region in a distributed manner, and the power distribution in the inner region is flattened.

FIG. 17 shows the state of the orifice in the equilibrium core. The number written on the fuel assembly indicates that the opening / closing degree of the orifice installed in the fuel support portion is different. Has become. The orifice diameter in the outermost core region (No. 1) where the fuel assembly output is small is smaller than the orifice diameter in the inner region. The distribution of the fissile Pu enrichment averaged in the horizontal section of the fuel assembly in the height direction is the same as that in FIG. 10 of the first embodiment.

In this embodiment, the area occupied by the control rods is reduced from one for the 19 fuel rod unit lattice cells of the first embodiment to two for the seven fuel rod unit lattice cells. The control rod value is almost the same as that of the first embodiment. On the other hand, in the present embodiment, the number of fuel rods loaded in the core is increased as compared with the first embodiment, the average linear power density is reduced, and the thermal margin is improved. Also in this embodiment, the effective volume ratio of water to fuel is 0.28 by a combination of a dense hexagonal fuel assembly, a large diameter control rod and a core average void fraction of 60%.
Is achieved. As a result, the core characteristics are equivalent to those of the first embodiment, and the same effects can be obtained.

Also in this embodiment, natural uranium, depleted uranium recovered from spent fuel, and low-enriched uranium are used in place of depleted uranium, and the same or better effects can be obtained with a fuel enriched with Pu. . In addition, other actinoid nuclides can be enriched with Pu. (Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. The present embodiment is a reactor core having improved core performance based on the configuration of the first embodiment. In this embodiment, the electric power is 1356 MWe, and the core sectional view is the same as FIG. 1 of the first embodiment. FIG. 18 shows a cross section of the fuel assembly lattice. In the channel box 3, fuel rods 4 having a diameter of 10.1 mm are arranged in an equilateral triangle with a fuel rod gap of 1.3 mm.
The rows form a regular hexagonal aggregate. At the center of the fuel assembly, a guide tube 6 into which the large-diameter control rod 5 enters three fuel rod rows, that is, a region of 19 fuel rod unit lattice cells.
Is arranged.

Outside the guide tube, a water elimination rod 12 for eliminating the moderator between the guide tube and the fuel rod adjacent thereto is provided. Large diameter control rod is B4C
Is formed of a stainless steel absorption rod filled with.
The large diameter control rod has a follower at the tip end made of carbon, which is a substance having a smaller moderating power than light water. The arrangement of the fuel in the reactor core, the state of the orifice, and the distribution of the enrichment of fissionable Pu in the height direction averaged in the horizontal section of the fuel assembly for the equilibrium core are all shown in FIGS. , And FIG.

In this embodiment, by eliminating the moderator around the guide tube, the effective volume ratio of water to fuel can be improved as compared with the first embodiment, and the output peaking in the assembly can be suppressed. . The core characteristics are equivalent to those of the first embodiment, and the same effects can be obtained.

Also in this embodiment, natural uranium, depleted uranium recovered from spent fuel, and low-enriched uranium are used in place of depleted uranium, and a similar effect can be obtained with a fuel enriched with Pu. . In addition, other actinoid nuclides can be enriched with Pu. (Fifth Embodiment) A fifth embodiment of the present invention will be described with reference to FIG. The present embodiment is a reactor core having improved core performance based on the configuration of the first embodiment. In this embodiment, the electric power is 1356 MWe, and the core sectional view is the same as FIG. 1 of the first embodiment. FIG. 19 shows a cross section of the fuel assembly lattice. In the channel box 3, fuel rods 4 having a diameter of 10.1 mm are arranged in an equilateral triangle with a fuel rod gap of 1.3 mm.
The rows form a regular hexagonal aggregate.

At three locations in the fuel assembly, guide tubes 11 are provided in which the large-diameter control rods 10 enter two rows of fuel rods, ie, a region of seven fuel rod unit lattice cells. The large-diameter control rod is composed of a stainless steel pipe absorption rod filled with B4C. The large diameter control rod has a follower at the tip end made of carbon, which is a substance having a smaller moderating power than light water. The arrangement of the fuel in the core, the state of the orifice, and the distribution of the enrichment of fissile Pu averaged in the horizontal section of the fuel assembly for the equilibrium core in the height direction are all shown in FIGS. , And FIG.

In this embodiment, the area occupied by the control rods is changed from one for the 19 fuel rod unit lattice cells of the first embodiment to three for the seven fuel rod unit lattice cells, so that the absorption rods are formed in the assembly. , And the control rod value is higher than that of the first embodiment. Other core characteristics are the same as those of the first embodiment, and the same effects can be obtained.

In the present embodiment, natural uranium, depleted uranium recovered from spent fuel, and low-enriched uranium are used instead of depleted uranium, and the same or better effects can be obtained with a fuel enriched with Pu. . In addition, other actinoid nuclides can be enriched with Pu. (Sixth Embodiment) In this embodiment, the present invention is applied to a square fuel assembly. FIG. 20 shows the configuration of the fuel assembly of this embodiment. The channel box 13 has a diameter of 1
The 0.8 mm fuel rods 14 were densely arranged in a triangular lattice with a minimum fuel rod gap of 1.3 mm. In the center of the fuel assembly,
A guide tube 16 in which the large-diameter control rod 15 enters is disposed in an area corresponding to two rows of the fuel rods, that is, an area corresponding to seven fuel rod unit lattice cells.

The large-diameter control rod is constituted by a stainless steel absorption rod filled with B4C, and the tip of the large-diameter control rod has a follower section composed of carbon, which is a substance having a smaller moderating power than light water. have. Further, the large-diameter control rod inserted into the four fuel assemblies is operated by one control rod drive mechanism. In order to flatten the fuel rod output peaking in the fuel assembly, in this embodiment, the fissile P of the fuel rod facing the channel box and the fuel rod facing the guide tube is set.
u enrichment is lower than that of fuel rods in other areas.

In this embodiment, an effective water-to-fuel volume ratio of 0 is obtained by combining a dense square fuel assembly having a triangular lattice with a minimum fuel rod gap of 1.3 mm, a large-diameter control rod and an average void fraction in the furnace of 60%. .34 and a growth ratio of 1.01 as in the other examples.

In the present embodiment, natural uranium, depleted uranium and low-enriched uranium recovered from spent fuel are used instead of depleted uranium, and a fuel enriched with Pu can be used. In addition, other actinoid nuclides can be enriched with Pu. (Seventh Embodiment) FIGS. 21 and 2 show a seventh embodiment of the present invention.
5 will be described. The present embodiment is a reactor core in which the number of fuel assemblies, the fuel assembly configuration, and the control rod drive mechanism are changed at the same electric output as in the first embodiment. FIG. 21 shows a horizontal cross section of a 1356 MWe core of the present embodiment. 31
The three fuel assemblies 17 and the large-diameter control rod inserted into one fuel assembly are operated by one control rod drive mechanism 313.
A control rod drive mechanism 18 is shown. FIG. 22 shows a cross section of the fuel assembly lattice. In the channel box 19, the fuel rods 4 having a diameter of 10.1 mm are arranged in a regular triangle with a fuel rod gap of 1.3 mm to form a regular hexagonal assembly of 15 fuel rod rows. At the center of the fuel assembly, a guide tube 21 in which the large-diameter control rods 20 enter four fuel rod rows, that is, a region of 37 fuel rod unit lattice cells is disposed. The large-diameter control rod is composed of a stainless steel pipe absorption rod filled with B4C. The large diameter control rod has a follower at the tip end made of carbon, which is a substance having a smaller moderating power than light water.

FIG. 23 shows the fuel arrangement of the equilibrium core. The number written on the fuel assembly 17 indicates the period of staying in the core by the number of cycles. The fifth cycle fuel, which has the longest residence time in the reactor, is loaded on the outermost periphery of the core having a low neutron importance. The fuel inside the core outside region is loaded with fuel having the highest neutron infinite multiplication factor during the first stay period in the furnace, and the power distribution in the radial direction of the core is flattened. In the core inner area, the period of stay in the furnace 2 to 4
The fuel of the cycle is dispersed and loaded, and the fuel of the fifth cycle during the furnace stay period is loaded at the center of the core, thereby flattening the power distribution in the inner region.

FIG. 24 shows the state of the orifice in the equilibrium core. The numbers written on the fuel assemblies indicate that the opening and closing degrees of the orifices installed on the fuel support portion are different. The opening / closing degree of the orifice is a total of six regions, five regions for each in-furnace stay cycle shown in FIG. 23 and one region at the core center. The orifice diameter of the core outermost region (No. 5) where the fuel assembly output is small is smaller than the orifice diameter of the inner region. FIG. 25 shows the height distribution of the fissile Pu enrichment averaged in the horizontal cross section of the fuel assembly for the equilibrium core. The uranium enriched with Pu is depleted uranium.

In the present embodiment, by increasing the number of fuel rods per fuel assembly and increasing the size of the fuel assembly,
The number of fuel assemblies to be loaded in the reactor core was increased from 504 in Example 1.
The core was reduced to 313 and the core was downsized. By increasing the size of the fuel assembly and the area occupied by the control rods from 19 fuel rod unit lattice cells of the first embodiment to 37 fuel rod unit cells, the control rod value was made substantially equal to that of the first embodiment. Further, one control rod drive mechanism is provided for each control rod inserted into the fuel assembly. Also in the present embodiment, an effective water-to-fuel volume ratio of 0.27 is achieved by a combination of a dense hexagonal fuel assembly, a large-diameter control rod, and a core average void fraction of 60%.
As a result, the core characteristics are equivalent to those of the first embodiment, and the same effects can be obtained.

In this embodiment, the core configuration is such that the large-diameter control rod is also inserted into the fuel assembly loaded on the outermost periphery. However, the outermost fuel assembly is less effective in securing the reactor stop margin. May have a core configuration in which no control rod is inserted.

In this embodiment, natural uranium, depleted uranium recovered from spent fuel, and low-enriched uranium are used in place of depleted uranium, and the same or better effects can be obtained with a fuel enriched with Pu. . In addition, other actinoid nuclides can be enriched with Pu. (Eighth Embodiment) An eighth embodiment of the present invention will be described with reference to FIG. The present embodiment is a reactor core in which the number of fuel assemblies, the fuel assembly configuration, and the control rod drive mechanism are changed at the same electric output as in the first embodiment. In this embodiment, the electric output 1356
In MWe, the core sectional view is the same as FIG. 21 of the seventh embodiment. FIG. 26 shows a cross section of the fuel assembly lattice. In the channel box 19, the fuel rods 4 having a diameter of 10.1 mm are arranged in a regular triangle with a fuel rod gap of 1.3 mm to form a regular hexagonal assembly of 15 fuel rod rows. At two locations in the fuel assembly, guide tubes 6 in which the large-diameter control rods 5 enter three rows of fuel rods, that is, a region of 19 fuel rod unit lattice cells are arranged.

The large-diameter control rod is composed of a stainless steel absorption rod filled with B4C. The large diameter control rod has a follower at the tip end made of carbon, which is a substance having a smaller moderating power than light water. The arrangement of the fuel in the reactor core, the state of the orifice, and the distribution of the enrichment of fissionable Pu in the height direction averaged in the horizontal section of the fuel assembly for the equilibrium core are all shown in FIGS. , And FIG.

In this embodiment, the area occupied by the control rods is changed from one for 37 fuel rod unit lattice cells of Embodiment 7 to two for 19 fuel rod unit lattice cells, so that the absorption rods And the control rod value is improved as compared with the seventh embodiment. Other core characteristics are the same as those of the seventh embodiment, and the same effects can be obtained.

In this embodiment, natural uranium, depleted uranium recovered from spent fuel, and low-enriched uranium are used in place of depleted uranium, and the same or better effects can be obtained with a fuel enriched with Pu. . In addition, other actinoid nuclides can be enriched with Pu. (Ninth Embodiment) This embodiment is a case where the present invention is applied to a square fuel assembly. FIG. 27 shows the configuration of the fuel assembly of this embodiment. In the channel box 22, fuel rods 23 having a diameter of 9.8 mm are densely arranged in a triangular lattice with a minimum fuel rod gap of 1.3 mm. In the center of the fuel assembly,
A guide tube 25 in which the large-diameter control rod 24 enters is disposed in an area corresponding to four rows of the fuel rods, that is, an area for 37 fuel rod unit lattice cells.

The large-diameter control rod is composed of a stainless steel absorption rod filled with B4C, and the tip of the large-diameter control rod has a follower section composed of carbon, which is a substance having a smaller moderating power than light water. have. Further, the large-diameter control rod inserted into one fuel assembly is operated by one control rod drive mechanism. In order to flatten the fuel rod output peaking in the fuel assembly, in this embodiment, the fissile P of the fuel rod facing the channel box and the fuel rod facing the guide tube is set.
u enrichment is lower than that of fuel rods in other areas.

In this embodiment, an effective water-to-fuel volume ratio of 0 is obtained by a combination of a dense square fuel assembly having a triangular lattice with a minimum fuel rod gap of 1.3 mm, a large-diameter control rod, and an average in-furnace void ratio of 60%. .34 and a growth ratio of 1.01 as in the other examples.

Also in the present embodiment, natural uranium, depleted uranium and low-enriched uranium recovered from spent fuel are used in place of depleted uranium, and a Pu-enriched fuel can be used therefor. In addition, other actinoid nuclides can be enriched with Pu. (Tenth Embodiment) A tenth embodiment of the present invention will be described with reference to FIG. This embodiment is a modification of the eighth embodiment, and is a core in which the number of fuel assemblies, the fuel assembly configuration, and the rod drive mechanism are changed at the same electric output as in the first embodiment. In this embodiment, the electric power is 1356 MWe, and the core sectional view is the same as FIG. 21 of the seventh embodiment. FIG. 28 shows a cross section of the fuel assembly lattice. The channel box 19 has a diameter of 10.
1 mm fuel rods 4 are arranged in a regular triangle with a fuel rod gap of 3 mm, forming a regular hexagonal assembly of 15 fuel rod rows.
At six locations in the fuel assembly, guide tubes 6 in which the large-diameter control rods 5 enter two fuel rod rows, that is, a region corresponding to seven fuel rod unit lattice cells, are arranged.

The large-diameter control rod is composed of a stainless steel absorption rod filled with B4C. The large diameter control rod has a follower at the tip end made of carbon, which is a substance having a smaller moderating power than light water. The arrangement of the fuel in the reactor core, the state of the orifice, and the distribution of the enrichment of fissionable Pu in the height direction averaged in the horizontal section of the fuel assembly for the equilibrium core are all shown in FIGS. , And FIG.

In the present embodiment, the area occupied by the control rods is changed from one for 37 fuel rod unit lattice cells of Embodiment 7 to six for seven fuel rod unit lattice cells, so that the absorption rods And the control rod value is improved as compared with the seventh embodiment. Other core characteristics are the same as those of the seventh embodiment, and the same effects can be obtained.

In this embodiment, natural uranium, depleted uranium and low-enriched uranium recovered from spent fuel are used in place of depleted uranium, and a similar effect can be obtained by using a fuel enriched with Pu. . In addition, other actinoid nuclides can be enriched with Pu.

[0104]

According to the present invention, a fuel obtained by adding Pu to depleted uranium, natural uranium, depleted uranium or low-enriched uranium to achieve a growth ratio of around 1.0 or 1.0 or more can be obtained.
By using Pu as a catalyst, depleted uranium, natural uranium, depleted uranium and low-enriched uranium can be burned, which can contribute to a long-term stable supply of energy.

[Brief description of the drawings]

FIG. 1 is a horizontal sectional view of a reactor core according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a fuel rod lattice constant required to represent a conversion ratio and an effective water to fuel volume ratio.

FIG. 3 is a characteristic diagram showing a relationship between a fuel rod gap and a geometrical water-to-fuel volume ratio.

FIG. 4 is a characteristic diagram showing the relationship between the fissionable Pu enrichment and the growth ratio.

FIG. 5 is an explanatory diagram showing a change in output distribution when the steam void ratio increases.

FIG. 6 is a characteristic diagram showing a relationship between a core average void ratio and the above-mentioned weight ratio at a core outlet.

FIG. 7 is a horizontal sectional view of a fuel assembly loaded in the core of FIG. 1;

FIG. 8 is a layout diagram of a fuel assembly at the time of an equilibrium core of the embodiment of FIG. 1;

FIG. 9 is a distribution diagram of orifices in the embodiment of FIG. 1;

10 is an axial enrichment distribution diagram of a fuel assembly loaded on the core of FIG. 1;

FIG. 11 is a fuel rod enrichment distribution diagram in a fuel assembly loaded in the core of FIG. 1;

FIG. 12 is a characteristic diagram showing axial power and void fraction distribution of the core in the embodiment of FIG. 1;

FIG. 13 is an axial enrichment distribution diagram of a fuel assembly loaded in a core according to a second embodiment of the present invention.

FIG. 14 is a horizontal sectional view of a reactor core according to a third embodiment of the present invention.

FIG. 15 is a horizontal sectional view of a fuel assembly loaded in the core of FIG.

16 is a layout diagram of a fuel assembly at the time of an equilibrium core of the embodiment of FIG. 13;

FIG. 17 is a distribution diagram of orifices in the embodiment of FIG.

FIG. 18 is a horizontal sectional view of a fuel assembly loaded in a core according to a fourth embodiment of the present invention.

FIG. 19 is a horizontal sectional view of a fuel assembly loaded in a core according to a fifth embodiment of the present invention.

FIG. 20 is a horizontal sectional view of a fuel assembly loaded in a core according to a sixth embodiment of the present invention.

FIG. 21 is a horizontal sectional view of a reactor core according to a seventh embodiment of the present invention.

FIG. 22 is a horizontal sectional view of a fuel assembly loaded in the core of FIG. 21.

FIG. 23 is a layout diagram of a fuel assembly at the time of an equilibrium core of the embodiment in FIG. 21;

FIG. 24 is a distribution diagram of orifices in the embodiment of FIG. 21.

FIG. 25 is an axial enrichment distribution diagram of a fuel assembly loaded in the core of FIG. 21;

FIG. 26 is a horizontal sectional view of a fuel assembly loaded in a reactor core according to an eighth embodiment of the present invention.

FIG. 27 is a horizontal sectional view of a fuel assembly loaded in a reactor core according to a ninth embodiment of the present invention.

FIG. 28 is a horizontal sectional view of a fuel assembly loaded in a reactor core according to a tenth embodiment of the present invention.

[Explanation of symbols]

1, 7, 17 ... fuel assembly, 2, 8, 18 ... control rod drive mechanism, 3, 9, 13, 19, 22 ... channel box, 4, 14, 23 ... fuel rod, 5, 10, 15, 20 ,
24: Large diameter control rod, 6, 11, 16, 21, 25: Guide tube, 12: Water exclusion rod.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) G21C 3/326 G21C 3/30 D 5/18 X 7/103 GBDT 3/32 N 7/10 L (72 Inventor Junichi Miwa 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Power and Electricity Research Laboratory, Hitachi, Ltd. Hitachi, Ltd. Electric Power and Electricity Development Laboratory

Claims (31)

[Claims] 1. A reactor having plutonium or a fuel enriched with plutonium and actinide nuclides in uranium containing at least one of depleted uranium, natural uranium, depleted uranium, and low-enriched uranium, wherein the fuel rods have a triangular lattice shape. The fuel assembly includes an arrayed fuel assembly, one or more absorption rods having a cross-sectional area larger than the cross-sectional area of the fuel rod unit lattice cell, and a large-diameter control rod inserted into the fuel assembly. A light water reactor core having a void coefficient of about 1.0 or more than 1.0 and having a negative void coefficient. 2. A reactor having plutonium or a plutonium-enriched actinide-nuclide-enriched fuel in uranium containing at least one of depleted uranium, natural uranium, depleted uranium and low-enriched uranium, wherein the fuel rods have a triangular lattice shape. The fuel assembly includes an arrayed fuel assembly, one or more absorption rods having a cross-sectional area larger than the cross-sectional area of the fuel rod unit lattice cell, and a large-diameter control rod inserted into the fuel assembly. A light water reactor core characterized by being near 1.0 or above 1.0 and having a negative power coefficient and a positive or zero void coefficient. 3. The method according to claim 1, wherein the growth ratio is 1.0.
From 1.15 to 1.15. 4. A fuel assembly comprising plutonium or a fuel enriched with plutonium and an actinoid nuclide on uranium containing at least one of depleted uranium, natural uranium, depleted uranium, and low-enriched uranium, arranged in a triangular lattice. A fuel assembly having a fuel rod having a cross-sectional area larger than a cross-sectional area of a fuel cell unit cell and one or more guide tubes into which a large-diameter control rod is inserted.
A fuel assembly characterized by being near or at least 1.0. 5. The fuel assembly according to claim 4, further comprising a water exclusion region formed on the surface of the guide tube with a substance having a smaller deceleration ability than light water. 6. The fuel assembly according to claim 4, wherein the fuel rods are densely arranged in a triangular lattice, and the gap between the fuel rods is 0.7 to 2.0 mm. body. 7. A light water reactor core comprising the fuel assembly according to claim 6. 8. The fuel assembly according to claim 4, wherein the fuel rods are densely arranged in a triangular lattice, and the effective water to fuel volume ratio is between 0.1 and 0.6. A fuel assembly comprising: 9. A light water reactor core comprising the fuel assembly according to claim 8. 10. An average fissile plutonium enrichment of 6 to 20 wt% in a core portion excluding a blanket portion at an outer peripheral portion and upper and lower end portions of a core according to any one of claims 1, 2, 3, 7 and 9. A light water reactor core, comprising: 11. The fuel according to claim 4, wherein the average fissile plutonium enrichment in the fuel region excluding the upper and lower blanket portions is 6 to 20 wt%. Aggregation. 12. The method according to claim 1, wherein the average core void ratio when operating at 50% or more of the rated output is 45 to 70%. Features a boiling water reactor core. 13. The method of claim 1, 2, 3, 7, 9, 10, or 1.
2, the large diameter control rods connected to one control rod drive mechanism are all inserted into one fuel assembly, and the large diameter control rods are located in an area excluding the outermost circumference of the core. A light water reactor core inserted into all the fuel assemblies to be loaded. 14. The light water reactor core according to claim 13, wherein the cross section of the fuel assembly is hexagonal or square. 15. The method of claim 1, 2, 3, 7, 9, 10, or 1.
2, the plurality of large diameter control rods connected to one control rod driving mechanism are inserted into three hexagonal fuel assemblies, and the large diameter control rods exclude the core outermost periphery. A light water reactor core inserted into all the fuel assemblies loaded in a region. 16. The method of claim 1, 2, 3, 7, 9, 10, or 1.
2, the plurality of large-diameter control rods connected to one control rod drive mechanism are inserted into four square fuel assemblies, and the large-diameter control rods are located in an area excluding the outermost periphery of the core. A light water reactor core, which is inserted into all the fuel assemblies loaded in the reactor. 17. The method of claim 1, 2, 3, 7, 9, 10, 1.
2. The light water reactor core according to any one of 2, 13, 14, 15 and 16, further comprising a follower portion made of a substance having a smaller deceleration ability than light water at a tip portion of the large diameter control rod. 18. The nuclear fission of a fuel rod located in a region adjacent to the guide tube and a fuel rod located in a region furthest from the center of the fuel assembly according to claim 6, 8, or 11. A fuel assembly having an average value of fissile plutonium enrichment lower than the average value of fissile plutonium enrichment of fuel rods located in other regions. 19. The method of claim 1, 2, 3, 7, 9, 10, 1.
In any one of 2, 13, 14, 15, 16, and 17, the average power density of the core except for the outer peripheral portion of the core and the blanket portions at the upper and lower ends is 100 to 300 kW / l. . 20. The method of claim 1, 2, 3, 7, 9, 10, 1.
In any of 2, 13, 14, 15, 16, and 17, in the core height direction excluding the blanket portions at the upper and lower ends, a portion where the average fissile plutonium enrichment of the horizontal section of the fuel assembly is 6 wt% or more But from 40cm to 140cm
A light water reactor core. 21. The fissionable plutonium average enrichment in a horizontal section of the fuel assembly in the height direction of the fuel assembly excluding the blanket portions at the upper and lower ends, according to any one of claims 4, 5, 6, 8, 11, and 18. The part whose degree is more than 6 wt%
A fuel assembly characterized by being between 40 cm and 140 cm. 22. The fuel cell according to claim 4, wherein the average value of the fissile plutonium enrichment value of the upper half of the fuel assembly, excluding the upper and lower blanket portions, is obtained. A fuel assembly characterized by a low average value in the lower half. 23. The method of claim 4, 5, 6, 8, 11, 18, 2.
In any one of 1 and 22, in the fuel assembly height direction excluding the blanket portions at the upper and lower ends, a portion having a fissile plutonium enrichment of 6 wt% or more is located above and below,
A fuel assembly, wherein the fissionable plutonium enrichment in a region near the center therebetween is 6 wt% or less. 24. The fissionable plutonium rich material in the upper and lower regions sandwiching a region near the center where the fissionable plutonium enrichment is 6 wt% or less in the height direction of the fuel assembly excluding the blanket portions at the upper and lower ends. A fuel assembly having different degrees of conversion. 25. The method of claim 1, 2, 3, 7, 9, 10, 1.
2,13,14,15,16,17,19 and 20, when the reactor is operated at 50% or more of the rated power, the core outlet steam weight ratio of the coolant is 20 wt% to 40 w
A boiling water reactor core characterized in that the core is t%. 26. The method of claim 1, 2, 3, 7, 9, 10, 1.
2,13,14,15,16,17,19,20 and 2
5, the area excluding the outermost periphery of the core is divided into two equal areas in the radial direction, and the average value of the number of core stay cycles of the fuel assemblies loaded in the outer core area is smaller than that of the inner core area. A light water reactor core, wherein a fuel assembly is loaded so as to be small. 27. The method of claim 1, 2, 3, 7, 9, 10, 1.
2,13,14,15,16,17,19,20,25
Or 26, the average value of the orifice pressure drop coefficient of the outermost periphery of the core and the fuel assembly adjacent thereto is
A light water reactor core characterized by being set to be larger than the average value of the orifice pressure loss coefficient in other regions. 28. The method of claim 4, 5, 6, 8, 11, 18, 2.
A fuel assembly according to any one of 1, 22, 23 and 24, wherein plutonium and uranium extracted from spent fuel are simultaneously loaded. 29. A light water reactor core comprising the fuel assembly according to claim 28. 30. The method of claim 4, 5, 6, 8, 11, 18, 2.
The fuel assembly according to any one of 1, 22, 23 and 24, wherein plutonium, uranium and actinoid nuclides taken out from spent fuel are simultaneously loaded. 31. A light water reactor core comprising the fuel assembly according to claim 30.