JPH087270B2 - Pressure tube reactor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure tube reactor using heavy water as a neutron moderator, and particularly to a reactivity coefficient which is important for operation control of the reactor. It relates to improved technology.

[Conventional technology]

BACKGROUND ART Conventionally, a pressure tube type reactor that uses heavy water as a neutron moderator has a plurality of calandria pipes vertically passed through a calander tank containing heavy water, and the pressure pipes are passed through the calandria pipes. The coated nuclear fuel is contained in the pressure pipe, and the heat of nuclear reaction by the nuclear fuel is given to the coolant passing through the pressure pipe to generate high-temperature high-pressure steam. The pressure tubes of a pressure tube type nuclear reactor are arranged in a square lattice shape in a calandria tank as described in, for example, JP-A-55-94190. In order to improve the controllability of the core of such a nuclear reactor, JP-A-58-3438
As described in No. 6, based on a square lattice arrangement of pressure tubes, the mutual spacing of the pressure tube lattice arrangement not arranging the control rods and instrumentation guide tubes placed in the core is narrowed,
As described in JP-A-49-103091, a carbon rod is arranged in the heavy water moderator in the calandria tank, or a pressure pipe and a heavy water pipe are connected as described in JP-A-61-26891. Or by inserting a water sealing rod into the pressure pipe as described in JP-A-52-61697.
As described in JP-A-52-100073, a structure has been proposed in which the outer diameter of the calandria tube is made larger in the central portion of the core than in other parts.

[Problems to be Solved by the Invention]

In the conventional pressure tube type reactor in which the pressure tubes are arranged in a square lattice, the pressure tubes and the calandria tubes penetrate the calandria tank.
The pitch of the through hole provided in the calandria tank is also narrowed, and the strength of the calandria tank is reduced. For this reason, in the conventional pressure tube type reactor in which the pressure tubes are arranged in a square lattice shape, it is difficult to narrow the arrangement lattice spacing of the pressure tubes. For this reason, the ratio of heavy water to nuclear fuel tends to increase. Those having such a tendency tend to have a large positive value of void reactivity, and the self-controllability of the reactor tends to be low.

In order to solve this point, the above items (1) to (4) have been proposed. However, since the arrangement of pressure pipes is complicated, the core performance evaluation and operation management are poor, and the pressure of the pressure pipe arrangement is partially narrowed, so the strength of the calandria tank through which the pressure pipes penetrate is partially reduced. It is easy to do, and to clear this, the Calandria tank tends to increase in size. In this method, part of the carbon rod is replaced with heavy water, but since the carbon rod itself is a relatively large neutron absorber, the neutron economy is poor and the carbon rod is simply parallel to the pressure pipe between the pressure pipes. The calandria tank tends to be large because it is installed. In the method of (1), the heavy water pipe is simply installed in parallel with the pressure pipe similarly to the method of (1), so that the calandria tank tends to be large. In this method, since the water sealing rod is partially replaced in the pressure pipe with the fuel rod in the pressure pipe, the fuel is reduced, and in order to cover this, the pressure pipe and the pressure pipe must be used to secure a space for the fuel. The calandria tank that houses the pressure pipe tends to be large. In this method, the diameter of the calandria pipe in the middle is thicker than other diameters.Therefore, when inserting the calandria pipe into the calandria tank and assembling it, the holes in the calandria tank for inserting the calandria pipe The diameter is inevitably large, and the space between the holes is naturally widened in order to secure strength, and the calandria tank becomes large.

As the calandria tank grows in size, the amount of heavy water entering it tends to increase, or the effect of reducing the amount of heavy water is small. Therefore, it is assumed that the improvement effect of reducing the volume ratio of heavy water to fuel and improving the self-control performance of the reactor is small, and the calandria tank is also large.

An object of the present invention is to improve the control performance of a nuclear reactor without enlarging the calandria tank.

[Means for solving the problem]

A first means for achieving the object of the present invention is to put a pressure pipe, in which nuclear fuel is contained and through which a coolant passes, in a calandria pipe, and the calandria pipe is arranged in a calandria tank in which heavy water is stored. The moderator pressure tube reactor is a pressure tube reactor characterized in that the calandria tubes are arranged in an equilateral triangular lattice shape at a density such that the volume ratio of heavy water to fuel is 9.0 or less. In a heavy water deceleration pressure tube reactor in which a pressure pipe containing the nuclear fuel and through which the coolant passes is contained in a calandria pipe, and the calandria pipe is arranged in a calandria tank containing heavy water, the outside of the calandria pipe is A pressure tube reactor characterized in that, in addition to the calandria tube replaced with the heavy water in the vicinity of the outer periphery thereof, a substitute with less neutron absorption is arranged. A third means is a pressure tube reactor for forming a heavy water holding region by liquid-tightly mounting a calandria pipe passing through the calandria tank to a constituent member of the calandria tank. After fixing the calandria pipe, a plurality of divided cylinders made of a material having less neutron absorption are carried into the outer periphery of the calandria pipe, and the plurality of divided cylinders are assembled into a shape covering the outer periphery of the calandria pipe. A fourth means is a method for assembling a calandria pipe, which is passed through the calandria tank, to a constituent member of the calandria tank in a liquid-tight manner to form a heavy water holding region. In a tubular reactor, a tubular member made of a material with low neutron absorption is carried into the heavy water holding region,
Next, when inserting the calandria pipe into the constituent member of the calandria tank, insert the calandria pipe into the tubular member that has already been carried in, and then attach the calandria pipe to the constituent member of the calandria tank. A fifth means is a member arranged on the outer periphery of the calandria pipe of the pressure tube reactor, wherein the member is made of a material having a small neutron absorption. A sixth aspect of the present invention is a replacement of a heavy water moderator for a pressure tube reactor, characterized in that the assembly shape is a tubular member having a size that allows the calandria tube to be inserted therethrough.
In the means, the pressure tube type reactor is characterized in that the pressure tubes are arranged in an equilateral triangular lattice shape at a density such that the volume ratio of heavy water to fuel is 9.0 or less, and the seventh means is the first means. Means or sixth means, wherein a control rod guide tube, a neutron instrumentation guide tube or a poison tube of the nuclear reactor is arranged at the array position instead of some of the pressure tubes. The eighth means is any one of the first means, the second means, and the sixth means, wherein a control rod with a fuel follower is arranged in a coolant inside some of the pressure pipes. A ninth aspect of the present invention is a pressure tube reactor characterized in that, in any one of the first, second, sixth, and eighth means, the outer periphery of the calandria tube is surrounded as a substitute for heavy water. The metal made of a material with low neutron absorption is the calandria tube. Is a pressure tube reactor which is characterized by being arranged separately from the tenth means,
In the ninth means, the metal as a substitute for the heavy water is a pressure tube type nuclear reactor characterized in that the assembled shape is a cylinder surrounding the outer periphery of the calandria tube. Means, in the tenth means, the cylinder as a substitute for the heavy water is a pressure tube reactor characterized in that the wall itself of the cylinder is hollow, the twelfth means,
In any one of the means 10 and 11, the cylinder as the replacement of the heavy water is a pressure tube reactor characterized by comprising a plurality of parts divided in at least one direction of a circumferential direction or an axial direction. The thirteenth means is the pressure tube reactor according to any one of the second and ninth means, characterized in that the material of the substitute for heavy water is a zirconium alloy or aluminum or an aluminum alloy. The means is
In any one of the second, 9, 10, 11, 12, 13 means, the calandria tube is a pressure tube reactor characterized by being arranged in an equilateral triangle, the fifteenth means, 9th, 10th, 1st
In any one of 1, 12, 13 is a pressure tube reactor characterized in that the substitution of heavy water is arranged in a region of relatively high power density in the calandria tank, A sixteenth means is a pressure tube reactor according to the fifteenth means, wherein the heavy water substitute has a thickness increased in proportion to a power density.

[Action]

According to the first means, by arranging the pressure tubes in a triangular lattice shape, the volume ratio of heavy water to fuel can be reduced to 9.0 or less without reducing the interval between the pressure tubes, and the core is enlarged. It is possible to obtain the effect of lowering the coolant void reactivity coefficient without increasing the temperature and improving the control performance without increasing the size of the core. The principle is as follows.

That is, the amount of heavy water assigned to each pressure pipe is
Considering the sectional view of FIG. 11, it is represented by the shaded area S ₁ and is calculated by the following equation.

However, l ₁ = lattice spacing R ₁ = calandria outer radius On the other hand, the amount of heavy water assigned to each pressure pipe arranged in a square lattice is the diagonally shaded area S when considering the sectional view of FIG. It is expressed by ₂ and is calculated by the following formula.

S ₂ = l ₂ ² -πR ₂ ² (2) where l ₂ = lattice spacing R ₂ = outer radius of the calandria tube Here, consider the case where the lattice spacing and the calandria tube diameter are the same for a triangular lattice and a square lattice, respectively. , L ₁
= L ₂ = l lattice spacing and R ₁ = R ₂ = R, the reduction ratio ΔM of the volume of heavy water allocated per pressure pipe when comparing the equilateral triangular lattice arrangement and the square lattice arrangement.
Is obtained by the following equation.

Here, concretely, considering the case of 1 = 24 cm lattice spacing and R = 8 cm, and substituting into the equation (3), the reduction ratio ΔM≈0.21.

The reduction rate ΔL of the core diameter that affects the size of the calandria tank is calculated by the following equation.

That is, when the lattice spacing is the same, the amount of heavy water can be significantly reduced (about 21% in the above example), and the core diameter can be reduced by 7%.

Therefore, according to the regular triangular grid arrangement, the volume of heavy water can be reduced without reducing the distance between the pressure pipes, the volume ratio of heavy water to the same fuel can be made small, and the calandria tank can be made small. Performance has improved,
It is also advantageous in terms of economy.

According to the second means, since the substitute is arranged around the outside of the calandria pipe and is present in place of part of the heavy water, the amount of heavy water around the calandria pipe is reduced and the volume ratio of heavy water to fuel for the same fuel is reduced. Also, since the replacement is placed around the outside of the pressure tube, the Calandria tank can be made smaller than when the replacement is separated from the pressure tube and placed between the Calandria tubes. The heavy water to fuel volume ratio (D / F) is calculated by the following equation in the case where the substitute having a thickness t is continuously placed around the outer circumference of the pressure pipe (the substitute is cylindrical).

D / F = {l ² −π (R + t) ² } / nπr ² (5) where, l = lattice spacing R = calandria outer radius n = number of fuel rods per fuel assembly r = fuel pellet radius heavy water pair The improvement width ΔD / F of the fuel volume ratio D / F is calculated by the following equation from the equation (5).

ΔD / F = − {π (R + t) ² −πR ² } ÷ nπr ² (6) According to the third means, a part of the heavy water and the substitute that replaces it are divided and carried into the outer periphery of the Calandria pipe. As a result, the replacement work space for the replacement and the space between the pressure pipes do not have to be increased because they are assembled around the outer periphery, and a core can be constructed that can improve the heavy water to fuel volume ratio without increasing the calandria tank.

According to the fourth means, when inserting the calandria pipe into the calandria tank, the tubular member is first carried into the calandria tank, and the calandria pipe is inserted into the calandria tank at the same time when the calandria pipe is inserted into the tubular member. It is possible to insert a tubular member as a substitute for heavy water around the outside of the calandria pipe without inserting a large working space inside the calandria tank.

According to the fifth means, a cylindrical heavy water substitute that covers the outer circumference of the Calandria pipe is obtained, and this is used to cover the outer circumference of the Calandria pipe to remove the heavy water around the outer circumference of the Calandria pipe. Used to replace the substitute to improve the heavy water to fuel volume ratio.

According to the sixth means, in addition to the function of the second means, in arranging the pressure tubes in an equilateral triangular lattice pattern,
Since the volume ratio of heavy water to fuel is arranged at a density of 9.0 or less, the coolant void reactivity coefficient in the pressure pipe is surely in the vicinity of zero or in the negative region, and the self-control performance of the reactor core is further improved. .

According to the seventh means, in addition to the action of the first or sixth means, the arrangement of all the tubes including the control rod guide tube of the reactor or the neutron instrumentation guide tube or the poison tube in addition to the pressure tube Is a triangular grid arrangement that can reduce the amount of heavy water,
The amount of heavy water is easily reduced.

Eighth means, in addition to the action of the first or second or sixth means, a control rod with a fuel follower inserted in the coolant inside some of the pressure pipes causes the coolant flowing in the pressure pipes to The effect of being cooled is obtained.

According to the ninth means, in addition to the action of any one of the first, second, sixth, seventh, and eighth means, the substitution of heavy water surrounding the calandria tube has a small neutron absorption capacity, so The economy is maintained well without any deterioration.

According to the tenth means, in addition to the function of the ninth means, since the outer periphery of the calandria pipe is surrounded by the cylinder, the heavy water is uniformly replaced by the cylinder from the outer periphery of the calandria pipe, and the fuel is converted into fuel. The intensity of the affected neutrons tends to be uniform around the circumference.

According to the eleventh means, in addition to the function of the tenth means, since the cylinder itself has a hollow wall, the neutron economy is further improved and the hollow volume is replaced with heavy water. Therefore, the action of replacing a large amount of heavy water with a lightweight structure can be obtained.

According to the twelfth means, in addition to the operation of any one of the tenth and eleventh means, the plurality of divided parts of the cylinder are carried into the calandria tank as they are, and then assembled as a whole. Therefore, it is possible to obtain an effect that the assembly can be performed in a small space.

According to the thirteenth means, in addition to the function of any one of the second and ninth means, the material of the substitute is a zirconium alloy or aluminum or an aluminum alloy,
It is difficult for these materials to absorb neutrons, which improves the neutron economy.

According to the fourteenth means, in addition to the action of any one of the second, ninth, tenth, eleventh, twelve, and thirteenth means, the calandria pipes are arranged in an equilateral triangle shape and the replacement with heavy water is performed. Both improve the volume ratio of heavy water to fuel, and when it is difficult to adjust the volume ratio of heavy water to fuel in either one of the arrangement and the use of the substitutes, it is easy to adjust the volume ratio of heavy water in combination with the other. To be

According to the fifteenth means, in addition to the action of any one of the ninth, tenth, eleventh, twelve, and thirteenth means, the substitute is disposed in a relatively high power density region in the calandria tank. Therefore, it is easy to balance the output with the low power density region, and by dividing the region into the axial direction of the reactor core, the radial direction, or both directions, it is possible to flatten the power distribution in the divided direction. Is obtained.

According to the sixteenth means, in addition to the action of the fifteenth means, since the thickness of the substitution product is increased in proportion to the power density, heavy water is increased as the power density becomes higher in a high power density region. The amount of substitution with and increases, and the effect that the heavy water to fuel volume ratio is adjusted in proportion to the power density is further obtained in the high power density region.

〔Example〕

An embodiment of a pressure tube reactor arranged in an equilateral triangular lattice according to the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a diagram showing an arrangement of calandria pipes and the like in a calandria tank according to the present invention. In the figure, in the calandria tank 2, as many calandria tubes 1 as necessary to obtain the rated output of the nuclear reactor are arranged in an equilateral triangle lattice shape, and between these lattice points are necessary for control and measurement. A number of control rod guide tubes 4 and neutron instrumentation tubes 5 are arranged.
As shown in FIG. 2, the calandria tube 1, the control rod guide tube 4, and the neutron instrumentation tube 5 have an upper tube sheet 6 and a lower tube sheet 7 so that heavy water can be retained in the calandria tank 2.
It is hermetically sealed with. According to the regular triangular lattice-shaped arrangement of the calandria tubes 1 as described above, the volume of heavy water can be reduced as compared with the conventional square lattice-shaped arrangement shown in FIGS. 14 and 15. There is.

However, in the present invention, the following points must be noted when installing the control rod guide tube 4. Third
As shown in the figure, when the control and instrumentation pipes such as the control rod guide pipe 4, the neutron instrumentation pipe 5, and the poison pipe are arranged in the central part of the triangular lattice, these pipes and the calandria pipe 1 and the upper pipe sheet 6 are arranged. In order to secure the mechanical strength of the joint part (usually a roll joint), secure the minimum gap 8 between the calandria pipe 1 and the one with the largest diameter (usually the control rod guide pipe 4) among these pipes. This condition determines the maximum allowable diameter of these tubes.

Since an equilateral triangular lattice has a smaller maximum allowable size as compared with a square lattice, when a thick control rod guide tube 4 needs to be used, several pressure tubes 1 forming a triangular lattice are used.
The control rod guide tube 4 is arranged at the position. In this case, since it is a pressure pipe, sufficient cooling is possible, and a control rod with a fuel follower can be used.

First, a more specific example of the equilateral triangular lattice will be shown.
When the control rod guide tube 4 is installed at the position of the pressure tube 1, the main dimensions when the grid size is set to 25 cm and a large-scale reactor employing 54 fuel assemblies and a heavy water to fuel volume ratio of 8.0 is designed are as follows. Show.

Lattice spacing l: 25.0 cm Pressure tube inner diameter: 12 cm Array: equilateral triangular grid array Number of fuel rods in fuel assembly: 54 Fuel pellet diameter: 1.0 cm Calandria tube core outer diameter: 16 cm with a heavy water to fuel volume ratio of 8.0 To be achieved.

Next, with reference to FIG. 5 and FIG. 6, an embodiment in which a cylinder is arranged on the outer circumference of a pressure pipe having a square lattice arrangement will be described. FIG. 5 is a diagram showing one embodiment of a structure in which a cylinder 9 is attached to the outer periphery of the calandria tube 1 for the calandria tube 1 of four square lattice-shaped arrays which is a unit inside the calandria tank 2 of the present invention. . The cylinder 9 is made of Zircaloy.
2, Made of metal such as zirconium-niobium alloy, aluminum alloy, etc., which has little neutron absorption and mechanical strength. The cylinder 9 has a circumferential direction of 2 to facilitate installation.
Alternatively, it can be divided into three parts, and the stopper 11 is moved in the stopper inserting direction 12 as shown in FIG. 12 to assemble as shown in FIG. Also,
If necessary, the cylinder 9 is divided into short pieces (50 cm to 200 cm) in the axial direction as well, and after connecting the calandria tube 1 to the upper tube sheet 6 and the lower tube sheet 7 of the calandria tank 2, as shown in FIG. The structure is such that it can be loaded into the calandria tank 2 and easily attached.

After installing all the cylinders 9, use heavy water 10 as a moderator.
Fill the Calandria tank 2.

As shown in FIG. 7, at the portion where the control rod guide tube 4 penetrates the upper tube plate 6 of the calandria tank 2, the mechanical parts of the joint between the calandria tube 1 and the control rod guide tube 4 and the upper tube sheet 6 are mechanically connected. In order to secure the strength, the required size of the minimum gap 8 between the calandria pipe 1 and the control rod guide pipe 4 must be secured.

Usually, since it is difficult to increase the diameter of the calandria tube of the upper tube sheet 6, conventionally, as shown in FIG. 6, a structure in which the diameter of the calandria tube 1 in the core of the calandria tank 2 is made larger than that of the upper part is used. It is adopted.

However, it is difficult to make the diameter of the calandria tube in the calandria tank extremely large because the shape of the expanded or throttled portion of the calandria tube is limited in terms of manufacturing and mechanical structure.

Therefore, the present invention proposes a structure in which the cylinder 9 is arranged on the outer periphery of the calandria tube 1 to reduce the shortage.

As shown in FIG. 7, the control rod guide tubes 4 and the neutron meter devices 5 of the number necessary for controlling and measuring the reactor power are
It is appropriately arranged in the gap of the Calandria tube arrangement.

Next, a more specific example in which the effect of the cylinder 9 is quantitatively shown will be described. The array is a square lattice array as shown in FIG.

Lattice spacing l: 24.5 cm Calandria tube outer radius R: 8 cm Number of fuel rods in fuel assembly n: 54 Fuel pellet radius r: 0.5 cm Applying cylinder thickness t: 1.0 cm, the heavy water to fuel volume ratio is from 9.4. Can be improved to 8.1.

Further, in order to exert economy, it is also possible to use a cylinder having a hollow wall itself as shown in FIG. The outer and inner plates 13 and 14 of the hollow cylinder are made of Zircaloy-2 or an aluminum alloy (1100), and a spacer 16 is used to maintain a gap in the hollow portion when necessary, and a split end 15
Are fixed with fasteners 11 or by welding. The circumferential ends of the outer plate 13 and the inner plate 14 are liquid-tightly welded to the divided ends 15 by welding points 18, and the facing divided ends 15 are connected by the stoppers 11. Each end of the hollow cylinder in the axial direction is liquid-tightly closed to form a hollow portion 17. The effective thickness of the hollow cylinder is from the outer surface of the outer plate 13 to the inner surface of the inner plate 14. A hollow cylinder with an effective thickness t = 1.2 cm was applied to a commercial grid-type reactor with a lattice spacing of l: 24 cm and a calandria tube outer radius of R: 8 cm, and the number of fuel rods in a fuel assembly was n: 48. In this case, the volume ratio of heavy water to fuel can be improved from 10 to 8.2.

Next, the control rod guide tube 4 is provided at the center of the triangular lattice,
Further, an embodiment in which a cylinder is arranged on the outer circumference of the calandria pipe in order to sufficiently improve the heavy water to fuel volume ratio will be described. For example, pressure tube inner diameter: 12 cm Array: equilateral triangular grid array Lattice pitch: 25.5 cm Number of fuel rods in fuel assembly: 54 Fuel pellet diameter: 1.0 cm Calandria tube core outer diameter: 16 cm Calandria tube upper tube outer diameter : 15cm Control rod guide tube outer diameter: 5cm Minimum clearance of upper tube sheet: 4.7cm Cylinder wall effective thickness: 0.5cm Heavy water to fuel volume ratio: 7.9.

According to the four embodiments described above, it has become clear that the heavy water to fuel volume ratio can be appropriately designed.

Although the void coefficient varies depending on the type of fuel used (plutonium mixed oxide fuel, uranium dioxide fuel), composition, enrichment, etc., according to the present invention, since the heavy water to fuel volume ratio can be optimally designed, As shown in Fig. 6, the void coefficient is
It is possible to obtain a value near 0 on the order of 10 ^-5 Δk / k /% void, and good operating performance can be obtained.

Further, since the core diameter can be reduced and the amount of heavy water can be reduced, it is also economically advantageous.

The cylinder 9 is mounted around the calandria pipe 1 by placing the completed cylinder 9 on the lower tube sheet 7 before attaching the calandria tube 1 to the calandria tank 2 and inserting the calandria tube 1 into the lower tube sheet 7. At the same time, a manufacturing method is adopted in which the calandria tube 1 is also inserted into the calandria tube 1 so that the cylinder 9 exists as a substitute for heavy water around the outside of the calandria tube 1. According to this method, it is not necessary to assemble the cylinder 9 around the calandria tube 1 in a narrow place, and it is less necessary to provide a wide space around the calandria tube 1 to secure a working space. The cylinder 9 is installed so as to be sandwiched between the upper and lower tube plates 7 and 8 via a spacer.

According to the arrangement of the calandria pipes 1 in the core in a triangular lattice shape, the volume ratio of heavy water to fuel can be appropriately set, and the reactivity coefficient such as the coolant void coefficient can be set to a more negative value,
It is possible to improve the self-control performance unique to the reactor. When the grid spacing is the same as before, the amount of heavy water is about 20% and the core diameter is about 7
%, Which is economically advantageous.

Further, when a cylinder is attached to the outer periphery of the calandria pipe 1 as a substitute for heavy water, the reactivity coefficient such as the void coefficient can be set to a more negative value, so that the self-controllability and the operation controllability are improved. . In addition, it has the effect of increasing the mechanical strength of the calandria tube.

Furthermore, the combined use of the triangular lattice array and the cylinders greatly improves the degree of freedom in design for improving drivability and economy.

In addition to the problems solved by the above-described embodiments, the next embodiment of the present invention has a problem to be solved to make the output distribution of the pressure tube reactor as uniform as possible.

 The example is as follows.

Generally, in the design range of a reactor using heavy water as a moderator, as the heavy water to fuel volume ratio becomes smaller, the coolant void reactivity coefficient tends to become smaller (self-controllability improves) as shown in FIG. There is. As shown in FIG. 16, the neutron multiplication factor tends to decrease as the ratio of heavy water moderator volume / fuel volume decreases.

In general, the same fuel has the advantage that the larger the neutron multiplication coefficient, the higher the burnup of the fuel (the better the fuel economy).

For this reason, an appropriate heavy water to fuel volume ratio is selected in consideration of self-controllability and fuel economy.

In addition, since neutrons leak in the peripheral portion of the core as compared with the central portion of the core, the neutron multiplication coefficient becomes small, the power density becomes small, and the flattening of the power distribution is adversely affected.

Therefore, in the following embodiments, the improvement of the self-controllability and the flattening of the output distribution can be achieved at the same time.

FIG. 17 shows the plane layout of the calandria tube 1, the neutron instrumentation tube, and the control rod guide tube in the calandria tank 2 in the core 4
In the Calandria pipe 1, a pressure pipe 3 through which the coolant 22 passes is built in as shown in FIG. 19, and a fuel containing pellet-shaped nuclear fuel is built in the pressure pipe 3. The bar 21 is built in. In the calandria tank 2 containing the heavy water 10, a number of calandria tubes 1 required to obtain the rated output of the pressure tube reactor are arranged in a square lattice shape, and the core is provided in some places between these lattices. A control rod guide tube 4 and a neutron instrumentation tube 5 necessary for the control and instrumentation of are installed. Further, if necessary, a poison tube for injecting poison into the heavy water of the core is also arranged in order to control the output of the core. Each of these pipes is inserted into the calandria tank 2, and each pipe and the upper tube plate 6 of the calandria tank 2 are arranged so that heavy water can be retained in the calandria tank 2.
And the lower tube sheet 7 is hermetically joined.

As shown in FIGS. 17, 18, and 19, a cylinder 9 is arranged around the outside of the calandria tube 1 in the center of the core in the calandria tank 2. The cylinder 9 may be attached so as to be supported by the calandria tube 1, or may be supported by the lower tube sheet 7 by removing a spacer.

As a material for the cylinder 9, a zirconium alloy (zircaloy-2, zircaloy-4, zirconium-niobium alloy, etc.), aluminum or an aluminum alloy is used as a metal having a small neutron absorption.

In order to increase the displacement volume of the cylinder 9 with heavy water,
As shown in the figure, the wall of the cylinder 9 itself is a hollow portion 17, and the hollow portion 17 is filled with a chemically stable gas such as helium or argon. Also in the previous embodiment, the cylinder 9
It is preferable that the hollow part 17 of the hollow type be filled with a chemically stable gas such as helium or argon. The hollow portion 17 is sealed as in the previous embodiment so that this gas does not escape. The cylinder 9 may be divided in consideration of installation as in the previous embodiment, and when divided, the divided end is configured so that it can be connected by a stopper as in the previous embodiment. .

The fuel rod built in the pressure pipe where the coolant flows is
With 60 fuel assemblies, the fuel assemblies are contained in the pressure pipe.

Below, a quantitative description will be given of an example in which a cylinder 9 having a hollow wall as a substitute for heavy water is provided around the outside of the calandria tube 1.

This example is an example in which the present invention is applied to a pressure tube reactor having an electric output of 1,000 MW, in which heavy water is used as a moderator and light water is used for cooling. The design example is shown below.

Electric output: 1,000 MW Number of pressure tubes: 688 Number of fuel rods in fuel assembly n: 60 Core effective height: 3.7 m Core radius: 7.8 m Fuel pellet radius r: 0.475 cm Pressure tube inner diameter: 12.3 cm Pressure Tube lattice spacing l: 24.5 cm Calandria tube outer radius R: 8.25 cm Control rod guide tube outer diameter: 9.5 cm Effective thickness of hollow cylinder t: 1.8 cm Number of Calandria tubes 1 to install hollow cylinders: 344 hollow cylinders Axial length to be installed: 2.22m Minimum clearance in the upper tube sheet (distance between the calandria tube 1 and the control rod guide tube 4): 4.3cm In this design example, the heavy water to fuel volume ratio of the part without the cylinder is It is 9.1, and that of the part where the tube is attached (core central part) is 6.7. Thus, when the heavy water to fuel volume ratio in the central part of the core is made smaller than that in the peripheral part, as can be seen from FIG. 16, the neutron multiplication factor in the central part of the core is larger than that in the peripheral part.
It gets smaller. For this reason, the number of neutrons generated in the central part decreases, and in combination with the output decrease in the peripheral part due to neutron leakage in the peripheral part, as shown in FIG. 20, the curve showing the output peaking coefficient is a solid curve rather than a dotted curve. Then, the power distribution in the core axis direction (vertical direction) becomes flat. Since the same can be said in the radial direction of the core, the power distribution in the axial direction and the radial direction of the core can be flattened.

In the above design example, the total (effective) heavy water to fuel volume ratio of the core is around 8, and as shown in FIG. 4, the void coefficient is 0 ⁻⁵ ΔK / k /% on the order of voids. The value can be set to a value close to the above value, good operation performance can be obtained, and the output distribution can be improved by about 20% without spoiling the neutron economy as much as possible, which is also advantageous from the economical aspect. Thus, according to this embodiment, the volume ratio of heavy water to the fuel rods can be appropriately set, the coolant void coefficient can be set to a more negative value, and the self-control performance unique to the reactor can be improved. In addition, since the cylinder 9 can be partially provided in a portion having a high power density to flatten the power distribution in the furnace, the number of control rods for the flattening can be reduced and the core performance management can be facilitated. It has a great advantage in terms of driving performance and economy.

If the cylinder 9 is thicker as the cylinder 9 arranged closer to the center of the core in the radial direction, the flattening of the output in the radial direction can be better achieved. In addition, if the thickness of the cylinder 9 is increased toward the center in the axial direction, flattening of the output in the axial direction can be achieved.

Furthermore, if the arrangement of the calandria pipes is made into a triangular lattice-like arrangement, even with this arrangement, the heavy water to fuel volume ratio can be adjusted without increasing the calandria tank,
The freedom of adjustment and design is expanded.

In any of the embodiments, it is preferable to set a slight gap between the calandria pipe and the cylinder, through which heavy water flows.

〔The invention's effect〕

According to the invention of claim 1, since the arrangement of the calandria pipes is made into a regular triangular lattice and the heavy water to fuel volume ratio is arranged in the calandria tank at a density of 9.0 or less, the amount of heavy water per calandria pipe is large. And the ratio of heavy water to fuel rods can be improved to improve self-control performance, and at that time, the Calandrita tank that holds the heavy water does not become large.

According to the second aspect of the present invention, a substitute with less neutron absorption is provided as a substitute for heavy water in the outer periphery of the calandria tube so as not to impair the neutron economy, so that the volume ratio of heavy water to fuel rods is improved by the substitute. However, the neutron economy is good, and the plate replacement is placed near the outer circumference of the calandria pipe in addition to the calandria pipe, so that the control performance can be economically improved without increasing the size of the calandria tank.

According to the invention of claim 3, the core structure capable of obtaining the same effect as that of claim 2 is loaded with the tubular structure divided after the setting of the calandria pipe as a replacement and the replacement is carried around the calandria pipe. Because I tried to assemble it in a tubular shape,
The tubular substitute can be easily carried in and assembled even in a narrow space.

According to the invention of claim 4, a core structure capable of obtaining the same effect as that of claim 2 can be easily manufactured by inserting the calandria tube into the tubular substitute at the same time when setting the calandria tube.

According to the fifth aspect of the present invention, it is possible to provide a heavy water substitute that improves the volume ratio of heavy water to fuel rods in the direction of improving self-controllability, and at that time does not lead to an increase in the size of the calandria tank.

According to the invention of claim 6, in addition to the effect of the invention of claim 2, by setting the volume ratio of heavy water to fuel rods to be 9.0 or less, the void coefficient can be made sure to be in the vicinity of zero or in the negative region to ensure the self-control performance. Improve to.

According to the invention of claim 7, in addition to the effect of the invention of claim / or claim 6, the volume ratio of heavy water to the fuel rods of the entire tube including the tubes in the core other than the calandria tube can be controlled by the self-control performance. It is easy to make arrangements for improvement in a positive direction.

According to the invention of claim 8, in addition to the effect of any one of claims 1, 2 and 6, since the control rod can be cooled by the coolant in the pressure pipe, the control rod with the fuel follower is used as the control rod. become able to.

According to the invention of claim 9, in addition to the effect of any one of claims 1, 2, 6, 7, 8, and 9, the metal having less neutron absorption surrounds the outer periphery of the calandria tube as a substitute. Therefore, the neutron economy is good and the effect of neutrons on the fuel is evenly obtained.

According to the invention of claim 10, when the effect according to the invention of claim 9 is obtained, the substitute can be obtained in a tubular shape or a divided tubular shape that can be easily obtained by pressing or drawing. According to the invention of claim 11, in addition to the effect of the invention of claim 10, since the cylinder is hollow, the amount of replacement with heavy water is large for the lightweight, and the neutron absorption is hollow for the large thickness. Since the amount of fuel is small, the volume ratio of heavy water fuel can be improved more economically.

According to the twelfth aspect of the invention, in addition to the effect of the tenth or eleventh aspect of the invention, since the cylinder is divided, it can be easily carried out even if the loading and assembling into the core is narrow.

According to the invention of claim 13, in addition to the effect of the invention of claim 2 or 9, in addition to the property of little neutron absorption, corrosion resistance and corrosion resistance can be obtained by using a zirconium alloy or aluminum or aluminum alloy as the material of the substitute. A practical structure with sufficient strength can be obtained.

According to the invention of claim 14, in addition to the effect of any of the inventions of claims 2, 9, 10, 11, 12, 13 and by devising the arrangement of the calandria pipe, Since the doria tank can be made without increasing the size, the degree of freedom in design is expanded.

According to the invention of claim 15, in addition to the effect of the invention of any one of claims 9, 10, 11, 12, 13 is, the substitution of heavy water is adopted in the region of relatively high power density in the core. , Because it is not adopted elsewhere, the neutron economy is good and the output distribution can be flattened.

According to the invention of claim 16, in addition to the effect of the invention of claim 15, by changing the thickness of the heavy water substitute for each power density region in the core, or the thickness of the substitute in the axial direction Since the thickness of the substitute is changed in proportion to the power density by using the difference or both,
The output distribution can be flattened better.

[Brief description of drawings]

FIG. 1 is a plan sectional view of the interior of a calandria tank showing an arrangement of calandria tubes in an embodiment of a pressure tube type reactor according to the present invention, and FIG. 2 is a calandria showing the structure of the reactor core portion of FIG. FIG. 3 is a side sectional view of the tank, FIG. 3 is an enlarged view showing an arrangement of pressure pipes as a unit of a portion including the control rod guide pipe or the neutron instrumentation pipe of the embodiment of FIG. 1, and FIG. 4 is a pressure pipe type. FIG. 5 is a graph showing the relationship between the void reactivity coefficient of a nuclear reactor and the volume ratio of heavy water to fuel, and FIG. 5 shows an embodiment in which a cylinder is attached to the outside of the calandria pipe in the calandria tank of the pressure tube reactor according to the present invention. FIG. 6 is a plan sectional view showing
FIG. 7 is a vertical cross-sectional view of the calandria tube portion of the embodiment shown in FIG. 7, and FIG. 7 is a plan view showing the penetration state of the tube of the upper tube sheet of the embodiment of FIG.
FIG. 8 is a sectional view showing the entire arrangement of the pipes inside the calandria tank of the embodiment of FIG. 5, FIG. 9 is a view of the present invention, and is a perspective view showing a mounting state of a cylinder by a stopper.
FIG. 10 is a view of the present invention, which is a partial cross-sectional view showing a mounting state of a cylinder by a stopper, FIG. 11 is a view of the present invention, which is a layout drawing of an equilateral triangular array of pipes, and FIG. 12 is Arrangement view of a square lattice arrangement of tubes, FIG. 13 is a view of the present invention, a plan sectional view showing a part of a hollow cylinder, FIG. 14 is a view showing an example of an arrangement of conventional Calandria tubes , FIG. 15 is a layout drawing showing the arrangement of pressure tubes as a unit of the conventional example of FIG. 14, and FIG. 16 is a graph showing the relationship between the neutron multiplication factor and the heavy water fuel volume ratio of the pressure tube reactor. FIG. 17 is a diagram of the present invention, a plane sectional view of a region of a quarter of the core of a pressure tube reactor, FIG. 18 is a diagram of the present invention, and FIG. Fig. 19 is a longitudinal sectional view of a 1/4 region, Fig. 19 is a diagram of the present invention, a plane sectional view of a 1/4 region in a calandria tube, Fig. 20 is a diagram of the present invention, and the axial direction of the core In Is a graph showing the force peaking factor. 1 ... Calandria tube, 2 ... Calandria tank, 3
...... Pressure tube, 4 Control rod guide tube, 5 Neutron instrumentation tube, 6 upper tube plate, 7 lower tube plate, 8 minimum gap, 9 cylinder, 10 heavy water , 11 …… stopper, 12 …… stopper insertion direction, 13 …… hollow cylinder outer plate, 14 …… hollow cylinder inner plate, 15 …… hollow cylinder split end, 16 …… spacer,
17 ... Hollow part, 18 ... Welding part.

Front Page Continuation (72) Kenichi Suzuki Inventor Kenichi Suzuki, 1-1, Sachimachi, Hitachi, Ibaraki Inside Hitachi Factory, Hitachi, Ltd. (56) References JP-A-2-243996 (JP, A)

Claims (16)

[Claims] 1. A heavy water deceleration pressure tube reactor in which a pressure pipe containing nuclear fuel and through which a coolant flows is contained in a calandria pipe, and the calandria pipe is arranged in a calandria tank containing heavy water. A pressure tube reactor characterized in that the tubes were arranged in an equilateral triangular lattice at a density such that the volume ratio of heavy water to fuel was 9.0 or less. 2. A heavy water deceleration pressure tube type nuclear reactor in which a pressure pipe containing a nuclear fuel and through which a coolant flows is contained in a calandria pipe, and the calandria pipe is arranged in a calandria tank containing heavy water. A pressure tube reactor characterized in that a substitute having a small amount of neutron absorption is arranged in the outer periphery of the pipe in addition to the calandria pipe replaced with the heavy water in the vicinity of the outer periphery thereof. 3. A pressure tube reactor for forming a heavy water holding region by liquid-tightly attaching a calandria pipe passing through the calandria tank to a constituent member of the calandria tank, wherein the calandria tank is included in the constituent member of the calandria tank. After fixing the pipe, a plurality of divided cylinders made of a material having a small neutron absorption are carried into the outer periphery of the calandria pipe, and the plurality of divided pipes are assembled into a shape covering the outer periphery of the calandria pipe. A method for assembling a pressure tube type reactor characterized by. 4. A tubular member made of a material having a low neutron absorption in a pressure tube type reactor for forming a heavy water holding region by liquid-tightly attaching a calandria pipe passing through the calandria tank to a constituent member of the calandria tank. To the holding area of the heavy water, and then when the calandria pipe is inserted into the component parts of the calandria tank, the calandria pipe is also inserted into the tubular member that has already been carried in, and then the calandria tank is inserted. A method for assembling a pressure tube nuclear reactor, characterized in that the calandria tube is attached to the above-mentioned constituent members. 5. A member arranged on the outer periphery of a calandria pipe of a pressure tube type reactor, wherein the member is made of a material having a small neutron absorption, and has an assembly shape of a cylindrical shape which can be inserted through the calandria pipe. A substitute for a heavy water moderator for a pressure tube reactor characterized by being a member. 6. The heavy water to fuel volume ratio as set forth in claim 2.
A pressure tube type reactor characterized in that the pressure tubes are arranged in an equilateral triangular lattice at a density of 0 or less. 7. The pressure according to claim 1, wherein some of the pressure tubes are replaced with a control rod guide tube of a nuclear reactor, a neutron meter device inner tube, or a poison tube. Tube reactor. 8. A pressure tube nuclear reactor according to claim 1, wherein a control rod with a fuel follower is arranged in a coolant inside some of the pressure tubes. 9. The calandria tube according to any one of claims 1, 2, 6.7 and 8, wherein a metal made of a material having a small neutron absorption so as to surround the outer periphery of the calandria tube as a substitute for heavy water is the calandria tube. A pressure tube reactor characterized by being installed separately. 10. The pressure tube type nuclear reactor according to claim 9, wherein the metal as a substitute for the heavy water has an assembled shape that forms a cylinder surrounding the outer periphery of the calandria tube. 11. The pressure tube reactor according to claim 10, wherein the cylinder as the substitute for the heavy water has a hollow wall itself. 12. The method according to any one of claims 10 and 11,
The pressure tube reactor, wherein the cylinder as the substitute of the heavy water is composed of a plurality of parts divided in at least one of a circumferential direction and an axial direction. 13. The pressure tube reactor according to claim 2, wherein the material of the substitute for heavy water is a zirconium alloy, aluminum or an aluminum alloy. 14. The pressure tube reactor according to claim 2, wherein the calandria tubes are arranged in an equilateral triangle shape. 15. The replacement of heavy water according to any one of claims 9, 10, 11, 12, and 13, wherein the replacement of heavy water is arranged in a region of relatively high power density in the calandria tank. And a pressure tube reactor. 16. The pressure tube nuclear reactor according to claim 15, wherein the heavy water substitute has a thickness increased in proportion to a power density.