JP2814981B2 - Fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel fuel assembly for a light water reactor, and more particularly to a fuel assembly loaded in a boiling water reactor.

[0002]

2. Description of the Related Art In recent years, the operation cycle of light water reactors has been prolonged,
There is increasing interest in increasing the burnup of uranium fuel. The reason is that there are high economic merits such as a reduction in the amount of spent fuel emitted and a reduction in power generation costs. In particular, nuclear power generation in Japan is based on the preprocessing of spent fuel, and there is a high demand for high burnup, including the reuse of plutonium extracted by reprocessing. The current removal burnup is about 3
Although it is 0 GWd / t, if the high burn-up fuel of the 60 GWd / t class is realized, the above-mentioned merit becomes higher.
Conventionally, in order to achieve the high burnup of the above light water reactors, improvement of corrosion resistance of materials, prevention of deformation of members under neutron irradiation environment, optimization of uranium fuel enrichment and layout, optimization of thermal hydraulic characteristics of fuel assemblies Improvements have been made.

[0003] High burnup fuel assembly members are required to have higher corrosion resistance than conventional materials. Current fuel assembly materials include Zircaloy (Zry: Zr-Sn-Fe-Cr-Ni alloy, component and composition (% by weight) Sn: 1.2-1.7%, F
e: 0.07 to 0.24%, Cr: 0.05 to 0.15%,
Ni: <0.08%, residual Zr and impurities) are used. Local corrosion called nodular corrosion occurs in a Zircaloy fuel assembly member in a boiling water reactor (BWR) environment. In order to prevent this corrosion, a method of improving the corrosion resistance of Zircaloy by a heat treatment in which it is heated to the α + β phase or β phase temperature range for a short time and then quenched (Japanese Patent Publication No. 61-61)
No. 45699, JP-B-63-58223) are known. Further, a technique for improving corrosion resistance by changing the alloy composition is also known, and JP-A-60-43450 and JP-A-62-228442 are known as alloys in which the amounts of Fe and Ni added to zircaloy are increased. I have.

[0004] Since the above Zr alloy member is used in a neutron irradiation environment, it undergoes irradiation growth deformation. In particular, when bending deformation or bulging deformation occurs in the channel box (FCB), the control rod driving gap is closed and the operation of the reactor is hindered. As a technique for preventing these deformations, Japanese Patent Application Laid-Open No. 59-229475 discloses a method of controlling the (0002) plane of hexagonal crystal Zr in the FCB longitudinal direction (FL value) to 0.15 to 0.5 to suppress irradiation growth. A gazette is known.

[0005] In a boiling water reactor, unsaturated cooling water flows from the lower tie plate of the fuel assembly into the fuel rod gap, and is heated and boiled as it flows between the fuel rods from the lower part to the upper part, resulting in a steam void. And flows out of the upper tie plate as a two-phase flow of water and water. The void fraction is 0% at the lower part of the fuel assembly but reaches about 70% at the upper part. That is,
The ratio of the number of hydrogen (H) to the number of heavy metal atoms (U) (H / U ratio) in the lower part and the upper part of the fuel rod is different. In the lower portion of the fuel assembly having a high H / U ratio, the average neutron energy is reduced, and the fission reaction with the nuclear fuel material is promoted. In the upper portion of the fuel assembly having a low H / U ratio, the fission reaction between the neutron and the nuclear fuel material is suppressed. You. As a result, the linear power density is higher at the lower part of the fuel assembly than at the upper part of the fuel assembly, and the power distribution in the axial direction of the fuel rod becomes non-uniform. The uneven power distribution also occurs in the radial direction of the fuel assembly. 8 × 8,9 × 9,10
The outermost periphery of the fuel rods arranged in a square lattice such as × 10 is F
It is surrounded by CB, and a water gap is formed between adjacent FCBs. That is, since the H / U ratio at the outermost periphery of the fuel assembly is higher than that inside the fuel assembly, the linear output density becomes higher. It is necessary to increase the uranium enrichment in order to achieve long-term operation cycles and high fuel burnup, and in fuel assemblies with high uranium enrichment, such uneven power density distribution will be further expanded. Become. In order to flatten the power distribution in the axial and radial directions, the shape and arrangement of the water rod, the distribution of uranium enrichment, the fuel length and the burnable poison such as Gd and B are changed. Is used to prevent local output peaking in the early stage of combustion.

[0006]

The above-mentioned prior arts are all elemental technologies. Even if a certain elemental technology is excellent, even if a part of the fuel assembly is inconvenient, a high burnup fuel assembly cannot be realized. For example, JP-A-59-2294
No. 75 discloses that the FL value is controlled to 0.15 to 0.5 as the orientation of the crystal orientation of the channel box to prevent irradiation growth and bending deformation. (Fr value) is important. Further, the fuel rod grows by irradiation and becomes longer than the initial length. As a result, the following inconveniences occur. Since the lower fuel rod is fixed to the lower tie plate, the longer fuel rod pushes up the upper tie plate. Since the upper part of the channel box is fixed to the upper tie plate, and the lower part of the channel box is inserted in the lower tie plate, the channel box is pushed upward by the irradiation growth of the fuel rods. The fitting allowance with the box is significantly reduced. In the case of the high burn-up fuel, since the irradiation growth amount of the fuel rod is large, there is a problem that the channel box is pushed upward beyond the fitting allowance between the lower tie plate and the channel box. An object of the present invention is to provide a fuel assembly for high burnup.

In order to load uranium of a predetermined amount or more in a limited space in the channel box, it is necessary to reduce the thickness of a zirconium alloy member such as a fuel cladding tube and a spacer. This is because the uranium loading space is reduced in the conventional fuel cladding tubes and spacers with the increase in the number of fuel rods arranged in a square lattice and the diversification of the shape of the water rods. When the thickness of the zirconium alloy member such as the fuel cladding tube and the spacer is reduced, hydrogen embrittlement due to the reduced thickness is particularly concerned. Hydrogen is generated by the corrosion reaction with the reactor water and a part of the hydrogen is absorbed by the member. However, even if the amount of absorbed hydrogen is the same, if the wall thickness is small, the hydrogen concentration of the member increases.
Corrosion of the fuel assembly members used up to a high burnup proceeds further than before, and therefore, higher corrosion resistance and lower hydrogen absorption characteristics are required for the high burnup fuel cladding tubes and spacers. An object of the present invention is to provide a fuel assembly for high burnup in which the corrosion resistance and hydrogen absorption resistance of a fuel assembly member and the bending deformation of a channel box caused by irradiation growth are optimized.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a plurality of fuel rods in which nuclear fuel is loaded in a zirconium-based alloy cladding tube, a spacer for arranging the fuel rods at desired positions, and the arranged fuel. An upper tie plate and a lower tie plate supporting the rod at the upper and lower ends thereof, and a zirconium-based alloy channel box covering the outer periphery of the zirconium-based alloy water rods arranged in the spacer integrally. In the fuel assembly provided with a burnup of 50 to 55 GWd / t , the cladding tube has a higher solid solution amount of tin, iron and nickel on the outer surface than a solid solution amount of the alloy element on the inner surface. The channel box and the water rod have an orientation ratio (Fr value) of the <0001> crystal orientation in the plate thickness direction of 0.25 to 0.50,
The corners of the channel box are thicker than the sides,
The cladding tubes, spacers and a channel box, by weight, of tin 1-2%, iron from 0.20 to 0.50%, chromium 0.0
5 to 0.15% and 0.03 to 0.16% nickel and the balance substantially zirconium. In particular, these are α
The fuel assembly is characterized in that fine intermetallic compounds of tin and nickel are extremely finely precipitated in the zirconium crystal grains of the phase.

According to the present invention, in the above-described fuel assembly, the cladding tube is quenched to a thickness of not more than half of the thickness, and the solid solution amount of the alloy element on the outer surface is increased by the solid solution of the alloy element on the inner surface. Preferably, it is higher than the dissolution amount.

After the final hot working, the spacer is subjected to a quenching treatment in which the spacer is rapidly cooled from the α + β phase or B phase temperature range.

The channel box and the water rod have an orientation ratio (Fr value) of 0.25 to 0.50 in the thickness direction (thickness direction) of the <0001> crystal orientation and an orientation ratio in the longitudinal direction (or rolling direction). It is preferable that (FL value) is 0.203 to 0.36 and the orientation ratio (Ft value) in the width direction (direction perpendicular to the rolling direction) is 0.25 to 0.36.

The member made of the zirconium-based alloy to be β-quenched preferably has a β-phase Zr average particle size of 50 to 300 μm.

According to the present invention, a plurality of fuel rods in which nuclear fuel is loaded in a cladding tube made of a zirconium-based alloy, a spacer for arranging the fuel rods at desired positions, and upper and lower ends of the arranged fuel rods are provided. And a zirconium-based alloy channel box that assembles integrally with a zirconium-based alloy water rod disposed in the spacer and covers the outer periphery of the upper tie plate and the lower tie plate supported in the spacer, up to 45 GWd / t. In the fuel assembly exposed to the burnup, the cladding tube is quenched, and the solid solution amount of iron and nickel on the outer surface is higher than the solid solution amount of the alloy element on the inner surface, and the channel box Is formed of a rectangular tube whose corners are thicker than the sides, and wherein the channel box and the water rod have a thickness of <000 in the thickness direction.
1> The orientation ratio (Fr value) of the crystal orientation is 0.25 to 0.50, and the cladding tube, the channel box and the water rod are tin 1.2 to 1.7% by weight, iron 0.07 to 0.20
%, Chromium 0.05 to 0.15%, nickel 0.03 to 0.1%
08% and the balance is the weight substantially zirconium and the spacer, tin 1-2%, iron from 0.20 to 0.50%, Black
Arm 0.05-0.15, in the fuel assembly, characterized in that 0.03 to 0.16 percent nickel and the balance being substantially zirconium.

According to the present invention, a plurality of fuel rods in which nuclear fuel is loaded in a cladding tube made of a zirconium-based alloy, a spacer for arranging the fuel rods at desired positions, and upper and lower ends of the arranged fuel rods are provided. And a zirconium-based alloy channel box that assembles integrally with a zirconium-based alloy water rod placed in the spacer and covers the outer periphery of the upper tie plate and the lower tie plate supported in the spacer, up to 38 GWd / t. In the fuel assembly exposed to the burnup, the cladding tube is quenched, and the solid solution amount of iron and nickel on the outer surface is higher than the solid solution amount of the alloy element on the inner surface, and the channel box Consists of a straight welded rectangular tube with a substantially uniform thickness at the corners and sides. The channel box and water rod are Has a <0001> crystal orientation orientation ratio (Fr value) of 0.25 to 0.50, and the cladding tube, the spacer, the channel box and the water rod are tin 1.2 to 1.7% by weight and iron A fuel assembly comprising 0.07 to 0.20%, 0.05 to 0.15% chromium, 0.03 to 0.08% nickel and the balance substantially zirconium.

Preferably, the spacer is subjected to a quenching treatment after the final hot working in which the spacer is rapidly cooled from the α + β phase or β phase temperature range.

According to the present invention, a plurality of fuel rods in which nuclear fuel is loaded in a cladding tube made of a zirconium-based alloy, a spacer for arranging the fuel rods at a desired position, and the upper and lower ends of the arranged fuel rods are provided. And a zirconium-based alloy channel box that assembles integrally with a zirconium-based alloy water rod disposed on the spacer and covers the outer periphery of the upper tie plate and the lower tie plate supported by the spacer, and has a capacity of up to 32 GWd / t. In the fuel assembly exposed to the burnup, the cladding is quenched so that the solid solution amount of iron and nickel on the outer surface is higher than the solid solution amount of the alloy element on the inner surface, and the channel box is The channel portion and the water rod are made of a straight welded rectangular tube having a substantially uniform thickness at the corners and sides. <0001> orientation ratio of crystal orientation (Fr value) of 0.25 to 0.50, the cladding tube, also
Is the cladding tube and channel box by weight, tin 1.2-
1.7%, iron 0.07 to 0.20%, chromium 0.05 to 0.5%
15% in fuel assemblies from 0.03 to 0.08 percent nickel and the balance being substantially <br/> zirconium arm or Ranaru.

This spacer is also preferably subjected to a quenching process of rapidly cooling from the α + β phase or β phase temperature range after the final hot working.

In the channel box according to the present invention, the plate made of the zirconium-based alloy is bent into a U-shaped member, and the U-shaped member is welded and connected to form a rectangular tube long member. The zirconium-based alloy of the zirconium-based alloy is moved by longitudinally moving the rectangular cylindrical long member, continuously heating and holding the same locally in the β-phase temperature region for a short period of time, and forcibly cooling the heated portion with a refrigerant. 000
1> The orientation ratio (Fr value) of the crystal orientation in the thickness direction is 0.25.
To 0.50.

The cladding tube according to the present invention is a thick-walled tube made of the zirconium-based alloy after the final hot plastic working or is moved in the longitudinal direction at any stage after the working and before the final cold plastic working. A quenching step in which the tube outer surface is locally heated and held for a short time while the tube inner surface is continuously cooled in the (α + β) phase or β phase temperature region, and the heated tube outer surface is forcibly cooled by a refrigerant. It is characterized by having.

The spacer according to the present invention moves in the longitudinal direction at any stage of the thick-walled tube made of the zirconium-based alloy after the final hot plastic working or the thin-walled tube after the working and before the final cold plastic working. A spacer cell having a quenching step of continuously heating and maintaining the (α + β) phase or β phase temperature region locally for a short time while forcibly cooling the heated portion with a refrigerant. And a frame formed integrally with the plate by a plate having the quenching step.

[0021] In another aspect of the present invention, the tube is replaced with a spacer having a lattice cell and a frame integrally forming the cell by a plate having the quenching step.

The present invention is based on the invention that, by weight, 1-2% tin, 0.2% iron.
0 to 0.50%, chromium 0.05 to 0.15%, nickel
0.03% to 0.16% and the balance substantially zirconium
Consisting of a zirconium-based alloy plate consisting of
<0001> Crystal orientation ratio (Fr value) of 0.25 or more
0.50, the orientation ratio (FL value) in the longitudinal direction (rolling direction)
0.25 to 0.36 and width direction (direction perpendicular to the rolling direction)
Has an orientation ratio (Ft value) of 0.25 to 0.36.
It is in the water rod for fuel assembly. In addition
Ming is tin 1.2 to 1.7% by weight, iron 0.07 to 0.20
%, Chromium 0.05 to 0.15%, nickel 0.03 to 0.1%
08% and the balance substantially zirconium
<0001> crystal in thickness direction
Orientation ratio (Fr value) 0.25 to 0.50, longitudinal direction
(Rolling direction) orientation ratio (FL value) is 0.25 to 0.36 and
Orientation ratio (Ft value) in the width and width direction (direction perpendicular to the rolling direction)
The fuel assembly has a diameter of 0.25 to 0.36.
On the water rod. The water rod according to the present invention, while moving in the longitudinal direction the final cold-plastically formed long tube made of the zirconium-based alloy, continuously and locally heats and maintains the heating in the β-phase temperature region for a short time. Forcibly cooling the zirconium-based alloy in the pipe thickness direction of the <0001> crystal orientation of the zirconium-based alloy in the pipe thickness direction (Fr value) from 0.25 to 0.50, (FL value) is 0.25 to 0.36 and the orientation ratio (Ft value) in the circumferential direction of the tube is 0.25 to 0.36.

(1) The deformation of the zirconium alloy member used for the channel box occurs because the <0001> crystal orientation of the hexagonal Zr is oriented substantially perpendicular to the member surface. Upon receiving neutron irradiation, the hexagonal lattice shrinks in the <0001> direction and expands in a direction perpendicular to the <0001> direction. Strictly speaking, neutron irradiation introduces a dislocation plane (atomic plane) in the <0001> direction, causing contraction and expansion in the specific direction. As a result, the channel box extends in the longitudinal direction and the width direction, and contracts in the thickness direction. The fuel rods extend longitudinally. Higher neutrons are received near the center of the core, and lower near the core. The channel box arranged around the core where the neutron irradiation amount changes rapidly has a difference in elongation between the surface on the center side of the core and the surface facing the surface, and is bent. The above deformation caused by neutron irradiation is a deformation that does not involve a change in volume. Even if individual crystal grains of the polycrystal are deformed in a specific direction, if the direction is random, it is equivalent to no deformation as a whole. Therefore, to suppress irradiation growth and bending, it is effective to randomize the crystal orientation.

In the present invention, the crystal orientation of the water rod as well as the channel box is randomized, and the crystal orientation of the fuel cladding tube is not randomized. As a result, only the fuel rods become longer due to the irradiation growth, and the lengths of the channel box and the water rod do not change. The position of the upper tie plate does not change because the water rod connected to the upper tie plate does not change in length. Even when the fuel rod is extended, the upper end plug of the fuel rod is not connected to the upper tie plate and only penetrates the hole provided in the upper tie plate, so that a force for pushing up the upper tie plate is generated. Without pushing up the channel box associated with the upper tie plate. as a result,
The fitting margin 8 does not decrease. That is, the problem of fuel rod elongation is eliminated by the fuel rod upper end plug protruding from the upper tie plate.

For quantitative evaluation of the degree of orientation of crystal orientation, usually,
Measure the diffraction intensity of the reflected and transmitted X-rays of the specific crystal plane,
A method of calculating the F value from (Equation 1) is generally used.

[0026]

(Equation 1)

In equation (1), φ is a specific direction (for example, a direction perpendicular to the plate surface) and a specific crystal orientation (for example, <000
1> crystal orientation), and V (φ) is the volume fraction of the crystal oriented in the φ direction. In the r direction, L direction, and t direction, the orientation rates of the normal direction (r), the longitudinal (rolling) direction (L), and the width direction (t) of the plate surface perpendicular to each other are F, respectively.
Assuming that r, FL and Ft are used, the value obtained by totaling them is 1, and when each value is 1/3, it indicates that the crystal orientation is completely random.

<0 of plate and tube manufactured by cold rolling
001> The crystal orientation is oriented in the normal direction (r direction) of the plate (tube) surface, and its Fr value is 0.6 to 0.7 and FL value is 0.05 to 0.5.
It becomes 15. Calculation results showing the effect of the Fr value on the amount of bending of the channel box irradiated with one cycle at the periphery of the furnace and the channel box irradiated with four cycles at the center of the core after three cycles of irradiation at the center of the core were examined. One cycle: operation for 18 months, and the neutron irradiation amount at the time of removing the fuel assembly is about 2 × 10 ²² (n / cm ² ). This is the most standard shuffling pattern. The amount of bending further increases as the stay cycle in the furnace periphery increases. The gap between the control rod and the channel box is about 3.3 mm at the initial stage of fuel loading, and the amount of deformation due to bulging in addition to bending deformation is about 2.2 mm. That is, in the channel box which has experienced the core peripheral region, when the bending by irradiation growth becomes 1.1 mm, the channel box and the control rod interfere with each other. It can be seen that the Fr value of the channel box experiencing the core peripheral region needs to be randomized to 0.25 or more. Further, it can be seen that the Fr value of the channel box that does not experience the core peripheral region needs to be randomized to 0.20 or more.

In order to randomize the crystal orientation, the zirconium alloy member is heated to the β phase temperature range (≧ 980 ° C.)
A method of cooling after growing Zr crystal grains is effective.
By this heat treatment, the hexagonal αZr crystal grains oriented in a certain direction are transformed into cubic βZr.
Transforms to Zr. In the state cooled to room temperature, the crystal system of the crystal grains is hexagonal αZr as before heating, but the orientation of the member transformed to cubic βZr is randomized. This randomization proceeds as the heating temperature is higher and the heating time is longer. In order for the Fr value to be equal to or greater than 0.20, the heat treatment parameter: P should be P = (3.5 + logt) × log (T-980) t: heating time (h), T: heating temperature (° C.) 0.8 or more It is necessary to control the heating temperature and the heating time so as to satisfy the following condition. Preferably, P ≧ 1.5. When P = 0.8, the average particle size of βZr crystal grains is 50 μm, and P ≧
At 1.5, the average particle size of the βZr crystal grains is 90 μm or more. It is preferably at most 300 μm or less.
１３０130 μm is preferred.

The F value of the channel box or the water rod of the present invention is FL 0.25 to 0.36, Ft 0.25 to 0.2.
36 and Fr 0.28 to 0.50 are preferred.
Is greater than Ft, FL, FL 0.30 to 0.35, Ft
0.30 to 0.35 and Fr 0.30 to 0.35 are most preferred. Ideally, both are 0.3333. These F values are determined by the heating temperature and the heating time. In particular, the treatment can be performed at a treatment temperature of 980 to 1350 ° C, and preferably 1050 to 1150 ° C. At such a temperature, the holding time is preferably as short as about 1 second to 1 minute.

As a method of manufacturing the channel box of the present invention, the heating in the β-phase temperature range is performed by heating the plate material locally and continuously for a desired holding time by an induction coil while simultaneously forcibly cooling after the heating. By heating the β phase, the <0001> orientation becomes random and a material having high corrosion resistance to high-temperature and high-pressure pure water can be obtained. Cooling is preferably performed by a fountain,
It is preferable to set the cooling rate to at least 150 ° C./sec. Infrared and electric furnaces are also used as heating means.

When heating in the β-phase temperature region, it is preferable to fix and restrict the member by using a member having a larger thermal expansion coefficient than that of the Zr-based alloy. Particularly, in the case of a tubular member, heat is applied so that the entire surface does not contact the inner surface of the member. It is preferable to insert a metal member that is partially in contact with each other and to fix both ends to each other to perform heating and cooling so that the tubular member is not deformed during heating and cooling. By providing such a restraining member, heating and cooling can be easily performed. SUS304,316,
Austenitic stainless steel such as 347 is preferred.

After the β-phase heat treatment, annealing for uniformly heating the whole is performed. Annealing is performed at 500 to 650 ° C. It is preferable that the annealing is also performed by restraining by the above-described restraining member, so that the tubular member can be shaped. These heat treatments are performed in a non-oxidizing atmosphere, particularly preferably in Ar.

After the final heat treatment, the oxide film on the surface is removed by sandblasting and pickling. After the oxide film is removed, the surface is oxidized by an autoclave, and a stable oxide film is formed on the surface to obtain a final product. In addition, the ends such as the screw holes for fixing at the both ends described above are used after being removed.

The channel box of the present invention is used after two U-shaped members are butted and plasma-welded into a rectangular tube, and the welded portion is flattened. An X-shaped restraining member is preferable for the heat treatment of the square tube. The heat treatment of the present invention may be in any state of a plate material, a U-shape, or a rectangular tube after welding.

The method of manufacturing the water rod is carried out at the above-mentioned temperature and time. However, as in the case of the cladding tube according to the present invention, the raw pipe after the final hot working to the pipe after the final cold working are manufactured. This can be done for any stage. However, if cold working and annealing are performed after quenching, randomization of crystal orientation changes to anisotropic, so if corrosion resistance is important, this method may be used, but heat treatment after final cold working with channel box Most preferred is the way that you do it.

(2) In order to achieve high corrosion resistance and low hydrogen absorption, Sn contains 1 to 2%, Fe 0.2 to 0.50%, preferably 0.2 to 0.35%, and Ni 0.03 to 0.3%. .16%
It is important to use a Cr-containing or Cr-free zirconium-based alloy. In particular, alloys composed of these elements are preferable. Nodular corrosion does not occur even when such a high corrosion-resistant and high-Fe-Ni alloy member is used in a BWR environment, and the hydrogen absorption amount is significantly reduced as compared with a member made of a current Zircaloy.

The oxide film formed on the surface of the zirconium alloy member has oxygen-deficient (ZrO _2-x ) n-type semiconductor characteristics. The oxygen deficient part exists in the oxide film as an anion defect. The anion defect is compensated by two electrons, and the electrical neutrality is maintained. Fe, Ni,
Oxygen vacancies are formed when the Cr ions are substituted for Zr ions, but the oxygen vacancies are not compensated by the two electrons and become cation vacancies. The two electrons associated with the anion defect have a high energy level and easily move according to the potential gradient, and thus determine the electron conductivity of the oxide film. That is, the higher the anion defect concentration, the higher the electron conductivity of the oxide film. Conversely, the cation vacancies serve as electron trap sites, which lower the electron conductivity of the oxide film. Corrosion (oxidation) of zirconium alloy members in reactor water
It is determined by the balance between the charge transfer to the metal side by oxygen ions in the film through the oxygen vacancies and the charge transfer from the metal side to the oxide film surface by the electrons. The slower charge transfer determines the rate of corrosion. In a BWR environment, the rate of charge transfer by electrons from the metal side to the oxide film surface is limited. Therefore, when the electron conductivity decreases due to the presence of Fe, Ni, and Cr ions in the oxide film, the corrosion resistance also improves. F in the oxide film
In order for e, Ni, and Cr ions to be present at the position of Zr ions, Fe, Ni, and Cr must be present as a solid solution in the Zr alloy or exist as a fine intermetallic compound phase. , The amount thereof must be greater than that of the current Zircaloy-2 material and be dispersed uniformly. Hydrogen absorption is Zr
Reacts with water, and a part of hydrogen generated by the corrosion reaction is absorbed in the alloy member. As the corrosion resistance increases, the amount of generated hydrogen decreases, and the amount of absorbed hydrogen also decreases.

Nodular corrosion is a phenomenon in which the above-mentioned corrosion reaction progresses locally, and the cause is locally caused by Z in the oxide film.
Fe, Ni, and Cr ions substituted with r are deficient. To prevent such a deficiency, it is necessary to homogenize the distribution of these elements in the alloy. In order to make alloy element distribution uniform, β phase temperature and / or α + β
It is effective to provide a heat treatment of heating to a temperature and rapidly cooling. By this heat treatment, the intermetallic compound phase containing the alloy element (Zr (Fe, Cr) ₂ , Zr (Fe, Ni) ₂ , Zr
₂ (Ni, Fe) etc.) having an average particle size of 0.4 μm or less or S
The n · Ni intermetallic compound can be finely divided to 0.2 μm or less and uniformly dispersed. Further, the Fe / Ni ratio is set to 1.4 to 15, preferably 10 or less, and
It is effective not to remove. Among these intermetallic compound phases, Zr (Fe, Cr) ₂ (hexagonal) is the finest,
Next is Zr (Fe, Ni) ₂ (cubic), and Zr ₂ (N
i, Fe) (hexagonal) is the coarsest. By adding Cr, fine Zr (Fe, Cr) ₂ (hexagonal) increases, and Fe
/ Ni ratio coarse Zr ₂ (Ni, Fe) due to an increase in the fine Zr (Fe, Ni) for the existence ratio of ₂ is increased. The effect of improving corrosion resistance by making these intermetallic compound phases finer and more uniformly dispersed will be described below. When a zirconium alloy member is irradiated with neutrons in a nuclear reactor, the phase stability of the intermetallic compound phase is reduced, and Fe, Ni, and Cr are dissolved and dissolved in the matrix. As described above, Fe,
When Ni and Cr form a solid solution, an effect of replacing the lattice position of Zr in the oxide film and lowering the electron conductivity can be obtained. The refinement of the intermetallic compound phase increases its surface area, promotes leaching, and increases the solid solution concentration of Fe, Ni, and Cr. By uniform dispersion, the solid solution concentration is also made uniform, the uniformity of the electronic conductivity of the oxide film is increased, and nodular corrosion is prevented. For the reasons described above, the corrosion resistance (nodular corrosion resistance) and the hydrogen absorption resistance of the zirconium alloy member are improved. As a result, the thickness of the zirconium alloy member can be reduced.

If the content of Sn is less than 1%, sufficient corrosion resistance and strength cannot be obtained. Conversely, if it exceeds 2%, not only a remarkable effect cannot be obtained but also the workability is lowered.
2%. In particular, it is preferably 1.2 to 1.7%.

Fe is required to be 0.20% or more to enhance corrosion resistance and hydrogen absorption resistance. Conversely, even if added over 0.50%, there is no remarkable effect, and the workability is not improved. Since it is lowered, it is set to 0.50% or less. In particular, 0.20 to 0.3
5%, more preferably 0.22 to 0.30%.

Ni is contained in a very small amount in an amount of not less than 0.03% to remarkably enhance the corrosion resistance, but is conversely promoted in hydrogen absorption to cause embrittlement. Especially 0.0
It is preferably from 5 to 0.10%.

The Zr-based alloy of the present invention contains Cr in an amount of 0.05 to 0.5%.
15%. Cr is required to be 0.05% or more to increase the corrosion resistance and strength. Conversely, if it exceeds 0.15%, the workability is reduced.

The alloy according to the present invention can be used for cladding tubes, spacers, channel boxes, and water rods. The use of the alloy of the present invention for the former three makes it possible to achieve an average burnup of 50 to 55 GWd / t. Even in this case, Zircaloy-2 alloy can be used for the water rod.

Zr used in the fuel assembly according to the present invention
Zircaloy 2 (tin 1.2-1.7%, iron 0.0)
7 ~ 0.20%, chromium 0.05 ~ 0.15%, nickel
0.03 to 0.08%, the balance being substantially zirconium) or zircaloy 4 (tin 1.2 to 1.7%, iron 0.18 to 0.24%,
Ni 0.007% or less and the balance substantially zirconium), which are used in combination with the above-mentioned alloys and depending on the average burn-up.

After the final hot working, the cladding tube according to the present invention
It is preferably manufactured by subjecting a zirconium-based alloy to a process of quenching from the α + β phase or β phase temperature range, and then repeating cold working and annealing. Particularly, rapid cooling from the α + β phase temperature is preferable because the subsequent cold plastic workability is higher than that of the β phase rapidly cooled.

The alloy is preferably subjected to quenching from the above-mentioned β phase or α + β phase, and the treatment is preferably carried out after the last hot plastic working and before the last cold plastic working. It is good to apply before plastic working.

Α + β phase is 790-950 ° C., β phase is 95
The temperature is preferably set to 1100 ° C. or lower from a temperature exceeding 0 ° C., and quenching is preferably performed from these temperatures by running water, spray water, or the like. In particular, it is preferable to carry out before the first cold plastic working, in which case it is preferable to locally heat the outer periphery by high frequency heating while flowing water through the raw tube.

As a result, the inner surface of the tube is not quenched, the ductility is high, the outer surface is quenched, and a material having high corrosion resistance and low hydrogen absorption is obtained. For heating in the α + β phase, it is preferable to select a temperature at which the formation amount of the α phase and the β phase is different depending on the temperature and at which the β phase is mainly formed. The α phase does not change even after quenching, and has a low hardness and high ductility. The quenching from the portion that has changed to the β phase forms a needle-like phase with high hardness and low cold workability. However, when the α-phase is slightly mixed, high cold plastic workability can be obtained, and low corrosion resistance and low hydrogen absorption can be obtained. 80-9 as β phase
It is preferable to heat at a temperature that results in an area ratio of 5% and rapidly cool. Heating is performed in a short time, and is preferably performed within 5 minutes, particularly preferably within 5 seconds to 1 minute. Prolonged heating is unfavorable because crystal grains grow and precipitates are formed, resulting in reduced corrosion resistance.

The annealing temperature after cold working is 500-70.
0 ° C is preferred, and particularly preferably 550-640 ° C. 64
If the temperature is 0 ° C. or lower, a material having high corrosion resistance can be obtained. This heating is preferably performed in Ar or in a high vacuum. The degree of vacuum is 1
It is preferably from 0 ^-4 to 10 ^-5 Torr, and it is preferable that an oxide film is not substantially formed on the surface of the alloy by annealing and the surface shows a colorless metallic luster. The annealing time is preferably 1 to 5 hours.

The welding is preferably performed by TIG, laser beam, or electron beam welding, and particularly preferably TIG welding. The end plug and the cladding tube are preferably made of the same material.
The gas is 3 to 20 atm and is filled with a high pressure according to the burnup.

(3) Combination of material and treatment at each burnup (a) Burnup 50 to 55 GWd / t The above-mentioned high corrosion resistant and high Fe-Ni based zirconium-based alloy is used for the cladding tube, the spacer, and the channel box. The cladding tube and the spacer are quenched in the aforementioned α + β or β phase, and the channel box used is a randomized heat treatment in the β phase. As the water rod, Zircaloy 2 is used, a randomized heat treatment is performed in the β phase, the wall rod has an axial thickness distribution, and a thick corner portion is used. The water rod is connected and fixed to the upper and lower tie plates.

(B) Burn-up 45 GWd / t Zircaloy 2Zr-based alloy is used for the cladding tube, the channel box and the water rod.
Alternatively, β-phase quenching is performed, and the channel box and the water rod are subjected to randomization in the β-phase. The spacer is made of a high corrosion-resistant and high-Fe-Ni-based zirconium-based alloy, and is subjected to α + β phase or β phase quenching. A channel box having a thick corner is used.

(C) Burn-up 38 GWd / t Zircaloy 2 alloy is used for the cladding tube, spacer, channel box and water rod. The cladding tube and spacer are quenched in α + β phase or β phase, and the channel box is β Stray with randomized heat treatment in the phase
Door ones are used. Water rods randomized treatment with β phase is facilities.

(D) Burn-up 32 GWd / t Zircaloy 2 is used for the cladding tube, and Zircaloy 4 is used for the others. Zircaloy 2 can also be used for the channel box. Clad tube and spacer are α + β phase or β
Phase hardening is performed, the channel box is subjected to randomization processing in the β phase, and a straight channel box having a constant thickness is used. Water rods randomized treatment with β-phase in the same manner as described above are facilities. The spacer is of a lattice type, and is formed by welding a plate material in a lattice shape. Therefore, the quenching is performed by a plate material, and cold working and annealing are necessarily performed once after quenching.

[0056]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 (1) FIG. 1 is a sectional view of a fuel assembly for a boiling water reactor according to the present invention.

As shown in the drawing, the BWR fuel assembly has a large number of fuel rods 1, a plurality of spacers 7 for holding them at a predetermined interval from each other, a rectangular channel box 4 for accommodating them, It is composed of an upper tie plate 5, a lower tie plate 6, which holds both ends of a fuel rod 1 in which a fuel pellet is contained in a cladding tube, a water rod 2, which is arranged at the center of a spacer, and a handle 11, which conveys the whole. . Further, when manufacturing these fuel assemblies, they are assembled through ordinary steps.

The channel box 4 accommodates the fuel rod and the water rod 2 integrated by the spacer 7 therein, and the upper tie plate 5 and the lower tie plate 6 are used in a state of being fixed by the water rod 2. The channel box 4 has a rectangular tube shape obtained by joining two U-shaped plate processed materials by plasma welding. This member rectifies the steam generated on the fuel rod surface and the high-temperature water flowing between the fuel rods during operation of the plant, and forcibly guides it to the upper portion. Since the internal pressure is slightly higher than the external pressure, it is used for a long time in a state where a stress that pushes the rectangular cylinder outward is applied.

In the fuel assembly of the present invention, three water rods 2 are symmetrically arranged at the center of the spacer 7, all of which are fixed to the tie plate with screws at both ends, and the channel box 4 is connected to the upper tie plate 5. And the fuel assembly is transported integrally by the handle 11. In this embodiment, the fuel rod is not fixed to the tie plate.

(2) The channel box is heat-treated as follows, and the orientation ratio (Fr value) of the <0002> crystal orientation in the plate thickness direction is 0.25 to 0.5, and the orientation ratio (F in the longitudinal direction) is
L) is 0.203 to 0.36, and the orientation ratio (Ft) in the width direction is 0.25 to 0.36. By orienting in this way by heat treatment, the βZr crystal grain size becomes 50-300 μm on average, and irradiation elongation is significantly prevented,
Interference between the channel box and the control rod is prevented.

FIG. 2 is a perspective view showing an example of manufacturing a channel box according to the present invention. Table 1 as alloy composition
The Zircaloy-C plate shown in FIG. 1 was cold-bent into a U-shape to form two U-shaped members having a length of 4 m. The unevenness of the weld is finished flat. The square tube 12 was rapidly cooled by cooling water sprayed from a water injection nozzle 16 provided immediately below a coil 14 for heating to a β-phase temperature range by high-frequency induction heating and high-frequency induction heating. The entire heat treatment is completed when the square tube 12 passes from above to below at a constant speed into the coil. The feeding speed of the rectangular tube 12 and the output of the high frequency power supply 15 were adjusted so that the heating temperature was 1100 ° C. and the holding time at 980 ° C. or more was 10 seconds or more. After heat treatment, width: 4
A test piece of 0 mm and length: 40 mm was cut out and the F value was measured. Table 2 shows the measurement results. The heat treatment parameter (P) is 1.96. The heat treatment was performed by fixing both ends of the austenitic stainless steel mandrel 18 to the square tube 12 with the screws 3. As can be seen from the table, the hexagonal prism (00
02) Both the bottom surface and the columnar surface are (1010) planes as F values.
Each of r, FL, and Ft becomes substantially 1/3, and a completely random crystal orientation is obtained. The average grain size of βZr was about 100 μm. After performing this heat treatment, a molding sandblast treatment and an acid washing are performed with high dimensional accuracy, and after removing a surface oxide film, an autoclave treatment with steam is performed.

[0062]

[Table 1]

[0063]

[Table 2]

FIGS. 3 to 5 are perspective views of the channel box. In this embodiment, the thick corner portion 20 of FIG. 5 is thicker than the side portion 21, the side portion is the upper portion 22 and the lower portion 23 is thinner. It has a thickness distribution in the longitudinal direction. Such a forming process is performed after the heat treatment. The forming process is performed by masking and chemical etching or mechanical processing using a mixed acid aqueous solution of hydrogen fluoride and nitric acid. In this embodiment, the outer surface side is processed and recessed. Such a thickness distribution may be concave on the inner surface side.

(3) FIG. 6 is a partial sectional view of a fuel rod according to the present invention. Fuel rods are clad tube 24, nuclear fuel pellets 25,
An end plug 27 and a plenum spring 26 are provided.
e is enclosed. In this embodiment, H of 15 to 25 atm is used.
e is enclosed. The cladding tube 24 is manufactured as follows. The coating tube 24 is provided integrally with a pure Zr liner inside. This liner is formed at the stage of the tube after the heat treatment described below, and is subjected to cold working and annealing.

Each of the alloys shown in Table 3 was formed into a tube having an outer diameter of 63.5 mm and a thickness of 10.9 mm by hot extrusion.
The tube was passed through a high-frequency induction heating coil and heated while flowing water from the bottom to the top. Water was wiped from the nozzle provided immediately below the coil to the outer surface of the tube to rapidly cool the tube. Maximum heating temperature is 930 ° C, α + β phase, 930 ° C
The average cooling rate from to 500 ° C. was about 150 ° C./s. The raw steel tube subjected to the induction quenching treatment was alternately subjected to cold rolling with a pilger mill and annealing in vacuum at 600 ° C. three times (final annealing temperature was 577 ° C.), thereby obtaining a fuel cladding tube and a round spacer. Was used as the material of the shape.
In the case of a spacer, heating was carried out without flowing water into the tube. The difference between the shapes of the fuel cladding tube and the spacer is the tube diameter and the wall thickness. By changing the degree of work in the final cold rolling, two types of tubes having different tube diameters and wall thicknesses were manufactured. The outer diameter of the spacer is larger than the cladding tube, and the thickness is smaller than the cladding tube. The cross-sectional reduction rate of the cold working was set to 70 to 80% per time. The thickness of the liner is about 10-100 μm. The cladding tube has a specific crystal orientation on the inside, and has a Fr value of 0.6 to 0.7.

Strip-shaped test pieces were cut out from the two types of tubes manufactured as described above, and exposed to a high-temperature and high-pressure steam environment of 500 ° C. and 10.3 MPa for 24 hours, and the weight increase due to corrosion and the appearance of corrosion were examined. Table 4 shows the results.

[0068]

[Table 3]

[0069]

[Table 4]

From Table 3, it can be seen that zircaloy conventionally used
Nodular corrosion occurred in Nos. 2 and -D, and showed high corrosion weight increase values. Fe / Ni ratio higher than 1.4 and F
In alloys (Zircaloy-A to -C) in which the addition amount of e and Ni is higher than the standard range of Zircaloy-2, nodular corrosion did not occur, a black oxide film having a uniform thickness was formed, and extremely high corrosion resistance was exhibited. From the above results, alloys with Fe / Ni ratio> 1.4, Cr added, and Fe and Ni added higher than the standard range of Zircaloy-2 can exhibit high corrosion resistance even when used in a furnace. I understand. The corrosion amount of this alloy after 6 years is about 130 mg / dm ² (oxide film thickness: 8 μm).
m), the hydrogen concentration of the 0.5 mm thick spacer is less than about 250 ppm.

The zirconium-based alloy of the cladding tube and the spacer is a tin-nickel intermetallic compound having a particle size of 0.2 μm or less in the α-phase zirconium crystal grains and an iron / nickel compound having a particle size of 0.1 to 0.5 μm.
Preferably, a nickel-zirconium intermetallic compound is deposited. In the present embodiment, the former has a particle size of about 0.01 μm.
It was extremely fine.

(4) FIGS. 7 and 8 are partial cross-sectional views of a water rod. In this embodiment, the water rod having the large diameter shown in FIG. 8 is used. Zircaloy 2 shown in Table 1 is used as the alloy of the alloy, and after the raw tube is quenched in the α + β phase or the β phase as described above, cold working and annealing are performed to a predetermined shape, It is constituted by a small diameter portion 28, a large diameter portion 29, and an end plug 30. The end plug 30 is provided with a screw and is fixed to the upper and lower tie plates as described above.

(5) FIGS. 9 and 10 are front views of the spacer. In this embodiment, the round cell type shown in FIG. 10 is used, and Zircaloy B in Table 3 is used. FIG. 11 is a perspective view of the round cell, which is subjected to a heat treatment of quenching from the α + β phase as described above, and then cold-worked and annealed repeatedly to form a thin-walled tube, thereby obtaining a desired shape by cutting. is there.

(6) The above-mentioned fuel rods are loaded with uranium 235 having an enrichment of about 4.5%, thereby achieving an average burnup of 50 to 55 GWd / t. The fuel usage period will be about 6 to 6６ years. The end plugs are butt laser welded.

The tie plate contains C 0.03% or less, Si
2% or less, Mn 2% or less, Ni 8 to 12%, Cr 17 to
An austenitic steel casting with 21% balance Fe is used. The casting is subjected to a solution treatment at 1100 ° C.

As a result of performing a fast neutron irradiation test on the above-described channel box, the amount of strain at 3 × 10 ²² n / cm ² was extremely small at 0.3 × 10 ^-4 .

Experimental Example 1 The relationship between the degree of randomness of the crystal orientation and the elongation due to neutron irradiation of the Zr-based alloy used in the channel box described above was subjected to the heat treatments shown in Table 5 using the alloys shown in Table 1 above. Was examined. The randomization of the crystal orientation was adjusted by changing the heat treatment.

[0078]

[Table 5]

Each of the alloys is a plate having a thickness of 2 mm, and has been repeatedly subjected to cold rolling and annealing at 650 ° C. for 2 hours before receiving. The heat treatment Nos. 2 to 5 shown in Table 5 are as follows:
A test piece having a width of 40 mm and a length of 40 mm was cut out of a receiving material, heated in an electric furnace, and cooled in water. Heat treatment No. 6 was carried out by holding a test piece cut from the receiving material in an infrared heating furnace and cooling it with water. Parameter: P was calculated by the above equation.

Table 6 shows (0) of hexagonal prisms of No. 1 to 6 heat-treated materials.
002) The bottom surface (parallel to the (0001) plane) and the columnar surface are (1)
The F-number measurement results of the (010) plane (: perpendicular to the (0001) plane) are shown. The Fr value indicates the orientation probability in the direction perpendicular to the sheet surface, the FL value indicates the orientation probability in the sheet rolling direction, and the Ft value indicates the orientation probability in the orthogonal direction to the former two. No difference in the F value due to the change in the alloy composition was found. In a sheet material (heat treatment No. 1) manufactured by repeating normal cold rolling and annealing, the Fr value of the (0002) plane is as high as about 0.7, and the (1010) plane has a Fr value of about 0.15. Table 6 shows that the (0002) plane is oriented substantially parallel to the plate surface. The F value of a sheet material (heat-treated No. 2) heated to 900 ° C. α + β temperature range and water-cooled is almost equal to the value of the receiving material, and the orientation of crystal orientation hardly changes by heating and cooling to α + β phase temperature range. I understand. Heat to 1000 ° C. and allow β phase temperature range (> 980
° C) for 5 seconds (heat treatment No. 6), the Fr value of the (0002) plane decreases compared to the receiving material, and the FL value, F
The t value has increased. Conversely, the column face is the (1010) plane F
The r value increases, and the FL value and the Ft value decrease. From this, it can be seen that by setting the P value to 0.8 or more, the crystal orientation is randomized, and the FL value becomes 0.20 or more. However, when it is arranged in the core peripheral region, a target value for preventing the channel box and the control rod from interfering with each other: (00
02) FL value of plane ≧ 0.25 is not satisfied. Heat treatment No.
It can be seen that the plate materials of Nos. 3 to 5 satisfy FL value ≧ 0.25, and the channel box and the control rod do not interfere with each other even if they are arranged in the core peripheral region.

[0081]

[Table 6]

The amount of growth strain caused by neutron irradiation was examined by changing the Fr value by the above-mentioned heat treatment.

FIG. 12 is a graph showing the relationship between the fast neutron irradiation dose and the irradiation growth strain. The figure shows the calculation results showing the effect of the Fr value on the bending amount of the channel box irradiated with one cycle at the periphery of the furnace and the channel box irradiated with four cycles at the center of the core after three cycles of irradiation at the center of the core. As shown in the figure, when the Fr value exceeds 0.4, the strain increases sharply with an increase in the neutron irradiation dose.
It can be seen that the strain saturates and does not increase even when irradiated below 0.4. In particular, the case of Fr = 0.35 is <00
01> Since the crystal orientation is substantially randomly oriented, the strains in the normal direction, the longitudinal direction and the thickness direction cancel each other out between the crystals, so that no more than 0.5 × 10 ^-4 is generated. . In the case of Fr = 0.4, the irradiation amount is 3 × 10 ²²
Although the amount of strain is small up to n / cm ² , the strain gradually increases with a higher neutron irradiation dose. However, Fr =
At 0.35, the strain does not increase even if the neutron irradiation dose increases.

Fr value and fast neutron 3 × 10 ²² n / cm ²
As a result of examining the relationship with irradiation growth strain due to irradiation of
The strain increases sharply with increasing r-value.
The strain of irradiation growth at Fr = 0.35 is about 0.2 × 10 ^-4.
Fr = 0.4 is remarkably small, about 1/7 of about 1.5 × 10 ⁻⁴ , and Fr = 0.4 is remarkably small, about 1/3 of Fr = 0.5. However, Fr = 0.5 is equivalent to Fr = 0.6.
And Fr = 0.6 is about half of Fr = 0.7. If Fr exceeds 0.4, no significant effect can be obtained.

No αZr crystal grains were present in the rounded crystal grains observed in the metal structures of the heat-treated materials of Nos. 1, 3, and 4. The observed polygonal crystal grains are βZr crystal grains formed during heating and holding in the β phase temperature range, and 1000
As the holding time in ° C increases from 1 minute to 10 minutes, βZ
The r crystal grain size was growing large. The layered or acicular structure found within the βZr crystal grain size
Is formed upon transformation to αZr again, and β
It is not a Zr crystal grain boundary.

Looking at the relationship between the βZr crystal grain size and the Fr value of the (0002) plane, when the βZr crystal grain size grows to 200 μm or more, a texture having a Fr value of 0.35 or less is formed.

As described above, the crystal orientation of the (0002) plane can be randomized by growing the crystal grains.
40, the FL value is 0.30, about 75%, the grain size at that time is about 100 μm, and when the crystal grain size is 150 μm or more, it is randomized to about 80% or more.
The value, FL value, is 0.385 at 0.320. Further, the random ratio at an Fr value of 0.35 and an FL value of 0.34 is about 90% or more, and the crystal grain size at that time is about 250 μm or more.

Looking at the relationship between the βZr crystal grain size and the irradiation growth strain, a strain of 4 × 10 ⁻⁴ or less for a grain size of 20 μm or more, and a strain of about 1.5 × 1 for a grain size of 90 μm or more.
It is extremely low at 0 ^-4 . Further, when the thickness is 150 μm or more, the strain becomes extremely small, 0.5 × 10 ⁻⁴ or less. In particular, the strain at 200 μm or more is about 0.3 × 10 ⁻⁴ .

FIG. 13 shows Table 1 at each temperature and holding time.
FIG. 4 is a diagram showing a relationship between Fl values of alloys shown in Table 3 and Table 3.
As shown in the drawing, when the temperature is lower than 980 ° C., the Fl value becomes 0.20 or less, and it is difficult to obtain a crystal having a random <0002> crystal orientation. However, heating at 980 ° C. or higher for 11 seconds or longer, or heating at 1240 ° C. or higher for 1.1 seconds or longer on a line connecting these points, a Fl value exceeding 0.25 can be obtained. Higher ones are obtained. Heating at 980 ° C. or more for 6 seconds or more and 1240 ° C. or more for 6 seconds or more, and above the line connecting these points, can provide Fl values larger than 0.20 and 0.25 or less.
Those lower than this line have an Fl value of 0.20 or less, have a low degree of randomness, and have a small effect on elongation.

The relationship between the heating temperature and the time can be expressed by the following parameter P.
Up to 200 ° C.

Parameter P = (3.5 + logt) × log
Looking at the relationship between (T-980) and the irradiation growth strain, the irradiation growth strain is greatly affected by the parameter P determined by the relationship between the temperature and the holding time in the heat treatment. The parameter P is an important factor that determines the orientation ratio of the <0001> crystal orientation of Zr. When P is 0.5 or more, the irradiation growth strain rapidly decreases, and further gradually decreases when P is 0.5 to 3.5, becomes almost constant when P is 3.5 or more, and becomes almost zero. In particular, the effect is large at P1.5 or more, and 3.0 to 5
Is preferred.

Experimental Example 2 Using sponge zirconium, alloys of various compositions were melted by vacuum melting. The alloy composition is about 1.5 Sn by weight.
%, Fe 0.10 to 0.50%, Ni 0 to 0.30%, C
r is 0.08 to 0.13%, and the balance substantially consists of Zr. Each ingot was subjected to hot rolling (700 ° C.) and annealing (700 ° C., 4 h), and then the α + β phase (900
° C) and β phase (1000 ° C) for 2 to 3 minutes, and then water-cooled. Next, cold rolling (working ratio 40%) and 600 ° C ×
Intermediate annealing for 2 hours was alternately repeated three times to obtain a plate having a thickness of 1 mm.

The corrosion test was performed at 410 at a pressure of 10.3 MPa.
8 hours in high-temperature steam, then maintain the same pressure for 5 hours.
It carried out by raising to 10 degreeC and holding for 16 hours, and measuring corrosion increase. Heating was performed at 530 ° C., 620 ° C., and 730 ° C. for 2 hours in order to investigate the influence of the material composition on corrosion at an accelerated rate.

Regarding the hydrogen absorption characteristics, an oxide (ZrO ₂ ) is formed at the same time as the reaction between Zr and water, and a hydrogen gas is generated. The number of moles of water that has been corroded can be determined, and the number of moles of hydrogen gas generated correspondingly can be determined. The hydrogen absorption rate was determined by calculating the number and determining the ratio of the generated hydrogen to the absorbed hydrogen.

FIG. 14 shows the presence or absence of nodular corrosion. In the figure, the circles indicate that nodular corrosion was not observed on the surface and side surfaces regardless of the final annealing temperature, and the corrosion increase was 4%.
It was less than 5 mg / dm ² . The “x” mark indicates that nodular corrosion occurred on the surface or side surface and the corrosion increase was more than 50 mg / dm ² . The number in the figure is the corrosion increase. It can be seen from the figure that the alloy composition that can prevent nodular corrosion exists on the high Ni and high Fe sides of the region divided by the dotted line in the figure. The dotted line is a value obtained by 0.15Fe + 0.25Ni = 0.0375.

FIG. 15 is a graph showing the influence of the contents of Fe and Ni on the increase in corrosion. As shown in the figure, it can be seen that the corrosion in the high-temperature and high-pressure water is significantly reduced by the increase of the Fe content and the Ni content. In particular, the addition of a very small amount of Ni sharply reduces the increase in corrosion. 0.06% or more for Fe around 0.10%, 0.04% for Fe around 0.15%
As described above, when the Fe content was 0.21% or more and the Ni addition was 0.03%, the corrosion increase was 45 mg / dm ² or less, and no nodular corrosion occurred.

FIG. 16 shows the effect of the amount of Fe added on the hydrogen absorption rate. In the figure, the symbol △ indicates the amount of Ni added:
The hydrogen absorption rate of the alloy of 0.11 wt% is shown.
The amount of addition: indicates the hydrogen absorption rate of the alloy of 0.05 wt%. The dotted line in the figure shows the experimental results for the alloys without α + β quench or β quench. The solid line shows the hydrogen absorption rate of the alloy subjected to α + β quenching in the thermomechanical process. It is understood from the figure that the hydrogen absorption rate can be reduced to 11% or less by performing the α + β quench. By setting the Fe content to 0.21% or more, the hydrogen absorption rate decreases regardless of the Ni content.

FIG. 17 shows the effect of Fe and N on the hydrogen absorption rate.
i shows the effect of the amount added. When the amount of Ni added is 0.16 wt% or less, the hydrogen absorption rate is as low as 11% or less, but is 0.2%.
When the content exceeds wt%, the hydrogen absorption rate rapidly increases and reaches 40%. Therefore, it is preferable that the amount of Ni added is 0.15 wt% or less. However, by setting the Fe content to 0.21% or more, the hydrogen absorption rate can be reduced to 10% or less.

FIG. 18 shows the effect of (Fe / N
i) Diagram showing the effect of the ratio. As shown in the figure, those with a circle and a triangle with an Fe content of less than 0.21% are (Fe /
Although the influence of the (Ni) ratio is not observed, it can be seen that the (Fe / Ni) ratio should be at least 1.4 at an Fe content of 0.20% or more. As described above, since the effects of Fe and Ni on the hydrogen absorption rate are completely opposite, the ratio of these elements is important. Fe content is 0.
When the content is less than 2% and the Ni content exceeds 0.2%, there is no correlation between these elements. However, when the content of both is opposite to each other, the two have a correlation.

The alloy with an increased Fe content of 0.48 wt% had a corrosion increase of 43 mg / dm ² and a hydrogen absorption rate of 12 mg / dm ² .
%Met. From this, it can be seen that from the viewpoints of corrosion resistance and hydrogen absorption, the Fe addition amount may be increased to 0.21 wt% or more and about 0.5 wt% if the Ni addition amount is 0.16 wt% or less. . However, as will be described later, if the total amount of Ni and Fe is as large as 0.64%, the cold plastic workability is sharply reduced. Therefore, it is not preferable for a member to be thinned by cold plastic working as described above. , Fe and Ni are preferably 0.40 or less.

Α + of a 0.25% Fe, 0.11% Ni alloy
As a result of observing the precipitates with a transmission electron microscope of the β-phase quenched, an intermetallic compound of tin and nickel was detected, and it was found that the intermetallic compound was uniformly dispersed and precipitated in the α-phase zirconium crystal grains. confirmed. The precipitate was a Sn ₂ Ni ₃ precipitate, and the particle size was very fine, about 10 nm. However, this precipitate was not observed in the same material that did not quench α + β.

Incidentally, even when the α + β quenching was performed, no precipitate of Sn and Ni was observed in the one subjected to hot plastic working after the quenching.

Example 2 An assembly was obtained in the same manner as in Example 1 above. The differences from the first embodiment are as follows.

In the cladding tube, Zircaloy 2 (Sn1-2) was used.
%, Fe 0.05 to 0.20%, Cr 0.05 to 0.15
%, Ni 0.03-0.1% and the balance Zr) are used,
The hot-extruded final hot-worked tube is subjected to a quenching treatment in the same manner as in Example 1 while flowing water therein, so that the outer surface side has a higher solid solution amount of the alloy element than the inner surface, and the outer surface side has corrosion resistance. It is expensive. Also in this example, a liner of pure Zr was formed on the inner surface, and was manufactured in the same manner as in Example 1. The fuel rod is the same as that shown in FIG. 6. The end plug 27 is made of the same material as that of the cladding tube. After the nuclear fuel pellets 25 are loaded, He is sealed and sealed by butt laser welding with the end plug. The sealing He pressure becomes about 10 atm, and the nuclear fuel pellet 2
5 has an average enrichment of about 4.0 wt%. The quenching process of the cladding tube can be performed at any stage immediately before the final cold working from the tube in the α + β phase, and the β phase can be performed in the same manner as the α + β phase. α + β phase, β
Any of the phases is preferably quenched with a raw tube, and the β phase is preferably performed before cold working before final cold working. The annealing temperature after cold working is preferably 640 to 500 ° C.

The channel box is made of an alloy having the same composition as that of the cladding tube. The channel box is heated in the β phase at 1100 ° C. for 10 seconds and then subjected to the water spray heat treatment as described above.
A value similar to the t value was obtained, whereby the amount of strain at 3 × 10 ²² n / cm ² as a neutron irradiation amount was 0.3 × 10 ^−4.
Was very few. In this embodiment, the channel box shown in FIG. 4 is used, and the corner portion is thicker than the side portion. 4 (b) is formed concave on the outer surface side, and FIG. 4 (c) is formed concave on the inner surface side, and is formed by machining or chemical etching.

The spacer has the same structure and material as in the first embodiment. The material was α + β phase or β as in Example 1.
A phase quenching process is performed.

The same structure and material as in the first embodiment are used for the water rod.

With the above configuration, the average burn-out is 45 G
Wd / t is achieved. Nodular corrosion did not occur in the cladding tube spacer and the water rod, and the elongation in the channel box was very small.

Example 3 An aggregate was obtained in the same manner as in FIG. The differences from the second embodiment are as follows.

A channel box having a strainer structure shown in FIG. 3 is used, and Zircaloy 2 is used as a material. The manufacturing method is the same as that of the first embodiment.
This was carried out by heating at 10 ° C. for 10 seconds and then cooling with water. At that time, the F value was almost the same as the value shown in Table 2. The average crystal grain size was about 100 μm. The treatment after the heat treatment was similarly performed.

The above-mentioned Zircaloy 2 is used for all of the cladding tube, the spacer and the water rod, and all used are those subjected to a quenching treatment in the α + β phase or the β phase after the final hot working. End plugs to the cladding tube and water rod are made by butt TIG welding, and the cladding tube is loaded with nuclear fuel pellets as in Example 2. The average enrichment of uranium 235 as a nuclear fuel is about 3.4% by weight and the He filling pressure is about 5 atm.

The fuel assembly having the above-described structure achieves a discharge average burnup of 38 GWd / t. This product will be used for about 4.5 years.

Example 4 A fuel assembly was obtained in the same manner as in FIG. The differences from the third embodiment are as follows.

Zircaloy 2 was used for the cladding tube and channel box, and Zircaloy 4 (Sn 1-2%, Fe 0.18-0.24%, Ni 0.2%) was used for the spacer and the water rod.
01% or less, with the balance being substantially Zr). The cladding tube and the spacer are subjected to an α + β phase or β phase quenching treatment and have high corrosion resistance.

As the spacer, a lattice type shown in FIG. 9 is used.
The quenched plate is formed by TIG welding.
The nuclear fuel pellets have an average enrichment of U235 of about 3%, an average burnup of 33 GWd / t, and a service life of about 4%.
Year.

[0116]

According to the present invention, since the crystal orientation of the channel box for storing the fuel assembly is made random, it can be used in the furnace for a long time with little deformation. Further, the corrosion resistance of each member of the fuel assembly is improved, and the hydrogen absorption can be greatly reduced. As a result, the burnup of the fuel assembly can be increased, which can contribute to the reduction of spent fuel waste. Further, it can contribute to improvement of the reliability of the fuel assembly member.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a fuel assembly according to the present invention.

FIG. 2 is a configuration diagram of a heat treatment apparatus for a channel box.

FIG. 3 is a perspective view of various channel boxes and a sectional view thereof.

FIG. 4 is a perspective view of various channel boxes and a sectional view thereof.

FIG. 5 is a perspective view of various channel boxes and a sectional view thereof.

FIG. 6 is a partial sectional view of a fuel rod.

FIG. 7 is a partial sectional view of a water rod.

FIG. 8 is a partial sectional view of a water rod.

FIG. 9 is a front view of a spacer.

FIG. 10 is a front view of a spacer.

FIG. 11 is a perspective view of a cell 31 of FIG. 10;

FIG. 12 is a diagram showing the relationship between irradiation growth strain and fast neutron irradiation dose for each Fr.

FIG. 13 is a diagram showing a relationship between a heating temperature and a holding time for each Fr.

FIG. 14 is a diagram showing the relationship between Fe and Ni content affecting corrosion.

FIG. 15 is a graph showing the relationship between the amount of Fe and the increase in corrosion.

FIG. 16 is a diagram showing a relationship between a hydrogen absorption amount and an Fe content.

FIG. 17 is a diagram showing a relationship between a hydrogen absorption amount and an Fe content.

FIG. 18 is a diagram showing a relationship between a hydrogen absorption amount and a (Fe / Ni) ratio.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel rod, 2 ... Water rod, 3 ... Water rod fixing screw, 4 ... Channel box, 5 ... Upper tie plate, 6 ... Lower tie plate, 7 ... Spacer, 8 ... Channel box fitting allowance, 9 ... Fuel rod Elongation allowance, 10: fuel rod through hole, 11: handle, 12: square cylinder, 14: coil, 15: power supply, 16: water spray nozzle, 17: welded part,
18: mandrel, 20: thick corner, 21: side,
22 ... upper side, 23 ... lower side, 24 ... cladding tube, 25
... nuclear fuel pellets, 26 ... plenum springs, 27,
30 ... end plug, 28 ... small diameter part, 29 ... large diameter part, 31 ... cell.

────────────────────────────────────────────────── ─── Continuing on the front page (51) Int.Cl. ⁶ Identification code FI G21C 3/34 G21C 3/34 Y (72) Inventor Hideaki Ishizaki 3-1-1 Kochicho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Inside Hitachi Plant (72) Inventor Shinpei Yamamoto 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Inside Hitachi Plant (72) Inventor Hideo Maki 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Co., Ltd. Hitachi, Ltd.Hitachi Plant (72) Inventor Junjiro Nakajima 3-1-1, Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Hitachi Plant (72) Inventor Shozo Nakamura 502, Kandamachi, Tsuchiura City, Ibaraki Prefecture Hitachi, Ltd. Inside the Machinery Research Laboratory (72) Inventor Satoshi Kanno 502, Kandachicho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. 80170 (JP, A)

Claims (8)

(57) [Claims] 1. A plurality of fuel rods loaded with nuclear fuel in a cladding tube made of a zirconium-based alloy, a spacer for arranging the fuel rods at desired positions, and the arranged fuel rods supported at upper and lower ends thereof. comprising an upper tie plate and a lower tie plate for, the zirconium-based alloy channel box which covers the outer periphery is set integrally with the zirconium-based alloy water rod arranged in said spacer, 50 ~
In a fuel assembly that is exposed to a burnup of 55 GWd / t, the cladding, spacers and channel box may contain, by weight, 1-2% tin, 0.20-0.50% iron, 0.00% chromium.
5 to 0.15% and nickel 0.03 to 0.16%, with the balance substantially consisting of zirconium. The cladding tube has a solid solution amount of the iron and nickel on the outer surface which is a solid solution amount on the inner surface. Higher, the channel box and the water rod have a <0001> orientation ratio in the thickness direction of the crystal orientation (Fr).
Fuel assemblies that value) is characterized in that the Ru der 0.25 to 0.50. 2. A plurality of fuel rods in which nuclear fuel is loaded in a cladding tube made of a zirconium-based alloy, spacers for disposing the fuel rods at desired positions, and supporting the disposed fuel rods at upper and lower ends thereof. An upper tie plate and a lower tie plate, and a zirconium-based alloy channel box that assembles integrally with a zirconium-based alloy water rod disposed in the spacer and covers the outer periphery thereof.
In a fuel assembly exposed to a burnup of up to Wd / t, the cladding is quenched and the solid solution of iron and nickel on the outer surface is higher than the solid solution of the alloy element on the inner surface. The channel box is formed of a rectangular tube whose corners are thicker than the sides, and the channel box and the water rod have an orientation rate (Fr value) of <0001> crystal orientation in the thickness direction of 0.25 to 0.25. 0.55, the cladding tube, channel box and water rod are 1.2 to 1.7% tin, 0.07 to 0.20% iron, 0.055 to 0.15% chromium, nickel by weight. 0.03 to 0.08% and the balance substantially consisting of zirconium ; the spacers are by weight 1 to 2% tin, 0.20 to 0.50 % iron, 0.055 to 0.15 chromium , nickel 0.03 to 0.16% and the balance substantially zirconium Fuel assembly, characterized in that it consists of. 3. A plurality of fuel rods loaded with nuclear fuel in a cladding tube made of a zirconium-based alloy, spacers for arranging the fuel rods at desired positions, and supporting the arranged fuel rods at upper and lower ends thereof. An upper tie plate and a lower tie plate, and a zirconium-based alloy channel box that assembles integrally with a zirconium-based alloy water rod disposed in the spacer and covers the outer periphery thereof.
In a fuel assembly exposed to a burnup of up to Wd / t, the cladding is quenched and the solid solution of iron and nickel on the outer surface is higher than the solid solution of the alloy element on the inner surface. The channel box is made of a straight welded rectangular tube having a substantially uniform thickness at the corners and sides, and the channel box and the water rod are oriented in the <0001> crystal orientation in the thickness direction (Fr). value)
Is 0.25 to 0.50, and the cladding tube, spacer, channel box and water rod are tin 1.
2 to 1.7%, iron 0.07 to 0.20%, chromium 0.05 to 5%
A fuel assembly comprising 0.15%, nickel 0.03% to 0.08% and the balance substantially zirconium. 4. A plurality of fuel rods loaded with nuclear fuel in a cladding tube made of a zirconium-based alloy, a spacer for arranging the fuel rods at desired positions, and supporting the disposed fuel rods at upper and lower ends thereof. An upper tie plate, a lower tie plate, and a zirconium-based alloy channel box that integrally assembles a zirconium-based alloy water rod disposed on the spacer and covers the outer periphery thereof;
In fuel assemblies exposed to burnups of up to d / t,
The cladding tube is quenched so that the solid solution amount of iron and nickel on the outer surface is higher than the solid solution amount of the alloy element on the inner surface, and the channel box has substantially uniform corners and sides. The channel box and the water rod have a <0001> crystal orientation orientation ratio (Fr value) in the thickness direction of 0.25 to 0.50, and the channel box and the water rod have a thickness of 0.25 to 0.50. The tube or the cladding tube and the channel box are, by weight, 1.2 to 1.7% tin, 0.07 to 0.20% iron, 0.05 to 0.15% chromium, and 0.03 to 0.08 nickel. % and the balance substantially fuel assembly, characterized in that zirconium <br/> U beam or Ranaru. 5. A plurality of fuel rods in which nuclear fuel is loaded in a cladding tube made of a zirconium-based alloy, spacers for disposing the fuel rods at desired positions, and supporting the disposed fuel rods at upper and lower ends thereof. Assembly comprising an upper tie plate, a lower tie plate, and a zirconium-based alloy water rod disposed in the spacer, and a zirconium-based alloy channel box covering the outer periphery thereof. in the previous SL cladding is higher than the solid solution amount of the iron and solid solution amount the inner surface of the nickel of the outer surface, wherein the channel box and water rod <0001> thickness direction of the orientation of the crystal orientation (Fr value ) Is 0.25 to 0.50. 6. A plurality of fuel rods loaded with nuclear fuel in a cladding tube made of a zirconium-based alloy, spacers for disposing the fuel rods at desired positions, and supporting the disposed fuel rods at upper and lower ends thereof. An upper tie plate and a lower tie plate, and a zirconium-based alloy channel box covering the outer periphery of the zirconium- based alloy water rod disposed in the spacer and integrally assembled with the fuel assembly, The cladding tube is quenched to a thickness of less than half of the thickness, the solid solution of iron and nickel on the outer surface is higher than the solid solution of the alloy element on the inner surface, and the channel box is Department has a thickness in the longitudinal direction and in the thick than the side portion a thick shape at the bottom than the top, front
The channel box and the water rod have an orientation ratio (Fr value) of <0001> crystal orientation in the plate thickness direction of 0.25 to 0.5.
0 Der Ru that the fuel assembly according to claim. 7. By weight, tin is 1 to 2%, iron is 0.20 to 0.50.
% , Chrome 0.05 to 0.15 %, nickel 0.03 to 0.1%
A zirconium- based alloy plate consisting essentially of zirconium and having a balance of 16% and a <0001> crystal orientation in the plate thickness direction (Fr value) of 0.25 to 0.50; It is characterized in that the orientation ratio (FL value) in the (rolling direction) is 0.25 to 0.36 and the orientation ratio (Ft value) in the width direction (direction perpendicular to the rolling direction) is 0.25 to 0.36. For fuel assemblies
Water rod . 8. Tin 1.2-1.7% by weight, iron 0.07-
0.20%, chrome 0.05 to 0.15%, nickel 0.0
3 to 0.08% and the balance substantially zirconium
Made of a zirconium-based alloy plate
1> Crystal orientation ratio (Fr value) is 0.25 to 0.50, long
The orientation ratio (FL value) in the hand direction (rolling direction) is 0.25 to 0.2 .
36 and orientation ratio in the width direction (direction perpendicular to the rolling direction)
(Ft value) is 0.25 to 0.36.
Water rod for a fuel assembly.