JP4975390B2 - Method of manufacturing fuel cladding for high burnup - Google Patents

Description

  The present invention relates to a high-burn-up fuel cladding tube having an inner liner layer used at a high burn-up and a method for manufacturing the same.

  In particular, it exhibits good corrosion resistance, hydrogen absorption resistance, and strength characteristics under long-term use and use environments such as hydrogen injection, and is also sound for debris fretting, PCI (pellet cladding interaction), and secondary hydrogenation. The present invention relates to a high-burn-up fuel cladding tube and a method for manufacturing the same.

  Zirconium alloys are widely used as nuclear fuel structural members.

  The most commonly used zirconium alloys are Zircaloy-2 (Sn: 1.2-1.7 wt%, Fe: 0.07-0.20 wt%, Cr: 0.05-0.15 wt%). %, Ni: 0.03-0.08 wt%, balance Zr) and Zircaloy-4 (Sn: 1.2-1.7 wt%, Fe: 0.18-0.24 wt%, Cr: 0.00 07-0.13% by weight, balance Zr).

  In addition, Zr-2.5% Nb, Zr-1% Nb alloys and the like are also applied to nuclear reactors.

  The above alloys are mainly developed in consideration of neutron economy, strength and corrosion resistance.

(1) Nodular corrosion However, when the above materials are used in a boiling water reactor, there has been a problem that a lens-like local corrosion called nodular corrosion occurs on the surface during the operation of the reactor.

  Nodular corrosion grows as the irradiation progresses, and may result in delamination when the corrosion layer becomes thicker.

  The occurrence of nodular corrosion not only results in thinning of the structural material, but when the corrosion layer is peeled off, there is a possibility that the radiation concentration in the coolant is increased and the exposure dose at the regular inspection is increased.

  In order to prevent nodular corrosion, a heat treatment method (Japanese Examined Patent Publication No. 61-45699, Japanese Examined Publication No. 63-58223) and a method of changing the alloy composition (Japanese Patent Laid-Open No. Sho-63) 60-43450 and JP-A-62-2228442) have been proposed.

  According to the above prior art, the occurrence of nodular corrosion is suppressed, and the corrosion form can be uniform corrosion in which an oxide film as a corrosion product grows uniformly. Further, according to the above prior art, the uniform oxide film to be formed has a very low protection property.

  It can be said that under the current operating conditions of actual furnaces, which are not the high burn-up and long-term use environment targeted by the present invention, the material according to the above prior art sufficiently performs the function of nodular corrosion resistance.

  In JP-A-10-260280, in a fuel cladding tube in which the sum of the Fe content to the whole and the Ni content to the whole is 0.25 weight percent or more and 0.35 weight percent or less, A technique is described in which the average surface roughness is reduced to 0.25 μm or less, thereby mitigating the influence on the occurrence of uniform corrosion.

(2) Hydrogen absorption characteristics On the other hand, when considering the soundness of Zircaloy members at high burnup, hydrogen absorption characteristics are an important material property along with corrosion resistance.

  Currently, fuel burnup is being promoted step by step to improve the economic efficiency of nuclear power plants. However, if the fuel assembly stays in the reactor for a long time, not only corrosion resistance but also hydrogen absorption characteristics are problematic. It becomes.

  From the knowledge so far, it has been pointed out that when the amount of hydrogen absorbed and accumulated in the zirconium alloy base material through a reaction with the coolant exceeds a certain level, the Zircaloy structural member may be embrittled.

  As shown in JP-A-62-2228442, a qualitative tendency that the amount of hydrogen absorption is reduced by increasing the Fe addition concentration in Zircaloy is now generally known.

  Based on this knowledge, for Zircaloy-2, which is mainly used in boiling water reactors, component adjustments such as increasing the Fe concentration within its specification range have been carried out. As a result, under the current operating conditions, It exhibits excellent performance in both corrosion resistance and hydrogen absorption characteristics, and fulfills the functions required for each fuel member.

  However, in recent years, due to changes in the reactor water environment such as hydrogen injection into the reactor water supply system of the nuclear reactor and changes in fuel design specifications such as thinning of the material components, structural materials are required from the viewpoint of corrosion and hydrogen absorption. The conditions of use are becoming stricter.

  Under such circumstances, in order to improve the reliability and performance of nuclear reactor fuel, development of technologies and materials for reducing hydrogen absorption is strongly demanded.

(3) Debris Fretting According to a recent report, debris fretting, abnormal corrosion, PCI (pellet cladding interaction), etc. are cited as the main causes of recent fuel failure cases that occurred in the United States (R. Yang, O. Ozer and HS Rosenbaum, An International Topical Meeting on Light-Water-Reactor-Fuel-Performance, April 10-13, 2000).

  Although it is said that the reliability of fuel in Japan is at a higher level than in other countries, it shows higher soundness against these damage factors in order to further improve the reactor economy and fuel reliability. Fuel is sought.

  As countermeasures against structural debris fretting, a structure in which the lower tie plate captures foreign matter or a structure in which a debris filter is provided in the lower tie plate has been proposed.

  As a countermeasure against debris fretting by improving the cladding tube, Japanese Patent Application Laid-Open No. 6-230160 discloses a technique for reducing the fretting wear by increasing the hardness of the lower outer surface of the cladding tube by ion beams from other portions. Proposed.

  In addition, by making the bottom end plug of the fuel rod longer, the cladding tube will not be worn even if foreign matter fretting occurs, or by applying an oxide film in advance to the cladding tube surface under the fuel rod to make it difficult to wear It has been known.

(4) PCI
As an improvement of the cladding tube for PCI, a method of reducing the stress applied to the cladding tube by lining a soft metal (mainly zirconium) with the cladding tube is known. Conventionally, this technique is generally used. This technique is useful in reducing the possibility of fuel damage.

  On the other hand, if the fuel cladding tube has a broken hole for some reason (primary breakage), cooling water enters the fuel rod from the broken hole and reacts with the metal lined to generate hydrogen, resulting in the generated hydrogen. It is known to produce secondary hydrogenation.

  Cracks tend to develop at locations where the ductility of the cladding tube has decreased due to hydrogenation.

  As a measure to suppress secondary hydrogenation of the zirconium liner cladding tube, a three-layer cladding tube with a thin zircaloy layer of 20 μm or less on the surface of the liner, an Sn alloy liner cladding tube, and an oxide film on the surface of the liner layer Known cladding tubes and cladding tubes with increased Fe content in the liner are known.

  Japanese Patent Publication No. 55-33037 discloses a zirconium alloy tube and a composite cladding tube comprising a zirconium layer metallurgically bonded to its inner surface and having an impurity content of less than 1000 ppm by weight and an oxygen concentration of less than 200 ppm by weight. Are listed.

  Japanese Patent Application Laid-Open No. 4-54491 discloses a fuel cladding having an inner surface made of a zirconium alloy having a thickness of 5 to 10 μm and excellent in corrosion resistance, an intermediate layer made of pure zirconium and an outer surface made of a zirconium alloy having excellent water corrosion resistance. A cladding tube consisting of a triple structure composed of layers is described.

  In Japanese Patent Publication No. 3-71078, as its prior art, a Zr-based alloy cladding tube is lined with a zirconium layer containing 0.1 to 1.0% by weight of Sn. Reactor fuel rods are described in which the total of other materials present in the zirconium in the bed is 0.5 wt% or less.

  Japanese Patent Publication No. 3-73832 discloses a technique in which the liner layer on the inner surface of the cladding tube is a Zr—Sn alloy, and the oxygen in the liner is 500 ppm by weight or less.

  Japanese Utility Model Laid-Open Nos. 53-25893 and 63-179286 describe a technique for forming an oxide film on a liner layer on the innermost surface of a cladding tube.

  Japanese Patent Application Laid-Open No. 63-179286 manufactures a nuclear fuel cladding tube characterized by forming an oxide film of 0.2 μm or more on the inner surface of an inner tubular member made of zirconium containing not more than 1200 ppm by weight of oxygen. The technology is described.

  In Japanese Patent Laid-Open No. 4-190191, in a zirconium liner-coated tube in which pure zirconium is lined inside a zircaloy alloy tube, the coated tube is immersed in an electrolytic solution containing Fe, Cr, Ni, and the coating is performed with an alternating current. A method for producing a nuclear fuel cladding tube is described in which an oxide film of 1 to 5 μm is formed on the inner surface of the tube.

  Japanese Patent Application Laid-Open No. 7-248391 describes a technique of oxidizing in an atmospheric pressure vessel equipped with a steam generator and a steam stirring device as a method of providing an oxide film on the inner surface of a zirconium liner.

  Japanese Patent Laid-Open No. 10-239473 discloses that a zirconium liner layer metallurgically bonded to a zirconium alloy tube has at least one of Fe, Ni, Co, Rh, and Pd of 0.05 wt% to 1 wt%. And a technique characterized in that an oxide film layer is formed on the inner surface of the liner layer.

JP 2001-66390 describes a fuel element characterized in that the inner metal barrier has a composition comprising Fe in the range of about 850 to 2500 ppm, the remainder zirconium and irreversible impurities.
JP-B 61-45699 JP-B 63-58223 JP 60-43450 A JP-A-62-2228442 Japanese Patent Laid-Open No. 10-260280 JP-A-6-230160 Japanese Patent Publication No.55-33037 JP-A-4-54491 Japanese Patent Publication No. 3-71078 Japanese Patent Publication No. 3-73832 Japanese Utility Model Publication No. 53-25893 JP-A 63-179286 Japanese Patent Laid-Open No. 4-190191 JP 7-248391 A Japanese Patent Laid-Open No. 10-239473 JP 2001-66390 A

  A part of the above prior art is applied to a high burnup fuel cladding tube having a fuel assembly average burnup of about 45 GWd / t, and functions for each purpose.

  However, in the near future, the fuel assembly will be used in an environment where the fuel assembly has an average burnup of about 45 GWd / t or more for a long period of time, or hydrogen injection, etc. due to plant aging countermeasure technology The use environment is expected to change.

  In such a use environment, the above-described conventional technology exhibits good corrosion resistance, hydrogen absorption resistance, strength characteristics, and cannot exhibit soundness in debris fretting, PCI, and secondary hydrogenation, and thus has a new configuration. There is an urgent need to develop a high burnup cladding tube.

  Therefore, the problem to be solved by the present invention is to exhibit good corrosion resistance, hydrogen absorption resistance and strength characteristics even with respect to further higher burnup and changes in use environment as described above, and debris fretting, An object of the present invention is to provide a high burnup cladding tube that exhibits soundness against PCI and secondary hydrogenation, and a method for producing the same.

  The inventor of the present application, as a result of investigating a material with higher economic efficiency and soundness when a high burnup of about 45 GWd / t or more is required, results in a liner type high burnup fuel cladding tube. A specific combination of the composition of the zirconium alloy cladding tube base and the composition of the zirconium liner layer produces unique effects that cannot be obtained with the prior art, exhibiting good corrosion resistance, hydrogen absorption resistance, strength properties, and The present inventors have newly found a high-burn-up fuel cladding tube and a method for producing the same that can show improved soundness in debris fretting, PCI, and secondary hydrogenation.

The fuel burner for high burnup according to the present invention is
In a high burnup fuel cladding used at a fuel assembly average burnup of about 45 GWd / t or greater,
Sn 1.2-1.7 wt%, Fe 0.20-0.35 wt%, Ni 0.03-0.08 wt%, Cr 0.05-0.20 wt%, unavoidable impurities And a zirconium liner layer made of zirconium containing the inevitable impurities and Fe in an amount of about 1000 ppm by weight or more inside the cladding substrate made of zirconium alloy with the balance being zirconium. It is characterized by.

  The average diameter of the intermetallic compound deposited in the zirconium alloy cladding tube base material may be 0.05 to 0.20 μm.

  Fe contained in the zirconium liner layer may be 1000 ppm by weight or more and 1500 ppm by weight or less.

  The surface roughness of the outer surface of the zirconium alloy cladding tube base material can be 0.2 μmRa or less.

  An oxide film may be formed on the surface of the zirconium alloy cladding tube base and the zirconium liner layer.

  The thickness of the oxide film formed on the surface of the zirconium alloy cladding tube base material may be 0.5 μm or more.

  Fe contained in the zirconium liner layer may be 1000 ppm by weight or more and 1500 ppm by weight or less.

The method for producing a high burnup fuel cladding according to the present invention comprises:
A zirconium alloy cladding tube base material containing nuclear fuel therein, and a zirconium liner layer metallurgically bonded to the zirconium alloy cladding tube substrate inside the zirconium alloy cladding tube substrate; The zirconium alloy cladding tube base material is 1.2 to 1.7% by weight of Sn, 0.20 to 0.35% by weight of Fe, 0.03 to 0.08% by weight of Ni, and 0.8% of Cr. High burnup fuel containing 05 to 0.20% by weight, containing inevitable impurities, the balance being made of zirconium, and the zirconium liner layer containing inevitable impurities of about 1000 ppm by weight or more of Fe, and the balance being made of zirconium In the manufacturing method of the cladding tube,
Performing a heat treatment for heating and cooling the fuel cladding tube for high burnup to a temperature of 900 ° C. or higher;
After the heat treatment step, performing a hot and / or cold plastic working treatment and an annealing treatment in the α phase,
Annealing the hot and / or cold plastic working process in the α phase, by the following equation, the average diameter D _A of the intermetallic compounds of the zirconium alloy cladding tube substrate in and a 0.05~0.20μm It is characterized by managing as follows.
D _A = [D ₀ ³ + 2.19 × 10 ⁴ × Σt _i ^0.74 × exp (−17100 / T _i )] ^1/3
Here, D ₀ : the average diameter of the intermetallic compound after heating to 900 ° C. or higher and cooling.
t _i : Holding time in the i-th annealing in the α phase.
T _i : i-th annealing temperature in the α phase.

In addition, a method for manufacturing a high burnup fuel cladding according to the present invention includes:
A zirconium alloy cladding tube base material containing nuclear fuel therein, and a zirconium liner layer metallurgically bonded to the zirconium alloy cladding tube substrate inside the zirconium alloy cladding tube substrate; The zirconium alloy cladding tube base material is 1.2 to 1.7% by weight of Sn, 0.20 to 0.35% by weight of Fe, 0.03 to 0.08% by weight of Ni, and 0.8% of Cr. High burnup fuel containing 05 to 0.20% by weight, containing inevitable impurities, the balance being made of zirconium, and the zirconium liner layer containing inevitable impurities of about 1000 ppm by weight or more of Fe, and the balance being made of zirconium In the manufacturing method of the cladding tube,
A step of applying a hot and / or cold plastic working treatment and an annealing treatment after metallurgically bonding the zirconium alloy cladding tube base and the zirconium liner layer;
After the step of applying the hot and / or cold plastic working treatment and annealing treatment, heat treatment is performed in air, water vapor or water, and the surface of the zirconium alloy cladding tube base and the zirconium liner layer is applied. And a step of forming an oxide film.

  In the present invention, Sn is 1.2 to 1.7% by weight, Fe is 0.20 to 0.35% by weight, Ni is 0.03 to 0.08% by weight, and Cr is 0.05 to 0.20% by weight. The zirconium liner layer containing the inevitable impurities including Fe of about 1000 ppm by weight or more and the remainder of zirconium is metallurgically metallized inside the zirconium alloy cladding tube base material containing Combined, it can be used for a long period of time with a high burnup of about 45 GWd / t or higher in the fuel assembly average burnup, or good corrosion resistance under the usage environment associated with plant aging countermeasure technologies such as hydrogen injection In addition, hydrogen absorption resistance and strength characteristics can be exhibited, and soundness can be improved with respect to debris fretting, PCI and secondary hydrogenation.

  Further, the method for producing a zirconium alloy cladding tube base material in a high burnup fuel cladding tube of the present invention can also be applied to members such as spacers, water rods, channel boxes, and the like, and the corrosion resistance and hydrogen resistance of the entire fuel assembly. It is possible to improve absorbency and secure strength characteristics.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
An example in which the high-burn-up fuel cladding tube of the present invention is applied to an actual reactor material will be described below.

  FIG. 1 is a perspective view of a fuel assembly loaded in a boiling water reactor, and FIG. 2 is a schematic diagram of the boiling water reactor.

  In the fuel irradiated in the BWR commercial reactor, a phenomenon that the hydrogen concentration in the cladding tube increases at a burnup of about 45 GWd / t or more has been observed (NUPEC high burnup fuel safety test, BWR high burnup fuel irradiation test) (Evaluation report, March 2002), the fuel average is required to reduce the hydrogen concentration when the burnup average is about 45 GWd / t or more.

  In FIG. 2, in a nuclear reactor, water 3 is changed to steam 4 by the thermal energy generated in the fuel element 2 in the core 1, and the turbine 5 is rotated by the steam 4 to generate power. The used steam is returned to the water 3 by the condenser 6 and circulated again to become the steam 4.

  The fuel element 2 in FIG. 2 is configured by arranging a large number of fuel assemblies shown in FIG. 1 as a unit.

  In general, the fuel assembly 7 has a predetermined number of fuel rods 9 and rod-like elements such as a water rod 10 arranged in a square shape in a channel box 8, and upper and lower tie plates 11 and lower tie plates via upper and lower ends thereof. The spacers 13 are respectively mounted at a plurality of positions at intermediate height positions at predetermined intervals.

  In FIG. 1, the channel box 8, the water rod 10, the fuel rod 9, and the spacer 13 are in direct contact with water.

  The fuel rods 9 contain nuclear fuel pellets therein, and the soundness of the fuel rod cladding tube is important for the soundness of the fuel rods and the fuel assembly and hence the reactor.

  Currently, Zircaloy-2 or Zircaloy-4 is used for the fuel rod cladding tube, and high corrosion resistance and reduction of hydrogen absorption are required at high burnup.

  Furthermore, based on the current situation where the use environment is expected to change due to plant aging countermeasure technology such as long-term use or hydrogen injection due to higher burnup, it shows good corrosion resistance, hydrogen absorption resistance, strength characteristics, In addition, the fuel burner tube for high burnup according to the present invention, which can show soundness for debris fretting, PCI, and secondary hydrogenation, was applied to the fuel rod 9.

  Moreover, the zirconium alloy cladding tube base material used for the high burnup fuel cladding tube of the present invention can be applied to members such as the channel box 8, the water rod 10, the spacer 13, and the like. By applying the zirconium alloy cladding tube base material used in the fuel cladding tube for high burnup according to the present invention, the corrosion resistance and hydrogen absorption resistance of the member are improved, and the soundness of the fuel assembly is further improved.

  The fuel cladding for high burn-up according to the present invention includes a zirconium alloy cladding tube base material containing nuclear fuel therein, and the zirconium alloy cladding tube base material and metallurgical inside the zirconium alloy cladding tube substrate. And a zirconium liner layer bonded to the substrate.

  In the concentration of the alloy element added to the zirconium alloy-coated tube base material, the Sn concentration is preferably 1.2 to 1.7% by weight (wt%) from the viewpoint of strength, corrosion resistance, and workability.

  The Fe concentration is preferably 0.20 to 0.35 wt% from the viewpoint of corrosion resistance, hydrogen absorption resistance, workability, and neutron absorption cross section. Furthermore, 0.20-0.30 wt% is suitable, More preferably, it is 0.25-0.30 wt%.

  The Ni concentration is preferably 0.03 to 0.08 wt% from the viewpoint of corrosion resistance and hydrogen absorption resistance. The Cr concentration is preferably 0.05 to 0.20 wt% from the viewpoint of corrosion resistance, hydrogen absorption resistance, and workability. Furthermore, 0.05-0.15 wt% is suitable, More preferably, it is 0.10-0.15 wt%.

  Further, the total of Fe, Ni and Cr concentrations is preferably 0.39 wt% or more from the viewpoints of nodular corrosion resistance, uniform corrosion resistance and hydrogen absorption resistance.

  When the Fe concentration of the zirconium liner layer is lower than about 1000 ppm in the corrosion test in 400 ° C. water vapor, the corrosion rate increases as the Fe concentration decreases, but the corrosion rate is saturated at about 1000 ppm or more (D. R. Lutz, SB Wisner, DM Farkas, RB Adamson, Topfuel '99, Avignon, 1999). For this reason, in the high burnup fuel cladding tube of the present invention, it is necessary to be about 1000 ppm or more in order to suppress secondary hydrogenation.

  On the other hand, the Fe concentration in the zirconium liner layer necessary for improving the PCI resistance performance is higher when the Fe concentration is higher than about 1000 ppm in a test simulating PCI (DR Lutz, S). B. Wisner, DM Farkas, RB Adamson, Topfuel '99, Avignon, 1999). For this reason, it is desirable that the Fe concentration is low as the PCI resistance performance, but the failure rate in the PCI simulation test is small in the increase in the Fe concentration between 1000 ppm and 1500 ppm, and rapidly increases between 1500 ppm and 3000 ppm. It is desirable that the Fe concentration is 1500 ppm or less.

  Therefore, in the fuel cladding tube for high burnup that combines the suppression of secondary hydrogenation by improving the corrosion resistance of the zirconium liner layer and the improvement of the PCI resistance performance, the Fe concentration of the zirconium liner layer is 1000 to 1500 ppm. Is preferred.

  The high burnup fuel cladding tube of the present invention and the comparative cladding tube were subjected to a corrosion test.

Table 1 shows the average diameter and alloy composition of the intermetallic compounds of the zirconium alloy cladding tube base subjected to the nodular corrosion test.

  The nodular corrosion test was carried out at 410 ° C. for 4 hours in water vapor at about 12 MPa and then at 520 ° C. in water vapor at about 12 MPa for 16 hours.

  The outer surface of the clad alloy base tube side of the cladding tube after the corrosion test was photographed, and the coverage of the nodular oxide film (oxide film observed as white or gray in appearance) occupying the outer surface was determined.

  FIG. 3 is a graph plotting the coverage of the nodular oxide film in the above corrosion test of the 12 types ((1) to (12)) of the cladding tubes shown in Table 1.

In FIG. 3, (7) to (12) are cladding tubes in which the alloy composition of the zirconium alloy cladding tube substrate is in the specification range of Zry-2 and the Fe concentration of the zirconium liner layer is about 1000 ppm or more. (1) to (6) in FIG. 3 are cladding tubes in which the alloy composition of the cladding tube base material made of zirconium alloy and the Fe concentration of the zirconium liner layer are both within the scope of the present invention.

  The solid line and the broken line in FIG. 3 are obtained by the least square method by power approximation for the plot points (1) to (6) and (7) to (12).

  As can be seen from FIG. 3, in any of (1) to (6) and (7) to (12), when the average diameter of the intermetallic compound increases, a nodular oxide film appears and the average diameter increases. As a result, the ratio tends to increase.

  However, for the cladding tubes (1) to (6), the average diameter of the intermetallic compound in which the nodular oxide film is generated is larger than (7) to (12).

  Particularly, in the cladding tubes (1) to (6) in which the alloy composition of the zirconium alloy cladding tube base material and the Fe liner concentration in the zirconium liner layer are both within the scope of the present invention, It can be seen that when the average diameter of the compound is about 0.20 μm or less, the ratio of the nodular oxide film is small.

  From this, in the cladding tube in which the alloy composition of the zirconium alloy cladding tube base material and the Fe liner concentration in the zirconium liner layer are both within the scope of the present invention, the average diameter of the intermetallic compound in the zirconium alloy cladding tube substrate is preferable. The range was about 0.20 μm or less.

  In the cladding tube in which the alloy composition of the zirconium alloy cladding tube base material and the Fe liner concentration in the zirconium liner layer are both within the scope of the present invention, the average diameter of the intermetallic compound in the zirconium alloy cladding tube substrate is about 0. Since the generation of nodular oxide film is hardly observed at 18 μm or less, the more preferable range of the average diameter of the intermetallic compound in the zirconium alloy cladding tube substrate is about 0.18 μm or less.

  4 and 5 show that the alloy composition of the cladding tube base material made of a zirconium alloy is within the specification range of Zry-2 (Zry-2 in the figure) and the alloy composition of the zirconium alloy cladding tube base material of the present invention. A cladding tube within the alloy composition specification range of a fuel cladding tube for high burnup (in the figure, the present invention, Sn concentration about 1.5 wt%, Fe concentration about 0.25 wt%, Cr concentration about 0.1 wt%, Ni concentration about 0 .05 wt%), a hydrogen corrosion rate and weight increase when a sample for corrosion test with a thickness of about 100 μm was prepared from the surface and subjected to a uniform corrosion test for 50 days in water vapor of about 10 MPa at 400 ° C. FIG.

  The appearance after the test was black, and the oxide film had a uniform thickness even in the observation of the gold phase in the cross section.

  In FIG. 4, the broken line and the solid line indicate the high combustion of the cladding tube in which the alloy composition of the zirconium alloy cladding tube base material is within the Zry-2 specification range and the alloy composition of the zirconium alloy cladding tube substrate, respectively. The hydrogen absorption rate of the cladding tube within the alloy composition specification range of the fuel cladding tube for a certain degree is obtained by the least square method by linear approximation with respect to the average diameter of the intermetallic compound.

  As is apparent from FIG. 4, the hydrogen absorption rate of the cladding tube in the alloy composition specification range of the high burnup fuel cladding tube of the present invention is the specification range in which the alloy composition of the zirconium alloy cladding tube base material is Zry-2. Compared to Zry-2, the cladding tube which is systematically smaller than the cladding tube in the above and is in the alloy composition specification range of the high burnup fuel cladding tube of the present invention has the effect of suppressing the hydrogen absorption rate. Moreover, it is shown that the hydrogen absorption rate becomes smaller as the average diameter of the intermetallic compound is larger.

  That is, to reduce the hydrogen absorption rate of the high-burn-up fuel cladding tube, the cladding tube within the alloy composition specification range of the high-burn-up fuel cladding tube of the present invention is used, and the zirconium alloy cladding tube base material It can be seen that it is effective to increase the average diameter of the intermetallic compound therein.

  In FIG. 5, the increase in the weight of the cladding tube in the alloy composition specification range of the fuel cladding tube for high burnup of the present invention is the same as the cladding tube in which the alloy composition of the zirconium alloy cladding tube base material is in the specification range of Zry-2. It is shown that the uniform corrosion amount of the cladding tube in the alloy composition specification range of the fuel cladding tube for high burnup of the present invention is equal to or somewhat smaller than Zry-2.

  That is, it can be seen that the cladding tube in the alloy composition specification range of the fuel cladding tube for high burnup of the present invention has a uniform corrosion resistance equal to or higher than that of Zry-2.

  FIG. 5 also shows that the increase in the weight of Zry-2 tends to increase somewhat when the average diameter of the intermetallic compound is about 0.05 μm or less.

  For this reason, the result shown in FIG. 5 of Zry-2 is applied to the cladding tube in the alloy composition specification range of the fuel cladding tube for high burnup of the present invention, and the fuel cladding tube for high burnup of the present invention is applied. For the cladding tube in the alloy composition specification range, the average diameter range of the intermetallic compound in the zirconium alloy cladding tube base material effective for suppressing the uniform corrosion amount was set to about 0.05 μm or more.

  As described above, Sn is 1.2 to 1.7% by weight, Fe is 0.20 to 0.35% by weight from the viewpoints of suppressing nodular corrosion, reducing the hydrogen absorption rate, and reducing the uniform corrosion amount. %, Ni is 0.03 to 0.08% by weight, Cr is 0.05 to 0.20% by weight, contains inevitable impurities, and the remainder of the zirconium alloy cladding tube base material is made of zirconium. Liner type high burnup nuclear fuel used at a fuel assembly average burnup of about 45 GWd / t or more, metallurgically bonded with a zirconium liner layer containing 1000 ppm by weight or more and inevitable impurities, the balance being zirconium. In the cladding tube, the average diameter of the intermetallic compound precipitated in the zirconium alloy cladding tube substrate was set to 0.05 to 0.20 μm.

  A more preferable range of the average diameter of the intermetallic compound precipitated in the zirconium alloy cladding tube base is 0.05 to 0.18 μm.

  The high burnup fuel cladding tube of the present invention can be manufactured, for example, by the following method.

  Zirconium alloy coated tube base material is Zr sponge with 1.2 to 1.7 wt% Sn, 0.20 to 0.35 wt% Fe, 0.03 to 0.08 wt% Ni, 0.05 to 0.00. After adding 20 wt% Cr, melting, hot forging, and drilling, it is heated at a temperature of about 1000 ° C. or higher and rapidly cooled.

  The drilling process may be performed after heating at a temperature of about 1000 ° C. or higher and rapid cooling.

  The zirconium liner layer is formed by adding about 1000 ppm or more of Fe to Zr sponge, melting and hot forging, heating and quenching at a temperature of about 1000 ° C. or more, and drilling.

  A zirconium alloy-coated tube base material and a zirconium liner layer are machined to form a billet, hot extruded, cold-rolled and then annealed to obtain a zirconium liner element tube.

  Cold rolling and annealing are repeated once or a plurality of times on the raw tube, the outer surface is polished, and a cladding tube having a predetermined diameter and thickness can be manufactured.

  In addition, in this manufacturing process, after heating and quenching at a temperature of about 1000 ° C. or higher, it is possible to add a heat treatment that heats and quenches at a temperature of about 900 ° C. or higher in the process before the final annealing. . The zirconium liner layer can also be hot extruded after drilling.

  In the final heating at a temperature of about 1000 ° C. or higher or about 900 ° C. or higher, in the hot and / or cold plastic working and annealing after quenching (annealing is about 800 ° C. or lower), a predetermined temperature and heating time are set. By selecting, a high burnup fuel cladding tube having an average diameter of the intermetallic compound in the zirconium alloy cladding tube substrate of 0.05 to 0.20 μm is obtained.

It is also possible to add a step of annealing the zirconium liner layer from the viewpoint of improving the PCI resistance performance of the zirconium liner layer in the step before machining the zirconium alloy cladding tube base material and the zirconium liner layer into a billet. It is. In addition, when the heat input in the α phase is high and / or cold plastic working or annealing after the heat treatment to be heated to 900 ° C. or higher and cooled, and the Fe concentration in the zirconium liner layer is low However, in the case of the present invention containing Fe of about 1000 ppm or more, even if the heat input is large, the zirconium liner layer is not suitable for the liner layer. A crystal grain size corresponding to suitable mechanical properties can be obtained.

  In the high burnup fuel cladding tube of the present invention, the outer surface of the zirconium alloy cladding tube base portion is in direct contact with the reactor water, so that the region near the outer surface, that is, the outer surface from 1/3 of the cladding tube wall thickness. Side region, more preferably, from 1/5 of the cladding tube thickness to the outer surface side region, and more preferably from 1/10 of the cladding tube thickness to the outer surface side region or from the outer surface to the thickness depth. The average diameter of the intermetallic compound in the zirconium alloy-coated tube base material in the region of 50 μm is more preferably 0.05 to 0.18 μm.

  Note that only the zirconium alloy cladding tube base material within the alloy composition specification range of the present invention is effective in reducing the hydrogen absorption amount at high burnup, suppressing the nodular corrosion, and reducing the uniform corrosion amount. When the fuel assembly average burnup is greater than or equal to / t, and under unusual water quality, it is not sufficient to maintain soundness from the viewpoint of PCI resistance. Moreover, by simply metallurgically bonding a zirconium liner layer containing about 1000 ppm by weight or more of Fe and unavoidable impurities and the balance of zirconium inside Zircaloy-2 or Zircaloy-4, anti-PCI performance can be obtained. Can be maintained, but not necessarily sufficient to maintain the integrity of the fuel assembly. On the other hand, Sn is 1.2 to 1.7% by weight, Fe is 0.20 to 0.35% by weight, Ni is 0.03 to 0.08% by weight, and Cr is 0.05 to 0.20%. A zirconium liner layer containing about 1000 ppm by weight of Fe and unavoidable impurities, the balance being zirconium and the remainder being zirconium is metallurgical inside the zirconium alloy cladding tube base material containing weight percent and inevitable impurities and the balance being zirconium. By using a cladding tube bonded to the fuel, it is used at a fuel assembly average burnup of about 45 GWd / t or more, or maintains the anti-PCI performance and the secondary hydrogenation suppression effect under unique water quality. Thus, it is possible to provide a fuel cladding tube for high burnup with improved soundness that can reduce the amount of corrosion and is effective in suppressing nodular corrosion.

  Next, the surface roughness of the cladding tube will be described.

Table 2 shows the results of a corrosion test performed on two types of Zry-2 cladding tubes (Zry-2 (A) and Zry-2 (B)) having different surface roughnesses.

  As shown in Table 2, it can be seen that in any type of cladding tube, the smaller the surface roughness, the better the corrosion resistance.

  Therefore, in order to improve the corrosion resistance, it is preferable to reduce the surface roughness as much as possible. However, in order to reduce the surface roughness, a plurality of surface finishing steps are introduced to sequentially reduce the surface roughness, or to increase the grain size. Therefore, it is necessary to reduce the surface roughness by using a small whetstone, polishing paper, abrasive, etc., and this is not practical because it causes a lot of time and cost.

  For this reason, the range of surface roughness that can be manufactured in the fuel burner for high burn-up of the present invention is set to 0.2 μmRa or less. Ra is arithmetic average roughness (centerline average roughness). In production, a more preferable range is 0.05 to 0.2 μmRa.

  Next, the case where an oxide film is formed on the surface of the high burnup fuel cladding tube will be described.

  FIG. 6 shows a high burnup fuel cladding tube according to the present invention, in which an oxide film is formed on the outer surface of the cladding tube to suppress fuel damage due to debris fretting, and a zirconium liner for suppressing fuel damage due to secondary hydrogenation. This is an example in which an oxide film is formed on the surface of the layer.

  In FIG. 6, reference numeral 14 denotes a zirconium alloy cladding tube base, reference numeral 15 denotes a zirconium liner layer, and reference numerals 16 and 17 denote oxide films.

  As described above, since the corrosion rate is small when the Fe concentration of the zirconium liner layer is about 1000 ppm or more, the high burnup fuel cladding tube of the present invention has relatively low corrosion characteristics on both the liner layer and the outer surface of the cladding tube. A close good oxide film can be obtained.

  In order to examine the oxide film thickness on the outer surface of the cladding tube, the microhardness of the outer surface including the oxide film was examined for the cladding tube having an oxide film formed on the outer surface.

  FIG. 7 shows an indentation formed on the outer surface of the coated tube on which the oxide film was formed at room temperature with a load of 200 g and a holding time of 30 seconds. It is the result of investigation.

  The dotted line is a linear approximation of the microhardness to the oxide film thickness by the least square method.

  After removing the liner layer from the cladding tube, an oxide film was formed by corrosion in water vapor at 400 ° C. on the 21st or 105th. The oxide film thickness is a value obtained from the weight change before and after the corrosion, and an oxide film of about 2 μm and about 5 μm is formed.

  As the microhardness, values of about 260 to 270 Hv and about 310 to 320 Hv were measured for the coated tubes on which oxide films of about 2 μm and about 5 μm were formed, respectively.

  The composition of the zirconium alloy-coated tube base material on which the oxide film is formed is as follows: Sn concentration: about 1.5 wt%, Fe concentration: about 0.25 wt%, Cr concentration: about 0.1 wt%, Ni concentration: about 0.05 wt%, The average diameter of the intermetallic compound is about 0.07 to 0.1 μm.

  Usually, since the hardness of an oxide is larger than that of a metal, the hardness of the surface is increased by forming an oxide film on the surface.

  On the other hand, the strength of the cladding tube increases with irradiation, but it is known that there is a saturation tendency with respect to the irradiation dose, and that there is a proportional relationship between the strength of the cladding tube at room temperature and the microhardness (Mishima Yoshitoshi et al., Journal of Atomic Energy Society of Japan, vol.29, 90, 1987).

  Also. It has been shown that the non-irradiated Zry-2 cladding tube has a microhardness at room temperature of 170 to 180 Hv and a microhardness after the first cycle irradiation of approximately 240 Hv (Mishima Yoshitoshi et al., Journal of the Atomic Energy Society of Japan , Vol. 29, 90, 1987).

  It is considered that the influence of debris on the cladding tube appears more in the radiation dose range immediately after the start of irradiation, where the strength of the cladding tube is relatively low. It has a great inhibitory effect on ting.

  In the case of the previous example, since the cladding tube tensile strength, that is, the hardness tends to be saturated with respect to the irradiation amount after one cycle of irradiation, an oxide film thickness range in which the microhardness of the outer surface of the cladding tube is about 240 Hv or more is set. Effective range was achieved by suppressing debris fretting. That is, in FIG. 7, an oxide film thickness of about 0.5 μm or more where the microhardness is about 240 Hv or more is set to a suitable range due to suppression of debris fretting.

  That is, the high burnup fuel cladding tube of the present invention has an oxide film formed on the surface, so that the surface hardness at the initial stage of irradiation with a relatively low intensity increases, and the debris flickering at a time when the influence of debris is relatively large. As a result, the soundness up to a high burnup can be improved.

  The thickness of the oxide film formed on the outer surface is more preferably about 0.5 μm or more, and a more preferable range for suppressing debris fretting is about 3 μm or more.

  Next, formation of an oxide film will be described.

  FIG. 8 shows the relationship between the oxide film thickness on the surface of the cladding tube and the holding time in the air at 400 ° C. in the oxide film forming process.

The fuel cladding tube for high burnup of the present invention shown in Table 3 was heated in air at 400 ° C., and the oxide film thickness was determined from the weight increase after heating.

Conversion from weight increase to oxide film thickness is weight increase 15 mg / dm ² = oxide film thickness 1 μm, and average of oxide film thickness formed on the surface of the zirconium alloy cladding tube base and the zirconium liner layer We are looking for a value.

  A, B, C, and D in FIG. It is.

  When the oxide film thickness is approximated to the power with respect to the heating time (horizontal axis in FIG. 8) and the exponent is obtained by the method of least squares, it becomes about 1/3, and the oxide film thickness tends to be saturated with respect to time. Indicated. This tendency was the same for all of A, B, C, and D.

  Thus, when the oxide film thickness (weight increase) increases according to the 1/3 power rule, it indicates that a good oxide film with strong adhesion and protection is formed. It is shown that the oxide film formed on the surface of both the zirconium alloy cladding tube base and the zirconium liner layer of the high burnup fuel cladding tube is a good oxide film with strong adhesion and protection.

  As described above, in the fuel cladding tube for high burnup according to the present invention, since the corrosion resistance of the zirconium liner layer is excellent, the surfaces of both the zirconium alloy cladding tube substrate and the zirconium liner layer in air or water vapor Even when an oxide film is formed simultaneously, a good oxide film having strong adhesion and protection can be formed simultaneously on the surfaces of both the zirconium alloy cladding tube base and the zirconium liner layer. The oxide film formed on the surface of the zirconium alloy cladding tube base material is also effective in suppressing shadow corrosion. The oxide film formed on the surface of the zirconium liner layer is also effective in improving the hydrogen absorption resistance.

  In the method for producing a high burnup fuel cladding tube of the present invention, as in the above example, Sn is 1.2 to 1.7 wt%, Fe is 0.20 to 0.35 wt%, Ni is 0.00. 03 to 0.08 wt%, Cr 0.05 to 0.20 wt%, containing unavoidable impurities, the zirconium alloy cladding tube base material consisting of zirconium, Fe about 1000 wtppm or more unavoidable impurities In addition, the cladding tube containing the zirconium liner layer, the balance of which is zirconium, is metallurgically bonded and subjected to hot and / or cold plastic working treatment and annealing treatment, and then the heat treatment is performed in air, steam or water. By doing so, a good oxide film with strong adhesion and protection can be formed simultaneously on the surfaces of the zirconium alloy cladding tube base and the zirconium liner layer.

  The heat treatment in air, water vapor or water can be performed after finishing processing such as external polishing, or after welding the fuel rod lower end plug.

  The temperature and time of the heat treatment can be determined depending on the oxide film thickness formed on the surfaces of the zirconium alloy cladding tube base and the zirconium liner layer. In order to obtain a good oxide film with strong adhesion and protection, it is desirable to perform heat treatment at a temperature of, for example, 300 to 400 ° C., but in order to obtain an oxide film with a predetermined thickness in a shorter time, 400 ° C. or higher. It is also possible to heat-process at the temperature of. However, the heat treatment is desirably performed at a temperature lower than the final annealing temperature.

  Next, management of the average diameter of the intermetallic compound in the zirconium alloy cladding tube base material will be described.

  A zirconium alloy cladding tube base material containing nuclear fuel therein, and a zirconium liner layer metallurgically bonded to the zirconium alloy cladding tube substrate inside the zirconium alloy cladding tube substrate; The zirconium alloy cladding tube base material is 1.2 to 1.7% by weight of Sn, 0.20 to 0.35% by weight of Fe, 0.03 to 0.08% by weight of Ni, and 0.8% of Cr. High burnup fuel containing 05 to 0.20% by weight, containing inevitable impurities, the balance being made of zirconium, and the zirconium liner layer containing inevitable impurities of about 1000 ppm by weight or more of Fe, and the balance being made of zirconium In the manufacturing method of the cladding tube, in the hot and / or cold plastic working treatment and annealing treatment in the α phase after the heat treatment that is heated to 900 ° C. or higher and cooled, The average diameter of manufacturing cladding tubes intermetallic compound substrates in the as controlled by the following principle.

As a result of examining the relationship between the size of Zry-4 intermetallic compound (Zr (Fe, Cr) ₂ ), time and temperature (JP GROS, JF WADIER, J. Nucl. Mater., 172) 85, 1990), it is reported that the size (diameter) and D of the intermetallic compound are given by the following equation (secondary cumulative annealing parameter).
D ³ −D ₀ ³ = [(k / T ² ) exp (−Q / RT)] t (1)
D ₀ : Size of intermetallic compound before annealing
T: Annealing temperature (K)
t: annealing time (h)
k: coefficient (= 1.11 × 10 ⁻¹¹ )
Q / R: coefficient (= 18700)

  In this report, when the size of the intermetallic compound before annealing is 0.12 μm, annealing is performed at temperatures of 650 ° C., 700 ° C., 750 ° C., and 780 ° C. for 5 hours, 15 hours, 30 hours, and 50 hours. The size of the intermetallic compound after performing the above is examined, and the above-described formula (1) is derived.

On the other hand, as a result of examining the relationship between time and temperature in more detail using the size of the intermetallic compound shown in this report, the present inventors have found that D ³ -D ₀ ³ is t ^{0. .74} is proportional to, we found that it is possible to accurately represents the size of the intermetallic compound by the following equation.
D ³ −D ₀ ³ = 2.19 × 10 ⁴ × t ^0.74 × exp (−17100 / T)
... (2)

Since the above formula (2) deals with the volume change of the intermetallic compound, it is considered that not only Zr (Fe, Cr) ₂ but also Zr ₂ (Fe, Ni) can be applied. 1.2 to 1.7 wt%, Fe 0.20 to 0.35 wt%, Ni 0.03 to 0.08 wt%, Cr 0.05 to 0.20 wt%, including inevitable impurities This is applied to the average diameter of the intermetallic compound in the zirconium alloy cladding tube base material with the balance being zirconium.

Thus, the average of intermetallic compounds in the zirconium alloy cladding tube base material in the hot and / or cold plastic working treatment and annealing treatment in the α phase, which is performed after the heat treatment of heating to 900 ° C. or higher and cooling. The diameter D _A can be obtained by the following formula (3).
D _A = [D ₀ ³ + 2.19 × 10 ⁴ × Σt _i ^0.74 × exp (−17100 / T _i )] ^1/3 (3)
D ₀ : Average diameter of intermetallic compound after heating to 900 ° C. or higher and cooling.
t _i : Holding time (h) in the i-th annealing in the α phase.
T _i : i-th annealing temperature (K) in the α phase.

Sn 1.2-1.7 wt%, Fe 0.20-0.35 wt%, Ni 0.03-0.08 wt%, Cr 0.05-0.20 wt%, unavoidable impurities A zirconium alloy clad tube base material comprising the remainder of zirconium, and a zirconium liner layer comprising Fe in an inevitable impurity of about 1000 ppm by weight or more and the remainder comprising zirconium, after being heated to about 1000 ° C. and rapidly cooled Machined to make a billet. The combined billet was hot extruded at about 600 ° C. for several minutes, cold-rolled, and then annealed at 670 ° C. or 635 ° C. for 2.3 hours. Subsequently, cold rolling was performed, annealing was performed at 621 ° C. for 1.3 hours, and this cold rolling and annealing process was repeated twice. Furthermore, it cold-rolled and annealed at 777 degreeC for 2.5 hours. Since the average diameter of the intermetallic compound in Zry-2 heated to about 1000 ° C. and rapidly cooled was 0.02 to 0.04 μm, D ₀ was set to 0.03 μm in the above formula (3), and D _A was obtained. On the way, the cladding tubes annealed at 670 ° C. or 635 ° C. for 2.3 hours were 0.10 μm or 0.09 μm, respectively.

  On the other hand, the average diameter of the intermetallic compound according to the formula (1) was about 0.07 μm in all cases.

When the average diameter of the intermetallic compound in the zirconium alloy cladding tube substrate of the manufactured cladding tube was examined with a transmission electron microscope, it was subjected to annealing at 670 ° C. or 635 ° C. for 2.3 hours. for each a 0.10μm or 0.09 .mu.m, the equation (3) shows precisely a mean diameter _{D a} of the intermetallic compounds of zirconium alloy cladding tube substrate in, in the formula (1) It has been found difficult to obtain the average diameter of the target intermetallic compound.

  In addition, the average diameter of the intermetallic compound of the cladding tube base material made of zirconium alloy was observed for the Zr-Fe-Cr-based and Zr-Fe-Ni-based intermetallic compounds with a transmission electron microscope for an arbitrary region of the outer surface, It was set as the average diameter when the intermetallic compound was approximated to a sphere.

Thus, a high burn-up liner mold comprising a zirconium alloy cladding tube base material containing nuclear fuel and a zirconium liner layer metallurgically bonded to the zirconium alloy inside the cladding tube base material. In the nuclear fuel cladding tube, the zirconium alloy cladding tube base material includes 1.2 to 1.7 wt% of Sn, 0.20 to 0.35 wt% of Fe, and 0.03 to 0.08 wt% of Ni. , A zirconium alloy cladding tube base material containing 0.05 to 0.20% by weight of Cr, in addition to unavoidable impurities, and the balance being zirconium, wherein the zirconium liner layer is about 1000 ppm by weight or more of Fe, Heat treatment that heats and cools to a temperature of 900 ° C. or higher in a high-burn-up fuel cladding tube that is a zirconium liner layer that contains inevitable impurities and the balance is zirconium. Performed in descending, hot and / or cold plastic working process in the α phase at the annealing process, heat treatment is performed according to the above formula (3), the average diameter D of the intermetallic compounds of zirconium alloy cladding tube substrate in It is possible to obtain a fuel cladding tube for high burnup in which _A is 0.05 to 0.20 μm.

The perspective view of the fuel assembly loaded into a boiling water reactor. Schematic diagram of a boiling water reactor. The graph which showed the relationship between an outer surface nodular oxide film coverage and an average intermetallic compound diameter. The graph which showed the relationship between an average intermetallic compound diameter and a hydrogen absorption rate. The graph which showed the relationship between an average intermetallic compound diameter and a weight increase. The cross section of the cladding tube of this invention which formed the oxide film in the surface. The graph which showed the relationship between the surface thickness of the outer surface of the cladding tube and the microhardness. The graph which showed the relationship between the oxide film thickness of the cladding tube surface in an oxide film formation process, and 400 degreeC air retention time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core 2 Fuel element 3 Water 4 Steam 5 Turbine 6 Condenser 7 Fuel assembly 8 Channel box 9 Fuel rod 10 Water rod 11 Upper tie plate 12 Lower tie plate 13 Spacer 14 Zirconium alloy cladding tube base material 15 Zirconium liner Layer 16 Oxide film 17 Oxide film

Claims (1)

A zirconium alloy cladding tube base material containing nuclear fuel therein, and a zirconium liner layer metallurgically bonded to the zirconium alloy cladding tube substrate inside the zirconium alloy cladding tube substrate; The zirconium alloy cladding tube base material is 1.2 to 1.7% by weight of Sn, 0.20 to 0.35% by weight of Fe, 0.03 to 0.08% by weight of Ni, and 0.8% of Cr. 05 to 0.20% by weight, containing inevitable impurities, the balance being made of zirconium, the zirconium liner layer containing Fe in an inevitable impurity of about 1000 ppm to 1500 ppm by weight, and the balance being made of zirconium, In the method of manufacturing a fuel cladding tube for high burnup,
Performing a heat treatment for heating and cooling the fuel cladding tube for high burnup to a temperature of 900 ° C. or higher;
After the heat treatment step, performing a hot and / or cold plastic working treatment and an annealing treatment in the α phase,
Annealing the hot and / or cold plastic working process in the α phase, by the following equation, the average diameter D _A of the intermetallic compounds of the zirconium alloy cladding tube substrate in and a 0.05~0.20μm A method for producing a high burnup fuel cladding tube, characterized by comprising:
D _A = [D ₀ ³ + 2.19 × 10 ⁴ × Σt _i ^0.74 × exp (−17100 / T _i )] ^1/3
Here, D ₀ : the average diameter of the intermetallic compound after heating to 900 ° C. or higher and cooling.
t _i : Holding time in the i-th annealing in the α phase.
T _i : i-th annealing temperature in the α phase.

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