Patent Number: 052232115
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a novel zirconium based alloy plate, a method of manufacturing this alloy plate, a fuel channel and a fuel assembly using this alloy plate. Zirconium is a material having high corrosion resistance and a small neutron absorption cross section and is therefore used for a reactor fuel assembly member. For this kind of use, Zr-Sn-Fe-Cr-Ni alloys called zircaloy-2 and zircaloy-4 are mainly used. If these alloys are used in a nuclear reactor for a long time, elongation, bending and deformation in particular directions occur as shown in FIG. 2, because (0001) planes thereof are oriented in the direction of plate thickness. If a bending deformation occurs in a fuel channel box, the space for driving the control rod is reduced. Such a phenomenon impedes the operation of the reactor. Also, if a bending deformation occurs, the distance to the fuel cladding tube is changed so that the ratio of water and uranium is locally changed, thereby causing a change in fission reactivity and, hence, abnormal heating. By this effect, corrosion of the fuel cladding tube is accelerated. Further, fuel damage may thereby be caused. To prevent bending deformation of the fuel channel box due to such non-uniformity of neutron exposure, uniformization of neutron exposure based on changing the fuel assembly loading position in the reactor core has been studied. This study, however, has not succeeded in preventing bending deformation. The reduction in the control rod driving space and the change in fission reactivity caused by bending deformation are major factors of limitation of the service life of the fuel channel box. The corrosion of the fuel channel box also is a factor of limitation of the service life. Japanese Patent Examined Publication Nos. 56-12310 and 60-44387 disclose a method for improving the corrosion resistance by a heat treatment based on quenching a Zr alloy from an .alpha.+.beta. phase temperature range or a .beta. phase temperature range. By this method, however, the bending deformation due to irradiation growth cannot be reduced for the reason described later, and this method provides no effective technique for limiting irradiation growth of zirconium alloy members. This conventional method uses a heat treatment for improving only the corrosion resistance of zirconium alloy members without changing the grain size, orientation and mechanical characteristics thereof. For this heat treatment, therefore, heating to an .alpha.+.beta. phase temperature range (800 to 980.degree. C.) rather than a .beta. phase temperature range (.gtoreq.980.degree. C.) in which coarsening of crystal grains occurs, followed by quenching, is effected. The crystal orientation, which is an important factor of limitation of irradiation growth, is not changed by this heat treatment and therefore no effective irradiation growth limiting technique is provided. Japanese Patent Unexamined Publication No.59-229475 discloses a method of orienting crystals so that an fl value is 0.15 to 0.5. This method also provides no irradiation growth limiting technique or rather promotes irradiation growth. SUMMARY OF THE INVENTION An object of the present invention is to provide a zirconium alloy member free from the above-mentioned elongation and bending deformation due to irradiation growth. Specifically, a main object of the present invention is to provide a long-life zirconium based alloy tubular member and a channel box in which the irradiation growth does not occur. According to the present invention, these objects can be achieved by making &lt;0001&gt; orientation of a hexagonal crystal of a zirconium alloy plate substantially perfectly random as shown in FIG. 1. According to one aspect of the present invention, there is provided a zirconium based alloy plate of low irradiation growth, containing not more than 5 wt % Sn and/or not more than 5 wt % Nb, and the balance Zr of not less than 90 wt %, the alloy plate having &lt;0001&gt; orientation of hexagonal crystal which orientation (Fr value) ranges from 0.20 to 0.5 with respect to direction perpendicular to the surface of the plate. According to another aspect of the present invention, there is provided a square tubular member made of a zirconium based alloy plate of low irradiation growth, containing not more than 5 wt % Sn and/or not more than 5 wt % Nb, and the balance Zr of not less than 90 wt %, the alloy member having &lt;0001&gt; orientation of hexagonal crystal in which &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the tubular member ranges 0.20 to 0.50, another orientation (Ft value) with respect to longitudinal direction of the cylindrical member ranges 0.25 to 0.36, and still another orientation (Fl value) with respect to circumferential direction of the tubular member ranges 0.25 to 0.36. According to still another aspect of the present invention, there is provided a zirconium based alloy plate of low irradiation growth, containing not more than 5 wt % Sn and/or not more 5 wt % Nb, and the balance Zr of not less than 90 wt %, the alloy having .alpha. phase, and the grain size of the alloy being in the range of 50 to 500 .mu.m. According to a further aspect of the present invention, there is provided a zirconium based alloy member of low irradiation growth, containing not more than 5 wt % Sn and/or not more than 5 wt % Nb, and the balance Zr of not less than 90 wt %, the alloy having .alpha. phase, the alloy plate having &lt;0001&gt; orientation of hexagonal crystal in which &lt;0001&gt; orientation is substantially random, and strain occurring due to fast neutron irradiation of 2.times.10.sup.22 (n/cm.sup.3) being not more than 3.times.10.sup.-4. According to still a further aspect of the present invention, there is provided a method of producing a zirconium based alloy plate of low irradiation growth which contains not more than 5 wt % Sn and/or not more than 5 wt % Nb and the balance Zr of not less than 90 wt %, in which the alloy is heated in a .beta. single phase temperature range and is cooled, the method comprising the steps of retaining the alloy in the .beta. single phase temperature range in a short period of time so that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the alloy member is 0.20 to 0.40. The method of producing a zirconium based alloy plate of low irradiation growth in accordance with the present invention is characterized by comprising the step of retaining in a short period of time the alloy member in the .beta. single phase temperature range so that value of parameter P defined by P=(3.55+log t).times.log(T-980) where t is a retention period of time and T(h) is a retaining temperature (.degree. C.) is not less than 0.8, and quenching the alloy. According to still a further aspect of the present invention, there is provided a method of producing a square tubular member made of a low irradiation growth zirconium based alloy containing not more than 5 wt % Sn and/or not more than 5 wt % Nb and the balance Zr of not less than 90 wt %, comprising the steps of: locally induction-heating and keeping the tubular member in a .beta. single phase temperature range; and forcibly cooling the heated portion of the tubular member by cooling medium, the improvement comprising the steps of retaining the tubular member portion in a short period of time in the .beta. single phase temperature range so that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the square tubular member is 0.20 to 0.40; and then quenching the heated portion. According to a further aspect of the present invention, there is provided a method of producing a square tubular member made of a zirconium based alloy, comprising the steps of continuously induction-heating a portion of the tubular member locally while moving it relatively, and forcibly cooling the heated portion by a cooling medium, the improvement comprising the steps of inserting in the tubular member a mandrel made of a metal material having a thermal expansion coefficient larger than that of the alloy, and heating the tubular member from the outer surface of the tubular member while fixing at least both ends of the tubular member by the mandrels. According to a further aspect of the present invention, there is provided a fuel channel box formed of a square tubular member formed by welding two channel-shaped members made of zirconium based alloy, the alloy having &lt;0001&gt; orientation (Fr value ) with respect to direction perpendicular to the surface of the square tubular member of 0.20 to 0.50, the whole surface of the channel box being provided with an oxide layer formed by an autoclave treatment. According to a further aspect of the present invention, there is provided a fuel assembly comprising a fuel rod provided within a fuel cladding tube with fuel pellets, a channel box receiving a plurality of pieces of the fuel rods, a spacer for partitioning the fuel rods received in the channel box, and upper and lower tie plates disposed respectively at the upper and lower portions of the channel box, the channel box being made of a zirconium based alloy containing not more than 5 wt % Sn and/or not more than 5 wt % Nb and the balance Zr, the alloy having a texture that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the plate ranges from 0.20 to 0.50. According to a further aspect of the present invention, there is provided a method of using a nuclear fuel channel box made of a zirconium based alloy in which channel box a plurality of nuclear fuel rods are disposed, the alloy having a texture that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the tubular member ranges from 0.20 to 0.50, the nuclear fuel being exchanged during the use of the channel box at least two times. According to still a further aspect of the present invention, there is provided a method of using a fuel channel box formed of a tubular member formed by welding two channel-shaped members made of a zirconium based alloy, the alloy having a texture that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the tubular member ranges from 0.20 to 0.50, the whole surface of the channel box being provided with an oxide film formed by an autoclave treatment, the channel box being used so that the degree of burn-up on taking-out is not less than 32 Gwd/t or so that nuclear fuel is exchanged at least two times during the use thereof. According to still a further aspect of the present invention, there is provided a method of using a fuel assembly having a fuel assembly having a fuel rod having fuel pellets disposed within a fuel cladding tube, a channel box receiving a plurality of pieces of the fuel rods, a spacer for partitioning the fuel rods received in the channel box, and upper and lower lattice plates disposed respectively at the upper and lower portions of the channel box, the channel box being made of a zirconium based alloy containing not more than 5 wt % Sn and/or not more than 5 wt % Nb and the balance Zr of not less than 90 wt %, the alloy having a texture that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of a plate ranges from 0.20 to 0.50, the channel box being used so that the degree of burn-up on taking-out is not less than 32 GWd/t or so that nuclear fuel is exchanged at least two times during the use thereof. According to a further aspect of the present invention, there is provided a method of using a nuclear fuel channel box made of a zirconium based alloy in which channel box a plurality of nuclear fuel rods are disposed, the alloy comprising hexagonal crystals having a texture that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the tubular member ranges from 0.20 to 0.50, the channel box being used so that the degree of burn-up on taking-out is not less than 32 GWd/t or so that it exposes neutron irradiation not less than 10.sup.22 n/cm.sup.2 during the use thereof. According to a further aspect of the present invention, there is provided a method of operating a nuclear reactor having within a reactor core a plurality of nuclear fuel channel boxes each formed of a tubular box made of a zirconium based alloy, comprising the steps of exchanging fuel after a predetermined period of operation time, and subsequently operating the reactor in a predetermined period of time, the alloy containing hexagonal crystals having a texture that &lt;0001&gt; orientation (Fr value) with respect to direction perpendicular to the surface of the tubular member ranges from 0.20 to 0.50, the channel boxes which are subjected to such operation as the degree of burn-up on taking-out is about 32 GWd/t or more being disposed in the same operation position as that of prior operation thereof, and fuel being exchanged at least two times during the use thereof. It is not only to exchange the channel box at least two times but also to use the channel box under a less deformation thereof for such period of time as a degree of burn-up on taking out becomes 32 GWd/t or more or for such a period of time as neutron irradiation at an amount of neutron exposure becomes 10.sup.22 n/cm or more. Specifically, the channel box can be effectively used at a high degree of burn-up of 38 GWd/t or higher, or 45 GWd/t or higher.