Patent Number: 061342904
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transport container of a fuel assembly of a light water reactor such as a boiling water reactor (hereinafter, referred simply to as BWR), a pressurized water reactor (hereinafter, referred simply to as PWR) or the like, and to a method of transporting the fuel assembly thereof. In particular, the present invention relates to a fuel assembly transport container and a fuel assembly transport method, which can transport the fuel assembly itself or a fuel protective container housing the fuel assembly while fixedly supporting a motion of the fuel assembly or the fuel protective container. 2. Description of the Prior Art A vibration generated in transporting a fuel assembly of a light water reactor such as BWR, PWR or other similar reactors, is a factor of causing wear in a metallic contact portion of the fuel assembly. In the fuel assembly, a spent fuel assembly has no problem as to somewhat of wear caused during transport because a waste disposal of the spent fuel assembly, reprocessing thereof and the like are carried out. Therefore, there is no need of subjecting a transport container of the spent fuel assembly to specific vibration measures for preventing vibrations of the fuel assembly, and the spent fuel assembly may be transported in a state of being safely accommodated in the transport container. As a result, in order to house a plurality of spent fuel assembly, a transport container, which has a large capacity and is compact in its structure, has been used. On the other hand, in the case of a transport container of a fuel assembly which is not used yet, since the fuel assembly is mounted to a reactor so that an operation of the reactor is carried out, it is very important that wear and damage should not be caused in a metallic contact portion or other similar portions of the fuel assembly which is not used yet by the vibration thereof during transporting the fuel assembly to the reactor, a store house or the like. So, when transporting the fuel assembly, a transport container of the fuel assembly is subjected to specific measures for preventing vibrations of the fuel assembly so that a reliability is maintained in the fuel assembly and a reactor using the fuel assembly. For preventing a vibration of the fuel assembly, there is a need of housing the fuel assembly in a fuel protective container (also, called as an inner container of a fuel transport container) in a state that a motion of the fuel assembly is fixedly supported, and further, housing the fuel protective container housing the fuel assembly in a basket of the transport container while fixedly supporting a motion of the fuel protective container. Here, FIGS. 25A and 25B show a conventional fuel protective container housing a fuel assembly in a state that the fuel assembly is fixedly supported. A fuel assembly 101 is constructed in the following manner. Specifically, a plurality of fuel rods are tied up in a bundle with a metallic upper tie-plate 102 which has a relatively large-mass and is situated on an upper portion when the fuel assembly 101 is accommodated in a reactor, and with a metallic lower tie-plate 103 which has a relatively large-mass and is situated on a lower portion when the fuel assembly 101 is accommodated in a reactor. The lower tie-plate 103 has step portions tapered toward the crosswise inner peripheral side surfaces 106c, 106c which are opposite each other, described hereinafter. This fuel assembly 101 has a square pillar shape having a square shape in its lateral cross section, and has a length of one side of the square cross section is substantially 4 m in a longitudinal direction of the fuel assembly 101. Further, bundled fuel rods (fuel rod group) constituting the fuel assembly 101 are supported by means of a fuel spacer 104 with a predetermined interval. A fuel protective container 105 comprises a container main body 106 having a substantially U shape in its lateral cross section, a cap member 107 which is detachably mounted on an upper portion (opening portion) of the container main body 106 which is transporting so as to cover the opening thereof, and protective members 108a.about.108d. The protective members 108a, 108b, 108c and 108d are formed along a bottom surface 106a of the container main body 106 along the horizontal direction when the container main body 106 is transported, longitudinally inner peripheral side surfaces 106b; 106b facing each other, crosswise inner peripheral side surfaces 106c; 106c which are opposite each other, and a lower surface 107a on the container main body side of the cap member 107, respectively. The fuel assembly 101 is accommodated in a fuel assembly housing space defined by the container main body 106 of the fuel protective container 105 and the cap member 107 so that the longitudinal direction of the fuel assembly 101 is parallel to the aforesaid horizontal direction during the transport of the container main body 106. In order to prevent a vibration when transporting the fuel protective container 105 in which the fuel assembly 101 is housed, several sets of transport (fastening) separators 110 are interposed between the fuel spacers 104, between the fuel spacer 104 and the upper tie-plate 102, and between the fuel spacer 104 and the lower tie-plate 103. These separators are arranged so that gaps between the separators and the protective members 108b mounted on the longitudinal inner peripheral side surfaces 106b; 106b are formed. That is, after the fuel assembly 101 is housed in the container main body 106, when the opening side upper portion of the container main body 106 is covered by the cap member 107 so as to be closed, the fuel assembly 101 is pressed down along a up and down direction (vertical direction) during the transport of the fuel assembly 101 by a fastening force of the cap 107 to the bottom surface 106a of the container main body 106 via the transport separator 110, and thus, is fixedly restricted therein. The fuel assembly 101 housed integrally with the fuel protective container 105 is transported while being fixedly supported by the fastening force via the transport separators arranged between the bottom surface 106a of the container main body 106 and the cap 107. However, in the aforesaid conventional fuel protective container 105 in which the fuel assembly 101 is fixedly supported, the fuel assembly 101 is merely fixedly supported by fastening the fuel assembly 101 from the vertical direction. As shown in FIGS. 25A and 25B, the fuel assembly 101 is not clamped in the horizontal direction along the crosswise direction. For this reason, the gap still exists between both sides of the fuel assembly 101 and the protective member 108b formed on the longitudinal inner peripheral side surfaces 106b, 106b of the container main body 106. As a result, there is the possibility that the fuel assembly 101 slides and moves on the protective member 108a formed on the bottom surface 106a of the container main body 106 along the aforesaid crosswise (lateral) direction. In this case, as a power of resistance to a relatively sliding motion between the fuel assembly 101 and the protective member 108a formed thereon, there are recited the own weight of the fuel assembly 101 and a frictional force between the fuel assembly 101 and the protective member 108a based on a fastening force by the cap 107. However, in the above power of resistance, concerning the fastening force by the cap member 107 recited as the frictional force, since the fastening portion is the transport separator 110 inserted into the fuel assembly 101, a compressive rigidity is small. When a great fastening force is applied on the transport separator 110, there is the possibility that the fuel assembly 101 is deformed; for this reason, a satisfied fastening force has not been provided by the cap member 107 on the transport separator 110. Therefore, concerning the frictional force resulting from the fastening force, a satisfied frictional force capable of preventing the sliding motion of the fuel assembly 101 has not been provided. Consequently, because a tightly restricting force of the fuel assembly 101 is short in the horizontal direction along the longitudinal direction with respect to the fuel protective container 105, there has arisen a problem that the fuel assembly 101 moves (vibrates) while sliding in the fuel protective container 105 according to a vibration of the horizontal direction of a relatively high acceleration during the transport of fuel protective container 105. In addition, a fastening force to the fuel assembly 101 is short in the horizontal direction along the longitudinal direction (axial direction) of the fuel assembly 101. Therefore, for example, in the case where a mixed-oxide fuel (MOX) assembly mixing a plutonium oxide (PuO.sub.2) and an uranium oxide (UO.sub.2) is used as the fuel assembly, during transport of the MOX fuel assembly, the MOX fuel assembly 101 is exothermic, and then, an elongation difference is caused due to a difference in thermal expansion between the MOX fuel assembly 101 and the fuel protective container 105. For this reason, a relatively positional shift is generated between the MOX fuel assembly 101 and the fuel protective container 105. In addition, a gap is defined between both end portions along the longitudinal direction (axial direction) of the MOX fuel assembly 101 and both side surfaces 106c of the fuel protective container 105 and between the MOX fuel assembly 101 and the bottom surface 106a of the fuel protective container 105. As a result, similar to the aforesaid case of the horizontal direction along the crosswise direction, there is the possibility that the fuel assembly 101 slides and moves (vibrates) on the protective member 108a formed on the bottom surface 106a of the container main body 106 along the longitudinal direction according to a vibration of the horizontal direction of relatively high acceleration which arises from transporting the fuel protective container 105. Moreover, in the conventional fuel protective container 105 in which the fuel assembly 101 is fixedly supported, since the fuel assembly 101 is fixedly supported by means of the transport separators 110 located between the fuel spacers 104, between the fuel spacer 104 and the upper tie-plate 102, and between the fuel spacer 104 and the lower tie-plate 103, a tightly fixing force is short in the attachment portions of the upper tie-plate 102 and the lower tie-plate 103 on both ends of the fuel assembly 101 in the longitudinal direction thereof. Therefore, resulting from mass of the upper tie-plate 102 and the lower tie-plate 103, there is the possibility that a remarkably different vibration is generated between the upper tie-plate 102 and the protective barrier 106 and between the lower tie-plate 103 and the same as compared with a vibration in the central portion of the fuel assembly 101 according to the aforesaid vibration of the horizontal direction during transport of the fuel protective container 105. As described above, because the tightly fixing force in the horizontal direction is short or the tightly fixing force on portions locating the upper and lower tie-plates 102 and 103 is short, the fuel assembly 101 has slid and vibrated in the fuel protective container 105 housing the fuel assembly 101. This sliding vibration of the fuel assembly 101 causes a problem of accelerating a wear of the metallic contact portion of the bundled fuel rods group. Furthermore, in the conventional fuel protective container 105 in which the fuel assembly 101 is fixedly supported, the fuel assembly 101, that is, the own weight of fuel rods group is supported by the transport separators 110. As a result, most of the own weight of fuel rods group are supported by a row of the fuel rods (the lowest row) which is closest to the bottom surface 106a of the fuel protective container 105 in the fuel rod groups. For this reason, in a transport process of the fuel assembly 101, when a transport container housing the fuel assembly 101 is loaded and unloaded with the use of a crane (hoist) or other similar machines, in the case where an instantaneous force having a relatively high acceleration is applied to the fuel assembly 101, there is the possibility that the fuel rods situated on the lowest row are plastically deformed. This causes a problem that a loading and unloading condition during transport of the fuel assembly 101 must be strictly limited. In particular, in a future fuel assembly, there is a tendency for a diameter of a fuel rod to be shortened. For this reason, there is the possibility that the loading and unloading restraint condition during the fuel assembly transporting process becomes further strict in future. Thus, it has been desired to present a proposal to immediately solve the above problem according to the deformation of the fuel assembly. On the other hand, the fuel assembly has long one side whose length is substantially 4 m in the longitudinal direction thereof; for this reason, vibration is not sufficiently prevented only by fixedly supporting both side portions of the fuel protective container in the longitudinal direction thereof. Therefore, in order to fixedly support the fuel protective container housing the fuel assembly in a basket of a transport container, there is a need of fixedly supporting an intermediate portion of the fuel protective container in the longitudinal direction thereof. However, specific fixedly supporting means for protecting the aforesaid fuel protective container has not been conventionally developed. Especially, the case of transporting the transport container which houses a plurality of fuel protective containers in the basket of the transport container, the fixedly supporting means basically needs to be provided for each fuel protective containers. However, conventionally, there is no existence of a small-size fixedly supporting means having a small spatial occupancy, and a spatial ratio occupied by the fixedly supporting means is large. This is the greatest factor of obstructing a development of a compact and large-capacity fuel transport container. Further, in the case where the MOX fuel assembly is used as the fuel assembly, since the MOX fuel assembly is exothermic during the transport of the MOX fuel assembly so that a temperature of the fuel protective container 105 becomes high, fixedly supporting means needs to be provided in order to maintain a high reliability under such a high temperature condition. However, there is a problem that fixedly supporting means having a high reliability under the high temperature condition has not been developed conventionally. Furthermore, according to the prior art, a plurality of fuel protective containers are fixedly supported in the basket of the transport container for each fuel protective container. For this reason, when the plurality of fuel protective containers are fixedly supported, manpower and time is much spent in accordance with the number of the fuel protective containers. Therefore, there has been strongly desired a development of a transport container having fixedly supporting means which is capable of reducing manpower and easily and fixedly supporting a plurality of fuel protective containers in a basket of the transport container in a short time. SUMMARY OF THE INVENTION The present invention is directed to overcome the foregoing problems. Accordingly, it is a first object of the present invention to provide a transport container of a fuel assembly and method of transporting the fuel assembly, which can prevent the fuel assembly from being slid and vibrated in an interior of a fuel protective container by improving (reinforcing) a tightly fixing (restricting) force of the horizontal direction along a crosswise direction and a longitudinal direction of the fuel assembly housed in the fuel protective container and a tightly fixing force of portions locating upper and lower tie-plates even if a relatively large-level vibration is generated during transporting the fuel protective container, making it possible to stably transport the fuel assembly. Further, a second object of the present invention is to provide a transport container of a fuel assembly and method of transporting the fuel assembly which can maintain a safety of a fuel assembly even in the case where a relatively high-acceleration instantaneous force is applied to the fuel assembly. Furthermore, a third object of the present invention is to provide a transport container of a fuel assembly and method of transporting the fuel assembly having fixedly supporting means which includes a small size and a low spatial occupancy, and is excellent in reliability under a high temperature condition thereby making the transport container compact and reducing the fixedly restriction work of the fuel assembly. To achieve the such objects, according to one aspect of the present invention, there is provided a transport container having at least one fuel assembly element including at least one fuel assembly for transporting the fuel assembly element, the transport container comprising container means having an inner surface portion to be fit to the at least one fuel assembly element for housing the at least one fuel assembly element, said inner surface portion having a predetermined shape substantially corresponding to a fit portion of the at least one fuel assembly element; and support means for pushing the at least one fuel assembly element against the inner surface portion of the container means along a fixedly support direction so as to fit the fit portion of the at least one fuel assembly element to the inner surface portion of the container means thereby fixedly supporting the at least one fuel assembly element to the container means. This aspect of the present invention has an arrangement that the container means is provided with a basket including at least one basket hole having the inner surface portion, said at least one basket hole having four inner side surfaces providing a substantially square-shaped cross section, said at least one fuel assembly element includes at least one fuel protective container in which the at least one fuel assembly is housed, said at least one fuel protective container having four outer side surfaces providing a substantially square-shaped cross section and being housed in the at least one basket hole so that the four outer side surfaces of the at least one fuel protective container are opposite to the four inner side surfaces of the at least one basket hole, respectively, said inner surface portion is formed by two inner side surfaces of the four inner side surfaces of the at least one basket hole which are adjacent each other so as to be shaped as a substantially V, said two inner side surfaces being set according to the fixedly support direction, and wherein said fit portion of the at least one fuel assembly element includes a corner portion defined by the two outer side surfaces of the four outer side surfaces of the at least one fuel protective container so as to be fitted in the V shaped inner surface portion. In preferred embodiment of this aspect, when the transport container is positioned along a horizontal plane in order to transport the transport container, the one of the two inner side surfaces of the at least one basket hole is inclined at a predetermined angle with respect to the horizontal plane or the one of the two inner side surfaces of the at least one basket hole is positioned along the horizontal plane. This aspect of the present invention has an arrangement that the support means is located so as to be interposed between remained two outer side surfaces of the four outer side surfaces of the at least one fuel protective container and remained two inner side surfaces of the four inner side surfaces of the at least one basket hole and is in contact with the remained two outer side surfaces and the remained two inner side surfaces so as to push the at least one protective container against the V shaped inner surface portion thereby fixedly supporting the corner portion of the at least one fuel protective container to the V shaped inner surface portion thereof. In preferred embodiment of this aspect, the basket has a substantially cylindrical shape and plurality of the basket holes arranged as a square shape and is divided into a plurality of basket portions in a longitudinal direction of the basket, said support means has a grid plate having substantially square shaped grid holes of a same arrangement as the plurality of basket holes, said grid plate being interposed between at least one adjacent basket portions and said at least one fuel protective container being inserted in at least one of the basket holes and at least one of the grid holes corresponding to the at least one of the basket holes and has a drive device for moving the grid plate along a diagonal direction of the at least one of the basket holes toward the V shaped inner surface portion thereof so as to push the at least one fuel protective container against the V shaped inner surface portion of the at least one of the basket holes thereby fixedly supporting the corner portion of the at least one fuel protective container to the V shaped inner surface portion thereof. This aspect of the present invention has an arrangement that the basket has a substantially cylindrical shape and plurality of the basket holes arranged as a square shape and is divided into a plurality of basket portions in a longitudinal direction of the basket, said support means has a pair of grid plates arranged so as to face each other each of which has substantially square shaped grid holes of a same arrangement as the plurality of basket holes, each of said grid plates being interposed between at least one adjacent basket portions and said at least one fuel protective container being inserted in at least one of the basket holes and at least one of the grid holes of each of the grid plates corresponding to the at least one of the basket holes and has a drive device for moving one of the grid plate along the one of the two inner side surface of the at least one of the basket holes toward the other of the two inner side surface thereof and moving other of the grid plate along the other of the two inner side surface thereof toward the one of the two inner side surface thereof so as to push the at least one fuel protective container against the V shaped inner surface portion of the at least one of the basket holes thereby fixedly supporting the corner portion of the at least one fuel protective container to the V shaped inner surface portion thereof. In order to achieve the such objects, according to another aspect of the present invention, there is provided a method of transporting at least one fuel assembly element including at least one fuel assembly, the method comprising the steps of providing a transport container including a basket which has at least one basket hole having an inner surface portion to be fit to the at least one fuel assembly element, said inner surface portion having a predetermined shape substantially corresponding to a fit portion of the at least one fuel assembly element; housing the at least one fuel assembly element in the at least one basket hole of the basket so that the fit portion of the at least one fuel assembly element is opposite to the inner surface portion of the at least one basket hole; and pushing the at least one fuel assembly element against the inner surface portion of the at least one basket hole along a fixedly support direction so as to fit the fit portion of the at least one fuel assembly element to the inner surface portion of the at least one basket hole thereby fixedly supporting the at least one fuel assembly element to the basket. In order to achieve the such objects, according to further aspect of the present invention, there is provided a method of transporting at least four fuel assemblies, the method comprising the steps of preparing at least one fuel protective container capable of housing at least four assemblies, housing the at least four fuel assemblies in the at least one fuel protective containers, preparing a transport container in which a basket is housed, said basket including at least one basket hole which is capable of accommodating the at least one fuel protective container and which has an inner surface portion to be fit to the at least one fuel protective container, said inner surface portion having a predetermined shape substantially corresponding to a fit portion of the at least one fuel protective container, housing the at least one fuel protective container in the at least one basket hole so that the fit portion of the at least one fuel protective container is opposite to the inner surface portion of the at least one basket hole and pushing the at least one fuel protective container against the inner surface portion of the at least one basket hole along a fixedly support direction so as to fit the fit portion of the at least one fuel assembly element to the inner surface portion of the at least one basket hole thereby fixedly supporting the at least one fuel assembly element to the basket. In order to achieve the such objects, according to further aspect of the present invention, there is provided a method comprising the steps of providing a transport container including a basket which has a plurality of basket holes arranged as a predetermined shape for housing at least one fuel assembly element in one of the basket holes, each of said basket holes being provided with an opening end portion preparing a fixing plate having a plurality of holes of a same arrangement as the plurality of basket holes attaching the fixing plate to the opening end portion of the basket holes so as to be detachable therefrom, said at least one fuel assembly element being housed in at least one of the basket holes and at least one of the holes of the fixing plate mounting a project portion on a position of the at least one fuel assembly element so that the project portion projecting toward the at least one of the basket holes, said mounted position of the at least one fuel assembly element being opposite to the opening end portion of the at least one of the basket holes and pushing the fixing plate against the project portion of the at least one fuel assembly element so as to fixedly support the at least one fuel assembly element to the fixing plate. In the above aspects of the present invention, the at least one fuel assembly element having a fit portion (corner portion) defined by two outer side surfaces thereof is pushed by the support means against the inner surface portions constituting the V shaped portion of the at least one basket hole of the basket which is opposite to the corner portion so that the corner portion of the at least one fuel assembly element is fit to the V shaped portion of the at least one basket hole whereby the at least one fuel assembly element is fixedly supported to the at least one basket hole of the basket. Therefore, the own weight of the fuel assembly element housing the fuel assembly is supported by the V shaped portion of the at least one basket hole of the basket and the movement of the at least one fuel assembly element is fixedly restriction by the supporting means, making it possible to prevent the at least one fuel assembly element from being slid and vibrated and to stably transport the fuel assembly element.