Patent Number: 050808583
Section: description

In FIG. 2, 7 designates the fuel assembly in the form of an elongated multi-corner channel with a wall 6. The fuel assembly 7 accomodates spacers 8 of a known type. The spacers 8 are here provided with windows 10 but may also be without such windows. FIG. 3 shows one of the same spacers 8 seen from above. FIG. 4 schematically shows a spacer 8 provided with a skirt 12 which extends the frame of the spacer 8 in a direction towards the direction of flow of the coolant. The skirt 12 is provided with windows 13 to reduce the amount of material and with deflection fins 14. If the spacer 8 is provided with windows 10, deflection fins 9 may also be arranged in these windows. As mentioned, FIGS. 5 and 6 show sections of FIG. 4. From FIG. 6 it is clear that the side pieces of the skirt may be made divided at 15 and be made resilient so that, when the fuel rod bundle is inserted into the fuel assembly 7, the side pieces of the skirt make good contact with the assembly wall 6, thus obtaining centering of the spacer 8. The invention functions in such a way that the lower edge of the skirt 12 scrapes cooling water from the assembly wall 6 and its fins contribute to increased turbulence and to conduct the cooling water towards the centre of the spacer 8. The lower edge of the skirt 12 is provided with guide studs 11 to facilitate the insertion of the fuel rod bundle into the fuel assembly. In addition, the lower edge has been given a convex configuration, also this to facilitate the insertion of the bundle into the fuel assembly. FIGS. 7-9 show a similar embodiment but with the skirt 12 being detachable. As previously, the skirt 12 is provided with deflection fins 14. At its top, the skirt 12 has a number of tape-formed insertion members 16 which may be inserted into the spacer 8 for fixing the skirt 12 to the frame of the spacer 8. At the top the insertion members 16 are bent inwards, at 18, to facilitate guiding the bundle in the fuel assembly. At the guide studs 11 the insertion members 16 have been provided with holes 19 to lock the members 16 and hence the skirt 12 in the spacer 8. The lower edge of the skirt 12 has also been designed arrow-shaped to facilitate the insertion of the bundle into the fuel assembly 7. For this purpose also the tips 17 are inwardly-bent. The skirt 12 may be designed in separate pieces-one for each side with openings at 15 and resilient towards the wall of the fuel assembly. Another possibility is that the skirt is designed as an undivided closed sleeve in both of the above-mentioned embodiments. A certain distance betweeen the assembly wall and the skirt 12 must then be maintained. This results in a somewhat less efficient device from the point of view of cooling. On the other hand, the risk of vibrations is then reduced. The design with a detachable skirt means that the skirt may be made of a material different from that of the spacer 8 itself, which may be an advantage. The skirt 12 may, for example, be made of Zircaloy, which has a lower neutron absorption than Inconel, from which the spacer 8 is normally made and which has a higher neutron absorption.