Patent Number: 045267456
Section: summary

TECHNICAL FIELD The present invention relates to a fuel assembly with a lower lattice device or element and a plurality of fuel rods supported by said lattice device, a fuel box which surrounds all the fuel rods, and a base with a downwardly-facing inlet opening for reactor coolant, the fuel assembly having at least one vertical by-pass channel for a water flow along but being separated from the fuel rods. DISCUSSION OF PRIOR ART More particularly, the invention relates to a a fuel assembly which is constructed in such a way that it is capable of being used, with advantage, in a boiling water reactor which is originally intended for fuel assemblies having no water channel of the kind mentioned above, without it being necessary to introduce any considerable change of the other components of the reactor. A problem, which will then be encountered, is how to achieve a necessary by-pass flow through the central water channel(s) when the reactor power is being reduced by reducing the speed of the circulating pumps. With a fuel assembly according to the invention, an automatic adjustment of the water flow supplied to the above-mentioned vertical water channels takes place in such a manner that the magnitude of this flow is dependent on the magnitude of the power supplied to these water channels. DISCLOSURE OF THE INVENTION A fuel assembly according to the invention is intended to be arranged in a reactor core in a conventional manner, with four fuel assemblies in each core module, water gaps between adjacent assemblies, and a control rod of cruciform cross-section in each module. In addition to the flow flowing along the fuel rods and in contact therewith, the reactor core is traversed by a first by-pass flow, which is located at the above-mentioned gaps formed between the fuel assemblies, and by a second by-pass flow which is located at the above-mentioned vertical water channels. According to the invention, there is provided a fuel assembly having a vertical center line and comprising a lower lattice device and a plurality of vertical fuel rods supported by said lattice device, a fuel box which surrounds all the fuel rods, and a sleeve-like base with a downwardly-facing inlet opening for reactor coolant, the fuel assembly having at least one vertical water channel for a water flow flowing along the fuel rods and being separated therefrom, wherein the at least one vertical water channel is hydraulically connected at its lower end to at least one substantially radially extending channel opening out at the side surface of the fuel assembly, the wall of said base being provided with at least one through-hole, the at least one through-hole being positioned at a lower level than the outlet openings of said substantially radial channels and beng arranged in hydraulic connection with said inlet opening via a space surrounded by said base.