Patent Number: 
Section: description

In FIG. 1-3 an absorber body according to an embodiment of the invention is shown. The absorber body 1 is formed as a rod of a neutron absorbing material, here boron carbide, B4C, with a length of approximately 100 mm, and a thickness t of in the order of magnitude 5.6 mm along a larger part of its length and with a reduced thickness of in the order of magnitude 5 mm at its two ends. As is clear from FIG. 3, the absorber body 1 has an essentially circular cross-section, whereby its thickness t is the same as its diameter. The absorber body 1 comprises a plurality of areas 2, 3, 4 with a locally reduced thickness. Two such areas 2, 3 are arranged at the opposite ends of the absorber body 1. The areas 2, 3 are defined by a bevel of the absorber body 1 such that its thickness decreases in the direction towards the respective ends. The length l of the areas 2, 3 corresponds essentially to the thickness of the absorber body 1. The length l of the areas 2, 3 is in this case thus of the order of magnitude 5 mm. Considerable deviations from these measures may however be the case. Consequently, the maximal thickness reduction in these areas 2, 3 may be of in the order of magnitude 2-20%, preferably 5-15% and most preferred 7-12%. The length l of the areas 2, 3 may be of in the order of magnitude 0.25xc3x97t to 2xc3x97t, preferably 0.5xc3x97t to 1.5xc3x97t, and most preferred 0.7xc3x97t to 1.2xc3x97t. The areas 2, 3 do not have to be defined by a bevel of the absorber body 1, but could also be defined by a stepped reduction of the thickness of the absorber body 1. A plurality of further areas 4 with a reduced thickness are also provided on the absorber body 1. These areas 4 are defined by recesses 4 or notches each of which extends around the circumference of the absorber body 1 and thereby defines circular notches in the same. At each recess 4 the absorber body 1 thus has a sharply marked waist which has a reduced thickness relative to the closest neighbouring portion 5 of the absorber body 1. The distance between the recesses 4 may vary and may for example be of in the order of magnitude 0.5xc3x97t to 10xc3x97t, preferably 1xc3x97t to 5xc3x97t, or, such as here, of in the order of magnitude 1.5xc3x97t to 2.5xc3x97t. The recesses 4 are essentially evenly distributed along the length of the absorber body 1. The material which is taken away for the provision for the respective notch 4 is small, i.e. the lowered absorption capacity of the absorber body 1 is small in relation to the possibility of expansion in axial direction of the peripheral portion of the body which such notches make possible. The recesses 4 have a depth d which may vary considerably from case to case. In order not to weaken the absorber body too much, the ratio between the depth d of said recesses 4 and the thickness t of the absorber body 1 is xe2x89xa60.4, preferably xe2x89xa60.35. In the shown embodiment all recesses 4 have essentially the same depth, but they could be provided in such a manner that they alternately have a larger or smaller depth, respectively, along the length of the absorber body 1. Each recess 4 has a width of in the order of magnitude 0.02xc3x97t to 0.4xc3x97t, preferably 0.05xc3x97t to 0.2xc3x97t. Thereby is meant the width of the recesses 4 at the outer surface of the absorber body 1. In the shown embodiment the width of the recesses 4 decreases in the direction towards the centre of the absorber body 1. The total width btot for all recesses 4 along the length of the absorber body 1 constitutes here 5-10% of said length. The recesses 4 reduce the existence of tensions between the peripheral portion of the absorber body 1 and its centre, whereby is meant the tensions which are caused due to the fact that a lower amount of radiation reaches the centre and that consequently the peripheral portions are subjected to a larger radiation induced expansion/swelling than the centre of the absorber body 1. Thanks to the existence of the recesses 4, the absorber body 1 will thus have an increased useful life in relation to a corresponding absorber body without said recesses 4. Such a solid rod will, based on experience, break into parts of about the length of the diameter or into a larger number of pieces than what is the case with the absorber body 1 provided with the recesses 4. Such a division of a solid rod leads, due to a certain repositioning, to a larger total axial elongation than the elongation which the centre part undergoes in the absorber body 1 provided with recesses 4 if this absorber body does not break. In FIG. 4 a control rod for controlling a neutron flux in a nuclear energy arrangement of a conventional type is shown. The control rod comprises four blades 7 each of which comprises a plurality of channels 8 which extend from the free outer end of the respective blade 7 towards the centre of the control rod 6, where the blades meet. In at least some of said channels 8 an absorber body 1 according to the invention is provided, preferably hermetically enclosed. One longer or a plurality of shorter absorber bodies 1 may be arranged in such a channel 8. It is obvious that the person skilled in the art will realise a plurality of possible variations and alternative embodiments of the subject of the invention without this person thereby leaving the scope of the invention. The invention should only be considered to be limited by the annexed claims, with support of the description and the annexed drawing. For example, the dimension of individual absorber rods will be adjusted to the expected expansion in the different positions in the control rods. Furthermore, it would also be possible to let the at least one recess extend along a helical curve along the length of the absorber body.