BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG. 1 is a diagrammatic, perspective view of a fuel assembly of a pressurized water reactor;
FIG. 2 is an exploded, perspective detailed view of a spacer with a damaged region, a replacement assembly with connecting parts, and a dummy fuel rod;
FIG. 3 is a perspective view of the parts shown in FIG. 2 when assembled;
FIG. 4 is a perspective view of a replacement assembly with two connecting parts;
FIG. 5 is a perspective view of spring tongues of a connecting part in an enlarged illustration;
FIG. 6 is a longitudinal sectional view of the connecting part;
FIG. 7 is a top plan view of a cell of a replacement assembly with connecting part plugged therein, in the direction of the arrow VII shown in FIG. 4;
FIG. 8 is a cross-sectional view through the connecting part taken along line VIII-VIII shown in FIG. 6;
FIG. 9 is a cross-sectional view through the middle part or the spacer piece of a connecting part taken along the line IX-IX shown in FIG. 6; and
FIG. 10 is a top view of a replacement assembly with alternatively fashioned connecting parts.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a fuel assembly 1 of a light water reactor, specifically a pressurized water reactor. The fuel assembly 1 contains a fuel rod cluster 3 formed from a multiplicity of fuel rods 2, a fuel assembly head 4, a fuel assembly foot 5 and a number of spacers 20 that laterally hold the fuel rods 2 and extend transverse to a central longitudinal axis 6 of the fuel assembly 1.
FIGS. 2 and 3 show a section of the spacer 20 and a replacement assembly 30 with two connecting parts 40. The spacer 20 is formed of a multiplicity of square cells 22, which are formed by crossed webs 21 and are respectively axially traversed, that is to say traversed in the direction of the central longitudinal axis 6 of the fuel assembly, by a fuel rod 2 (omitted in FIGS. 2 and 3 for reasons of simplification). An outer edge of the spacer 20 is formed by outer webs 23. Flow vanes 26 are formed integrally on the upper and lower edge of the outer webs 23. When “above” and “below” are spoken of here and below, reference is made to the installed state of the fuel assembly. In a damaged region 24, for example, two outer webs 23 interconnected via the corners are damaged, and a few cells 27 directly adjoining at the edge, specifically at the outer webs 23, are damaged such that proper holding, above all holding free from vibration, of a fuel rod 2 is no longer ensured. This picture of damage is the basis of the further description. However, also conceivable is damage to cells lying further inside and not directly adjacent to the outer web 23.
The function of the defective cells 27 is taken over by a replacement assembly 30, which is fixed on the underside of the spacer with the aid of two connecting parts 40 with an axial spacing (FIG. 3). The replacement assembly 30 is a subregion separated out from a spacer of identical configuration to the damaged spacer 20, and contains two outer webs 23a interconnected via the corners, and in each case a first row of cells bordering the outer webs and a further second row of cells adjoining radially inward. The first row contains at least a number of replacement cells 27a that corresponds to the number of the damaged cells 27 of the damaged region 24. In the case illustrated, the damaged region 24 contains five defective cells 27, the first cell row of the replacement assembly 30 including a total of eight cells, of which 5 are replacement cells 27a. The second cell row of the replacement assembly 30 contains six cells 22, two of them serving as assembly cells 22, that is to say for the purpose of fixing a connecting part 40. The replacement assembly 30 is aligned in the array of the spacer 20 such that its replacement cells 27a are congruent with the defective cells 27 of the spacer 20 and its outer webs 23a are flush with the outer webs 23 of the spacer 20 in an axial fashion, that is to say in the direction of the central longitudinal axis 6 of the fuel assembly. The connecting parts 40 serving for fixing the replacement assemblies 30 on the spacer 20 interact, on the one hand, with an assembly cell 22a of the replacement assembly 30 and, on the other hand, with a corresponding assembly cell 22a of the spacer 20 in the manner of a snap connection, the assembly cells 22a of the spacer 20 not being damaged cells.
As is best to be gathered from FIGS. 4 and 6, the connecting part 40 is composed of a spacer piece 41, configured as padding, and, for example, eight spring tongues 42. The spacer piece 41 is penetrated by a central opening 48 that extends axially and whose diameter is chosen such that it can hold a fuel rod 2 or a dummy fuel rod 60 in a fashion substantially free from play. Four spring tongues 42 distributed equally in the circumferential direction respectively project in the direction of a central longitudinal axis 47, running parallel to the central longitudinal axis 6 of the fuel assembly, of the connecting part 40 from the end surfaces of the spacer piece 41, which extend at right angles to the central longitudinal axis 6 of the fuel assembly 1 and which form a stop surface 52—explained further below. The spring tongues 42 are of substantially strip-shaped configuration, their inner surfaces 49 facing the central longitudinal axis 47, being curved in accordance with the circumferential surface of a fuel rod 2, and being against the latter in the assembled state. The free ends of the spring tongues 42 are respectively provided on the outside with a latching projection 43 that has two radial shoulders 51 and an insertion bevel 44 for facilitating the plugging in of the spring tongues 42 into an assembly cell 22a. Furthermore, two stop surfaces 45 adapted to the corner region 25 of a cell 22a that is to say running at right angles to one another in the direction of the central longitudinal axis 47 of the connecting part 40, are present on the latching projection 43. The stop surfaces 45 respectively adjoin a radial shoulder 51, the radial shoulder 51 and the stop surface 45 forming a right angle with one another.
The procedure for repairing a fuel assembly 1 having a picture of damage of the type under discussion with the aid of one or more manipulators is preferably as follows: a defective fuel assembly 1 is removed from the reactor core, brought into a spent fuel storage tank and rotated such that the fuel assembly foot is accessible and can be dismounted. After the dismounting of the latter, the fuel rods 2 penetrating a damaged region 24 are withdrawn from the fuel rod cluster 3. The outer webs 23 of the spacer 20 are, if appropriate, deburred in the damaged region 24 and aligned such that they do not protrude beyond the normal plan area or width across flats of a spacer 20. A replacement assembly 30 adapted to the damaged region 24 is positioned on one or the other flat side, or—referred to the assembled state—above or below the spacer 20 such that in each case a damaged cell 27 is axially assigned a replacement cell 27a of the replacement assembly 30. In the replacement assembly 30, connecting parts 40 are fixed in at least two assembly cells 22a, the spring tongues 42 of the connecting parts traversing the assembly cells 22a, and the latching projections 43 present at their free ends engaging behind the end edges 31 (covered in the illustrations) facing them on the webs 21 of the replacement assembly 30. The replacement assembly 30 thus prepared is then made to approach the spacer 20 in an axial fashion, the spring tongues 42 which project in the direction of the spacer 20, being pushed into its assembly cells 22 until—as already described above—their latching projections 43 engage behind the end edges 31, facing them, of the webs 21. Further manipulations for fixing the replacement assembly 30 on the spacer 20 are not required. The fuel rods previously removed—or at least a portion thereof—are inserted into the fuel assembly 1 such that they respectively traverse a damaged cell 27 and a replacement cell 27a axially assigned to it, of the replacement assembly 30.
In the assembled state produced in the way outlined, the stop surfaces 45 of the latching projections 43 bear against the respective corner regions 25 of an assembly cell 22a, as a result of which the connecting part 40 is reliably protected against rotating in relation to the spacer 20 or the replacement assembly 30. The radial shoulders 51 engaging behind the end edges 31 of the webs 21, and the regions of the latching projectors 43 supporting the radial shoulders are dimensioned such that the latching projections do not project into neighboring cells 22, or project in only so far (see FIG. 7, in particular) that these cells can be traversed by a fuel rod 2 without hindrance.
In the assembled state, the spacer piece 41 maintains a prescribed axial distance between the spacer 20 and replacement assembly 30. The end edges 31a, averted from the respective latching projections 43, of the webs 21 in this case bear against the end surfaces 52, extending at right angles to the central longitudinal axis 47 of the connecting part 40, of the spacer piece 41. The axial distance between the end surfaces 52 and the radial shoulders 51 of the latching projections corresponds to the height of the web 21. In a way similar to the case of the latching projections, there are likewise present on the base 32, extending radially outward, of the spring tongues 42 two stop surfaces 45a (see FIG. 5) that enclose a right angle, are situated in a corner region 25 of an assembly cell 22a, and additionally ensure that the connecting part 40 is protected against rotating in relation to the spacer 20 or the replacement assembly 30.
The spacer piece 41 is traversed by an opening 48. A fuel rod 2 can be inserted into this opening. However, the spacer piece embracing the fuel rod practically without play prevents access by primary coolant, or certainly restricts it so strongly that a fuel rod can be inserted into a connecting piece 40 only when this involves the uppermost spacer 20 that is disposed in the region of the plenum of the fuel assembly. The plenum forms the upper end of a fuel rod 2 and contains no nuclear fuel, and so there is no need for cooling or for dissipating the decay heat. Instead of a fuel rod 2, a dummy fuel rod 60 can be inserted into a connecting part 40 in the case of all other spacers 20. This ensures flow conditions such as correspond to the original, undamaged fuel assembly. A fuel rod 2 inserted into a connecting part 40 or a dummy fuel rod 60 keep the spring tongues 42 in their assembled position, in which they engage with their latching projections 43 behind the end edges 31a of the webs 21 such that a reliable connection is ensured between the spacer 20 and replacement assembly. In order to facilitate the insertion of a fuel rod 2 or a dummy fuel rod, insertion bevels 50 pointing toward the central longitudinal axis 47 are present on the latching projections 43.
FIG. 10 shows a replacement assembly 30 with connecting parts 40a that have two spring tongues 42, the latter being diametrically opposite one another and respectively operating with a corner region 25 of an assembly cell 22a. The other two corner regions 25a are free, and so it may be expedient, for example, for reasons of fluid flow, for the spacer piece 41a to have lateral oblique surfaces 53 diametrically opposite one another, and thus for a flow channel 54 to remain free in the respective corner regions 25a.
Patent Application
20080056428
