JPS61112808A - Joint for fixing member made of metal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a joint for fixing a metal member to a wall portion of a fuel conduit made of a zirconium alloy for a nuclear fuel assembly, thereby forming a conical shape. a bolt having a longitudinally extending central axis thereof is arranged to pass through a hole in said wall portion and press said wall portion against a contact surface provided on said metal member; , the bolt head is made of a material with a coefficient of thermal expansion larger than that of the zirconium alloy, and the bolt head is configured such that the annular conical layer surface of the bolt head contacts the corresponding conical layer surface of the hole at room temperature. is recessed into a countersink in said wall portion.

[Prior art and its problems]

In the above-mentioned scale fittings, and during heating from room temperature to reactor temperature, the conical part of the bolt is more sensitive to the thermal expansion of the hole provided in the fuel conduit wall and having a corresponding conical contact surface. Subjected to significantly greater thermal expansion: circulation has almost twice as much thermal expansion. This means that
This means that the bolt head is subjected to a compressive stress acting perpendicular to its conical layer surface, meaning that the bolt is subjected to a corresponding axial tension. In known joints of the above-mentioned type, this tension becomes so great that it constitutes an unacceptable stress in the bolt.

[Means for solving problems]

The aim of the invention is to obviate the above-mentioned drawbacks.

The characteristics of the invention will become apparent from the appended claims.

In the following, the invention will be explained with reference to the accompanying schematic drawings.

〔Example〕

In the drawing, 1 indicates a fuel conduit for a nuclear fuel assembly. At its top, the fuel conduit is formed with a lifting eye bolt 2, which is to be used as an additional device for the lifting member during lifting and lowering of the complete fuel assembly. For the lower end,
The fuel conduit 1 encircles the upper part of the bottom part 3 without significant play and is provided with a plurality of threaded bolts 4,
Only one of them is shown in the drawing and is thereby fixed there. The threaded bolt 4 has a central vertical axis 5 and a conical bolt head 6 embedded in a corresponding through hole in the wall section of the conical bolt head 1 . In cold conditions - and before the illustrated joint is exposed to temperature B - the annularity of the bolt head 6,
The conical contact surface 7 is placed in mechanical contact with a corresponding contact surface 8 of the fuel guiding wall, as shown in FIG. 3Δ. The contact surface 8 constitutes the defined surface of the above-mentioned hole in the fuel conduit wall. The bolt 4 is screwed into a tapped hole 9 in the bottom part 3. hole 9
is formed with an annular conical layer surface 10 at its outermost side, which surface in cold conditions is a conical layer surface 7 of a bolt head located inside a fuel conduit as shown in FIG. 3A. in contact with a portion of, or
It also has a small play in relation to said part of the conical layer surface 7. As shown in FIG. 3B, such play occurs upon heating, although no corresponding play exists in cold conditions. Bolt conical layer surface 7
The generatrices of form an angle α with the central axis 5 of the bolt, and the angle α
is in the range of 30° to 50°, preferably 35° to 4
It is in the range of 5°.

The fuel conduit 1 is made from a zirconium alloy, the thermal expansion of which is less than 10.times.10.degree. C.-1. An example of such an alloy is called 7ircaloy4, which has a thermal expansion of less than 8.2×10 −6° C.

The bolt 4 is made of a material having a yield point of 12 ON/Im2 or more at 286 DEG C., preferably 14 ON/m2 or more, such as Eva InCOIOy800. And its thermal expansion is 1 in the range of 20 to 286℃.
3X10" Greater than 6℃-6.20~28
The thermal expansion of the J3 bolt material in the 6° C. range exceeds the specific expansion of the zirconium alloy used in the fuel conduit over the same temperature range by more than 50%, and by more than 70% of the ordinary material.

The bottom part 3 is made of stainless steel. It has a specific thermal expansion that is somewhat greater than the thermal expansion of the bolt material, which is approximately 10% or more.

The shortest distance E between the inner wall surface of the fuel conduit 1 and the threaded part of the bolt 4 is smaller than the largest diameter of the bolt head. Usually, E is smaller than 0.5D.

contact surface 1 between the inside of the fuel conduit 1 and the outside of the bottom part 3
2 has a vertical extension H along the main part of the circumference of the fuel conduit. For each bolt head 4, the vertical extension of the contact surface has a minimum value M.

On that surface of the bottom part 3 facing the fuel conduit wall, there is provided, around each hole 9, a milled annular shape facing the fuel conduit wall and placed directly adjacent to the hole 9. in,
A generally flat surface portion 11 is formed. Surface part 1
1 is displaced in the lane direction (bolt axis 5) in relation to the contact surface 12 such that an annular gap 13 is defined between the fuel conduit@wall 1 and the bottom part 3. In the case of a new and unused fuel assembly, the gap 13 closest to the bolt head 6
The width of the fuel conduit 1 is at least 7% and at most 50% of the wall thickness. Preferably the gap width is between 0.3 and 0.8
selected within the range of

According to the part of the bottom part 3 shown in FIG. It varies between a small width and almost twice the large minimum width. In the coupling according to the invention, the above-mentioned minimum width is 30% of the maximum diameter of the hole 9.
It is chosen to be larger, preferably larger than 50%. The same minimum width is selected to be less than 200%, preferably less than 150%, of the maximum diameter of the hole 9.

The fitting shown in Figure 3A is brought up to reactor temperature, e.g.
When heating to a temperature of 50°C or higher, the different diameters of the bolt head 6 should be
The corresponding diameter of the diaphragm is increased to a larger dilation. The gap 13 is between the limited surface of the hole 9 and the bolt head 6.
uniformly with a moderate compressive stress at the contact surfaces between the bolts 4 and 4, allowing the deformation of the fuel conduit wall around the bolt head 6, as shown in FIG. 3B, resulting in a tensile stress in the bolt 4. , which is significantly smaller than the corresponding value for a joint that does not have any gap 13, but is otherwise identical to the joint shown in FIGS. 3A and 3B.

The idea is that in the case of a joint in which the different dimensions are related to each other, the fuel conduit 1 is made of zirconium 4 and the bolt 4 is made of +nco+ys, as shown in the accompanying drawings.
OO, by introducing the tensile stress of the bolt into the gap 13 200 N/tttm
” showed that it is possible to reduce the tensile stress in bolts from 20 N/mm2.

Alternatively, the annular milled area can be formed circular and with a contact annular width, such as section 1111' shown in FIG.

The invention also provides that two milled surfaces of a shape similar to surface 11 in FIG. 4 jointly constitute an elongated surface intended for a joint with two bolts. , horizontally adjacent to each other and rotated by 90°. A further widening of the latter surface and a corresponding increase in the number of bolts are also conceivable.

[Brief explanation of the drawing]

FIG. 1 shows a fuel conduit for a nuclear fuel assembly and the associated bottom part, a partial g! A side view similar to the M sectional view; Figure 2 is a horizontal sectional view taken along II-II in Figure 1;
Figure A is a partial horizontal sectional view along the line ■-m of Figure 1 of a fitting according to the invention at room temperature and in a new and unused fuel assembly; Figure 3B is the same fitting as in Figure 3A, but in hot conditions; , for example, a cross-sectional view along line III--III of FIG. 1 of the joint at 4 degrees in a normal nuclear reactor; FIG. 4 is a side view of a portion of the bottom portion shown in FIG. 1; and FIG. FIG. 4 is a side view of a modified part shown in FIG. 4; 1...Fuel conduit, 3...Bottom part, 4
...Threaded bolt, 5...Horizontal central axis, 6...Conical bolt head, 7...
- Annular circular contact surface, 8...Contact surface, 9
...Screw hole, 11 ...Surface part, 12
...Contact surface, 13...Annular gap.

Claims (4)

[Claims] (1) Metal members (3) on the wall of the fuel conduit (1) made of zirconium alloy for nuclear fuel assembly.
A joint for fixing a bolt (4) having a conical head (6) and a central axis (5) extending in the longitudinal direction.
) is arranged to pass through a hole (9) in said wall part and press said wall part against a contact surface (12) formed in said metal member, said bolt (4) The bolt head (6) is made of a material with a coefficient of expansion greater than the coefficient of thermal expansion of the zirconium alloy, and the bolt head (6) has an annular, conical surface (7) that at room temperature: A joint formed by being embedded in a countersunk hole in the wall portion so as to be in contact with a corresponding conical surface of the hole,
Said metal member (3) faces said wall portion and has a surface portion (11) arranged directly adjacent to said bolt head and distributed around said bolt (4), said surface The part has a gap (13) between the wall part and the metal member (3).
) a fitting for fixing a metal member to a wall portion of a fuel conduit made of a zirconium alloy, characterized in that it is axially displaced with respect to said contact surface so as to be defined between . (2) A joint according to claim 1, in which the metal member (3) is the bottom part of the nuclear fuel assembly, and the upper part of the bottom part is accompanied by a play that needs to be mentioned. screwed in horizontal direction, surrounded by the lower part of the fuel conduit (1), and in which the bolt (4) is screwed into a hole (9) provided in the upper part of the bottom part. A joint characterized by being a bolt with (3) In the joint according to claim 2, the shortest distance (E) between the inner wall surface of the fuel conduit (1) and the threaded portion of the bolt (4) is the bolt head ( 6) A joint characterized in that it is smaller than the largest diameter (D). (4) The joint according to claim 2, wherein the bolt is made of a material having a coefficient of thermal expansion that exceeds at least 50% of the coefficient of thermal expansion of the zirconium alloy. Fittings to do.