JP3534529B2 - Reactor fuel assembly with foreign matter filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a fuel assembly for a nuclear reactor, and more particularly to a reactor fuel provided with a foreign matter filter for trapping foreign matter flowing into a reactor coolant. Regarding the aggregate. 2. Description of the Related Art The structure of a conventional fuel assembly will be described by taking a pressurized water reactor as an example. In FIG. 6, which shows a cross section of a typical example of a pressurized water reactor, a core vessel 7 is suspended and supported in a reactor vessel 5 having an inlet nozzle 1 and an outlet nozzle 3 for coolant. Fuel assembly 10
Is loaded and used. As shown in FIG. 7 which is a partially cutaway perspective view of the fuel assembly 10, the fuel assembly 10 has an upper nozzle 11 and a lower nozzle 12 which face each other at a distance.
Which are connected by a plurality of hollow guide tubes 13 extending parallel to and apart from each other. Hollow guide tube 13
Is for receiving and guiding a control rod or the like. A plurality of support grid assemblies 14 having openings for receiving the hollow guide tubes 13 are arranged at intervals in the longitudinal direction of the fuel assembly 10. The support grid assembly 14 further has a plurality of openings, and a plurality of nuclear fuel rods 15 are respectively inserted and supported in these openings. Then, the coolant flowing into the reactor vessel 5 through the inlet nozzle 1 flows as shown by the arrow, passes through the lower nozzle 12 of the fuel assembly 10, enters between the nuclear fuel rods 15, and flows upward. However, as described above, the amount of coolant flowing is enormous, and foreign matter is contained therein, flows into the fuel assembly 10 by wake, and is caught by the support grid assembly 14 to be moored. It has been empirically found that the outer surface of the nuclear fuel rod 15 may be damaged. Therefore, in order to prevent foreign matter from flowing into the fuel assembly 10, a conventional practical proposal has been made by making the coolant flow hole of the lower nozzle 12 corresponding to the inlet as small as possible as shown in FIG. . FIG. 8 is a plan view of the lower nozzle 12 for preventing the inflow of foreign matter. The lower nozzle 12 is provided with a guide tube mounting hole 17 formed corresponding to the position of the hollow guide tube 13 and is distributed in other portions. The coolant flow hole 19 has a small diameter. Foreign matter larger than the coolant flow hole 19 is prevented from flowing in at the inlet side. As described above, the lower nozzle is located at the lower part of the fuel assembly and supports its own weight and the mounting support load, so that it also has the function of a strength member. In order to ensure the strength and rigidity for that, a proper thickness is required. Accordingly, as the flow passage cross-sectional area or the inner diameter of the coolant flow hole is reduced, there is a problem that the pressure loss of the coolant flowing therethrough becomes excessive. Processing a long small hole also involves various difficulties in manufacturing technology. Therefore, the diameter of the coolant flow hole of the lower nozzle and the reduction of the cross-sectional area of the lower nozzle are naturally limited, allowing the intrusion of foreign matter of small diameter, and although the probability is small, the friction of nuclear fuel rods by foreign matter of small diameter,
There was a risk of causing damage. Accordingly, the present invention provides a fuel assembly for a reactor or a reactor fuel assembly with a foreign matter filter having a foreign matter intrusion prevention structure that has little pressure loss of a coolant flow and can capture and prevent fine foreign matter. It is a subject. In order to solve the above problems, according to the present invention, an upper nozzle and a lower nozzle facing each other at a distance from each other, and both ends arranged in parallel with each other between these two nozzles A plurality of hollow guide tubes connected to both nozzles, a support grid assembly having an opening for receiving the hollow guide tube and fixed to the hollow guide tube, and individually inserted into the plurality of openings of the support grid assembly. A reactor fuel assembly with a foreign matter filter having a plurality of nuclear fuel rods supported and supported and extending in parallel and apart from each other, and a foreign matter filter disposed over the upper surface of the lower nozzle, wherein a plurality of the lower nozzles are provided. The coolant flow hole is formed in an oval cross section, and a hexagonal pore group is formed in the foreign matter filter facing the outlet of the flow hole having the oval cross section, and the width of the ligament around the hexagonal pore is formed. Is formed smaller than the plate thickness. Embodiments of the present invention will be described below with reference to the accompanying drawings. The fuel assembly according to the embodiment of the present invention has basically the same structure as the above-described fuel assembly 10 except for a lower nozzle and a foreign matter filter described below.
FIG. 1 shows the upper shapes of the lower nozzle 40 and the foreign matter filter 60 of the fuel assembly 30 by omitting the hollow guide tube. Both of them have a rectangular planar outline, but the lower nozzle 40 is larger than the foreign matter filter 60. Slightly larger. FIG. 2 shows the shape of the upper surface of the lower nozzle 40. The lower nozzle 40 has legs 41 having an L-shaped cross section at four corners on the lower surface, and the following holes are provided in the nozzle plate 43 on the upper surface. That is, the mounting hole 45 of the hollow guide tube
Are provided, and elliptical flow holes 47, 49, 51, 53, 55, and 57 are provided so as to obtain a large flow path area as a whole in a range allowed in terms of strength. . The reason why the cross sections of the flow holes 47 to 57 are made oval is to secure as large an area as possible, and the use of a circular one is not excluded depending on the surrounding conditions. When the fuel assembly 30 is loaded in the reactor vessel and the reactor is operated, the reactor coolant flows through the flow holes 47 to 57 literally. The foreign matter filter 60 provided over the upper surface of the lower nozzle 40 is made of a metal plate having a thickness of about 1.0 mm.
Are provided with relief holes 61 aligned with each other. This relief hole 6
1, the hollow guide tube 13 as described above is inserted. The lower nozzle 40 has a group of pores 63, 65, 67, 69, 71, 73 and the like individually covering the flow holes 47 to 57. The basic structure of these pore groups is such that hexagonal pores 75 are arranged in a honeycomb shape as shown in an enlarged manner in FIG. The plate portion or ligament 77 between the adjacent hexagonal pores 75 has a width (about 0.65 mm) smaller than the thickness of the plate. In the present embodiment, the diameter of the inscribed circle of the hexagonal pore 77 is about 3.4 mm, and the small hexagonal pore 75 and the ligament 7
In order to form the group of pores 65 having a diameter of 7, for example, the strain is too large by the usual press punching, and therefore, it is preferable to manufacture the holes by photochemical etching. Such pore groups do not create a significant pressure drop for the flowing coolant flow. Referring to FIG. 5, it will be described with reference to FIG. 5 that the pore group having the hexagonal pores 75 has a small pressure loss and an excellent foreign matter trapping property. A square hole and an equilateral triangle hole having the same opening area are shown in FIGS. (B) and (c) for comparison.
A ligament of the same width is also shown, but the opening ratio obtained by dividing the opening area by the area surrounded by the outline of the ligament is hexagonal hole> square hole> equilateral triangular hole, in this order. A channel area having a relatively large group of pores can be obtained. Further, when the diagonal distances of the holes are a, b, and c, respectively, as shown in the figure, there is a relationship of a <b = c. Therefore, the diagonal distance of the hexagonal hole is the smallest, and the passage of smaller foreign matter can be blocked. As described above, according to the present invention,
The coolant flow hole of the lower nozzle of the fuel assembly has an elliptical cross section as much as possible to increase the flow area, and the flow path of the foreign matter filter covering the upper surface is formed from hexagonal pore groups, so that the pressure loss is smaller. Thus, the passage of fine foreign matter can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial top view showing a main part of an embodiment of the present invention. FIG. 2 is a top view showing a part of the member shown in FIG. 1 separately. FIG. 3 is a top view showing a part of the members shown in FIG. 1 separately. FIG. 4 is a partially enlarged view showing a part of FIG. 3 in an enlarged manner. FIG. 5 is an explanatory diagram illustrating the operation and effect of the embodiment. FIG. 6 is a schematic sectional view showing an example of a nuclear reactor in which the fuel assembly according to the present invention is used. FIG. 7 is a partially cutaway perspective view showing an example of a conventional fuel assembly. FIG. 8 is a partial top view showing one member of the conventional fuel assembly. DESCRIPTION OF SYMBOLS 11 Upper nozzle 13 Hollow guide tube 14 Support grid assembly 15 Nuclear fuel rod 30 Fuel assembly 40 Lower nozzle 41 Leg 43 Nozzle plate 47, 49, 51, 53, 55, 57 Flow hole 60 Foreign matter filter 63 , 65, 67, 69, 71, 73 pore group 75 hexagonal pore 77 ligament

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-232893 (JP, A) JP-A-8-271672 (JP, A) JP-A-5-27087 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G21C 3/30 G21C 3/33

Claims (1)

(57) [Claim 1] An upper nozzle and a lower nozzle facing each other at a distance from each other, and a plurality of hollow guide tubes arranged between the nozzles in parallel with each other and both ends connected to the nozzles. A support grid assembly having an opening for receiving the hollow guide tube and fixed to the hollow guide tube; and a plurality of openings of the support grid assembly, the support grid assemblies being separately inserted and supported, and extending parallel to and away from each other. A plurality of nuclear fuel rods, and a foreign matter filter disposed over the upper surface of the lower nozzle, wherein the plurality of coolant flow holes of the lower nozzle are formed in an oval cross section and face the flow holes. Forming a hexagonal pore group in the foreign matter filter, and forming a ligament width around the pores of the hexagonal pore group smaller than a plate thickness. .