JPH0943375A - Bottom tie plate for fuel assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent foreign matters from flowing into a fuel assembly by providing a plurality of guide vanes for deflecting the flow direction of coolant which flows into a coolant inlet in the bottom plate, and a plurality of filters for capturing foreign matters which are axially erected in the adjacent to an outlet of the guide vanes. SOLUTION: Coolant 8 containing foreign matters supplied from a recirculation system passes through an orifice of a control rod guide pipe and raises toward a coolant inlet of a bottom tie plate. This coolant 8 flows into guide vanes 10 provided in the coolant inlet. The coolant 8 flown into the guide vanes 10 is deflected by a circulation flow 16 circulating in the circumferential direction along the guide vanes 10. The circulation flow 16 flows into filters 11 for capturing foreign matters so that the foreign matters are captured by the filters 11. The captured foreign matters 20 are sedimented in the filters 11 as they are by hydrodynamic force of the coolant 17 passing through the filters 11. When the foreign matters 20 are sedimented so as to cause clogging, the circulation flow 16 becomes an upward flow 18 or flows out from the top grid 19 of the bottom tie plate as it is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly for a nuclear reactor, and more particularly to a lower tie plate suitable for capturing foreign matters contained in a coolant.

[0002]

2. Description of the Related Art In a nuclear power plant, daily inspections and periodic inspections are obligatory in order to improve the reliability of operation and to ensure plant safety. If a defect is found in these inspections / inspections, the plant or equipment is opened and repair work is performed. Such inspection work and repair work are increasing with the aging of the plant, and the amount of foreign matter such as metal scraps, electric wire chips, welding scraps, and dust left behind in the plant after the work is also increasing. Seem. Especially, it is considered that the small foreign matter left in the furnace flows into the in-core equipment along with the flow of the coolant circulating in the furnace. In the fuel assembly, which is an important in-core device shown in FIG. 2, the fuel rods and spacers may be deformed or damaged by collision with foreign matter, and if the foreign matter is moored to these members, fretting wear due to flow vibration of foreign matter and It may cause fretting corrosion. Therefore, there are known examples 1 to 3 shown in FIGS. 3 to 7 for preventing foreign matter from flowing into the fuel assembly. FIG.
6 to FIG. 6 relate to a filter attached to the coolant inlet of the lower tie plate, and FIGS. 3 and 4 are for arranging the inflow direction of the filter grid in an inclined or labyrinth shape to prevent the inflow of foreign matter. In FIG. 5, the metal mesh is formed into a bag shape to prevent the inflow of foreign matter, and the coolant passage is enlarged to secure the coolant passage even if foreign matter is deposited on the filter. Further, in FIG. 6, the number and shape of the nosepieces of the lower tie plate are changed to narrow the space between the nosepieces and prevent the inflow of large foreign matter. FIG. 7 relates to the mounting position of the filter, in which the mounting position of the filter is mounted upstream of the lower tie plate to the orifice portion of the control rod guide tube.

However, in the filters of these known examples, although depending on the size and the number of foreign matters contained in the coolant, the clogging of the coolant passage of the filter occurs due to the accumulation of the foreign matters and the flow rate of the coolant is reduced. There is a risk of causing it (Japanese Patent Laid-Open No. 1-2
51319 gazette).

[0004]

In any of the above-mentioned prior arts, the filter is directly attached to the place where the coolant flows in in the above-mentioned prior arts. Therefore, if foreign matter accumulates on the filter, clogging will occur, and the flow rate of the coolant passing through the fuel assembly may decrease. A decrease in the coolant flow rate may reduce the heat output of the core and the cooling capacity of the fuel rods, and at the same time may impair the integrity of the fuel assembly.

An object of the present invention is to improve the trapping performance of foreign matter contained in the coolant to prevent the foreign matter from flowing into the fuel assembly, and at the same time to secure the flow rate of the coolant passing through a predetermined fuel assembly. To establish a capture method.

[0006]

In order to achieve the above object, the present invention provides a plurality of guide vanes for deflecting the flow direction of the coolant flowing into the coolant inlet of the lower tie plate, and the guide vanes. A plurality of filters for trapping foreign matter are provided upright in the axial direction near the outlet of the.

[0007]

The coolant containing foreign matters rises from below the lower tie plate toward the coolant inlet of the lower tie plate. This upward flow of the coolant flows into the guide vanes provided at the coolant inlet. The ascending flow that has flowed in is deflected by the guide vanes into a swirling flow that swirls in the circumferential direction. The coolant that has turned into a swirling flow passes through a filter for trapping foreign matter that stands in the axial direction near the outlet of the guide blade. At this time, the coolant and fine foreign matter can pass through the filter, but the other foreign matter is captured by the filter. The captured foreign matter is stuck and deposited on the filter as it is due to the fluid force of the coolant passing through the filter. The coolant that has passed through the filter gradually flows upward while decelerating, and flows out from the upper grid of the lower tie plate. In such a flow state, if foreign matter accumulates on the filter and clogging occurs, the swirling flow rate passing through the filter becomes smaller, but the swirling flow becomes upward flow by that amount and either passes through a part without clogging or remains as it is. It flows out from the upper grid of the lower tie plate. For example, even if the entire filter becomes clogged, the coolant flowing out of the guide vanes will flow upwards along the filter, and as it flows out of the upper grid of the lower tie plate, it will pass through the lower tie plate or fuel assembly. The flow rate of the coolant used is almost unchanged.
Further, the filter is tilted slightly to the upstream side so that the foreign matter accumulated on the filter does not re-flow due to the upward flow flowing out from the lower tie plate.

[0008]

An embodiment of the present invention will be described below. BWR
The structure of the fuel assembly is shown in FIG. The fuel assembly 1 is composed of a plurality of fuel rods 2, a water rod 3, an upper tie plate 4 and a lower tie plate 5 for restraining and supporting the upper and lower ends thereof, and a spacer 6 for aligning and supporting them. A fuel bundle and a channel box 7 for accommodating the fuel bundle and forming a coolant flow path
It is composed of

9 and 10 show an embodiment of the structure of the lower tie plate 5 of the fuel assembly 1 of the present invention. FIG. 9 is an axial sectional view of the lower tie plate 5, and FIG. -A
FIG. The lower tie plate 5 restrains and supports the lower end of the fuel rod 2 and also serves as an inlet portion of the coolant 8 flowing into the fuel assembly 1. The lower tie plate 5 has a plurality of guide vanes 10 at the coolant inlet 9 which is a feature of the present invention, and a plurality of foreign matter trapping filters 11 standing upright in the axial direction near the outlet of the guide vanes 10. . The guide vanes 10 are fan-shaped with a spread on the outer peripheral side,
The inflow end 12 faces the inflow direction of the coolant 8, and the outflow end 13 is parallel to the foreign substance capturing surface of the filter 11. Further, the filter 11 has a mesh shape or a lattice shape, and the mesh thereof has an interval slightly smaller than the minimum flow path in the spacer 6. Moreover, the filter 11 is made of a solid material and is not damaged by the fluid force of the coolant.

The flow of the coolant and the method of capturing the foreign matter 20 in the lower tie plate 5 structure as described above are as follows. FIG. 1 is a schematic diagram showing a method of capturing the foreign matter 20. The coolant 8 containing foreign matter supplied from the recirculation system passes through the orifice 15 (not shown) of the control rod guide tube 14 and rises toward the coolant inlet 9 of the lower tie plate 5. The upward flow 8 of the coolant flows into the guide vanes 10 provided at the coolant inlet port 9. As described above, the inflow end 12 of the guide vane 10 faces the inflow direction, and the upward flow 8 smoothly flows into the guide vane 10. The upward flow 8 flowing into the guide vanes is deflected into a swirling flow 16 having a swirl in the circumferential direction along the streamline of the guide vanes 10. The coolant 16 that has become a swirling flow flows into and passes through the filter 11 for capturing foreign matter.
At this time, the coolant and fine foreign matter can pass through the filter 11, but the other foreign matter is captured by the filter 11. The captured foreign matter 20 passes through the filter 11 and the coolant 17
The fluid is directly deposited on the filter 11.
Therefore, the foreign matter 20 is not separated from the filter 11 if the flow of the coolant passing through the filter 11 exists. Further, the outflow end 13 of the guide vane is parallel to the foreign matter capturing surface so that the foreign matter 20 contained in the coolant can be effectively captured, and most of the coolant passes through the filter 11. . The coolant passing through the filter 11 gradually becomes an upward flow 18 while decelerating, and flows out from the upper grid 19 of the tie plate. When foreign matter 20 is deposited on the filter 11 and clogs in such a flow state, the swirling flow rate passing through the filter 11 decreases, so that the swirling flow becomes an upward flow 18 correspondingly, and passes through a non-clogging portion. Or, as it is, it flows out from the upper grid 19 of the lower tie plate 5. For example, even if the entire filter 11 is clogged, the coolant flowing out from the guide vanes 10 becomes an upward flow 18 along the filter 11 and flows out from the upper grid 19 of the lower tie plate 5 as it is. Rate 5,
That is, the coolant flow rate 8 passing through the fuel assembly 1 hardly changes. Further, the filter 11 is slightly tilted to the upstream side so that the foreign matter 20 accumulated on the filter 11 does not flow out again by the upward flow 18 flowing out from the lower tie plate 5. In this way, the coolant 8 that has passed through the lower tie plate 5 flows into the region of the fuel rods 2,
At the same time as the fuel rod 2 is cooled, it is heated and brought into a vapor-water mixed state. The steam becomes the driving source of the steam turbine, and the hot water returns to the recirculation system again.

[0011]

According to the present invention, when the foreign matters left in the furnace try to flow into the fuel assembly along the flow of the coolant, the foreign matters are captured by the filter to damage the fuel rods and spacers. And fretting wear and fretting corrosion can be prevented. Further, even if foreign matter is deposited on the filter and clogging occurs, a predetermined coolant flow rate can be secured without reducing the coolant flow rate passing through the lower tie plate. As a result, the health of the fuel assembly can be secured, and at the same time, the safety of the reactor operation can be secured.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic structure in a lower tie plate which is an embodiment of the present invention and an explanatory view of its function.

FIG. 2 is a sectional view of a conventional fuel assembly.

FIG. 3 is a cross-sectional view showing a conventional foreign matter capturing method, in which a tilted grid is arranged at a coolant inlet of a lower tie plate.

FIG. 4 is a cross-sectional view showing a conventional foreign matter capturing method in which a labyrinth-shaped lattice is arranged at a coolant inlet of a lower tie plate.

FIG. 5 is a cross-sectional view showing a conventional foreign matter capturing method in which a bag-shaped wire net is arranged at the coolant inlet of the lower tie plate.

FIG. 6 is a cross-sectional view showing a conventional foreign matter capturing method, showing a structure in which the number and shape of the nosepieces of the coolant inlet of the lower tie plate are changed to reduce the interval.

FIG. 7 is a perspective view showing a conventional foreign matter capturing method, in which a filter is attached to an orifice portion of a control rod guide tube.

FIG. 8 is a sectional view showing a configuration diagram of a fuel assembly according to an embodiment of the present invention.

FIG. 9 is a cross-sectional view of a lower tie plate structure which is an embodiment of the present invention.

10 is a horizontal sectional view taken along the line AA in FIG.

[Explanation of symbols]

8 ... Coolant flow, 9 ... Coolant inlet, 10 ... Guide vane, 11 ... Filter, 12 ... Guide vane inflow end, 13 ...
Outflow end of guide vane, 17 ... Filter passing flow, 18 ... Upward flow, 19 ... Lower tie plate grid, 20 ...
Foreign material.

Front page continuation (72) Inventor Yasushi Aizawa ▲ Hiroshi 2-1 3-chome, Sachimachi, Hitachi City, Ibaraki Hitachi Engineering Co., Ltd. (72) Inventor Junjiro Nakajima 3-2, Sachimachi, Hitachi City, Ibaraki Prefecture No. 1 in Hitachi Engineering Co., Ltd. (72) Inventor Hideki Kurosaki 3-1-1, Saiwai-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Kenichi Ito San-cho, Hitachi, Ibaraki No. 1-1 No. 1 Hitachi Ltd. Hitachi factory

Claims (1)

[Claims] 1. A fuel bundle assembled from members such as upper and lower tie plates for restraining and supporting upper and lower ends of a fuel rod and a water rod, and spacers for aligning and supporting the fuel rods at equal intervals, and the fuel bundle. And a channel box that forms a coolant flow path, and a guide vane is provided at the coolant inlet of the lower tie plate and a foreign matter trapped upright near the outlet of the guide vane. A lower tie plate of a fuel assembly characterized by being provided with a filter.