JP2009128038A - Lower support structure with debris capturing function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preventing debris from flowing into fuel assemblies in a boiling water reactor (BWR), and to eliminate or reduce defects of a porous debris filter adopted at present. <P>SOLUTION: In a lower support structure which supports the fuel assemblies and includes the inlet port for cooling water on its lateral face to guide a cooling water flow channel upward by bending it from the inlet port, the debris in the cooling water is captured in a debris capture pot by placing it between the inside of the upper part of the lower support structure and a nozzle wall below the fuel assemblies, and the debris capture pot is a debris capture groove equipped with protrusions for preventing the inflow debris from reflowing out. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lower support structure suitable for preventing debris from flowing into a fuel assembly and avoiding fuel rod breakage due to fretting in a boiling water reactor (BWR).

  First, an outline of a pressure vessel of a boiling water reactor (BWR) as the background of the present invention will be described below.

  FIG. 1 conceptually illustrates a portion of a boiling water reactor (BWR) pressure vessel. FIG. 2 also shows the lower support structure that receives the fuel rods of the boiling water reactor.

  As shown in FIG. 1, a jet pump 2 is installed in a pressure vessel 1 of a boiling water reactor. The cooling water is driven by the recirculation pump 3, and the cooling water 7 in the downcomer 6 partitioned by the pressure vessel wall 1 and the shroud wall 5 from the suction pipe 4 connected to the pressure vessel is discharged to the discharge pipe 8 of the recirculation pump. To be supplied to the nozzle 9 of the jet pump 2. The cooling water ejected from the nozzle 9 entrains the cooling water 7 in the downcomer 6 (indicated by the streamline a), increases the amount of water, and flows into the lower plenum 10 (indicated by the streamline b). Cooling water flowing into the lower plenum 10 enters from the orifice 12 of the lower support structure 11 and flows into the fuel assembly 14 via the lower tie plate 13. In this fuel assembly 14, fuel rods 16 assembled by spacers 15 are stored.

  The cooling water passing through the fuel assembly 14 receives heat in the fuel assembly 14 and rises into a gas-liquid two-phase flow, and the vapor separated by the steam separator (not shown) is removed from the dryer (not shown). ) Through an external steam turbine (not shown). On the other hand, the high-temperature water separated by the steam separator is discharged to the upper part of the downcomer 6. Here, as shown in FIG. 2, the lower support structure 11 supports four fuel assemblies 14, and an insertion port 17 into which the lower tie plate 13 is inserted and an orifice 12 are provided in each fuel assembly 14. Correspondingly provided.

  In the above boiling water reactor (BWR), tools used during construction, especially wire brush remnants, and cutting chips, etc., ride on the flow of cooling water, flow into the fuel assembly, get caught by the spacer, and cool water There is a problem that the fuel rod is broken by contacting with the fuel rod while generating vibration induced by the flow of the fuel. In order to deal with this problem, it has been proposed to provide a filter.

  For example, in Patent Document 1, in a fuel support fitting and fuel assembly of a boiling water reactor, a filter for capturing foreign matter in the coolant is installed in the fuel support fitting in which the lower tie plate of the fuel assembly is set. The technology to do is disclosed. Patent Document 2 discloses that in a fuel support fitting and a fuel assembly of a boiling water reactor, a net-like foreign matter filter is installed at a coolant inlet of the fuel support fitting.

  FIG. 3 shows an example in which a debris filter is installed in the lower part of the fuel assembly of the boiling water reactor shown in FIGS. 1 and 2. FIG. 4 shows an enlarged part of the debris filter shown in FIG.

  As shown in FIG. 3, the debris filter 19 is provided in the lower tie plate 13 into which the lower end plug 18 of the fuel rod 16 is inserted. The debris 20 is carried by the fluid flowing from the orifice 12 and is captured by the debris filter 19 provided in the lower tie plate 13. As shown in FIG. 4, the debris filter has a small hole 22 provided around the hole 21 into which the fuel rod end plug is inserted. In the actual machine, this small hole is a tapered small hole having a diameter of about 2 to 3 mm.

Japanese Patent Laid-Open No. 2003-232879 JP-A-2005-49132

In order to prevent the debris from flowing into the fuel assembly in the boiling water reactor (BWR), the measures using the filter as described above have the following problems.
・ The debris that can physically pass through the small hole in the filter (tapered small hole 22 in the debris filter shown in FIG. 4) repeatedly changes the flow rate and whether or not there is a flow even if it is once captured by the filter. When it is received, it eventually passes through the filter and flows into the fuel assembly. Then, the debris caught in the assembly may vibrate due to the coolant flow and wear and damage the cladding on the fuel rod surface. When this damage progresses, uranium and splitting from the inner nuclear fuel pellets may occur. Since the products and the like are leaked into the coolant, the operation efficiency is deteriorated, for example, the plant is stopped and replacement work is required.
-Depending on the shape and properties of the filter, the filter itself may be damaged. In such a case, the damaged piece of the filter itself will flow into the fuel assembly, causing the same problem as the inflow of debris described above. Let
-By providing a filter, pressure loss occurs in the filter section. FIG. 5 shows the result of measuring the pressure loss by the debris filter with respect to the flow rate in an actual machine. The pressure loss increases as the flow rate increases, and the pressure loss is about 3 kPa at the rated flow rate (80 m ³ / h). was there.

  The present invention provides a new debris capturing method that achieves this problem, with the solution of the above-described problems as a problem.

  In order to solve the above problems, the lower support structure part of the boiling water reactor (BWR) of the present invention supports a fuel assembly and has a cooling water inlet on the side surface, and a cooling water flow path. In the lower support structure that bends from the inlet and guides it upward, a debris catching pot is provided between the upper inner side of the lower support structure and the nozzle wall below the fuel assembly, and debris in cooling water is Capturing in a pot.

  Further, the lower support structure part of the boiling water reactor (BWR) of the present invention, in addition to the above-mentioned features, the debris trapping pot is a debris trapping groove provided with a projection for preventing reflow of the introduced debris. It is characterized by that.

  In addition to the above features, the lower support structure part of the boiling water reactor (BWR) of the present invention, the debris capture groove is provided over the entire inner periphery of the upper part of the lower support structure part It is characterized by.

  Further, the lower support structure part of the boiling water reactor (BWR) of the present invention, in addition to the above features, the debris capture groove has a depth of the groove in the radial direction of the lower support structure part. It is characterized in that it is shallowest at a position opposite to the cooling water inlet and deeper as it goes away from the opposite position in the circumferential direction.

  Further, the lower support structure part of the boiling water reactor (BWR) according to the present invention, in addition to the above features, the debris trapping groove is positioned opposite to the cooling water inlet part in the radial direction of the lower support structure part. The groove is formed on both sides from the vicinity toward the position of the cooling water inlet portion, and the depth of the groove is formed so as to become deeper as the position of the cooling water inlet portion is approached. .

  Further, the lower support structure part of the boiling water reactor (BWR) of the present invention, in addition to the above features, the inner wall of the lower support structure part is positioned opposite to the cooling water inlet part in the radial direction. In addition, a debris guide groove is formed on the upper and lower sides.

  Further, the lower support structure part of the boiling water reactor (BWR) of the present invention is characterized in that, in addition to the above characteristics, the debris capturing groove is integrally formed inside the lower support structure part. To do.

  According to the present invention, the debris contained in the cooling water can be captured in the debris capturing pot and prevented from entering the fuel assembly. Therefore, the debris filter used in the conventional boiling water reactor (BWR) Since it is possible not to use, there is no pressure loss, which is advantageous in terms of cost. Even when a debris filter is used in combination, large and heavy debris is captured by the debris capturing pot, so that the possibility of clogging of the debris filter and damage to the fuel rod due to fretting can be greatly reduced.

  Further, according to the present invention, it is possible to prevent the debris once captured from flowing out even if the flow changes, and to flow the captured debris so as to concentrate at a position away from the inflow position to the debris capturing pot. Thus, the storage capacity in the debris catching pot can be maximized.

  Further, according to the present invention, the debris catching pot is made of the same metal as the lower support structure, and is not damaged by being provided in a portion where the flow on the upper wall side in the lower support structure does not act so much, Excellent safety.

  Further, according to the present invention, the debris trapping pot is provided not on the cooling water flow path but on the inner upper wall side of the lower support structure portion, so that it does not become a resistance to the flow of the cooling water, so that the debris trapping is performed. There is no increase in pressure loss due to the installation of pots, and improvement in reactor performance can be expected.

  An embodiment of a lower support structure with a debris capturing function according to the present invention will be described below.

  FIG. 6 shows Example 1 according to the present invention. In the first embodiment, the debris catching pot 23 is provided at the upper part in the lower support structure 11, and as shown in FIG. There is no filter installed, and the large opening hole 24 is open. Therefore, there is no pressure loss due to the debris filter. The shape of the debris catching pot 23 is provided with a ring-shaped groove inside the upper part of the lower support structure 11, and a circumferential projection 25 is provided inside the groove so that the debris 20 once captured does not escape. ing.

  The cooling water flowing in from the orifice 12 provided in the lower support structure 11 is bent at a right angle and rises immediately after flowing in, as shown by the streamline in FIG. 6, and flows into the nozzle below the lower tie plate 13. . When the cooling water is bent at a right angle, the debris 20 having a large specific gravity moves to the inner wall of the lower support structure portion and rises along the inner wall as indicated by an arrow 26 by the action of centrifugal force. The debris 20 that has risen passes through the gap 28 between the lower tie plate nozzle wall surface 27 and the circumferential protrusion 25 and is stored in the debris catching pot 23. The debris 20 once stored cannot escape from the debris catching pot 23 due to the circumferential protrusion 25.

  FIG. 8 shows a second embodiment according to the present invention. In the second embodiment, a debris filter 19 is installed on the fuel rod support portion of the lower tie plate 13 (see FIG. 9). Further, in the second embodiment, the groove of the capture pot 23 is provided over the entire circumference in the same manner as in the first embodiment, but the depth thereof is such that the orifice 12 is provided as shown by a broken line in FIG. The bottom of the groove is inclined deeper from the position on the opposite side (position indicated by a in FIG. 8) to the position where the orifice is provided (position indicated by b in FIG. 8). ing. The reason for this is that the part indicated by b in the figure is depressurized more than the part indicated by a in the figure due to the influence of the flow, so that a flow is generated from the debris trapping area high pressure part a to the debris trapping area low pressure part b. The debris 20 is carried to the portion b in the figure and accumulated there.

  In the second embodiment, the combined use of the debris filter 19 and the debris trapping pot 23 can more reliably prevent the debris 20 from flowing into the fuel assembly 14. In addition, the combined use of the debris filter 19 cannot completely eliminate the above-mentioned problem of the pressure loss of the filter, but the combined use of the debris catching pot can cause large and heavy debris that damages the fuel rods due to fretting. All, even small and light debris, are captured by the debris catch pot, greatly reducing the pressure loss problem caused by filter clogging.

  FIG. 10 shows a third embodiment according to the present invention. In the third embodiment, the debris filter 19 and the debris catching pot 23 are used in combination as in the second embodiment (see FIG. 11). However, the shape of the catching pot 23 is the same as that shown in the first and second embodiments. The groove of the debris catching pot 23 is not provided with a groove over the circumference, but is cut off on the opposite side of the orifice 12 (see FIG. 12), and the upper inner side of the lower support structure 11 and the wall surface of the lower tie plate nozzle The gap 28 with 27 is widened to facilitate the inflow of debris. In FIG. 12, an arrow 29 indicates the flow direction of the fluid.

  In the third embodiment, in addition to the combined use of the debris filter 19 and the debris catching pot 23, the debris can be easily flown into the supplement pot and easily stored, thereby preventing the debris from flowing into the fuel assembly 14 more reliably. can do. Although the above-mentioned problem of the pressure loss of the filter cannot be completely solved by using the debris filter 19 together, the pressure loss due to the clogging of the filter described in the second embodiment can be achieved by using the debris catching pot. This problem can be greatly reduced.

  FIG. 13 shows a fourth embodiment according to the present invention. FIG. 14 shows details of a part of the debris filter provided in the lower tie plate of the fourth embodiment. FIG. 15 shows the end of the debris catching pot 23 separated in Example 4.

  In the fourth embodiment, as in the third embodiment, the debris filter 19 and the debris catching pot 23 are used together, but the two ends of the separated debris catching pot 23 on the opposite side of the orifice 12 in the lower support structure 11 are used. The third embodiment differs from the third embodiment in that a debris guide groove 30 extending vertically is provided on the inner wall between the portions. By providing the debris guide groove 30, the debris 20 rising along the inner wall on the side farther from the orifice 12 in the lower support structure 11 is guided to the debris catching pot 23 to make it easier to catch. In addition, by using the debris filter 19 in combination, the above-mentioned problem of the pressure loss of the filter cannot be completely solved, but the combined use of the debris capturing pot can greatly reduce the above problem due to the use of the filter, The same as in Examples 2 and 3.

  As mentioned above, although four examples from Example 1 to 4 were shown, each example provides a debris trapping pot in the lower support structure, and it is necessary to change the structure of the lower tie plate of the fuel assembly. However, a conventional one can be used. Therefore, it is possible to use the fuel assemblies of 8 × 8, 9 × 9, and 10 × 10, which are used for the current nuclear reactor fuel, as they are.

  The present invention can be used for a lower support structure part that serves as an inlet of a cooling part of a boiling water reactor (BWR), but can also be used for the purpose of capturing debris in cooling water in other parts.

A part of the inside of a boiling water reactor (BWR) pressure vessel is shown conceptually. The lower support structure that receives the fuel rods of the boiling water reactor is shown. An example in which a debris filter is installed in the lower part of a fuel assembly of a boiling water reactor is shown. A part of the debris filter shown in FIG. 3 is shown in detail. The result of measuring the pressure loss by the debris filter with respect to the flow rate in the actual machine is shown. Example 1 which concerns on this invention is shown. A part of lower tie plate in Example 1 is expanded and shown. Example 2 which concerns on this invention is shown. The part of debris filter provided in the lower tie plate in Example 2 is expanded and shown. Example 3 according to the present invention will be described. The part of debris filter provided in the lower tie plate in Example 3 is expanded and shown. FIG. 11 is an AA arrow view in FIG. 10 and shows an end portion of the debris catching pot 23 separated in Example 3. Example 4 which concerns on this invention is shown. The part of debris filter provided in the lower tie plate of Example 4 is expanded and shown. It is an AA arrow line view in FIG. 13, and shows the edge part of the debris capture | acquisition pot 23 cut away of Example 4. FIG.

Explanation of symbols

  1 ... Reactor pressure vessel, 2 ... Jet pump, 3 ... Recirculation pump, 4 ... Suction pipe, 5 ... Shroud wall, 6 ... Downcomer, 7 ... Cooling water, 8 ... Discharge pipe, 9 ... Nozzle, 10 ... Lower plenum , 11 ... Lower support structure, 12 ... Orifice, 13 ... Lower tie plate, 14 ... Fuel assembly, 15 ... Spacer, 16 ... Fuel rod, 17 ... Insertion port, 18 ... Fuel unit lower end plug, 19 ... Debris filter 20 ... Debris, 21 ... Hole into which fuel rod end plug is inserted, 22 ... Tapered small hole, 23 ... Debris trapping pot, 24 ... Large opening hole, 25 ... Circular projection, 26 ... Debris streamline, 27 ... Lower tie plate nozzle wall, 29 ... gap, 29 ... debris streamline, 30 ... debris guide groove, a ... debris capture region high pressure part, b ... debris capture region low pressure part

Claims (7)

In the lower support structure that supports the fuel assembly and includes a cooling water inlet on the side surface, and bends the cooling water flow path upward from the inlet.
A boiling water reactor characterized in that a debris trapping pot is provided between the upper inner side of the lower support structure and the nozzle wall below the fuel assembly, and traps debris in the cooling water. BWR) lower support structure. In the lower support structure part of the boiling water reactor (BWR) according to claim 1,
The debris trapping pot is a debris trapping groove provided with a protrusion that prevents reflow of the debris that has flowed in. A lower support structure part of a boiling water reactor (BWR). In the lower support structure of a boiling water reactor (BWR) as claimed in claim 2,
The debris trapping groove is provided over the entire inner periphery of the upper part of the lower support structure, and the lower support structure of a boiling water reactor (BWR). In the lower support structure of a boiling water reactor (BWR) as claimed in claim 2,
The debris capturing groove is formed such that the depth of the groove is shallowest at a position opposite to the cooling water inlet portion in the radial direction of the lower support structure portion, and becomes deeper as the distance from the opposite position in the circumferential direction increases. Boiling water reactor (BWR) lower support structure, characterized by In the lower support structure of a boiling water reactor (BWR) as claimed in claim 2,
The debris catching grooves are formed on both sides in the radial direction of the lower support structure part from the vicinity of the position opposite to the cooling water inlet part toward the position of the cooling water inlet part, and the depth of the groove is A lower support structure portion of a boiling water reactor (BWR), wherein the lower support structure portion is formed so as to become deeper as it approaches the position of the cooling water inlet portion. In a lower support structure of a boiling water reactor (BWR) according to claim 5,
The lower wall of the boiling water reactor (BWR) is characterized in that a debris guide groove is formed on the inner wall of the lower support structure portion at the opposite position of the cooling water inlet portion in the radial direction. Support structure. In the lower support structure of a boiling water reactor (BWR) according to any one of claims 2 to 6,
The debris trapping groove is integrally formed inside the lower support structure, and the lower support structure of a boiling water reactor (BWR).

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