JP5031665B2 - Boiling water reactor fuel assembly to prevent abnormal landing - Google Patents

Description

  The present invention relates to a core structure of a boiling water reactor, and in particular, when a fuel assembly is loaded on the core of a boiling water reactor, the fuel assembly rides on a part of a core support plate or a fuel support fitting. The present invention relates to a fuel assembly (including a lower tie plate, an upper tie plate, and a channel fastener of a fuel assembly), an upper lattice plate, and a fuel support bracket of a boiling water reactor capable of preventing an abnormal landing.

  The core of a boiling water reactor is equipped with a fuel support fitting on the core support plate attached to the reactor vessel, a fuel assembly is inserted from above the reactor, and the lower end of the fuel assembly is attached to the fuel support fitting. The upper end of the fuel assembly is supported by the upper lattice plate.

  FIG. 15 shows the core structure of a boiling water reactor using one of the fuel assemblies in the center of the core.

  As shown in FIG. 15, the core of the boiling water reactor is provided with a horizontal core support plate 1 attached to a reactor vessel (not shown), and a fuel support fitting 2 is provided on the core support plate 1. It is attached.

  A fuel support fitting insertion hole 4 for receiving the lower end of the fuel assembly 3 is provided in the upper part of the fuel support fitting 2. Since FIG. 15 shows the fuel assembly in the center of the core, the fuel support fitting 2 is provided with four fuel support fitting insertion holes 4 in one fuel support fitting 2 (hereinafter referred to as fuel in the outer periphery region of the core). When distinguishing from the support bracket, it is referred to as “core support region fuel support bracket 2”).

  In the vicinity of the upper end of the fuel assembly 3, an upper grid plate 5 attached to the reactor vessel is provided. The upper lattice plate 5 is formed by combining plate materials in a lattice shape, and can support the upper end of the fuel assembly 3 at the portion of the lattice.

  Since FIG. 15 shows the fuel assembly at the center of the core, four fuel assemblies 3 are inserted into one lattice of the upper lattice plate 5. A control rod 6 having a cross-shaped cross section can be inserted between the four fuel assemblies 3 from below.

  Each fuel assembly 3 has a plurality of fuel rods 7 mounted therein. 8 × 8 or 9 × 9 fuel rods 7 are loaded per fuel assembly 3. The upper end of the fuel rod 7 is held by the upper tie plate 8. Although only the lug portion of the upper tie plate 8 is shown in FIG. 15, the upper tie plate 8 has a network portion and can hold the upper end portion of the fuel rod 7.

  The lower end of the fuel rod 7 is held by the lower tie plate 9. Although only the lower part of the lower tie plate 9 is shown in FIG. 15, the lower tie plate 9 has a network part and is configured to hold the lower end part of the fuel rod 7.

  The periphery of the fuel rod 7 is surrounded by a channel box 10, and the upper and lower ends of the channel box 10 are fitted to the upper tie plate 8 and the lower tie plate 9 of the fuel assembly 3, respectively.

  In order to maintain a gap in which the control rod 6 can be inserted, a channel fastener 11 and a spacer 12 are provided on the side surface of the upper end portion of each fuel assembly 3.

  FIG. 16 shows the channel fastener 11 in an enlarged manner.

  The channel fastener 11 has a bifurcated leaf spring, and is fixed by screwing from above the upper tie plate projection into the hole in the horizontal plate joined to the upper inner corner of the channel box 10. Has been.

  When the leaf spring comes into contact with the leaf spring of the adjacent channel fastener 11, a gap is maintained between the fuel assemblies 3 so that the control rod 6 can be inserted. However, since the leaf spring protrudes from the side surface of the fuel assembly 3, there arises a problem of contact between the channel fastener 11 and the upper lattice plate, which is a problem of the present invention.

  FIG. 17 shows the lower tie plate 9.

  The lower tie plate 9 is fitted to the lower end of the channel box 10 and includes a square tube portion 13 containing a network portion (not shown) that supports the lower end of the fuel rod 7 (not shown), a funnel portion 14, and a nose cone 15. And have. The nosecone 15 further has a nosecone base 16 and a lead 17. The lead 17 is a guide member for correctly landing the fuel assembly 3 in the fuel support fitting insertion hole 4, and the tips 17 are curved and coupled to each other.

  FIG. 18 shows the entire fuel support fitting 2 for the core central region.

  The core support region fuel support fitting 2 has a cylindrical portion 18 in the lower portion and a portion having four fuel support fitting insertion holes 4 in the upper portion. The cylindrical portion 18 is fitted into the hole of the core support plate 1, so that the core central region fuel support fitting 2 is supported by the core support plate 1.

  An orifice 19 through which a coolant flows is provided on the side surface of the cylindrical portion 18 at a position corresponding to each fuel support fitting insertion hole 4 (position aligned vertically).

  The outer peripheral portion of the fuel support fitting insertion hole 4 is formed in a partial cup-shaped cup portion 20. The cup portion 20 is formed in a shape that can receive the nose cone 15 of the lower tie plate of the fuel assembly, and the outer peripheral portion has a curved surface.

  A cross-shaped through hole 21 through which the control rod 6 is inserted is provided between the fuel support fitting insertion holes 4.

  FIG. 19 shows a cross-sectional view of a state where the lower tie plate 9 of the fuel assembly 3 is mounted in the fuel support fitting insertion hole 4 of the fuel support fitting 2 for the core center region.

  Only the right half of the cross section of the fuel support fitting 2 for the core center region in FIG. 19 is shown, and a symmetrical cross section (not shown) exists on the left side. As shown in FIG. 19, in the state where the lower tie plate 9 of the fuel assembly 3 is mounted in the fuel support fitting insertion hole 4, the nose cone 15 is fitted in the fuel support fitting insertion hole 4, and the lead 17 is connected to the cup portion. It comes to fit in 20.

  The coolant enters from the orifice 19 toward the center of the fuel support fitting 2 for the core center region, changes its flow upward inside the fuel support fitting 2 for the core center region, and passes through the lower tie plate 9 to Flows into the interior.

  The above is a description of the fuel assembly 3 in the central region of the core. However, as shown by reference numeral B in FIG. 20, there is a fuel assembly 3 that is loaded alone in a part of the outermost peripheral region of the core.

  A symbol A in FIG. 20 indicates a fuel assembly in which four fuel assemblies 3 are combined and a control rod 6 is inserted therebetween, similar to the fuel assembly in the core central region. In contrast, in a part of the outermost peripheral region of the core, one fuel assembly is loaded alone in one section of the upper lattice plate.

  FIG. 21 shows the structure around the fuel assembly 3 in the outermost peripheral region of the core.

  One fuel assembly 3 in the outermost peripheral region of the core is inserted into one lattice of the upper lattice plate 5 as shown in FIG.

  In order to support such a fuel assembly 3, a fuel support fitting 22 for the outermost peripheral region of the core is used (hereinafter referred to as “fuel support fitting 22 for the outermost peripheral region of the core when distinguished from the fuel support fitting in the central region of the core”. ").

  The fuel support fitting 22 for the outermost peripheral region of the core has a generally cylindrical shape as a whole, and a step portion is formed on the outer peripheral surface, and is supported by the core support plate 1 at the step portion. .

  The fuel support fitting 22 for the outermost peripheral area of the core has only one fuel support fitting insertion hole 23 at the top. The core outermost peripheral region fuel support fitting 22 has only one orifice 24 into which the coolant flows on the bottom surface.

  The coolant flows from the orifice 24 on the bottom surface of the fuel support fitting 22 for the outermost peripheral region of the core and flows into the fuel assembly 3 through the lower tie plate 9.

A channel fastener 11 is provided on the upper side surface of the fuel assembly 3. The fuel assembly 3 in the outermost peripheral region of the core is configured such that one fuel assembly 3 is inserted into one lattice of the upper lattice plate 5, and the leaf spring of the channel fastener 11 serves as a side surface of the fuel assembly 3. Therefore, there is a relatively high possibility of contact between the channel fastener 11 and the upper lattice plate 5 which causes a problem in the present invention.
Japanese Patent Laid-Open No. 2001-183484

  In a conventional boiling water reactor, when loading a fuel assembly into the core, the fuel assembly is moved up to the target position by a crane for moving the fuel assembly, and then slowly waits until the shaking stops. Lower.

  If the fuel assembly shakes when it descends, the fuel assembly that has passed through the upper grid plate will normally land on the fuel support bracket directly below.

  However, even if the work is performed carefully, the fuel assembly may come into contact with the core components while descending, which causes a large shaking, and the lower end of the fuel assembly is not attached to the core support plate or the fuel support bracket. There is no possibility of abnormal landing, such as riding a part.

  In particular, in a region where only one fuel assembly is loaded in one section of the upper lattice plate on the outermost periphery of the core (core outermost peripheral region), the channel fastener may come into contact with the upper lattice plate. When the cycle fuel (unirradiated fuel) is loaded or when the replacement core fuel is loaded, the fuel assembly may be shaken by the channel fastener coming into contact with the upper lattice plate.

  By the way, even if the fuel assembly comes into contact with the core component while descending, and the fuel assembly shakes, the lower end of the lower tie plate of the fuel assembly (the tip of the nose cone or nose piece) ) Has reached the insertion hole of the fuel support bracket, the movement of the lower end of the fuel assembly is restricted to the inside of the fuel support bracket insertion hole, so that even if a slight fluctuation occurs, the fuel support bracket is normal. Implant to the floor.

  However, if the lower end of the lower tie plate of the fuel assembly does not reach the fuel support fitting insertion hole, the lower end of the lower tie plate of the fuel assembly will be inserted into the fuel support fitting when the fuel assembly shakes. There is a possibility of landing without being in the hole.

  Of the possibility that the fuel assembly comes into contact with the core component while descending, the possibility that the lower end of the channel fastener of the fuel assembly and the upper lattice plate are in contact with each other in the outermost peripheral region of the core is relatively high. In addition, when the lower end of the channel fastener of the fuel assembly and the upper lattice plate come into contact with each other, the swing width at the lower end of the fuel assembly becomes large, and there is a relatively high possibility that an abnormal landing will occur.

  Therefore, if the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate is longer than the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting, Even when the channel fastener (the lower end or side surface of the channel fastener) and the upper lattice plate contact, the lower end of the fuel assembly reaches the insertion hole of the fuel support bracket, and the fuel assembly sways due to the contact. However, it is possible to normally land, and to effectively prevent the fuel assembly from landing abnormally.

  However, the conventional fuel assembly, when not irradiated, has a channel box length of about 4.2 m, a lower tie plate height of about 17 cm, and a channel fastener length of about 10 cm. When the channel fastener was in contact with the upper lattice plate, the tip of the nose piece of the lower tie plate did not reach the insertion hole of the fuel support bracket by about 2 to 3 cm.

  For this reason, in a core structure including a conventional fuel assembly, the fuel assembly may sway due to contact between the channel fastener and the upper lattice plate, which may cause abnormal landing.

  On the other hand, before the channel fastener comes into contact with the upper lattice plate, the lower end of the fuel assembly (the tip of the nose cone of the lower tie plate) reaches the insertion hole of the fuel support fitting so that the fuel assembly It is conceivable to increase the length.

  However, in the core, if the length of the fuel assembly is extended, the position of the fuel rod, that is, the vertical position of the fuel pellet is affected. Since the upper and lower positions of the fuel pellets are related to the neutron irradiation region, simply extending the length of the fuel assembly affects the output of the reactor, which is not preferable. Therefore, with the upper and lower positions of the fuel pellets held in the existing core or the position specified by the standard, before the channel fastener comes into contact with the upper grid plate, the lower end of the fuel assembly (the nose cone of the lower tie plate) The tip must reach the insertion hole of the fuel support bracket.

  The problem to be solved by the present invention is that the lower end of the fuel assembly (the nose of the lower tie plate) is affected when the fuel assembly sways in contact with the core component while descending without affecting the output of the core. To provide a boiling water reactor fuel assembly, an upper grid plate, and a fuel support bracket that can prevent the abnormal landing of the fuel so that the cone tip) reaches the insertion hole of the fuel support bracket. It is in.

  Japanese Patent Laid-Open No. 2001-183484 aims to prevent the fuel assembly from getting on the upper surface of the upper lattice plate of the core or the tip of the cross-shaped control rod when the fuel assembly is loaded on the core. It is not intended to avoid abnormal landing on the bracket. In addition, as a method of avoiding abnormal landing, the arrangement of the lead base end portion of the nose cone similar to a part of the present invention is devised, but the arrangement of the lead base end portion is the opposite of the present invention with respect to the control rod. The arrangement is taken.

The fuel assembly of the boiling water reactor according to the present invention is:
In the boiling water reactor core, the fuel pellets of the fuel rods have dimensions that hold the upper and lower ends of the fuel pellets at predetermined positions, and the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate, to be longer than the distance to the fuel support insertion hole upper end of the fuel support from the upper end of the upper grid plate, it has a lower tie plate which sets the vertical length of the nose cone, and the lower tie plate of the nose From the center of the fuel support fitting insertion hole of the fuel support fitting for the core central region, the lead tip joint portion of the cone is moved to a deep part of the cup portion of the fuel support fitting for the core central region. The control rod is eccentric toward the center line .

Another fuel assembly of the boiling water reactor according to the present invention is:
In the boiling water reactor core, the fuel pellets of the fuel rods have dimensions that hold the upper and lower ends of the fuel pellets at predetermined positions, and the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate, It has a lower tie plate provided with a rod-like projection on the lower end of the nose cone so as to be longer than the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting.

  The lower tie plate has a nose cone base portion on the line connecting the center of the fuel support fitting insertion hole of the fuel support fitting for the core center region and the control rod center line with the base ends of the three leads of the nose cone of the lower tie plate. And a line connecting the center of the nose cone base and the first lead base end is 120 ° clockwise and counterclockwise around the center of the nose cone base. The second and third lead base ends can be arranged at the nose cone base at the rotated position.

Another fuel assembly of the boiling water reactor according to the present invention is:
In the boiling water reactor core, the fuel pellets of the fuel rods have dimensions that hold the upper and lower ends of the fuel pellets at predetermined positions, and the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate, A channel fastener having a length in the vertical direction is set so as to be longer than the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting.

The upper lattice plate of the boiling water reactor according to the present invention is:
In the core of a boiling water reactor, the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate is longer than the distance from the upper end of the upper grid plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting. Thus, the upper end position of the upper lattice plate is adjusted within a range not interfering with the upper end position of the fuel pellet of the fuel rod.

The other upper lattice plate of the boiling water reactor according to the present invention is:
In the core of a boiling water reactor, the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate is from the upper end of the upper lattice plate at the portion contacting the channel fastener to the fuel supporting bracket insertion hole of the fuel supporting bracket. A groove is provided in the upper end portion of the upper lattice plate at the portion in contact with the channel fastener so as to be longer than the distance to the upper end.

The fuel support fitting for the boiling water reactor according to the present invention is:
A funnel-shaped guide is provided above the fuel support fitting insertion hole so as to receive the lower end of the fuel assembly before the channel fastener and the upper lattice plate come into contact with each other when the fuel is loaded.

Another fuel assembly of the boiling water reactor according to the present invention is:
In the boiling water reactor core, the fuel pellets of the fuel rods have dimensions that hold the upper and lower ends of the fuel pellets at predetermined positions, and the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate, It has an upper tie plate in which the length of the post portion is set so as to be longer than the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting.

  In the fuel support fitting of the boiling water reactor of the present invention, the cup portion of the fuel support fitting insertion hole can be formed deeply so as not to contact the lower end of the lower tie plate of the fuel assembly.

  According to the present invention, the fuel assembly has dimensions that hold the positions of the upper and lower ends of the fuel pellets of the fuel rods at predetermined positions, and the length from the lower end of the channel fastener to the lower end of the lower tie plate is Fuel assembly (including fuel assembly lower tie plate, upper tie plate, channel fastener), upper lattice plate, so as to be longer than the distance from the upper end of the grid plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting Since the fuel support bracket is formed, there is no effect on the reactor output. If the channel fastener comes into contact with the upper grid plate, the lower end of the fuel assembly (the lower tie plate nose) The lower end of the cone or the lower end of the rod-like projection at the tip of the nose cone) reaches the insertion hole of the fuel support bracket, and even if the fuel assembly shakes, it can land normally. It is possible to effectively prevent the implantation abnormality of the fuel assembly by.

  By the way, in order to make the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate longer than the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting, When the length of the direction is increased or a rod-shaped protrusion is provided at the lower end of the nose cone, when the fuel assembly is attached to the fuel support fitting for the core central region, the lower end of the nose cone or the tip of the nose cone There is a possibility that the lower end of the rod-shaped protrusion comes into contact with the inner surface (curved surface of the outer peripheral bottom portion) of the cup portion of the fuel support fitting for the core center region.

  In contrast, the present invention has a lower tie plate in which the lead tip coupling portion of the nose cone of the lower tie plate is decentered toward the control rod center line from the center of the fuel support fitting insertion hole of the fuel support fitting for the core central region. According to the fuel assembly of the invention, the nose cone lead tip coupling portion is located in the deep part of the cup portion of the fuel support fitting insertion hole of the fuel support fitting for the central region of the core. It is possible to prevent contact between the lower end of the projection (including the projection) and the curved surface of the outer peripheral bottom portion of the cup portion of the fuel support fitting insertion hole.

  Also, the base end of the three leads of the nose cone is connected to the nose cone base on the line connecting the center of the fuel support fitting insertion hole of the fuel support fitting for the central region of the core and the control rod center line. And a line connecting the center of the nose cone base and the first lead base end to the nose cone base at a position rotated 120 ° clockwise and counterclockwise around the center of the nose cone base. According to the fuel assembly of the present invention having the lower tie plate in which the second and third lead base end portions are arranged, with respect to the shallow portion where the curved surface of the outer peripheral bottom portion of the cup portion of the fuel support fitting insertion hole is present, Since the second and third lead base end portions are distributed so as to avoid this, the lead of the nose cone is prevented from coming into contact with the curved surface of the bottom portion of the cup portion of the fuel support fitting insertion hole. Can

  Further, according to the fuel support fitting of the boiling water reactor of the present invention in which the cup portion of the fuel support fitting insertion hole is formed deeply so as not to contact the lower end of the lower tie plate of the fuel assembly, For the same reason, that is, by inserting the nose cone into the cup portion of the fuel support fitting for the central region of the core where the nose cone is formed deeply, the lower end of the nose cone (including the rod-shaped protrusion) and the outer bottom of the cup portion of the fuel support fitting insertion hole It is possible to prevent the curved surface from contacting.

  The upper lattice plate of the boiling water reactor of the present invention with the position of the upper end adjusted, or the upper lattice plate of the boiling water reactor of the present invention in which a groove is provided at the upper end portion of the upper lattice plate in contact with the channel fastener Since the plate has a lower upper end of the upper lattice plate in contact with the channel fastener, the channel fastener does not contact the upper lattice plate until the lower end of the fuel assembly enters the fuel support fitting insertion hole. After the lower end of the fuel assembly is inserted into the fuel support fitting insertion hole, there is a possibility that the channel fastener and the upper lattice plate come into contact with each other. The lower end of the body (the lower end of the nose cone of the lower tie plate or the lower end of the rod-like protrusion at the tip of the nose cone) has already reached the insertion hole of the fuel support bracket, so that even if the fuel assembly shakes, it will land normally it can.

  Further, according to the fuel support bracket of the boiling water reactor of the present invention provided with a funnel-shaped guide at the upper portion of the fuel support bracket insertion hole, the fuel assembly is performed before the channel fastener and the upper lattice plate come into contact with each other when the fuel is loaded. The lower end of the body is received by the funnel-shaped guide, so that even if the fuel assembly shakes, it can be normally landed.

  In any of the above cases, the present invention maintains the positions of the upper and lower ends of the fuel pellets of the fuel rods at the predetermined positions defined by the existing core or standard, and within this range, the lower tie plate from the lower end of the channel fastener. To adjust the distance from the upper end of the upper grid plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting without affecting the output of the reactor. Can be prevented.

  Next, the best mode for carrying out the present invention will be described below.

  In the following description, the same parts as those in FIGS. 15 to 21 will be described using the same reference numerals.

  First, with the upper and lower ends of the fuel pellets of the fuel rods held in place, the length from the lower end of the channel fastener to the lowest end of the lower tie plate is adjusted from the upper end of the upper grid plate to the fuel support bracket. An embodiment in which the vertical length of the nose cone or channel fastener of the lower tie plate of the fuel assembly is adjusted to be longer than the distance to the upper end of the fuel support fitting insertion hole will be described.

  FIG. 1 shows the concept of the above embodiment.

  FIG. 1 shows the fuel assembly 3 in the outermost peripheral region of the core.

  As shown in FIG. 1, the length from the lower end of the channel fastener 11 to the lowermost end of the lower tie plate 9 is X, and the distance from the upper end of the upper lattice plate 5 to the upper end of the fuel support fitting insertion hole 23 of the fuel support fitting 22. In this embodiment, the dimension of the channel fastener 11 or the lower tie plate 9 is adjusted so that X−Y = about 1 cm so that X> Y is satisfied.

  However, as shown in FIG. 1, the positions of the upper and lower ends of the fuel pellets need to be held at existing cores or at positions defined by standards in order not to affect the output. For this reason, the dimensional adjustment of the fuel assembly must be performed within a range that maintains the positions of the upper and lower ends of the fuel pellet, that is, the position of the fuel rod.

  In order to satisfy the above-described conditions, the dimensional adjustment method is specifically performed by increasing the vertical length of the nose cone 15 of the lower tie plate 9 while maintaining the position of the fuel rod, A method is employed in which a bar-like protrusion is provided at the lower end of the channel fastener or the length of the channel fastener 11 in the vertical direction is shortened.

  FIG. 1 (b) shows the lower end of the fuel assembly 3 when the lower end of the channel fastener 11 is in contact with the upper end of the upper lattice plate 5 in the fuel assembly 3 configured to have XY = about 1 cm. The state is shown enlarged.

  As shown in FIG. 1B, since XY is configured to be about 1 cm, the fuel assembly 3 before the lower end portion of the channel fastener 11 of the fuel assembly 3 contacts the upper end of the upper lattice plate 5. 3 (the lower end of the nose cone 15) enters the fuel support fitting insertion hole 23 of the fuel support fitting 22 for the outermost peripheral region of the core, and the lower end of the channel fastener 11 of the fuel assembly 3 is at the upper end of the upper lattice plate 5. When contacted, the lower end of the fuel assembly 3 (the lower end of the nose cone 15) is about 1 cm from the upper end of the fuel support fitting insertion hole 23 of the fuel support fitting 22 for the outermost peripheral region of the core.

  Therefore, even if the channel fastener 11 of the fuel assembly 3 comes into contact with the upper lattice plate 5 and the fuel assembly 3 is shaken, the movement of the lower end portion of the fuel assembly 3 is caused by the fuel support fitting insertion hole of the fuel support fitting. The lower end of the fuel assembly can be correctly landed by guiding the nose cone 15.

  Although FIG. 1 described the fuel assembly in the outermost peripheral region of the core, the fuel assembly can be used in the central region of the core. Even in this case, since the distance from the lower end of the channel fastener 11 of the fuel assembly to the lower end of the fuel assembly 3 (lower end of the nose cone 15) is long, the lower end of the fuel assembly 3 (relative to the nose cone 15) is relatively large. The lower end) can be easily inserted into the fuel support fitting insertion hole of the fuel support fitting, and therefore, the possibility that the fuel assembly 3 is normally landed can be improved.

  2 shows the length from the lower end of the channel fastener to the lowermost end of the lower tie plate (X in FIG. 1), and the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting (in FIG. Y) An embodiment of the present invention in which the length in the vertical direction of the nose cone is increased in order to make it longer is shown in comparison with a conventional nose cone.

  FIG. 2 (a) shows a conventional nose cone of a lower tie plate, and FIG. 2 (b) shows a nose cone of a lower tie plate according to the present invention.

  As shown in FIG. 2, the lower tie plate 9 of the present embodiment reduces the curvature of the lead 17 of the nose cone 15. As a result, the distance from the lower end of the tip coupling portion of the lead 17 to the upper end of the nose cone base 16 is changed from the conventional 5 cm to 8 cm, and as a result, the length from the lower end of the channel fastener to the lowermost end of the lower tie plate (FIG. 1). The distance X) is extended by 3 cm.

  Note that even if the length of the nose cone in the vertical direction is increased, the distance from the nose cone base 16 to the lower end of the fuel pellet (not shown) does not change. Therefore, the upper and lower end positions of the fuel pellet can be held at predetermined positions. it can.

  In the conventional fuel assembly, X is about 2 cm shorter than Y in the unirradiated state. However, according to this embodiment, X is about 1 cm longer than Y, and the lower end portion of the channel fastener 11 of the fuel assembly 3 is Before contacting the upper end of the upper lattice plate 5, the lower end of the fuel assembly 3 (the lower end of the nose cone 15) enters the fuel support fitting insertion hole 23 of the fuel support fitting 22, and the channel fastener 11 of the fuel assembly 3. In the unlikely event that the lower end contacts the upper end of the upper grid plate 5, the lower end of the fuel assembly 3 (the lower end of the nose cone 15) is about 1 cm from the upper end of the fuel support fitting insertion hole 23 of the fuel support fitting 22. .

  Thus, even if the channel fastener 11 of the fuel assembly 3 and the upper lattice plate 5 come into contact with each other and the fuel assembly 3 is shaken, the fuel assembly 3 can be correctly landed.

  3 shows the length from the lower end of the channel fastener to the lowermost end of the lower tie plate (X in FIG. 1), and the distance from the upper end of the upper grid plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting (in FIG. Y) In order to make it longer, an embodiment of the present invention in which a rod-like protrusion is provided at the lower end of the nose cone is shown in comparison with a conventional nose cone.

  3A shows a conventional lower tie plate nose cone, and FIG. 3B shows a lower tie plate nose cone according to the present invention.

  As shown in FIG. 3B, in the present embodiment, a rod-like protrusion 25 is provided at the lower end of the nose cone 15 without changing the shape and dimensions of the nose cone 15 itself.

  As shown in FIG. 3, in the present embodiment, by providing a rod-like protrusion 25 at the lower end of the nose cone 15, the distance from the lower end of the nose cone 15 (lower end of the rod-like protrusion 25) to the upper end of the nose cone base 16 is increased. As a result, the length (X in FIG. 1) from the lower end of the channel fastener to the lowermost end of the lower tie plate (the lower end of the rod-like protrusion 25) extends by 3 cm.

  Even if the rod-shaped protrusion 25 is provided at the lower end of the nose cone, the distance from the nose cone base 16 to the lower end of the fuel pellet (not shown) does not change, so that the upper and lower end positions of the fuel pellet can be held at a predetermined position.

  In the conventional fuel assembly, X is about 2 cm shorter than Y in an unirradiated state, but according to this embodiment, the distance X is about 1 cm longer than the distance Y, and the lower end of the channel fastener 11 of the fuel assembly 3 Before the portion comes into contact with the upper end of the upper lattice plate 5, the lower end of the fuel assembly 3 (the lower end of the rod-like protrusion 25) enters the fuel support fitting insertion hole 23 of the fuel support fitting 22 and the channel of the fuel assembly 3. If the lower end of the fastener 11 contacts the upper end of the upper grid plate 5, the lower end of the fuel assembly 3 (the lower end of the rod-like protrusion 25) enters about 1 cm from the upper end of the fuel support fitting insertion hole 23 of the fuel support fitting 22. It becomes a state.

  As a result, even if the channel fastener 11 of the fuel assembly 3 and the upper lattice plate 5 come into contact with each other and the fuel assembly 3 is shaken, the movement of the lower end of the fuel assembly 3 (the lower end of the rod-like protrusion 25) is the fuel. The inside of the support fitting insertion hole 23 is limited, and as a result, the fuel assembly 3 can be correctly landed.

  By the way, as shown in FIGS. 2 and 3, when the length of the nose cone 15 in the vertical direction is increased or the rod-like protrusion 25 is provided at the lower end of the nose cone 15, the fuel assembly 3 is placed in the center of the core. When attaching to the region fuel support bracket 2, the lower end of the nose cone 15 or the lower end of the rod-shaped protrusion 25 may come into contact with the inner surface (curved surface of the outer peripheral bottom) of the cup portion 20 of the core center region fuel support bracket 2. There is.

  Three embodiments for solving this problem are shown below.

  4 and 5, the tip coupling portion of the lead 17 of the nose cone 15 of the lower tie plate 9 is eccentric from the center of the fuel support fitting insertion hole 4 of the fuel support fitting 2 for the core center region toward the control rod center line. An embodiment is shown.

  4A is a longitudinal sectional view of a normal lower tie plate 9 in which the tip coupling portion of the lead 17 of the nose cone 15 is not decentered, and FIG. 4B is a diagram showing the eccentricity of the tip coupling portion of the lead 17 of the nose cone 15. The longitudinal cross-sectional view of the made lower tie plate 9 of this embodiment is shown.

  FIG. 5A is a bottom view of a normal lower tie plate 9 in which the tip coupling portion of the lead 17 of the nose cone 15 is not decentered, and FIG. 5B is a diagram of the tip coupling portion of the lead 17 of the nose cone 15 eccentric. The bottom view of lower tie plate 9 of this embodiment is shown.

  As shown in FIGS. 4 and 5, in this embodiment, the tip coupling portion P of the lead 17 of the nose cone 15 of the lower tie plate 9 is moved from the center of the fuel support fitting insertion hole 4 of the fuel support fitting 2 for the core center region. , Eccentric toward the center line of the control rod.

  4 (a) and 5 (a) show the lower tie plate 9 in which the tip coupling portion P of the lead 17 of the nose cone 15 is not eccentric, but as shown, the tip coupling portion P of the lead 17 is eccentric. The lower tie plate 9 that is not to be disposed is located at a position where the tip coupling portion P of the lead 17 coincides with the center of the fuel support fitting insertion hole 4, that is, the center of the fuel assembly 3.

  4 (b) and 5 (b) show the lower tie plate 9 in which the tip coupling portion P of the lead 17 of the nosecone 15 is eccentric. The tip coupling portion P is eccentric toward the control rod center line (C).

  In particular, as shown in FIG. 5 (b), according to the present embodiment, the tip coupling portion P of the lead 17 of the nose cone 15 moves to a deep portion of the cup portion 20 of the fuel support fitting 2 for the core central region, As a result, the lead 17 does not come into contact with the curved surface of the outer peripheral portion of the cup portion 20.

  Thereby, it can prevent that a nose cone lower end contacts with the inner surface (curved surface of an outer peripheral bottom part) of the cup part 20 of the fuel support metal fitting 2 for core center area | regions.

  In the above-described embodiment, the lower tie plate 9 having the nose cone whose length in the vertical direction is increased has been described. However, the lower tie plate 9 having the nose cone having the rod-like protrusion 25 provided at the tip of the nose cone is also used. It is the same.

  6 and 7, the base ends of the three leads 17 of the nose cone 15 of the lower tie plate 9 are connected to the center of the fuel support fitting insertion hole 4 of the fuel support fitting 2 for the core center region and the control rod center line (C ) On the nose cone base 16 on the line connecting the first lead 17a, the line connecting the center (O) of the nose cone base 16 and the base end of the first lead 17a, An embodiment in which the base ends of the second and third leads 17b and 17c are arranged on the nose cone base at positions rotated 120 ° clockwise and counterclockwise about the center (O) of the nose cone base. Show.

  6A is a longitudinal sectional view of a lower tie plate 9 having a nose cone having a conventional lead arrangement, and FIG. 6B is a lower tie plate 9 having a nose cone having an adjusted lead arrangement according to the present embodiment. The longitudinal cross-sectional view of is shown.

  FIG. 7A is a bottom view of the lower tie plate 9 having a nose cone having a conventional lead arrangement, and FIG. 7B is a bottom view of the lower tie plate 9 having a nose cone having an adjusted lead arrangement according to the present embodiment. The figure is shown.

  As shown in FIGS. 6 and 7, in this embodiment, the position of the base end portion of the lead of the nose cone is adjusted.

  6 (a) and 7 (a) show a lower tie plate 9 having a conventional nose cone. As shown in FIG. 7 (a), a nose cone 15 having a conventional lead arrangement is The base end of the first lead 17a is connected to the nose cone base 16 on the line connecting the center of the fuel support fitting insertion hole 4, that is, the center O of the nose cone base 16 and the midpoint of one side of the cross section of the fuel assembly 3. And a line connecting the center O of the nose cone base and the base end of the first lead 17a is rotated at 120 ° clockwise and counterclockwise around the center O of the nose cone base. The base end portions of the second and third leads 17b and 17c are arranged on the base portion 16.

  On the other hand, FIGS. 6B and 7B show the lower tie plate 9 having the nose cone according to the present embodiment, but as shown in FIG. The nose cone 15 having the lead arrangement is located at the base end of the first lead 17a at the center of the fuel support fitting insertion hole 4, that is, the nose cone base 16 on the line connecting the center O of the nose cone base 16 and the control rod center line C. The nose at a position where the line connecting the center O of the nose cone base and the base end of the first lead 17a is rotated 120 ° clockwise and counterclockwise about the center O of the nose cone base. The proximal end portions of the second and third leads 17b and 17c are arranged on the cone base portion 16.

  The arrangement of the base end portion of the lead of this embodiment is deviated by about 15 ° as a whole from the arrangement of the base end portion of the conventional lead (15 ° counterclockwise in FIG. 7), and cooling. The base end portions of the second and third leads 17b and 17c are equally distributed with respect to the curved surface in the material inflow direction, that is, the outer peripheral direction of the cup portion 20.

  Accordingly, as can be seen by comparing FIGS. 6A and 6B, the leads 17b and 17c are avoided with respect to the curved surface of the outer peripheral bottom portion of the cup portion 20, and the lead of the nose cone is the core. It is possible to prevent contact with the inner surface (curved surface of the outer peripheral bottom) of the cup portion 20 of the center region fuel support fitting 2.

  FIG. 8 shows an embodiment in which the cup portion of the fuel support fitting insertion hole is formed deep so as not to contact the lower end of the lower tie plate of the fuel assembly.

  FIG. 8 (a) shows a conventional fuel support fitting for a core central region having a cup portion, and FIG. 8 (b) shows a fuel support fitting for a core central region having a cup portion according to the present embodiment. .

  As can be seen by comparing (a) and (b) of FIG. 8, the fuel support fitting 2 for the core central region according to the present embodiment is a fuel that does not contact the lower end of the lower tie plate of the fuel assembly 3. The cup portion of the support fitting insertion hole is deeply formed.

  In the core center region fuel support fitting 2 having the conventional cup portion 20, as shown in FIG. 8A, the lead 17 of the nose cone 15 may come into contact with the curved surface S of the outer peripheral bottom portion of the cup portion 20. However, according to the fuel support fitting 2 for the core center region of the present embodiment, as shown in FIG. 8B, the cup portion 20 is formed deeply, and the lead 17 of the nose cone 15 is connected to the outer periphery of the cup portion 20. There is no contact with the curved surface S at the bottom.

  When the fuel assembly 3 in which the length in the vertical direction of the nose cone 15 is increased or the rod-like protrusion 25 is provided at the lower end of the nose cone 15 is attached to the fuel support fitting 2 for the core center region, the nose It is description about embodiment which prevented that the cone 15 lower end or the lower end of the rod-shaped protrusion 25 contacted the inner surface (curved surface of an outer peripheral bottom part) of the cup part 20 of the fuel support metal fitting 2 for core center area | regions.

  Next, an embodiment of a fuel assembly having a channel fastener whose length in the vertical direction is shortened will be described.

  FIG. 9 shows an embodiment of a fuel assembly having a channel fastener 11 with a shortened length in the vertical direction.

  FIG. 9A shows a fuel assembly 3 having a conventional channel fastener 11, and FIG. 9B shows that the length from the lower end of the channel fastener 11 of the fuel assembly to the lower end of the lower tie plate 9 is upper. The fuel assembly 3 of the present embodiment having the channel fastener 11 whose length in the vertical direction is shortened so as to be longer than the distance from the upper end of the grid plate 5 to the upper end of the fuel support fitting insertion hole of the fuel support fitting 22 is shown. Yes.

  The fuel assembly 3 of the present embodiment shortens the length of the channel fastener 11 in the vertical direction, but the other dimensions of the fuel assembly 3 are the same as the fuel assembly 3 of FIG. 9A. For this reason, the positions of the fuel rods in the fuel assembly 3, that is, the positions of the upper and lower ends of the fuel pellets of the fuel rods are held at the predetermined positions, and the output of the reactor is not affected.

  As can be seen by comparing (a) and (b) of FIG. 9, the length L ′ in the vertical direction of the channel fastener 11 of the fuel assembly 3 of the present embodiment is equal to the channel fastener 11 of the conventional fuel assembly 3. Is formed shorter than the vertical length L.

  9B, according to this embodiment, when the lower end of the channel fastener 11 contacts the upper end of the upper lattice plate 5, the lower end of the lower tie plate 9 is the fuel for the outermost peripheral region of the core. It is possible to make it reach the fuel support fitting insertion hole 23 of the support fitting 22.

  Thereby, even when the channel fastener 11 contacts the upper lattice plate 5 and the fuel assembly 3 is shaken, the fuel assembly 3 can be normally landed.

  FIG. 10 shows an embodiment of the upper grid plate in which the position of the upper end is adjusted.

  FIG. 10A shows a conventional upper lattice plate in which the upper end position is not adjusted, and FIG. 10B shows the length from the lower end of the channel fastener 11 of the fuel assembly to the lower end of the lower tie plate 9. The upper lattice plate 5 of the present embodiment is shown in which the upper end position is adjusted so that is longer than the distance from the upper end of the upper lattice plate 5 to the upper end of the fuel support fitting insertion hole of the fuel support fitting 22.

  The dimensions of the fuel assembly 3 in FIGS. 10 (a) and 10 (b) are the same. For this reason, the positions of the fuel rods in the fuel assembly 3, that is, the positions of the upper and lower ends of the fuel pellets of the fuel rods are as follows. It is held in a predetermined position and does not affect the reactor power.

  As can be seen by comparing (a) and (b) of FIG. 10, the upper grid plate 5 of this embodiment has a lower upper end position than the conventional upper grid plate 5.

  Accordingly, as shown in FIG. 10B, according to the present embodiment, when the lower end of the channel fastener 11 contacts the upper end of the upper lattice plate 5, the lower end of the lower tie plate 9 is the fuel for the outermost peripheral region of the core. It is possible to make it reach the fuel support fitting insertion hole 23 of the support fitting 22.

  According to this embodiment, even when the channel fastener 11 contacts the upper lattice plate 5 and the fuel assembly 3 is shaken, the fuel assembly 3 can be normally landed.

  In addition, as a method of adjusting the upper end position of the upper lattice plate, the attachment position of the upper lattice plate 5 can be lowered in addition to reducing the thickness of the upper lattice plate 5 as shown in FIG.

  However, when the mounting position of the upper grid plate 5 is lowered, if the mounting position of the upper grid plate 5 is lowered by a certain distance or more, the upper grid plate 5 is applied to the fuel pellets at the upper end of the fuel rod, which affects the output of the reactor. give. For this reason, the upper end position of the upper lattice plate must be adjusted within a range that does not interfere with the upper end position of the fuel pellet of the fuel rod.

  FIG. 11 shows an embodiment of an upper lattice plate in which a groove is provided in the upper end portion of the upper lattice plate in a portion that contacts the channel fastener.

  As shown in FIG. 11, the upper lattice plate 5 of the present embodiment is such that the length from the lower end of the channel fastener 11 of the fuel assembly 3 to the lower end of the lower tie plate 9 is the portion of the upper lattice plate that contacts the channel fastener 11. A groove 26 is provided in the upper end portion of the upper lattice plate 5 at a portion in contact with the channel fastener 11 so as to be longer than the distance from the upper end of the plate 5 to the upper end of the fuel support fitting insertion hole 23 of the fuel support fitting.

  Thus, according to the present embodiment, when the lower end of the channel fastener 11 comes into contact with the upper end of the upper lattice plate 5 in contact therewith, the lower end of the lower tie plate 9 is the fuel support of the fuel support fitting 22 for the outermost peripheral region of the core. It can be made to have reached in the metal fitting insertion hole 23.

  That is, according to the present embodiment, even when the channel fastener 11 comes into contact with the groove 26 and the fuel assembly 3 is shaken, the fuel assembly 3 can be normally landed.

  In FIG. 11, for the sake of clarity, the groove 26 is provided around the entire upper lattice plate 5 with which the fuel assembly 3 abuts. However, the groove 26 may be provided only at the portion with which the channel fastener 11 abuts. it can.

  FIG. 12 shows an embodiment of a fuel support fitting in which a funnel-shaped guide is provided above the fuel support fitting insertion hole.

  As shown in FIG. 12, the fuel support fitting 22 of the present embodiment has a core outermost peripheral region so as to receive the lower end of the fuel assembly 3 before the channel fastener (not shown) and the upper lattice plate come into contact with each other when fuel is loaded. A funnel-shaped guide 27 is provided above the fuel support fitting insertion hole 23 of the fuel support fitting 22 for use.

  Thereby, according to this embodiment, before the channel fastener and the upper lattice plate come into contact with each other when the fuel is loaded, the lower end of the fuel assembly 3 is received in the funnel-shaped guide 27. Even when the fuel assembly 3 is shaken by contact, the fuel assembly 3 can be normally landed.

  In the present embodiment, since the funnel-shaped guide 27 is provided on the fuel support fitting 22, the size of the fuel assembly 3 itself is not changed. Therefore, the position of the fuel rod in the fuel assembly 3, that is, the position of the fuel rod. The positions of the upper and lower ends of the fuel pellets are held at predetermined positions, and do not affect the reactor power.

  FIG. 13 shows the post portion so that the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate is longer than the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting. The upper end part of the fuel assembly which has the upper tie plate which lengthened was shown.

  The upper tie plate 8 has a lug 28 as a handle and a network part 29 for fixing the upper end of the fuel rod.

  The channel fastener 11 is fixed by screwing into a hole in a horizontal plate joined to a corner portion at the upper end of the channel box 10 after passing through a post portion 30 extending from the upper tie plate 8.

  In this embodiment, the post portion 30 of the upper tie plate 8 is lengthened so that the length from the lower end of the channel fastener 11 of the fuel assembly 3 to the lower end of the lower tie plate is from the upper end of the upper lattice plate to the fuel support fitting. This distance is longer than the distance to the upper end of the fuel support fitting insertion hole.

  The upper end portion of the channel box 10 is preferably elongated in accordance with the post portion 30 of the upper tie plate 8.

  Further, according to the present embodiment, since only the post portion 30 is extended, the upper and lower positions of the fuel rods, that is, the positions of the upper and lower ends of the fuel pellets in the fuel rods can be held at predetermined positions. Does not affect the output.

  According to the present embodiment, since the position of the channel fastener 11 is raised, before the channel fastener comes into contact with the upper lattice plate during fuel loading, the lower end of the fuel assembly 3 is connected to the fuel of the fuel support fitting 22 for the outermost peripheral region of the core. Even when the channel fastener is received in the support fitting insertion hole 23 and the channel assembly comes into contact with the upper lattice plate and the fuel assembly 3 is shaken, the fuel assembly 3 can be normally landed.

  FIG. 14 shows a modification of the present invention.

  In the embodiments so far, the positions of the upper and lower ends of the fuel pellets of the fuel rods are held at predetermined positions so as not to affect the power of the reactor, but the power of the reactor is not greatly affected. It is conceivable to change the positions of the upper and lower ends of the fuel pellet within the range.

  This modification relates to the fuel assembly in such a case, and the rectangular tube portion 13 of the lower tie plate 9 is extended.

  As shown in FIG. 14, the lower tie plate 9 has a rectangular tube portion 13, a funnel portion 14, and a nose cone 15. A network portion 31 that supports the fuel rod 7 is provided at the upper end portion of the rectangular tube portion 13.

  The lower tie plate 9 of the present modification increases the vertical length of the rectangular tube portion 13 so that the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate is The distance is longer than the distance from the upper end to the upper end of the fuel support fitting insertion hole of the fuel support fitting.

  Thus, before the lower end of the channel fastener contacts the upper end of the upper lattice plate, the lower end of the lower tie plate (the lower end of the nose cone 15) reaches the fuel support fitting insertion hole of the fuel support fitting for the outermost peripheral region of the core. Even if the channel fastener comes into contact with the upper lattice plate, the fuel assembly can be normally landed.

The figure explaining this invention which makes the length from the channel fastener lower end of the fuel assembly to the lower end of the lower tie plate longer than the distance from the upper end of the upper lattice plate to the upper end of the fuel support fitting insertion hole of the fuel support fitting . The explanatory view showing one embodiment of the present invention which lengthened the length of the nose cone in the up-and-down direction compared with the conventional nose cone. Explanatory drawing which showed one Embodiment of this invention which provided the rod-shaped protrusion in the lower end of the nose cone compared with the conventional nose cone. The longitudinal cross-sectional view which showed one Embodiment of this invention which made the lead tip coupling | bond part of the nose cone eccentric, compared with the conventional nose cone. The bottom view which showed one Embodiment of this invention which made the lead tip coupling | bond part of the nose cone eccentric, compared with the conventional nose cone. The longitudinal cross-sectional view which showed one Embodiment of this invention which has the nose cone which adjusted lead arrangement | positioning compared with the conventional nose cone. The bottom view which showed one Embodiment of this invention which has the nose cone which adjusted lead arrangement | positioning compared with the conventional nose cone. The longitudinal cross-sectional view which showed one Embodiment of this invention formed in the cup part deeply of the fuel support metal fitting insertion hole compared with the conventional fuel support metal fitting. Explanatory drawing which showed one Embodiment of this invention which has the channel fastener which shortened the length of the up-down direction compared with the fuel assembly which has the conventional channel fastener. The explanatory view showing one embodiment of the present invention which adjusted the upper end position of an upper lattice board compared with the conventional upper lattice board. The side view which showed one Embodiment of this invention which provided the groove | channel in the part which contact | connects a channel fastener. The longitudinal cross-sectional view of the fuel support metal fitting for outermost periphery area | regions of a core by one Embodiment of this invention which provided the funnel-shaped guide. The side view which showed the upper tie plate by one Embodiment of this invention which lengthened the post part. The longitudinal cross-sectional view of the lower tie plate by the modification of this invention which made the square cylinder part long. The perspective view which showed the core structure of the boiling water reactor using one of the fuel assemblies of the core center part. The perspective view of a channel fastener. A side view of a lower tie plate. The perspective view of the fuel support metal fitting for core center area | regions. Sectional drawing of the fuel support metal fittings for core center area | regions of the state with which the lower tie plate was mounted | worn. The top view of a core. The side view which showed the upper lattice board, the fuel assembly, and the fuel support metal fitting in a core outermost periphery area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core support plate 2 Core support area fuel support bracket 3 Fuel assembly 4 Fuel support bracket insertion hole 5 Upper lattice plate 6 Control rod 7 Fuel rod 8 Upper tie plate 9 Lower tie plate 10 Channel box 11 Channel fastener 12 Spacer 13 Corner Cylindrical portion 14 Funnel portion 15 Nose cone 16 Nose cone base portion 17 Lead 18 Cylindrical portion 19 Orifice 20 Cup portion 21 Through hole 22 Core support outermost peripheral region fuel support fitting 23 Fuel support fitting insertion hole 24 Orifice 25 Rod-like protrusion 26 Groove 27 Funnel shape Guide 28 Lug 29 Network part 30 Post part 31 Network part

Claims (1)

In the boiling water reactor core, the fuel pellets of the fuel rods have dimensions that hold the upper and lower ends of the fuel pellets at predetermined positions, and the length from the lower end of the channel fastener of the fuel assembly to the lower end of the lower tie plate, to be longer than the distance to the fuel support insertion hole upper end of the fuel support from the upper end of the upper grid plate, it has a lower tie plate which sets the vertical length of the nose cone, and
The fuel support fitting of the fuel support fitting for the core central region so that the lead tip joint portion of the nose cone of the lower tie plate moves to a deep part of the cup portion of the fuel support fitting for the core central region. A fuel assembly for a boiling water reactor, wherein the fuel assembly is eccentric from the center of the insertion hole toward the center line of the control rod.

Images