JP2012058155A - Used fuel storage rack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a used fuel storage rack which can be easily manufactured without enlarging the shape thereof and attains the improvement of strength flexibly in response to a strength requirement corresponding to the increase of a lateral load in earthquake or the like.SOLUTION: The present invention relates to a used fuel storage rack 1 for preserving used fuels by accommodating the used fuels in a number of cells formed in an angular tube shape. The used fuel storage rack 1 includes: a neutron shield cell 3 formed by assembling a neutron shield in a number of cells; a compound cell 5 formed by combining the neutron shield with a high-strength structure member; and frame plates 4a, 4b and 4c for positioning the neutron shield cell 3 and the compound cell 5 so as to hold the neutron shield cell and the compound cell at a fixed interval each other, and the compound cell 5 is disposed in at least one of a number of cells.

Description

  The present invention relates to a spent fuel storage rack for storing and storing spent fuel taken out from a nuclear reactor in a fuel storage pool.

  In general, in a nuclear power plant, after operating a nuclear reactor for a certain period, spent fuel taken from the core is stored in a spent fuel storage rack installed in the fuel storage pool until reprocessing. The decay heat of spent fuel is removed by cooling and storing.

  In recent years, there is a demand to increase the storage capacity of the fuel storage pool, and it is necessary to further effectively utilize the existing space. In order to meet this demand, a material having excellent neutron absorption capability is used for the spent fuel storage rack, and the fuel interval is narrowed while maintaining the subcriticality between the fuels. Moreover, such a material excellent in neutron absorption capability is also used as a high-strength structural material for spent fuel racks during an earthquake. As a spent fuel storage rack capable of increasing the density of spent fuel stored using such a technique, there is a technique described in Patent Document 1, for example.

  Thus, conventionally, in addition to the above-mentioned Patent Document 1, as in the technique described in Patent Document 2, the boron concentration of the spent fuel storage rack material is excellent in neutron absorption capability and high in structural strength up to 1%. There is a fuel storage cell structure in which boron-added stainless steel is applied and welded in a lattice shape.

Japanese Patent Laid-Open No. 10-213693 JP 2007-024609 A

  By the way, in order to meet the demand for further densification of spent fuel stored in the fuel storage pool, boron addition of boron with a high boron concentration exceeding 1% is superior to the conventional boron-added stainless steel sheet of 1% or less and has a higher neutron absorption capacity. The need to use stainless steel sheets has arisen.

  However, boron-added stainless steel with a high boron concentration of over 1% decreases the strength of the welded part and decreases toughness, making it difficult to weld and bend. Therefore, there is a problem that it becomes difficult to manufacture cells formed in a lattice shape.

  In some countries, neutron shielding materials are prohibited by law from being used as high-strength structural materials. For this reason, a square tube formed of a boron-added stainless steel plate with a high boron concentration is used as a neutron shielding material, and it is a high-strength structural material that appropriately retains spent fuel even when subjected to lateral loads such as earthquakes. Not. Therefore, there is a problem that it is difficult to increase the strength according to the increase in the lateral load.

  Furthermore, in the past, it was possible to arrange a high-strength structural material at the center of the spent fuel storage rack in order to cope with an increase in lateral load, but an independent high-strength structural material was used to store spent fuel. In order to place it in the center of the rack, it is necessary to attach it to the grid-like frame plates installed at the top, middle, and bottom, respectively. Therefore, the construction work between the fuel storage cells requires high accuracy and is difficult to manufacture. A new problem arises that is difficult.

  Similarly, when high strength materials are required in a high earthquake zone, placing a high strength structural material between each cell of the spent fuel storage rack may lead to an increase in the distance between the cells. Since the outer shape of the spent fuel storage rack is enlarged, there is a problem against the demand for densification.

  The present invention has been made in consideration of the above-described circumstances, and is easy to manufacture without increasing the outer shape, and can be used flexibly to meet the strength requirements according to an increase in lateral loads such as earthquakes. An object is to provide a fuel storage rack.

  In order to achieve the above object, a spent fuel storage rack according to the present invention is a spent fuel rack for storing and storing spent fuel in a number of cells formed in a rectangular tube shape. The neutron shielding cell formed by assembling the neutron shielding material, the composite cell formed by combining the neutron shielding material and the high-strength structural material, and the neutron shielding cell and the composite cell are positioned so as to be held at a predetermined interval. And at least one of the composite cells is disposed in the plurality of cells.

  According to the present invention, it is easy to manufacture without increasing the outer shape, and it is possible to increase the strength flexibly in response to the strength requirement according to an increase in lateral load such as an earthquake.

It is a perspective view showing the whole composition of a 1st embodiment of the spent fuel storage rack concerning the present invention. It is a perspective view which shows the state which removed the neutron shielding cell from the spent fuel storage rack of FIG. It is a perspective view which shows the assembly state of the neutron shielding cell of FIG. It is a principal part expanded sectional view which shows the state which assembled the neutron shielding cell in FIG. 3 using the clip. It is a top view which shows the state which superimposes a stainless steel plate on the neutron shielding cell of this embodiment. It is a top view which shows the composite cell comprised by superposing | stacking a stainless steel plate on the neutron shielding cell in FIG. It is a top view which shows the case where the composite cell is installed in the center part in the spent fuel storage rack of 1st Embodiment. It is a perspective view which shows the assembly state of the neutron shielding cell in 2nd Embodiment of the spent fuel storage rack which concerns on this invention. It is a principal part expansion perspective view which shows the assembly state of the composite cell in 2nd Embodiment. It is a principal part expansion perspective view which shows the state after the assembly of the composite cell in 2nd Embodiment. It is a top view which shows the composite cell after the assembly in 2nd Embodiment.

  Embodiments of a spent fuel storage rack according to the present invention will be described below with reference to the drawings. In the following description, the description will be made based on the posture in which the bottom of the spent fuel storage rack is installed horizontally.

(First embodiment)
FIG. 1 is a perspective view showing an overall configuration of a first embodiment of a spent fuel storage rack according to the present invention. FIG. 2 is a perspective view showing a state where the neutron shielding cell is removed from the spent fuel storage rack of FIG. 3 is a perspective view showing an assembled state of the neutron shielding cell of FIG. FIG. 4 is an enlarged cross-sectional view of a main part showing a state in which the neutron shielding cell in FIG. 3 is assembled using a clip.

  As shown in FIG. 1, the spent fuel storage rack 1 according to the present embodiment is formed in a rectangular column shape that is vertically long as a whole in the installed state. The spent fuel storage rack 1 includes a large number of neutron shielding cells 3. As shown in FIG. 3, these neutron shielding cells 3 are composed of boron-added stainless steel plates 2a and 2b having a high boron concentration exceeding 1%, which is a neutron shielding material. In each neutron shielding cell 3, the upper frame plate 4a, the middle frame plate 4b, and the lower frame plate 4c are horizontally fixed as lattice-like frame plates 4 at the upper end portion, the substantially vertical center portion, and the lower end portion. ing. In the following description, when one of the boron-added stainless steel plates 2a and 2b is not specified, it will be described as a boron-added stainless steel plate 2 as shown in FIG.

  Furthermore, the spent fuel storage rack 1 has the composite cells 5 formed in the shape of a rectangular tube at the four corners so as to stand upright at the same height. These four composite cells 5 are respectively arranged at the peripheral corners of the base 6. The base 6 constitutes the bottom of the spent fuel storage rack 1 and is formed in a flat square plate shape. Each of the four composite cells 5 has a double structure in which a stainless steel plate is superposed on the outer surface of a boron-added stainless steel plate having a high boron concentration exceeding 1%, which is a neutron shielding material. The stainless steel plate has a side surface fixed to the frame plates 4a, 4b, and 4c by welding and a bottom portion fixed to the base 6 by welding.

  As shown in FIG. 2, each frame plate 4a, 4b, 4c is assembled in a square lattice by crossing horizontally long stainless steel plates vertically and horizontally at regular intervals in a square peripheral frame. Thus, a large number of square neutron shielding cells 3 penetrating in the vertical direction are inserted into the respective frame plates 4a, 4b, 4c so as to maintain a constant interval. And the square-tube-type spent fuel storage rack 1 which has many cells is comprised by arrange | positioning each composite cell 5 in the four corner parts of each frame board 4a, 4b, 4c, respectively.

  A spent fuel (not shown) is loaded in the neutron shielding cell 3 and the composite cell 5, and loads of the neutron shielding cell 3, the composite cell 5 and the spent fuel are all supported by the base 6.

  Further, as shown in FIG. 2, four composite cells 5 are arranged on the base 6, and in order to position these composite cells 5, the upper end portion, the vertical center portion and the lower end portion of the composite cell 5 An upper frame plate 4a, a middle frame plate 4b, and a lower frame plate 4c are respectively attached.

  As shown in FIG. 3, the neutron shielding cell 3 is configured by combining a pair of boron-added stainless steel plates 2 a and 2 b having a high boron concentration exceeding 1% in a square tube shape. Each of these boron-added stainless steel plates 2a and 2b is a rectangular flat plate, and has the same length and the same width.

  One boron-added stainless steel plate 2a is in the vicinity of both ends in the width direction, and a plurality of vertically long slits 7 are formed along the length direction. The other boron-added stainless steel plate 2b is integrally formed so that the insertion portions 8 project at both ends in the width direction at the upper and lower positions corresponding to the plurality of slits 7. Each insertion portion 8 is formed with a longitudinal slit 9 along the length direction.

  When the insertion portion 8 of the other boron-added stainless steel plate 2b is inserted into the slit 7 of one boron-added stainless steel plate 2a, the slit 9 passes through the slit 7 and is exposed to the outer surface side of the one boron-added stainless steel plate 2a. Thus, the position in the insertion portion 8 is set.

  Therefore, in order to assemble the neutron shielding cell 3 with the boron-added stainless steel plates 2a and 2b, the boron-added stainless steel plates 2a and 2b face each other one by one and are combined in a cross (square tube) shape. Specifically, as shown in FIG. 3, a plurality of insertion portions 8 formed at one end in the width direction of the boron-added stainless steel plate 2b are respectively inserted into the plurality of slits 7 formed at one end in the width direction of the boron-added stainless steel plate 2a. A pair of insertion steps are performed.

  Next, by inserting the plurality of insertion portions 8 formed at the other end in the width direction in the boron-added stainless steel plate 2b into the plurality of slits 7 formed at the other end in the width direction of the boron-added stainless steel plate 2a, respectively, In combination, the neutron shielding cell 3 is formed.

  In such a state of being combined in a square shape, the slit 9 of the insertion portion 8 is positioned so as to be exposed on the outer surface side of the boron-added stainless steel plate 2a as described above, so as shown in FIG. By attaching a stainless steel clip 10 through the slit 9, the corner (intersection) between the boron-added stainless steel plate 2a and the boron-added stainless steel plate 2b is fixed, and the square shape of the neutron shielding cell 3 is maintained. ing.

  Next, the composite cell 5 in which a stainless steel plate is superimposed on the neutron shielding cell 3 will be described. FIG. 5 is a plan view showing a state in which a stainless steel plate is superimposed on the neutron shielding cell of the present embodiment. FIG. 6 is a plan view showing a composite cell constructed by superposing a stainless steel plate on the neutron shielding cell in FIG.

  As shown in FIG. 5, the neutron shielding cell 3 is composed of a composite cell 5 by combining two pairs of stainless steel plates 12 and 14 so as to face each other and combining them in a rectangular tube shape. In the pair of stainless steel plates (first stainless steel plates) 12 and 12, slits 11 and 11 are formed over the entire length in the longitudinal direction near the both ends in the width direction, on the side overlapped with the boron-added stainless steel plate 2, respectively. Yes. Further, the pair of stainless steel plates (second stainless steel plates) 14 and 14 are respectively overlapped with the boron-added stainless steel plate 2 and have the same width as the slits 11 and 11 over the entire length in the longitudinal direction at both ends in the width direction. Notches 13 and 13 are formed. Here, the widths of the slits 11 and 11 and the notches 13 and 13 are equal to the thickness of the boron-added stainless steel plate 2.

  As shown in FIG. 6, the composite cell 5 is overlapped by fitting the slit 11 and the notch 13 of the stainless steel plates 12 and 14 into the corners of the neutron shielding cell 3, and after assembling in this way, The outer peripheral portions of the joint portions 15a, 15b, 15c, and 15d of the stainless steel plates 12 and 14 are joined by a joining means such as welding.

  Next, the specific dimensional relationship of the above components will be described.

  The case where the spent fuel storage rack 1 of this embodiment is applied to, for example, a pressurized water reactor (PWR) will be described.

  In the spent fuel storage rack for pressurized water reactors, when the thickness of the boron-added stainless steel plate 2 is 3 mm and the inner diameter of the neutron shielding cell 3 is 225 mm, the outer diameter of the cell is 225 + 3 × 2 = 231 mm. The insertion portion 8 for use protrudes about 10 mm from the outer surface of the boron-added stainless steel plate 2a, and the maximum width of the outer shape plate is about 231 + 10 × 2 = 251 mm. In order to cover the protruding portion of the neutron shielding cell 3, the thickness of the stainless steel plates 12 and 14 is preferably about 14 mm.

  At this time, the maximum dimension of the outer plate width of the neutron shielding cell 3 is 251 mm, whereas the outer dimension of the composite cell 5 is about 231 + 14 × 2 = 259 mm. In order to cover, it is necessary to provide relief portions of round holes at the four corners of each opening of the frame plate 4, and the maximum inner diameter dimension is about 261 mm. There is no effect on the pitch.

  FIG. 7 is a plan view showing a case where a composite cell is installed in the center of the spent fuel storage rack of the first embodiment.

  As shown in FIG. 7, the cross-sectional dimension of the composite cell 5 of the present embodiment is substantially the same as that of the neutron shielding cell 3, so that the composite cell 5 of the spent fuel storage rack 1 as shown in FIGS. In addition to the arrangement at the four corners, at least one may be inserted and installed in the lattice hole at an arbitrary position opened in the frame plate 4. Thus, by installing at least one composite cell 5 in the spent fuel storage rack 1, the structural strength of the spent fuel storage rack 1 can be easily improved.

  In FIG. 7, the corner of the neutron shielding cell 3 is not fixed by attaching the clip 10 as in the present embodiment, but the front end side of the protruding portion of the neutron shielding cell 3 is covered by the notch bar 16. Is fixed. The notch bar 16 is formed, for example, by cutting a quarter of the circumferential direction of the cylindrical body by 90 degrees over the entire length. Thus, the corner | angular part (intersection part) of the neutron shielding cell 3 should just be fixed by one of the said fixing means.

  Next, the operation and effect of this embodiment will be described.

  In the spent fuel storage rack 1 of the present embodiment, spent fuel is stored inside the neutron shielding cell 3 and the composite cell 5, and by positioning the neutron shielding cell 3 and the composite cell 5 by the frame plate 4, It becomes possible to maintain the distance between spent fuels appropriately and to guarantee subcriticality and cooling performance of spent fuels.

  The spent fuel storage rack 1 according to the present embodiment is conventionally formed by combining the boron-added stainless steel plate 2 that is a neutron shielding material and the stainless steel plates 12 and 14 that are high-strength structural materials to form a composite cell 5. Whereas the high strength structural material is arranged at a position different from that of the cell 3, the structural strength can be equal to or higher than that of the neutron shielding cell 3 in almost the same space. No effect.

  Conventionally, when responding to the demand for a high-strength structure, a high-strength structural material that is structurally independent of the neutron shielding material may be disposed between the neutron shielding cells 3, and in this case, the pitch between cells is increased. May need to be made. However, in this embodiment, since the composite cell 5 can be accommodated in substantially the same space as the neutron shielding cell 3, there is no need to increase the inter-cell pitch, and the spent fuel storage rack can be improved when the structural strength is improved. 1 can be maintained in the same manner as before the composite cell 5 is accommodated.

  Further, conventionally, a reinforcing beam is installed on the outer periphery of the rack in addition to the high-strength structural material. However, in the present embodiment, the composite cell 5 having both the high-strength structural material and the neutron shielding material is disposed at an arbitrary position. Since the structural strength can be improved by arranging them easily, these reinforcing beams are not required, so that the structural strength can be flexibly met and the structure can be simplified.

  And conventionally, there was a case where the high-strength structural material was arranged outside the frame plate 4 at the upper end portion, the substantially vertical center portion and the lower end portion, but in this embodiment, it also served as the high-strength structural material. Since the composite cell 5 is disposed inside the frame plate 4, the distance between the spent fuel storage racks 1 can be further shortened, and further densification is possible.

  Further, according to the present embodiment, the structural strength is ensured by the composite cell 5 in which the high-strength structural material and the neutron shielding material are integrated. Since the composite cell 5 has a structure in which the stainless steel plates 12 and 14 are overlapped around the neutron shielding cell 3, the structural strength is ensured with the substantially same sectional area as the neutron shielding cell 3 in the cross section of the spent fuel storage rack 1. can do.

  Furthermore, according to the present embodiment, the neutron shielding cell 3 is assembled to the boron-added stainless steel plate 2 using the clip 10 without performing welding or bending, so that the weld strength when using high boron-added stainless steel is used. It is possible to avoid problems such as lowering of toughness and lowering of toughness.

  Further, according to the present embodiment, the high-strength structural material is secured by the stainless steel plates 12 and 14 of the composite cell 5, and no load is transmitted to the boron-added stainless steel plate 2 that is a neutron shielding material. It is possible to respond to the law that high-strength structural materials must be separated.

  And according to this embodiment, a neutron shielding material and a high-strength structural material secure the structural strength with the composite cell 5, thereby providing a high-strength structural material at an arbitrary position in the cross section of the spent fuel storage rack 1. Can be arranged.

  As described above, in the present embodiment, without increasing the outer shape of the spent fuel storage rack 1, the manufacturing is easy, and the strength can be improved in accordance with an increase in lateral load such as an earthquake.

(Second Embodiment)
FIG. 8 is a perspective view showing an assembled state of the neutron shielding cell in the second embodiment of the spent fuel storage rack according to the present invention. FIG. 9 is an enlarged perspective view of a main part showing an assembled state of the composite cell in the second embodiment. FIG. 10 is an essential part enlarged perspective view showing a state after assembly of the composite cell in the second embodiment. FIG. 11 is a plan view showing the composite cell after assembly in the second embodiment. In addition, the same code | symbol is attached | subjected to the part which is the same as that of the said 1st Embodiment, or respond | corresponds, and a different structure is demonstrated.

  As shown in FIG. 8, the boron-added stainless steel plate 2A having a high boron concentration exceeding 1% is a rectangular flat plate, and has the same length and the same width as the boron-added stainless steel plate 2b. In the boron-added stainless steel plate 2A, notches 18 are partially formed at both ends in the width direction along the length direction, and slits 19 are formed in portions where the notches 18 are not formed.

  The boron-added stainless steel plate 2b is vertically formed corresponding to the plurality of slits 19, and is integrally formed so that the insertion portions 8 protrude from both ends in the width direction as in the first embodiment. Each insertion portion 8 is formed with a longitudinal slit 9 along the length direction.

  Therefore, in order to assemble a neutron shielding cell using the boron-added stainless steel plates 2A and 2b, the boron-added stainless steel plates 2A and 2b are faced to each other and assembled into a rectangular tube shape. Specifically, as shown in FIG. 8, a plurality of insertion portions 8 formed at one end in the width direction of the boron-added stainless steel plate 2b are respectively inserted into the plurality of slits 19 formed at one end in the width direction of the boron-added stainless steel plate 2A. A pair of insertion steps are performed.

  Next, a plurality of insertion portions 8 formed at the other end in the width direction of the boron-added stainless steel plate 2b are respectively inserted into a plurality of slits 19 formed at the other end in the width direction of the boron-added stainless steel plate 2A. Are combined to form a neutron shielding cell.

  As shown in FIGS. 9 and 10, a stainless steel plate 20 is overlaid on the boron-added stainless steel plate 2b, while a stainless steel plate 21 is overlaid on the boron-added stainless steel plate 2A. At both ends in the width direction of the stainless steel plate 20, notches 22 are formed in order to avoid portions where the slits 19 are formed and the notches 18 are not formed when assembled. Moreover, the notch part 23 is formed in the width direction both ends of the stainless steel plate 21 in order to avoid the insertion part 8 when it assembles.

  Then, in order to form the composite cell 5A, the stainless steel plate 20 is overlapped with the boron-added stainless steel plate 2b, and the stainless steel plate 21 is overlapped with the boron-added stainless steel plate 2A. Are joined at the joining portion 24 on the boron-added stainless steel plates 2A and 2b, and the joining portion 24 and the cutout portion 18 are joined by a joining means such as welding. This is shown in FIG.

  As described above, according to the present embodiment, the stainless steel plates 20 and 21 that are high-strength structural materials are located on the inner side of the outermost part of the square tube formed by the neutron shielding materials 2A and 2b, and thus the outer shape of the composite cell 5A. And the increase in the hole diameter of the frame plate 4 corresponding to the insertion position of the composite cell 5A can be suppressed.

  The present invention is not limited to the above embodiments, and various modifications can be made. In each of the above-described embodiments, the upper frame plate 4a, the middle frame plate 4b, and the lower frame plate 4c are attached to the upper end portion, the vertical center portion, and the lower end portion of the composite cell 5, respectively. What is necessary is just to attach a frame board other than one lower end part.

  In each of the above embodiments, the stainless steel plates are superposed on the four outer peripheral surfaces of the neutron shielding cell, and then the stainless steel plates are fixed using welding fixing means. A fixing means such as may be used.

DESCRIPTION OF SYMBOLS 1 ... Spent fuel storage rack 2, 2a, 2b ... Boron addition stainless steel plate 3 ... Neutron shielding cell 4, 4a, 4b, 4c ... Frame plate 5, 5A ... Composite cell 6 ... Base 7 ... Slit 8 ... Insertion part 9 ... Slit 10 ... Clip 11 ... Slit 12 ... Stainless steel plate (first stainless steel plate)
13 ... Notch 14 ... Stainless steel plate (second stainless steel plate)
15a, 15b, 15c, 15d ... Junction 16 ... Notch bar 18 ... Notch 19 ... Slit 20 ... Stainless steel plate 21 ... Stainless steel plate 22 ... Notch 23 ... Notch 24 ... Joint

Claims (5)

A spent fuel rack for storing and storing spent fuel in a number of cells formed in a rectangular tube shape,
A neutron shielding cell formed by assembling a neutron shielding material in the multiple cells;
A composite cell formed by combining the neutron shielding material and a high-strength structural material;
A frame plate that positions the neutron shielding cell and the composite cell so as to hold each other at a constant interval, and
A spent fuel rack, wherein at least one of the composite cells is disposed in the plurality of cells.   The composite cell has a pair of first stainless steel plates in which slits having a width equal to the plate thickness of the neutron shielding material are formed in the vicinity of both ends in the width direction on four outer peripheral surfaces of the neutron shielding material assembled in a rectangular tube shape. And a pair of second stainless steel plates in which notches having a width equal to the thickness of the neutron shielding material are formed at both ends in the width direction, and the slits and the notches are respectively placed on the neutron shielding material. 2. The spent fuel storage rack according to claim 1, wherein the first and second stainless steel plates are fitted to each other by a coupling means.   The composite cell is constructed by assembling a neutron shielding material in which notches are formed at both ends in the width direction into a square cylinder, and superposing stainless steel plates shaped to match the shape of the notches on the four outer surfaces. The spent fuel storage rack according to claim 1, wherein the stainless steel plates are joined together by a joining means.   4. The spent fuel storage rack according to claim 2, wherein the neutron shielding member has four intersections assembled in a square cylinder shape fixed with clips. 5.   The spent fuel storage rack according to any one of claims 1 to 3, wherein the neutron shielding material is a boron-added stainless steel plate having a high boron concentration exceeding 1%.

Images