JP2005207975A - Cask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cask capable of suppressing increase of gross weight of the cask itself by minimizing a thickness of a tertiary lid. <P>SOLUTION: In the cask 1, an opening 2a of a cask body 2 is triply sealed by a primary lid 3, a secondary lid 4, and the tertiary lid 5. A gap e between an outer circumferential face of the secondary lid 4 and an inner circumferential face of the cask body 2 is regarded as a boundary, a collar part of the tertiary lid 5 in an outer side of the gap e is fixed to an end face of the cask body 2 by a first fastening bolt 21, and an inland portion of the tertiary lid 5 in an inner side of the gap e is fixed to the secondary lid 4 by a second fastening bolt 24. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cask for use in storage and transportation of radioactive materials such as spent fuel.

  Conventionally, spent fuel used in a nuclear power plant is cooled and stored for a certain period in a spent fuel pool in the nuclear power plant, and then transported to a reprocessing plant. However, the storage period in the spent fuel pool may be prolonged due to delays in construction of the reprocessing plant and limitations on processing capacity.

  However, since there is a limit to the amount that can be stored in the spent fuel pool, the spent cask is used to store spent fuel inside and outside the nuclear power plant other than the spent fuel pool.

The basic structure of the storage cask is a double lid structure in which the opening of the cask main body is sealed with a primary lid and a secondary lid. However, when an abnormality occurs in the sealing of the primary lid, the primary lid is exposed to radiation. The primary lid seal cannot be replaced. Therefore, it is necessary to cope with either welding of the secondary lid or installation of the tertiary lid (for example, see Patent Document 1).
Japanese Patent No. 2941250 (page 2-3, FIG. 1)

  However, when the secondary lid is welded to the cask body, not only the approval of the competent authority is required, but also a welding operation by remote operation, there are various problems such as an increase in welding work time.

  On the other hand, as described in Patent Document 1, when a tertiary lid is provided outside the secondary lid, the total weight of the cask itself increases as the tertiary lid is added. In addition, when the flange portion 20 of the tertiary lid 5 is fixed to the tertiary step portion 50 of the cask main body 2 with the tertiary lid fixing bolt 21 as shown in FIGS. 8 and 9, the secondary lid 4. In order to seal the gap e between the outer peripheral surface 17 of the secondary casing 14 and the inner peripheral surface 18 of the secondary step portion 14 of the cask body 2 with a pressure between the secondary lid and the tertiary lid of about 0.2 MPa, the plate of the tertiary lid 5 It is necessary to increase the thickness. For example, when the radius of the tertiary lid 5 is 1150 mm, the plate thickness of the tertiary lid 5 is 50 mm and its weight is about 1.8 tons.

  8 and 9, 1 is a cask, 2 is a cask body, 2a is an opening of the cask body, 3 is a primary lid, and 4 is a secondary lid.

  The thickness of the primary lid and secondary lid of the cask is determined by the radiation shielding function and the structural strength of the cask. The number of spent fuel stored in the cask is set under the condition that the total weight of the cask itself is less than the limit weight.

  As mentioned above, the tertiary lid is a lid added to cope with the sealing abnormality of the primary lid, so if the weight is heavier than necessary, the tertiary lid was added due to the limit weight. Therefore, it is necessary to reduce the amount of spent fuel stored.

  The present invention has been made to solve the above-described problems, and its purpose is to make the plate thickness of the tertiary lid as thin as possible, thereby suppressing an increase in the total weight of the cask itself. It is to provide a cask that can.

  In order to solve the above problems, the present invention is configured as follows.

  The invention according to claim 1 is the cask in which the opening of the cask main body is triple-sealed by the primary lid, the secondary lid, and the tertiary lid, and the outer peripheral surface of the secondary lid and the inner peripheral surface of the cask main body. The eaves of the tertiary lid outside the gap e is fixed to the end face of the cask main body by the first fastening bolt, and the inward of the tertiary lid inside the gap e The cask is characterized in that the portion is fixed to the secondary lid by a second fastening bolt.

  According to a second aspect of the present invention, the second fastening bolt includes a head portion and a screw portion, a plurality of annular grooves are provided concentrically on the back surface of the head portion, and each of the annular grooves has an O in the annular groove. The cask according to claim 1, further comprising a ring.

  In the third aspect of the invention, the tertiary lid is formed in an annular shape, and the gap 3 between the outer peripheral surface of the secondary lid and the inner peripheral surface of the cask body is defined as a boundary. The outer lid of the secondary lid is fixed to the end face of the cask body with fastening bolts, and the inner flange of the tertiary lid inside the gap e is fixed to the secondary lid with fastening bolts. The cask according to claim 1.

  According to a fourth aspect of the present invention, the end surface of the cask body is sealed by a plurality of O-rings in an annular groove around the outer periphery provided on the back surface of the tertiary lid, and the outer surface of the secondary lid is sealed with the tertiary lid. 4. The cask according to claim 3, wherein the cask is sealed by a plurality of O-rings in an inner annular groove provided on the back surface of the cask.

  As described above, the invention according to claim 1 is the cask in which the opening of the cask body is triple sealed with the primary lid, the secondary lid, and the tertiary lid, and the outer peripheral surface of the secondary lid and the cask. With the gap e between the inner peripheral surfaces of the main body as a boundary, the collar portion of the tertiary lid outside the gap e is fixed to the end surface of the cask main body by the first fastening bolt, and the inner side of the gap e Since the inland portion of the tertiary lid is fixed to the secondary lid by the second fastening bolt, the plate thickness of the tertiary lid can be significantly reduced compared to the conventional tertiary lid. As a result, since the increase in the total weight of the cask itself could be suppressed, it was possible to avoid a situation in which the amount of stored radioactive materials such as spent fuel was reduced.

  The invention according to claim 2 is constituted by a head and a screw portion, and a plurality of annular grooves are provided concentrically on the back surface of the head, and an O-ring is provided in each of the annular grooves. It became possible to seal the gap between the two fastening bolts and the tertiary lid.

  In the invention according to claim 3, since the tertiary lid is formed in an annular shape, the weight of the tertiary lid can be further reduced as compared with the case of a disk.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, in the dry cask 1, the opening 2a of the cask body 2 has a primary shielding lid (hereinafter referred to as a primary lid) 3, a secondary shielding lid (hereinafter referred to as a secondary lid) 4, and It is sealed in a triple manner by a sealing tertiary lid (hereinafter referred to as a tertiary lid) 5. The storage chamber 6 of the dry cask 1 stores a radioactive material such as spent fuel (not shown), a basket, and helium gas.

  Specifically, as shown in FIG. 2, the flange portion (flange portion) 7 of the primary lid 3 is fixed to the primary step portion 9 of the cask main body 2 by primary lid fixing bolts 8. At that time, the primary step portion 9 of the cask body 2 is sealed by a metal gasket (not shown) in an annular groove 10 provided on the back surface of the primary lid 3. Further, the flange portion (flange portion) 12 of the secondary lid 4 is fixed to the secondary step portion 14 of the cask main body 2 by a secondary lid fixing bolt 13. At that time, the secondary step portion 14 of the cask main body 2 is sealed by a metal gasket (not shown) in an annular groove 15 provided on the back surface of the secondary lid 4.

  On the other hand, as shown in FIG. 2, the tertiary lid 5 has a gap e between the outer peripheral surface 17 of the secondary lid 4 and the inner peripheral surface 18 of the secondary step portion 14 of the cask body 2 as a boundary. The outer portion is fixed to the end face 22 of the cask body 2 by the first tertiary lid fixing bolt 21, and the inner portion from the gap e is fixed to the secondary lid 4 by the second tertiary lid fixing bolt 24. It is fixed.

  Specifically, the flange portion 20 of the tertiary lid 5 is fixed to the end surface 22 of the cask main body 2 by the first tertiary lid fixing bolt 21 and the outer peripheral surface 17 of the secondary lid 4 and the cask main body 2 are fixed. An inland portion 23 of the tertiary lid 5 located inside the gap e between the inner peripheral surfaces 18 of the next step portion 12 is fixed to the secondary lid 4 by a second tertiary lid fixing bolt 24. At that time, the end face 22 of the cask body 2 is sealed by a rubber O-ring (not shown) in an annular groove 25 provided on the back face of the tertiary lid.

  As shown in FIG. 3, the first and second tertiary lid fixing bolts 21 and 24 are arranged concentrically, and the first tertiary lid fixing bolt 21 is placed on the circular first virtual line 27. Provided at equal intervals, the second tertiary lid fixing bolts 24 are provided at equal intervals on a second virtual line 29 having a smaller diameter than the first virtual line 27. Note that the second tertiary lid fixing bolts 24 may be provided in multiples instead of single as described above.

  In addition, the secondary lid 4 is provided with a bolt attachment portion 30 for attaching the second tertiary lid fixing bolt 24 to a portion corresponding to the second imaginary line 29, and a neutron shielding filler 31 is provided. .

  As shown in FIGS. 4A and 4B, the second tertiary lid fixing bolt 24 includes a head 33 and a threaded portion 34. In addition, rubber O-rings 37 are arranged in two inner and outer annular grooves 35, 36 provided on the back surface of the head 33, respectively, and the tertiary lid 5 and the second tertiary lid fixing bolt 24. Is sealed (see FIG. 2). In addition, a leakage inspection hole 38 is provided between the inner and outer annular grooves 35 and 36.

  As described above, in the present invention, the tertiary lid 5 is separated from the outer circumferential surface 17 of the secondary lid 4 and the gap e between the inner circumferential surface 18 of the secondary step portion 14 of the cask main body 2 by the boundary. The outer portion is fixed to the end face 22 of the cask body 2 by the first tertiary lid fixing bolt 21, and the inner portion of the gap e is fixed to the secondary lid 4 by the second tertiary lid fixing bolt 24. Therefore, the plate thickness of the tertiary lid 5 can be halved.

  FIG. 5 shows another embodiment of the present invention, and the tertiary lid 5a is not a disk as in the first embodiment but is formed in an annular shape or a circle shape, thereby further reducing the weight. It is intended.

  In this example, an annular tertiary lid 5a is placed on the gap e between the outer peripheral surface 17 of the secondary lid 4 and the inner peripheral surface 18 of the secondary step portion 14 of the cask body 2, and the outer lid The portion 20 is fixed to the end surface 22 of the cask body 2 by the tertiary lid fixing bolt 21, and the inner flange portion 40 is fixed to the flange portion 41 of the secondary lid 4 by the tertiary lid fixing bolt 21.

  At that time, the end face 22 of the cask main body 2 is sealed by a rubber O-ring 44 in an annular groove 43 around the outside provided on the back surface of the tertiary lid 5a as shown in FIG. The outer surface is sealed by a rubber O-ring 46 in an annular groove 45 around the inside provided on the back surface of the tertiary lid 5a. In addition, a leakage inspection hole 47 is provided between the plurality of annular grooves 43 around the outer side, and a leakage inspection hole 47 is provided between the plurality of annular grooves 45 around the inner side.

  FIG. 7 shows another embodiment of the present invention, and the tertiary lid 5b is not a disk as in the first embodiment but is formed in an annular shape or a circle shape, thereby further reducing the weight. It is intended.

  This tertiary lid 5b is provided with an annular recess 48 on the back surface, and adapted to the case where the collar portion 41 of the secondary lid 4 protrudes from the end face 22 of the cask body 2. The other parts are the same as those of the second embodiment, so the same numbers are assigned to the same parts and the detailed description is omitted.

(Example)
Table 1 shows the results of the strength evaluation of the cask of the present invention and the conventional cask in which only the collar portion of the tertiary lid is bolted.

From this “Table 1”, it can be seen that the cask of the present invention has the same level of stress as that of the conventional case even if the plate thickness of the tertiary lid is halved.
P (MPa): Pressure between the lids of the secondary lid and the tertiary lid a (mm): Radius of the tertiary lid h (mm): Plate thickness of the tertiary lid b (mm): From the center O of the tertiary lid 2 Distance to the axis of the tertiary lid fixing bolt

It is sectional drawing of the cask which concerns on this invention. It is a principal part expanded sectional view of the cask of FIG. It is a top view of the cask of FIG. (A) Sectional drawing of 2nd tertiary lid fixing bolt, (b) Bottom view of 2nd tertiary lid fixing bolt. It is principal part sectional drawing of other embodiment of the cask which concerns on this invention. It is a principal part expanded sectional view of the cask of FIG. It is principal part sectional drawing of other embodiment of the cask which concerns on this invention. It is sectional drawing of the conventional cask. It is a principal part expanded sectional view of the cask of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cask 2 Cask main body 2a Opening part 3 Primary lid 4 Secondary lid 5 Tertiary lid 17 Secondary cover outer peripheral surface 18 Cask main body inner peripheral surface 20 Tertiary lid collar 21 First fastening bolt 22 Cask main body End face 23 Inland part of the tertiary lid 24 Second fastening bolt

Claims (4)

In a cask in which the opening of the cask body is triple sealed with a primary lid, a secondary lid, and a tertiary lid, with the gap e between the outer peripheral surface of the secondary lid and the inner peripheral surface of the cask body as a boundary. The flange portion of the tertiary lid outside the gap e is fixed to the end surface of the cask body by the first fastening bolt, and the inland portion of the tertiary lid inside the gap e is fixed by the second fastening bolt. A cask characterized by being fixed to the next lid. The second fastening bolt includes a head and a screw portion, and a plurality of annular grooves are provided concentrically on the back surface of the head, and an O-ring is provided in each of the annular grooves. The cask according to claim 1. The tertiary lid is formed in an annular shape, and the outer flange of the tertiary lid outside the gap e is fastened with the gap e between the outer circumferential surface of the secondary lid and the inner circumferential surface of the cask body as a boundary. The cask according to claim 1, wherein the cask is fixed to the end face of the cask main body with a bolt, and further, a collar portion inside the tertiary lid inside the gap e is fixed to the secondary lid with a fastening bolt. The end surface of the cask body is sealed by a plurality of O-rings in an annular groove around the outer periphery provided on the back surface of the tertiary lid, and the outer surface of the secondary lid is an inner ring provided on the back surface of the tertiary lid. The cask according to claim 3, wherein the cask is sealed by a plurality of O-rings in the groove.

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