JP6919023B2

JP6919023B2 - Buffer structure

Info

Publication number: JP6919023B2
Application number: JP2020094923A
Authority: JP
Inventors: 岡田　潤; 潤岡田
Original assignee: Hitachi Zosen Corp
Current assignee: Hitachi Zosen Corp
Priority date: 2016-09-07
Filing date: 2020-05-29
Publication date: 2021-08-11
Anticipated expiration: 2036-09-07
Also published as: JP2020126085A

Description

本発明は、キャスクの端部に外装される緩衝構造体に関する。 The present invention relates to a buffer structure that is exteriorized at the end of the cask.

従来、原子炉等で使用された使用済燃料は、放射線量が所定のレベル以下となるまで、原子力発電所内に設けられた冷却プールにて保管された後、遮蔽機能および密封機能等を有するキャスクに収容され、中間貯蔵施設または燃料再処理施設等へと輸送される。キャスクには、輸送時等の万一の落下事故の際に、所定の遮蔽機能および密封機能等を維持することが要求される。 Conventionally, spent fuel used in nuclear reactors and the like is stored in a cooling pool provided in a nuclear power plant until the radiation dose falls below a predetermined level, and then a cask having a shielding function and a sealing function. It is housed in the nuclear power plant and transported to an interim storage facility or a fuel reprocessing facility. The cask is required to maintain a predetermined shielding function, sealing function, etc. in the event of a fall accident such as during transportation.

キャスクの落下時の機能維持は、キャスクの中心軸が鉛直方向を向く姿勢で落下する垂直落下、当該中心軸が水平方向を向く姿勢で落下する水平落下、および、当該中心軸が鉛直方向および水平方向に対して傾斜する方向を向く姿勢で落下するコーナー落下のそれぞれに対して要求される。そこで、キャスクが搬送される際には、特許文献１および特許文献２に示されるように、キャスクの上下端部の外面にキャスク用緩衝体が取り付けられ、万一の落下時にキャスクに加わる衝撃を低減する対策が取られる。 To maintain the function when the cask is dropped, the vertical fall in which the central axis of the cask falls in the vertical direction, the horizontal fall in which the central axis falls in the horizontal direction, and the central axis in the vertical and horizontal directions are maintained. It is required for each corner fall that falls in a direction that is inclined with respect to the direction. Therefore, when the cask is transported, as shown in Patent Document 1 and Patent Document 2, a cask buffer is attached to the outer surface of the upper and lower ends of the cask, and an impact applied to the cask should be applied in the event of a fall. Measures will be taken to reduce it.

特開２００１−８３２９１号公報Japanese Unexamined Patent Publication No. 2001-83291 特開２０１４−１４５６７４号公報Japanese Unexamined Patent Publication No. 2014-145674

近年、キャスクに収容されている被収容物（例えば、バスケットおよび使用済燃料）の遅れ落下衝撃によるキャスクへの影響を低減するために、キャスク用緩衝体の緩衝性能の向上が求められている。遅れ落下衝撃とは、キャスクが地面等に衝突した瞬間にはキャスク内において落下中である被収容物が、キャスクの上記衝突から遅れてキャスク内面に衝突する際に生じる衝撃である。また、キャスク落下時の使用済燃料への衝撃荷重を低減するためにも、キャスク用緩衝体の緩衝性能の向上が求められている。緩衝性能を向上させるためには、例えば、キャスク用緩衝体の密度を低くして大型化することが考えられるが、キャスクの輸送時のサイズ制限を考慮すると、キャスク用緩衝体の大型化には限界がある。また、特許文献１の木製のキャスク用緩衝体では、落下時に地面と衝突した部位、および、衝突部位の近傍の部位のみが破壊されるため、緩衝性能の向上に限界がある。 In recent years, in order to reduce the influence on the cask due to the delayed drop impact of the objects to be contained in the cask (for example, the basket and the spent fuel), it is required to improve the cushioning performance of the cushioning body for the cask. The delayed drop impact is an impact generated when an object being dropped in the cask collides with the inner surface of the cask after the collision of the cask at the moment when the cask collides with the ground or the like. Further, in order to reduce the impact load on the spent fuel when the cask falls, it is required to improve the cushioning performance of the cask buffer. In order to improve the cushioning performance, for example, it is conceivable to reduce the density of the cask buffer and increase the size. However, considering the size limitation during transportation of the cask, the cask buffer may be increased in size. There is a limit. Further, in the wooden cask buffer of Patent Document 1, only the portion that collides with the ground when falling and the portion in the vicinity of the collision portion are destroyed, so that there is a limit to the improvement of the cushioning performance.

本発明は、上記課題に鑑みなされたものであり、キャスクに取り付けられる緩衝構造体を過剰に大型化することなく、キャスクに生じる衝撃を低減することを目的としている。 The present invention has been made in view of the above problems, and an object of the present invention is to reduce the impact generated on the cask without making the buffer structure attached to the cask excessively large.

請求項１に記載の発明は、燃料集合体が収容される柱状のキャスクの端部に外装される緩衝構造体であって、キャスクの長手方向の端面に接するとともに前記端面の外縁から径方向外方へと広がる緩衝底部と、前記緩衝底部から前記長手方向に沿って筒状に突出して前記キャスクの側面に接する緩衝側部とを備え、前記緩衝底部の外周部および前記緩衝側部のうち少なくとも一方の部位が、全周に亘って分散するとともに、衝撃力を受けた場合に衝撃荷重部近傍において初期的に応力集中が生じて破壊される初期破壊部と、全周に亘って分散するとともに前記衝撃荷重部近傍において前記初期破壊部の破壊に続いて破壊される後続破壊部とを備え、前記初期破壊部は、前記後続破壊部よりも密度が低い低密度部および前記低密度部の周囲の部位、または、前記後続破壊部よりも剛性が低い低剛性部および前記低密度部の周囲の部位であり、前記初期破壊部は、前記後続破壊部の内部において周方向に略等角度間隔に離間して配置される。 The invention according to claim 1 is a cushioning structure that is externally attached to the end of a columnar cask in which a fuel assembly is housed, and is in contact with the longitudinal end face of the cask and radially outside the outer edge of the end face. It is provided with a cushioning bottom portion that extends toward the side and a cushioning side portion that projects from the cushioning bottom portion in a tubular shape along the longitudinal direction and is in contact with the side surface of the cask, and at least one of the outer peripheral portion of the cushioning bottom portion and the cushioning side portion. One part is dispersed over the entire circumference, and at the same time, it is dispersed over the entire circumference with the initial fracture part where stress concentration is initially generated and destroyed in the vicinity of the impact load part when an impact force is applied. A subsequent fracture portion that is destroyed following the destruction of the initial fracture portion is provided in the vicinity of the impact load portion, and the initial fracture portion has a low density portion having a lower density than the subsequent fracture portion and a periphery of the low density portion. Or a portion around the low-rigidity portion and the low-density portion having lower rigidity than the subsequent fracture portion, and the initial fracture portions are located inside the subsequent fracture portion at substantially equal angular intervals in the circumferential direction. They are placed apart .

請求項２に記載の発明は、燃料集合体が収容される柱状のキャスクの端部に外装される緩衝構造体であって、キャスクの長手方向の端面に接するとともに前記端面の外縁から径方向外方へと広がる緩衝底部と、前記緩衝底部から前記長手方向に沿って筒状に突出して前記キャスクの側面に接する緩衝側部とを備え、前記緩衝底部の外周部および前記緩衝側部のうち少なくとも一方の部位が、全周に亘って分散する球状、多面体状または楕円球状の複数の空洞と、全周に亘って分散するとともに、衝撃力を受けた場合に衝撃荷重部近傍において初期的に応力集中が生じて破壊される初期破壊部と、全周に亘って分散するとともに前記衝撃荷重部近傍において前記初期破壊部の破壊に続いて破壊される後続破壊部とを備え、前記初期破壊部は、前記複数の空洞における各空洞の周囲の部位であり、前記初期破壊部は、前記後続破壊部の内部において周方向に略等角度間隔に離間して配置される。 The invention according to claim 2 is a cushioning structure that is externally attached to an end of a columnar cask in which a fuel assembly is housed, and is in contact with an end surface in the longitudinal direction of the cask and outside the radial direction from the outer edge of the end surface. It is provided with a cushioning bottom portion that extends toward the side and a cushioning side portion that projects from the cushioning bottom portion in a tubular shape along the longitudinal direction and is in contact with the side surface of the cask, and at least one of the outer peripheral portion of the cushioning bottom portion and the cushioning side portion. One part is dispersed over the entire circumference with a plurality of spherical, polyhedral or elliptical spherical cavities dispersed over the entire circumference, and when an impact force is applied, initial stress is applied in the vicinity of the impact load portion. The initial fracture portion is provided with an initial fracture portion that is destroyed due to concentration and a subsequent fracture portion that is dispersed over the entire circumference and is destroyed following the destruction of the initial fracture portion in the vicinity of the impact load portion. , A portion around each cavity in the plurality of cavities, and the initial fracture portion is arranged inside the subsequent fracture portion at substantially equal angular intervals in the circumferential direction .

本発明では、キャスクに生じる衝撃を低減することができる。 In the present invention, the impact generated on the cask can be reduced.

関連技術に係る緩衝構造体が取り付けられたキャスクを示す斜視図である。It is a perspective view which shows the cask to which the cushioning structure which concerns on a related technique is attached. 緩衝構造体の縦断面図である。It is a vertical sectional view of a buffer structure. 緩衝底部の横断面図である。It is a cross-sectional view of the cushion bottom part. 緩衝側部の横断面図である。It is a cross-sectional view of a cushioning side part. 緩衝底部の横断面図である。It is a cross-sectional view of the cushion bottom part. 緩衝底部の横断面図である。It is a cross-sectional view of the cushion bottom part. 緩衝構造体の要素モデルの重錘落下試験結果を示す図である。It is a figure which shows the weight drop test result of the element model of a buffer structure. 比較例の試験体の重錘落下試験結果を示す図である。It is a figure which shows the weight drop test result of the test body of the comparative example. 第１の実施の形態に係る緩衝構造体の緩衝底部を示す横断面図である。It is a cross-sectional view which shows the buffer bottom part of the buffer structure which concerns on 1st Embodiment. 緩衝側部の横断面図である。It is a cross-sectional view of a cushioning side part.

図１は、本発明の関連技術に係る緩衝構造体８が取り付けられたキャスク１を示す斜視図である。キャスク１は、使用済燃料集合体（以下、単に「燃料集合体」という。）を収容可能な柱状の容器である。キャスク１は、例えば、図１中の上下方向を向く中心軸Ｊ１を中心とする略円柱状である。以下の説明では、図１中の上下方向を「長手方向」ともいう。 FIG. 1 is a perspective view showing a cask 1 to which the buffer structure 8 according to the related technique of the present invention is attached. The cask 1 is a columnar container capable of accommodating a spent fuel assembly (hereinafter, simply referred to as “fuel assembly”). The cask 1 is, for example, a substantially cylindrical shape centered on the central axis J1 facing in the vertical direction in FIG. In the following description, the vertical direction in FIG. 1 is also referred to as a "longitudinal direction".

キャスク１は、放射線を遮蔽する遮蔽機能、放射性物質を密封する密封機能、燃料集合体を未臨界状態にて維持する未臨界維持機能、および、燃料集合体の熱を放散する除熱機能等を有する。キャスク１が搬送される際等には、キャスク１の長手方向の両側の端部に２つの緩衝構造体８が外装される。緩衝構造体８は、例えば、中心軸Ｊ１を中心とする有蓋円筒状または有底円筒状である。 Cask 1 has a shielding function that shields radiation, a sealing function that seals radioactive substances, a subcriticality maintenance function that maintains the fuel assembly in a subcritical state, and a heat removal function that dissipates heat from the fuel assembly. Have. When the cask 1 is transported or the like, two buffer structures 8 are attached to both ends of the cask 1 in the longitudinal direction. The buffer structure 8 has, for example, a covered cylinder or a bottomed cylinder centered on the central axis J1.

図２は、一方の緩衝構造体８を中心軸Ｊ１を含む面で切断した縦断面図である。他方の緩衝構造体８の構造は、図２に示すものと略同じである。図２では、キャスク１の一部も合わせて描いている。緩衝構造体８は、本体部８１と、高剛性部８２とを備える。本体部８１は、キャスク１の長手方向の端面１１（すなわち、上面または下面）および側面１２に接する。本体部８１は、例えば、高分子材料製（例えば、木製または硬質ポリウレタンフォーム製）である。本体部８１の密度は、例えば、０．１ｇ／ｃｍ^３以上かつ０．９ｇ／ｃｍ^３以下である。 FIG. 2 is a vertical cross-sectional view of one of the buffer structures 8 cut along a plane including the central axis J1. The structure of the other buffer structure 8 is substantially the same as that shown in FIG. In FIG. 2, a part of Cask 1 is also drawn. The buffer structure 8 includes a main body portion 81 and a high-rigidity portion 82. The main body 81 is in contact with the longitudinal end surface 11 (that is, the upper surface or the lower surface) and the side surface 12 of the cask 1. The main body 81 is made of, for example, a polymer material (eg, made of wood or rigid polyurethane foam). The density of the main body 81 is, for example, 0.1 g / cm ³ or more and 0.9 g / cm ³ or less.

本体部８１は、緩衝底部８３と、緩衝側部８４とを備える。緩衝底部８３は、中心軸Ｊ１を中心とする略円板状の部位である。緩衝底部８３は、キャスク１の長手方向の端面１１に接する。緩衝底部８３は、キャスク１の端面１１の外縁から、中心軸Ｊ１を中心とする径方向（以下、単に「径方向」という。）外方へと広がる。緩衝底部８３は、中心軸Ｊ１を中心とする略円環板状であってもよい。緩衝底部８３が略円環板状である場合、例えば、緩衝底部８３の外径は、キャスク１の端面１１の直径よりも大きく、緩衝底部８３の内径は、キャスク１の端面１１の直径よりも小さい。なお、緩衝底部８３が略円環板状である場合、緩衝底部８３の内径は、キャスク１の端面１１の直径以上であってもよい。緩衝側部８４は、緩衝底部８３から長手方向に沿って筒状に突出する。緩衝側部８４は、中心軸Ｊ１を中心とする略円筒状の部位である。緩衝側部８４は、キャスク１の端面１１近傍において側面１２に接する。 The main body 81 includes a buffer bottom 83 and a buffer side 84. The buffer bottom portion 83 is a substantially disk-shaped portion centered on the central axis J1. The buffer bottom 83 is in contact with the longitudinal end face 11 of the cask 1. The buffer bottom 83 extends outward from the outer edge of the end surface 11 of the cask 1 in the radial direction (hereinafter, simply referred to as “diameter direction”) about the central axis J1. The buffer bottom portion 83 may have a substantially annular plate shape centered on the central axis J1. When the buffer bottom 83 has a substantially annular plate shape, for example, the outer diameter of the buffer bottom 83 is larger than the diameter of the end face 11 of the cask 1, and the inner diameter of the buffer bottom 83 is larger than the diameter of the end face 11 of the cask 1. small. When the buffer bottom portion 83 has a substantially annular plate shape, the inner diameter of the buffer bottom portion 83 may be equal to or larger than the diameter of the end surface 11 of the cask 1. The buffer side portion 84 projects from the buffer bottom portion 83 in a tubular shape along the longitudinal direction. The buffer side portion 84 is a substantially cylindrical portion centered on the central axis J1. The buffer side portion 84 is in contact with the side surface 12 in the vicinity of the end surface 11 of the cask 1.

図３は、本体部８１の緩衝底部８３を中心軸Ｊ１に垂直な面にて切断した横断面図である。図４は、本体部８１の緩衝側部８４の横断面図である。図２ないし図４に示すように、高剛性部８２は、本体部８１内に配置される。高剛性部８２は、本体部８１の全周に亘って分散する複数の高剛性要素８２１を含む。高剛性部８２（すなわち、複数の高剛性要素８２１）は、本体部８１よりも剛性が高い高剛性材料製である。高剛性要素８２１は、例えば、金属製の略球状の部材（すなわち、鋼球）である。高剛性部８２の密度は、本体部８１の密度よりも高い。各高剛性要素８２１の直径は、本体部８１の緩衝底部８３の直径よりも十分に小さい。高剛性要素８２１は、例えば、中実の部材である。複数の高剛性要素８２１は、例えば、互いに略同じ大きさであり、略同じ形状である。 FIG. 3 is a cross-sectional view of the buffer bottom portion 83 of the main body portion 81 cut along a plane perpendicular to the central axis J1. FIG. 4 is a cross-sectional view of the cushioning side portion 84 of the main body portion 81. As shown in FIGS. 2 to 4, the high-rigidity portion 82 is arranged in the main body portion 81. The high-rigidity portion 82 includes a plurality of high-rigidity elements 821 dispersed over the entire circumference of the main body portion 81. The high-rigidity portion 82 (that is, the plurality of high-rigidity elements 821) is made of a high-rigidity material having higher rigidity than the main body portion 81. The high-rigidity element 821 is, for example, a metal substantially spherical member (that is, a steel ball). The density of the high-rigidity portion 82 is higher than the density of the main body portion 81. The diameter of each high-rigidity element 821 is sufficiently smaller than the diameter of the cushioning bottom 83 of the main body 81. The high-rigidity element 821 is, for example, a solid member. The plurality of high-rigidity elements 821 are, for example, substantially the same size and substantially the same shape as each other.

図２および図３に示すように、緩衝底部８３では、複数の高剛性要素８２１が、例えば、中心軸Ｊ１を中心とする略同心円状に配置される。各円周上の高剛性要素８２１は、中心軸Ｊ１を中心とする周方向（以下、単に「周方向」という。）において、略等角度間隔に配置される。換言すれば、緩衝底部８３では、複数の高剛性要素８２１は周方向に略均等に配置される。緩衝底部８３では、複数の高剛性要素８２１は、緩衝底部８３の外周部のみに配置されてもよい。 As shown in FIGS. 2 and 3, in the buffer bottom 83, a plurality of high-rigidity elements 821 are arranged in a substantially concentric circle centered on, for example, the central axis J1. The high-rigidity elements 821 on each circumference are arranged at substantially equal angular intervals in the circumferential direction (hereinafter, simply referred to as “circumferential direction”) about the central axis J1. In other words, at the buffer bottom 83, the plurality of high-rigidity elements 821 are arranged substantially evenly in the circumferential direction. In the buffer bottom 83, the plurality of high-rigidity elements 821 may be arranged only on the outer peripheral portion of the buffer bottom 83.

図２および図４に示すように、緩衝側部８４では、複数の高剛性要素８２１が、例えば、中心軸Ｊ１を中心とする円周上に配置される。当該複数の高剛性要素８２１は、周方向において略等角度間隔に配置される。換言すれば、緩衝側部８４においても、複数の高剛性要素８２１は周方向に略均等に配置される。 As shown in FIGS. 2 and 4, in the buffer side portion 84, a plurality of high-rigidity elements 821 are arranged on a circumference centered on, for example, the central axis J1. The plurality of high-rigidity elements 821 are arranged at substantially equal angular intervals in the circumferential direction. In other words, even in the cushioning side portion 84, the plurality of high-rigidity elements 821 are arranged substantially evenly in the circumferential direction.

図２ないし図４に示す例では、本体部８１において、複数の高剛性要素８２１は周方向に略均等に配置される。換言すれば、本体部８１の周方向の一部を所定の角度分だけ切り出した場合、当該部位に含まれる高剛性要素８２１の数は、周方向のいずれの部位においても略同じである。 In the example shown in FIGS. 2 to 4, in the main body 81, the plurality of high-rigidity elements 821 are arranged substantially evenly in the circumferential direction. In other words, when a part of the main body 81 in the circumferential direction is cut out by a predetermined angle, the number of high-rigidity elements 821 included in the portion is substantially the same in any portion in the circumferential direction.

図５および図６は、緩衝構造体８が取り付けられたキャスク１が水平落下した場合の緩衝構造体８の破壊の様子を示す図である。図５および図６では、本体部８１の緩衝底部８３の横断面を示す。なお、水平落下とは、上述のように、キャスク１の中心軸Ｊ１が略水平方向を向く姿勢で落下することを意味する。 5 and 6 are views showing the state of destruction of the buffer structure 8 when the cask 1 to which the buffer structure 8 is attached falls horizontally. 5 and 6 show a cross section of the buffer bottom 83 of the main body 81. As described above, the horizontal fall means that the central axis J1 of the cask 1 falls in a posture of facing a substantially horizontal direction.

緩衝構造体８が落下して地面等と接触すると、まず、本体部８１の接地面近傍の部位が変形する。本体部８１の接地面近傍の部位は、例えば、落下方向（すなわち、径方向）に圧縮されて歪む。本体部８１の変形が進むと、接地面近傍の高剛性要素８２１と接地面とが接近する。これにより、図５に平行斜線を付して示すように、本体部８１のうち当該高剛性要素８２１の近傍の部位８１１に大きな負荷が加わり、当該部位８１１に局所的な著しい破壊が生じる。以下の説明では、本体部８１の部位８１１を「局所破壊領域８１１」と呼ぶ。図５では、本体部８１のうち局所破壊領域８１１以外の部位の平行斜線を省略する（図６においても同様）。 When the buffer structure 8 falls and comes into contact with the ground or the like, first, the portion of the main body 81 near the ground plane is deformed. The portion of the main body 81 near the ground plane is compressed and distorted in the falling direction (that is, the radial direction), for example. As the deformation of the main body 81 progresses, the high-rigidity element 821 near the ground contact surface and the ground contact surface come close to each other. As a result, as shown by the parallel diagonal lines in FIG. 5, a large load is applied to the portion 811 in the vicinity of the high-rigidity element 821 of the main body portion 81, and the portion 811 is locally significantly destroyed. In the following description, the portion 811 of the main body 81 is referred to as a “local destruction region 811”. In FIG. 5, the parallel diagonal lines of the portion of the main body 81 other than the local fracture region 811 are omitted (the same applies to FIG. 6).

本体部８１の変形がさらに進むと、図６に示すように、接地面近傍に位置する高剛性要素８２１の数が、図５に示す状態よりも増加する。換言すれば、高剛性部８２が、図５に示す状態よりも接地面に相対的に近づく。そして、接地面近傍の複数の高剛性要素８２１が連成して本体部８１の破壊を進展させ、局所破壊領域８１１が拡大される。緩衝側部８４における破壊の様子も、図５および図６に示す例と略同様である。 As the deformation of the main body 81 further progresses, as shown in FIG. 6, the number of high-rigidity elements 821 located near the ground plane increases from the state shown in FIG. In other words, the high-rigidity portion 82 is closer to the ground plane than in the state shown in FIG. Then, a plurality of high-rigidity elements 821 in the vicinity of the ground contact surface are coupled to promote the fracture of the main body 81, and the local fracture region 811 is expanded. The state of destruction at the buffer side portion 84 is also substantially the same as the examples shown in FIGS. 5 and 6.

このように、緩衝構造体８が、キャスク１の長手方向の端面１１および側面１２に接する本体部８１と、本体部８１内に配置され、本体部８１よりも剛性合高い高剛性材料製の高剛性部８２とを備えることにより、落下時のキャスク１および緩衝構造体８の位置エネルギーが、本体部８１の変形に加えて、高剛性要素８２１による本体部８１の局所的な著しい破壊、および、局所破壊領域８１１の拡大により大きく消費される。このため、本体部８１の圧縮方向の歪みを抑制し、本体部８１における圧縮応力の急激な増大を抑制することができる。その結果、緩衝構造体８の地面との衝突時にキャスク１に作用する加速度を低減することができ、落下時にキャスク１に生じる衝撃を低減することができる。 In this way, the cushioning structure 8 is arranged in the main body portion 81 in contact with the end face 11 and the side surface 12 in the longitudinal direction of the cask 1 and in the main body portion 81, and is made of a high-rigidity material having a higher rigidity than the main body portion 81. By providing the rigid portion 82, the potential energy of the cask 1 and the buffer structure 8 at the time of dropping is not only the deformation of the main body 81, but also the local significant destruction of the main body 81 by the high rigidity element 821, and the significant local destruction of the main body 81. It is greatly consumed by the expansion of the local destruction region 811. Therefore, distortion in the compression direction of the main body 81 can be suppressed, and a rapid increase in compressive stress in the main body 81 can be suppressed. As a result, the acceleration acting on the cask 1 when the buffer structure 8 collides with the ground can be reduced, and the impact generated on the cask 1 when dropped can be reduced.

図７は、緩衝構造体８の要素モデルの重錘落下試験結果を示す図である。当該試験では、１辺が７０ｍｍの立方体の試験体に対して、３００ｋｇの重錘を３ｍの高さから落下させ、試験体により伝達される荷重を測定した。図７中の横軸は試験開始からの経過時間を示し、縦軸は試験体により伝達される荷重を示す（図８においても同様）。試験体は、緩衝構造体８の要素モデルとして、木製の立方体の上面に、直径１０ｍｍの９つの鋼球を配置したものである。図８は、緩衝構造体８と比較するために、木材のみにより形成された試験体を用いて同様の条件下で行った重錘落下試験結果を示す図である。図７および図８に示すように、緩衝構造体８の要素モデルである試験体では、木材のみにより形成された比較例の緩衝構造体に対応する試験体に比べて、伝達される荷重の最大値（すなわち、キャスク１に生じる衝撃に対応する値）が、約６０％に低減される。 FIG. 7 is a diagram showing the results of a weight drop test of the element model of the buffer structure 8. In this test, a weight of 300 kg was dropped from a height of 3 m on a cubic test body having a side of 70 mm, and the load transmitted by the test body was measured. The horizontal axis in FIG. 7 indicates the elapsed time from the start of the test, and the vertical axis indicates the load transmitted by the test piece (the same applies to FIG. 8). The test body is an element model of the buffer structure 8 in which nine steel balls having a diameter of 10 mm are arranged on the upper surface of a wooden cube. FIG. 8 is a diagram showing the results of a weight drop test performed under the same conditions using a test piece formed only of wood for comparison with the buffer structure 8. As shown in FIGS. 7 and 8, in the test body which is an element model of the buffer structure 8, the maximum load transmitted is maximum as compared with the test body corresponding to the buffer structure of the comparative example formed only of wood. The value (ie, the value corresponding to the impact generated on the cask 1) is reduced to about 60%.

上述のように、高剛性部８２は、本体部８１の全周に亘って分散する複数の高剛性要素８２１を含む。これにより、緩衝構造体８の周方向のいずれの部位が地面等に衝突した場合であっても、落下時にキャスク１に生じる衝撃を好適に低減することができる。また、複数の高剛性要素８２１は、周方向に実質的に均等に配置される。これにより、緩衝構造体８の周方向のいずれの部位が地面等に衝突した場合であっても、落下時にキャスク１に生じる衝撃をさらに好適に低減することができる。 As described above, the high-rigidity portion 82 includes a plurality of high-rigidity elements 821 dispersed over the entire circumference of the main body portion 81. As a result, the impact generated on the cask 1 when dropped can be suitably reduced regardless of which portion of the buffer structure 8 in the circumferential direction collides with the ground or the like. Further, the plurality of high-rigidity elements 821 are arranged substantially evenly in the circumferential direction. As a result, even if any part of the buffer structure 8 in the circumferential direction collides with the ground or the like, the impact generated on the cask 1 when dropped can be further preferably reduced.

上述の例では、複数の高剛性要素８２１が球状である。これにより、緩衝構造体８と地面等との衝突時に、高剛性要素８２１に対していずれの方向から力が加わった場合であっても、当該高剛性要素８２１の周囲に効率良く力を伝達することができる。その結果、本体部８１における局所破壊領域８１１を速やかに拡大することができ、落下時にキャスク１に生じる衝撃をさらに好適に低減することができる。なお、高剛性部８２では、複数の高剛性要素８２１が、球状の高剛性要素８２１を含んでいれば、全ての高剛性要素８２１が球状である必要はない。換言すれば、複数の高剛性要素８２１は、球状以外の形状を有する高剛性要素８２１を含んでいてもよい。この場合であっても、上述と略同様に、落下時にキャスク１に生じる衝撃をさらに好適に低減することができる。 In the above example, the plurality of high-rigidity elements 821 are spherical. As a result, when a force is applied to the high-rigidity element 821 at the time of a collision between the buffer structure 8 and the ground or the like, the force is efficiently transmitted to the periphery of the high-rigidity element 821. be able to. As a result, the local fracture region 811 in the main body 81 can be rapidly expanded, and the impact generated on the cask 1 when dropped can be further preferably reduced. In the high-rigidity portion 82, if the plurality of high-rigidity elements 821 include the spherical high-rigidity element 821, it is not necessary that all the high-rigidity elements 821 are spherical. In other words, the plurality of high-rigidity elements 821 may include the high-rigidity element 821 having a shape other than the spherical shape. Even in this case, the impact generated on the cask 1 at the time of dropping can be further preferably reduced in the same manner as described above.

緩衝構造体８では、例えば、複数の高剛性要素８２１は、多面体状の高剛性要素８２１を含んでいてもよい。具体的には、例えば、正四面体、立方体または直方体の高剛性要素８２１が、複数の高剛性要素８２１に含まれる。多面体状の高剛性要素８２１により、高剛性要素８２１と本体部８１との接触面積を大きくすることができる。これにより、落下時のキャスク１および緩衝構造体８の位置エネルギーを、高剛性要素８２１と本体部８１との摩擦エネルギーとして大きく消費することができる。その結果、落下時にキャスク１に生じる衝撃を低減することができる。 In the buffer structure 8, for example, the plurality of high-rigidity elements 821 may include a polyhedral high-rigidity element 821. Specifically, for example, a regular tetrahedron, a cube, or a rectangular parallelepiped high-rigidity element 821 is included in the plurality of high-rigidity elements 821. The polyhedral high-rigidity element 821 can increase the contact area between the high-rigidity element 821 and the main body 81. As a result, the potential energy of the cask 1 and the buffer structure 8 when dropped can be largely consumed as the frictional energy between the high-rigidity element 821 and the main body 81. As a result, the impact generated on the cask 1 when dropped can be reduced.

緩衝構造体８では、例えば、複数の高剛性要素８２１は、楕円球状の高剛性要素８２１を含んでいてもよい。楕円球状の高剛性要素８２１の曲率が小さい部分により、緩衝構造体８と地面等との衝突時に高剛性要素８２１に加わる力を、周囲の比較的広い範囲に亘って伝達することができる。これにより、局所破壊領域８１１を大きくする（すなわち、緩衝構造体８の利用範囲を拡大する）ことができ、落下時にキャスク１に生じる衝撃を低減することができる。また、楕円球状の高剛性要素８２１の曲率が大きい部分により、緩衝構造体８と地面等との衝突時に高剛性要素８２１に加わる力を、本体部８１に効率良く伝達することができる。これにより、本体部８１の局所的な破壊を速やかに実現することができ、落下時にキャスク１に生じる衝撃を低減することができる。 In the buffer structure 8, for example, the plurality of high-rigidity elements 821 may include an elliptical spherical high-rigidity element 821. Due to the small curvature portion of the elliptical spherical high-rigidity element 821, the force applied to the high-rigidity element 821 when the buffer structure 8 collides with the ground or the like can be transmitted over a relatively wide range around it. As a result, the local fracture region 811 can be enlarged (that is, the range of use of the buffer structure 8 can be expanded), and the impact generated on the cask 1 when dropped can be reduced. Further, due to the portion of the elliptical spherical high-rigidity element 821 having a large curvature, the force applied to the high-rigidity element 821 when the buffer structure 8 collides with the ground or the like can be efficiently transmitted to the main body 81. As a result, local destruction of the main body 81 can be quickly realized, and the impact generated on the cask 1 when dropped can be reduced.

複数の高剛性要素８２１は、例えば、第１の高剛性要素８２１と、当該第１の高剛性要素８２１よりも大きい第２の高剛性要素８２１とを含んでいてもよい。具体的には、例えば、第１の高剛性要素８２１は直径１０ｍｍの鋼球であり、第２の高剛性要素８２１は直径２０ｍｍの鋼球である。この場合、第２の高剛性要素８２１により、緩衝構造体８と地面等との衝突時に加わる力を、周囲の広い範囲に亘って伝達することができる。これにより、局所破壊領域８１１を大きくする（すなわち、緩衝構造体８の利用範囲を拡大する）ことができ、落下時にキャスク１に生じる衝撃を低減することができる。また、第１の高剛性要素８２１により、緩衝構造体８と地面等との衝突時に加わる力を、本体部８１に効率良く伝達することができる。これにより、本体部８１の局所的な破壊を速やかに実現することができ、落下時にキャスク１に生じる衝撃を低減することができる。 The plurality of high-rigidity elements 821 may include, for example, a first high-rigidity element 821 and a second high-rigidity element 821 that is larger than the first high-rigidity element 821. Specifically, for example, the first high-rigidity element 821 is a steel ball having a diameter of 10 mm, and the second high-rigidity element 821 is a steel ball having a diameter of 20 mm. In this case, the second high-rigidity element 821 can transmit the force applied at the time of collision between the buffer structure 8 and the ground or the like over a wide range of the surroundings. As a result, the local fracture region 811 can be enlarged (that is, the range of use of the buffer structure 8 can be expanded), and the impact generated on the cask 1 when dropped can be reduced. Further, the first high-rigidity element 821 can efficiently transmit the force applied at the time of collision between the buffer structure 8 and the ground or the like to the main body 81. As a result, local destruction of the main body 81 can be quickly realized, and the impact generated on the cask 1 when dropped can be reduced.

複数の高剛性要素８２１は、例えば、中空の高剛性要素８２１を含んでいてもよい。具体的には、例えば、中空の略球状の高剛性要素８２１が、複数の高剛性要素８２１に含まれる。中空の高剛性要素８２１により、緩衝構造体８と地面等との衝突時に本体部８１を局所的に破壊することができるとともに、中空の高剛性要素８２１が破壊されることにより、地面等との衝突時に緩衝構造体８に加わる力を吸収することもできる。その結果、落下時にキャスク１に生じる衝撃を低減することができる。 The plurality of high-rigidity elements 821 may include, for example, a hollow high-rigidity element 821. Specifically, for example, a hollow substantially spherical high-rigidity element 821 is included in the plurality of high-rigidity elements 821. The hollow high-rigidity element 821 can locally destroy the main body 81 when the buffer structure 8 collides with the ground or the like, and the hollow high-rigidity element 821 is destroyed to the ground or the like. It is also possible to absorb the force applied to the buffer structure 8 at the time of collision. As a result, the impact generated on the cask 1 when dropped can be reduced.

図９は、本発明の第１の実施の形態に係る緩衝構造体８ａの緩衝底部８３を示す横断面図である。図１０は、緩衝構造体８ａの緩衝側部８４の横断面図である。緩衝構造体８ａの形状は、図１に示す緩衝構造体８と略同様である。 FIG. 9 is a cross-sectional view showing a buffer bottom 83 of the buffer structure 8a according to the first embodiment of the present invention. FIG. 10 is a cross-sectional view of the buffer side portion 84 of the buffer structure 8a. The shape of the buffer structure 8a is substantially the same as that of the buffer structure 8 shown in FIG.

図９および図１０に示すように、緩衝構造体８ａは、緩衝底部８３と、緩衝側部８４とを備える。緩衝底部８３は、キャスク１の長手方向の端面１１（図２参照）に接する。緩衝底部８３は、当該端面１１の外縁から径方向外方へと広がる。緩衝側部８４は、緩衝底部８３から長手方向に沿って筒状に突出してキャスク１の側面１２（図２参照）に接する。 As shown in FIGS. 9 and 10, the buffer structure 8a includes a buffer bottom 83 and a buffer side 84. The buffer bottom 83 is in contact with the longitudinal end face 11 (see FIG. 2) of the cask 1. The buffer bottom 83 extends radially outward from the outer edge of the end face 11. The buffer side portion 84 projects from the buffer bottom portion 83 in a tubular shape along the longitudinal direction and comes into contact with the side surface 12 (see FIG. 2) of the cask 1.

緩衝構造体８ａでは、緩衝底部８３の外周部および緩衝側部８４のうち少なくとも一方の部位が、初期破壊部８５と、後続破壊部８６とを備える。初期破壊部８５は、当該少なくとも一方の部位の全周に亘って分散するとともに、衝撃力を受けた場合に衝撃荷重部（例えば、落下した場合に最初に地面に接触した部位）近傍において初期的に応力集中が生じて破壊される部位である。後続破壊部８６は、上記少なくとも一方の部位の全周に亘って分散するとともに、当該衝撃荷重部近傍において初期破壊部８５の破壊に続いて破壊される部位である。 In the buffer structure 8a, at least one of the outer peripheral portion of the buffer bottom portion 83 and the buffer side portion 84 includes an initial fracture portion 85 and a subsequent fracture portion 86. The initial fracture portion 85 is dispersed over the entire circumference of the at least one portion, and is initially in the vicinity of the impact load portion (for example, the portion that first contacts the ground when dropped) when an impact force is applied. It is a part that is destroyed due to stress concentration. The subsequent fracture portion 86 is a portion that is dispersed over the entire circumference of at least one of the above portions and is destroyed following the destruction of the initial fracture portion 85 in the vicinity of the impact load portion.

これにより、落下時のキャスク１および緩衝構造体８ａの位置エネルギーが、緩衝構造体８ａの変形に加えて、初期破壊部８５近傍における緩衝構造体８ａの局所的な著しい破壊により大きく消費される。このため、緩衝構造体８ａの圧縮方向の歪みを抑制し、緩衝構造体８ａにおける圧縮応力の急激な増大を抑制することができる。その結果、緩衝構造体８ａの地面との衝突時にキャスク１（図１参照）に作用する加速度を低減することができ、落下時にキャスク１に生じる衝撃を低減することができる。 As a result, the potential energy of the cask 1 and the buffer structure 8a at the time of falling is greatly consumed by the local significant destruction of the buffer structure 8a in the vicinity of the initial fracture portion 85 in addition to the deformation of the buffer structure 8a. Therefore, the strain of the buffer structure 8a in the compression direction can be suppressed, and the rapid increase of the compressive stress in the buffer structure 8a can be suppressed. As a result, the acceleration acting on the cask 1 (see FIG. 1) when the buffer structure 8a collides with the ground can be reduced, and the impact generated on the cask 1 when falling can be reduced.

緩衝構造体８ａは、例えば、内部に複数の空洞（ボイド）８５１が設けられた高分子材料製（例えば、木製または硬質ポリウレタンフォーム製）の部材である。緩衝構造体８ａでは、各空洞８５１の周囲の部位が初期破壊部８５であり、初期破壊部８５の周囲の部位（すなわち、空洞８５１から離れた部位）が後続破壊部８６である。複数の空洞８５１は、上述の複数の高剛性要素８２１と同様に配置される。空洞８５１の形状は、例えば、球状、多面体状または楕円球状である。空洞８５１の大きさは１種類であってもよく、２種類以上であってもよい。 The buffer structure 8a is, for example, a member made of a polymer material (for example, made of wood or rigid polyurethane foam) provided with a plurality of cavities (voids) 851 inside. In the buffer structure 8a, the portion around each cavity 851 is the initial fracture portion 85, and the portion around the initial fracture portion 85 (that is, the portion away from the cavity 851) is the subsequent fracture portion 86. The plurality of cavities 851 are arranged in the same manner as the plurality of high-rigidity elements 821 described above. The shape of the cavity 851 is, for example, spherical, polyhedral or elliptical spherical. The size of the cavity 851 may be one type or two or more types.

緩衝構造体８ａでは、空洞８５１に代えて、周囲の部位よりも密度が低い低密度部が設けられてもよい。この場合、低密度部およびその周囲の部位が初期破壊部８５であり、初期破壊部８５の周囲の部位が後続破壊部８６である。あるいは、空洞８５１に代えて、周囲の部位よりも剛性が低い（すなわち、柔らかい）低剛性部が設けられてもよい。この場合、低剛性部およびその周囲の部位が初期破壊部８５であり、初期破壊部８５の周囲の部位が後続破壊部８６である。 In the buffer structure 8a, a low-density portion having a density lower than that of the surrounding portion may be provided instead of the cavity 851. In this case, the low-density portion and the portion surrounding the low-density portion are the initial fracture portion 85, and the portion around the initial fracture portion 85 is the subsequent fracture portion 86. Alternatively, instead of the cavity 851, a low-rigidity portion having a lower rigidity (that is, softer) than the surrounding portion may be provided. In this case, the low-rigidity portion and the portion surrounding the low-rigidity portion are the initial fracture portion 85, and the portion around the initial fracture portion 85 is the subsequent fracture portion 86.

上述の緩衝構造体８，８ａでは、様々な変更が可能である。 Various changes can be made in the buffer structures 8 and 8a described above.

図１ないし図４に示す緩衝構造体８では、本体部８１は、木製または硬質ウレタンフォーム製には限定されず、例えば、発泡アルミニウム製であってもよい。また本体部８１は、ハニカム構造を有する金属製であってもよい。図９および図１０に示す緩衝構造体８ａも同様に、例えば、発泡アルミニウム製であってもよく、ハニカム構造を有する金属製であってもよい。 In the buffer structure 8 shown in FIGS. 1 to 4, the main body 81 is not limited to wood or rigid urethane foam, and may be made of foamed aluminum, for example. Further, the main body 81 may be made of metal having a honeycomb structure. Similarly, the buffer structure 8a shown in FIGS. 9 and 10 may be made of, for example, foamed aluminum or a metal having a honeycomb structure.

緩衝構造体８では、例えば、本体部８１の表面が金属板等により被覆されてもよい。緩衝構造体８ａでも同様に、緩衝底部８３および緩衝側部８４の表面が金属板等により被覆されてもよい。 In the buffer structure 8, for example, the surface of the main body 81 may be covered with a metal plate or the like. Similarly, in the buffer structure 8a, the surfaces of the buffer bottom portion 83 and the buffer side portion 84 may be covered with a metal plate or the like.

緩衝構造体８では、高剛性部８２に含まれる複数の高剛性要素８２１の形状、構造および大きさは、１種類のみであってもよく、２種類以上であってもよい。 In the buffer structure 8, the shape, structure, and size of the plurality of high-rigidity elements 821 included in the high-rigidity portion 82 may be only one type, or may be two or more types.

緩衝構造体８では、高剛性部８２は、必ずしも複数の高剛性要素８２１を含む必要はなく、１つの高剛性部８２のみが本体部８１内に配置されてもよい。高剛性部８２は、少なくともその一部が本体部８１内に配置されていればよく、高剛性部８２の一部が本体部８１の表面に露出していてもよい。この場合であっても、上記と同様に、落下時にキャスク１に生じる衝撃を低減することができる。 In the buffer structure 8, the high-rigidity portion 82 does not necessarily include a plurality of high-rigidity elements 821, and only one high-rigidity portion 82 may be arranged in the main body portion 81. At least a part of the high-rigidity portion 82 may be arranged in the main body portion 81, and a part of the high-rigidity portion 82 may be exposed on the surface of the main body portion 81. Even in this case, the impact generated on the cask 1 when dropped can be reduced in the same manner as described above.

緩衝構造体８では、高剛性部８２は、本体部８１のいずれの部位に配置されていてもよいが、好ましくは、緩衝底部８３の外周部および緩衝側部８４のうち少なくとも一方の部位に配置される。より好ましくは、高剛性部８２は、緩衝底部８３の外周部および緩衝側部８４の双方に配置される。さらに好ましくは、高剛性部８２は、緩衝底部８３の外周部以外の部位にも配置される。 In the buffer structure 8, the high-rigidity portion 82 may be arranged at any portion of the main body portion 81, but is preferably arranged at at least one of the outer peripheral portion of the buffer bottom portion 83 and the buffer side portion 84. Will be done. More preferably, the high-rigidity portion 82 is arranged on both the outer peripheral portion of the buffer bottom portion 83 and the buffer side portion 84. More preferably, the high-rigidity portion 82 is also arranged at a portion other than the outer peripheral portion of the buffer bottom portion 83.

上記実施の形態および各変形例における構成は、相互に矛盾しない限り適宜組み合わされてよい。 The above-described embodiment and the configurations in each modification may be appropriately combined as long as they do not conflict with each other.

１キャスク
８，８ａ緩衝構造体
９燃料集合体
１１（キャスクの）端面
１２（キャスクの）側面
８１本体部
８２高剛性部
８３緩衝底部
８４緩衝側部
８５初期破壊部
８６後続破壊部
８２１高剛性要素 1 Cask 8,8a Cushioning structure 9 Fuel assembly 11 (Cask) End face 12 (Cask) Side surface 81 Main body 82 High rigidity part 83 Cushion bottom 84 Cushion side 85 Initial failure part 86 Subsequent failure part 821 High rigidity element

Claims

A buffer structure that is exteriorized at the end of a columnar cask that houses a fuel assembly.
A cushioning bottom that is in contact with the longitudinal end face of the cask and extends radially outward from the outer edge of the end face.
A cushioning side portion that protrudes from the cushioning bottom portion in a tubular shape along the longitudinal direction and is in contact with the side surface of the cask.
With
At least one of the outer peripheral portion of the buffer bottom portion and the buffer side portion
An initial fracture part that disperses over the entire circumference and is destroyed by initial stress concentration near the impact load part when an impact force is applied.
A subsequent fracture portion that is dispersed over the entire circumference and is destroyed following the destruction of the initial fracture portion in the vicinity of the impact load portion, and a subsequent fracture portion.
With
The initial fracture portion is a low-density portion having a lower density than the subsequent fracture portion and a portion around the low-density portion, or a low-rigidity portion having a lower rigidity than the subsequent fracture portion and a periphery of the low-density portion. It is a part,
The initial fracture portion is a buffer structure characterized in that the initial fracture portion is arranged inside the subsequent fracture portion at substantially equal angular intervals in the circumferential direction.

A buffer structure that is exteriorized at the end of a columnar cask that houses a fuel assembly.
A cushioning bottom that is in contact with the longitudinal end face of the cask and extends radially outward from the outer edge of the end face.
A cushioning side portion that protrudes from the cushioning bottom portion in a tubular shape along the longitudinal direction and is in contact with the side surface of the cask.
With
At least one of the outer peripheral portion of the buffer bottom portion and the buffer side portion
Multiple spherical, polyhedral or elliptical cavities dispersed over the entire circumference,
An initial fracture part that disperses over the entire circumference and is destroyed by initial stress concentration near the impact load part when an impact force is applied.
A subsequent fracture portion that is dispersed over the entire circumference and is destroyed following the destruction of the initial fracture portion in the vicinity of the impact load portion, and a subsequent fracture portion.
With
The initial fracture portion is a portion around each cavity in the plurality of cavities.
The initial fracture portion is a buffer structure characterized in that the initial fracture portion is arranged inside the subsequent fracture portion at substantially equal angular intervals in the circumferential direction.