JP2005069831A - Concrete cask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concrete-made cask which is a vessel for storing and transporting spent nuclear fuel of nuclear power station. <P>SOLUTION: The cask comprises a cylindrical outer shell consisting of a multitude of precast prestressed concrete segments 11 split circumferentially and generatrix direction, inner liner 14 consisting of steel pipe, and concrete 15 inserted in between the segments 11 and the inner liner 14 and is provided with a bottom plate and an upper lid. The segments 11 are arranged in stagger on the cylindrical surface and combined in one by stressing PC tension members 12 and 13 arranged in X-shaped net in circumferential direction and cross direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a concrete cask.

  A cask is a container for storing and transporting spent fuel from a nuclear power plant. It has a steel body inside a metal outer wall that has previously contained a neutron shielding material, and contains recycled fuel. The basket which accommodated the accommodated basket and provided with the double lid | cover of a primary lid and a secondary lid is used. The storage capacity is usually about 10 tons, and the outer diameter of the container is 2 to 3 m in diameter and 5 to 6 m in height.

  The cask is required to have various functions in order to safely store the spent recycled fuel of the nuclear power plant. For example, radiation generated from recycled fuel is shielded by a neutron shielding material or the like, heat is released to the outside of the cask by heat transfer fins or the like provided outside the trunk portion, and cooling is performed by natural convection of outside air. It also prevents the fission chain reaction from occurring in the basket with neutron absorber. Furthermore, the radioactive material can be reliably enclosed by making the lid into a double structure.

A crack performance evaluation test of a steel sheet concrete cask formed by placing concrete between steel sheet inner and outer cylinders has been reported (Non-patent Document 1).
Japan Atomic Energy Society "Spring Annual Meeting 2002" (March 27-29, 2003, Kobe MOL) p296-297

  Spent fuel from nuclear power plants is reprocessed at a reprocessing plant, but requires intermediate storage until reprocessing, and cask is used. It is said that concrete cask has already been put to practical use overseas.

  The present inventors have conducted research on the production of a practical concrete cask, and the influence of the temperature stress on the concrete container due to the heat of hydration of the concrete during the production of the concrete cask and the decay heat of the fuel during storage of the recycled fuel. We have clarified and developed a durable and economical concrete container using precast concrete formwork (outer shell) which is excellent in terms of quality.

  The present invention aims to develop and provide a practical concrete cask based on these research results.

  The present invention has been developed in view of the above circumstances, and technical means thereof include a cylindrical prestressed concrete outer shell made of precast concrete, an inner peripheral liner made of steel pipe, and an intermediate between the outer shell and the inner peripheral liner. A concrete cask comprising a bottom plate and a top cover. Hereinafter, the prestressed concrete outer shell is referred to as a PC outer shell.

  In the above-described concrete cask, the cylindrical outer shell is composed of a number of segments divided in the circumferential direction and the generatrix direction, and the segments are arranged in a staggered manner on the cylindrical surface, and are arranged in a circumferential and vertical and horizontal X-shaped mesh shape. When the arranged PC shell is made into an integrated outer shell by tension, it is easy to manufacture and is preferable.

  The cylindrical outer shell may be formed of a plurality of rings divided in a circular ring shape, and may be an outer shell obtained by tensioning and integrating PC tendons arranged in the hoop direction and the busbar direction.

  Further, the cylindrical outer shell is an arc-shaped plate obtained by dividing the cylinder along the generatrix, the arc-shaped plates are arranged in the circumferential direction, and the PC tension members arranged in the circumferential direction are tensioned and integrated. The outer shell may be a modified one.

  According to the present invention, it is possible to estimate an increase in temperature due to the placement of internal concrete by an analytical value, and it is possible to suppress cracking of the internal concrete due to a temperature drop. In addition, cracking of the internal concrete due to thermal stress accompanying the temperature rise of the spent fuel can be suppressed. Furthermore, the precast prestressed concrete outer shell can control the occurrence of cracks by prestress, and no defects occur in the concrete cask. These measures can respond to various conditions by designing the introduction amount of prestress in consideration of the use condition of the concrete cask, the location condition of the use place, and other conditions.

  It should be noted that the amount of prestress introduced in the busbar direction can be appropriately determined in accordance with the thermal stress caused by the fall or the temperature distribution in the vertical direction.

  Thus, the concrete cask of the present invention can completely prevent cracking of the PC outer shell and the internal concrete due to the thermal stress of the internal concrete due to the bending rigidity and tensile rigidity of the PC member into which the prestress is introduced.

  Therefore, a highly reliable and high-quality concrete cask can be obtained and contributes greatly.

  First, the course of research that led to the completion of the present invention will be described.

  In a conventional concrete cask, a basket charged with spent fuel of a nuclear reactor is built in a cylindrical metal canister, and a concrete cylindrical wall is provided on the outer periphery of the metal canister. And cooling air is taken in from the cooling air inlet provided in the bottom part, this cooling air is made to pass through the clearance gap between a metal canister and a concrete cylindrical wall, and is discharged | emitted from the cooling air discharge port near upper end.

  According to the report, a concrete material that has improved heat resistance and can be used for a long time at a high temperature of 150 ° C. is reported.

  The inventors studied with a different approach. That is, the thermal stress generated in an actual concrete cask was analyzed, the possibility of omitting the passage of cooling air was pursued, and a technique for imparting sufficient strength to the concrete cylindrical wall (shell) was examined.

  Hereinafter, an experiment and an embodiment of the present invention will be described with reference to the drawings.

  As a preliminary test, as shown in FIG. 5, a synthetic cylinder 30 in which a reinforced concrete cylinder 31 is formed on the outer periphery of an inner peripheral liner 32 made of a steel pipe is manufactured, and used nuclear fuel is charged into the inner peripheral liner 32. , Sealed and left. As a result, many cracks 33 occurred in the reinforced concrete cylinder 31. This was recognized as a crack originating from the expansion of the concrete due to the heat generated from the spent nuclear fuel.

  Next, a concrete cask model experiment was conducted assuming that the concrete cask was manufactured. Further, temperature analysis and stress analysis during storage of spent nuclear reactor fuel were performed, and heat transfer tests were performed on the concrete cask. Was completed.

  FIG. 6A shows a plan view of an experimental container 40 for temperature and strain analysis at the time of manufacturing a concrete cask, and FIG. 6B shows a longitudinal sectional view thereof. As shown in FIGS. 6A and 6B, a concrete container 40 having an inner diameter of 2000 mm, an outer diameter of 2350 mm, and a height of 2430 mm is manufactured by a piece 41 divided into four circumferences, and a chloroprene having a thickness of 5 mm is formed on the joining end face 42. Rubber was stuck and assembled together, and 8 1T15.2 wires were wound around the outer periphery as PC steel strands 43 and tightened. Concrete using early-strength Portland cement was placed in the container 40.

  FIG. 7A shows the arrangement of the thermocouple 45 and is a plan view, and FIG. 7B is a vertical cross-sectional view taken along the line AA in FIG. 7A. 8A shows a strain measurement position of the container 40, FIG. 8A is a plan view, and FIG. 8B is a vertical cross-sectional view taken along the line BB. As shown in FIG. 8A and FIG. 8B, a strain gauge 46 and a mold gauge 47 are provided at various locations.

  Concrete was placed and the temperature and strain were measured. The transition of elapsed time (days) and temperature (° C.) is shown in FIG. In FIG. 9, the thick solid line 51 and the broken line 52 indicate the actual measurement value and analysis value of the central portion, the thin solid line 54 and the broken line 55 indicate the actual measurement value and analysis value of the side surface, and the two-dot chain line 57 indicates the transition of the outside air temperature. is there. The central portion had a maximum temperature 53 of approximately 90 ° C., and the side surface had a maximum temperature 56 of approximately 42 to 45 ° C. As shown in FIG. 9, the actual measurement value and the analysis value are in good agreement.

  The physical property values used in the analysis are as follows.

Adiabatic temperature rise type (℃):
T = 64.2 (1-e- ^2.29t )
Surface heat transfer coefficient (W / m ² ° C):
Upper surface = 3, side surface = 10, lower surface = 6
Thermal conductivity (W / m ² ° C): 2.4
Density (kg / m ³ ): 2400
Specific heat (kJ / kg ° C): 1.3
Next, the relationship between elapsed time (days) and strain (μm) is shown in FIG. The thick solid line 61 and the broken line 62 are the actual measurement value and analysis value of the PC formwork, and the thin solid line 63 and the broken line 64 are the actual measurement value and analysis value of the comparison formwork, respectively. The actual measurement values 61 and 63 are almost in good agreement with the analysis values 62 and 64.

  Next, temperature and stress analysis was performed assuming that spent fuel was stored.

  The analysis conditions are as follows.

  The outside air temperature (° C.) was 25 ° C., and the internal air temperature increase rate was 2 (° C./h).

  FIG. 11 is a cross-sectional view of the wall of the test container 70. A PC outer shell 74 is disposed outside the steel pipe 71 to form a mold, and a concrete wall 75 is placed between them. A heat insulating material 76 is provided on the upper and lower surfaces of the concrete wall. FIG. 12 is a diagram showing the temperature analysis result of the cross section of FIG. FIG. 13 shows the result of the stress analysis for the case where the edge of the PC outer shell and the internal concrete is cut, and FIG. 14 shows the result of the stress analysis for the integral structure.

  In FIG. 13, a high stress portion is generated in the inner concrete and no large stress is generated in the PC outer shell. However, in FIG. 14, the inner concrete has a low stress and a high stress portion is generated in the PC outer shell. If prestressed concrete is used in the part where the stress is high, the proof stress will be sufficient and the concrete will not crack.

  Next, an experiment at the time of storage was performed on the container 80 shown in FIG. In FIG. 15, a PC mold 82 having an outer diameter of 3400 mm, a height of 1800 mm, and a thickness of 200 mm is disposed outside a steel pipe liner 81 having an inner diameter of 1640 mm and a thickness of 9 mm, and a concrete wall 83 having a thickness of 671 mm is formed therebetween. It is a thing. A heat insulating material 85 is disposed on the upper and lower surfaces of the concrete wall 83, and a PC steel wire 84 is wound around the outer peripheral surface of the PC mold.

  FIGS. 16 and 17 show the temperature measurement position 86 and the strain measurement position provided in the container 80, respectively. 16 (a) is a plan view of the container 80, FIG. 16 (b) is its CC arrow view, FIG. 17 (a) is its top view, and FIG. 17 (b) is its DD arrow view. FIG. The strain gauges are an embedded strain gauge 87 and a mold gauge 88.

  A heater and water were placed in the container, and the water temperature was raised by the heater. The water temperature was raised from the preliminary test data conducted in the container shown in FIG. 5 to 70 ° C. so that it reached 65 ° C. inside the steel pipe liner.

  FIG. 18 shows the relationship between temperature and elapsed time. The horizontal axis indicates the number of days elapsed, and the vertical axis indicates the temperature. In the figure, the curve 91 is the side of the formwork, the curve 92 is the formwork and the internal concrete surface, the curve 93 is the center of the internal concrete, the curve 94 is the liner and the internal concrete surface, and the curve 95 Indicates the temperature of the liner side surface, and the curve 96 indicates the outside air temperature.

  FIG. 19 shows the temperature distribution in the middle step radial direction. The horizontal axis indicates the center in the radial direction, the liner side, and the mold side, and the vertical axis indicates the temperature (° C.) curves 101, 102, 103, 104, 105, 106, 107, and 108, respectively. Data on the 2nd, 3rd, 7th, 10th, 14th, and 16th are shown.

  FIG. 20 shows the relationship between elapsed time and strain. Curve 111 is the upper internal concrete formwork side, curve 112 is the formwork side 270 mm from the middle internal concrete center, curve 113 is the middle internal concrete center, and curve 114 is 270 mm from the middle internal concrete center, the mold side liner side, curve 115 indicates the strain on the lower internal concrete form side.

  FIG. 21 shows the relationship between the temperature and the elapsed time in the heat transfer test. The horizontal axis indicates the number of days elapsed, and the vertical axis indicates the temperature (° C.). The curve 121 is the side of the mold, the curve 122 is the mold and the inner concrete surface, the curve 123 is the center of the inner concrete, and the curve 124 is the liner and the inner concrete surface. , Curve 125 shows the temperature of the liner side surface, curve 126 is the transition of the outside air temperature, and curve 127 is the heater temperature.

  FIG. 22 shows the temperature distribution in the radial direction of the middle stage. Curve 131 is the temperature distribution at the start of temperature rise, and curves 132, 133, 134, 135, 136, 137, 138, and 139 are the elapsed days 1, 2, 3, 4, 5, 6 and 7, respectively. The temperature distribution data on the 8th and 8th are shown.

  FIG. 23 shows the relationship between strain and elapsed time. Curve 141 is the upper inner concrete formwork side, curve 142 is the 270 mm formwork side from the middle inner concrete center, curve 143 is the middle inner concrete center, curve 144 is the mold side liner side 270 mm from the middle inner concrete center, curve 145 Indicates the strain on the lower internal concrete formwork side.

  FIG. 24 shows the relationship between the tension force ΔP and the elapsed time. The horizontal axis represents the number of days elapsed, and the vertical axis represents the tension force ΔP (N). When 16 days passed, the heater started to rise in temperature. Curve 151 indicates the second PC steel wire from the top, and curve 152 indicates the fifth PC steel strand from the top.

  Next, the change of the surface strain from the start of temperature rising of the mold is shown in FIG. FIG. 25 is a side view of the mold 74, and K1 to K8 in the figure indicate measurement positions and measurement directions at which strain is measured. FIG. 26 is a chart showing the change over time, and K1 to K8 are shown in agreement with those shown in FIG.

  From the change with time of the mold surface strain gauge shown in FIG. 26, it is shown that no cracks occur. Also, cracks are not generated in the internal concrete due to the restraining force caused by the hoop direction or vertical prestress caused by the PC steel material.

As a result of the above experiment,
(1) In the concrete cask experiment assuming the time of production, the measured values of the temperature and strain and the analytical values almost coincided with each other by appropriately setting the adiabatic temperature rise equation, the surface heat transfer coefficient, and the linear expansion coefficient.
(2) It was clarified that the tensile stress at the intermediate part of the internal concrete can be reduced by integrating the PC shell and the internal concrete by the temperature stress analysis assuming storage.
(3) The concrete cask heat transfer test obtained the temperature and strain history of the concrete cask due to the heat of hydration of cement during concrete production.
(4) Schematic tests during spent fuel storage revealed temperature distribution, strain distribution, and changes with time. Therefore, it became clear that the PC outer shell can be appropriately designed on the outer periphery of the concrete cask based on these data.

  Based on the above findings, we have obtained the knowledge that a spent fuel storage container can be obtained with an appropriate design using the PC outer shell as a formwork.

  Based on the above results, the present invention has developed a spent fuel storage container using a PC outer shell. A specific example will be described with reference to the drawings. 1 to 4 are perspective views showing a concrete cask according to an embodiment of the present invention.

  The concrete cask of the present invention comprises a cylindrical outer shell made of precast prestressed concrete, an inner peripheral liner made of steel pipe, and concrete interposed between the outer shell and the inner peripheral liner, and includes a bottom plate and an upper surface lid. ing.

  A concrete cask 10 shown in FIG. 1 includes a polygonal segment 11 obtained by dividing a plurality of circular cut circumferences into a cylindrical shape, a combined circumferential PC steel material 12, and an X-shaped circumferentially and longitudinally inclined PC steel material. 13 is formed, and concrete 15 is placed between the inner steel liner 14 and the PC shell. Naturally, the concrete 15 is a concrete having radiation shielding performance.

  FIG. 2 is an example in which a rectangular arc segment 11 is used instead of the polygonal segment 11 of FIG.

  FIG. 3 shows an example in which cylindrical ring-shaped segments 16 are joined in the longitudinal direction and the longitudinal direction is fastened with a PC steel material 17 parallel to the bus bar.

  In the embodiment shown in FIGS. 1 to 3, after prestress is introduced into the PC outer shell, the cast-in-place concrete 15 is preferably placed between the steel liner and the mold.

  FIG. 4 is an example in which circular plate-like segments 21 each having a plurality of circumferences are combined, and the circumferential direction is coupled by a circumferential PC steel material 22. Pillars 23 are formed on the outer surface of each segment 21. The steel is crossed here and tightened. In the longitudinal direction, prestress may be introduced in advance by a pretension method. In this embodiment, the precast formwork is assembled and cast-in-place concrete is cast, and then circumferential prestress is introduced.

  The size of the above concrete cask is 2 to 3 m in outer diameter and 5 to 6 m in height. The circumferential PC steel material only needs to have a tension that suppresses the strain obtained from the above-described experiment, and there is no need to provide a special air intake or air discharge port or the like for cooling.

It is a perspective view which shows the concrete cask of the Example of this invention. It is a perspective view which shows the concrete cask of the Example of this invention. It is a perspective view which shows the concrete cask of the Example of this invention. It is a perspective view which shows the concrete cask of the Example of this invention. It is a perspective view of the synthetic cylinder of a preliminary test. It is a top view of the container for experiment for the temperature and strain analysis at the time of concrete cask manufacture. It is a longitudinal cross-sectional view of Fig.6 (a). 3 is a plan view showing an arrangement of thermocouples 45. FIG. It is an AA arrow longitudinal cross-sectional view of Fig.7 (a). 4 is a plan view showing a strain measurement position of the container 40. FIG. It is a BB arrow longitudinal cross-sectional view of Fig.8 (a). It is a chart which shows transition of elapsed time and temperature. It is a chart which shows transition of elapsed time and distortion. It is sectional drawing of the wall of the container for a test. It is a figure which shows the temperature analysis result of the cross section of FIG. It is a figure which shows the stress analysis result of the cross section of FIG. It is a figure which shows the stress analysis result of the cross section of FIG. It is a top view of the container for storage experiment. It is a longitudinal cross-sectional view of Fig.15 (a). It is a top view which shows a temperature measurement position. It is a longitudinal cross-sectional view of Fig.16 (a). It is a top view which shows a strain measurement position. It is a longitudinal cross-sectional view of Fig.17 (a). It is a chart which shows transition of elapsed time and temperature. It is a graph which shows the temperature distribution of a middle step part radial direction. It is a chart which shows change of elapsed time and distortion. It is a chart which shows the change of elapsed time and temperature. It is a graph which shows the temperature distribution of a middle step part radial direction. It is a chart which shows change of elapsed time and distortion. It is a chart which shows change of elapsed time and tension. It is a side view of a formwork which shows a strain measurement position and direction. It is a chart which shows the time-dependent change of the distortion of a formwork.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Concrete cask 11 Segment 12 PC steel 13 PC steel 14 Steel liner 15 Concrete 16 Segment 17 PC steel 21 Segment 22 PC steel 23 Pillar 30 Composite cylinder 31 Reinforced concrete cylinder 32 Inner peripheral liner 33 Crack 40 Container 41 Piece 43 PC steel Wire 45 Thermocouple 46 Strain gauge 47 Mold gauge 51 Solid line of thick line 52 Broken line 53 Maximum temperature 54 Solid line of thin line 55 Broken line 56 Maximum temperature 57 Two-dot chain line 61 Solid line of thick line 62 Broken line 63 Solid line of fine line 64 Broken line 61, 63 Actual measurement 62 64 Analysis value 70 Test vessel 71 Steel pipe liner 72 Concrete 73 Lid 74 PC outer shell 75 Concrete wall 76 Insulation material 80 Container 81 Steel pipe liner 82 PC formwork 83 Concrete wall 84 From PC steel Wire 85 Thermal insulation material 86 Temperature measurement position 87 Embedded strain gauge 88 Mold gauge 91-96 Curve 101-108 Curve 111-115 Curve 121-127 Curve 131-139 Curve 141-145 Curve 151, 152 Curve

Claims (4)

A concrete comprising a cylindrical outer shell made of precast prestressed concrete, an inner peripheral liner made of steel pipe, and a concrete interposed between the outer shell and the inner peripheral liner, and comprising a bottom plate and a top cover. Cask. The cylindrical outer shell is composed of a large number of segments divided in the circumferential direction and the generatrix direction. The segments are arranged in a staggered manner on the cylindrical surface, and are arranged in a circumferential and vertical and horizontal X-shaped mesh pattern. The concrete cask according to claim 1, wherein the concrete cask is an outer shell integrated by tensioning a tendon. The cylindrical outer shell is composed of a plurality of rings divided in a circumferential ring shape, and is an outer shell obtained by tensioning and integrating PC tendons arranged in a hoop direction and a busbar direction. Item 2. A concrete cask according to item 1. The cylindrical outer shell is formed of an arc-shaped plate obtained by dividing a cylinder along a generatrix, the arc-shaped plates are arranged in the circumferential direction, and the PC tension members arranged in the circumferential direction are tensioned and integrated. The concrete cask according to claim 1, wherein the concrete cask is an outer shell.

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