JP2011232089A - Nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear reactor with which the amount of metal in fusion furnace in the pressure vessel in the nuclear reactor can be more reliably increased, thereby enhancing the reliability of IVR.SOLUTION: The nuclear reactor is provided with a pressure vessel 10 including a reactor core, a reactor core bath 13 surrounding the reactor core, a support plate 11 supporting the reactor core from the bottom, and a supporter 12 vertically arranged below the nuclear reactor pressure vessel 10 and supporting the support plate 11 from the bottom. When the support 12 melts, the support plate 11 is designed to fall down.

Description

  The present invention relates to a nuclear reactor having a function of cooling and holding a core melt melted in a reactor pressure vessel when a severe accident occurs.

  Even when a severe accident occurs in the nuclear reactor, even if the fuel in the core melts in the reactor pressure vessel and the molten state progresses and the molten material falls from the core to the lower head, By cooling the outside of the pressure vessel or cooling the inside of the reactor pressure vessel, the core melt is cooled in the lower head, and the method of holding the in-vessel retention (In Vessel Retention, hereinafter) This method is abbreviated as IVR) and is attracting attention as one of the most effective measures for converging accidents. In addition, having such a function of cooling the molten core in the reactor pressure vessel is becoming a basic requirement for nuclear reactors in terms of global regulations and operations.

  This will be specifically described with reference to FIG. FIG. 7 is a configuration diagram showing an elevational cross section of a conventional reactor pressure vessel having an IVR function.

  As shown in FIG. 7, the reactor pressure vessel 1 has a heat insulating material 2 outside. A gap 4 is formed between the heat insulating material 2 and the pressure vessel wall 1 a of the reactor pressure vessel 1.

  In the reactor pressure vessel 1 configured as described above, when the fuel is melted and the molten debris 3 is deposited inside, the heat is transmitted to the outside through the pressure vessel wall 1a, and the pressure vessel wall 1a, the heat insulating material 2, Water in the gap 4 formed between the two is heated and boiled, and a flow rising in the gap 4 is formed by the buoyancy of the steam.

  The gas-liquid two-phase fluid boiled in the gap 4 is discharged from the outlet 4 a formed in the upper gap 4, while new water flows in from the inlet 4 b formed in the lower gap 4. The molten debris 3 is cooled and held in the reactor pressure vessel 1 by removing heat from the molten debris 3 by the natural circulation flow caused by boiling in the gap 4.

  In the IVR, sufficient heat removal is performed on the outer surface of the reactor pressure vessel 1 so that heat can be easily transferred on the outer surface of the reactor pressure vessel 1 and a high heat load can be withstood. There is a need to.

  For example, Non-Patent Document 1 discloses that a thick metal layer is formed by melting a core support plate during melting of a core.

Analysis of In-Vessel Retention and Ex-Vessel Fuel Coolant Interaction for AP1000 (issued in August 2004) EXECUTIVE SUMMARY (Xi) U.S. Nuclear Regulatory Commission

  By the way, in order to evaluate the success rate of the IVR, that is, the probability that the molten debris 3 is cooled and held in the reactor pressure vessel 1, it is necessary to consider every event. For example, the success rate of IVR varies greatly depending on the amount of metal in the melt, the deposition on the lower part of the reactor pressure vessel 1 and the stratification state on the upper part.

  In particular, the success rate of IVR is low because the amount of metal is small as shown in FIG. 8, so that a thin molten metal layer 6 is deposited in layers on the upper surface of the molten oxide layer 5 to form a layer. This is the case where heat is transferred through the pressure vessel wall 1 a of the reactor pressure vessel 1 through the layer 6. Here, the reason why the thin molten metal layer 6 is deposited on the upper surface of the molten oxide layer 5 is that the specific gravity of the molten metal layer 6 is lighter than that of the molten oxide layer 5.

  In this case, since the heat conductivity of the molten metal layer 6 is good, the heat generated at the time of the accident is concentrated on the pressure vessel wall 1a where the thin molten metal layer 6 is in contact, and the high heat load is locally applied. Since (high heat flux) is applied, the pressure vessel wall 1a may be damaged and the molten debris 3 may not be held in the reactor pressure vessel 1. As a result, the success rate of IVR is low.

  The present invention has been made in consideration of the above-described circumstances, and provides a nuclear reactor in which the amount of metal in the molten core in the reactor pressure vessel can be increased more reliably and the reliability of the IVR is improved. For the purpose.

  In order to achieve the above object, a nuclear reactor according to the present invention includes a reactor pressure vessel having a core inside, a reactor core surrounding the reactor core, a support plate for supporting the reactor core from below, and the reactor pressure. A support that is erected at a lower portion of the container and supports the support plate from below, and the support plate is configured to drop when the support is melted.

  According to the present invention, when the support is melted, the support plate falls, so that the amount of metal in the melting core can be reliably increased and the reliability of the IVR can be greatly improved.

It is a lineblock diagram showing an elevation section of a reactor pressure vessel in a first embodiment of a nuclear reactor concerning the present invention. It is a top view which shows the arrangement | positioning aspect of the support of FIG. It is a block diagram which expands and shows a part of standing section of the reactor pressure vessel in 2nd Embodiment of the reactor which concerns on this invention. It is a block diagram which expands and shows a part in the standing cross section of the 1st modification of 2nd Embodiment. It is a block diagram which expands and shows a part in the standing cross section of the 2nd modification of 2nd Embodiment. It is a block diagram which expands and shows a part of standing section of the reactor pressure vessel in 3rd Embodiment of the reactor which concerns on this invention. It is a block diagram which shows the elevation cross section of the reactor pressure vessel which has the conventional IVR. It is a block diagram which shows the elevation cross section in the reactor pressure vessel at the time of a severe accident.

  Embodiments of a nuclear reactor according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a configuration diagram showing an elevational cross section of a reactor pressure vessel in a first embodiment of a nuclear reactor according to the present invention. FIG. 2 is a plan view showing the arrangement of the support shown in FIG. The same parts as those in the conventional configuration will be described using the same reference numerals as those in FIG.

  As shown in FIG. 1, a reactor pressure vessel 10 having a core (not shown) is installed inside the reactor. The reactor pressure vessel 10 has a heat insulating material 2 on the outside, and a gap 4 is formed between the heat insulating material 2 and the pressure vessel wall 10 a of the reactor pressure vessel 10. The upper portion of the gap 4 is formed with an outflow port 4a, and the lower portion is formed with an inflow port 4b.

  On the other hand, inside the reactor pressure vessel 10, there is a core tank 13 that surrounds the outer periphery of the core, a lower support plate 11 that is welded to the lower part of the core tank 13 and supports the fuel in the core from below, and a nuclear reactor. And a plurality of supports 12 that are erected on the pressure vessel 10 and support the lower support plate 11 from below. Here, the load of the lower support plate 11 is received by the core tank 13 and the plurality of supports 12 in a distributed manner. The core tank 13 is connected to the lower support plate 11 by welding, for example, and is configured so that the entire load of the lower support plate cannot be supported by the core tank 13 alone. In other words, when the support 12 is lost, the connection portion between the core tank 13 and the lower support plate 11 is broken and the lower support plate 11 falls.

  The lower support plate 11 and the plurality of supports 12 are each made of a metal such as stainless steel. In the present embodiment, as shown in FIG. 2, the plurality of supports 12 are arranged in a radial manner on the reactor bottom portion 10 b of the reactor pressure vessel 10 at regular intervals. The number, arrangement, length, and thickness of these supports 12 are not particularly limited, and are determined based on various conditions such as workability and meltability.

  In the present embodiment configured as described above, after the fuel is melted in a severe accident and the molten debris 14 falls to the reactor bottom 10b of the reactor pressure vessel 10, first, the plurality of supports 12 are melted, The lower support plate 11, which has dispersed and fixed the load between the support 12 and the core tank 13, is melted by dropping onto the furnace bottom 10 b. In this case, since the lower support plate 11 falls when the support 12 is lost as described above, when the plurality of supports 12 are melted, the lower support plate 11 quickly falls onto the furnace bottom 10b.

  When the molten debris 14 is deposited on the furnace bottom 10b, the heat is transmitted to the outside through the pressure vessel wall 10a, and the water in the gap 4 formed between the pressure vessel wall 10a and the heat insulating material 2 is heated. Then, it boils and a flow rising in the gap 4 is formed by the buoyancy of the steam.

  The gas-liquid two-phase fluid boiled in the gap 4 is discharged from the upper outlet 4a, while new water flows from the lower inlet 4b. The molten debris 14 is cooled and held in the reactor pressure vessel 10 by removing heat from the molten debris 14 by the natural circulation flow caused by boiling in the gap 4.

  Accordingly, in the present embodiment, the support 12 is melted in a severe accident, and the lower support plate 11 is reliably and quickly dropped and melted to increase the amount of metal in the melt, thereby forming a thickened metal. Can be made. Thereby, the event that the reactor pressure vessel 10 is damaged due to the metal being formed as a thin layer on the molten debris 14 can be prevented, and the success probability of the IVR for holding the core melt can be increased.

  As described above, according to the present embodiment, when the support 12 is melted, the lower support plate 11 is dropped, thereby reliably increasing the amount of metal in the melting core and greatly improving the reliability of the IVR. it can.

(Second Embodiment)
FIG. 3 is an enlarged schematic view showing a part of a vertical section of a reactor pressure vessel in the second embodiment of the reactor according to the present invention. In the present embodiment, the same or corresponding parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The same applies to other embodiments and modifications.

  As shown in FIG. 3, the reactor pressure vessel 10 includes a reactor core tank 13 having a thin wall portion 13 a that surrounds the outer periphery of a core (not shown) and is formed by thinning a lower wall surface from the inside. A lower support plate 11 that is welded to the lower part of the reactor core 13 and supports the fuel of the core from below; and a plurality of supports 12 that are erected on the reactor pressure vessel 10 and support the lower support plate 11 from below. It is equipped with. Here, the lower support plate 11 is supported by both the upper core tank 13 and the lower plurality of supports 12, and the lower support plate 11 falls when the support 12 is lost, as in the first embodiment. It is. Further, the thickness and length of the thin portion 13a of the core tank 13 are determined by various conditions such as welding workability.

  In the present embodiment configured as described above, the lower portion of the core tank 13 has a thin portion 13a formed thinly, and the thin portion 13a and the lower support plate 11 are connected to each other, so that the support 12 is lost. In addition, the lower support plate 11 can be configured to easily fall more quickly. Therefore, when the plurality of supports 12 are melted, the lower support plate 11 can be immediately dropped to the furnace bottom 10b and melted.

  Therefore, in the present embodiment, as in the first embodiment, the support 12 is melted in a severe accident, and the lower support plate 11 is reliably and quickly dropped and melted, thereby increasing the amount of metal in the melt. Thus, the layered metal can be formed thick. Thereby, the event that the reactor pressure vessel 10 is damaged due to the metal being formed as a thin layer on the molten debris 14 can be prevented, and the success probability of the IVR for holding the core melt can be increased.

  As described above, according to the present embodiment, in addition to the effects of the first embodiment, when the support 12 is melted by having the thin wall portion 13a formed by thinning the wall thickness of the lower portion of the reactor core 13, the lower support The plate 11 can be reliably and quickly dropped onto the furnace bottom 10b.

  For example, as shown in FIG. 4, the thin wall portion 13a is formed by cutting out the lower wall surface from the outside, or the thin wall portion 13b is cut out from both sides as shown in FIG. It is also possible to use a thin portion 13c.

(Third embodiment)
FIG. 6 is an enlarged configuration diagram showing a part of a vertical section of a reactor pressure vessel in the third embodiment of the reactor according to the present invention.

  As shown in FIG. 6, inside the reactor pressure vessel 10, there are a reactor core tank 13 that surrounds the outer periphery of a reactor core (not shown), a lower support plate 11 that is fixed to the lower part of the reactor core tank 13 by a fixed plug 31, And a plurality of supports 12 which are erected on the furnace pressure vessel 10 and support the lower support plate 11 from below. For example, a bolt is used as the fixed plug 31.

  The fixed plug 31 is fixed by arranging a plurality of lower support plates 11 at a predetermined interval below the core tank 13. The fixed plug 31 is preferably a metal having a melting point lower than that of stainless steel, which is a metal used for the lower support plate 11 and the support 12, and a melting point higher than the normal operating temperature of the reactor pressure vessel 10.

  Further, in the present embodiment, the load of the lower support plate 11 cannot be supported by the core tank 13 alone, and when the support 12 is lost, the fixed plug 31 itself is broken, or the core tank 13 or the lower support plate of the fixed plug 31 is lost. The support plate 11 is configured to fall by dropping from the support plate 11.

  In the present embodiment configured as described above, the molten debris 14 drops to the reactor bottom 10b of the reactor pressure vessel 10 in a severe accident, so that the support 12 of the lower support plate 11 is first melted, and then the fixed plug 31. If the material has a low melting point, the lower support plate 11 melted by radiant heat and dispersed and fixed by the core tank 13 and the support 12 via the fixed plug 31 falls to the furnace bottom 10b. Melted.

  The fixed plug 31 does not have to be a material having a lower melting point than stainless steel. If the material is a material whose temperature is increased by radiant heat at the time of a severe accident and the mechanical strength is lowered, the fixed plug 31 is caused by the occurrence of a severe accident. Is easily damaged, and the lower support plate 11 is more likely to fall.

  As described above, according to the present embodiment, in addition to the effects of the first embodiment, the lower support plate 11 is fixed to the lower portion of the core tank 13 by the low melting point fixing plug 31, so that the support 12 is melted. After that, the fixed plug 31 is melted by radiant heat, and the lower support plate 11 can be reliably and quickly dropped onto the furnace bottom 10b.

  The present invention is not limited to the above embodiments, and various modifications can be made. For example, in each of the above embodiments, the load of the lower support plate 11 is received by the core tank 13 and the plurality of supports 12 in a distributed manner. You may make it receive. If comprised in this way, after the support 12 is fuse | melted, the lower support plate 11 can be dropped more reliably and rapidly.

  Moreover, in the said 2nd Embodiment, although the lower support plate 11 was fixed to the lower part of the reactor core tank 13 by welding, you may make it fix with a fixed plug other than this to the said 3rd Embodiment. .

  Furthermore, in the said 2nd Embodiment and each modification example, although the wall surface of the lower part of the core tank 13 was notched at right angles from one side or both sides, it became a thin part, but it becomes thin as it goes to the lower end of the core tank 13 besides this. You may form in such a taper-shaped thin part.

DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel 1a ... Pressure vessel wall 2 ... Insulating material 3 ... Molten debris 4 ... Gap 5 ... Molten oxide layer 6 ... Molten metal layer 7 ... Lower support plate 10 ... Reactor pressure vessel 11 ... Lower support plate 12 ... Support 13 ... Core tank 13a ... Thin-walled portion 14 ... Molten debris 31 ... Fixed plug

Claims (4)

A reactor pressure vessel having a core inside;
A reactor core surrounding the reactor core;
A support plate for supporting the core from below;
A support that is erected at the bottom of the reactor pressure vessel and supports the support plate from below,
A nuclear reactor, wherein the support plate is configured to fall when the support is melted. The core tank receives a part of the load of the support plate, and has a thin wall portion formed with a thin wall surface at the bottom of the core tank,
The reactor pressure vessel according to claim 1. The core tank receives a part of the load of the support plate, and has a fixed plug for fixing the core tank and the support plate;
The reactor pressure vessel according to claim 1 or 2, wherein The fixed plug is made of a material having a lower melting point than the support plate;
The reactor pressure vessel according to claim 3.

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