nuclear power plant

Abstract

To achieve with simple configuration, suppression of decrease of a coolant amount in a reactor pressure vessel and suppression of increase of pressure in the reactor pressure vessel until an isolation valve is fully closed.SOLUTION: A nuclear power plant 100 comprises a reactor pressure vessel 1, isolation valves 3, 4 and an enlarged reducer 7 inside a reactor containment vessel 2. The reactor pressure vessel and the isolation valves are connected by means other than welding. The inner diameter or the flow path cross-sectional area of the isolation valves is smaller than the inner diameter or the flow path cross-sectional area of a penetration portion 6 which penetrates the reactor containment vessel of piping (a main steam piping 5) in which steams generated in the reactor pressure vessel flow, and a steam flow volume measurement mechanism 8 measuring flow volume of steam between a small diameter portion and a large diameter portion of the enlarged reducer is arranged around the enlarged reducer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to nuclear power plants. [Background technology]

[0002] To operate a nuclear power plant safely and reliably, it is desirable to maintain and manage the release of radioactive materials from the nuclear power plant to the external environment within acceptable limits and at the lowest possible level. To this end, a nuclear power plant houses the reactor core, which contains a large amount of radioactive material, in a reactor pressure vessel (RPV). The reactor pressure vessel is further housed in a primary containment vessel (PCV), which is made of steel and / or reinforced concrete. This ensures that even if an abnormality occurs in the nuclear power plant, the release of radioactive materials from the reactor core to the external environment can be kept within acceptable limits and at the lowest possible level with high reliability.

[0003] In addition, in nuclear power plants, piping systems are installed to guide the fluid circulating in the reactor to the outside of the reactor pressure vessel in order to extract the energy required for power generation from the reactor. Furthermore, safety equipment is installed so that even if an abnormality such as damage occurs in the piping systems through which the fluid circulates to cool the reactor core, the abnormal event will be contained within the reactor containment vessel.

[0004] In the case of recently developed highly economical small light water reactors, even if a piping break occurs between the reactor pressure vessel and the reactor, a loss of coolant accident (LOCA) can be contained in a short time and its impact can be mitigated by fully closing a duplicated isolation valve (hereinafter referred to as "RPV-integrated isolation valve") directly attached to the reactor pressure vessel. Because such highly economical small light water reactors can mitigate the impact of a LOCA by installing an RPV-integrated isolation valve, the types of safety equipment (such as emergency core cooling equipment) required to deal with a LOCA, which was previously installed in conventional boiling water reactors (BWRs), and the capacity of the reactor containment vessel can be reduced.

[0005] However, even in such small, highly economical light water reactors, if a LOCA occurs due to a rupture of a main steam pipe connected to the reactor pressure vessel, it is desirable to limit the amount of steam flowing out as much as possible in order to maintain the decrease in the amount of coolant in the reactor pressure vessel and the increase in pressure inside the containment vessel within an allowable range until the RPV-integrated isolation valve is fully closed. For this purpose, small, highly economical light water reactors and conventional boiling water reactors are equipped with a flow restriction mechanism, as described in, for example, Patent Document 1. The flow restriction mechanism described in Patent Document 1 is a mechanism in which a restricted diameter portion is provided in the main steam nozzle of the reactor pressure vessel upstream of the ruptured portion of the pipe. The restricted diameter portion is also used to measure the steam flow rate, which is an important measurement item.

[0006] Some nuclear power plants are designed so that a flow restrictor is installed integrally with the reactor pressure vessel to limit as much as possible the amount of steam that escapes in the event of an abnormality such as a broken pipe, and a flow meter mechanism is used to measure the flow rate of steam (fluid) that escapes from the reactor pressure vessel through the flow restrictor to the outside. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 4-102095 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in conventional nuclear power plants, when the diameter of the pipe downstream of the main steam nozzle of the reactor pressure vessel is enlarged to keep the pressure loss and steam flow velocity of the main steam pipe within an allowable range, the isolation valve must be enlarged accordingly, which raises the problem of increased costs for the isolation valve. In addition, this increases the weight of the isolation valve, which necessitates the installation of a support mechanism to ensure earthquake resistance, which also raises the problem of increased costs for installing the support mechanism.

[0009] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to provide a nuclear power plant that suppresses increases in costs. Other objects of solving the problems will be described as appropriate in the description of the invention. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a nuclear power plant, in which a reactor pressure vessel, an isolation valve, and an expansion reducer are provided inside a reactor containment vessel, the reactor pressure vessel and the isolation valve are connected by a means other than welding, the inner diameter or the flow path cross-sectional area of the isolation valve is smaller than the inner diameter or the flow path cross-sectional area of a penetration portion that penetrates the reactor containment vessel of a piping through which steam generated in the reactor pressure vessel flows, and a steam flow measurement mechanism that measures the flow rate of the steam between a small diameter portion and a large diameter portion of the expansion reducer is arranged around the expansion reducer. The small diameter portion of the expansion reducer is located at a distance from the isolation valve that is at least 3.5 times the inner diameter of the isolation valve, and the expansion angle of the expansion reducer is in the range of 15 degrees to 35 degrees. The composition is as follows. Other means will be described later. [Effects of the Invention]

[0011] According to the present invention, costs can be reduced. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a configuration diagram of a nuclear power plant according to a first embodiment. [Figure 2] FIG. 10 is a configuration diagram of a nuclear power plant according to a second embodiment. [Figure 3] FIG. 1 is a configuration diagram of a nuclear power plant of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings. Each drawing is merely a schematic illustration to allow a sufficient understanding of the present invention. Therefore, the present invention is not limited to the illustrated examples. Furthermore, in each drawing, common or similar components are given the same reference numerals, and redundant explanations thereof will be omitted.

[0014] Note that nuclear power plants having the flow rate limiting mechanism described in Patent Document 1 or other flow rate limiting mechanisms have the following problems, and the present embodiment also aims to provide a nuclear power plant having a flow rate limiting function that can solve these problems.

[0015] In a nuclear power plant having a flow limiting mechanism as described in Patent Document 1, the diameter of the RPV-integrated isolation valve installed in the main steam pipe that conducts steam generated in the reactor pressure vessel from the reactor pressure vessel to the turbine is the same as the diameter of the main steam pipe to suppress an increase in pressure loss. In a nuclear power plant with such a configuration, as a countermeasure in the event of a main steam pipe rupture downstream of the RPV-integrated isolation valve, a dedicated flow limiter is installed to limit the amount of steam flowing out in the event of an abnormality in order to maintain the decrease in the amount of coolant in the reactor pressure vessel and the increase in pressure in the containment vessel within an allowable range until the RPV-integrated isolation valve is fully closed. Therefore, there is a problem in that the cost increases due to the flow limiter. This embodiment also aims to provide a nuclear power plant that achieves a flow limiting function in the main steam line without a dedicated flow limiter.

[0016] Another nuclear power plant with a flow rate limiting mechanism is one in which the diameter of the RPV-integrated isolation valve and the downstream piping are reduced to eliminate the need for a dedicated flow rate limiter. A nuclear power plant with this configuration can reduce the size of the isolation valve and improve seismic resistance. However, a nuclear power plant with this configuration has a problem in that the pressure loss in the main steam piping increases due to the provision of an expansion reducer downstream of the downsized RPV-integrated isolation valve, reducing the thermal efficiency of the plant. This embodiment is also intended to provide a nuclear power plant that reduces the pressure loss in the main steam piping and improves the thermal efficiency of the plant.

[0017] [Embodiment 1] <Configuration of a nuclear power plant> The configuration of a nuclear power plant 100 according to the first embodiment will be described below with reference to Fig. 1. Fig. 1 is a configuration diagram of the nuclear power plant 100.

[0018] Fig. 1 shows the configuration of a steam flow measurement mechanism 101 with a flow limiting function installed on a main steam line L1 connecting a reactor pressure vessel 1 located inside a reactor containment vessel 2 with a turbine facility (not shown) located outside the reactor containment vessel 2. In Fig. 1, the main steam line L1 is made up of isolation valves 3 and 4, an expansion reducer 7, and a main steam piping 5, and the main steam line L1 is linear, but in an actual nuclear power plant, the configuration and shape of the main steam line L1 may be different. Also, an actual nuclear power plant may have multiple main steam lines, and the present invention is applied to at least one of these systems.

[0019] As shown in Fig. 1, a nuclear power plant 100 according to the first embodiment includes a reactor pressure vessel 1 containing a reactor core in which nuclear fuel is loaded, and a reactor containment vessel 2 that holds the reactor pressure vessel 1 therein. The reactor pressure vessel 1 contains a reactor core 21, control rods (not shown), and the like. The reactor core 21 and the control rods (not shown) are immersed in reactor water 22. Although omitted from Fig. 1, turbine facilities (not shown) are provided outside the reactor containment vessel 2.

[0020] Inside the reactor containment vessel 2, a reactor pressure vessel 1, two isolation valves 3 and 4, and an expansion reducer 7 are arranged in this order. The isolation valve 3 is an RPV-integrated isolation valve. The isolation valve 4 is an isolation valve located downstream (on the outlet side) of the isolation valve 3 to provide multiple shutoff functions for the steam (fluid). In the event of an abnormality such as a piping rupture, the isolation valves 3 and 4 shut off the main steam line L1 to prevent the steam (fluid) generated inside the reactor pressure vessel 1 from leaking to the outside. In this explanation, it is assumed that the isolation valve 3 is located upstream (on the reactor pressure vessel 1 side) and the isolation valve 4 is located downstream (on the turbine facility side, not shown). A main steam pipe 5 is connected to the expansion reducer 7. The main steam pipe 5 is arranged to penetrate the bulkhead of the reactor containment vessel 2. As a result, the main steam pipe 5 is drawn from inside the reactor pressure vessel 2 to the outside, and guides the steam generated inside the reactor pressure vessel 1 to a turbine facility (not shown) outside the reactor pressure vessel 2. The main steam pipe 5 is made up of a plurality of pipes connected together, and is connected to the turbine facility (not shown). In addition to the main steam line L1, various pipes such as a feedwater pipe are connected to the reactor pressure vessel 1.

[0021] The isolation valves 3 and 4 are connected to the reactor pressure vessel 1 without a weld. Here, "without a weld" means a state in which they are connected by direct attachment, flange connection, or other means other than welding. The nuclear power plant 100 is equipped with a steam flow measurement mechanism 101 with a flow limiting function to limit the amount of steam that flows out in the event of a rupture in the main steam pipe 5 connected to the isolation valve 4.

[0022] The steam flow measurement mechanism with flow limiting function 101 has isolation valves 3 and 4, a main steam pipe 5, an expansion reducer 7, and a steam flow measurement mechanism 8. The expansion reducer 7 has an expansion section 7a whose bore (inner diameter) is expanded. The expansion reducer 7 is arranged so that the small diameter section 7aa of the expansion section 7a faces the isolation valves 3 and 4, and the large diameter section 7ab of the expansion section 7a faces the main steam pipe 5. The steam flow measurement mechanism 8 measures the flow rate of steam between the small diameter section 7aa and the large diameter section 7ab of the expansion section 7a of the expansion reducer 7.

[0023] The steam flow measurement mechanism 101 with flow limiting function has an expansion reducer 7 between the isolation valve 4 and the main steam pipe 5 to prevent the pressure loss of the entire main steam line L1 from the reactor pressure vessel 1 to the turbine facility (not shown) from rising above the allowable range.

[0024] The small-diameter portion 7aa of the expansion reducer 7 is located at a distance B1 from the downstream isolation valve 4, at least 3.5 times the inner diameter A1 of the isolation valve 4. The expansion angle of the expansion reducer 7 ranges from 15 to 35 degrees. Here, the "expansion angle of the expansion reducer 7" refers to the angle of the inner diameter of the expansion reducer 7 that expands as it moves from the small-diameter portion 7aa to the large-diameter portion 7ab. The steam flow measurement mechanism 8 generates pressure loss when measuring the steam flow rate, but by configuring the expansion reducer 7 in this way, the pressure loss can be kept within a specified range. Therefore, the steam flow measurement mechanism 8 can maintain good steam flow rate measurement.

[0025] The diameter (inner diameter or flow path cross-sectional area) of the isolation valves 3, 4 should be at least 25% (inner diameter) or 44% (flow path cross-sectional area) smaller than the diameter (inner diameter or flow path cross-sectional area) of the main steam pipe 5 at the penetration 6 where it penetrates the bulkhead of the reactor containment vessel 2.

[0026] The steam flow measurement mechanism with flow restriction function 101 indirectly measures the pressure loss caused by the expansion of the inner diameter of the expansion reducer 7 by measuring the flow rate of steam passing through the expansion reducer 7 with the steam flow measurement mechanism 8. To generate a pressure loss that allows appropriate flow measurement, the expansion angle of the expansion reducer 7 should be in the range of 15 to 35 degrees. Pressure taps 9 and 10 of the steam flow measurement mechanism 8 are installed at the small diameter portion 7aa and the large diameter portion 7ab of the expansion reducer 7. The steam flow measurement mechanism with flow restriction function 101 also ensures a distance B1 between the isolation valve 4 and the small diameter portion 7aa of the expansion reducer 7, which is the straight pipe length of at least 3.5 times the inner diameter A1 of the isolation valve 4, thereby avoiding interference with the flow rate measurement due to turbulence occurring downstream of the isolation valve 4.

[0027] In the nuclear power plant 100 according to this embodiment, the diameters of the isolation valves 3 and 4, which are connected to the reactor pressure vessel 1 without a weld seam, are made smaller than the diameter of the main steam pipe 5 at the penetration 6. In addition, an expansion reducer 7 equipped with a flow rate measurement device is installed at one location between the isolation valves 3 and 4 and the reactor containment vessel 2, thereby realizing a steam flow rate measurement mechanism 101 with flow rate limiting function, which has a reactor-integrated isolation valve mechanism on the main steam line L1 that has a flow rate limiting function and a flow rate measurement function.

[0028] <Comparison between Nuclear Power Plant of Comparative Example and Nuclear Power Plant of First Embodiment> Here, in order to explain the action and effect of the steam flow measurement mechanism 101 with a flow rate limiting function in the nuclear power plant 100 according to this embodiment, the configuration of a nuclear power plant 1000 of a comparative example will be explained with reference to Fig. 3. Fig. 3 is a configuration diagram of the nuclear power plant 1000 of the comparative example. The nuclear power plant 1000 of the comparative example corresponds to a conventional nuclear power plant.

[0029] As shown in FIG. 3, the nuclear power plant 1000 of the comparative example differs from the nuclear power plant 100 of the present embodiment (see FIG. 1) in that the main steam line L3 is composed of a nozzle 1007, isolation valves 1003 and 1004, and a main steam pipe 1005, which are integrally formed with the reactor pressure vessel 1, and that a pressure outlet tap of the steam flow measurement mechanism 8 is installed on the reactor pressure vessel 1 and the nozzle 1007. The nozzle 1007 functions as a flow restrictor that limits the amount of steam that flows out in the event of an abnormality. The nozzle 1007 has an expanding diameter (inner diameter), and the isolation valve 1003 is located on the larger diameter side. The main steam line L3 penetrates a bulkhead at a penetration 1006. In the event of an abnormality, such as a rupture of a pipe, the isolation valve 1003 shuts off the main steam line L3 to prevent steam (fluid) generated inside the reactor pressure vessel 1 from flowing out.

[0030] In the nuclear power plant 1000 of the comparative example, a nozzle 1007 functioning as a flow restrictor is provided integrally with the reactor pressure vessel 1 in order to restrict the amount of steam flowing out as much as possible in the event of some abnormality such as a piping breakage, and a steam flow measuring mechanism 8 measures the flow rate of steam (fluid) flowing out from the reactor pressure vessel 1 to the nozzle 1007. Since the isolation valves 1003 and 1004 are arranged downstream (on the outlet side) of the nozzle 1007, the diameters of the isolation valves 1003 and 1004 are larger than the diameter of the main steam piping 1005. In the nuclear power plant 1000 of the comparative example, the isolation valves 1003 and 1004 are larger than the isolation valves 3 and 4 (see FIG. 1 ) of the nuclear power plant 100 according to the first embodiment, and therefore the cost of the isolation valves 1003 and 1004 increases. Furthermore, in this case, the weight of the isolation valves 1003 and 1004 increases, and a support mechanism 1008 must be provided to ensure earthquake resistance, which increases the installation cost of the support mechanism 1008.

[0031] In contrast, the nuclear power plant 100 according to the first embodiment is equipped with a steam flow measurement mechanism 101 with a flow rate limiting function, which can limit the amount of steam flowing out as much as possible when some abnormality, such as a piping breakage, occurs in the main steam line L1 inside the containment vessel 2. Therefore, in the nuclear power plant 100 according to the first embodiment, the diameters of the isolation valves 3 and 4 (see FIG. 1 ) can be made smaller than the diameters of the isolation valves 1003 and 1004 of the nuclear power plant 1000 of the comparative example. In the nuclear power plant 100 according to the first embodiment, the isolation valves 3 and 4 (see FIG. 1 ) can be made smaller than the isolation valves 1003 and 1004 of the nuclear power plant 1000 of the comparative example, and therefore the cost can be reduced by the amount of the smaller isolation valves 3 and 4 (see FIG. 1 ). Note that the isolation valves 3 and 4 can be made smaller by, for example, 25% or more than the isolation valves 1003 and 1004 of the nuclear power plant 1000 of the comparative example. Furthermore, because the weight of the isolation valves 3 and 4 can be reduced, unlike the nuclear power plant 1000 of the comparative example, it is not necessary to provide a support mechanism 1008 for ensuring earthquake resistance. Therefore, the nuclear power plant 100 according to the first embodiment can reduce installation costs by the amount corresponding to the elimination of the support mechanism 1008. Furthermore, because the nozzle 1007 for flow rate restriction can be eliminated, installation costs can be reduced by the amount corresponding to the elimination of the nozzle 1007. Furthermore, a simple configuration can be used to suppress the decrease in the amount of coolant in the reactor pressure vessel 1 until the isolation valves 3 and 4 are fully closed, and to suppress the increase in pressure inside the containment vessel. Furthermore, it is possible to reduce the cost of the RPV-integrated isolation valves, improve earthquake resistance by reducing the weight of the isolation valves, realize a flow rate restriction function in the event of a LOCA, and measure the steam flow rate, thereby improving both safety and economy.

[0032] <Major features of nuclear power plants> (1) As shown in FIG. 1 , in a nuclear power plant 100 according to this embodiment, a reactor pressure vessel 1, isolation valves 3 and 4, and an expansion reducer 7 are provided in this order inside a reactor containment vessel 2. The reactor pressure vessel 1 and the isolation valves 3 and 4 are connected by means other than welding. Here, "means other than welding" means direct mounting, flange connection, or other means. The inner diameter or flow path cross-sectional area of the isolation valves 3 and 4 is smaller than the inner diameter or flow path cross-sectional area of a penetration 6 of a main steam pipe 5, through which steam generated in the reactor pressure vessel 1 passes, that penetrates the reactor containment vessel 2. A steam flow measurement mechanism 8 is disposed around the expansion reducer 7 to measure the flow rate of steam between a small diameter portion 7aa and a large diameter portion 7ab of the expansion reducer 7.

[0033] The nuclear power plant 100 according to this embodiment can measure the steam flow rate and limit the amount of steam that flows out in the event of an abnormality, without providing a dedicated flow restrictor such as the nozzle 1007 (see FIG. 3 ) of the nuclear power plant 1000 of the comparative example. The nuclear power plant 100 according to this embodiment 1 can reduce the size of the isolation valves 3 and 4, thereby reducing costs accordingly. Furthermore, since the weight of the isolation valves 3 and 4 can be reduced, it is not necessary to provide the support mechanism 1008 for ensuring earthquake resistance as in the nuclear power plant 1000 of the comparative example. Therefore, the installation cost can be reduced by the amount corresponding to the elimination of the support mechanism 1008. Furthermore, since the nozzle 1007 for restricting the flow rate can be eliminated, the installation cost can be reduced by the amount corresponding to the elimination of the nozzle 1007.

[0034] (2) As shown in FIG. 1 , in the nuclear power plant 100 according to this embodiment, the small diameter portion 7aa of the expansion reducer 7 is installed at a position that is 3.5 times or more the inner diameter of the isolation valves 3 and 4 away from the isolation valves 3 and 4, and the expansion angle of the expansion reducer 7 is preferably in the range of 15 degrees to 35 degrees.

[0035] The nuclear power plant 100 according to this embodiment can keep the pressure loss within a range defined by regulations, and therefore can maintain good steam flow rate measurement.

[0036] (3) In the nuclear power plant 100 according to this embodiment, the inside diameter of the isolation valves 3 and 4 is preferably smaller than the inside diameter of the penetration portion 6 of the main steam pipe 5 by at least 25% or more.

[0037] The nuclear power plant 100 according to this embodiment can quickly fully close the isolation valves 3 and 4 if any abnormality occurs. This allows a loss of coolant event (LOCA) to be resolved in a short time and its impact to be mitigated. Furthermore, the nuclear power plant 100 according to this embodiment can reduce the size of the isolation valves 3 and 4, thereby reducing costs accordingly. Furthermore, because the weight of the isolation valves 3 and 4 can be reduced, it is not necessary to provide the support mechanism 1008 for ensuring earthquake resistance as in the nuclear power plant 1000 of the comparative example. Therefore, the installation costs can be reduced by the amount of the support mechanism 1008 being omitted.

[0038] (4) In the nuclear power plant 100 according to this embodiment, the flow path cross-sectional area of the isolation valves 3 and 4 is preferably smaller than the flow path cross-sectional area of the penetration 6 of the main steam pipe 5 by 44% or more.

[0039] The nuclear power plant 100 according to this embodiment can quickly fully close the isolation valves 3 and 4 if any abnormality occurs. This allows a loss of coolant event (LOCA) to be resolved in a short time and its impact to be mitigated. Furthermore, the nuclear power plant 100 according to this embodiment can reduce the size of the isolation valves 3 and 4, thereby reducing costs accordingly. Furthermore, because the weight of the isolation valves 3 and 4 can be reduced, it is not necessary to provide the support mechanism 1008 for ensuring earthquake resistance as in the nuclear power plant 1000 of the comparative example. Therefore, the installation costs can be reduced by the amount of the support mechanism 1008 being omitted.

[0040] [Embodiment 2] The configuration of the nuclear power plant 100A will be described below with reference to Fig. 2. Fig. 2 is a configuration diagram of the nuclear power plant 100A.

[0041] As shown in FIG. 2, the nuclear power plant 100A according to the second embodiment differs from the nuclear power plant 100 according to the first embodiment (see FIG. 1) in that it has a steam flow rate measuring mechanism 101A with a flow rate limiting function instead of the steam flow rate measuring mechanism 101 with a flow rate limiting function.

[0042] The steam flow measurement mechanism with flow limiting function 101A has a main steam line L2. The main steam line L2 is bent twice at right angles inside the reactor containment vessel 2. In this configuration, a piping bend 11, such as a 90-degree elbow, is provided upstream of the expansion reducer 7. The small diameter portion 7aa of the expansion portion 7a of the expansion reducer 7 is located at a position 3.0 times or more the inner diameter of the piping bend 11 away from the piping bend 11. The expansion angle of the expansion reducer 7 is in the range of 15 degrees to 35 degrees.

[0043] In the nuclear power plant 100A, a pipe bend 11 is installed downstream of the isolation valves 3 and 4 for reasons such as absorbing thermal expansion of the main steam pipe 5. In addition, in order to avoid interference with the flow rate measurement due to the pipe bend 11, it is preferable that the small diameter portion 7aa of the expansion reducer 7 is installed at a position at a distance B2 that is 3.0 times or more the inner diameter of the pipe bend 11 from the pipe bend 11.

[0044] 2, the main steam line L2 is bent twice at right angles, but the configuration and shape of the main steam line L2 may differ in an actual nuclear power plant. Also, an actual nuclear power plant may have multiple main steam lines, and the present invention is applied to at least one of the lines.

[0045] In the nuclear power plant 100A according to this embodiment, the main steam line L2 has a bent shape inside the reactor containment vessel 2, so the size (width) of the reactor containment vessel 2 can be made smaller than that of the nuclear power plant 100 according to the first embodiment (see FIG. 1).

[0046] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. It is possible to replace part of the configuration of the embodiments with other configurations, and it is also possible to add other configurations to the configuration of the embodiments. Furthermore, it is possible to add, delete, or replace part of each configuration with other configurations. [Explanation of symbols]

[0047] 1. Reactor Pressure Vessel (RPV) 2. Primary Containment Vessel (PCV) 3,4,1003,1004 Isolation valve 5,5A,1005 Main steam piping (piping) 6,1006 Penetration 7 Expanding Reducer 7a Enlarged section 7aa small diameter section 7ab Large diameter part 8 Steam flow measurement mechanism 9,10 Pressure outlet tap 11 Pipe bends 21 Reactor Core 22 Reactor water 100,100A,1000 Nuclear Power Plant 101,101A Steam flow measurement mechanism with flow limiting function 1007 Nozzle (flow restriction mechanism) 1008 Support Organization A1,A2 Inner diameter B1,B2 distance L1, L2, L3 main steam lines

Claims

1. A reactor pressure vessel, an isolation valve, and an expansion reducer are provided inside a reactor containment vessel, the reactor pressure vessel and the isolation valve are connected by means other than welding; an inner diameter or a flow path cross-sectional area of the isolation valve is smaller than an inner diameter or a flow path cross-sectional area of a penetration portion of a piping through which steam generated in the reactor pressure vessel flows, the penetration portion penetrating the reactor containment vessel; a steam flow rate measuring mechanism that measures a flow rate of the steam between the small diameter portion and the large diameter portion of the expansion reducer is disposed around the expansion reducer; the small diameter portion of the expansion reducer is located at a distance from the isolation valve that is at least 3.5 times the inner diameter of the isolation valve; The expansion angle of the expansion reducer ranges from 15 degrees to 35 degrees. A nuclear power plant characterized by:

2. A reactor pressure vessel, an isolation valve, and an expansion reducer are provided inside the reactor containment vessel, the reactor pressure vessel and the isolation valve are connected by means other than welding; an inner diameter or a flow path cross-sectional area of the isolation valve is smaller than an inner diameter or a flow path cross-sectional area of a penetration portion of a piping through which steam generated in the reactor pressure vessel flows, the penetration portion penetrating the reactor containment vessel; a steam flow rate measuring mechanism that measures a flow rate of the steam between the small diameter portion and the large diameter portion of the expansion reducer is disposed around the expansion reducer; A piping bend is provided upstream of the expansion reducer, the small diameter portion of the expansion reducer is disposed at a position away from the pipe bend that is 3.0 times or more the inner diameter of the pipe bend, The expansion angle of the expansion reducer ranges from 15 degrees to 35 degrees. A nuclear power plant characterized by:

3. A reactor pressure vessel, an isolation valve, and an expansion reducer are provided inside the reactor containment vessel, the reactor pressure vessel and the isolation valve are connected by means other than welding; an inner diameter or a flow path cross-sectional area of the isolation valve is smaller than an inner diameter or a flow path cross-sectional area of a penetration portion of a piping through which steam generated in the reactor pressure vessel flows, the penetration portion penetrating the reactor containment vessel; a steam flow rate measuring mechanism that measures a flow rate of the steam between the small diameter portion and the large diameter portion of the expansion reducer is disposed around the expansion reducer; The inside diameter of the isolation valve is at least 25% smaller than the inside diameter of the penetration of the piping. A nuclear power plant characterized by:

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