JPH0529279B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to light water nuclear reactors, and uses natural forces to transfer thermal energy from core decay heat released into the reactor containment vessel over a long period of time in the event of a loss of coolant accident. The present invention relates to a natural heat dissipation type reactor containment vessel suitable for removal to the outside. [Prior Art] As an example of the prior art, the reactor containment vessel of a current boiling water reactor and its auxiliary equipment, a residual heat removal system, will be described with reference to FIG. The reactor containment vessel 2 of a boiling water reactor is a pressure suppression type, and includes a dry well 3 containing the reactor pressure vessel 1, a suppression chamber 4 containing a suppression pool 5, and further a dry well 3 and a suppression chamber 4 containing a suppression pool 5. It consists of a vent pipe 6 that connects a suppression pool 5. In a hypothetical loss of coolant accident, reactor pressure vessel 1
The high-temperature, high-pressure steam discharged into the dry well 3 passes through the vent pipe 6 and is discharged into the suppression pool 5 where it is condensed. This suppresses a transient pressure rise within the reactor containment vessel 2. In addition, a residual heat removal system 7 is installed to deal with core decay heat that occurs over a long period of time. After loss of coolant accident
After the ECCS is activated and the core is re-submerged, core decay heat is transferred to the dry well by ECCS water and further to the suppression pool 5 via the vent pipe 6. The heat of the pool water is removed to the outside of the reactor containment vessel by the heat exchanger 9 of the residual heat removal system 7. [Problems to be solved by the invention] In the reactor containment vessel of the boiling water reactor of the above-mentioned prior art, a residual heat removal system is installed to deal with the removal of core decay heat over a long period of time. However, the cost is high and the pool water containing fission products is routed outside the reactor containment vessel.
There were problems such as a slight decrease in inherent safety due to the installation of dynamic equipment such as pumps and valve heat exchangers. An object of the present invention is to provide a reactor containment vessel suitable for significantly increasing the natural heat radiation from the walls of the reactor containment vessel of the prior art and improving economic efficiency and inherent safety. [Means for Solving the Problems] The means for achieving the above object is to provide a steel reactor containment vessel containing a reactor pressure vessel of light water reactor equipment, with a plurality of reactor containment vessels inside the walls of the reactor containment vessel. The protrusions are installed only in the dry well space containing the reactor pressure vessel and the gas phase part in the suppression chamber containing pool water, and the protrusions are installed around the outer periphery of the suppression chamber. This is a natural heat dissipation type reactor containment vessel characterized by being equipped with an outer peripheral pool in contact with the steel wall of the reactor containment vessel. [Operation] According to the means for achieving the above object, in the gas phase part in the suppression chamber containing the dry well space and the pool water, the projection part
It is possible to increase the heat transfer area and reduce the heat transfer inhibition caused by the formation of a thin film layer on the wall surface of non-condensable gas, so it is possible to increase the steam condensation heat transfer coefficient on the wall surface. The heat transferred to the pool water inside the tunnel chamber causes convection in the pool water, which contacts the steel walls of the reactor containment vessel and transfers heat to the steel walls. Convection is promoted in the pool water in the outer pool that is in contact with the steel wall, and the water in the outer pool comes in contact with the steel walls of the reactor containment vessel one after another, absorbing heat from the steel walls to the pool water in the outer pool, and dissipating the heat to the outer pool. The effect of
Each of these effects promotes natural heat dissipation from the reactor containment vessel walls without relying on dynamic equipment. [Example] Examples of the present invention will be described below. The natural heat dissipation type reactor containment vessel to which the present invention is directed is designed to remove core decay heat over a long period of time by natural heat dissipation from the walls of the reactor containment vessel. It is characterized by the installation of multiple protrusions (fins). After loss of coolant, the gas phase inside the reactor containment vessel is filled with a mixture of high-temperature, high-pressure steam and the air that was initially present. During the steam condensation process on the walls of the reactor containment vessel, a thin film of non-condensable air is formed on the condensing surface, which tends to significantly deteriorate the condensation heat transfer coefficient. This is because a laminar flow region where the atmosphere is stagnant is formed near the condensing surface, and non-condensable gas accumulates in this region. Therefore, in the present invention, a plurality of protrusions (fins) having the shape of No. 4 in Table 1 are provided on the inner wall of the reactor containment vessel.
was installed. This not only increases the heat transfer area between the atmosphere inside the reactor containment vessel and the walls of the containment vessel, but also increases the heat transfer coefficient without being affected by air accumulation on the condensing surface, and increases the heat transfer coefficient from the containment vessel space to Natural heat dissipation can be increased. Depending on the shape of the steam condensation surface (heat transfer surface), as shown in Table 1, it is possible to avoid the influence of the thin film layer of air and increase the steam heat transfer performance.

[Table] **Containment vessel wall shape of the present invention The effect of improving heat transfer by the protrusions (fins) will be explained below with reference to FIG. An atmosphere in which high-temperature non-condensable gas (air) and steam coexist (the atmosphere inside the reactor containment vessel after a loss of coolant accident has approximately the same amount of air and steam) and steam condensation on the low-temperature side. When considering heat transfer between the surface (the reactor containment vessel) and the steam condensing surface, a homogeneous mixed atmosphere of air and steam (the atmosphere is activated by the driving force from the release of coolant from the fracture) is transferred to the steam condensing surface. The steam is condensed and the heat transfer is very good. However, a part of the air in the atmosphere, which has a poor heat transfer coefficient, stagnates on the steam condensation surface, forming a very thin laminar flow region, as shown in FIGS. 1 and 2. Due to this air thin film layer, heat transfer between the air/steam mixed atmosphere inside the air/steam mixture atmosphere and the vapor condensing surface is performed only by vapor diffusion through the air thin film layer, resulting in extremely poor heat transfer. Regarding the relationship between the ratio of the amount of air to the amount of steam and the heat transfer coefficient, as shown in FIGS. 3 and 4, it is known that as the ratio of the amount of air increases, the heat transfer coefficient deteriorates. Since the above-mentioned thin air film is a laminar flow region formed very close to the vapor condensing surface (approximately 1 to 2 mm), if a protrusion from the condensing surface is installed, it will not be formed on the surface of the protrusion. (There is no problem even if it may be formed in a minute part at the base of the protrusion.) In the present invention, by utilizing the effect of the protrusion (fin) described above, the air/steam mixed atmosphere area and the protrusion (fins), and the protrusions (fins) increase the heat transfer area, promoting natural heat radiation from the walls of the reactor containment space. More specific embodiments of the present invention based on the above principle of operation will be described with reference to the drawings. FIG. 1 shows a reactor containment vessel of a self-radiating nuclear reactor according to the present invention. In Figure 1, the natural heat dissipation type reactor containment vessel 2
1 is a dry well 3 in which a protrusion (fin) 14 is provided on the inner wall of a space containing a reactor pressure vessel 1, and a suppressor in which a protrusion (fin) 14 is provided in an inner wall of a space containing a suppression pool 5. It is composed of a vent pipe 6 that connects the suppression chamber 4, dry well 3, and suppression pool 5, and an outer peripheral pool 11 installed around the outer periphery of the suppression chamber 4. In the unlikely event that a loss of coolant accident occurs, high-temperature, high-pressure steam will be released from the reactor pressure vessel 1 to the dry well 3, the pressure and temperature inside the dry well 3 will rise rapidly, and the atmosphere inside the dry well 3 will be vented. tube 6
It is discharged into the suppression pool 5 through the suppression pool 5.
The steam is completely condensed in the suppression pool 5, suppressing a transient pressure rise inside the containment vessel 2. Therefore, the air in the dry well 3 passes through the pool 5 and moves into the suppression chamber 4 space, increasing the pressure in the suppression chamber space. For a long period after the accident, the core decay heat will be reduced to ECCS.
It is absorbed by water and transferred to the dry well 3, and further transferred to the suppression pool 5 via the vent pipe 6, where it is distributed to the dry well space, the suppression chamber space, and the suppression pool water. Ru. The protrusion (fin) 14 installed on the inner wall of the reactor containment vessel 2 space increases the heat transfer coefficient and heat transfer area, and its shape effect reduces the influence of heat transfer inhibition caused by the thin air film layer. Promote heat transfer of the core decay heat released into the dry well 3 and suppression chamber 4 spaces to the reactor containment vessel 2 walls, and increase the amount of natural heat radiation from the reactor containment vessel 2 walls. . In addition, the core decay heat transferred to the suppression pool 5 is transferred to the outer peripheral pool 5 through the inner wall of the pool 5.
Transfer to water. The specific heat removal capacity is shown below. A comparison of the amount of heat removed from the reactor containment vessel space wall when the protrusion (fin) of the present invention is employed and when it is not employed is shown below. As a result, the amount of heat removed from the space when the protrusion (fin) is installed is about 2 to 10 times as much as when it is not installed, as shown in Table 2.

〔Effect of the invention〕

According to the present invention, the suppression chamber, to which the heat in the reactor containment vessel is transferred in the event of an accident, can be efficiently removed by water cooling by being in contact with the outer circumferential pool, and furthermore, the suppression chamber can be efficiently removed by water cooling. This increases the heat transfer area between the containment vessel internal atmosphere and the containment vessel wall, reduces the inhibition of heat transfer by the air thin film layer, increases heat transfer, and increases the heat transfer area between the containment vessel internal atmosphere and the containment vessel wall. By increasing heat dissipation, it is possible to improve inherent safety and improve economic efficiency by eliminating or reducing the need for a residual heat removal system.

[Brief explanation of the drawing]

FIG. 1a is a vertical cross-sectional view of a nuclear reactor containment vessel according to an embodiment of the present invention, FIG. 1b is an enlarged cross-sectional view of the section A in FIG. e, f,
g, h are perspective views showing respective modifications of the protrusion shown in Fig. 1b, Fig. 3 are graphs of each characteristic caused by the protrusion of Fig. 1b, FIG. 4 is a graph showing the relationship between natural heat radiation and core decay heat in an embodiment of the present invention, FIG. 5 is a vertical cross-sectional view of a conventional reactor containment vessel, and FIG. FIG. 6b is an enlarged sectional view of the arrow A in FIG. 6a. 1...Reactor pressure vessel, 2...Reactor containment vessel, 3
...dry well, 4...suppression chamber,
5... Suppression pool, 6... Vent pipe, 7...
Residual heat removal system, 8... Residual heat removal system pump, 9... Residual heat removal system heat exchanger, 10... Spray header, 1
1...Outer circumference pool, 12...Outer circumference pool space, 13
...Reactor building, 14...Protrusion (fin).

[Claims]

1. When assembling a fuel assembly that includes a support grid having a large number of grid spaces, and fuel rods that are inserted into the grid spaces of the support grid and supported by the wall surfaces forming the grid spaces, thin-walled strip-shaped A lattice member consisting of a strap forming a lattice member and a plurality of strap members erected at regular intervals in the longitudinal direction on one surface of the strap, formed by the strap and two adjacent strap members. The fuel rod is inserted into the U-shaped groove from the open side by moving in a direction perpendicular to the axis of the fuel rod, and then the next lattice member is inserted between the strap members of the lattice member into which the fuel rod has been inserted. The process of fixing the other side of the strap and inserting the fuel rod into the groove of the next fixed lattice member is repeated, and then the fuel rods are finally inserted to form a layered lattice member. A method for assembling a fuel assembly, comprising fixing a strap having a similar shape to the above strap between the strap members. 2. A first lattice member comprising a thin strip-shaped strap and a plurality of strap members erected at regular intervals in the longitudinal direction and each having a protrusion at a free end, and the first lattice member. The grid members have the same shape and are arranged in layers between the ends of the strap members in the same direction as the first grid members, and each strap has an adjacent first grid member.