JPH0464038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to nuclear reactors, and more particularly to nuclear reactors in which a coolant, such as water, at a critical temperature and pressure is circulated through a reactor core located within a reactor vessel. The reactor core has fuel and is located in the lower region of the reactor vessel. The reactor also includes a control rod assembly. A control rod assembly includes a control rod, a support for the control rod, and a drive shaft for a number of control rods and other associated elements. Generally, the core, together with the fuel assembly, is called the lower internals of a nuclear reactor. Control rods and control rod guides are called the upper internals of a nuclear reactor. The control rods are movable by drive shafts between upper reactor internals and recesses or control rod guide tubes in the reactor core.

The control rods are mounted in clusters on the drive shaft by spiders. The control rods include a control rod cluster (RCC) that has a large absorption cross section for neutrons. This control rod cluster is
It is used to reduce reactor power or shut down the reactor, and is moved between the core and the guide system many times during the reactor's fuel cycle. There are also so-called gray control rods, which have a much smaller neutron absorption cross-section than the highly absorbent control rod clusters, and are useful for load following, ie controlling or slowing down the power of the reactor. The gray control rod is
During the fuel cycle of a nuclear reactor, they are moved between the reactor core and the guide system significantly more times than highly absorbent control rod clusters (typically about 5,600 times). Additionally, there are water rejection rod clusters (WDRC), these water rejection rods having the same diameter as those of the control rod cluster.
The water removal rod is used to maintain a relatively large amount of water coolant in the reactor core during the early stages of reactor operation, and to increase the amount of water coolant by removing the water removal rod during subsequent reactor operation. used for. Such water displacement rod clusters are typically in the core for the first 60% of the fuel cycle and are raised into the upper internals for the remainder or 40% of the fuel cycle.

Generally, the control rods and gray control rods of each cluster are supported by a cruciform support and are movable within a hollow cruciform guide. Traditionally, the same guide devices have included grooves through which the coolant flows. Water exclusion rod clusters are not so protected. A number of these water displacement rods are conventionally movable within a rectangular or square guide device with holes through which coolant flows. Later in the fuel cycle, the water displacement rod cluster is moved into the perforated guide and retained there. All guiding devices are part of the upper internals of the reactor.

Coolant flows vertically through the core and into the upper internals. Vessel outlet nozzles are located between the ends of the upper internals to provide horizontal flow of coolant. The coolant then flows generally laterally through the control rod assembly as it passes to the outlet nozzle. For example, the vertical flow speed of coolant through the core is approximately 5 m/sec. The flow velocity through the nozzle is about 15 m/sec, and the lateral flow velocity in some parts of the upper internals can be as high as 9-12 m/sec. At these speeds, the coolant causes the vertical members, particularly the water displacement rod clusters, to vibrate late in the fuel cycle.

Mechanisms that cause this vibration include, for example, vortex shedding, turbulent buffetting or vibratory hydroelastic interaction, and cavitation.

It has been proposed to provide a calandria structure directly above the reactor core with tubes for receiving and guiding the control rods, with the calandria structure supporting the control rods. In the calandria, cooling water from the core is directed in a relatively high-velocity transverse flow to radial exit nozzles outside the calandria, but the control rods are protected from the high-velocity cooling water by the tubes described above. There is.

However, such calandrias are complex because they require multiple closely spaced tubes, one for each control rod. The large number of tubes limits the radial flow area, resulting in high flow velocities and relatively high pressure drops.

The aim of the invention is therefore to obtain a nuclear reactor which has all the advantages of the calandria mentioned above and eliminates the disadvantages.

To achieve the above object, the present invention provides a vessel, a core barrel suspended within the vessel by a support flange, a reactor core supported within the core barrel, a reactor core movably supported within the vessel, A control rod assembly guided by a control rod guide device vertically installed in a plenum above the reactor core, and connected to a yoke member that supported the control rod assembly in order to move the control rods into and out of the reactor core. a drive shaft, the vessel having at least one inlet nozzle for supplying coolant to the core, and at least one inlet nozzle for discharging incoming coolant from the vessel after passing through the interior of the core. and an outlet nozzle, further comprising a calandria extending across the vessel above the core, the calandria including a plurality of hollow members mounted between an upper support plate and a lower support plate. , the lower support plate is provided with holes through which coolant flowing axially upward from the reactor core can pass, and the calandria are radially open and communicate with the outlet nozzle, in a nuclear reactor,
The calandria is arranged at a sufficient distance above the reactor core, and the yoke member that supported the control rod assembly is movable within a space between the calandria and the reactor core. The drive shaft extends through and is guided by the hollow member and is protected from coolant flowing across an outer surface of the hollow member to the outlet nozzle, the outlet nozzle being an annular flow path disposed substantially below the calandria and between the calandria and the outlet nozzle to guide coolant from the calandria to the outlet nozzle; further, the support flange of the core barrel is disposed below the outlet nozzle that is in open communication with the interior of the calandria via the annular flow path;
It is characterized in that it is disposed above the inlet nozzle that is in open communication with the core inlet area at the bottom of the vessel via an annular space surrounding the core barrel.

With this configuration, it is possible not only to obtain a reactor that achieves the above-mentioned objectives, but also to make the core barrel substantially shorter, and the support flange of the core barrel necessitates an annular flow path and an annular space. separated. This eliminates the need for the outlet nozzle to extend outward through the annular space between the core barrel and the vessel, eliminating the need for special sealing devices and eliminating leakage problems.

Next, before describing the embodiment of the present invention shown in FIG. 7, reference examples of the nuclear reactor structure shown in FIGS. 1 to 6 will be described.

1 to 6, the nuclear reactor 11 has a cylindrical body 15 closed at the bottom by a spherical bottom 17.
It is equipped with a pressure vessel having a The container comprises a hemispherical head 19 bolted to the body 15 at a flange 21. The body 15 includes a plurality of outlet nozzles 25 and a plurality of inlet nozzles 23 distributed around the circumference thereof. There are typically four inlet nozzles 23 interposed in pairs between four outlet nozzles 25. In the lower region of the barrel 15 there is a reactor core 27 . The core is fuel assembly 2
9 and a control rod guide tube 31 for receiving a control rod (not shown). The fuel assembly 29 and the control rod guide tube 31 are mounted between an upper core plate 33 and a lower core plate 35. The control rods are mounted in clusters using yoke members, and are divided into a control rod cluster (RCC) with a large neutron absorption cross section, a gray control rod cluster with a small neutron absorption cross section, and a water rejection rod cluster (WDRC). Contains. Control rod clusters function to shut down a nuclear reactor or reduce its thermal output. The gray control rod cluster acts as load following control. The water rejection rod cluster rejects coolant in control rod guide tubes that do not accept control rod clusters or gray control rod clusters. This removal occurs early in the reactor's fuel cycle, typically during about the first 60% of the fuel cycle.

In the upper part of the body 15, there is an upper reactor internal structure 37.
and calandria 39 are accommodated. The upper reactor internals 37 includes a vertical guide device 41 (FIG. 3) for the control rod cluster and the gray control rod cluster, and a vertical guide device 43 for the water displacement rod cluster. The control rod cluster and the gray control rod cluster are mounted on a cruciform structure 40, and the guide device 41 for these control rods and the gray control rod is a hollow cruciform can. The guide device 43 for the water removal rod cluster has a substantially rectangular or square cross section with the four corners cut off, and more precisely, it can be said to be an octagonal can. The sides 38 of the guide device 43 are surrounded by the projecting arms of the four guide devices 41 and extend parallel to these arms. Multiple plates 45 with coaxial holes 47
are vertically spaced along and inside the guide device 43 (FIG. 3A). The plate 45 serves to support the sides 38 and the water displacement rod cluster extends through and is guided within the hole 47. The guide devices 41 and 43 are connected to vertical side walls 49, 51 (first
(Fig.) is substantially imperforate, but is open at its top and bottom. Small holes 53 and 55 can also be provided in the guide devices 41 and 43 to stabilize or balance the coolant pressure.

The calandria 39 (FIG. 6) includes a substantially horizontal lower support plate 54 (FIG. 4) and a substantially horizontal upper support plate 56 (FIG. 5).
A generally vertical hollow member 58 is supported. Hollow member 58 is typically a tube of circular cross section. These tubes are fixed in countersinks 62 in the upper support plate 56 by fillet welds 60 (FIG. 6), and are secured to the lower support plate 5 by fillet welds 60 (FIG. 6).
It passes through 4. The hollow member 58 is connected to the lower support plate 5
There is a slight taper at the joint with 4. Lower support plate 54 has a generally oblong hole 64 therein. Each hollow member 58 is surrounded by four holes 64. Further, the lower support plate 54 is connected to the guide device 41
and 43 have pin holes 71 for alignment. The top of the guide device is provided with a pin (not shown) that enters the pin hole 71.

The lower and upper support plates 54, 56 are circular;
The hollow members 58 are substantially uniformly spaced apart within the cylindrical space formed between these support plates. These support plates are surrounded by a shell 66 (FIG. 6) having an opening 72 that mates coaxially with and spaced from the opening 61 (FIG. 2) of the inner barrel 57. It has a lower portion 68.

A shell or support cylinder 74 extends from the upper support plate 56 and has an upper cylindrical portion 76 and a flange member 78 . The upper cylindrical portion 76 is welded to the upper support plate 56 at its lower end and has a flange member 78.
is welded to the upper end of the upper cylindrical portion 76.

Upper reactor internals 37 and calandria 39 are housed within barrel 57 (FIG. 2). The barrel 57 is cylindrical and has an opening 61 below the top.
The opening 61 is shaped to mate with the edge of the outlet nozzle 25 and the opening 72 of the calandria shell 66. Barrel 57 has a flange 65 at its top and supports upper core plate 33 at its lower end.

The guide devices 41 and 43 are tightly mounted except near the periphery. Therefore, the coolant flowing from the core 27 into the space between the guide devices has a high velocity and tends to flow toward the periphery. The pressure of this coolant decreases from the bottom to the top of the upper internals 37. Closely arranged guide devices 41
A horizontal former plate 67 is provided along the barrel 57 to suppress lateral flow of coolant due to pressure between the upper internals 37 and the relatively free space around the upper internals 37 .

Core 27 , upper internals 37 and calandria 39 are enclosed within outer barrel 81 . The lower core plate 35 is attached to the lower end of this barrel 81. At the upper end of the barrel 81 is a flange 85. Barrel 81 has an opening aligned with outlet nozzle 25 in a position and shape that mates with the edge of opening 61 in calandria shell 66.

The reactor core 27, upper reactor internals 37, and calandria 39 are mounted substantially coaxially. The upper core plate 33 has a pin 87 (see FIGS. 1 and 2) that engages the fuel assembly 29 to center the fuel assembly 29.
(Figure). Sidewall 76 and shell 66 and barrels 57 and 81 are mounted substantially coaxially to each other and to core 27, upper core structure 37, and calandria 39. The flange 85 is connected to the shelf 8 on the inner surface of the body 15.
It's on top of 9. Flange 65 of barrel 57 rests on flange 85, with a spring (not shown) inserted between the flanges. flange 78
is placed on the flange 65. Shell 66, barrels 57 and 81 border 9 of openings 72 and 61.
1 and 93 meet each other, and the opening 61 of the barrel 57
are circumferentially oriented such that a boundary 93 (FIG. 1) of the opening of the barrel 81 meets an opening boundary 95 of the barrel 81 and an inner edge 97 of the outlet nozzle 25. An annular space 99 between barrel 81 and body 15 communicates inlet nozzle 23 with the lower end of core 27 . The coolant entering from the inlet nozzle 23 flows downward through the annular space 99, enters the bottom 17, flows upward within the core 27, straight upward through the upper reactor internals 37, enters the calandria 39, and enters the calandria 39. The flow flows almost horizontally inside the outlet nozzle 2.
Leave from 5. The junctions between boundaries 91, 93 and 93, 95 and between boundaries 95 and inner edge 97 form pressure-tight seals at the outlet nozzle and provide a bypass for coolant to flow directly from the annular space 99 to the outlet nozzle 25. It is either completely absent or kept to a minimum.

As shown, the outlet flow path of the outlet nozzle 25 is
Directly above the upper reactor internals and calandria 3
Since it is at almost the same level as the hollow member 58 of No. 9,
The coolant that has passed through the calandria exits directly from the outlet nozzle 25. The lower support plate 54 of the calandria 39 is positioned adjacent to the top of the upper internals 37, and the coolant passes into the calandria through openings in the guide devices 41 and 43 and the space between these guide devices. , and also the horizontal former plate 67
and the periphery of the upper internals. The calandria 39 acts as an upper support for the upper internals. Control rod drive shaft 10
1 (FIG. 5) from the coolant flowing at high speed radially outwardly toward the outlet nozzle 25 through the hollow member 58 of the calandria.
Protected by 8.

Calandria lower and upper support plates 54, 56
and hollow member 58 are made of stainless steel. The outlet nozzle 25 is typically about 1 meter in diameter. Hollow member 58 typically has an outer diameter of 8.8 cm, an inner diameter of 5.5 cm, and a length of approximately 125 cm. Both ends of the hollow member 58 having such a structure are connected to the lower and upper support plates 54,
56, the stress caused by the high velocity lateral coolant flow of 13 m/sec is minimized and the hollow member is not damaged.

Next, a preferred embodiment of the present invention shown in FIG. 7 will be described, in which the same or corresponding parts are denoted by the same reference numerals throughout the drawings.

According to the invention, the outlet nozzle can be located lower, resulting in a lower vessel height, and the radially outward flow of the reactor coolant through the calandria is lower, but with a higher pressure drop. It becomes uniform.

That is, in FIG. 7, the nuclear reactor according to the present invention has a container 15, a reactor core 27 supported within the container 15, and
A control rod assembly (not shown) movably supported within the vessel 15 and guided by a control rod guide device (representatively indicated by reference numeral 41) vertically disposed in a plenum above the reactor core 27; A drive shaft 10 connected to a yoke member (not shown) that supported the control rod assembly in order to move the control rod assembly into and out of the reactor core 27.
1. The vessel 15 has at least one inlet nozzle 23 for supplying coolant to the core 27 and at least one outlet nozzle 25 for discharging the incoming coolant from the vessel 15 after passing through the interior of the core 27. have Additionally, the reactor includes a calandria 39 extending across the vessel 15 above the core 27 , the calandria 39 extending across the vessel 15 .
includes a plurality of hollow members 58 mounted between an upper support plate 161 and a lower support plate 181, and the lower support plate 181 has holes through which coolant flowing axially upward from the core 27 can pass. 64 are provided. Further, the calandria 39 is open in the radial direction and communicates with the outlet nozzle 25.

According to the invention, the calandria 39
It is arranged at a sufficient distance above 7,
Yoke member that supported the control rod assembly (not shown)
is movable in the space between the calandria 39 and the reactor core 27, the drive shaft 101 extends through and is guided by the hollow member 58,
Exit nozzle 25 extends across the outer surface of hollow member 58.
and the outlet nozzle 25 is disposed substantially below the calandria 39 to direct coolant from the calandria 39 to the outlet nozzle 35. An annular flow path 160 is provided between the outlet nozzle and the outlet nozzle.

Furthermore, the support flange 85 of the core barrel 81 is
An annular space 99 surrounding the core barrel 81 is disposed below the outlet nozzle 25 that is in open communication with the inside of the calandria 39 via an annular flow path 160.
It is arranged above an inlet nozzle 23 which is in open communication with the core inlet region in the bottom 17 of the vessel 15 via the inlet nozzle 23 .

The calandria 39 has a funnel-shaped cross section, and the cross-sectional area of the flow passage increases toward the outer side in the radial direction, and as the flow direction turns toward the outlet nozzle 25, the flow velocity of the coolant is considerably reduced in the downward direction. There is. Also in this configuration, the control rod and the control rod drive shaft 101
are protected from radially outward high velocity coolant flow. The reason is that the control rod drive shaft 101 inside the calandria 39 has a radial flow as described above.
This is because there is no radial flow in the region below the calandria 39, and there is no axial flow that does not cause vibrations in the control rods and the control rod drive shaft 101. This is because there is only a flow.

When the outlet nozzle 25 is provided below the calandria 39 as shown in FIG. , then enters the radial outlet nozzle 25.
In this configuration, the radial exit flow out of the calandria 39 is more uniform, but the flow is diverted downwardly at the outer periphery of the calandria 39 and then outwardly into the outlet nozzle 25. I have to go in. As shown in Figure 7, calandria 39
includes an upper support plate 161 and a lower support plate 181. These support plates 161 and 181 are
Since the space 163 between them has a shape that expands in the flow direction, the calandria 3
The coolant flow at the outer periphery of 9 is relatively slow and the pressure drop where the coolant flow is diverted is relatively small. Furthermore, as can be seen from FIG. 7, according to this configuration, the calandria 39 supported on the lower support plate 181 is located inside the reactor head 19 as shown in the figure, so it is not shown in FIG. It is possible to use a reactor vessel with a lower height than in a conventional configuration.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing a reference structure example of a nuclear reactor, Figure 2 is a vertical cross-sectional view of the calandria and upper reactor internals barrel of the reactor shown in Figure 1, and Figure 3 is a vertical cross-sectional view of the reactor shown in Figure 1. Figure 3A is a partial enlarged view of the upper reactor internals taken along line - in Figure 3. Figure 4 is a partial plan view of the calandria taken along line - in Figure 1. 5 is a partial plan view of the upper support plate of the calandria taken along the line - in FIG. 1; FIG. 6 is a partial longitudinal sectional view of the calandria; FIG. FIG. 1 is a longitudinal cross-sectional view showing a nuclear reactor according to an embodiment of the invention. 15... Container (body), 17... Bottom of the container,
23...Inlet nozzle, 25...Outlet nozzle, 27
... Core, 39 ... Calandria, 41 ... Control rod guide device, 58 ... Hollow member, 64 ... Hole, 8
1...Core barrel, 85...Support flange, 99
... annular space, 101 ... drive shaft, 160 ... annular flow path, 161 ... upper support plate, 181 ... lower support plate.

Claims (1)

[Claims] 1 a container 15 and a support flange 8 within the container 15;
5, the core 27 supported within the core barrel 81, and the vessel 1.
a control rod assembly movably supported within the reactor core 27 and guided by a control rod guide device vertically installed in a plenum above the reactor core 27; and a control rod assembly for moving control rods into and out of the reactor core 27. A drive shaft 101 connected to a yoke member that supported the body,
The vessel 15 has at least one inlet nozzle 23 for supplying coolant to the core 27 and at least one outlet for discharging incoming coolant from the vessel 15 after passing through the interior of the core 27. The nozzle 25 further includes the core 27.
A calandria 39 extends above and across the container 15, the calandria 39 including a plurality of hollow members 58 mounted between an upper support plate 161 and a lower support plate 181; 18
1 is provided with a hole 64 through which the coolant flowing axially upward from the reactor core 27 can pass, and the calandria 39 is radially open and communicates with the outlet nozzle 25. 39 is arranged at a sufficient distance above the reactor core 27, and the yoke member that supported the control rod assembly is movable within the space between the calandria 39 and the reactor core 27. The drive shaft 101 extends through and is guided by the hollow member 58 and is protected from coolant flowing across the outer surface of the hollow member 58 to the outlet nozzle 25. and the outlet nozzle 25 is disposed substantially below the calandria 39 so as to guide coolant from the calandria 39 to the outlet nozzle 25 and around the calandria 39 and the outlet nozzle. An annular passage 160 is provided between the core barrel 81 and the outlet 25, and the support flange 85 of the core barrel 81 is in open communication with the interior of the calandria 39 via the annular passage 160. Although it is arranged below the nozzle 25,
A nuclear reactor, characterized in that the reactor is disposed above the inlet nozzle 23 which is in open communication with the core inlet area in the bottom 17 of the vessel 15 via an annular space 99 surrounding the core barrel 81.