JPH0413678B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to the structure of a nuclear reactor.

In conventional pressurized water reactors, the reactor coolant is
After rising through the reactor core while being heated and passing through a number of holes in the upper core plate, the flow direction is changed laterally in an exit plenum defined by the core barrel, the upper support plate, and the upper core plate, and the control rods It flows towards the outlet nozzle through the wide gap between the guide tube and the upper core support column.

The control rod guide tube guides the control rod assembly vertically and protects the thin control elements from the flow of coolant radially outward or lateral to the reactor vessel, preventing long-term wear of the control elements. Preventing.

However, in a nuclear reactor where the number of control elements is extremely large and they are distributed throughout the reactor core, if the reactor superstructure is adopted as described above,
There is almost no gap between adjacent control rod guide tubes, and the flow of coolant toward the exit nozzle is obstructed, making it difficult to obtain a sufficient coolant flow rate. Furthermore, even if a sufficient flow rate can be obtained, the flow velocity will inevitably increase, and the fluid force acting on the guide tube will increase, leading to various problems. Furthermore, during a reactor trip, decay heat must be removed by generating a natural circulating flow of coolant.

The present invention has been made in view of the above-mentioned circumstances.

That is, the present invention provides a reactor vessel equipped with an inlet nozzle and an outlet nozzle for coolant on an upper side thereof, a lid detachably attached to an upper opening of the reactor vessel, and a lid that is detachably attached to an upper opening of the reactor vessel. Drop-supported core barrel,
A plurality of fuel assemblies are loaded inside and below the core barrel and constitute the core, and are disposed above the core at a distance from and inside the core barrel, and cooperate with the core barrel to define an annular space. an inner cylinder having a small hole opening into the annular space in the lower part; a plurality of control rod drive devices installed in the upper part of the lid; and a plurality of control rod drive devices movable into the reactor vessel by the control rod drive devices. a plurality of control rod assemblies supported and individually surrounded by vertical guide tubes provided within the inner cylinder and including a plurality of control elements; a plurality of protection tubes individually surrounding only the drive shaft; and a coolant diverting plenum surrounding the protection tubes, extending across the reactor vessel, and opening radially to communicate with the annular space. , the outlet nozzle comprises:
A nuclear reactor structure is provided that extends radially through the core barrel and opens into the annular space at a location below the coolant diversion plenum.

According to the invention, the lateral flow of coolant towards the outlet nozzle occurs only around the protective tube and around the narrow control element of the control rod assembly, guided by the guide tube in the longitudinal direction of the control element. flows along the
Since no lateral fluid force is applied to the control element, the occurrence of fluid vibration in the control element is suppressed. In addition, the outlet nozzle opens into the annular space between the core barrel and the inner cylinder at a position below the coolant diversion plenum, and the inner cylinder has a small hole that opens into the annular space at a lower part. During a reactor trip, the temperature of the coolant increases due to the decay heat generated from the core, and a portion of it flows into the annular space through small holes formed in the inner cylinder and heads towards the exit nozzle. In addition, the remaining part becomes a downward flow and has inertia when going from the coolant diverting plenum to the outlet nozzle through the annular space, so that the natural circulation of the coolant is promoted.

The present invention will be explained below based on illustrated embodiments. In FIG. 1, a reactor core barrel 5 is suspended and supported in a reactor vessel 3 to which a lid 1 is removably attached. 37. A core 9 made up of a large number of fuel assemblies 11 is supported on a porous lower core support plate 7 located below the core tank 5 . Although there are many fuel assemblies 11 forming the reactor core 9, only two are shown to avoid complicating the drawing.

The fuel assembly 11 is a normal one, in which a large number of fuel rods and control element guide tubes arranged in parallel are fixed in a bundle by egg-frame-shaped support grit, and further has end plate nozzles at the top and bottom. be.

Above the reactor core 9, an upper core body 13 for positioning the fuel assemblies 11 extends horizontally, forming an in-core upper structure 15 as described later. The inner cylinder 17 of the in-reactor upper structure 15 has a lower end connected to the upper core plate 1.
3, and its upper end is joined to the upper support plate 19. Moreover, this inner cylinder 17 cooperates with the core barrel 5 to define an annular space.

An intermediate plate (intermediate support plate) 21 is provided between the upper support plate 19 and the upper core plate 13 and extends in the horizontal direction, and includes a large number of control rod assemblies 23 (partially shown).
A plurality of guide tubes 25 are provided extending vertically to individually surround the guide tubes 25. When the control element of the control rod assembly 23 is lowered into the core 9, the drive shaft 27 of the control rod assembly 23 is located in the guide tube 25, and when the control rod assembly 23 is pulled up, the control element is drawn into the guide tube 25. The number of control rod assemblies 23 corresponds to the number of guide tubes 25.

The control rod assembly 23 is made up of a spider (not shown) located at the lower end of the drive shaft 27 and a large number of thin rod-shaped control elements hanging in the shape of a bunch. The control element moves inside the guide tube. A plurality of drive devices 29 and 31 provided on the lid 1 are individually connected to one of the many control rod assemblies 23, and move them up and down during operation of the reactor to perform reactivity control and power control. .

A plurality of protective tubes or hollow tubes 33 whose upper and lower ends are connected to the middle plate 21 and the upper support plate 19 individually surround only the drive shaft 27. As mentioned above, the upper core plate 13, the upper support plate 19, the inner cylinder 1
7. A large number of guide tubes 25, intermediate plates 21, and hollow tubes 33 cooperate to form the inner furnace upper structure 15.

In one embodiment of the configuration described above, the coolant flowing from the primary cooling system piping (not shown) through the inlet nozzle 35 of the vessel 3 flows through the annular channel 37 and reaches the lower plenum 39 .

The coolant whose direction has been reversed in the lower plenum 39 rises through flow holes (not shown) in the lower core support plate 7 and enters the core 9 .

In the core 9, the coolant flows through the fuel assemblies 11.
The fuel rises around the fuel rods, is heated by nuclear reaction heat, and then enters the guide tube 25 through a hole (not shown) in the upper core plate 13. After that, each guide tube 25
, i.e. in the axial direction along the drive shaft 27 of the control rod assembly 23 or the outer surface of the control element.

FIG. 2 shows a plan cross section of the guide tube 25, which has a non-perforated can 41 with a substantially rectangular cross section and a guide plate 43 disposed at a proper position in the axial direction.

The control element is supported laterally through a small hole 45 in the guide plate 43, and the drive shaft 27 is supported through a large hole 4 in the center.
Pass through 7. A narrow passageway interconnecting a number of small holes 45 is traversed by a spider that connects the control elements together. Therefore, this spider (not shown) is movable within the space between the coolant diverting plenum 49 and the core 9, that is, within the guide tube 25.

The coolant rises primarily between the can 41 and the guide plate 43 and flows out into a diverting plenum 49 formed on the outside of the hollow tube 33. A small portion of the coolant leaving the core 9 flows through the narrow gap between adjacent guide tubes 25 .

In the diverting plenum 49, the coolant changes direction by 90 degrees and exits radially outwardly through a plurality of holes 51 in the top of the inner cylinder 17. And the inner cylinder 17
It descends through the outer annular space, flows out of the container 3 from the outlet nozzle 53, and flows into the primary cooling system piping. As shown in the figure, the outlet nozzle 53 penetrates the core barrel 5 at a position below the turning plenum 49 and opens into the annular space. These heated coolants return to the inlet nozzle 35 through a steam generator included in a typical primary cooling system.

As can be seen from the above description, according to the present invention, the coolant is guided to (the can 41 of) the guide tube 25 in the area where the control element, which is thin and has low rigidity and easily vibrates, moves, particularly in the guide tube 25. Since the fluid flows in the axial direction, no excitation force is generated, and fluid vibration and wear of the control element can be effectively prevented.

Also according to the invention, the coolant diverting plenum 4
9, a thin protection tube 33 is provided instead of the relatively thick guide tube 25 to guide the drive shaft 27, so that not only is the coolant suitably diverted toward the outlet nozzle 53, but the drive shaft 27 is Protected from sideways flowing coolant.

Furthermore, according to the present invention, when a nuclear reactor is tripped due to a breakage accident in the primary cooling system piping, for example, part of the coolant whose temperature has risen due to decay heat is transferred to the small pipe formed in the inner cylinder 17. Not only does it flow into the annular space through the hole 55 and head toward the outlet nozzle 53, but also
The remaining part becomes a downward flow and has inertia when it heads from the coolant diverting plenum 49 to the outlet nozzle 53 through the annular space. In this way, natural circulation of the coolant is promoted, and the scrammed core 9 can be appropriately cooled. Note that since the number and area of the small holes 55 are small, almost no coolant flows through them during normal operation.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG.
The figure is a partial sectional view of FIG. 1. 1...Lid, 3...Reactor vessel, 5...Reactor barrel,
9... Core, 11... Fuel assembly, 17... Inner cylinder, 23... Control rod assembly, 25... Guide tube, 2
7... Drive shaft, 29, 31... Control rod drive device,
33... Protection tube, 35... Inlet nozzle, 49...
Coolant diverting plenum, 51... hole in inner cylinder opening into annular space, 53... outlet nozzle, 55... small hole.

Claims (1)

[Claims] 1. A reactor vessel equipped with an inlet nozzle and an outlet nozzle for coolant on the upper side, a lid detachably attached to the upper opening of the reactor vessel, and a core suspended and supported within the reactor vessel. a plurality of fuel assemblies that are loaded inside and below the core barrel and constitute the core; a plurality of fuel assemblies that are spaced apart from and arranged inside the core barrel above the core and cooperate with the core barrel to form an annular space; an inner cylinder having a small hole opening into the annular space at the lower part; a plurality of control rod drive devices installed in the upper part of the lid; a plurality of control rod assemblies movably supported and individually surrounded by vertical guide tubes provided within the inner cylinder and including a plurality of control elements; a plurality of control rod assemblies located above the guide tube; a plurality of protection tubes that individually surround only the drive shaft of the reactor; and a coolant that surrounds the protection tubes and is disposed to extend across the reactor vessel, opening in the radial direction and communicating with the annular space. A nuclear reactor structure comprising a turning plenum, the outlet nozzle extending radially through the core barrel and opening into the annular space below the coolant turning plenum.