JPS5823912B2 - Reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to nuclear reactors and, more particularly, to core support structures thereof that include means for separating, containing, and cooling core debris in the event of a core meltdown accident.

There are a number of devices capable of containing, cooling and separating molten debris in the event of a core meltdown.

Some of these devices are installed inside the reactor vessel and are designed to contain debris at the bottom of the reactor vessel, but the majority are installed outside the reactor vessel. be.

These devices generally consist of large structures that "capture" molten debris.

The arrangement of the device is further adapted to direct the molten debris into separate areas, and the configuration is such that the molten debris is collected in the separate areas.

Other types of devices use dense materials to lift and separate the debris, and the material also serves as a heat transfer means to cool the molten debris or as a means for neutron absorption. There is also.

However, all of these devices are large and expensive to manufacture, and their cooling capacity is relatively small.

Furthermore, if large equipment is to be used in a pressure vessel, the coolant flow path becomes extremely complex, and the flow resistance pressure at the vessel inlet increases, requiring a large pump capacity. It will also happen.

The basic purpose of this invention is to simplify the structure so that debris from any fuel assembly can be collected, and to separate and cool it better, reducing the amount of supporting material that could melt in the event of a melting accident. It is possible to provide a device that can reduce the amount of time required.

For the above purpose, the nuclear reactor of the present invention includes a reactor vessel, a reactor core disposed within the reactor vessel and supported on a lower core support plate, and consisting of a large number of fuel assemblies, each mounted on the lower core support plate. The lower core support plate has a lower end projecting downward, and the upper end located above the lower core support plate receives at least one fuel assembly, and the lower core support plate receives at least one fuel assembly. a plurality of inlet modular units in communication with the reactor vessel; a member for directing coolant into the reactor vessel such that coolant passes through the inlet modular units and the reactor core; and a member for directing coolant past the reactor core to exit the reactor vessel. and wherein at least some of the coolant inlet members have containers of refractory material positioned to receive core debris in the event of an accident, and wherein the inlet modular unit has a fuel inlet modular unit. It is characterized by supporting and communicating with the fuel assembly so as to collect debris falling from the assembly.

The inlet modular unit can be designed for the lifetime of the reactor, but is easily removable for maintenance and replacement.

Preferably, the coolant is injected into the reactor vessel below the inlet modular unit, so that the inlet modular unit is always well cooled.

In the event of a melting accident, the molten debris will enter the inlet modular unit under its own weight and be contained in a container.

In this case, since the lower end of the inlet modular unit is located within the lower plenum of the reactor vessel, the heat of the multiple molten debris within the vessel will be transferred to the coolant within the lower plenum.

This configuration allows molten debris to pass through the lower support structure without damaging the lower support structure.

Hereinafter, details of the present invention will be explained based on the drawings showing one embodiment.

FIG. 1 shows a generally cylindrical pressure vessel 10 closed at the bottom by a curved plate 12 having an inlet plenum 14. As shown in FIG.

Reactor coolant, such as liquid sodium, enters the pressure vessel 10 under pressure through a number of inlet nozzles 16 , and the hot coolant that has passed through the reactor core passes through a number of outlet nozzles 20 into the outlet plenum 18 . from the pressure vessel 10.

A thermal shield 22 is permanently attached to the pressure vessel 10 to protect the vessel from thermal shock.

The thermal shield 22 is disposed surrounding the outlet plenum 18 and the upper and lower portions thereof.

At the top of the reactor is a lid (not shown) that is bolted to a flange (not shown) of the pressure vessel 10.

Also within the pressure vessel 10 is an upper mechanism 24 supported from a lid (not shown).

The upper mechanism 24 has functions such as a backup mechanism for suspending the reactor core 26, positioning, protection, guidance and support for core instrumentation, adjustment of the control rod system, and control of coolant flow in the outlet plenum 18. .

In addition, inside the pressure vessel 10, from the outside in the radial direction to the inside, there is a fuel storage section 28, a core tube 30, a fixed shield 32, a series of removable shield assemblies 34 surrounding a surveillance test sample storage area 36, and other core structural members and a lower part. There is a mechanism, and furthermore, there is a control rod assembly 38 in the center.

The core tube 30 is permanently welded to a horizontal support plate 40.

The horizontal support plate 40 is thick-walled and permanently fixed to the pressure vessel 10 by a plate 42 in the shape of an inverted truncated cone.

As shown in FIG. 2, the horizontal support plate 40 has many support holes 4.
4 is passing through.

The support hole 44 has a bypass opening 46, which is combined with other components to be described later to form a bypass path 48 toward the periphery of the horizontal support plate 40.

The multiple liners 50 are generally hollow cylindrical and have members for attachment to the horizontal support plate 40.

An inlet modular unit 52 is removably mounted to the liner 50.

As best shown in FIG. 3, each liner 50 is formed with a liner inlet opening 54 located below the horizontal support plate 40 to permit coolant to enter under pressure from the inlet plenum 14. Also, a liner bypass hole 56 is formed which communicates with the bypass opening 46 of the horizontal support plate 40 and allows a bypass flow to be described later to flow therethrough.

At the bottom of the liner 50 are bosses 58 and alignment posts 60 attached by pins 62.

Each liner 50 receives a removable inlet modular unit 52.

Here, the alignment posts 60 differ depending on the type of inlet modular unit 52 they receive, so that a particular liner will only receive a particular inlet modular unit 52.

For this purpose, exchange means are provided for installing and identifying the input lomodulator unit.

A plate 64 is suspended from the bottom of the liner 50 into the inlet plenum 14.

This plate 64 is for flow distribution and prevention of channel blockage.

In the liquid metal cooled fast breeder reactor according to the embodiment of the present invention, there are two types of inlet modular units 52, one of which is a fissile fuel assembly 66 and a control rod assembly 38. One is for receiving those that require a large coolant flow rate, and the other is for receiving those that require a small coolant flow rate in the outer portion of the core 26.

Some inlet modular units have these dual functions and may receive the inner and outer assemblies of the core 26.

The internal structure of the inlet modular unit 52 varies depending on the flow requirements, but each consists of a number of structural members.

Each inlet modular unit 52 is an elongated body having a hexagonal cylindrical head 68 and a hollow body 70.

The bottom of the body 70 is tapered to provide guidance during insertion.

Similarly, there is an alignment hole 72 at the bottom of the body 70,
Hole 72 receives alignment post 60 of liner 50.

The head 68 has a plurality of openings (FIG. 4) into which various receiving containers γ4 are inserted and fixed.

Each receiving vessel 74 has a substantially cylindrical shape, and its internal shape is designed to receive an inlet pipe at the lower part of the fuel assembly 66, a pipe of the control rod assembly 38, or an assembly (not shown) on the outside of the core. It is suitable.

A typical receiving vessel is shown in detail in FIG. 3 and in FIGS. 5 and 6.

There are different types of receiving containers 74, and each type has a block 76 as an identification member fixed with a pin (not shown).

Block 76 identifies the collection to be entered.

Each receiving vessel 74 has a slot 78 formed in the tube of the assembly that is received in the receiving vessel 74.
Matches 0.

Each assembly includes a piston ring 82 and other sealing members located above and below the slot 78.

These sealing members minimize leakage of coolant under pressure entering slot T8 and thus minimize pressure build-up in the low pressure area below the tubes of the assembly.

Instead of using this seal 82 to limit leakage, it is also possible to provide a fluid-tight fit between the assembly tube and the receiving vessel.

In either case, the flow to the low pressure region of the receiving vessel 74 is eliminated.

Each mass is of greater specific gravity than the coolant, and the mass is located within the receiving vessel by fluid equilibrium and self-weight.

Fluid equilibrium here means that the geometry of the interengaging members and the reactor coolant acting on or passing through the members are such that the coolant is in substantially equilibrium fluid pressure and engaged. This refers to a state in which the mating members can be held in place by their own weight.

In other words, fluid equilibrium refers to a balance of forces such that the weight of a member is sufficient to keep it in place.

The lower end of each receiving container 74 is tapered and connected to a hollow bar 84, and the bar 84 is attached to a spider arm 86.

A spider arm 86 is attached to the head 68 of the inlet modular unit.

A sealing member 8 is provided between the bar 84 and the spider arm 86.
8 is provided to prevent pressurized fluid from leaking around the rod 84.

A boss 90 extends from the bottom surface of the spider arm 86.

Boss 90 engages a filter-type flow distribution plate 92.

Flow distribution plate 92 distributes coolant and prevents solid debris from flowing into receiving vessel 74.

Means are provided for attaching the flow distribution plate 92 to the boss 90.

Each spider arm 86 has a passageway 94.

The interior space of rod 84 communicates with its receiving vessel 74 and passageway 94 to permit coolant leakage through seal member 88 and seal member 82 to flow into passageway 94 .

Means are provided near the head 68 of the inlet modular unit 52 for sealing the passageway 94 of the spider arm 86.

The passageway 94 of each spider arm 86 communicates with a bypass tube 96.

A bypass tube 96 extends downwardly from the spider arm 86 along the inlet modular unit 52 and extends into a space 98 between the lower end of the inlet modular unit 52 and the liner 50.
It is open to

A horizontal hole 100 is formed in the bypass pipe 96.

The lateral hole 100 communicates with the bypass channel 48 through a liner bypass hole 56 formed in the wall of the liner 50 and a bypass hole 102 formed in the wall of the inlet modular unit 52.

Bypass channel 48 allows coolant to flow to a low pressure region of pressure vessel 10 .

The body 70 of the inlet modular unit 52 has a primary inlet opening 104 that mates with the liner inlet opening 54 formed in the wall of the liner 50.

Inlet seal members 106 (generally piston ring seal members) are provided above and below the openings 104 and 54.

During normal operation, high-pressure coolant in the inlet plenum 14 enters and rises through the trunk 70 through openings 104 and 54 and up inside the core assembly through flow distribution plates 92 and slots 80. .

The coolant is discharged at low pressure into the outlet plenum 18.

The inlet seal member 106 is connected to the inlet modular unit 52.
Balance the pressure by restricting the downward flow of coolant.

The inlet modular unit 52 has a greater specific gravity than the coolant and cooperates with pressure balancing to ensure that it is retained within the liner 50.

The inlet seal member 106 also has a liner 50 above it.
and coolant inlet member 52 .

Leakage leaks downward through the inlet seal member 106 into the space 9.
8 into the bypass pipe 96 and further into the opening 100,
102° 56 and 46 and enters the low pressure region of the pressure vessel 10.

Different types of inlet modular units 52 may receive fuel assemblies 66 or control rod assemblies 38, or other assemblies that may require lower coolant flow than the fuel assemblies 66 or control rod assemblies 38. is received in the outer region of the core 26.

The outer inlet modular unit 52 is connected to the body 7 to control coolant flow to surrounding components during normal operation.
An orifice plate 108 may be provided at the bottom of 0.

A similar orifice plate 110 (FIG. 6) is inserted into the receiving vessel 7.
4 and directly above the flow distribution plate 92 (not shown).

These substantially reduce the pressure of the coolant flow and inhibit the flow.

The flow to the outer assembly enters the inlet modular unit 52 and is divided into a portion directly upstream toward the receiving vessel 74 and a portion flowing downwardly through a bypass path.

Flow toward receiving vessel 74 passes directly through orifice plate 110 and into the outer assembly.

Flow through the bypass passage descends through the orifice plate 108, ascends within the bypass tube 96, and passes through the bypass hole.

Flow through orifice plate 110 ascends between the wall of receiving vessel 74 and an inner cylinder with vertical holes (not shown) within the receiving vessel.

Flow through the vertical holes enters the assembly tube contained in the receiving vessel 74.

The receiving vessel 74 allows a small portion of the flow therein to flow down the hollow stud 84 and into the bypass pipe 96.

The outer inlet modular unit 52 is generally similar to the inner inlet modular unit.

There are various types of outer assemblies, and the required flow rates vary accordingly.

These necessary flow rates can be controlled by increasing or decreasing the number of orifice plates.

The above is a description of the core support structure and coolant flow during normal operation.

A container 112 is housed within each inlet modular unit 52 in case of an accident.

An embodiment of the container 112 is shown in FIGS. 7 and 8.

The container 112 can maintain its original shape even when containing core fragments at elevated temperatures of 2,760°C (5,000'F).
It has the function of collecting and containing debris and also transfers heat from the molten core debris to the coolant in the inlet plenum 14.

Since the container 112 is housed within the inlet modular unit 52, it disperses the debris and minimizes the possibility of a critical mass of debris collecting in one place.

As shown in FIG. 7, the container 112 preferably has a substantially hollow cylindrical shape with a funnel-shaped skirt 114 at its upper end.

In addition to the skirt 114, the container 112 has a lower container portion 116.
, has an upper container portion 118 and a mounting shoulder portion 120.

The lower container portion 116 has a substantially cylindrical shape and a flat or hemispherical bottom portion.

As best shown in FIG. 8, the wall of the container 112 has a fan-shaped inwardly projecting portion 121 which surrounds the lower outer member of the bypass tube 96.

The upper container portion 118 also has a substantially cylindrical shape and has a coolant inlet opening 122 formed therein.

Inlet opening 122 is mutually aligned with inlet openings 54 and 104 of liner 50 and inlet modular unit 52.

A bypass opening 124 is further formed in the upper container.

The bypass openings include transverse holes 100 in bypass pipe 96, liner 50, and inlet modular unit 52, respectively.
It communicates with the liner bypass hole 56 and the bypass hole 102.

The container 112 is suspended from the head 68 of the inlet modular unit 52 by a mounting shoulder 120 at the upper end of the upper container section 118 thereof.

A funnel-shaped skirt 114 is attached to the upper end of the container 112, and this portion serves as a guide for debris entering the container 112.

A slot 1 is provided at the boundary between the upper container portion 118 and the lower container portion 116.
26 is formed, and this slot 126 is connected to the bypass pipe 9.
6 is passing.

Assuming that an accident should occur, a portion of the reactor core 26 would melt and descend due to gravity.

The flow of molten debris in this case is the opposite of the flow of coolant during normal operation, that is, it first descends the upper end of the receiving vessel 74, then exits the receiving vessel slot 78, and then moves up the spider arm 86. over the flow distribution plate 92 (although the flow distribution plate 92 may then have melted or lost structural strength at the temperature of the molten debris) and then into the vessel 112 by the skirt 114. You will be guided.

The debris that enters the container 112 continues down to the "working section", ie, the portion of the interior of the container located below the inlet opening 122.

The debris is contained in this "working section" and is cooled by heat transfer through the vessel 112, the coolant inlet member 51, and the can wall of the liner 50 to the coolant in the inlet plenum 14.

Here, the fragments collected in one container 112 are contained in container 11.
2 is not used, compared to the amount of debris that would collect at the bottom of the pressure vessel, and the debris would be distributed horizontally to each manual modular unit 52, and vertically between the "working part" and the top of the horizontal support plate 40. It is unlikely that the molten debris will reach a critical mass in the "working part" since it is divided between the two.

The capacity of vessel 112 is determined by considering other operating parameters such as vessel 112, inlet modular unit 52, and liner 50.
The length of the tube can be modified to provide maximum containment and optimal cooling while remaining subcritical.

Providing a large number of inlet modular units 52 and distributing and accommodating the molten debris in small amounts in large numbers increases the surface area, which is advantageous for cooling.

Additionally, a distinct advantage of using the inlet modular unit of the present invention is that a large amount of molten debris is kept away from the horizontal support plate 40.

The receiving portion or “working portion” of the container 112 is the inlet opening 122.
In other embodiments, the container 112 may be positioned such that its upper end is below or in a portion of the inlet opening 104.

In this case, the way the molten debris flows is the same as described above, but the skirt 114 is omitted.

Various specifications can be used for the material of the container 112, but the minimum standard is 2760°C (5000'
F) Must be capable of retaining its shape while containing and discharging thermal energy from molten core material.

As such a material, a metal such as stainless steel, a ceramic, a composite material of metal and ceramic, etc. can be used.

Materials that can be used include molybdenum, tantalum,
These include columbium, tungsten, and most other metals that are generally considered fireproof.

The container 112 may be a single unit or may be a combination of many parts.

In one method, a number of parts may be butt-bonded to form the outer surface of the container 112, which is then placed over the inner surface.

You can also attach accessories to facilitate cooling.

All or a portion of the interior surface of container 112 may be lined with a high density, high melting point material to absorb heat as it melts and combines with the molten debris.

Ideally, a material with the same density as the molten debris could be used, such as unenriched uranium dioxide (UO2).

If the internal shape of the inlet modular unit is made into a container shape, the inlet modular unit and the liner alone can serve as a container.

As previously mentioned, the externally located inlet modular unit has an orifice plate 110 in the receiving vessel 74, an orifice plate 108 in the bottom of the inlet modular unit, and an orifice plate (not shown) in the flow distribution plate 92. It may be installed directly above.

If the orifice plate is exposed to molten debris, the orifice plate will melt.

This is not a problem for the orifice plate installed at the top, but it can be a problem for the orifice plate installed at the bottom. In the event of an accident, it may melt and create a hole in the bottom of the container 112.

This hole becomes a passage for molten debris in the event of an accident, and the original function of the container is lost.

However, the functional properties and materials of the outer aggregates are different from those of the inner aggregates, and the possibility of them actually melting in the unlikely event of a gross accident is extremely small.

Therefore, the container 112 does not have to be integrated into the inlet modular unit 51 that supports the outer assembly.

Alternatively, a container 112 and inlet modular unit 52 as shown schematically in FIG. 9 may be used.

FIG. 9 shows a typical liner 50, inlet modular unit 52 and container 112.

In what is shown here, the lower orifice plate 108
The container 112, the inlet modular unit 52, and the lower portion of the liner 50 are circumferentially and above surrounded by a housing 128.

Means are provided for securing the housing 128 to the inlet modular unit 52 and communicating with the bypass tube 96.

Communication with the low pressure coolant is provided by an annular groove (not shown) in the inlet modular unit below the seal member 106.

In normal operation, the bypass flow of coolant flows through vessel 112.
, enters the assembly consisting of inlet modular unit 52 and liner 50 and then passes through orifice plate 108 using the low pressure of the orifice/bypass system.

In the event of a melting accident, the container 112 will perform a containment function.

In any of the cases described above, some of the molten debris will communicate with the bypass tube 96.

In such a case, the molten debris either melts the bypass tube and enters the vessel 112 or solidifies in the tube.

If either of these were to occur, it would be at the portion 130 where the bypass pipe has a thin neck, but this does not impair the original function of the present invention in the event of an accident.

[Brief explanation of the drawing]

Figure 1 is a front sectional view of the reactor, Figure 2 is a partial plan view of the lower horizontal plate of the reactor shown in Figure 1, and Figure 3 is the connection of the removable inlet modular unit housed within the liner. 4 is a partial sectional view of the IV-IV section in FIG. 3; FIG. 5 is a simplified front sectional view showing a typical example of the receiving container of the inner inlet modular unit; 6 is a simplified front sectional view showing a typical example of a receiving container for an outer inlet modular unit; FIG. 1 is a front sectional view showing an embodiment of the container; FIG. 8 is a front sectional view showing the container shown in FIG. FIG. 9 is a partial front view of another embodiment of the lower part of the inlet modular unit connection shown in FIG. 3; 10...Pressure vessel, 12...Curved plate, 14
...Inlet plenum, 16...Inlet nozzle, 18...Outlet plenum, 20...
- Outlet nozzle, 22... Heat shield, 24...
... Upper mechanism, 26 ... Core, 28 ...
... Fuel storage section, 30 ... Core tube, 32 ...
... fixed shielding, 34 ... shielding assembly, 36.
...Sample storage area for surveillance tests, 38...
... Control rod assembly, 40 ... Horizontal support plate, 4
2...Plate, 44...Support hole, 46...
...Bypass opening, 48...Bypass path,
50...liner, 52...inlet modular unit, 54...liner inlet opening, 5
6... Liner bypass hole, 58... Boss, 60... Aligning column, 62... Pin, 64... Plate, 66 ...Fuel assembly,
68... Head, 70... Torso, 72.
... Hole, 14 ... Receiving container, 76 ...
...Block, 78...Slot hole, 80...
...Slot hole, 82... Seal member, 84...
...rod shape, 86...spiter arm, 88.
... Seal member, 90 ... Boss, 92.
...flow distribution plate, 94 ... passage, 96.
...Bypass pipe, 98...Space, 100
...Horizontal hole, 102 ... Bypass hole, 1
04... Inlet opening, 106... Inlet seal member, 108... Orifice plate, 110
... Orifice plate, 112 ... Container,
114... Skirt, 116... Lower container part, 118... Upper container part, 120...
・・Mounting shoulder part, 122・・・・Entrance opening, 124・
...Bypass opening, 126...Bypass pipe.

Claims (1)

[Scope of Claims] 1. A reactor vessel, a core consisting of a number of assemblies supported on a lower core support plate in the reactor vessel, and a core mounted on the lower core support plate, the lower core support plate being mounted on the lower core support plate. an extending portion extending downward from the lower core support plate, the extending portion having a coolant inlet opening, and a top portion extending above the lower core support plate receiving at least one aggregate; a plurality of inlet modular units in communication with an area below the lower core support plate; a plurality of inlet modular units in which coolant enters the area below the lower core support plate in the reactor vessel; a member for permitting flow through the assembly and a member for discharging coolant that has passed through the reactor core from the reactor vessel, wherein at least some of the plurality of inlet modular units have a lower end thereof. The inlet modular unit is equipped with a heat-resistant container to receive core debris in the event of an accident, and the inlet modular unit is connected to the supporting assembly to collect debris that falls from the assembly. A nuclear reactor characterized by being in communication. 2. The nuclear reactor of claim 1, wherein the vessel is made of stainless steel. 3. The nuclear reactor of claim 1, wherein the vessel is made of a ceramic material. 4. The nuclear reactor according to claim 1, wherein the container comprises an inner layer made of ceramic and an outer layer made of metal. 5. The nuclear reactor according to claim 1, wherein the vessel has a layer of UO2 concentrated to one volume having a density substantially equal to that of the molten debris. 6. A nuclear reactor according to any one of claims 1 to 5, characterized in that the vessel has a hopper formed at its top suitable for collecting molten debris.