RU61927U1 - SYSTEM PROVIDING DELAY OF A FUSIONED ACTIVE ZONE IN THE NUCLEAR REACTOR HOUSING TYPE VVER-440 / V-213 - Google Patents

Abstract

The utility model relates to a system for delaying the molten core in a VVER-440 / V-213 reactor vessel, which includes pressurized equipment, including air pipelines for the ventilation system for cooling the reactor shaft, the reactor shaft, and the heat shield of the elliptical bottom of the reactor vessel, while the air (1) pipelines of the ventilation cooling system of the shaft (2) of the reactor are equipped with closing inlet valves (1a) and check valves (1b), and the closing inlet valves (1a) are located above the level protective grids of the receiver of the sprinkler system, the air (1) pipelines of the ventilation system for cooling the shaft (2) of the reactor are equipped with grids (1c) on the neck in the shaft 2 of the reactor, and on the floor of the shaft of the reactor (2) the inlet (2a) of the special sewage system is equipped with a closing valve (2b) , in the side wall of the reactor shaft (2) there is a hermetic door with heat-resistant seal, and on the ceiling of the reactor shaft (2) there is a heat shield (7) of the elliptical bottom (6a) of the reactor vessel (6), equipped in the middle with a symmetrical closing hole (7b), which stub snaschena bursting diaphragm, the inspector radial clearance in the thermal screen (7) of an elliptic bottom (6a) of the housing (6) reactor equipped consuming blocks (7a) having a rigid wall.

Description

Technical field

The technical solution relates to a system for delaying the molten core in a VVER-440 / V-213 type nuclear reactor vessel in the event of a severe accident.

The current state of technology

In connection with the general trend of constantly improving the safety of operation of nuclear power plants, more and more demands are being placed on the ability to cope with the consequences of unlikely accidents associated with core damage (configuration of fuel cells in which the fission reaction and heat release) of the reactor. In the case of pressurized water reactors, such damage can occur only as a result of multiple failure of the process equipment and safety systems, for example, as a result of loss of the primary circuit cooler and simultaneous failure of all three independent emergency core cooling systems.

Damage to the fuel cells of the core and the formation of a "self-heating" melt (the so-called "corium"), i.e. a melt with continued heat release occurs due to overheating of the fuel cells by decay heat, which is released by the radioactive decay of the fuel even after the fission reaction ceases. The molten core may drain onto the bottom of the reactor vessel and form a pool of molten fuel cells and structural materials. Despite the fact that the decay heat is only a fraction of the rated power of the reactor,

not only damage to the coating of fuel cells and melting of the fuel matrix may occur, but also melting of the reactor vessel, which will affect the reinforced concrete wall of the containment zone, which is the last barrier to discharge fission products into the environment.

The thermochemical interaction of the melt with concrete causes the gradual destruction of the foundation plate of the hermetic zone and the release of steam and non-condensable gases, which exert a long-term pressure load on the wall of the hermetic zone. Some of these gases (H ₂ and CO) are combustible, therefore, in the event of combustion or explosion (detonation), a sharp increase in pressure can occur, which is a very serious threat to the integrity of the wall of the containment zone. One damage to the reactor vessel, especially at high pressure, can be accompanied by undesirable dynamic effects, as a result of which mechanical damage to the wall of the containment zone and the release of fission products into the environment can occur.

The most effective way to prevent the subsequent uncontrolled development of a severe accident after core melting is to prevent failure ("melting") of the reactor vessel. The essence of the delay of the molten core in the reactor vessel by cooling the outer surface of the vessel wall consists in flooding the reactor shaft and removing the decay heat generated in the melt through the vessel wall into the surrounding water.

A necessary condition for cooling the outer surface of the wall of the reactor vessel is to supply a sufficient volume of cooler to the surface of the vessel wall from the side of the reactor shaft through the heat shield of the elliptical bottom of the reactor and to ensure the flow of coolant in the region between the outer wall of the reactor vessel and the insulation of the cylindrical part of the reactor.

The currently known solution has been implemented at Lovisa NPP in Finland, where VVER-440 / V-213 reactors are operated. Water is supplied to the bottom of the reactor shaft through the air duct of the reactor shaft ventilation system. Throat air

piping system is equipped with a mesh for trapping material debris, thermal insulation of pipelines and other solid particles that can get into the cooler during an accident. Hydraulic equipment is placed in the reactor shaft, which, in the event of a severe accident, will insert the heat shield of the elliptical bottom of the reactor. This ensures that the cooler is supplied both to the elliptical bottom of the reactor and to the region between the outer wall of the reactor vessel and the insulation of the cylindrical part of the reactor.

It must be emphasized that at the Lovisa NPP, despite the fact that VVER-440 / V-213 reactors are operated there, the design of the containment shell (containment) differs from the standard block of the indicated type of reactor, which is equipped with a pressurized zone and bubbler and which is operated in Slovakia and others countries of middle and eastern Europe.

From a technical and financial point of view, the most difficult part of the system for delaying the molten core in the reactor vessel is hydraulic equipment, which allows in case of a severe accident to reliably insert the heat shield of the elliptical bottom of the reactor. Such a solution requires a general change in the layout of the equipment of the reactor shaft and the installation of large-sized hydraulic equipment capable of inserting a heat shield on the elliptical bottom of the reactor.

The purpose of this technical solution is to develop such a system for delaying the molten core in a VVER-440 / B-213 type nuclear reactor vessel, which will supply a sufficient amount of coolant to the surface of the outer wall of the reactor vessel and a sufficient flow of cooler from the side of the external wall of the reactor vessel removing the heat shield of the elliptical bottom of the reactor vessel in the event of a serious accident; in this case, only minimal changes in the state of the containment zone will be carried out without any effect on existing emergency safety systems.

The essence of the technical solution

The stated goal can be achieved, according to this technical solution, using the delay system of the molten core in the reactor vessel type VVER-440 / V-213. The essence of the solution is to modify the equipment of the hermetic zone of a nuclear reactor, including the air pipelines of the ventilation system for cooling the reactor shaft, the reactor shaft, and the heat shield of the elliptical bottom of the reactor vessel. The air pipelines of the ventilation shaft cooling system of the reactor shaft are equipped with a closing inlet valve and a check valve, and the closing inlet valves are located above the protective nets of the receiver of the sprinkler system. The necks of the air pipelines are equipped with a grid from the side of the reactor shaft. At the bottom of the reactor shaft there is a special sewage inlet equipped with a closing valve. An airtight door with a heat-resistant seal is located on the side wall of the reactor shaft. On the ceiling of the reactor shaft there is a heat shield of the elliptical bottom of the reactor vessel, in the middle of which there is a symmetrical and closing hole. The symmetric hole plug is equipped with a bursting diaphragm. The radial inspection gap in the heat shield of the elliptical bottom of the reactor vessel is blocked by removable blocks having a rigid wall.

It is very advantageous to place closing intake valves and check valves on the air pipelines in the part located in the connecting corridor of the box of steam generators and bubbler. This is advantageous because the air pipelines are closest to the floor in this part and also because the next cooler source in the bubbler is very close.

Closing inlet valves can be placed close to check valves. This arrangement reduces the floor area of the containment area during installation of the closing intake valves and

reverse gates.

It is very beneficial to make check valves in the form of a reverse siphon and use a pipe of the same diameter as the air pipes of the ventilation system of the reactor shaft. This will make it very easy to install a check valve in the pipeline and practically automate the work without using mechanical moving parts.

The closing inlet valves can be placed both on the horizontal part of the pipeline with a back-lock, and on the vertical part of the pipeline of the back-shutter in the form of a back siphon, provided that in both cases they will be above the level of the protective grids of the receiver of the sprinkler system. This arrangement also reduces the floor area of the containment area during installation of the closing intake valves and check valves.

The installation of closing inlet valves on the air pipelines of the ventilation shaft cooling system of the reactor shaft above the protective nets of the receiver of the sprinkler system will allow to keep the purpose of the air pipelines of the ventilation system unchanged during normal operation, and will also prevent the normal operation of the existing pressurized sprinkler system even in the event of a false opening of the intake during design accidents. In a severe accident, this will make it possible to supply water from the box floor of the steam generators through the pipeline to the reactor shaft.

Check valves prevent the chiller from leaking from the flooded air line to the center of the ventilation system. The grids on the neck of the air pipelines from the side of the reactor shaft prevent the ingress of material debris, thermal insulation of pipelines and other solid particles that may fall into the channel during the accident between the outer wall of the reactor vessel and the heat shield and the insulation of the cylindrical part of the reactor. These solid particles can impair the transfer of heat from the wall of the reactor vessel to the surrounding cooler and the flow of cooler along the wall of the vessel

the reactor.

The shut-off valve on special sewers on the floor of the reactor shaft will provide the sewage function during normal operation, and during the accident, because of its closure, the cooler will not leak through the sewer.

The heat-resistant seal of the pressurized door of the reactor shaft will provide long-term reliable sealing of the pressurized door in the event of an accident and thus prevent the leakage of coolant from the reactor shaft.

A symmetric closing hole in the middle of the heat shield of the bottom of the reactor vessel will provide, in case of an accident, the supply of cooler to the wall of the reactor vessel, and the movement of heavy insulation will not be necessary. During normal operation, the opening is closed to prevent air from flowing from the bottom of the reactor shaft to the wall of the reactor vessel. Installing a bursting diaphragm in the plug of a symmetric hole will compensate for the installation of a bursting diaphragm in one of the blocks that overlap the radial inspection gap in the heat shield of the elliptical bottom of the reactor vessel, and thus, in case of a sudden increase in pressure in this area, it will be relieved. Detachable blocks covering the radial inspection gap in the heat shield of the elliptical bottom of the reactor vessel have only a fixed wall. Thus, damage to the wall of the detachable blocks cannot occur, and the cooler will only flow through a symmetrical closing opening and the cooling of the reactor vessel will be uniform.

The list of drawings in the drawings

The technical solution is explained in more detail using the drawings. Figure 1 shows the current state of technical equipment, the location of the system with a heat shield of the elliptical bottom of the reactor vessel, subtracted (the lowered position is shown by a dashed line) using a hydraulic

systems for supplying coolant to the wall of the reactor vessel; Fig. 2 depicts in cross section the overall arrangement of the reactor vessel in the containment zone; Fig. 3 is a top cross-sectional top view of a pressurized installation with the arrangement of the pipelines of the ventilation system for cooling the reactor shaft with shutting inlet valves, the design of the protective grids of the receiver of the sprinkler system and the connecting corridor of the box for steam generators and bubbler; Fig. 4 is a bottom view of the arrangement of the system with the heat shield of the elliptical bottom of the reactor vessel with a closing opening for supplying the cooler, removable blocks of the radial inspection gap and the corresponding mechanisms for turning the screen; Fig. 5 is an image of the location of the closing intake valve and the check valve of the air pipe of the ventilation shaft cooling system of the reactor shaft.

For a more overview image, the figures do not indicate all parts of the installation of the containment zone, such as a system for constantly tilting the floor of the steam generator box or a platform of large swing mechanisms in the reactor shaft, which is located under the heat shield of the elliptical bottom of the reactor vessel and a hermetic door allowing maintenance personnel to enter the shaft the reactor. A hydraulic device for moving the heat shield of the elliptical bottom of the reactor vessel is also not shown in Fig. 1.

Execution examples

The system for delaying the molten core in the VVER-440 / V-213 reactor vessel is located in the containment zone in accordance with Figs. 2, 3, 4 and 5 and consists of an air pipe 1 of the ventilation shaft cooling system of the reactor shaft 2, which is in the region of the connecting corridor 3 Box 4 of steam generators and bubbler 5 is equipped with closing intake valves 1b and check valves 1b. There are also options when the closing intake valves 1a and check valves are located on air

pipelines 1 in another part of the containment zone. The closing intake valves 1a are located above the protective nets 9 of the receiver of the sprinkler system. In this manufacture, the check valves 1b are in the form of a reverse siphon, and they are made of a pipe of the same diameter as the air pipes 1 of the ventilation system of the reactor shaft 2. In other solutions, any closing gate valve with mechanical moving parts can be used for the back closures 1b. The closing inlet valves 1a are arranged in the present embodiment on the horizontal part of the air 1. pipe of the ventilation cooling system of the reactor shaft 2 near the check valves 1b. In other solutions, the closing intake valves 1a can be placed in the vertical part of the check valve 1b in the form of a back siphon. In this case, it is necessary that they are above the level of the protective nets 9 of the receiver of the sprinkler system. The air pipe 1 is equipped with a grid 1c on the neck in the shaft 2 of the reactor.

On the floor of the reactor shaft 2, the special sewer inlet 2a is equipped with a closing valve 2b. This closing valve 2b may be located anywhere in the special channel of the reactor shaft 2 before it is connected to the common part of the special channel.

On the side wall of the shaft 2 of the reactor there is a hermetic door (not shown in the figures), which provides access for maintenance personnel to the shaft 2 of the reactor. There is a heat-resistant seal on the door.

On the ceiling of the reactor shaft 2, there is a heat shield 7 of the elliptical bottom 6a of the reactor vessel 6, where there is a radial inspection gap covered by removable blocks 7a. The heat shield 7 has in the middle a symmetrical and lockable hole 7b, the plug (not shown in the figure) which is equipped with a bursting diaphragm. The removable blocks 7a of the radial inspection gap in the heat shield 7 of the elliptical bottom of the reactor vessel 6 have a rigid wall.

The size of the closing hole 7b specified in this

performance, the drawings are only schematic and in no way limits the scope of protection defined in the claims.

The size of the closing hole 7b may vary depending on various factors such as, for example, the amount of necessary changes to the heat shield 7, the supply of the required volume of cooler, the requirements and the mechanics of the closing hole 7b.

The size of the closing hole 7b may, for example, correspond to the cross-sectional area in the narrowest part of the channel formed between the outer wall of the reactor vessel 6, the heat shield 7 of the elliptical bottom 6a of the reactor vessel 6 and the insulation 8 of the cylindrical part 6b of the reactor. This is the case when the flow rate of the cooler in the above described channel is not limited by the size of the closing hole 7a.

The calculation showed that the flow rate of the cooler in the channel with the size of the closing hole 7b equal to the cross-sectional area in the narrowest part of the channel will provide sufficient cooling of the outer wall of the reactor vessel 6 and thereby the integrity of the reactor vessel 6.

Since the heat shield 7 of the elliptical bottom of the reactor vessel 6 is made (welded) from conical areas 7c and the flat bottom of the heat shield 7 (the flat bottom is not indicated in the figures due to the image of the hole 7b in the heat shield 7), it is possible to form a closing hole 7b in other manufactures , taking into account these structural elements of the heat shield 7. If the closing hole 7b is formed by separating the flat bottom of the heat shield 7, which may be technologically advantageous in the formation of the hole, then the size of the closure yvayuschego holes 7b greater cross-sectional area of the narrowest part of the channel described above.

The system in the event of a serious accident works as follows. A symmetrical closing hole 7b is opened in the biological and thermal screen 7 of the elliptical bottom 6a of the reactor vessel 6. The special sewage inlet 2a on the floor of the reactor shaft 2 and the pressurized door of the reactor shaft 2 are open during operation. The closing intake valves 1a will open to connect the boxes.

4 steam generators, on the floor of which there is water, with a pipe 1 of the ventilation cooling system of the mine shaft 2 of the reactor. The reactor shaft 2 will be filled with water from the boxes 4 of the steam generator, and through the open closing hole 7b in the heat shield 7 of the elliptical bottom 6a of the reactor vessel 6, water enters the wall of the reactor vessel 6, namely, in the channel between the outer wall of the reactor vessel 6, the heat shield 7 and insulation 8 of the cylindrical portion 6b of the reactor vessel 6. The difference between the temperature of the water and the vapor content in the pipe of the ventilation 1 of the cooling system of the reactor shaft 2 and in the channel near the reactor vessel 6 allows the cooling water to circulate along the wall of the reactor vessel 6 and thereby cooling the molten core in the reactor vessel 6, without the case melting 6 of the reactor, leakage of the molten core into the shaft 2 of the reactor and other undesirable consequences.

Industrial applicability

The system, according to the technical solution given, can be used at nuclear power plants with VVER-440 / V-213 reactors, and the remaining safety system functions will remain unchanged.

Claims (6)

1. A system for delaying the molten core in a VVER-440 / V-213 type reactor vessel, which includes pressurized equipment, including air pipelines of the ventilation shaft cooling system of the reactor shaft, the reactor shaft and the heat shield of the elliptical bottom of the reactor vessel that the air (1) pipelines of the ventilation cooling system of the shaft (2) of the reactor are equipped with closing inlet valves (1a) and check valves (1b), and the closing inlet valves (1a) are located above the level of the protective set ok receiver of the sprinkler system, the air (1) pipelines of the ventilation system for cooling the shaft (2) of the reactor are equipped with grids (1 s) on the neck in the shaft (2) of the reactor, and on the floor of the shaft of the reactor (2) the inlet (2a) of the special sewage system is equipped with a closing valve ( 2b), there is a hermetic door in the side wall of the reactor shaft (2) with a heat-resistant seal, and on the ceiling of the reactor shaft (2) there is a heat shield (7) of the elliptical bottom (6a) of the reactor vessel (6), equipped in the middle with a symmetrical closing hole (7b ), the cap of which is equipped a discontinuous diaphragm, and the radial inspection clearance in the heat shield (7) of the elliptical bottom (6a) of the reactor vessel (6) is equipped with removable blocks (7a) having a rigid wall. 2. The system according to claim 1, characterized in that the air (1) pipelines of the ventilation cooling system of the shaft (2) of the reactor are equipped with closing intake valves (1a) and check valves (1b) in the part located in the connecting corridor of the box (4) steam generators and bubbler (5). 3. The system according to any one of claims 1 and 2, characterized in that the closing intake valves (1a) are located next to the check valves (1b). 4. The system according to any one of claims 1 and 2, characterized in that the check valves (1b) have the form of a return siphon of the same diameter as the air (1) pipelines of the ventilation system of the shaft (2) of the reactor. 5. The system according to claim 4, characterized in that the closing intake valves (1a) are located on the horizontal part of the air (1) pipeline of the ventilation cooling system of the shaft (2) of the reactor near the check valves (1b). 6. The system according to claim 4, characterized in that the closing inlet valves (1a) are located on the vertical part of the pipe with a check valve (1b).