RU2079904C1 - Device for catching, cooling and confining of reactor core melt - Google Patents

Abstract

FIELD: nuclear power engineering. SUBSTANCE: device has toroidal melt collectors placed in horizontal planes in a melt collector compartment behind a catcher body where core melt is caught and distributed through melt pipings into the collectors. At least one collector is connected at least with one piping. Heat is removed from the melt by evaporation of cooling water provided in the compartment. There are two barriers, except for a baseplate of a building (containment), capable of confining core melt and preventing its release beyond the building. EFFECT: enhanced safety of nuclear reactors in core melt accidents. 2 dwg

Description

 The device relates to nuclear energy, and in particular to the safety systems of a nuclear power plant in case of accidents leading to the melting of fuel and core materials.

 A device for cooling and trapping a melting or molten core of a nuclear reactor [1] is a cooling bath made of thermoconductive metal and located in a room under the reactor vessel (in the reactor shaft). The inside of the chilled bath is covered with a refractory material. Above the cooled bath are grates, serving as a protective grill against heavy reactor parts. The underside of the chilled bath rests on a chilled chamber filled with coolant. Steam is diverted to the outdoor areas through the steam lines.

 The disadvantages of this device include: the relatively low efficiency of heat removal due to the thermal resistance of the backfill, the absence of absorbers of the kinetic energy of the incident melt, which can lead to significant dynamic effects on the bath elements, the possible accumulation of critical mass, the absence of an additional barrier to cooling and holding the melt in case of penetration of the bath.

 A device is known for holding molten materials from the core [2] located under the reactor vessel, under the cover of the emergency shell, which is an insulated cylindrical shell (shaft), inside of which there are devices for holding falling parts after core melting. A trap (heat exchanger) has been built under the cylinder (shaft) to receive molten materials that have passed through the shaft. The cross-sectional shape of the heat exchanger eliminates the accumulation of critical mass. The heat exchanger has a thin closed water jacket with upper and lower pipelines, an inner lining of a material that is well conductive of heat. The main disadvantages of this device include: the concentration of the entire mass of the melt in a single volume, the large height dimensions of one heat exchanger, the absence of additional barriers to the spread of the melt in cases of damage, penetration of the heat exchanger wall.

 Closest to the claimed is a device for holding molten materials of their active zones (US patent N 4442065, CL 376-280), taken as a prototype.

 The objective of the invention is to increase the safety of a nuclear power plant by uniformly distributing the melt throughout the volume of the trap, improving cooling, creating additional barriers to the spread of the melt, and reducing the height.

 The problem is solved in that in the trap body installed under the reactor body on the bottom of the concrete shaft, closed with a thin curly metal cover, the following are made and fixed: truss of heat-resistant material; storage chamber with overflow windows; leveling lattice made of heat-resistant material with openings closed by fusible inserts; distribution chamber with outlet overflow windows and openings connected to the pipelines for removal of the melt; melt discharge pipes made of heat-resistant material, at least one melt receiver in the form of a torus tank (1st barrier), made of heat-resistant, well-conducting material, connected to at least one melt pipe, while the melt receiver or its the halves are located at a small angle to the horizontal plane to organize the natural spreading of the melt, and the outlet end of the melt pipe inside the melt receiver is deployed tangentially to its axis; ring tray made of heat-resistant material (2nd barrier) located under the melt receiver; an annular collector of cooling water with nozzles passing through the bottom of the pallet and supplying cooling water to the room of the melt receiver, under the melt receiver, located under the pallet; pipelines with passive and active supply of cooling water to the annular collector, steam pipelines for the removal of steam from the premises of the melt receiver, supporting structures.

 In FIG. 1 shows a general view of the device for the case of using one melt receiver connected by two melt pipelines to a distribution chamber; in FIG. 2 is a view of an AA device.

 A device (trap) for collecting, cooling and holding the melt of the active zone of a nuclear reactor according to the claims is located under the reactor vessel 1, in the concrete shaft 2 of the reactor 1, on the bottom 3 of the concrete shaft 2 of the reactor 1 and consists of the body 4 of the trap made of heat-resistant material and which serves for placement, securing of internals, preventing the core melt from entering the volume of the concrete shaft 2 of the reactor 1. On top of the trap body 4 is closed a curly metal cover 5 with a cowl 6, cat paradise initially melt flow is further configured to partially melt distribution over the cross section of the trap, for preventing its splash trap housing 4 and to reduce the kinetic energy. Under the cover 5 there is a truss 7 made of heat-resistant material, the elements of which have a trapezoidal or triangular cross-section, which serves to detain falling parts from the reactor, partially distribute the trap over the cross-section and reduce its kinetic energy. Below is a storage chamber 8, the bottom of which is a leveling grate made of heat-resistant material with holes evenly distributed over the surface of the grating and closed by low-melting inserts 10, overflow windows 11 are located uniformly around the perimeter in the volume of the storage chamber 8 along the perimeter 11. Under the leveling grating 9 are a distribution chamber 12 with holes in the lower part of the chamber and with overflow windows 11 on the inner surface of the housing 4 of the trap, evenly distributed Jelenia on the perimeter. The overflow windows 11 of the accumulation chamber 8 are connected by channels passing in the wall of the trap body 4 to similar overflow windows of the distribution chamber 12 and are intended for overflowing the melt from the accumulation chamber 8 into the distribution chamber 12 at high melt flow rates when the melt accumulation time is short compared to the melting time of the fusible inserts 10. The holes in the lower part of the distribution chamber 12 are connected to the outlet pipes 13 of the melt made of heat-resistant material.

 In the concrete shaft 2 of reactor 1, behind the trap body 4, there is a room 14 of melt receivers, in which there is a melt receiver 15 (1st barrier), made in the form of a torus container made of heat-resistant, well-conducting material, equipped with an air vent 16, supports 17 of the receiver 15 of the melt, under the melt receiver 15 there is an annular tray 18 (2nd barrier), through the holes in the bottom of which there are pipes 19 of the annular collector 20 of cooling water and its support 21, a pipe 22 for supplying cooling water to the annular collector 20, steam pipelines 23. The melt receiver 15 is connected by the melt pipelines 13 to the lower part of the distribution chamber 12.

 The device (trap) operates as follows.

 The molten core of the nuclear reactor from the reactor vessel 1 flows down onto the curly metal cover 5 of the trap body 4, where it is partially distributed over the cross section of the trap and loses kinetic energy. The shape of the side surface of the lid 5 prevents the melt from spilling over the body 4 of the trap. Next, the melt enters farm 7, where individual parts of the reactor internals are retained, and the melt propagates over the cross section of the trap and loses part of its kinetic energy. After passing the farm, the melt enters the surface of the leveling grating 9, spreads over its surface and accumulates in the storage chamber 8 over a period of time equal to the time of fusion of the fusible inserts 10. If the melt flow rate is high, then the melt through the overflow windows 11, bypassing the leveling grating 9, poured into the distribution chamber 12. This pattern of melt flow will remain until the fusible inserts 10 melt and the level of the melt in the storage chamber 8 drops below the overflow con or a reduction in exhaust velocity. Next, the melt enters the distribution chamber 12, from which it is fed through the melt pipelines 13 to the melt receiver 15, where, due to the inclination of both halves of the torus tank to the horizontal plane and the kinetic energy of the stream at the outlet of the pipeline, the melt receiver 15 flows. The air contained in the melt receiver and the gases released during the melt flow are removed through air vents 16 to the room 14 of the melt receivers and then, being mixed into the steam, are discharged outside the trap through the steam line 23. Another part of the air and gas generated along the path of the melt, is discharged through the housing 4 of the trap into the concrete shaft 2 of the reactor 1 and further into the volume of the protective shell. In the receiver 15 of the melt (1st barrier), the melt is intensively cooled by evaporation of the cooling water located in the premises of the melt receiver. The generated steam is discharged outside the trap through the steam lines 23. At the initial moment of melt cooling, a layer of chilled “frozen” or solid melt forms on the walls of the melt receiver 15. A kind of crucible forms with cooled walls, which contributes to reliable retention of the melt. If there is a penetration of the wall of the receiver 15 of the melt (a hypothetical case), then the melt will pour out on an annular tray (2nd barrier) and will be directly cooled by water.

Claims (1)

 A device (trap) for trapping, cooling and retaining the melt of the core of a nuclear reactor, containing a trap body made of heat-resistant material, located in a concrete shaft under the body of a nuclear reactor, inside of which a leveling grid with low-melting inserts are located and fixed from the heat-resistant material, and a truss forming between a storage chamber with overflow windows, a figured cover for the trap body, a supply line and an outlet for cooling coolant, characterized in that under the leveling solution Coy located distribution chamber with holes in the bottom and overflow windows, at least one receiver in the form of a melt torus capacitance coupled with at least one melt pipe with the distribution chamber, with a torus an annular sump capacity.

Images