GB2037056A

GB2037056A - Traps for nuclear reactors

Info

Publication number: GB2037056A
Application number: GB7942467A
Authority: GB
Original assignee: European Atomic Energy Community Euratom
Current assignee: European Atomic Energy Community Euratom
Priority date: 1978-12-11
Filing date: 1979-12-10
Publication date: 1980-07-02
Also published as: FR2444322A1; LU80638A1; DE2948932A1

Abstract

Catchers for the cores of liquid- cooled nuclear fission reactors, especially sodium-cooled fast breeder reactors, are disclosed in which the side of the trap facing the core is covered with at least one layer of a porous material, e.g. a wire mesh.

Description

SPECIFICATION Traps for nuclear reactors The present invention relates to traps for nuclear fission reactors.

Some traps are known for the cores of liquid-cooled nuclear fission reactors, more particularly for the cores of sodium-cooled fast breeder" reactors. These traps are located in the coolant circuit usually beneath the reactor so that if a fault occurs these traps catch the fragments of the broken reactor core. The fragments, which consist of nuclear fuel and structural parts of the reactor core, are very hot or even molten when they fall on to the trap. If a fault occurs, the temperature at the surface of the trap may rise by up to 1 000'C.

The present invention seeks to reduce the maximum temperature rise which can occur with a prior-art trap, thus ensuring that the structural material of the trap retains sufficient mechanical strength to ensure its required load carrying capacity.

In accordance with the present invention there is provided a trap for the core of a liquid-cooled nuclear fission reactor character ised in that the side of the trap facing the core is covered with at least one layer of a porous material.

The advantage of the trap of the present invention is that if a fault occurs and the surface of the porous layer is heated by hot fragments of the reactor core, convection cur rents of coolant occur against gravity through the layer of porous material, which preferably has an open porosity of about 60-80%. As a result, the heat in the hot fragments is transferred to the coolant. The surface of the trap remains substantially at the same temperature as the coolant, apart from a slight increase through thermal conduction via the porous layer.

An embodiment of the invention will now be described with reference to the accompa nying drawings, in which: Figures 1 and 2 show two embodiments in plan and in cross-section of the porous layers of the present trap in the form of wire meshes, and Figure 3 is a diagrammatic sectional view through a reactor vessel, showing the position of the trap, the porous layer and the space filled with coolant.

Figs. 1 and 2 show two different methods of stacking wire meshes to produce a porous layer for the present trap.

Fig. 1 shows two wire meshes, one consist ing of wires 1 and the second of wires 2, stacked without interlocking. In Fig. 1 the two mats are at a maximum distance apart, so that the ducts of the open porosity also have the maximum volume.

Coolant 3 flows by convection in the direction of arrow 4 away from the surface of trap 5.

Fig. 2 shows two wire meshes, one consisting of wires 1 and the second of wires 2, stacked with interlocking. In this case the stack does not have the maximum height, so that the volume of open porosity is smaller than that of the embodiment shown in Fig. 1.

The coolant 3 flows by convection in the direction of arrow 4 away from the surface of trap 5. The wire mesh which, like trap 5, is usually made of stainless steel, is stacked to form a porous layer and is sintered or welded together.

As shown in Fig. 3, trap 5 is disposed in the bottom part of a reactor vessel 6 under the reactor core 4. Vessel 6 is filled with a coolant 3 and a layer of porous material, e.g.

wire mesh 7, is disposed on a plate 8 forming part of trap 5.

1. A trap for the core of a liquid-cooled nuclear fission reactor characterised in that the side of the trap facing the core is covered with at least one layer of a porous material.

2. A trap as claimed in claim 1 wherein the porous material has an open porosity of from 60 to 80%.

3. A trap as claimed in claim 1 or claim 2 wherein the porous material comprises a wire mesh.

4. A trap as claimed in any one of the preceding claims when adapted for use in a sodium-cooled fast breeder reactor.

5. A trap for the core of a liquid-cooled nuclear fission reactor substantially as hereinbefore described with reference to and as illustrated in either Figs. 1 and 3 or Figs. 2 and 3 of the accompanying drawings.

6. A liquid-cooled nuclear fission reactor including a trap for its core as claimed in any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Traps for nuclear reactors The present invention relates to traps for nuclear fission reactors. Some traps are known for the cores of liquid-cooled nuclear fission reactors, more particularly for the cores of sodium-cooled fast breeder" reactors. These traps are located in the coolant circuit usually beneath the reactor so that if a fault occurs these traps catch the fragments of the broken reactor core. The fragments, which consist of nuclear fuel and structural parts of the reactor core, are very hot or even molten when they fall on to the trap. If a fault occurs, the temperature at the surface of the trap may rise by up to 1 000'C. The present invention seeks to reduce the maximum temperature rise which can occur with a prior-art trap, thus ensuring that the structural material of the trap retains sufficient mechanical strength to ensure its required load carrying capacity. In accordance with the present invention there is provided a trap for the core of a liquid-cooled nuclear fission reactor character ised in that the side of the trap facing the core is covered with at least one layer of a porous material. The advantage of the trap of the present invention is that if a fault occurs and the surface of the porous layer is heated by hot fragments of the reactor core, convection cur rents of coolant occur against gravity through the layer of porous material, which preferably has an open porosity of about 60-80%. As a result, the heat in the hot fragments is transferred to the coolant. The surface of the trap remains substantially at the same temperature as the coolant, apart from a slight increase through thermal conduction via the porous layer. An embodiment of the invention will now be described with reference to the accompa nying drawings, in which: Figures 1 and 2 show two embodiments in plan and in cross-section of the porous layers of the present trap in the form of wire meshes, and Figure 3 is a diagrammatic sectional view through a reactor vessel, showing the position of the trap, the porous layer and the space filled with coolant. Figs. 1 and 2 show two different methods of stacking wire meshes to produce a porous layer for the present trap. Fig. 1 shows two wire meshes, one consist ing of wires 1 and the second of wires 2, stacked without interlocking. In Fig. 1 the two mats are at a maximum distance apart, so that the ducts of the open porosity also have the maximum volume. Coolant 3 flows by convection in the direction of arrow 4 away from the surface of trap 5. Fig. 2 shows two wire meshes, one consisting of wires 1 and the second of wires 2, stacked with interlocking. In this case the stack does not have the maximum height, so that the volume of open porosity is smaller than that of the embodiment shown in Fig. 1. The coolant 3 flows by convection in the direction of arrow 4 away from the surface of trap 5. The wire mesh which, like trap 5, is usually made of stainless steel, is stacked to form a porous layer and is sintered or welded together. As shown in Fig. 3, trap 5 is disposed in the bottom part of a reactor vessel 6 under the reactor core 4. Vessel 6 is filled with a coolant 3 and a layer of porous material, e.g. wire mesh 7, is disposed on a plate 8 forming part of trap 5. CLAIMS