Patent Number: 056129831
Section: claims

1. A device for filtering water to at least one emergency cooling system in a nuclear power plant of the type comprising a reactor arranged in a containment which substantially consists of an upright, suitably cylindrical container whose bottom part forms a pool for collecting water formed by condensation of steam present in the containment, the condensation pool including a number of back-flushable strainers (3) serving to filter water which is taken from the pool and, if required, is supplied to nozzles in the emergency cooling system in order to cool the reactor core in the event of an inadmissible temperature rise therein, each strainer having the shape of a housing with at least one, suitably cylindrical, apertured strainer wall (10) through which the water can flow from the outside and into the housing, and being connected, by a first conduit (4) passing through the container wall (1), to a suction pump disposed outside the container wall, as well as connected to a second conduit (7) for supplying wash water to the interior of the housing in order, if required, to flush the strainer wall (10) by flowing the wash water through it from the inside and out, thereby removing filtrate deposited on the outside of the strainer wall, characterised in that a number of secondary strainers (24), each consisting of an elongate, apertured tube which is substantially vertically mounted and has a diameter or maximum cross-sectional dimension from about 200 mm to about 400 mm and a length dimension at least five times greater than the diameter dimension, are connected either directly or indirectly by a third conduit (23) to the first conduit (4) connected to the suction pump. 2. A device as set forth in claim 1, characterised in that the secondary strainer tubes (24) are mounted on a vertical upright, preferably in the form of a column (2) arranged in the containment and forming part of the load-bearing structure thereof. 3. A device as set forth in claim 2, characterised in that the structure is achieved by means of a number of clamp sets which are vertically spaced apart along the upright (2) and which each comprise a main clamp (25) consisting of two first part-circular hoop elements (25', 25") which enclose the upright (2) and are interconnected by bolted joints (26, 26'), and that at least one of the two first hoop elements (25', 25") has a number of radially projecting support means (27) which at a free end support one of two second particular hoop elements (28', 28") which together enclose an individual strainer tube (24) and are interconnected by bolted joints (29, 29') or the like. 4. A device as set forth in claim 1, characterised in that the strainer wall (10) of the back-flushable strainer (3) includes means (17) for dividing a fibre mat or layer built up on the outside of the strainer wall into several part sections. 5. A device as set forth in claim 4, characterised in that the means (17) consist of a number of longitudinal, peripherally spaced-apart and radially projecting wings or wing-like elements (17). 6. A device as set forth in claim 4, characterised in that the second conduit consists of a tube (7) which, in the area of an opening located concentrically in relation to the strainer wall (10), includes rotation-generating means (18) comprising a set of curved blades (20) extending between the tube and a substantially conical body located centrally therein, whereby water passing through the annular gap between the tube and said body is caused to rotate or circle so as to be pressed out against the strainer wall (10). 7. A device as set forth in claim 1, characterised in that the housing of the back-flushable strainer (3) includes an upper end and a lower end, said strainer being closed at said upper end the first conduit (4) being connected to the lower end, and the wash-water conduit (7) being concentrically inserted in a portion (4') of the first conduit (4). 8. A device as set forth in claim 1, characterised in that the third conduit (23) is connected to the first conduit (4) at a point (30) between the back-flushable strainer (3) and the suction pump. 9. A device as set forth in claim 2, characterized in that the strainer wall (10) of the back-flushable strainer (3) has means (17) for dividing a fibre mat or layer built up on the outside of the strainer wall into several part sections which separately are more easily released than a continuous circumferential fibre mat. 10. A device as set forth in claim 3, characterized in that the strainer wall (10) of the back-flushable strainer (3) has means (17) for dividing a fibre mat or layer built up on the outside of the strainer wall into several part sections which separately are more easily released than a continuous circumferential fibre mat. 11. A device as set forth in claim 5, characterized in that the second conduit consists of a tube (7) which, in the area of an opening located concentrically in relation to the strainer wall (10), is provided with a rotation-generating means (18) in the form of a set of curved blades (20) extending between the two and a substantially conical body located centrally therein, so that water passing through the annular gap between the tube and said body is cause to rotate or circle so as to be pressed out against the strainer wall (10). 12. A device as set forth in claim 1 wherein said maximum cross-sectional dimension of said secondary strainer is between about 250 mm and 350 mm. 13. A device as set forth in claim 1, characterized in that said length dimension is at least ten times greater than the diameter dimension. 14. A device for filtering water to at least one emergency cooling system in a nuclear power plant of the type comprising a reactor arranged in a containment which substantially consists of an upright, suitably cylindrical container whose bottom part forms a pool for collecting water formed by condensation of steam present in the containment, the condensation pool including a number of back-flushable containers (3) searing to filter water which is taken from the pool and, if required, is supplied to nozzles in the emergency cooling system in order to cool the reactor core in the event of an inadmissible temperature rise therein, each strainer having a shape of a housing with at least one, suitably cylindrical, apertured strainer wall (10) through which the water can flow from the outside and into the housing, and being connected, by a first conduit (4) passing through the container wall (1), to a suction pump disposed outside the container wall, as well as connected to a second conduit (7) for supplying wash water to the interior of the housing in order, if required, to flush the strainer wall (10) by flowing the wash water through it from the inside and out, thereby removing filtrate deposited on the outside of the strainer wall, characterized in that a number of secondary strainers (24), each consisting of an elongate, apertured tube having a diameter or maximum cross-sectional dimension from about 200 mm to about 400 mm and a length dimension at least five times greater than the diameter dimension, are connected either directly or indirectly by a third conduit (23) to the first conduit (4) connected to the suction pump.