Strainer for filtering water to an emergency cooling system in a

Details Strainer for filtering water to an emergency cooling system in a Strainer for filtering water to an emergency cooling system in a

1994-07-12

1995-09-26

Silverman, Stanley S.

Liquid purification or separation

Structural installation

Closed circulating system

210408, 210411, 210443, 376313, B01D 2933, B01D 3502, B01D 35027

Patent

active

054531802

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a strainer 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 whose bottom part forms a pool for collecting water formed by condensation of steam present in the containment, the strainer being arranged in the condensation pool and 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, the strainer further having the shape of a housing with at least one, suitably cylindrical, apertured strainer wall through which the water can flow from the outside and into the housing, and being connected, by a first conduit, to a suction pump disposed outside the reactor containment, as well as connected to a second conduit for supplying wash water to the interior of the housing in order, if required, to flush the strainer wall by flowing the wash water through it from the inside and out, thereby removing filtrate deposited on the outside of the strainer wall.


BACKGROUND OF THE INVENTION

In actual practice, the above-mentioned emergency cooling system consists of a first sprinkler system comprising a plurality of nozzles or sprinklers mounted in the upper part of the reactor and adapted to spray large amounts of water on the fuel rods in order to cool these when there is an emergency. The plant further includes a second sprinkler system comprising a plurality of nozzles or sprinklers which, like those of the first system, take their water from the condensation pool in the containment, but which are mounted outside the reactor proper and are adapted to sprinkle the gas phase in the containment in order to reduce any remaining excess pressure therein as well as to cool conduits or other components found inside the containment but outside the reactor itself. In both instances, it is of great importance that the water supplied to the nozzles is free from all sorts of impurities, such as fibres, grains and particles, that might clog the nozzles. Naturally, this is especially important in the emergency cooling system, which has to be absolutely reliable. Many of the components mounted inside the containment, such as the conduits, are wholly or partly heat insulated. In most of today's nuclear power plants, this insulation is made up of fibres of mineral wool, which constitute an element of risk with regard to the two sprinkler systems, in that unintentionally released fibres may clog the nozzles if reaching the sprinkler systems. For this reason, nuclear power plants have been equipped with strainers of the type stated by way of introduction.
In actual practice, it takes about 5-10 min to back-flush a conventional strainer which is contaminated with a fibre mat tending to clog the strainer holes. It was previously held that the strainers could operate for at least 10 h without any need of back-flushing. However, real-life incidents have shown that this estimated minimum operating time is too long. In functional tests, it has happened that discharged steam has entrained mineral-wool insulation, which has dropped into the condensation pool and clogged the-strainers even after about 30 min. Back-flushing, which takes 5-10 min, is not a critical operation 10 h after a possible reactor trip, since the decay power of the reactor core then has been considerably reduced, as has the need for cooling. However, if back-flushing is required after less than 1 h, the need for cooling of the core is still considerable, and an interruption of the water supply to the emergency cooling system for 5-10 min therefore is unacceptable for reasons of safety.
One reason why back-flushing of the strainer takes such a comparatively long time is that the fibres accumulating on the outside of the strainer wall form a continuous, circumferential mat or cake in which they are closely intertwined. The wash water flowed from the inside and radially outwar

REFERENCES:
patent: 3066803 (1962-12-01), Seils, Jr.
patent: 3071251 (1963-01-01), Szwargulski
patent: 3164164 (1965-01-01), Pall et al.
patent: 3187898 (1968-06-01), Baker
patent: 3392842 (1968-07-01), Anderson
patent: 3545621 (1970-12-01), Lamort
patent: 4834885 (1989-05-01), Misgen et al.
patent: 4969994 (1990-11-01), Misgen et al.
patent: 5104537 (1992-04-01), Stifelman et al.

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