GB2149561A - Floor for fast breeder nuclear reactors - Google Patents

Abstract

There is disclosed a floor (20) for fast breeder nuclear reactors, which is built of reinforced and possibly, precompressed concrete. This concrete floor, resting against or fixed to the upper end of the wall (30) of the reactor well (50) is surrounded by a steel casing providing a tight seal. The steel casing may be in two layers providing a interspace therebetween for circulation of a cooling fluid. <IMAGE>

Description

SPECIFICATION Floor for fast breeder nuclear reactors The invention relates to a floor for fast breeder nuclear reactors.

It is known that a fast breeder nuclear reactor comprises, in its principal structural elements, a substantially cylindrical steel reactor vessel, equipped with a spherical, or in any case convex vessel, which is supported by the reactor floor.

This floor is opportunely supplied with passages for various functional elements which are a part of the reactor, such as heat exchangers, pumps, control devices, as well as fuel element substitutions, and the like.

The floor mentioned, in known solutions, normally rests against a reactor ring made of reinforced concrete, which laterally constitutes the well of the reactor, within which the reactor vessel is contained.

This reactor well constitutes a base on the bottom, forming a single body with the aforementioned reactor ring.

The reactor floor must accomplish the task of carrying out diverse functions: The first of these functions is that of supporting the reactor, the liquid sodium contained in it and all the component elements necessary to the proper functioning of the reactor.

In known reactors, the reactor floor is placed against, or hung onto the top edge of the reactor ring and it acts as a circular plate leaned against its edge : therefore, a considerably high degree of rigidity is required, in order to reduce the rotation of the ridge of the reactor floor, in correspondence with its peripheral support, within acceptable limits.

In known reactors, the reactor floor is constructed of steel; in general, it is composed of a couple of plates connected at their perimeters by an external ferrule. Furthermore, the two horizontally parallel plates are furnished with aligned holes for the passage of various elements of the reactor and in correspondence with said passages the two plates are connected by corresponding intermediate ferrules.

The second function carried out by the reactor floor is that of a closing element : the reactor floor must, therefore, function as a tight joint element between the inside of the reactor vessel and the area above the reactor floor.

This function, in the floors of known reactors of the type described, is carried out by the same structural elements in steel which carry out the function of support.

A third function of the reactor floor is that of creating a biological protection (= screening) against the radiation which originates within the reactor vessel.

For this purpose, known reactors which possess a reactor floor with a supporting structure made of steel have a concrete filling.

The floors of known reactors, furthermore, comprise different cooling and insulation systems for the reactor floor, in order to create a sufficient gap in temperature between the inside of the vessel and the area above it.

As has been mentioned above, reactor floors of the known type have, in most cases, the following characteristics: the reactor floor is composed of two parallel and overlapping steel plates, peripherically connected by a peripherical ferrule and by intermediate ferrules, in correspondence with the openings of the reactor floor designed for the passage of the various functional elements of the reactor; the reactor floor rests against or is hung onto the top border of the reactor ring, which laterally constitutes the reactor well; besides the function of support, the metal structure of the reactor floor also has that of closure, in other words of tight joint; biological protection is carried out by means of a concrete filling.

These characteristics present the following inconveniences: the double function of support and closure of the metallic structure involves expensive construction solutions; the floor resting against its circumference, calls for a high rigidity and therefore requires a heavy weight, equivalent to the weight load it must bear.

The invention seeks to obviate or mitigate against the inconvenience and disadvantages listed above.

According to the invention, the reactor floor is constructed of reinforced concrete, possibly precompressed, assuring its structural function, in place of the metallic plate box structure. The way in which the floor is fixed to the head of the reactor well constitutes a further improvement (even though not indispensable for the solution).

The reinforced concrete floor is coated with a metallic liner which, connected to the seals of the penetrating parts of the reactor components, assures the tight joint function between the reactor atmosphere and the area above the reactor.

Between this "liner" and the metallic caisson represented by the "formwork" of the structure in reinforced concrete, an interspace of adequate thickness creates the envelope which contains a thermoconvector fluid, preferably gaseous, for creating uniformity of temperature within the structure and in order to maintain the average temperature of the structure, within a given interval of time.

The main advantages of the solution can be summarised as follows: separation of the structural function from the tight joint one, with simplification (abolition) of the in-service inspections; high thermal capacity of the structural element, which is therefore better able to withstand accident conditions in the cooling system of the reactor and/or in the cooling system of the reactor floor itself; greater protection of the structure against "sodium fire" accidents; higher rigidity against vertical movements of the reinforced concrete structure, with a minor overall thickness of the structure, which render it more suitable to "filtering" the low frequency seismic excitations for the structure of the reactor unit.

This characteristic is increased by the use between the peripheral area and the well-head; the absence of on in-service inspection requirement of the structure allows the possibility of adapting the height of the canal in which the thermoconvector fluid flows to the requirements of the desired local thermal exchange without any limits of minimum height; saving of direct construction costs, due to the lower cost of the metallic structure and saving on the reactor components, because of the reduction in height of the penetrations through the floor.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows, in a vertical section and in simplified form, the right half of a reactor equipped with a reactor floor according to the invention; Figure 2 shows, an a larger scale, a detail of the fixing of the reactor to the reactor ring, which allows for the obtaining of the reactor well; Figure 3 shows a section along the plane Ill-Ill of Figure 2, of the suspension and means of anchorage of the reactor vessel the floor of the same on a yet larger scale; and Figure 4 shows a partial view of the plant with the floor according to the invention.

With particular reference to these figures 10 indicates the reactor vessel, comprised of a cylindrical shell, closed on the underside by a convex bottom.

This reactor vessel 10 is supported by the reactor floor 20, fixed, at its border, to the top end of the reactor ring 30, which, together with plate 40 constitutes the reactor well 50.

The reactor floor 20 is crossed by passages 21, 22 which allow for the collocation of the various components of the reactor, such as heat exchangers, equipment for the placement and the removal of the fuel modules and so on.

The structure of the reactor floor is illustrated in detail in Figure 2 : the precompressed, reinforced concrete floor 20 is fixed at its edge to the top end of the reactor ring 30, in that it forms one body with it, as can be seen form the figure.

The internal surface of passages 21 and 22 of the reactor floor, 20 are lined with ferrules here called, for the sake of convenience, "intermediates" 23 and 24. These ferrules are made of steel sheets and are connected in a tight way to a steel plate 25, which constitutes, on the bottom, the reinforced concrete reactor floor. In correspondance with the attachment between the reactor floor 20 and the reactor ring 30, the reactor floor comprises an annular groove 26 bound by a metallic lining 27 formed by a peripheral ferrule 28 welded on the bottom to the edge of the restraining plate 25 and on the top welded to an annular plate 29 in which lines the bottom of groove 26. This annular plate 29 is welded, on its external peripheral end, to a frustuconical plate 31, which ends on the bottom with a flange 32 and which encloses the external surface of the groove 26.

Finally, welded to the flange 32, there is a plate 33 enclosing in a continuous way the inside walls of the reactor well 50. Plates 23, 24, 25, 28, 29 and 31 therefore constitute the means of closure which renders the reactor floor tight. It must be noted that these plates function also as a tight formwork for the reactor floor at the moment of its molding.

Analogously, plate 33 represents the lateral clos ing wall of the reactor well 50.

The reactor vessel 10 is supported by an over hanging ferrule 34, of greater width with respect to the vessel 10 and this overhanging ferrule 34 passes through the annular sheet 29 and protrudes within the thickness of the floor 20. As demon strated in detail in Figure 3, on the top edge of the overhanging ferrule 34 some alternatingly vertical stirrups are welded, inclined towards the interior of the reactor, and respectively towards the outside of the reactor.

In this way, the weight of the vessel 10 of the so dium contained in it and of the equipment con tained inside the vessel 10 is efficaciously supported by this triple crown of anchorage stir rups 35', 35', 35". Each row of stirrups 35 origi nates from a common plate 36 welded, in 37, to the top edge of the overhanging ferrule 34, which, between each plate 36, is opportunely supplied with a circular notch 38. As can be seen from Fig ure 3, the three anchoring stirrups 35 are obtained by cutting the plate 36; this cut being interrupted on the bottom by means of circular widenings 39 having, just as the grooves 38, the function of avoiding concentrations of stress.

For the purpose of increasing the anchorage ef fect of the stirrup, 35, each of them ends on top with a hammer-head 41.

Both the ferrule and the plate 25 are supplied with welded anchorage stirrups, which protrude within the reinforced concrete iayer for which, as has been stated before, they act as a tight formwork.

The reinforcement of the reinforced concrete floor is presented in schematic form in Figure 4, where the precompressed areas are indicated, by means of broken lines; indicated instead by contin uous lines are the sole irons aimed at carrying out the pre-compression effect of the reinforced con crete.

For the purpose of allowing cooling of the inter nal surface of ferrules 28, 23 and 24, as well as the bottom side of the reactor floor, the reactor floor comprises a second metallic liner, composed of tu bular bodies 123, 124, 128, as well as a plate 125 with holes.

Between plates 23, and 123, 24 and 124, 28 and 128, 25 and 125, therefore, a slight interspace is created, within which cooling fluid can be made to flow, for example, a gaseous one.

In Figure 2, for example, a duct, 42, is shown, for the inflow and outflow of such a gaseous cooling fluid.

The cylindrical ferrules 28, 128 are connected on top in an adequate way, for example by means of flanging of the one and welding.

In the case of ferrules 21 and 121, 22 and 122, these same ferrules are welded two to two, to a corresponding flanged tubular body, 221, respectively 222, which also acts as a supporting element for the components which comprise the reactor and which are mounted through opening 21 and 22.

The top side of the reinforced concrete floor shall be suitably provided with a central recessing, 43, which assures the collection of any liquid sodium which could possibly have overflowed through the passages in the floor. Analogously, some disposal ducts 44 will be provided for.

Finally, in order to complete the biological protection, above the reactor floor, besides the insulated liners 45 there will be a thick metallic plate 46.

Even though the present invention is based on what has been previously described and illustrated, for purposes of example only, with particular reference to the enclosed tables of drawings, many modifications and variations may be carried out in the construction of this find.

Claims (10)

1. Nuclear reactor floor, of the type which is characterised by the fact that the principal components of the reactor (pumps and exchangers), or possibly the reactor vessel, are supported by a reactor floor, which is supported in turn by a reactor ring, which, with a concrete bed, constitutes the well of the reactor, characterised in that the floor is built of reinforced concrete and is fixed to the top end of the reactor ring.

2. Reactor floor according to Claim 1, characterised by the fact that the bottom side of the reactor floor is enclosed by a closure plate, which prolongs itself, through ferrules in openings provided in the thickness of the reactor floor.

3. Reactor floor according to any one of the preceding claims, characterised in that it is constructed in a double structure which differentiates the structural function (reinforced concrete slab) and the tight joint function (closing plate-liner).

4. Reactor floor according to any one of the preceding claims, characterised in that, in the area of its attachment to the reactor ring, the bottom side of the reactor floor provides for an annular groove enclosed by a metallic plate, through which extends a supporting ferrule the lower end of which is welded to the top edge of the reactor vessel and the upper end of which is connected to a crown of anchorage stirrups (35) that are embedded within the thickness of the reinforced concrete floor.

5. Reactor floor, according to Claim 4, characterized by the fact that the anchorage stirrups mentioned are alternatingly placed, lying on a cylindrical surface; on a conical surface they are collocated with their apex above the floor and with their apex below the floor on another conical surface.

6. Reactor floor according to the preceding claim, characterized by the fact that each row of stirrups, each one oriented in different fashion, originates from the same plate and is supplied on top with a hammer-head.

7. Reactor floor, according to one or more of the preceding claims, characterized by the fact that on the bottom side of the floor and on the inside of the passages which cross the floor, there is predisposed on interspace, through which in use passes a cooling fluid, by means of a second metallic casing parallel to the first.

8. Reactor floor according to the preceding claims, characterized by the fact that the double ferrules are connected on top to flanged bodies, which act as supports for the elements composing the reactor which cross the floor of the same.

9. Reactor floor according to the preceding claims, supplied with a reinforcement in reinforced concrete in the top part of the slab, having a protective function with regard to "sodium fire (thermal and physiochemical effects) for the remaining section of the reinforced concrete slab.

10. A nuclear reactor floor substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.