CH615477A5 - Device for the thermal insulation of a prestressed concrete vessel - Google Patents

Abstract

The vessel (1) which is intended for a nuclear reactor, more particularly of the boiling water type, contains two shell rings (25 and 27) arranged one above the other and joined to the wall of the vessel by means which provide both the leaktightness and the support of the shell rings at the passages (33 and 39) for the inlet and outlet pipes (37 and 31). The two shell rings are independent, the lower shell ring being engaged inside the external shell ring. A cooling liquid fills the space between the shell rings up to a level where the latter overlap, whilst a gas fills the space (43) between the vessel and the upper shell ring which furthermore carries the cover (29). <IMAGE>

Description

The present invention relates to the thermal insulation of a prestressed concrete box for resistance to the pressure of a fluid contained inside said box.

It is known that such a box is used in particular in a nuclear reactor cooled by a vaporizable liquid, said box being coated internally with a metal sealing sheet.

In a known manner, the thermal insulation of the casing of such a nuclear reactor is carried out by placing inside said. box an envelope trapping the hot fluid under pressure so as to constitute between the internal wall of said box and said envelope a gas insulation.

In order to identify the problems solved by the present invention, reference is made to FIG. 1 attached representing known art.

This figure shows the prestressed concrete box 1 closed by the slab 3 of a nuclear reactor cooled by a vaporizable liquid inside which the main organs of said reactor are arranged.

There is in particular inside said box 1 an internal metallic casing 5 in the form of a bell which, attached to said box 1 and associated with a liquid seal 9, traps the coolant 11 of the reactor core 13. Thus said bell 5 defines with the internal wall of said box 1 an annular space 15 filled with a thermal insulating gas under a suitable pressure.

It goes without saying that in said bell 5 open conduits, such as 17a and 17b, produced and arranged in bushings, such as 19a and 19b, so that the expansions of said bell 5 are absorbed.

It can be noted that such thermal insulation has a number of drawbacks.

In fact, it can be seen that appropriate means must be used to balance, during operation of the reactor, the pressures prevailing respectively inside said bell 5 and the annular space 15.

Furthermore, due to both longitudinal and radial expansions of said bell 5 in line with a bushing 19, the arrangement of a pipe 17 in a bushing 19 has a complex and unsatisfactory character in terms of maintaining etan-cheity of the annular space 15. It is also necessary to set up around the heart a security envelope 21 to avoid dewatering of the heart in the event of gas leakage. Finally, there is a large volume of compressed gas inside the casing which provides certain constraints.

The present invention specifically relates to a device for isolating a prestressed concrete box such as that of a nuclear reactor of the so-called boiling water type, making it possible in particular to overcome the drawbacks presented by the device of the prior art described above.

The device which is the subject of the invention is a device for isolating a prestressed concrete box for resistance to the pressure of a vaporizable fluid contained inside said box, in two phases separated by an interface, at least two families coplanar crossings being arranged in the lower and upper parts of the box for the establishment of inlet pipes of said fluid in the liquid state and outlet of said fluid in the gaseous state.

This device is characterized in that it comprises:

- two ferrules disposed respectively in the lower and upper parts of said box, the upper ring being closed by a cover, said rings having different diameters, being coated with a metallic insulation, and delimiting between said vaporizable fluid and the internal wall of said box a chamber filled with liquid phase fluid up to the level of the liquid vapor interface of said fluid and filled with gas above said level, the covering of said ferrules constituting a liquid seal in cold fluid;

- Means by means of which said ferrules are each supported by said box in line with at least three

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615 All of said crossings of the same family, said means authorizing the right of these crossings the radial expansion of said ferrules;

- watertight means arranged in line with the bushings capable of absorbing the radial expansion of said ferrules. The device of the invention as characterized above makes it possible to isolate in a simple and safe manner the casing of a nuclear reactor cooled by a vaporizable fluid since the tightness of said chamber remains satisfactory during the operation of said reactor without requiring a complex arrangement of the conduits in the crossings and by bringing to a smaller volume the external regulation of the pressure prevailing in said chamber.

In fact, said chamber is advantageously constituted by two independent ferrules whose longitudinal expansions are zero at the crossings and whose overlap is such that it allows the pressures prevailing on both sides to be balanced during operation of the reactor. other of each of said ferrules.

According to a preferred embodiment of the device, object of this invention, said ferrule disposed in the lower part of the box has, between said inlet pipes of said fluid and the bottom of said box, an annular opening whose lower edge is secured to an annular part rising inside said ferrule parallel to the latter, said ferrule being tightly connected to the bottom of said box and said part being coated at least vis-à-vis said annular opening, with a metallic insulation.

Thus, the device of the invention in accordance with this preferred variant of embodiment has the advantage of avoiding that the balancing of the pressures by the liquid seal creates a significant difference between the levels of the fluids situated on either side of the lower shell, these fluids having very different temperatures. In fact, according to this variant, the pressures of the abovementioned fluids are advantageously equalized, by virtue of said annular opening, clearly above the bottom of the box.

According to the above-mentioned preferred embodiment of the device of the invention, said annular opening is preferably formed in said lower ferrule as close as possible to said fluid intake pipes.

Furthermore, according to this variant, said lower ferrule can be connected by its lower edge to the bottom of said box either directly or via the internal structure enveloping the reactor core.

According to a particular arrangement of the invention, said lower and upper ferrules of the device of the invention, whether or not conforming to the aforementioned preferred embodiment, are respectively supported by said box through the liquid intake pipes and steam outlet pipes, these pipes being produced so as to be able to slide inside their bushings in order to allow the radial expansion of said ferrules to the right of the latter.

According to another particular arrangement, said ferrules are each supported by bearing surfaces integral with said box located in the plane of the crossings.

On the other hand, according to the invention, sealing bellows are interposed in said liquid inlet or vapor outlet pipes so as to absorb the radial expansions of each of the ferrules while maintaining satisfactory sealing of said chamber. .

Said bellows can be arranged either inside the bushings, or outside the latter, the latter arrangement allowing easier and faster inspection and disassembly.

The characteristics and advantages of the present invention will appear more clearly on reading the following description of embodiments of the device of the invention for the thermal insulation of the casing of a nuclear reactor of the so-called boiling water type, given by way of illustration, but in no way limiting.

This description will be made with regard to the schematic figures appended 2 to 6 in which there is shown:

in fig. 2, in vertical section, a first alternative embodiment of the isolation device of the invention;

in fig. 3, in vertical section a second preferred embodiment of the isolation device of the invention according to which the lower shell has an annular opening, this shell being connected to the bottom of the reactor vessel through the structure enveloping the core ;

in fig. 3a, also in vertical section, the lower part of the device of the invention according to the second preferred embodiment for which the lower ferrule is connected directly to the bottom of the box;

in fig. 4, also in vertical section, the device of the invention in line with a crossing according to a first particular arrangement of the invention, the ferrule shown being supported by the box through the conduits opening out inside that -this ;

in fig. 5, a cutaway view of the device of the invention at the right of a crossing according to a second particular arrangement of the invention, the ferrule shown being supported by bearing surfaces integral with said box at the level of the crossings to cancel the vertical expansions at the right of these latter ;

in fig. 6, the device of the invention in line with a crossing in accordance with an embodiment allowing the bellows to be checked in a simple manner and the crossing of the box to be dismantled.

In fig. 2, the concrete box 1 of a so-called boiling water nuclear reactor is recognized, said box closed at its upper part by the slab 3 being coated on the inside with a metal sealing sheet 23.

It can be seen that inside said box 1, the refrigerating fluid 11 of the heart 13 is trapped in an envelope internal to said box, constituted, according to the essential characteristic of the invention, by two ferrules 25 and 27 of low weight respectively arranged in the upper and lower parts of said box 1, the upper shell closed at its upper part by a cover 29 being closer to the internal wall of said box 1 than the lower ring 27. The cover 29 is fixed to the upper ring 25 by classic quick-release systems symbolized in 29 '.

For the nuclear reactor shown in fig. 2, the refrigerating fluid 11 is introduced into the interior of the lower shroud 27 by conduits such as 31 each arranged in bushings such as 33, coplanar bushings similar to the bushing 33 being regularly formed in the wall of said box 1 .

Said refrigerating fluid 11 heated in the heart 13 of the reactor escapes in the form of vapor by pipes such as 37 each arranged in a bushing such as 39, said bushing 39 belonging to a second family of coplanar bushings formed in the upper part of said box 1.

According to a particular arrangement of the invention, the lower ferrule 27 is supported at the right of at least 3 of the bushings such as 33 and the upper ferrule 25 is at the right of at least 3 of the bushings such as 39.

The annular space 41 delimited by the lower ferrule 27 with the internal wall of the box 1 is filled with water over a height corresponding approximately to the height of the coolant contained in said lower ferrule 27 so as to constitute an insulation in cold water. , said ferrule 27 being coated on the outside with a suitable metallic insulation, such as "metalisol". It is specified that the annular space 41 is filled with cold insulation water when the reactor is filled before it is started.

The space 43 delimited by the upper shell 25 with the internal wall of the box is filled with gas so as to constitute a thermal insulation in gas, said shell 25 being coated with an appropriate metallic insulation such as “metalisol”. It is specified that the introduction of gas into space 43 and the regulation of

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its pressure are carried out by a loop external to the reactor, not shown.

It can be seen that according to one of the characteristics of the invention, said upper ferrule 25 enters the water filling said annular space 41 so as to constitute, with the lower ferrule 27 rising above the water level, a seal liquid in cold water 16.

It may be noted that the lower ferrule 27 is provided at its base with a system of baffles 45 preventing rapid transfers of fluid on either side of said ferrule 27 at the base of said box 1.

There is shown in this fig. 2 very symbolically the pipes 31 and 37 opening respectively into the ferrules 27 and 25. The precise embodiment of these pipes as well as their arrangement in a crossing will be described with reference to Figs. 4 to 6 which will make it possible to show the realization of the means of the invention allowing the point of support of each of the ferrules to expand radially and to maintain the tightness of said annular spaces 41 and 43.

We simply symbolized in this fig. 2 the link which must exist between the pipes and the bushings to seal the annular spaces 41 and 43.

Before explaining the mode of action of the device as described above, it is recalled that as the reactor operates, the refrigerant 11 vaporizes while passing through the heart 13 thus causing an increase in temperature and an increase in pressure inside the internal envelope formed by said ferrules 25 and 27.

Thus, the mode of action of the device of the invention is such that, when the vapor pressure inside said shell 25 increases, the pressure prevailing inside said annular space also increases, said liquid seal occurring under the shape of a siphon.

We can now note that thanks to the liquid seal 16 balancing the pressures prevailing on either side of said ferrules 25 and 27 during operation of the reactor, the sealing at the right of the bushings can be obtained in a simple manner as we will see with regard to figs. 4 to 6.

In fig. 3, the device of the invention is shown according to a preferred variant of embodiment making it possible to avoid the establishment of a significant difference in level between the fluids located on either side of the lower shell during operation of the reactor. . In this fig. 3, the elements already shown in FIG. 2 will keep their reference.

Thus, in this figure, it is recognized the internal envelope of said box which, trapping the refrigerating fluid 11 of the heart 13, is constituted by the two low-weight ferrules 25 and 27 respectively arranged in the upper and lower parts of said box 1 and supported by the box in the plane of the bushings 33 and 39, the covering of said ferrules 25 and 27 constituting a liquid seal in cold water 16 knowing that said annular spaces 41 and 43 are respectively filled with water and gas for the insulation of the box.

On the other hand, it can be noted that the pipes 31 and 37 are also shown in FIG. 3 very symbolically. Their construction and their arrangement in the bushings 33 and 37 will be described with reference to FIGS. 4 to 6.

It can be seen that, according to the essential characteristic of the embodiment of the device of the invention shown in this FIG. 3, the lower ferrule 27 has, between said bushings 33 and the bottom of said box 1, an annular opening 51, the lower edge 53 of which is integral with an annular part 55 rising inside said ferrule 27 parallel to this last.

On the other hand, it can be seen in this figure that said annular part 55 is coated externally, facing said annular opening 51, with an appropriate metallic insulation 57, preferably identical to that which covers said ferrules 25 and 27, such as for example "metalisol".

Furthermore, we note in FIG. 3 that said ferrule 27 is tightly connected by its lower edge to the structure 59, which envelops the heart 13, is itself connected to the bottom of the vessel 1 of the reactor.

We also note that a metal plate 61 is held by supports symbolized at 63 above the bottom of the box 1 so as to delimit with the latter, for its thermal insulation, a compartment 65 inside which the refrigeration fluid 11 is not circulated by the pumps 67 for circulating this fluid.

In fig. 3a for which the references of FIG. 3 are retained, it can be seen that the lower shroud 27 can be directly connected in a sealed manner, to the bottom of the box 1.

The mode of action of the device shown in FIGS. 3 and 3a is as follows. The annular opening 51 formed in the lower shell 27 at an appropriate height above the bottom of the box 1, preferably as close as possible to the bushings 33, makes it possible to equalize, at this annular opening 51, the respective pressures fluids which, located on either side of said shell 27, have different densities due to the difference between their temperatures.

Furthermore, it is noted that the pressure equalization via said annular opening 51 is carried out by avoiding fluid transfers on either side of said ferrule 27 thanks to said annular part 55 which, of sufficient height, is connected to the lower edge 53 of said opening 51 and disposed inside said ferrule 27.

In addition, thanks to the non-insulated extension of the annular part 55, above the annular opening 51, the volume of cold water which can reach the heart is limited in the event of an incident.

On the other hand, by virtue of the thermal insulation 57 covering said part 55 at an appropriate height, it is ensured, in line with said annular opening 51, the continuity of the thermal screen produced along said ferrules 25 and 27.

Thus, the device according to the variant embodiment of FIGS. 3 and 3a makes it possible to significantly and safely limit the difference in level which is established between the fluids located on either side of said ferrule 27 during the balancing of their pressures by said liquid seal in cold water. 16 during the operation of said reactor.

As a result, the bushings 33 can advantageously be positioned sufficiently above the core 13 of the reactor.

In fig. 4, 5 and 6 there is shown the device of the invention, according to one or other of the embodiments of FIGS. 2 and 3, in line with the bushings 33, 39, these figures showing two modes of support by the box 1 of the ferrules 25, 27 and the embodiments of the pipes 31, 37 as well as their arrangement in the said bushings.

In fig. 4, we recognize for example the upper shell 25 delimiting the annular space 43 with the internal wall of said box 1, this shell being coated with a layer of heat-insulating material 26 suitable for producing gas insulation such as for example "metalisol", said thermal insulation being protected by a thin sheet of steel 28.

It can be seen that the edge 147 of said ferrule 25 delimited by the orifice 149 formed in the latter is integral with the pipe 37 in which a sealing bellows 151 is inserted. It can be seen that said pipe 37 is internally provided with a horn removable 153 fixed by the screw 154 to said pipe 37 at its point of attachment to said ferrule 25, the free end of said tube 153 being capable of sliding inside the pipe 37 while being guided in the bore 37a serving to support the said tube 153.

The outer wall of said pipe 37 is connected to the inner wall of said box 1 in the bushing 39 by means of the frustoconical skirt 155 so as to close the annular space 43 in line with said bushing 39, a thermal insulation 156 being interposed between said box 1 and the pipe 37 on either side of said skirt 155.

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Thus during the operation of the reactor, the radial expansion of said ferrule 25 is authorized by virtue of the simultaneous displacement of said tube 153 inside said pipe and absorbed by said bellows 151 maintaining the tightness of said space 43.

It will be recalled that the longitudinal expansion of said ferrule 25 5 is zero at the right of the bushing 39 since said ferrule 25 supported by said box 1 at the right of the bushing 39 by means of the horn 153 is free.

We find for the alternative embodiment of the device of the invention shown in FIG. 5 the elements of fig. 4 which 10 will therefore retain the same references.

It is noted that said ferrule 25 carries, for example at its point of attachment to the pipe 37 as in FIG. 4, a part 157 capable of bearing on a bearing surface 159 integral with the internal wall of said box 1, the respective embodiments of said part 157 and of said bearing surface 159 being such that said ferrule 25 can expand radially during the reactor operation.

It goes without saying that the parts such as 157 can be distributed over the periphery of said ferrule 25 at points distinct from the 2o points of attachment of said ferrule 25 with the pipes such as 37 since it suffices that said parts are located in the plan of crossings such as 39.

Furthermore, to eliminate the angular displacement of said ferrule 25 inside said box 1, the box 1 also carries a part 161 capable of fitting into a centering yoke 163 secured to said pipe 37.

The only difference between the embodiments shown diagrammatically in FIGS. 4 and 5 therefore resides in the method of supporting the ferrule 25 in line with a crossing. It goes without saying that the description given with reference to FIGS. 4 and 5 also apply for the lower part of the device of the invention at the bushings 33 to the right of which the lower ferrule 27 is supported.

Fig. 6 shows another alternative embodiment of the arrangement of the means capable of authorizing and absorbing the expansion of a ferrule in line with a crossing.

The realization of the device in line with one or other of the families of bushings 33 and 39 which will be described below is particularly desirable for the lower bushings closest to the core in order to facilitate the inspection of the casing 1.

In fact, it can be seen that the pipe 31 is secured by simple screwing 165 with the ferrule 27, which is possible without causing sealing problems since the liquid seal balances the pressures prevailing on either side of said ferrule, and which makes it possible to separate said pipe 31 and said ferrule 27 from outside the box 1.

It goes without saying that the shell 27 is coated with a thermal insulation 28 suitable for producing water insulation in the space 41 such as for example “metalisol”.

It can be seen that said pipe 31 bears against the wall of the box 1 at two points A and B situated inside the bushing 33 so as to support said shell by said box 1 in line with said bushing 33, said pipe 31 being able to slide inside said bushing 33 when said ferrule 27 expands radially.

Thus the bellows 151 can be advantageously placed, to facilitate its control, outside the box 1. The annular connecting cap 167 with quick disassembly connecting said pipe 31 to the bushing 33 closes the annular space 41.

In conclusion, it may be recalled that when the device of the invention is implemented in a nuclear reactor, the heart of the latter may no longer be surrounded by a safety shell, given the position of the balancing siphon , which reduces the internal diameter of the reactor vessel.

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4 sheets of drawings

Claims (10)

615,477 1. A device for thermal insulation of a prestressed concrete box for resistance to the pressure of a vaporizable fluid contained inside said box in two phases separated by an interface, at least two families of coplanar crossings being arranged in the lower and upper parts of the box for the establishment of pipes for admitting said fluid in the liquid state and leaving said fluid in the gaseous state, characterized in that it comprises: - two ferrules (25, 27) disposed respectively in the lower and upper parts of said box, the upper ferrule being closed by a cover (29), said ferrules having different diameters, being coated with a metallic insulation (26) and delimiting between said vaporizable fluid and the internal wall of said box a chamber filled with liquid phase fluid up to the level of the vapor liquid interface of said fluid and filled with gas above said level, the covering of said ferrules constituting a liquid seal (16 ) in cold fluid; Means (157, 159, 165) by means of which said ferrules are each supported by said box in line with at least three of said crossings of the same family, Said means authorizing the right of these crossings the radial expansion of said ferrules; - watertight means (151) arranged in line with the bushings capable of absorbing the radial expansion of said ferrules. 2. Device according to claim 1, characterized in that the ferrule (27) disposed in the lower part of said box has, between said fluid inlet pipes and the bottom of said box, an annular opening (51) whose lower edge (53) is integral with an annular part (55) rising inside said ferrule parallel to the latter, said ferrule being tightly connected to the bottom of said box and said part being coated, at least vis- with respect to said annular opening, a metallic insulation (57). 2 3. Device according to claim 2, characterized in that said annular opening (51) is formed, in said ferrule, as close as possible to said fluid intake pipes. 4. Device according to claim 2, characterized in that said ferrule is connected directly to the bottom (5) of said box. 5. Device according to claim 2, characterized in that said ferrule is connected to the bottom of said box through the internal structure enveloping the heart of said reactor. 6. Device according to any one of claims 1 to 5, characterized in that said means by means of which said ferrules are each supported by said box are constituted for the lower ferrule (27) by the pipes (31) of liquid inlet and for the upper shell by the steam outlet pipes, said pipes being able to slide inside said bushings. 7. Device according to any one of claims 1 to 5, characterized in that said means by means of which said ferrules are supported, are constituted by bearing surfaces (157, 159) of said box. 8. Device according to any one of claims 1 to 5, characterized in that said sealed means capable of absorbing the radial expansion of the ferrules are constituted by bellows (151) interposed in each of the fluid intake pipes and steam outlet. 9. Device according to claim 8, characterized in that said bellows are located inside the bushings. 10. Device according to claim 8, characterized in that said bellows are located outside the bushings.