Reactor building

Reactor building structure comprising a ring building roof embedded in the cylindrical skirt of the confinement enclosure. The structure is constituted by a confinement enclosure comprising a cylindrical skirt and a dome, as well as by a ring building surrounding the confinement enclosure. The ring building comprises a cylindrical skirt and a roof, the confinement enclosure and the ring building being erected on a common general foundation raft or floor. The internal structures are positioned with the confinement enclosure. The roof of the ring building is toroidal or frustum-shaped, being embedded in the cylindrical skirt of the confinement enclosure. The internal structures are disengaged from the confinement enclosure.

BACKGROUND OF THE INVENTION 
The invention relates to a reactor building construction comprising a ring 
building roof embedded in the cylindrical skirt of the confinement 
enclosure. 
In general terms, the building in which a nuclear reactor is installed 
comprises a confinement enclosure within which are placed internal 
structures supporting the components of the primary circuit. In general, a 
ring building containing most of the auxiliary and safety systems 
surrounds the confinement enclosure. Preferably, the confinement enclosure 
and ring building are constructed on a joint foundation raft or floor, 
which obviates the problem of different settlement levels which would 
occur with foundations on independent rafts or floors. 
A construction of this type is described in French Pat. No. 2,226,729, 
filed on Apr. 18th 1974 and entitled "Nuclear power station with a 
protective envelope surrounded by a concrete building" in the name of the 
SIEMENS AKTIENGESELLSCHAFT. This patent describes a nuclear reactor 
building construction having a protective envelope and a concrete building 
surrounding the latter, whilst forming therewith an annular space 
containing ancillary installations and in particular emergency cooling 
devices. The concrete building and the concrete protective envelope have a 
joint concrete foundation. The concrete building bears on the concrete 
cylinder and has a flat roof in the bearing zone. 
BRIEF SUMMARY OF THE INVENTION 
The invention relates to a building construction for a nuclear reactor 
making it possible to still further improve the protection in the case of 
an earthquake and against large missiles from the outside. 
More specifically, the nuclear reactor building structure constituted by a 
confinement enclosure comprises a cylindrical skirt sealed in its upper 
part by a dome, a ring building surrounding the confinement enclosure and 
which is constituted by a cylindrical skirt and a roof connected to the 
cylindrical skirt of the confinement enclosure, whereby the latter and the 
ring building are erected on a common foundation raft or floor, and 
internal structures positioned within the confinement enclosure, wherein 
the ring building roof has a frustum or toroidal shape and is embedded in 
the cylindrical skirt of the confinement enclosure, the internal 
structures being disengaged from the skirts of the confinement enclosure 
and the ring building. 
Preferably, the foundation raft or floor comprises a high-inertia 
honeycombed or cellular part positioned below the ring building and a 
solid part, lowered with respect to the cellular part and positioned 
beneath the confinement enclosure.

This reactor building structure comprises a general foundation raft or 
floor 2 on which is erected a confinement enclosure 4. The latter 
comprises a cylindrical skirt 6 sealed by a dome 8 in its upper part. The 
function of the confinement enclosure is to prevent any leak of 
radioactive substances in the case of an accident and to withstand 
pressure and temperature effects resulting from a possible fracture of the 
primary or secondary circuits. 
The confinement enclosure houses the internal structures 10, which 
essentially comprise a so-called internal structure floor 12, a vessel 
well 14 surrounding and supporting reactor vessel 16 and casemates 18 
positioned around the said well. 
The ring building 20 surrounding confinement enclosure 4 is erected around 
the latter. This ring building comprises a cylindrical skirt 22 erected on 
the foundation raft 2 and a roof 24 connected to skirt 6 of the 
confinement enclosure. Within the ring building are installed auxiliary 
means associated with the protection of the reactor or having a high 
radiological risk. 
Confinement enclosure 4, ring building 20 and internal structures 10 are 
installed on the general foundation raft or floor 2, thereby overcoming 
the problem of different settlements which could occur if they were 
erected on independent floors or rafts. 
This structure provides protection against missiles striking the reactor 
building and auxiliary means linked with the protection of the reactor or 
having a high radiological risk. The missile in question could even be a 
military aircraft which, during impact, would have a static load 
equivalent to 1100 metric tons distributed over 7 m.sup.2. 
According to the invention, the roof 24 of the ring building is embedded in 
the cylindrical skirt 6 of the confinement enclosure. The ring building 
roof is fixed to the confinement enclosure by means of meridian passive 
reinforcing members anchored on either side of the embedding or fixing 
section. 
Rendering the ring building integral with the confinement enclosure offers 
the following advantages: 
(1) In the case of a fall of an external missile, it improves the 
performance of the ring building roof 24. 
(2) As the mass in question is greater, the relative displacements of the 
assembly formed by the confinement enclosure and the ring building are 
smaller with respect to the structures. 
(3) The vibration mode of the assembly formed by the confinement enclosure 
and the ring building is at a higher frequency than those of each 
structure taken in isolation, so that the structure has a reduced response 
level to earthquakes. 
(4) It prevents the development of complex vibration modes in the raft or 
floor. 
(5) For ventilation reasons and due to the contamination risks of certain 
rooms located at the final level of the ring building, a building 
structure in which the confinement enclosure and ring building are not 
integral, makes it necessary to have an air-tight joint at the junction of 
the ring building roof and the confinement enclosure skirt, this 
constraint not existing if embedding is used. 
Preferably, the joining level coincides with the brackets of the handling 
bridge of the reactor building. 
The roof 24 of the ring building 20 has a toroidal or frustum shape, as 
shown in the drawing. It can have a single or double curvature. 
The internal structures 29 of the ring building are disengaged from the 
confinement enclosure skirt and the ring building envelope. Thus, in the 
case of impact by a missile, it is possible to integrally benefit from the 
hull effect produced by the shape of the envelope, the high forces and 
loads are not transmitted to the internal structures 29 and they are not 
directly shaken or loosened. Finally, this disengagement permits the free 
development of dimensional variations of the envelope with respect to the 
internal structures 29 under the action of contraction and heat. 
The general foundation raft or floor 2 comprises two parts having different 
designs. Beneath the ring building 20, there is a high-inertia honeycombed 
or cellular raft or floor part 26, the honeycombs or cells being used for 
the installation of certain protective and safety equipment. Beneath the 
confinement enclosure 4, there is a solid raft or floor part 28, which is 
lowered with respect to the first-mentioned part. The lowering of part 26 
of the raft compared with the solid part 28 makes it possib1e to lower the 
level of the assembly of internal structures 10 and ring building 20, as 
well as the components supported by them. Thus, the height of the ring 
building is reduced. By lowering the centre of gravity level of the masses 
of the ring building, it is possible to reduce the stresses therein in the 
case of seismic shocks. 
Due to its considerable rigidity, the cellular raft or floor undergoes 
little deformation which makes it possible to ensure the mechanical 
stability of the embedding of the ring building covering in the 
confinement enclosure skirt. 
Thus, there is only slight differential vertical deformation between the 
point of the raft or floor level with the confinement enclosure skirt and 
the point of the raft or floor level with the ring building envelope. 
Thus, the supports of the ring building roof constituted by the 
confinement enclosure and the ring building envelope skirt has a 
difference in level which is sufficiently small not to produce significant 
stresses level with the fixing of the ring building roof on the 
confinement enclosure. 
In the case of an accident or incident producing an overpressure in the 
confinement enclosure, the latter is grouped or banded by the ring 
building roof, which then supports the circumferential tensile stresses, 
whose value decreases as from the fixing or embedding point. 
In the case of particularly large missiles, such as e.g. a military 
aircraft, the embedding or fixing of the ring building roof to the 
confinement enclosure skirt makes it possible to significantly reduce the 
weight of the ring building envelope structure. 
There are two embodiments of the reactor building construction according to 
the invention. According to a first embodiment, the confinement enclosure 
and ring building are made from reinforced concrete. According to a second 
embodiment, the confinement enclosure is made from concrete which is 
prestressed in the horizontal and vertical directions, whilst the ring 
building is made from reinforced concrete. 
Compared with a confinement enclosure made from prestressed concrete, the 
embodiment in which the structure is made from reinforced concrete makes 
it possible to eliminate the prestressing ribs, which cause a problem for 
the installation in the ring building. 
For part of the confinement enclosure positioned above the ring building 
and which must be able to resist the impact of the missile, the passive 
reinforcing members are dimensioned so as to withstand the greatest 
possible load, e.g. in the case of an earthquake or large missile. In the 
case of a prestressed concrete confinement enclosure, there are two types 
of reinforcing members, namely prestressed members for the reference 
accident and passive reinforcing members for the missile. For this first 
embodiment, there is no need to provide a provisional roof for the ring 
building. 
During the concreting of the confinement enclosure skirt, weighting 
reinforcing members are provided to the right of the ring building roof 
and can be either in the form of traditional reinforcing members or in the 
form of Caldwell sleeves. 
In the case of the second embodiment, the prestressing of the confinement 
enclosure takes place before the production of the embedding in such a way 
that only the prestressing deformations or creep act on the complete 
structure. The stresses resulting from the differential contraction of the 
ring building envelope compared with the confinement enclosure and by the 
creep under the prestressing of the confinement enclosure have an opposite 
sign and therefore partly neutralize one another. 
Bearing in mind the constructional requirements, in the case of the 
construction of this second embodiment it must be ensured that the ring 
building is out of the water before completing the prestressing of the 
confinement enclosure. Therefore, a partly or completely tight provisional 
roof must be provided, which serves as shuttering for the final roof, 
which can then be concreted after completing the prestressing of the 
confinement enclosure. It is then possible either to integrate this 
provisional roof into the final roof or to dismantle it after concreting 
the final roof.