Patent Number: 039309428
Section: description

Referring to the drawings, the inner surface of a buried concrete casing 1 is lined with a metal lining 2 which is in turn lined with a layer 3 of insulating material. A stainless steel vessel 4 having a cylindrical wall 5 and an inverted-dome base 6 is adapted to receive a sodium-cooled nuclear reactor core in accordance with known features of which primary wall 6A is typical, the vessel 4 and the protected casing 1 forming primary and secondary barriers for the sodium. According to the invention, the bare outer surface of the vessel 4 is provided, at isolated points, with elements 7 which are used for locating purposes and which, if required, may be in the form of fixing studs for inspection, maintenance or repair equipment. A door 8 formed in the secondary barrier 2, 3 gives access to the space formed by the two barriers, through the agency of a tunnel 9 and an air-lock 8A. This space is of a size such as to be able to receive a trolley 10 (FIG. 3). The trolley 10 is provided with a wheel set 11 mounted on jacks for vertical adjustment and enabling the trolley to move along the tunnel to the interior of the space over a radial track 13 so that a second wheel set 14 with which the trolley is provided is situated level with a second circumferential track 15 laid on the flat base of the casing 1. A hydraulic system 16 can then actuate the jacks 12 to retract the wheels 11 upwardly and enable the trolley to rest on the track 15. Another two jacks 17 controlled by the hydraulic system 16 and fixed to the trolley frame 18 bear a guide track 19 of a similar profile to that of the base of the vessel 4. This guide track, whose distance from the surface of the vessel can be adjusted by means of the jacks 17, serves as a support and a runway for a television camera 20, movement of the latter along the track being by a hydraulic drive. A hydraulic motor 21 also acts on at least one of the wheels 14 of the trolley to move it along the circumferential track 15. The resulting assembly enables the camera 20 to sweep the entire outer surface of the base 6 of the vessel 4. The space formed by the vessel base 6 and the secondary barrier 2, 3 is occupied for the most part by a train of elements 22 disposed to roll on the circumferential track 15, each of these elements being bounded by two meridian planes. At least some of these meridian surfaces are fitted with elements 23 which provide a drive connection between the units 22, simply by contact and thrust and/or by traction. Safety means (not shown) are also provided to avoid vertical displacement of the elements or trolleys by the effect of the Archimedes thrust which would result from a rupture of the vessel, and thus avoid derailment of this train of elements. The train of elements 22 is so devised as to leave a free space at the radial track 13 to receive the trolley 10. In a variant, a special filling unit for use as a storage tank 22A may be arranged therein, being adapted to be withdrawn from the casing 1 to be replaced at the required time by the trolley 10. The units 22 are of any suitable material having some compatability with liquid sodium. In the event of a leakage in the wall of the vessel 1 they have the effect of greatly reducing the fall in the sodium level and prevent any risk of "draining" or exposure of the reactor core. Inspection and maintenance of the vessel by means of the trolley 10 are carried out as explained hereinbefore, the trolley being capable of exerting sufficient force to displace the train of filling elements 22. The above-described features according to the invention relate to only one of the possible applications of this invention and therefore have no limitative character. They may therefore be modified and varied in different ways without thereby departing from the scope of the invention. For example, the trolley may be equipped with any suitable means for inspection, analysis, supervision, maintenance and repair, or means for engagement with the vessel. If required, it may also be used for the transportation of the inspection and maintenance personnel. A vertical telescopic guide track having a similar function to that of the track 19 may be used for inspecting and repairing the cylindrical part of the vessel. As another example, with such a trolley it is possible to place at a predetermined location in the vessel measuring or monitoring or other means borne by equipment fixed on the studs 7; said means can then be withdrawn by a similar operation on completion of servicing, or at any other time favourable to the user.