Patent Number: 039309428
Section: summary

This invention relates to installations for the storage or use of fluids which are harmful or noxious to the environment. It applies particularly to tanks which contain chemical products or fluids at a very low temperature, nuclear vessels in light water and sodium-cooled installations, and contaminated effluent tanks. In such tanks, inspection and small repair operations must be carried out quickly in order to minimise intervention times on equipment for which such intervention makes the equipment unavailable for operation. Such inspection must frequently be carried out under extreme operating temperature conditions (for example in cryogenic fluid tanks or in sodium reactors) which do not allow access by operators. It would be advantageous to provide automatic fast inspection means as a precaution. It would also be advantageous to provide automatic safety features for conditions where spacing and obstacles make access difficult. For safety reasons, the conventional system comprises constructing two fluid-tight barriers. The first barrier contains the dangerous or expensive fluid and the second is adapted to provide a seal in the event of rupture of the first during operation of the installation, and such an accident may be serious and result in prolonged or even complete stoppage of the installation. Disregarding rupture, even a minimal leakage may result in the installation being unavailable for operation, in which case the secondary barrier is then used simply for recovery of the product and for protective purposes. The object of this invention is to facilitate examination, maintenance and repair of the first barrier under difficult environmental conditions, and more particularly allow the use of inspection methods which can be applied easily and quickly, and means for logging the zone which is to be monitored. For reasons associated with the environment, and in view of the disorder and expense that may result from non-availability of the equipment, it is also advantageous to provide quick and automatic inspection equipment, fault locating equipment, and equipment for minor work, even work of a type which would not merit any special attention in less dangerous circumstances. To this end, the invention proposes systematically to promote free access to the primary barrier, to leave the outer surface free of any thermal insulation or any other protective layer, and transfer such insulation or layers to the secondary barrier, and to provide between the two barriers adequate space for the inspection and maintenance operations. Conveniently, locating members disposed on the surface of the barrier enable those zones which it is required to inspect from time to time to be accurately located. Advantageously, studs secured to the surface of the primary barrier enable the preceding aims to be accomplished and also facilitate the introduction and operation of automated control or working equipment. The above steps are not sufficient in every case of application of the invention. To enable equipment of all kinds to be readily used, the space between the primary and secondary barriers must be amply dimensioned. If no other steps were taken, the large space thus formed would be invaded by the fluid in the event of rupture of the primary barrier, and the level of fluid would drop abruptly inside said barrier. This may create extremely dangerous situations. This applies, for example, to nuclear reactors in which, for safety reasons combined with the operation of fission products, the reactor core must not be drained or exposed irrespective of the accidents occurring. The reason for this is that heating due to the gamma effect is sufficient to cause fusion of the core if the latter is not cooled by convection of the coolant fluid. To obviate this catastrophic situation, the invention proposes to fill the space between the two barriers by displaceable members, thus preventing any excessive fall in the level of liquid in the event of rupture of the primary barrier. In most cases, the space to be filled is in the form of a volume of revolution and the filling members or blocks are in the form of segments bounded by meridian planes and disposed consecutively in a circumferential series. They are placed on a circular track and an access door to the space fitted out in this way is provided in the secondary barrier. In the event of intervention, the door is opened, one of the filling segments is withdrawn if necessary to clear a space into which the inspection, monitoring, repair or, more generally, maintenance equipment is introduced. The assembly formed by the train of filling blocks and the equipment is moved along the outer circular surface of the primary barrier to bring the equipment to a predetermined zone, and work is continued by remotely controlled and remotely monitored operations. If necessary, the space liberated by removal of a segment may also be used for the introduction of personnel to enable them to reach the primary barrier. If required, the filling blocks may act as storage tanks which may, for example, be used to facilitate vessel emptying operations. On completion of the maintenance operations, the reverse sequence of events takes place, i.e. the train is set in motion to bring the equipment to the opening, the equipment is withdrawn and, where applicable, the missing segment is returned and the secondary barrier closed. The objects, characteristics and advantages of the invention will also be apparent from the following description of one exemplified embodiment illustrated in the accompanying drawings. The example selected, which has no limitative character, relates to a sodium-cooled nuclear reactor, but the invention applies equally to light water cooled reactor vessels and other tanks for dangerous products.