Quelques considérations sur le choix du système prise-rejet des grands aménagements thermiques selon leur localisation

Abstract

With the speed-up Electricite de France's large nuclear power plant programme, total megawatt capacity on a single site may now be the order of 10 times what it was ten years ago. Cooling water requirements for such capacities amount to several hundred cubic metres per second. When studying the various hydraulic, sediment-transport, heat-dissipation and ecological problems associated with cooling circuits, one should distinguish between power plants sited estuaries, on the coast and ports. (i) For plants on an estuary site, one of the first problems is to decide on the cooling capacity which the estuary can provide. This requires knowledge of the disturbances to estuarine equilibrium liable to be caused by heated effluents. This problem should be studied both locally at the site and from the standpoint of the estuary as a whole. Mixing characteristics between different-density fluids the estuary must be known. Another problem is to design the intake and outlet system such a way that no inconvenience is caused to shipping (e.g. by creating cross-currents the estuary) and that hydraulic or thermal pollution effects do not disturb estllarine fauna of flora. A further problem relates to sediment behaviour, which depends on detailed flow features and may therefore be decisively altered by cooling water draw-off. In many estuaries, fine sand and silt brought down from upstream form sandbanks which are very sensitive to small variations river flow. (ii) For coastal plants, as for plants estuaries, the recycle problem arises. Various solutions are studied for tidal sites (alternating intake and output) and for sites on lagoons. Water intake operation is linked with the silting problem which cannot be separated from the problem of structure stability under breaking waves. A design method is proposed for determining correct intake submergence when waves cause sand particules to become suspended. These difficulties may be avoived by putting the power plant in the sea i.e. on an artificial island. (iii) For port-sited plant, intake and outlet problems are considerably simpler because intake and outlet may be placed separate pools or docks which are not connected with each other. Care should be taken to ensure that there are no cross-currents liable to endanger shipping and also that dredging operations do not prohibit use of the cooling circuit.