Patent Number: 040381340
Section: summary

FIELD OF THE INVENTION The invention relates generally to nuclear reactors, and in particular, to an improved pressurized water-cooled reactor system. DESCRIPTION OF THE PRIOR ART Pressurized water-cooled reactor systems are known at present and are generally configured so that the steam generators and coolant pumps thereof are separated from the reactor core pressure vessel and the safety houding enclosing the pressure vessel, and may include a steam pressure relief mechanism. See, for example, German Offenlegungsschrift No. 20 20 046, which discloses a condensation chamber containing ice which is coupled to the reactor core pressure vessel to effect condensation of steam escaping from the reactor system to reduce the steam pressure exerted on the safety housing enclosing the pressure vessel. Such reactor systems generally have coolant line design features which are unduly complex, and it has been proposed to combine structural components of such reactor systems in order to both reduce reactor fabrication costs and simplify the coolant line design. Specifically, the steam generators of gas-cooled reactor system have been structurally combined with reactor core pressure vessels. The fabrication costs of reactor systems using such a design, however, have not been significantly reduced since the cost of fabricating the reactor pressure vessel itself has increased. SUMMARY OF THE INVENTION It is therefore a general object of the invention to provide an improved pressurized water-cooled reactor system having a rupture-proof protection system for the primary loop components which is less expensive to fabricate than heretofore known reactor systems and which includes simplified coolant line design features. It is a more particular object of this invention to provide an arrangement of and a rupture-roof protection system for the primary components, i.e. pressure reactor vessel, steam generators, the connecting pipes and at least the main coolant pump impeller, which avoids bulkiness and warrants accessibility for periodical inspections to the steel walls of the primary components. Still another object of the invention is to improve the conditions for the personal working close to the primary components, i.e. provide for an improved biological and thermal shield of the primary components. Still another object of the invention is to protect the containment more efficiently, in the event that a loss of primary coolant accident might occur, by limiting the size of the potential cracks and by restricting internal parts, having a tendency to fly outwardly, within rupture-roof encasings. To accomplish the above cited objects, the invention comprises essentially the concept of a pressurized-water reactor pressure vessel positioned in the usual pit formed by concrete surrounding the vessel. The reactor's steam generators are vertically positioned adjacent to the pit and connected directly with the reactor pressure vessel by single straight pipes internally constructed to provide the two flow paths required to circulate the pressurized-water coolant through the pressure vessel and the steam generators. According to the invention the steam generators, the reactor pressure vessel and the pipes, hereinafter referred to as primary components, are each individually provided with rupture-proof protection means which comprises reinforced concrete encasements directly and individually enclosing each of said primary components, in each instance. With this rupture-proof protection encasing each primary component additional safety is obtained, because in case of a crack in the components's housing -- though the probality of such an event is very low -- the rupture-roof encasing prevents growing of the cracks, and the gap of the crack remains very small. Further no parts can "explode" through the encasing. The above construction introduces the problem of where to put the main coolant pumps required to circulate the coolant loop formed by the two (or more) flow paths of each pipe and the steam generator, in each instance. According to the present invention, this is solved by positioning the pump impellers inside the bottoms of each of the steam generators, with the motors on the outside of the rupture-proof encasement, in each instance. Within the aforementioned PWR primary loops in case of a crack or rupture of a pipe or the steel compartment of the impeller (loss of primary coolant accident) a pressure drop on either the upstream or the downstream-side might occur, so that the pump impeller comes into overspeed thus being submitted to increased centrifugal forces. However, due to the fact that the pipes as well as the compartment for the impeller are enclosed by rupture-proof encasings, the crack remains small in size, thus limiting the escape of coolant and limiting the pressure drop, so that the acceleration momentum with regard to the drive shaft and the impeller can be limited and a stop mechanism for the fly-wheel, normally coupled to the shaft, can be actuated. Simultaneously an emergency cooling system for the core can be put into operation to take over the core cooling. Similarely, the rupture-proof encasings protect the steam generator and the primary loop cooling function in case of a loss of secondary coolant accident (crack of the pipes or the steam generator within the secondary loop system). Thus the invention solves the problem to cope with rupture-proof housings and pipes and simultaneously avoiding bulky, voluminous piping and housings for the primary loop of a PWR. Further, the construction appears to be designed to provide positive protection against the impeller shaft, and the impeller also in the event that parts thereof might get loose.