Patent Number: 053496159
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The reactor plant 1 in FIG. 1 with the reactor pressure vessel 2 and the containment 3 contains a core melt-through retention device 4. The containment 3 is connected to a device 10 for filtered pressure relief, the connection line comprising a controllable shut-off device 11. If necessary water can be introduced into the containment with the pump 12. The reactor pressure vessel 2 with the reactor core 5 is cooled by the primary water 20 and 20' respectively. In the foundation plate 31 of the containment 3 is located the cooling basin 32 of the retention device 4 according to the invention constructed as a cavity. The cooling basin 32 forms the lowest part of the containment sump; it is connected to the remaining part of the sump by ducts 33. The device 4 is composed of a crucible 40, which consists of a vat 41 and a plurality of tubular protuberances 42, and a lid 43. The cooling tubes 42 are connected to the concrete foundation 31 by means of a connecting structure 44, which consists of brackets, for example. The connecting structure 44 enables firstly the cooling of the cooling tubes 42 on its underside; secondly its purpose is to permit an unimpeded extension of the retention device 4 in order to keep thermal stresses small. Between the reactor pressure vessel 2 and retention device 4 is shown a collecting structure 6, and function of which has already been explained above. The level 34 indicates the water level of the cooling basin 32 in the state of readiness; the dot-dash line 35 signifies the water level if the requirements are met. The section of a retention device 4 according to the invention shown in FIG. 3 shows four cooling tubes 42, two of these tubes 42 being shown longitudinal section. The walls of the vat 41 and of the tubes 42, which form the crucible 40, are formed by a steel wall 40a and a ceramic lining 40b made of HIP-NB, for example. The vat base is covered by a guard plate 40c. The crucible lid 43 consists of a cover plate 43a and a honeycomb-like reinforcing structure 43b. The lid 43 is tightly connected to the crucible 40. The curve T in the diagram of FIG. 4 shows the radial distribution of the calculated temperature T' in a cooling tube 42. The dot-dash line M corresponds to the axis of the cooling tube. The zones W, A, B and C correspond to the cooling water of the cooling basin 32, the steel wall 40a, the ceramic lining 40b (made of HIP-BN) and the interior of the cooling tube 42 respectively. The following parameters govern the calculation of the curve T: afterheat production=1 MW/m.sup.3, internal diameter of the cooling tube=30 cm, wall thickness of the steel tube=8 mm, wall thickness of the boron nitride tube=10 mm; between the two tubes is assumed a gap having a resistance of 0.55 W/cm.sup.2 .multidot.K. The three temperatures given in FIG. 4 are rounded values; the distribution of curve T has only been roughly reproduced. For a reactor having a thermal output of 3000 MW (afterheat of roughly 20 MW, three hours after subjection to the nuclear fission) is to be provided a core melt-through retention device as specified by the invention, which comprises a height of roughly 2.5 m and a diameter of roughly 7 m. The number of cooling tubes having an internal diameter of 30 cm and a length of 1.8 m is roughly 170 with this device.