Patent Number: 050892126
Section: description

Referring now in detail to the figures of the drawing in which parts that correspond with one another are provided with the same reference numerals and first, particularly, to FIG. 1 thereof, there is seen a reactor pressure vessel 1 for an advanced pressurized water reactor. The reactor pressure vessel 1 has a cylindrical shell 2 that is closed off at the bottom by a rounded or partly spherical bottom 3. A ring 4 with a connection neck or piece 5 for pipelines carrying coolant away from the reactor pressure vessel 1, is disposed in the vicinity of the shell 2. Seated above the ring 4 is a curved dome or cover 6, having a flange 7 which has bores 8 formed therein for receiving non-illustrated cover screws. A core container or barrel 10 that encloses a reactor core 11 is disposed in the reactor pressure vessel 1. A core baffle or envelopment 12 is installed between the core container 10 and the reactor core 1 and protects the core container 10 from neutrons given off by the reactor core 11 during operation. The reactor core 11 includes individual fuel assemblies 13, a selected number of which are provided with control elements 14. Each control element 14 includes a bundle of control rods 15 and a support structure 16, also known as a spider, on which the control rods 15 are retained. The fuel assemblies 13 are mounted on a lower grid or grating 17 in a lower grid or lattice plate 18. The fuel assemblies 13 are guided in an upper grid or lattice plate 20 on the lower surface of an upper core framework or support structure 19. For a 1300 MW plant, the reactor pressure vessel is approximately 12 m high, has an inside diameter of approximately 5 m, and has a wall thickness in the cylindrical portion of approximately 250 mm. The reactor pressure vessel has an empty weight of approximately 500 tons. The reactor pressure vessel 1 is constructed for an operating pressure of 175 bar and an operating temperature of approximately 350.degree. C. In an advanced pressure water reactor, the ratio between the height of the reactor pressure vessel 1 and the height of the reactor core 11 is approximately 4:1. The core container 10 has a flange 21 which is suspended in the reactor pressure vessel 1 from an inner shoulder 22 of the ring 4. The lower end of the core container 10 has an inwardly pointing flange 23, from which the lower grid 17 is suspended. The core container 10 is cylindrical like the shell 2 of the reactor pressure vessel 1 and it forms an annular chamber 24 together with the shell 2, that carries coolant flowing in at a coolant inlet 25a, downward in the direction of an arrow 26. There the coolant is deflected at the rounded bottom 3, so that it enters the reactor core 11 from the bottom through the lower grid 17 and flows out of the reactor pressure vessel 1 through a coolant outlet 25b. Since the deflection would concentrate the flow to the middle region of the core, a sieve, strainer or screen barrel 27 supported on the rounded bottom 3 is provided in order to make the flow uniform over the cross section of the reactor core 11 Centering grids or lattices 28 are additionally disposed in the upper core framework 19 of the advanced pressurized water reactor. The centering grids 28, together with an upper core support grid or lattice 29 and guide tubes 30, form a removable insert. The interiors of the guide tubes 30 are provided with guide plates 31 in which drive rods 32 for the control elements 14 are guided. The guide rods 32 pass through the rounded cover 6 to control element drive mechanisms 33, only one of which is shown in the drawing. According to the invention, some of the guide tubes 30 are constructed in such a way as to guide a group of a plurality of control elements 14. FIG. 1 also shows a guide tube 30 for a group of two control elements 14. The guide rods 32 of the control elements 14 of such a group are converted into one guide rod 32 through a connecting piece 34. In FIG. 2, the reactor pressure vessel 1 of FIG. 1 is shown in cross section, with a fuel rod grid or lattice structure having a hexagonal cross section. If a rectangular coordinate system having an origin at a center of area M of the reactor pressure vessel 1 is placed in the plane of the drawing, then the abscissa represents a 0.degree. axis 35, and the ordinate represents a 90.degree. axis 38. The reactor pressure vessel 1 is provided with eight connection necks or pieces 5 for carrying coolant in four primary coolant loops. The coolant inlets 25a and the coolant outlets 25b are disposed in mirror symmetry relative to the axes 35 and 38. In this exemplary embodiment, the reactor core 11 surrounded by the core baffle 12 includes 349 fuel assemblies 13 with hexagonal cross sections, 151 of which are provided with control elements 14. The control elements 14 that are combined into groups according to the invention and are associated with a selected number of fuel assemblies 13, are represented in the drawing by outlines 45. As FIG. 2 shows, beginning at the center of area M, six groups each having three control elements 14, are disposed about a group having a single control element 14. Each group is surrounded by fuel assemblies 13 that are not provided with control elements 14. In the peripheral region of the reactor core 11, groups each having two control elements 14 are additionally geometrically disposed on the 0.degree. axis 35 and on axes 37 and 39 that are shifted relative thereto by an integral multiple of 60.degree.. For the sake of providing an area-covering, symmetrical distribution of the 151 control elements 14 over the entire cross section of the reactor core 11, thirteen groups each having one control element 14, six groups each having two control elements 14, and forty-two groups each having three control elements 14, are advantageously provided. The resultant disposition of fuel assemblies 13 provided with control elements 14 is symmetrical to six axes 35-40, having an angle therebetween which is an integral multiple of 30.degree.. When constructing the reactor core 11, the part of the calculation relating to geometry can thus be limited to an arbitrary 30.degree. portion, since each of the axes 35-40 is a mirror axis. In FIGS. 1 and 3, a three-armed guide plate 50 is shown, in which adjacent arms each form an angle of 120.degree. with one another. The guide plate 50 serves to guide a connecting piece 34, with which three drive rods 32 of three control elements 14 are converted into a single guide rod 32. To this end, the guide plate 50 is recessed with a profile 51 that matches the connecting piece 34.