Patent Number: 047012986
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a steel reinforced concrete subterranean cylindrical pressure vessel 1. The vessel encloses a cavity 2. The vessel 1 has a center opening 4, in a cover region 3 which is closed by a removable cover 5. The cavity 2 houses a nuclear reactor 6. The core of the reactor 6 is a stationary pile 7 of spherical fuel elements. The pile 7 has a diameter of approximately 1.2 to 1.5 m and a height of 1.5 to 2.5 m. The power density in the core is approximately 4 to 6 MW/m.sup.3 and has a total capacity yield of 10 to 20 MW. The fuel elements, which are prepared by a hot or cold press method, contain approximately 20 to 40 g heavy metal per pellet. The pile 7 is surrounded, on all sides, by a graphite reflector 8, having a bottom reflector 9, a side reflector 10 and a roof reflector 11. The graphite reflector 8 is approximately 0.75 to 1.0 m thick. The roof reflector 11 rests directly on the pile 7. A free space 12 is located between the roof reflector 11 and the cover 5. Another free space 13 is provided between the bottom reflector 9 and the bottom of the pressure vessel 1. A metal support installation 14 is located in the free space which supports the nuclear reactor 6 on the bottom of the pressure vessel. A blower 15 circulates cooling gas, preferably helium, which flows from top to bottom through the pile 7. The blower 15 is located in a vertical position centrally under the cover 5, its rotor protrudes into the free space 12. The blower drive motor 27 equipped with an external closure part 17 is installed in a passage 16 of the cover 5. A steel core vessel 18, closed at the bottom, laterally surrounds the pile 7 and houses part of the side reflector 10 and bottom reflector 9. The side and bottom reflectors are divided into inner 19, 22 and outer 20, 23 reflector portions respectively. A plurality of vertical channels 28 are provided in the inner side reflector 19. Absorber rods 21 for trimming and shutdown are located in a displaceable manner in the channels 28. Drives 29 for the absorber rods 21 are provided in passages 38 of the cover 5. The core vessel 18 together with the inner side reflector 19, the roof reflector 11, the fuel elements and the absorber rods 21, may be removed from above following removal of the cover 5. A shielding bell is used in the process. The absorber rods 21 assure and maintain a subcritical state of the pile 7 during the removal and installation process. The core vessel 18 is removed after the fuel elements are sufficiently burned off. A cooling system 24 is mounted over the entire inner side of the pressure vessel 1. The cooling system 24 is made up of pipes through which cooling water flows and is designed for safe removal of heat generated in the pile 7 during normal operation and during the removal of the decay heat. A gas tight jacket 25 is provided in the cavity 2 in front of the cooling system 24 to prevent entry of water into the primary loop. An annular space 26 is located between the jacket and the outer side reflector 20. A gas conduction jacket 30 is provided in the free space 12 separating the suction side 50 and compression side 51 of the blower 15. It is connected to the upper end of the core vessel 18. The output of the reactor is regulated by the rpm of the blower 15 and the secondary flow of the cooling system 24 alone, utilizing the negative temperature coefficient inherent in fuel pile reactors. The blower 15 suctions the cooling gas from the free space 12 and transports it into the pile 7. In normal operation the pressure is adjusted to approximately 8 to 10 bar. The temperature of the gas rises from 300.degree. C. to 500.degree. C. during its flow through the pile 7. The heated cooling gas passes into the free space 13 through openings in the core vessel and the bottom reflector 9. It is there distributed and moved into the annular space 26. From the annular space 26 the gas returns to the space 12. The pressure of the cooling gas is chosen so as to be higher than the pressure of the water in the cooling system 24. According to the invention a design as in nuclear reactor 6 advantageously avoids requirement of installations such as a charging device, a gas purification installation, a reactor protection system, and active regulating systems which are therefore not provided. The reactor thus has very low energy generation costs and a low necessary maintenance effort. FIG. 2 shows the entire nuclear reactor installation with the pressure vessel 1, located underground in a cavity 40, and resting on a foundation 31. A concrete shield 32 closes off the top of the cavity 40 in a light duty hall 33. The hall 33 has a gate 36 and is divided into a workshop and operating room 37 and a room 39 for the installation and removal of the core vessel 18. For installation and removal of the core a crane 34 running on a plurality of rails 35 is provided. The cavity 40 is lined with concrete. The intermediate space 41 between the wall of the cavity and the pressure vessel 1 is monitored for leakage and activity. A slight underpressure may be established in relation to the environment by a slight suction. Potential leakages are drained off discontinuously in a programmed manner.