Patent Number: 048428108
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The FIGURE shows a high temperature reactor 3 eccentrically installed in the cavity 2 of a prestressed concrete pressure vessel. The core exhibits a pile of spherical fuel elements. Helium coolant flows downward through the pile. The pile is surrounded on all sides by a graphite reflector 4. The reflector is enclosed by a spaced thermal shield 5. A hot gas collector chamber 6 is located under the bottom reflector. A cold gas chamber 7 is located between the roof reflector and the upper thermal shield. The cold gas chamber 7 is adapted to withstand elevated temperatures (500.degree.-600.degree. C.) in order to enable operation of the decay heat removal system in certain cases upon reversal of coolant flow direction. The cold, compressed helium passes through orifices in the thermal shield 5 to an annular space 8 defined by the shield and the lateral graphite reflector 4, in which it flows upward into the cold gas chamber 7. Two different systems are provided for control and shutdowns of the high temperature reactor 3. First, a plurality of core rods 9 are insertable directly into the pile of fuel elements. The core rods are provided for long term shutdowns (with a cold, subcritical core). Normally, they remain in an extreme retracted position. The second system is used for control and rapid shutdown. It comprises the reflector rods 10, i.e., absorber rods displaceable in bores of the lateral graphite reflector 4. They are also used, to the extent possible, for long term shutdowns. At least two heat exchangers 11 (only one is shown) are located in the cavity 2 and arranged in the helium circulation loop. They are operated with down evaporation. Each heat exchanger 11 is followed in the coolant flow direction by a circulating blower 12, installed in a vertical position in a passage 13 provided in the prestressed concrete pressure vessel. All passages 13 are equipped with vessel closures 14. The secondary side of each heat exchanger 11 is connected to a steam circulation loop for power generation. Only the feed water line 15 and the live steam line 16 of the heat exchanger are shown. The feed water line 15 comprises a device 17 for the resupply of water. Each heat exchanger 11 is simultaneously intended for operational heat removal and for the removal of decay heat. In order to utilize natural convection, the heat exchangers 11 are installed parallel to the high temperature reactor 3 and upwardly offset relative to said high temperature reactor 3. The cavity 2 of the prestressed concrete pressure vessel 1 is lined with a metal liner 18, to which a thermal insulation 19 is applied. A cooling system 20 exhibiting a plurality of tubes is welded to the liner 18 and embedded in the concrete of the vessel. The cooling system is connected by an external loop 21 to an elevated water-filled reservoir 22. Water may be supplied to the external loop 21 and thus to the liner cooling system 20 with the aid of a refill device 23. The elevated reservoir 22 is connected to a further heat sink (not shown) by a recooling circulating loop 24. The reservoir 22 is also equipped with a drain valve 25. The flow of the cooling gas in normal operation has been described above. The coolant flows downward through the core, upwards through the heat exchanger 11 to the circulating blower 12. This direction of the flow is also maintained during the normal decay heat removal, i.e., when the heat exchangers 11 and the circulating blowers 12 are available. As at least two heat exchangers 11 are provided, availability is adequate. The decay heat is safely removed both with the reactor under pressure and without pressure. If the circulating blowers 12 fail, the decay heat is removed by natural convection, i.e., with flow reversal with the reactor under pressure to the heat exchangers 11. If the heat exchangers 11 are not available, decay heat is removed with the reactor under pressure, by natural convection through the liner cooling system 20, which is laid out accordingly. The water supply present in the elevated reservoir connected is sufficient to maintain decay heat removal for several days. If the circulating blowers 12 and/or the heat exchangers 11 fail when the reactor is not under pressure, the decay heat is tranferred, as discussed above, by conduction and radiation to the liner cooling system 20.