[en] The patent claims apply to the reflector wall of a pebble-bed reactor. The graphite of the reflector wall is doped with neutron-absorbing materials except in that part of the wall through which the absorber rods are led and which encloses the absorber rods. These materials are doped over the thickness of the reflector wall in such a way that esup(- Σaxd) <= 10^-3, where Σa is the mean macroscopic cross section. (UA)

[en] The insertion depth of the absorber rods of a pebble-bed reactor with graphite reflector shielding is reduced without increasing the number of absorber rods. For this, the parts of the reflectors not in contact with the absorber rods are doped with neutron poison in order to achieve the reduction of reactivity desired for control and shutdown. The doping, e.g. of the bottom reflector and parts of the side reflector with absorber rods inserted from above, is done with boron. It follows the relation esup(-Σad) <= 10^-3, where d is the thickness of the reflector walls and Σa, the averaged macroscopic cross-section for neutron absorption. This arrangement also enables a reduction of the neutron flux in reactor parts inaccessible to the absorber rods. (RW/AK)

No abstract available

[en] If a graphite reflector of a pebble bed reactor is equipped with insertable absorber rods power control is achieved by less insertion depth of these rods than would be required for conventional designs for the same type of reactor. Therefore the difficulties growing with insertion depth and the danger of damaging fuel elements are reduced. With less stroke, the drives of the control rods are simplified, too. A means for this is doping the graphitic reflector bottom and the lower part of the reflector with neutron-absorbing material. A partial flow of neutrons forced downwards on insertion of the control rods into the upper zone of the reflector will be absorbed in this lower region. A formula is given for this doping. (HP)

[en] The representation of control rod regions in reactor calculations requires a combination of transport and diffusion theory calculations. A method is described which produces equivalent cross sections for a rodded region. These cross sections used in a diffusion theory calcualtion yield the same rod efficiency and reaction rate distribution as the transport theory calculation for the explicit heterogeneous control rod. The description of the method is complemented by sample problems. (orig.)

[en] An analysis of the HITREX 1 reactor experiment has been jointly performed by the DRAGON project/KFA and the CEGB, Berkeley, applying methods and codes currently in use within these organisations. The different methods are described and the results of the analyses are compared with each other and with experiment. Although in general the various methods give comparable results, there are two areas of significant discrepancy. First, the thermalisation data in the DRAGON codes is shown to be inadequate, so that the Pu/U fission ratio is over-estimated by some 3%, and secondly, there are differences of about 2 or 3% in the ²³⁸U absorption rates. From existing analyses, it is not possible to conclude which method gives the best overall representation of the resonance events. Concerning thermal reaction rate distribution, it is concluded that for an accuracy of about +- 1% it is necessary to perform a reactor spectrum calculation in many groups before condensation. The 32-group WIMS model achieves this, but the XSDRN/CITATION 10-group model does not. The DRAGON/KFA power reactor method predicts reaction rates in the core to within a few per cent. All methods grossly under-estimate the gradient of fast neutron flux at the core/reflector interface. (author)

[en] It is by now fairly widely known that the high temperature reactor (HTR) is a unique nuclear energy source which can supply heat at temperatures up to 1000⁰C for application in chemical processes, for which previously exclusively conbustion heat sources have been used. With the HTR, it is possible to apply nuclear energy not only for electrical power production but also for the synthesis of liquid or gaseous energy carrier. Nuclear coal gasification appears most promising as the first step for the demonstration and industrial application of nuclear process heat technology in the Federal Republic of Germany. Reactor manufacturers and coal mining companies in co-operation with the Nuclear Research Center established a joint project in 1975 for the development of an HTR with a coolant outlet temperature of 95⁰C, for the development and testing of nuclear coal gasification, for the detailed engineering of a prototype plant consisting of an HTR and gasification plant and finally for the construction and operation of this prototype plant for nuclear process heat (PNP). The authors describe the status of the PNP-project and the scope for future development. (Auth.)

No abstract available

No abstract available

[en] An analysis of the HIRTEX 1 reactor experiment at Berkeley Nuclear Laboratories has been jointly performed by the DRAGON project/KFA and the CEGB, Berkeley, using the methods and codes currently in use within these organisations. This report describes the different methods and compares the results of the analyses with each other and with experiment. An investigation into the various observed discrepancies has been made in order to identify the reasons for them. (orig.)