[en] Summary only

[en] A description is given of the critical test facility KAHTER which is used to validate theoretical models, codes and data bases for the gas cooled high temperature pebble bed reactor. The homogeneous loading phase, results for heterogeneous poisoning and the effects of axial inhomogeneous fuel loading are all discussed. (U.K.)

[en] The present report deals with a material which is used as a neutron absorber in High Temperature Graphite Reactors. There were no multigroup data for Hafnium in the thermal and epithermal libraries of VSOP code. On the other hand, natural Hafnium is one of the materials for which ENDF/B-VI data are now available. Neutron absorption by Hafnium occursat the thermal energies, and in many resonances, most of which are above the thermal energy region. The preparation of multigroup libraries for natural Hafnium in the VSOP format from the ENDF/B-VI basic data is discussed. (author)

[en] An efficient method has been developed to represent the space-time behavior of neutron detector signals in nuclear reactors. The method is based on a simplified solution to the neutron shape function in the framework of a quasi-static approximation to the timedependent diffusion equation. The shape function is obtained as a sum of a modal expansion, representing the global flux perturbations, and a local function, representing the direct perturbations due to reactor parameter changes. The method was applied to the analysis of both integral and differential rod worth measurements obtained at the critical hightemperature gas-cooled reactor test facility, Kahter. The analysis of the Kahter data indicates the applicability of the proposed method in accounting for space-time effects in detector signals

[en] The critical facility KAHTER has been used to verify and to adjust theoretical models describing the nuclear behaviour of HTR pebble bed reactors. Methods such as evaluating critical masses, flux mappings and reaction rate measurements, more sophisticated experimental and theoretical methods have been developed to get exact information and interpretation of control rod efficiency, power determination and fast neutron damage. (author)

[en] This work deals with the numerical solution of the neutron diffusion equation under conditions, which follow from engineering applications. The Finite Element Method (FEM) was chosen as the solution method. It is the aim of this work to demonstrate the potential of the FEM for solving problems resulting from nuclear engineering applications. From this a concept is derived which allowed the development of a program system. Calculational results achieved with this system confirm the theoretical considerations. (orig.)

[en] Methods and programs of calculation were considered within the framework of diffusion approximation of HTGR with large cavity and their approbation was performed using data on KAHTER critical assemblies. Calculation of elementary cells was conducted according to the WIMS program. Resonance effects in double heterogeneity systems were taken account of according to NEKTAR program. Effective multiplication factor, spatial-energy distribution of neutrons at the presence and the absence of absorbing rods were determined by means of QUM-3-HER three-dimensional program. PENAP two-dimensional program was used for calculating systems without absorbing rods. A technique using neutron transfer matrix is realized in the DOP two-dimensional progra. Satisfactory agreement of experimental data on KAHTER critical assemblies with cavity between a top endreflector and the core with calcultional results is shown