Kernforschungszentrum Karlsruhe Research Articles

Competition of modes resonant with arbitrary cyclotron harmonics in a gyrotron with nonfixed axial structure of the high-frequency field

A general theory is developed for self-consistent calculations of mode competition in a gyrotron with nonfixed axial structure of the RF field for arbitrary cyclotron harmonics. The theory is applied to the gyrotron operating at the Kernforschungszentrum Karlsruhe with a frequency of 150 GHz. The formalism presented allows a self-consistent calculation of mode competition for the operating and parasitic modes at the cyclotron resonance at arbitrary harmonics. Specific calculations are carried out for the cases n/sub 0/=1, n/sub 1/=2 and n/sub 0/=2, n/sub 1/=1. It is emphasized that the formalism considered applies only to the case in which the azimuthal orthogonality condition is satisfied: n/sub 0/m/sub 1/ not=n/sub 1/m/sub 0/. There are circumstances when this condition is not satisfied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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Mesoscale atmospheric dispersion experiments using tracer and tetroons

In April 1983, March 1984 and March 1985 four mesoscale atmospheric dispersion experiments were performed near the Kernforschungszentrum Karlsruhe. The experiments comprised: tracking of tetroons by radar up to distances of more than 100 km; release of the tracer SF 6 at a height of 100 m or 140 m, respectively, and downwind sampling at more than 50 locations during up to seven successive periods of 30 min duration each up to source distances of 66 km; meteorological measurements at a 200 m high tower and radiosonde ascents up to a height of at least 2000 m. The measured data have been analyzed to obtain dispersion parametersσ y and σ z as a function of downwind distance and sampling time.σ y derived from tracer concentrations and from tetroon trajectories can be well compared, if the duration of the sampling time is taken into account. Vertical wind speeds and turbulence intensities are determined from tetroon trajectories. The turbulence intensities are compared to stability classes derived from meteorological measurements.

Experimental and Numerical Investigations of Sodium Boiling Experiments in Pin Bundle Geometry

In the framework of the liquid-metal fast breeder reactor safety analysis program, out-of-pile sodium boiling experiments have been run at Kernforschungszentrum Karlsruhe in a 37-pin bundle simulating a fast reactor subassembly. Three representative runs are analyzed in detail in terms of experimental evaluation and numerical simulation. The latter is performed with the three-dimensional, two-phase flow computer code BACCHUS-3D/TP, which describes coolant behavior in bundle geometry. The comparison between computed and experimental results has helped in correlating data from different instruments, thus allowing deeper insight into the details of the boiling behavior. Experimental data also provided a valuable code verification. By modifying the drift-flux model, the code validity range has been enlarged.

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A multi-transputer system for parallel Monte Carlo simulations of extensive air showers

A multiprocessor computer system has been brought into operation at the Kernforschungszentrum Karlsruhe. It is dedicated to Monte Carlo simulations of extensive air showers induced by ultra-high energy cosmic rays. The architecture consists of two independently working VMEbus systems each with a 68020 microprocessor as host computer and twelve T800 transputers for parallel processing. The two systems are linked via Ethernet for data exchange. The T800 transputers are equipped with 4 Mbyte RAM each, sufficient to run rather large codes. The host computers are operated under UNIX 5.3. On the transputers compilers for PARALLEL FORTRAN, C, and PASCAL are available. The simple modular architecture of this parallel computer reflects the single purpose for which it is intended. The hardware of the multiprocessor computer is described as well as the way how the user software is handled and distributed to the 24 working processors. The performance of the parallel computer is demonstrated by well-known benchmarks and by realistic Monte Carlo simulations of air showers. Comparisons with other types of microprocessors and with large universal computers are made. It is demonstrated that a cost reduction by more than a factor of 20 is achieved by this system as compared to a universal computer.

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Performance of a piping system and equipment in the HDR simulated seismic experiments

This paper describes a portion of the analysis and results of the United States Nuclear Regulatory Commission/Idaho National Engineering Laboratory (USNRC/INEL) participation in the SHAG (Shakergebaude) Seismic Research Program conducted by Kernforschungszentrum Karlsruhe (KfK) at the Heissdampfreaktor (HDR), a decommissioned nuclear reactor. The program analyzed the responses of a piping system and associated line-mounted equipment when subjected to various seismic and hydraulic loadings. Of interest was to evaluate the influence that piping support system flexibility has on piping system responses. The results of the studies will contribute to the technical basis for assessing the responses of light water reactor (LWR) piping and fine-mounted equipment to earthquakes.

A Review of the BETA Experimental Results and Code Comparison Calculations

The results from the BETA molten core/concrete interaction (MCCI) experiments conducted at Kernforschungszentrum Karlsruhe (KrK) and the associated analysis using computer models developed by KfK and by Sandia National Laboratories, e.d., WECHSL and CORCON, are described. Two important observations were made in the BETA steady-state tests: a distinctly larger downward erosion rate than previously measured in transient tests or predicted; dispersion and mixing of the metallic layer in the oxidic layer at high-melt input powers and associated gas velocities.

Experimental Investigations of MHD Flow Tailoring for First Wall Coolant Channels of Self-Cooled Blankets

Results of experiments on the concept of flow tailoring, the use of salient features of MHD flows in strong magnetic fields to create desirable velocity profiles in the coolant ducts of the first wall and the blanket, are reported. Proof-of-principle testing of flow tailoring has been chosen as the first joint activity on liquid metal MHD between Argonne National Laboratory (ANL) and Kernforschungszentrum Karlsruhe (KfK) because flow tailoring offers the possibility of significant improvement in blanket design and performance. The joint tests are conducted at ANL's ALEX facility on a test article fabricated at KfK. A 3-D MHD thermal hydraulic code developed at ANL is used to demonstrate the increased thermal performance of first wall coolant channels with flow tailoring. Sample results of detailed measurements of velocity and voltage distributions are compared to theoretical predictions provided by analytical tools developed at ANL with the collaboration of the University of Illinois.

Mhd flow tailoring in first wall coolant channels of self-cooled blankets

MHD flow tailoring, the use of salient features of MHD flows in strong magnetic fields to create desirable velocity profiles in single ducts, presents the possibility of significant reduction in blanket complexity and cost as well as enhancement of thermal hydraulic performance. A particular form of flow tailoring, involving ducts with alternating expansions and contractions, lends itself to the design of first wall coolant ducts. The potential benefits of this configuration and its immediate applicability to blanket design have made it the choice as the first joint Argonne National Laboratory (ANL)/ Kernforschungszentrum Karlsruhe (KfK) test on liquid-metal MHD. Testing is being carried out at ANL's ALEX facility on a test article fabricated at KfK. A description of the test article, its important features, and the associated instrumentation are presented. A fully 3-D code capable of treating MHD flows in ducts of complex geometry has been developed and used in the flow trailoring experiments. The features and capabilities of the code are discussed and a sample of the code predictions for the geometry and conditions of the experiments are presented. A sample of the preliminary test results from the ongoing testing is also given.

High power particle beams (Report on the 7th International Conference Karlsruhe 4-8 July 1988)

The 7th International Conference on High Power Particle Beams – “BEAMS '88” – took place in Karlsruhe from 4 to 8 July 1988. It was organized by the Kernforschungszentrum Karlsruhe GmbH. About 270 participants convened in the recently constructed Congress Centre.

Validation of Neutronic Codes for Distorted Core Configurations with the SNEAK-12 Critical Assemblies

The reactivity effect sof material rearrangements, simulating conditions in a postulated liquid-metal fast breeder reactor accident, were measured in three different critical assemblies: SNEAK-12A, a single-zone core, fueled with enriched uranium metal plates; SNEAK-12B, which had a central test zone fueled with PuO/sub 2/O/sub 2/ rod bundles surrounded by a buffer and a driver zone; and SNEAK-12C, which had nearly the same integral compositions as SNEAK-12B but was loaded totally with plates. The reactivity effects were calculated using current Kernforschungszentrum Karlsruhe methods and data and, in part, also using the corresponding modules of the SIMMER-II accident analysis system. Also, for some configurations, a comparison of measured and calculated fission rate distributions was performed. The evaluation yielded similar results for the three assemblies. For most cases investigated, satisfactory agreement between theory and experiment was reached when two-dimensional transport eigenvalue calculations or exact transport perturbation methods were used. As long as larger deviations occurred, transport results generally were on the conservative side. First-order transport perturbation theory only worked well in a limited number of cases. Diffusion calculations often led to large discrepancies, particularly when the experiments involved fuel dilution.

Tritium-Enrichment via CECE-Process with High Temperature Steam Electrolysis (HOT ELLY)

Aqueous waste which is a by-product of nuclear fuel reprocessing plants, is contaminated with tritium in the form of HTO. This waste must be disposed of in a suitable compact manner. In order to minimize waste volume, tritiated water is enriched by several orders of magnitude of its original concentration. This task is accomplished by using the existing combined electrolysis catalytic exchange (CECE)-Process, which is presently in pilot operation with tritium in a German nuclear research facility (Kernforschungszentrum Karlsruhe, KfK, FRG). Substantial energy reduction can be achieved by substituting the conventional water electrolysis by high-temperature steam electrolysis (HOT ELLY) for separating tritiated water into its components. Further and even more important advantages of implementing HOT ELLY is that the amount of radioactive inventory is minimized and no secondary waste is produced. The process engineering and safety aspects arising through the combination of the above two processes (CECE-Process and HOT ELLY) are explained.

Large Scale Gas Chromatographic Demonstration System for Hydrogen Isotope Separation

A large scale demonstration system was designed for a throughput of 3 mol/day equimolar mixture of H,D, and T. The demonstration system was assembled and an experimental program carried out. This project was funded by Kernforschungszentrum Karlsruhe, Canadian Fusion Fuel Technology Projects and Ontario Hydro Research Division. Several major design innovations were successfully implemented in the demonstration system and are discussed in detail. Many experiments were carried out in the demonstration system to study the performance of the system to separate hydrogen isotopes at high throughput. Various temperature programming schemes were tested, heart-cutting operation was evaluated, and very large (up to 138 NL/injection) samples were separated in the system. The results of the experiments showed that the specially designed column performed well as a chromatographic column and good separation could be achieved even when a 138 NL sample was injected.

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The Chemical State of Fission Products in Oxide Fuels at Different Stages of the Nuclear Fuel Cycle

A survey of work at the Kernforschungszentrum Karlsruhe is presented on the chemical state of selected fission products that are relevant in the fuel cycle of light water reactor (LWR) and fast bre...

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Mode competition in a gyrotron with tapered external magnetic field

A general method is developed for the analysis of mode competition in a gyrotron with tapered external magnetic field. Exploratory calculations show strong dependence of the operating regime of a gyrotron on tapering of the magnetic held. Detailed results are presented for the gyrotron operating at the Kernforschungs-zentrum Karlsruhe with frequency 150 GHz in the TE03 mode

Taper analysis of the 150 GHz KfK-gyrotron including the electron beam

The overmoded taper used in the gyrotron of the Kernforschungszentrum Karlsruhe (KfK) is analysed by numerically integrating the coupled wave equations in order to estimate the level of the spurious modes. A method is presented to characterize the hollow electron beam by an anisotropic dielectric. Coupling coefficients are calculated and included in the analysis describing approximately the effect of the electron beam. Several results are presented.