Band 68, Heft 5-6

A first order biokinetic model is presented for the calculation of dose coefficients from human activity excretion data after intravenous and oral administration of 14 C labeled drugs. It is intended for the dose estimation in human studies in drug research, where the number of measurements is low and their uncertainty rather high. The model depends on only 6 parameters that are to be adjusted with the help of the measurement data. A comparison of measured and calculated activities in excreta of four human studies on 14 C labeled drugs revealed considerable agreement, although some limitations have to be accepted. In contrast to the biokinetic model for 14 C in organic compounds recommended by the International Commission on Radiological Protection (ICRP) the present model does not assume a fixed biological half-life of 40 days, but follows the experimental data. In consequence, the resulting dose coefficients differ from the ICRP value. For experimental data tested and assuming uniform activity distribution, the committed effective doses amount between one twenty-fifth to one fiftieth of the values calculated from the ICRP model. The uncertainty of the derived dose coefficients is estimated to be about ± 50% .

First nuclear activation experiments have been carried out using the new accelerator for relativistic particles NUCLOTRON in Dubna. The distribution of neutrons emitted during the irradiation with 0.65, 1.0 and 1.5 GeV protons from a lead target (∅ = 8 cm, l = 20 cm) and moderated by surrounding paraffin of 6 cm thickness was studied with radiochemical sensors along the beam axis on top of the moderator. Small 139 Lasensors of approximately 1 g each were used to measure essentially the thermal neutron fluence at different depths near the surface: i. e. on top of the moderator, in 10 mm deep holes and in 20 mm deep holes, respectively. The reaction 139 La (n, γ) 140 La (τ 1/2 = 40.27 h) was studied using standard procedures of gamma-ray spectrometry and data analysis. The induced activity of 140 La increases strongly with the depth of the hole inside the moderator. Its activity distribution along the beam direction on top of the moderator has its maximum about 10 cm downstream the entrance of the protons into the lead and the activity increases about linearily with the proton energy. Some comparisons of the experimental results with model estimations based on the LAHET code are also presented. The experiments were carried out in the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna, Russian Federation.

Data analysis is carried out for four detector stacks composed of passive Lexan polycarbonate detectors exposed in space by the Ultra Heavy Cosmic Ray Experiment on board NASA’s Long Duration Exposure Facility. Scanning and analysis of the 0.21 m 2 detector area resulted in the finding of 72 ultra heavy (68 ≤ Z ≤ 96) cosmic ray nuclei. About 15% of the cosmic ray nuclei show charge fragmentation within the detector stack of 5.6 g × cm –2 . A detailed analysis of these fragmented cosmic ray nuclei is presented, including a discussion within the context of “physical anomalons”. This last term, describing a sub-set of all anomalon phenomena, is defined in the text .

Neutron and gamma spectra were measured behind and inside of modules consisting of variable iron and water slabs which were installed in radial beams of the zero-power training and research reactors AKR of the Technical University Dresden and ZLFR of the University of Applied Sciences Zittau/Görlitz. The applied NE-213 scintillation spectrometer allowed the measurement of gamma and neutron fluence spectra in the energy regions 0.3–10 MeV for photons and 1.0–20 MeV for neutrons. Measurements with thermoluminescence dosemeters (TLD) between slabs supplied additional information about the space distribution of energy integrated fluxes. The paper describes the experiments and presents some important results of the measurements. They will be compared with the results of transport calculations made by means of MCNP and TRAMO in another paper .

Experimental and analytical studies have been performed to determine the temperature distribution as a function of reactor power in the TRIGA Mark-II reactor at the Istanbul Technical University (ITU). The lumped parameter model with four governing equations was used in the analytical model. Based on the mathematical model, a computer code has been developed for calculating fuel and coolant temperatures in the reactor core. The calculated results for fuel and coolant temperature in the reactor core for different reactor power levels have been compared with the experimental data. Agreements between experiment and results from the computer code are fairly good .

A passive containment cooling system with immersed condensers has been proposed as one of the alternatives for the Advanced Heavy Water Reactor (AHWR) being designed in India. The system removes residual/decay heat released into the containment through the immersed condensers kept in a pool of water following loss of coolant accident. An important aspect of the immersed condensers is the potential degradation of its performance due to the presence of noncondensable gases. Experiments are performed to obtain reliable data on condensation phenomena in presence of air. These experiments are conducted on full-scale tubes of condensers immersed in a pool of water maintaining similar conditions as in the prototype of AHWR. A method has been proposed for the determination of the local heat transfer rate using correlations given in literature. The parametric effects of air mass fraction, pressure, steam flow, etc. on condensation heat transfer in presence of noncondensable gas have been studied. The experimental results are compared with the correlations given in literature .

Based on a physical model of the test loop HRTL-5 simulating the 5 MW nuclear heating reactor, a drift-flux model of two-phase flow has been derived, in which the sub-cooled boiling and saturated boiling in the heated section, condensation and void flashing in the adiabatic riser etc, are taken into account. It is suitable to investigate the natural circulation two-phase flow, especially at heating reactor conditions. By introducing the concept of condensation boundary layer, a condensation formula has been derived and complemented into the drift-flux model, which was used to investigate the behavior of the HRTL-5 in our previous research works. Based on the mathematical model, a computer program has been developed. At first, through comparing the calculations with the experimental results, the parameters in the two-phase drift-flux model have been determined. Then calculations on the flow characteristics of HRTL-5 have been performed, including the simulation of the mass flow rate and the distribution of various physical variables. At last, the characteristic curves of natural circulation have been simulated; thereby, also useful experiences have been acquired.

This paper presents results of an experimental study on natural convection in the vertical enclosure of a double coaxial cylinder where the inner wall is at constant heat flux. It is the objective of this experiment to understand the basic characteristics of heat transfer under the condition of natural convection coupled with thermal radiation in a vertical enclosure. The range of Rayleigh numbers based on the width of the double coaxial cylinder is set to be 5.6 × 10 5 < Ra < 1.04 × 108, the radius ratio is 2.73, the aspect ratio is 3.43 (cylinder length divided by annular gap). The heat transfer coefficient of natural convection coupled with thermal radiation was obtained as function of the Rayleigh number, aspect ratio of the enclosure, and temperature of the hot and cold surfaces. The experimental results show that thermal radiation can’t be neglected in analyzing heat transfer of vertical annulus with natural convection. The results provide the basic data for the design and the performance assessment of the future passive cooling system used in a high-temperature engineering test reactor.

Expressions approximating the experimental integral cross-sections for elastic and inelastic interactions of light and heavy nuclei at energies up to several GeV/nucleon are presented. The calculated cross-sections are inside the corridor of experimental errors or very close to it.

As an example of the application of Fermat’s optics for burnup waves in multiplying media the fast burn-wave ring reactor is presented. By the spatial decoupling of the energy producing zone from the final fission product zone a continuous mode of operation ± by loading only fertile material and without reprocessing ± seems to be possible for a fast reactor system.