[en] The paper presents the experimental and theoretical results from investigating the effects occurring during the cooling of HLW glass melts in canisters. It was intented to produce monolithic HLW glass blocks by controlled cooling. The experimental and numerical tools are specified and the results of measurements are compared with computed data. The influence of lining, isolation materials and crack systems in glass blocks on the heat transfer were modelled. Temperature calculations were performed for heat producing HLW glass blocks and the computed center-line temperature were analysed for various canister diameters and various conditions of interim storage. The calculations were performed by means of the finite element programs ADINA/ADINAT. For stress calculations only those volume elements were considered having temperatures below the transition temperature. A thermoelastical material model was applied. Model calculations were also performed for radioactive glass products with a thermal power of 17 W/l. The development of mechanical stresses depending on variations of heat flow from the canister surface and on change of thermal power by the radioactive decay were studied. Temperatures and arising stresses of vitrified waste forms in canister having 0.30 m and 0.43 m diameter respectively, were compared. (orig.)

No abstract available

[en] Using Monte Carlo simulations we calculate the topological susceptibility for the CP³ model on a simplicial lattice approximating the sphere S². Our data exhibit the right scaling behaviour but do not show a suppression of topologically relevant fluctuations in the small volume limit. 11 refs.; 1 fig

[en] The effect of particle desorption from Al mirror surfaces by the influence of pulsed UV laser radiation has been studied. The investigations are closely related to the demands of astronomers, who are looking for a more effective way of cleaning the Al coatings of future very large telescope (VLT) mirrors. A systematic parameter study has been performed in order to determine the irradiation conditions which yield the highest dust removal efficiency (i.e. reflectivity increase) on contaminated samples, taking particularly into account laser induced damage and degradation effects of coating and substrate. The particle removal rate increases with increasing laser fluence, being limited however by the damage threshold of the coating. Therefore, parameters influencing the damage threshold of metal coatings like wavelength, pulse width and number of pulses have been studied in detail. Data indicate that on Al coated BK7 and Zerodur samples KrF laser radiation yields the optimum result, with cleaning efficiencies comparable to polymer film stripping. The initial reflectivity of the clean coating can nearly be reinstalled, in particular when an additional solvent film on the sample surface is applied. Hence, laser desorption seems to be a viable method of cleaning large Al mirrors for telescopes

[en] It is shown that the nonlocal light-cone expansion of composite operators, introduced first by Anikin and Zavialov, is well suited to treat large momentum transfer processes in the framework of QCD in a concise (and rather direct) manner. The Altarelli-Parisi kernel and the Brodsky-Lepage kernel are shown to be the partially averaged and the restricted anomalous dimensions of appropriately defined nonlocal light-ray operators respectively; on the basis of these relations the Altarelli-Parisi kernel is given as the asymptotic limit of an extended Brodsky-Lepage kernel. (author). 15 refs

No abstract available

[en] The superconducting Darmstadt linear accelerator (S-DALINAC) is a 130 MeV superconducting recirculating electron accelerator serving several nuclear and radiation physics experiments as well as driving an infrared free-electron laser. For the experiments an energy stability of 10^-4 should be reached. Therefore noninvasive beam position monitors will be used to measure the beam energy. For the measurement the differences in flight time of the electrons to the ideal particle are compared, that means in the simulations the longitudinal dispersion of the beam transport system is used for the energy detection. The results of the simulations show that it is possible to detect an energy difference of 10^-4 with this method. The results are also verified by measurements. (orig.)

[en] This report contains a comprehensive evaluation of the sewage-gas-operated combined heat-and-power stations currently supported by the State government of Hessen. The energy-political aim of this policy is to save primary energy and, at the same time, protect the environment by extending the use of sewage gas. Provided the capacity and operation of the power station are appropriate, the sewage treatment plant can cut down its energy costs. (orig.)

[en] This concerns the improvement of the composition of a reflector ceiling of graphite blocks for a pebble bed reactor. The reflector ceiling is composed of single blocks which are superposed in several layers. In order to improve security it is proposed to fasten the blocks of each layer separately by a bar- or tube shaped anchoring rod. Each anchoring rod is separately coupled. (UWI)

[en] The first-order dissolution rate law is used for nuclear waste glass performance predictions since 1984. A first discussion of the role of saturation effects was initiated at the MRS conference that year. In paper (1) it was stated that ''For glass dissolution A^* (the reaction affinity) cannot become zero since saturation only involves the reacting surface while soluble elements still might be extracted from the glass''. Saturation of silica at the surface and condensation of surface silanol groups was considered as being responsible for the slow down of reaction rates by as much as a factor of 1000. Precipitation of Si containing secondary phases such as quartz was invoked as a mechanism for keeping final dissolution affinities higher than zero. Another (2) paper stated that ''... under repository conditions the extent of glass dissolution will be moderate due to saturation with respect to certain major elements (in particular, Si, Al and Ca). Consequently, the concentration levels of the more soluble glass constituents in the aqueous medium are expected to fall appreciable below their solubility limit.'' The formation of dense surface layers was considered responsible for explaining the saturation effect. The mathematical model assumed stop of reaction in closed systems, once solubility limits were achieved. For more than 15 years the question of the correctness of one or the other concept has seldom been posed and has not yet been resolved. The need of repository performance assessment for validated rate laws demands a solution, particularly since the consequences of the two concepts and research requirements for the long-term glass behavior are quite different. In concept (1) the stability of the 'equilibrium surface region' is not relevant because, by definition, this region is stable chemically and after a potential mechanical destruction it will be reformed instantaneously. The same is true for radiation damage. The dissolution of silica from the surface in this concept is considered as rate limiting for the release of soluble elements from the glass. After surface stabilization by local solid/solution equilibrium the release of soluble radionuclides continues with lower rates, but this is considered as resulting from parallel leaching mechanism. In fact, the deconvolutions of the overall leach mechanism into individual parallel and sequential rate limiting steps (not necessarily elementary reactions) is fundamental to this concept. In concept (2) surface stability as well as surface morphology are fundamental. A fracture in the protective surface would increase glass corrosion. The protective effect is based on the low diffusivities of radionuclides and other glass constituents in this layer. However, a true relation between layer thickness and rates is seldom observed. Diffusion coefficients are considered to vary with time as well as with the surface area to solution volume S/V ratio. Sometimes, extremely low diffusivities in extremely thin layers are invoked to explain experimental data. The two concepts are not so different from each other and one is tempted to think of a problem of semantics. In fact, there are two alternative ways by which the protective layer concept can be coupled to the saturation concept: (a) the layer may be formed by solubility effects as proposed in [loc.cit] and/or (b) the layer plays the role of a silica diffusion barrier limiting glass dissolution rates according to the first-order rate law at the interface between the pristine glass and the surface layer. However, the mathematical models based on these conceptual models yield quite different long-term predictions, even though the models may equally well fit a given set of experimental data. The models are also different with respect to the number of interrelated parameters. In the case of a model based on a surface layer slowing down glass network dissolutio n, the numerical value of the diffusion coefficient of silica, the layer thickness and the saturation concentration of dissolved silica are interrelated. Often, none of the parameters are measured directly. As a consequence this leads to not-sufficiently constrained models with poor predictive capacity. Recent research has indicated that there might be problems with the applicability of the first-order rate law. Fresh glass or pre-altered glass samples were put in solutions over-saturated with silica. A decrease in reaction rates by as much as a factor of 10 was observed, but the rates remained much higher than predicted from a first-order rate law. It was argued that none of the kinetic models based on the notions of 'chemical affinity' and 'deviation from an equilibrium' is adapted to describe the kinetics of glass corrosion. In contrast, the formation of a surface gel and condensation of silanol groups are considered responsible for the decrease in reaction rates. The present communication argues against this view. Based on recent results of Monte Carlo calculations it is shown that some time of surface restructuration is necessary before saturation effects become fully effective in controlling long-term release of soluble glass constituents. The formation of a gel layer is not opposed to an affinity based kinetic concept, but it is in contrast a manifestation of this concept. It is the belief of the authors that much of the confusion related to the first-order rate law results from the fact that glass network dissolution is not considered as only one of a series of reaction mechanism and that glass network hydration and alkali ion exchange were ignored as parallel leaching mechanism. Our experimental results show that glass network hydration and ion exchange are important in short-term laboratory tests and in certain cases (closed system) also in the long term. (original, shortened by A.K.)