Zur selbsttätig sicheren Begrenzung von nuklearer Leistung und Brennstofftemperatur in innovativen Kernreaktoren

Nuclear energy probably will not contribute significantly to the future worldwide energysupply until it can be made catastrophefree. Therefore it has to be shown, that theconsequences of even largest accidents will have no major impact to the environmentof a power plant.In this paper one of the basic conditions for such a nuclear technology is discussed.Using mainly the modular pebble-bed high-temperature reactor as an example, thedesign principles, analytical methods and the level of knowledge as given today incontrolling reactivity accidents by inherent safety features of innovative nuclear reactorsare described. Complementary possibilities are shown to reach this goal with systems ofdifferent types of construction . Questions open today and resulting requirements forfuture activities are discussed .Today's knowledge credibly supports the possibility of a catastrophefree nucleartechnology with respect to reactivity event

Angular momentum transport and turbulence in laboratory models of Keplerian flows

We present angular momentum transport (torque) measurements in two recent experimental studies of the turbulent flow between independently rotating cylinders. In addition to these studies, we reanalyze prior torque measurements to expand the range of control parameters for the experimental Taylor-Couette flows. We find that the torque may be described as a product of functions that depend only on the Reynolds number, which describes the turbulent driving intensity, and the rotation number, which characterizes the effects of global rotation. For a given Reynolds number, the global angular momentum transport for Keplerian-like flow profiles is approximately 14% of the maximum achievable transport rate. We estimate that this level of transport would produce an accretion rate of $\dot{M}/\dot{M_0} \sim 10^{-3}$ in astrophysical disks. We argue that this level of transport from hydrodynamics alone could be significant.Comment: 17 pages, 7 figures, 2 tables, submitted to Astronomy & Astrophysics (2011

Auswirkungen eines spontanen Druckbehaelterversagens beim HTR-Modul

Der HTR-Modul (Hochtemperaturreaktor) versteht sich als ein Reaktor, der das gesamte Know-How der HTR-Technik in sich vereint. Der erste Teilaspekt ist die Betrachtung der nichtnuklearen Effekte. Anhand von bekannten Untersuchungen an Explosions- und Berstvorgaengen wird ein Vergleichsmassstab fuer den HTR-Modul entwickelt. Detaillierte Untersuchungen zum dynamischen Bruchstueckverhalten werden mit den neuen Programmen FRAG2 und XerXes gemacht. Anschliessend wird untersucht, inwiefern der Berstvorgang auch nukleare Auswirkungen implizieren kann. Dabei wird eine Beschraenkung auf den unmittelbar auf das Bersten folgenden Zeitraum gemacht, das heisst Korrosionseffekte werden nicht beruecksichtigt und der Leervolumenanteil der Kugelschuettung bleibt konstant. Die so berechneten Ueberschussreaktivitaeten werden als Eingangsgroessen zur Analyse von Belastungen der Coated Particles in den Brennelementen genommen. Dabei werden die schnellen Reaktivitaetstransienten mit dem Programm HTRKIN punktkinetisch untersucht und dann mit dem neuen Programm FAST2 in transiente Belastungen umgesetzt. Die Belastungen der relevanten CP-Schichten werden dann anhand von Vergleichswerten bewertet. Als Ergebnis der Untersuchungen ist festzuhalten, dass die Kurzzeittransienten, die zwangslaeufig, ohne moeglichen Eingriff von aussen, abgelaufen, gemessen an den vergleichbaren experimentellen Daten, ein nur relativ geringes Gefaehrdungspotential liefern. Die Langzeittransienten hingegen sind mit entsprechendem Aufwand zu beherrschen. Es bleibt zu ueberlegen, inwieweit durch moeglich Kurzzeittransienten eine Vorschaedigung der Coated Particles eintritt und dies negativ auf das Langzeitverhalten wirkt. (orig./GL)The HTR-Module (High Temperature Reactor) is supposed to be a reactor, which comprises of the complete know-how of HTR-technology. The first part evaluates the non-nuclear effects. Through the means of known investigations of explosions and burst processes, a comparison measure for the HTR-Module is developed. More detailed investigations of the dynamic fragment behaviour are made with the new computer programs FRAG2 and Xerxes. In the following, it is investigated in which way the burst process also implies nuclear effects. A limitation is made to be time period immediately following the burst of the vessel, meaning that corrosion of the fuel elements is not regarded and the void fraction of the pebble bed remains constant. Thus the calculated reactivities are input data for the analysis of the stress of the Coated Particles in the fuel elements. The fast reactivity transients are calculated with means of the pointkinetic program HTRKIN and then transformed to transient stresses with use of the new program FAST2. The stresses of the CP-layers of interest are rated with the use of comparison values. The result of the investigations is that the shortterm transients, which will occur without any outer influence, have a relatively small hazardous potential in comparison to experimental results. The longterm transients can be handled through a fitting accident management. The way in which the possible shortterm transients result in a remaining prefailure of the Coated Particles and negatively influence the longterm behaviour still needs to be considered. (orig./GL)SIGLEAvailable from TIB Hannover: RA 831(3067) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Zur selbsttaetig sicheren Begrenzung von nuklearer Leistung und Brennstofftemperatur in innovativen Kernreaktoren

Nuclear energy probably will not contribute significantly to the future worldwide energy supply until it can be made catastrophe-free. Therefore it has to be shown, that the consequences of even largest accidents will have no major impact to the environment of a power plant. In this paper one of the basic conditions for such a nuclear technology is discussed. Using mainly the modular pebble-bed high-temperature reactor as an example, the design principles, analytical methods and the level of knowledge as given today in controlling reactivity accidents by inherent safety features of innovative nuclear reactors are described. Complementary possibilities are shown to reach this goal with systems of different types of construction. Questions open today and resulting requirements for future activities are discussed. Today's knowledge credibly supports the possibility of a catastrophe-free nuclear technology with respect to reactivity events. (orig.)SIGLEAvailable from TIB Hannover: RA 831(2960) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The Importance of the Mining Subsidence Reservoirs Located Along the Trans-Regional Highway in the Conservation of the Biodiversity of Freshwater Molluscs in Industrial Areas (Upper Silesia, Poland)

The objectives of the survey were to analyse the structure of the mollusc communities in the mining subsidence reservoirs that were created as a result of land subsidence over exploited hard coal seams and to determine the most predictive environmental factors that influence the distribution of mollusc species. The reservoirs are located in urbanised and industrialised areas along the Trans-Regional Highway, which has a high volume of vehicular traffic. They all have the same sources of supply but differ in the physical and chemical parameters of the water. In total, 15 mollusc species were recorded including four bivalve species. Among them Anodonta cygnea is classified as Endangered according to the Polish Red Data Book of Animals and also as Near Threatened according to the European Red List of Non-marine Molluscs. Eleven of the 15 mollusc species are included on the European Red List of Nonmarine Molluscs as Least Concern. Conductivity, pH and the concentration of calcium were the parameters most associated with the distribution of mollusc species. Canonical correspondence analysis showed that Potamopyrgus antipodarum, Radix balthica, Physella acuta, Gyraulus crista and Pisidium casertanum were associated with higher conductivity and lower pH values. A. cygnea, Anodonta anatina and Ferrissia fragilis were negatively influenced by these parameters of the water. The results of this survey showed that the mining subsidence reservoirs located in urbanised and industrialised areas provide refuges for rare and legally protected species and that they play an essential role in the dispersal of alien species as well