Electronic transport in graphene with particle-hole-asymmetric disorder

We study the conductivity of graphene with a smooth but particle-hole-asymmetric disorder potential. Using perturbation theory for the weak-disorder regime and numerical calculations we investigate how the particle-hole asymmetry shifts the position of the minimal conductivity away from the Dirac point $\varepsilon = 0$. We find that the conductivity minimum is shifted in opposite directions for weak and strong disorder. For large disorder strengths the conductivity minimum appears close to the doping level for which electron and hole doped regions ("puddles") are equal in size

Radiant heat exchange in a space environment Scientific technical report, 1 Feb. - 31 Jul. 1970

Spectral and directional surface property effects on radiant heat transfer in space environmen

Radiant heat exchange in a space environment Scientific technical report, 1 Aug. 1969 - 31 Jan. 1970

Spectral surface property effects on radiant heat transfer in aerospace environmen

Radiant heat exchange in a space environment Scientific technical report, 1 Feb. - 31 Jul. 1969

Analytical methods development for predicting radiant heat transfer and temperature of engineering surfaces in space environmen

Integration of new experiments into the reflood map

The reflood map, developed in the last decade, was designed as a tool to focus on preventive and mitigative measures to prevent severe core damage scenarios and to identify research areas. In the meanwhile, additional experiments were performed and their data are available, so that an update seems necessary. For homogeneous particulate debris configurations, several experimental programs shed light on coolability. For the transition from in-core early phase to in-core late phase i.e. the loss of the rod like geometry, experimental database is still rather scarce due to the difficulty to describe the state of the core components and the fluid adequately. According to the new insight, an update of the database and the reflood map is discussed, also with respect to assess available grace times

Liquid metal cooled fast reactors

Fast spectrum reactors offer the capability for a better utilization of uranium resources. They are in principle capable to produce (“breed”) but also to transmute (“burn”) fissile materials either by means in a critical or in case of lead alloys even in a sub-critical configuration coupled with an accelerator (ADS).. Associated with the fast spectrum, they require not only a different core design but also many other technological solutions to establish a “safe reactor configuration”. Herein, especially sodium and lead (-alloy) facilitate the option to realize a compact and simple reactor design. While lead in contrast to sodium exhibits a higher neutronic efficiency associated with some often advantageous considered safety coefficients sodium cooled reactors proofed already long term operational experience and material compatibility. Irrespective of the liquid metal reactor concept chosen, liquid metals as coolant formulate new challenges with respect to thermal-hydraulics, material choice, design and system dynamics. Furthermore, the safety demonstration demands a broad validation/verification and in some cases even a modification of presently availalble physical models and technological solutions for a reliable monitoring and long term operation. After a short introduction into different kinds of some liquid metal reactor options currently developed within international programs the presentation formulates the major challenges related to the use of liquid metals addressing the thermal hydraulics and adapted instrumentation, some material issues and examples for a reliable component design. Herein, the progress attained in the recent years is shown and issues still open are elaborated. The research conducted in the frame of European R&D programs on sodium fast reactors as well as lead and LBE reactors and ADS impacted significantly their design and their operational safety. For some selected examples the safety behaviour of typical incidents in reactor operation are discussed and open issues are addressed