Hermann Unger

Net employment effects of an extension of renewable-energy systems in the Federal Republic of Germany

Renewable-energy potential exists in the Federal Republic of Germany to a great extent, but it is barely used as yet. A change in the power-supply structure seems to be too risky with regard to finance and the sensitive labour market. Nevertheless, an extension of renewable energy systems in the German state North-Rhine Westphalia would lead to improved employment prospects.

Investigation of Core Degradation (COBE).

Abstract The COBE project started in February 1996 and finished at the end of January 1999. The main objective was to improve understanding of core degradation behaviour during severe accidents through the development of computer codes, the carrying out of experiments and the assessment of the computer codes’ ability to reproduce experimental behaviour. A major effort was devoted to quenching behaviour and a substantial achievement of the project was the design and commissioning of a new facility for the simulation of quenching of intact fuel rods. Two tests, carefully scaled to represent realistic reactor conditions, were carried out in this facility and the hydrogen generated during the quenching process was measured using two independent measuring systems. The codes were able to reproduce the results in the first test, where little hydrogen was generated but not the second test, where the extra steam produced during quenching caused an invigorated Zircaloy oxidation and a substantial hydrogen generation. A number of smaller parametric experiments allowed detailed models to be developed for the absorption of hydrogen and the cracking of cladding during quenching. COBE also investigated other areas concerned with late-phase phenomena. There was no experimental activity – the work included code development and the analysis of experimental data available to the project partners – either from open literature or from other projects such as Phebus-FP. Substantial improvement was made in the codes’ ability to simulate heat transfer in debris beds and molten pools and increased understanding was reached of control rod material interactions, the swelling of irradiated fuel and the movement of molten material to the lower head.

Radionuclide re-entrainment at bubbling water pool surfaces

Abstract In case of a nuclear reactor accident involving a failure of the primary system, a liquid-coolant pool, contaminated by suspended or solved radionuclides, may be formed. For scenarios, where gas is injected into the liquid or bubbles are generated, the release of low volatile species from liquid surfaces into a gas atmosphere due to re-entrainment/resuspension is identified as a decisive release mechanism. This aerosol source is relatively weak. However, in the late phase of an accident, where radionuclides are possibly accumulated in the pool, this weak but long-lasting source term may contribute considerably to aerosol generation. Depending on the gas flux through a pool, different droplet production mechanisms can be observed. With the modelling of the liquid release from the pool due to film and jet droplet generation as well as the droplet production in case of churn turbulent flow conditions, the resuspension of suspended radionuclides can be quantified as the product of their concentration at the pool surface and the liquid droplet mass flux released.

Aerosol Generation by Bubble Collapse at Ocean Surfaces

Sea salt particles are part ofmarine aerosols in the troposphere. A fraction ofthese particles is released by droplets generatedduring the bursting of bubbles at the ocean surface.Droplets result from fragmentation of film caps (filmdroplets) and the disintegration of water jets formedsubsequent to the bubble collapse (jet droplets).This release process is also of importance fortechnical applications and, consequently, simulationtools have been developed, which now may be used toquantify the contribution of these effects to marineaerosol generation. To calculate the amount of filmdroplets generated, it is necessary to determine thevolume of the film cap, which is a function of itsthickness and surface area. While surface areas ofsmall bubbles can be determined by an analyticalsolution of a simplified balance of forces, shapes oflarge non-spherical bubbles are calculatednumerically. The determination of the film thicknessis based on a resonance model for bubbleoscillations. For a detailed analysis of the jetdroplet generation, the bubble burst induced jetformation and disintegration is simulated numericallyusing a SOLA-MAC algorithm.

Volatile fission product and sodium release from liquids

Abstract For the improvement of radioactive source term calculations the computer code revols has been developed for the mechanistic modeling of the evaporative release of volatible species (e.g. water, sodium and volatile fission products as NaJ, Cs and Rb) from different hosts into an inert gas atmosphere. The code, showing a modular structure, has been developed to be coupled with reactor containment safety analysis codes as the contain / lmr and lmfbr version. In substituting existing constant-retention-factor formulations by introducing a geometry and state dependent, instationary retention factor, an improved aerosol and fission product source calculation can be obtained. The comparison of theoretical predictions with experimental results performed at the Karlsruhe Research Center shows good agreement.

Investigation of the transition from forced to natural convection in the research reactor Munich II

The new research reactor Munich II (FRM-II), which is under construction at the Technical University of Munich (TUM), Germany, makes use of a compact reactor core consisting of a single fuel element, which is assembled of two concentric pipes. Between the fuel elements inner and outer pipe 113 involutely bent fuel plates are placed rotationally symmetric, forming 113 cooling channels of a constant width of 2.2 mm. At the Department for Nuclear and New Energy Systems of the Ruhr-University of Bochum, Germany, a test facility has been built in order to confirm the concept of the decay heat removal in the FRM-II, to acquire data of single and two phase natural convection flows and to detect the dry out in a narrow channel. All results have proved the possibility to cool the fuel element by means of natural convection.

Verification of the two-phase stratified-flow model in ATHLET by separate effect tests

Abstract The athlet code which is being developed by the Gesellschaft fur Anlagen- und Rcaktorsicherheit (GRS) mbH is intended to cover, by means of a single code, the entire spectrum of loss-of-coolant and transient accidents in pressurized and boiling water reactors. The actual athlet version Mod 1.1-Cycle A has a five-equation two-phase model based on the conservation laws for liquid mass, liquid energy, vapor energy and overall momentum. The relative velocity between liquid and vapor is determined by a full-range drift-flux model for two-phase flow in horizontal and vertical pipes. The verification of this drift-flux model is carried out by both large-scale experiments and single-effect tests. The single-effect test ECTHOR investigates stratified flow during the clearance of a water-filled loop seal by a forced air flow through the loop. ECTHOR is a French test for the consideration of two-phase flow regimes in pipes for the development of the cathare codes. The experiments are dedicated to investigating typical two-phase flow during small break loss of coolant accidents (LOCA) in pressurized water reactors (PWR). As a measure, the remaining water level in the loop is determined as a function of the air flow rate. For the verification, a comparison between athlet and cathare computations, on the one hand, and experiments on the other hand is carried out. The results compare very well to each other. Test runs on different numerical grids show convergence to an asymptotic limit with increasing grid refinement.

Investigation of the Fission Product Release From Molten Pools Under Oxidizing Conditions With the Code RELOS

With the purpose of modeling and calculating the core behavior during severe accidents in nuclear power plants system codes are under development worldwide. Modeling of radionuclide release and transport in the case of beyond design basis accidents is an integrated feature of the deterministic safety analysis of nuclear power plants. Following a hypothetical, uncontrolled temperature escalation in the core of light water reactors, significant parts of the core structures may degrade and melt down under formation of molten pools, leading to an accumulation of large amounts of radioactive materials. The possible release of radionuclides from the molten pool provides a potential contribution to the aerosol source term in the late phase of core degradation accidents. The relevance of the amount of transferred oxygen from the gas atmosphere into the molten pool on the specification of a radionuclide and its release depends strongly on the initial oxygen inventory. Particularly for a low oxygen potential in the melt as it is the case for stratification when a metallic phase forms the upper layer and, respectively, when the oxidation has proceeded so far so that zirconium was completely oxidized, a significant influence of atmospheric oxygen on the specification and the release of some radionuclides has to be anticipated. The code RELOS (Re lease of Lo w Volatile Fission Products from Molten S urfaces) is under development at the Department of Energy Systems and Energy Economics (formerly Department of Nuclear and New Energy Systems) of the Ruhr-University Bochum. It is based on a mechanistic model to describe the diffusive and convective transport of fission products from the surface of a molten pool into a cooler gas atmosphere. This paper presents the code RELOS, i. e. the features and abilities of the latest code version V2.3 and the new model improvements of V2.4 and the calculated results evaluating the implemented models which deal with the oxygen transfer from the liquid side of the phase boundary to the bulk of the melt by diffusion or by taking into account natural convection. Both models help to estimate the amount of oxygen entering into the liquid upper pool volume and being available for the oxidation reaction. For both models the metallic, the oxidic and a mixture phase can be taken into account when defining the composition of the upper pool volume. The influence of crust formation, i. e. the decrease of the liquid pool surface area is taken care of because it yields the relevant amount of fission products released into the atmosphere. The difference of the partial density between the gas side of the phase boundary and the bulk of the gas phase is the driving force of mass transport.Copyright

Seasonal Storage of Solar Low Temperature Heat in Mines

Publisher Summary This chapter explains seasonal storage of solar low temperatures heat in mines. The solar assisted heat supply of buildings offers a great technical potential for the substitution of fossil. The chapter examines the use of mines in the Ruhr area. Due to the small thermal conductivity of the rock, some years pass by until a quasi-stable status is achieved. Simulations with TRNSYS show that good efficiencies can be realized. Depending on favorable boundary conditions, storages in mines can be built with lower investment costs in comparison to other storage designs. An analysis of the pit locations in the Ruhr area shows that there are many suitable sites available. As a result, it can be observed, that seasonal heat storage in mines represents a very interesting alternative in comparison to the established concepts. At this time there are neither technical nor economical reasons not to pursue such mine storage projects further on. With regard to the positive results of the first project phase, the feasibility of seasonal heat storage in mines should be demonstrated by means of a first pilot project in the future.

Labour Market Prospects of Resource-Conserving Energy Technologies

Publisher Summary This chapter describes the labor market prospects of resource-conserving energy technologies.Renewable energy potentials exist in the Federal Republic of Germany to a great extent, but they are barely used as yet. A change in the power supply structures seems to be too risky with respect to the financing as well as with regard to the sensitive labor market situation. Referring to this, the economic effects in the field of employment as a result of a strengthened extension of renewable energy systems and energy systems for a more efficient use of energy are examined in this study. Based on a static input-output analysis, the required annual investments and running costs, the necessary refinancing and the resulting effects in the conventional power economy are converted into net employment effects and displayed in a sectorally disaggregated form. Although the employment effects should not be overestimated, at least a securing of the actual number of jobs can be assumed in the case of a long-term integration of renewable energy carriers into the present supply structure.