Volume 77, Issue 2

Germany is to undertake a structured phasing-out of power generation from nuclear energy. Until the last nuclear power plant is shut down, safety must be guaranteed in line with the very latest developments in science and technology. The R&D work performed is in accord with the resolution for the structured phasing-out of the use of nuclear power. The Federal Ministry of Education and Research (BMBF) with its “Basic Energy Research 2020+” funding concept supplements institutionally funded work of Helmholtz Institutes in a few core areas to further extend co-operation with universities. Close coordination between institutional and project funding will be ensured via the Alliance for Competence in Nuclear Technology in Germany (“Kompetenzverbund Kerntechnik”). In the area of nuclear safety and disposal research, R&D is carried out on the scientific and technological aspects of safety in existing nuclear reactors, the safety of nuclear disposal, the minimisation of highly radioactive substances ultimately requiring disposal and radiation research. Special attention is to be paid within this concept to the funding of young scientists. In addition to doctorate posts in research projects, special funding instruments are to be offered to promote the next generation of scientists.

Condensation induced water hammer (“condensation hammer”, CIWH) represent a dangerous phenomenon in pipings, which can endanger the pipe integrity. If they cannot be excluded, they have to be taken into account for the integrity proof of components and pipe structures. Up to now, there exists no substantiated model, which sufficiently determines loads due to CIWH. Within the framework of the research alliance CIWA, a tool for estimating the potential and the amount of pressure loads will be developed based on theoretical work and supported by experimental results. This first study discusses used computational models, results of experimental observations and gives an outlook onto future techniques.

Experiments were conducted for the purpose of investigating the phenomenon of condensation-induced waterhammer in an ammonia refrigeration system. Waterhammer was initiated by introducing hot ammonia gas over static subcooled ammonia liquid placed in a horizontal 146.3mm diameter carbon steel pipe approximately 6.0m long. By means of fast response piezoelectric pressure transducers and a high speed data acquisition system rapid dynamic pressures were recorded whenever a condensation-induced event occurred. Moreover, by means of top-mounted diaphragm pressure transducers sensing gas pressure the speed of liquid slugs propagating along the pipe was determined. Based upon careful interpretation of the results criteria for the transition from initial stratified flow to slug flow were established, similar to the so-called Taitel-Dukler correlation in two-phase flow literature.

Simulations of condensation-induced water hammer with one-dimensional two-fluid model requires explicit modeling of slug formation, slug propagation, and in some cases slug decay. Stratified flow correlations that are more or less well known in 1D two-fluid models, are crucial for accurate description of the initial phase of the slug formation and slug propagation. Slug formation means transition to other flow regime that requires different set of correlations. To use such two-fluid model for condensation induced water hammer simulations, a single slug must be explicitly recognized and captured. In the present work two cases of condensation-induced water hammer simulations performed with WAHA code, are described and discussed: injection of cold liquid into horizontal pipe filled with steam and injection of hot steam into horizontal pipe partially filled with cold liquid.

This paper deals with the 1-D Delayed Equilibrium Model (DEM) for choked or critical flow rate in steady state or quasi-steady state conditions and the selection of the relevant experimental data for assessing such models. In particular, the focus is made on thermodynamic non-equilibrium conditions, which prevail in the flashing process near the critical section. In this regard, relaxation models such as the DEM developed and tested in previous studies at UCL was revisited and improved in view of their implementation in the next CATHARE code generation during the EU NURISP (NUclear Reactor Integrated Software Platform) project. A methodology to implement the DEM into is developed. Some new results of the DEM are compared against experimental data such as Super Moby-Dick experiments done in CEA and the well-known Marviken experiments performed at quasi-real scale geometry of Nuclear Plant.

For the realistic simulation of condensation induced water hammer (CIWH) in horizontal pipes resulting from the contact of steam at sub-cooled water, an appropriate model for the mass and energy transfer due to phase change is needed. For this purpose the tripartite mass transfer (TMT) model has been developed that is introduced in the present paper. The TMT model is based on the assumption of isentropic processes and accounts for vaporization due to flashing, condensation due to isentropic decompression (homogenous condensation) and direct contact condensation at the phase interface. The TMT model shall be considered as a frame for sub-models which may be arranged for the three above-mentioned phase change phenomena. The TMT model has been implemented in the one-dimensional two-phase pressure surge code DYVRO mod 3. A verification and validation procedure was performed based on experiments at test facilities in Oberhausen (PPP), Rossendorf (CWHTF) and Budapest (PMK-2).

A condensation induced water hammer is a severe effect that has caused damages and even fatalities worldwide. This effect is not limited to the nuclear industry only. Generally it can occur in every pipe that contains water and steam (two-phase-flow). To date many experiments were executed to study this phenomenon and to validate existing water hammer codes. But theoretically versus measured results show a very high degree of deviation. Information about those experiments was obtained by literature review. This information is presented additionally to a test facility, which has been developed in order to generate water hammers. The test device is introduced in this paper and its main functions are briefly explained. In contrast to other experiments, water hammers at the UniBw are performed under controlled conditions. Air in water is a disruptive parameter that causes vigorous deviations between the theoretical system code and the experimental measurements. As in the test device presented in this paper, deionised water without air is used, this effect is ruled out. Furthermore the inception of a water hammer is controlled by a scientist. The experimental results will characterise the dynamic response of the test device as a function of system pressure, filling degree and sub-cooling.

It is well known that the one-dimensional equations of motion for two-phase flow are non-hyperbolic. Non-hyperbolicity can lead to numerical instabilities, destroying the solution. However, researchers in the last few decades were able to show that inclusion of virtual mass and/or phase-to-interface pressure differences in the momentum equations successfully render the equations of motion hyperbolic. In the present paper, the effect of including virtual mass and phase-to-interface pressure terms in the momentum equations on the hyperbolicity of the two-phase model in the CATHENA 4 code is discussed. The study is motivated by the fact that the inclusion of either model has been shown in the open literature to lead to a hyperbolic system separately. However, no known study exists that examine hyperbolicity in the presence of both these terms in the momentum equations. In this work, both terms are considered in the model equations simultaneously and their implications on the hyperbolicity of the two-phase model are discussed. Specifically, it is shown that in the case of mixed flow, there is a distinct region of non-hyperbolicity that developers need to be aware of when their equations include both the virtual mass and the phase-to-interface terms. Selecting the coefficients of phase-to-interface pressure difference terms properly ensures that the equations are hyperbolic for a wide range of conditions.

Fusion is the energy production technology, which could potentially solve problems with growing energy demand of population in the future. Wendelstein 7-X (W7-X) is an experimental stellarator facility currently being built in Greifswald, Germany, which shall demonstrate that in the future energy could be produced in such type of fusion reactors. Lithuanian energy institute (LEI) in the frames of European Fusion Development Agreement (EFDA) program is cooperating with Max Planck Institute for Plasma Physics (IPP, Germany) by performing safety analysis of fusion device W7-X. In this paper the consequences of potential water hammer effects were analysed only for the case, when the plasma vessel is operating in the “baking” mode. “Baking” is the mode of facility operation during which the plasma vessel structures are heated up to 150°C in order to release absorbed gases from the surfaces and to pump them out of the plasma vessel before plasma operation. For the analysis the thermal-hydraulic model of target (torus) modules cooling / heating systems in W7-X facility was developed using RELAP5/Mod3.3 code. The performed analyses showed that the pressure pulsations in pipelines of cooling / heating systems are possible only in case of very fast closure of automatic valves in torus modules inlets and check valves in torus modules outlets. The maximum dynamic loading to cooling / heating systems pipelines due to such valves activations is in the range 0.12–0.28 MPa. Such dynamic load is insignificant and integrity of pipelines remains not violated. The pressure surge in pipeline connecting torus module in case of erroneous closure of automatic valve is eliminated due to operation of check valve on pipeline in torus module outlet.

Most people will have been exposed to some aspect of the debate about the Athabasca Oil Sands in North-Eastern Alberta and the significant role that the oil sands are expected to play in supplying conventional fossil fuels. Part of the bitumen is recovered from mines and part is recovered from in situ projects utilizing the Steam Assisted Gravity Drainage Process (SAGD). SAGD utilizes a considerable amount of steam, that is injected into geological formations. Hot water, bitumen and some vapour are recovered from the production wells. With significant steam generation, transmission and injection, there is the very real possibility of condensation induced water hammers. There have been a number of catastrophic failures to date. The intent of the paper is to provide interesting background information on the in situ oil sands industry. More importantly, to show some interesting and broader applications of thermalhydraulics developed in the nuclear industry. The expertise developed may have potential markets, with some adaptation, to the oil sands industry. Finally, there has been some discussion about using nuclear power for steam generation in the oil sands.