atw - International Journal for Nuclear Power | 08/09.2019

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atw Vol. 64 (2019) | Issue 8/9 ı August/September 430 AMNT 2019 | | Fig. 4. Technical sketch of ATHOS facility (left) and picture of 3 x 3 TPCT bundle condenser section installed in ATHOS chimney (right). The major modification to laboratory experiments is the shift to an atmospheric ultimate heat sink. The heat transfer coefficient at ambient air flow conditions is expected between 5 to 45 W/(m 2 K), depending on the air flow velocity in the chimney. The laboratory measurements result in heat transfer coefficients 100 times higher using water as heat sink. Hence, the performance of TPCT is determined by the heat sink, the heat transfer of the pipe bundle is estimated by one order of magnitude below the laboratory measurements so far. In Figure 5 the thermal operation of one cornerpositioned TPCT in the ATHOS facility is compared to previous water-heated laboratory experiments. Both experiments are performed at 60 °C heating temperature and about 10 °C heat sink temperature. The shown temperatures in the graphs are measured nearly at the same TPCT heights. As mentioned before, it has to be considered that the segmentation of evaporation, adiabatic and condenser section is different for both configurations. The beginning and end of the TPCTs adiabatic section in ATHOS is measured at 2000 mm and 5000 mm from the lower pipe end. Whereas the ATHOS temperatures are measured mainly along the condenser section, the measurements at the same heights in the laboratory setup are along the adiabatic section. The shown temperatures at 9500 mm and 10000 mm in the right graph envelop the double-pipe cooler condenser section of the laboratory setup. It is noticeable, that the temperatures in the ATHOS pipe are stable over the measurement time. The water temperature at the evaporator end is approximately 60 °C in the TPCT and enters with nearly 50 °C the adiabatic section (2000 mm). The temperature at the condenser end (10000 mm) is still around 45 °C. The laboratory measurements shows a pulsating TPCT operation. Especially the temperature measured in the condenser section fluctuates between the heat sink temperature (10 °C) and the average adiabatic temperature (30 °C). In general, the ATHOS pipe operates at higher temperatures. On the one hand, the heat transfer coefficient of the heat source and therefore the heat input is lower due to the natural convection flow in the ATHOS water tank by contrast with the forced convection flow through the double-pipe heater in the laboratory setup. Otherwise, the heat transfer coefficient of the heat sink and thus the heat output is magnitudes less with ambient air and the condensate temperature is 25 K higher in ATHOS although the heat sink temperature is nearly the same. The average temperatures of the experiments shown in Figure 5 are listed in Table 1. The heat flow rate of TPCT in the laboratory experiment is 1350 W, calculated from the mass flow and the temperatures in the secondary cooling circuit. The determination of the TPCT heat transfer performance in the ATHOS facility is quite complex and a comprehensive energy balance is presently elaborated but not finished yet. Nevertheless, a first rough estimate based on the heating power of the water tank and considering heat losses to the environment and a heat transfer distribution over the 3 x 3 TPCT bundle yields to a transferred heat of about 350 W per TPCT, which is only 26 % compared to the water-cooled laboratory experiment. | | Fig. 5. Temperature sequence for one hour measurement time in ATHOS facility, pipe in corner position (left) and in water-heated laboratory setup (right). Position Evap. 2000 mm 5000 mm 7500 mm 9500 mm 10000 mm Cond. Sink ATHOS 60.1 52.4 51.6 48.4 49.1 43.7 47.1 7.5 Laboratory 54.1 34.2 33.8 33.4 33.3 17.3 19.6 10.2 | | Tab. 1. Average temperatures [°C] of ATHOS and laboratory setup for TPCT d=32 mm, 70 % filling ratio, 60 °C heat source and 10 °C heat sink. AMNT 2019 Atmospheric Spent Fuel Pool Cooling by Passive Two-Phase Closed Thermo syphons ı Claudia Graß, Rudi Kulenovic and Jörg Starflinger
atw Vol. 64 (2019) | Issue 8/9 ı August/September Conclusions The functionality and thermal operation of TPCTs for various boundary conditions were experimentally investigated. The direct electric heating experiments show that with increasing heat input the thermal pulsating operation of TPCTs stabilizes and minor pipe diameters operate at lower evaporation temperatures. In the water-heated experiments, a heat transfer up to 2 kW by a single TPCT was reached at 60 °C heat source temperature depending on the heat sink temperature. Experiments in the ATHOS facility proved successfully the functionality and applicability of long-length TPCTs for passive spent fuel pool cooling at 60 °C pool temperature. Although the removed heat is with approximately 350 W per TPCT quite low, it has to be considered that these experiments are performed for conservative basic con figuration. The optimization of the condenser section for example by enlargement of the condenser area by fins or airflow arrangements in the chimney is essential for a final application. References | | A. Faghri, Heat Pipes Science and Technology, Taylor&Francis, London, 1995, ISBN 1560323833 | | D.A. Reay, P.A. Kew, Heat pipes: theory, design and applications, 2006, ISBN 9780080982663 | | M. Groll, S. Rösler, Operation Principles and Performance of Heat Pipes and Closed Two-Phase Thermosyphons, J. Non-Equilib. Thermosyn. (17), 91-151, 1992 | | Z. Xiong, C. Ye, M. Wang, H. Gu, “Experimental study on the sub-atmospheric loop heat pipe passive cooling system for spent fuel pool”, Progress in Nuclear Energy, 2015, 79, pp. 40-47 | | C. Graß, R. Kulenovic, J. Starflinger, “Experimental Investigation on Passive Heat Transfer by Long Closed Two-Phase Thermosiphons”, Int. J. for Nuclear Power, Vol. 62, 2017, Issue 7, pp. 481-485 | | C. Graß, R. Kulenovic, J. Starflinger, Experimental study on heat transfer characteristics of long twophase closed thermosiphons related to passive spent fuel pool cooling, Proceedings of Joint 19 th International Heat Pipe Conference and 13 th International Heat Pipe Symposium, Pisa, 2018 Author Claudia Graß Rudi Kulenovic Prof. Jörg Starflinger Universität Stuttgart Institut für Kernenergetik und Energiesysteme Abteilung Energiewandlung und Wärmetechnik Pfaffenwaldring 31 70569 Stuttgart 431 AMNT 2019 Acknowledgement The presented work is funded by the German Federal Ministry of Economic Affairs and Energy (BMWi, project no. 1501515) on the basis of a decision by the German Bundestag. Analytical Model for the Investigation of the Out-of-Plane Behavior of Unreinforced Masonry Walls Moritz Lönhoff, Lukas Helm and Hamid Sadegh-Azar Introduction & Objective Load-bearing and non-load-bearing unreinforced masonry (URM) is used for many types of buildings in Europe and all over the world. In nuclear power plants (NPP), non-load-bearing partition walls are often built as URM. While for ordinary building structures, static load-bearing capacity verification is sufficient in many cases, for NPP’s there are high requirements on the earthquake-resistant design. The building structure itself as well as substructures and secondary structures need to be stable in case of an earthquake. Although, in most cases, only secondary non-safety relevant elements or structures (e.g. cable trays or piping systems) are anchored or fixed to partition walls, their collapse however can be a risk for safety relevant structures and components, due to falling debris or sequential effects (Class IIa structures/components according to KTA 2201.1 [1]). Therefore, it must be verified that there is no risk of collapsing walls or falling debris. For this purpose, in-plane and out-of-plane (Figure 1) load-bearing capacities are required to be determined. Since the out-of-plane capacity (stability transverse to the plane) often is decisive in an earthquake scenario, it is investigated here. Young Scientists Workshop WINNER Moritz Lönhoff was awarded with the 3 rd price of the 50 th Annual Meeting on Nuclear Technology (AMNT 2019) Young Scientists Workshop. According to the German code DIN EN 1996 [2] and guideline KTA 2201.3 [1], simple force-based quasi-static methods, using the peak ground acceleration (PGA) as an input | | Fig. 1. URM in-plane and out-of-plane failure modes. parameter are recommended for the seismic design and evaluation of masonry walls. More advanced energy- and displacement-based models are available in the literature. Investigations [3, 4] have already shown that the actual seismic load-bearing capacity of URM walls can be higher than the one predicted using simplified models. However, disregarding important influencing parameters can lead to unnecessary and uneconomical rehabilitation of existing masonry or replacement by other construction types. For this purpose, based on the findings from analytical, numerical and experimental investigations on the out- ofplane behavior of URM walls conducted at the TU Kaiserslautern (TUK), an analytical model to determine the force-displacement- relationship considering key influencing factors is developed. The state of the art, conducted investigations and the developed analytical model are briefly presented in this paper. Analytical Model for the Investigation of the Out-of-Plane Behavior of Unreinforced Masonry Walls AMNT 2019 ı Moritz Lönhoff, Lukas Helm and Hamid Sadegh-Azar
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atw - International Journal for Nuclear Power | 08/09.2019

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