atw 2018-09v3

• Short-link
• Link
• Embed

<strong>atw</strong> Vol. 63 (<strong>2018</strong>) | Issue 8/9 ı August/September 456 DATF NOTES hardly be attributed to the primary water inlet temperature variations, which remain relatively well known since decades, because the noise has essentially no time shift dependence along the water flow through the assembly channel. The high neutron flux noise is concentrated essentially in one quarter of the core, radial and azimuthal correlations build a consistent picture supporting this observation. The model explaining the increase of the neutron flux noise is at the present time associated with the replacement of FOCUS fuel assemblies by the HTP assemblies, which took place basically since 2010. The current core configuration has no longer FOCUS assemblies, and the (high) neutron noise achieved seems to be saturated, bracketing the period of insertion of the HTP-assemblies well. The reason for the neutron noise increase is associated to the thermalhydraulics pattern in the core, not fully symmetric (3 loops with asymmetries), probably promoting a more intense cross flow towards one specific loop that exercises a lateral dragging force on the HTP assemblies. Since these assemblies hold the fuel rods in a less fixed way than the previous FOCUS, with the purpose of minimising the rod-to-grid fretting potential further, the guiding tubes do not count in HTP assemblies with the stiffness of the fuel rods themselves to give a combined, stronger assembly stiffness, as it was the case of the FOCUS assemblies. HTP are considered to be mechanically more prone to elastic lateral oscillations. The ­increase of neutron flux noise would be the result of larger variations of the water gap thickness between HTP assemblies, an effect that was enhanced as the core was loaded increasingly with HTP assemblies. Further work is ongoing to bring complementary information to support or discard this assembly behaviour model. In particular, KKG participates in the CORTEX international research programme within the Horizon 2020 EU Framework Programme for Research and Innovation, and a different organisation will take independent new measurements to refine the analyses available. Acknowledgments The authors would like to thank the Electrical Division at KKG for their support and collaboration, in particular R. Härry, K. Heydecker and A. Ploner for performing several additional measurements during last cycle. We are also thankful to the director of the Nuclear Fuel Division, B. Zimmermann, for his support during the course of this research. References [1] Neutronenflussrauschen, R. Meier, ANO-D-41205, 2010. Restrictive. [2] Noise Analysis of KKG’s neutron flux detector signals, A. Alander, Studsvik Scandpower, TN-04/2011, Document Kernkraftwerk Gösgen-Däniken AG. 2011. Restrictive. [3] Studie des Neutronenflussrauschens im Zyklus 36, G. Girardin, Kernkraftwerk Gösgen-Däniken, BER-F-78937, Internal Document Kernkraftwerk Gösgen- Däniken AG, 2015. Restrictive. [4] Use of Neutron Noise for Diagnosis Of In-Vessel Anomalies in Light-Water Reactors, ORNL/TM-8774, 1984. [5] KKGG – Reaktorphysikalische Rechnungen für den 36. Zyklus; FS1- 0016977 v1, Endgültiger Umsetz plan für den 35. BE-Wechsel (Stand: 10.06.2014), Internal Document Kernkraftwerk Gösgen-Däniken AG, 2014. Restrictive. [6] Handbook of statistical Distributions with Applications (Statistics: A Series of Textbooks and Monographs), K. Krishnamoorthy, ISBN-978-1584886358. Authors Dr. Gaëtan Girardin Fuel Assembly Design Dr. Rudolf Meier Nuclear Technic Phys. Lukas Meyer Core Surveillance Phys. Alexandra Ålander Transport and Storage Dr.-Ing. Fabian Jatuff Projects and Processes Kernkraftwerk Gösgen-Däniken AG Kraftwerksstrasse 4658 Däniken, Switzerland Notes For further details please contact: Nicolas Wendler DAtF Robert-Koch-Platz 4 10115 Berlin Germany E-mail: presse@ kernenergie.de www.kernenergie.de First half of <strong>2018</strong>: Electricity production in Germany For the first half of <strong>2018</strong>, the seven nuclear power plants in Germany produced about 34.8 billion kWh (net) electricity and had therefore a share of 12.9 % of the whole production. Although five power plants were tem porarily shut down due to scheduled inspections, the nuclear energy shows a rise of 9 % relating to its electricity pro duction of the first half of 2017. Net electricity production (269.5 billion kWh) for first half of <strong>2018</strong> in percent 12.9 Nuclear energy 41.4 Renewable energy among: 20.4 Wind power 8.5 Biomass 8.3 Photovoltaics 4.2 Hydro power 24.7 Lignite 7.6 Gas 13.4 Hard coal Quelle: VGB; AG Energiebilanzen; Fraunhofer ISE DAtF Notes

<strong>atw</strong> Vol. 63 (<strong>2018</strong>) | Issue 8/9 ı August/September Effects of Airborne Volatile Organic Compounds on the Performance of Pi/TiO 2 Coated Ceramic Honeycomb Type Passive Autocatalytic Recombiner Chang Hyun Kim, Je Joong Sung, Sang Jun Ha and Phil Won Seo 1 Introduction Ensuring the containment integrity during a severe accident in nuclear power reactor by maintaining the hydrogen concentration below an acceptable level has been recognized to be of critical importance after Fukushima Daiichi accidents. Although there exist various hydrogen mitigation measures, a passive autocatalytic recombiner (PAR) has been considered as a viable option for the mitigation of hydrogen risk under the extended station blackout conditions because of its passive operation characteristics for the hydrogen removal [1]. As a post-Fukushima action item, all Korean nuclear power plants were equipped with PARs of various suppliers. The capacity and locations of PAR as a hydrogen mitigation system were determined through an extensive analysis for various severe accident scenarios [2]. For some plants, dual hydrogen mitigation systems were equipped with a combination of newly installed PARs and the existing igniters that each system has 100 % of full capacity for hydrogen control for postulated severe accident conditions. Among a total of 24 operating units in Korea, a Pt/TiO 2 coated ceramic honeycomb type PAR supplied by Ceracomb Co. Ltd. [10] has been installed in 18 operating plants and almost units have reached the second or the third overhaul period since their first installation in 2013. 457 RESEARCH AND INNOVATION The PAR makes use of a catalyst to convert hydrogen (H 2 ) and oxygen (O 2 ) into water vapor and heat. The heat of reaction creates a natural ­convective flow through the recombiner, eliminating the need of pumps or fans to transport new hydrogen to the surface of the catalyst. In spite of an advantage of its passive operation, there have been concerns about adverse effects on the performance of PARs by potential deactivators (chemical poisons and physical inhibitors) [3, 4, 5]. PARs are required to perform their safety function not only after exposure to potential contaminants during operation, but also in an accident environment that may contain various gases or aerosols that are potentially poisonous to the PAR catalyst elements [6]. The Ceracomb also has performed various tests and demonstrated that its performance degradation of hydrogen removal capacity is within 25 % in severe ­accident conditions such as fission product poisons, aerosols, cable burns, carbon monoxide, etc. However, its performance under the longterm exposed condition to containment air has not been fully investigated because the Ceracomb PAR has no operational experience in nuclear power plants. Under the long-term exposed condition by airborne substances, it has been known that the catalyst shows a delayed response for hydrogen removal [6]. These airborne substances are known as volatile organic compounds (VOC) that adsorb on active sites of the catalyst surface thus making them unavailable for catalytic reaction to proceed. As a result, the recombiner would require either a higher hydrogen concentration, or a higher temperature, or both, to start the hydrogen recombination reaction, compared with the catalyst in as-new condition. The VOCs could be originated from solvents, lubricants, oils, insulations and paints, etc. which are commonly used materials in the plant maintenance. The key prameters of catalyst performance under the longterm exposed condition of VOCs could be the start-up delay time for catalyst reaction and its hydrogen depletion (removal) rate because these parameters directly affect the results of hydrogen control analyses in design basis and severe accident conditions. The catalyst performance should be verified up to sufficient periods of plant operation and be compared with the parameters on the PAR performance used in the hydrogen control analysis. Therefore, with the exposure time to containment air, the VOC effects will play a more important role in PAR maintenance during normal nuclear power plant operation [7]. In comparison to the performances under the accident conditions, however, the performances under the long term exposed condition to containment air during normal operation (i.e., effects of volatile organic compounds) have not been fully investigated becaue it requires long time up to several overhaul periods in the containment to obtain catalyst samples and it includes the proprietary information of PAR suppliers and utilites. This paper describes the test results on the effect of airborne volatile organic compounds in the containment air on the performance of TiO 2 coated ceramic honeycomb type PAR in Korean nuclear power plants performed in 2014 ~ 2016 overhaul periods. The test plants are extended to seventeen (17) operating plants compared to the previous eight (8) operating plants [8]. A total of 152 tests have been performed with 680 catalyst samples to investigate the effect of volatile organic compounds (VOC) on the start-up performance on the hydrogen removal. A total of 62 tests have been performed with 248 catalyst samples to identify the influence on the hydrogen depletion rate by the VOC effects. The analysis for VOC components has been performed for selected samples from seven (7) plants to identify airborne substances adsorbed on the surface of catalysts using a qualitative GC/MS (gas chromatograph/mass spectrometer) method. 2 Test method 2.1 Pt/TiO 2 ceramic honeycomb PAR Figure 1 shows an illustrated view of Pt/TiO 2 coated ceramic honeycomb type PAR that has been installed in eighteen (18) operating units. This type of PAR has been developed and Research and Innovation Effects of Airborne Volatile Organic Compounds on the Performance of Pi/TiO 2 Coated Ceramic Honeycomb Type Passive Autocatalytic Recombiner ı Chang Hyun Kim, Je Joong Sung, Sang Jun Ha and Phil Won Seo