atw 2017-12

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atw Vol. 62 (2017) | Issue 12 ı December 758 AMNT 2017 Environment, Nature Conservation, Building and Nuclear Safety (BMUB)). First Mr. Wild introduced IAEA Safety Fundamentals, namely Principle 1 (Responsibility for safety) and Principle 2 (Role of government), followed by some general safety requirements (GSR, part 1 (rev. 1)) dealing with sharing operating and regulatory experience, organisational structures of the regulatory body and its re sources, the connection between regulatory bodies and authority parties, the stability and consistency of regulatory control, and the requirement of corrective actions by authorized parties. Further guidelines for nuclear regulators were also shown such as the CNRA series of regulatory guidance reports by OECD/ NEA. Afterwards, the question how the regulator can judge if its actions assure an acceptable level of safety at nuclear facilities was discussed. Mr. Wild summed up some actions based on OECD/NEA guidelines which have to be carried out in order to ensure licensees their responsibility. Finally, the German nuclear regulatory system was presented with the focus on the interaction between the federal ministry, the Länder ministries and the advisory organisations. The cooperation between the federation and the Länder in nuclear law is documented and published in a handbook. The second presentation Heavy Ions Irradiation as a Tool to Minimize the Number of In-Pile Tests in UMo Fuel Development was given by Dr. Harald Breitkreutz (co-authors: R. Jungwirth, T. Zweifel, H.-Y. Chiang, J. Shi, W. Petry, Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München). Dr. Breitkreutz introduced the method of accelerator based out-of-pile irradiation using I-127 as representative fission product and samples with UMu fuel dispersed in an aluminum matrix. The reason to use UMo alloy as low enriched Uranium in the frame of non-proliferation efforts was figured out. The growth of the interdiffusion layer (IDL) between UMo and the Al matrix was identified as an important application for ions in this context with all corresponding effects, such as swelling. Afterwards, the role of IDL was discussed regarding growth dynamics, composition and fission gas behaviour. To avoid or limit IDL the most preferable option would be would be to add silicone. Other possibilities are e.g. the coating of the UMo with a Zr layer or the application of Mg instead of Al as matrix material, which would prevent chemical reactions, but showed higher embrittlement. For all possibilities test series were carried out to identify the advantages and disadvantages. The tests at FRM-II showed that the approach to use I-127 irradiation for qualitative and even quantitative experiments is reliable to simulate numerous in-pile irradiation effects. Finally, it was summarized that this technique will open the door to the analysis of highburn-up effects like recrystallization of UMo kernels with the advantages that no additional radioactivity is involved and the complete cycle starting from the designing of the experiment, followed by the irradiation and the post-irradiation examinations can be carried out in a few weeks. In the last presentation of the first session Investigations of Long-Term Interactions Between Graphite Dust and Hot Metallic Surfaces Under High Temperature Reactor Conditions by Andreas Andris (co-authors: F. Fischer, W. Lippmann, A. Hurtado, Chair of Hydrogen and Nuclear Energy, Technische Universität Dresden) the author started with the description of the applied facility, DRESDEN-TANK, to investigate the behaviour of the dust under HTR conditions. Therefore, the DRESDEN-TANK was constructed for temperatures up to 1,000 °C, 60 bars and for test durations exceeding 1,000 h. Different alloys, including Inconel, were tested and investigated via laser raster microscopy (LRM). The results of the experiments indicated thermal aging effects in the case of alloy 800H and Inconel 617, where sintering effects were confirmed for the interaction between the hot temperature dust and the metal surface. Furthermore, the formation of needleshaped monocrystals (whiskers) during swelling tests of the alloy 800H at 800 °C was observed and analysed in detail. A decrease of the crystallization temperature is observed due to the high pressure, which led to a change in the crystallization process as well as crystal growth. The achieved results can be used for the development and validation of computational models for HTR conditions. Containment and SFP The second session Containment and SFP was opened with the keynote speech How Safe is Safe Enough After 50 Years of NPP Operational Experience by Uwe Jorden (Preussen- Elektra) which gave a wide overview about the challenges and changes in safety objectives. Mr. Jorden pointed out four aspects and their basis during the search for an appropriate safety concept: Deterministic for design, construction and manufacture, Probabilistic and “Restrisiko”, Human- Technology-Organisations, and Qua lity assurance of pressure boundary. Afterwards, the way from more technical design via human to organisational topics was demonstrated, which started with the development and design, the risk evaluation as well as the assurance of standards in the period from about 1960 to the mid-1980s/1990. Other, still ongoing topics, started subsequently like Human Technology- Orga nisations (app. 1970), Severe Accident Management (app. Mid-1980s) and Management Systems (2000). The defence in-depth concept, as a multilevel safety concept with its installations and measures, was presented and the lacks of this concept during the Fukushima-Daiichi accident were pointed out, which led to improvements on emergency preparedness. Another focus point was the basics of plant operation inter acting with technology, processes and organisation. Therefore, enough financial resources for safety operation have to be available, specifications for safety issues have to be binding and its do cu mentation updated for operating, giving priority to safety over all business objectives. Additionally, the importance of human resources was pointed out, that means enough and permanent human resources regarding safety have to be in readiness, as a consequence of the relationship between safety culture, safety climate and behaviour characterizing an organization. On the way from technical to organisational issues the com plexity by the means of necessity and builds on competences of a holistic model were shown by the distinction between meta-competencies and core components. Additionally, the typical environment of an NPP was shown e.g. economy, plant, authority, government and licence holder, to demonstrate that different interests regarding safety aspects have to be considered. Finally, Mr. Jorden shared the prospects and challenges regarding the phase out in Germany, like challenges for the staff, knowledge transfer, competence in the supervision of NPP, and the balance between energy market and operational costs. In her presentation Detective Application Security Controls for Nuclear Safety Deeksha Gupta (coauthors: K. Waedt, Y. Gao, AREVA GmbH, Germany) first introduced the importance of cybersecurity for AMNT 2017 Key Topic | Enhanced Safety & Operation Excellence: Technical Session: Operation and Safety of Nuclear Installations, Fuel ı Thorsten Hollands
atw Vol. 62 (2017) | Issue 12 ı December nuclear power plants (already running or new-build) and its I&C systems, which changed from non-digital equipment to digital techniques and interconnected systems. Mrs. Gupta pointed out that the complete prevention of such attacks as well as Advance Persistent Threats, cannot be addressed by protective only security control. It was shown that additionally detective security controls are necessary to identify attacks, and that they are the precondition for protective measures. The most important detective controls were discussed such as logging at all relevant levels. The benefits of the generated data were explained together with the architectures that used the collected data, as input of a central Security Information and Event System. Furthermore, two conceptual extensions were introduced: the security control on the basis of independent (physical) data collection as well as the monitoring and evaluation of binary and analogue signals. Finally, Mrs. Gupta concluded that the implementation of a combination of protective security control would improve the security posture of refurbished or new plants. Hans-Joachim Scholtka (Siempelkamp NIS Ingenieurgesellschaft mbH) showed in his presentation NIS-PAR – Passive Autocatalytic Recombiners for Depletion of Hydrogen in Nuclear Power Plants during Severe Accidents the principles of NIS-PAR and its application in a Hydrogen Emergency Removal System. Mr. Scholtka presented the advantages of the NIS-PAR with the catalyst material Palladium to work even at low hydrogen concentrations and low temperatures. As a second criterion the distribution of the catalyst material on a large surface was identified and investigated leading to porous AL 2 O 3 was found to have the best distribution attributes. Based on these principles and a description of the housing of the NIS-PAR Mr. Scholtka described the procedure to implement the NIS-PAR in a Hydrogen Emergency Removal System (HERS) of a Ukrainian power plant, which consists of several stages, including the qualification tests performed by independent companies as well as by the power plant. The results of the qualification and verification tests showed a good start-up of the system which is necessary to mitigate hydrogen risks. The presentation Preliminary Results on Simulation of Re- Entrainment Phenomena with the Containment Code System COCOSYS given by Tobias Jankowski (co- author: M. K. Koch, Reactor Simulation and Safety Group, Chair of Energy Systems and Energy Economics, Ruhr-Universität Bochum (RUB)) dealt with the application of COCOSYS on the experiments THAI TH25.1 and TH25.2. At first an overview of available empirical approaches for the estimation of re entrainment in the containment during a severe accident were discussed and an explanation why the models of Kataoka-Ishii as well as REVENT were chosen for the current study was presented. Afterwards, Mr. Jankowski shortly described the THAI+ facility and the investigated tests which dealt with the release of soluble and in-soluble aerosols from a boiling sump over a wide range of superficial gas velocities. The results of the simulation of TH25.1 with COCOSYS using the REVENT correlation showed good agreement with the experiment in the bubbly flow regime, while for increasing entrainment the trend for rising superficial gas regimes in the bubbly flow regime was predicted. Additionally, the results of the resuspension test TH25.2 are also well predicted with the REVENT correlation, if the superficial gas velocity is high enough and the enrichment is neglected. Mr. Jankowski concluded that the REVENT correlation used in COCOSYS is applicable for reentrainment processes considering soluble gases. In the presentation Blind Simulation of the TH28 Experiment with COCOSYS held by Philipp Gurski (co-authors: M. K. Koch, M. Freitag, Reactor Simulation and Safety Group, Chair of Energy Systems and Energy Economics, Ruhr-Universität Bochum (RUB)), first the experiment THAI TH28 was presented which dealt with the hydrogen behaviour in a generic two-room system (THAI+ facility), where hydrogen is substituted by helium and was used for blind calculations applying the containment code COCOSYS. Afterwards, the modelling of the facility and the implemented boundary conditions were discussed. The results of the simulation showed good agreement with the experiment regarding pressure, temperature and helium concentration. The differences were particularly noticeable during the dissolution process of the helium stratification. Furthermore, a delay is predicted by COCOSYS for the complete mixing of the gas atmosphere in the facility. Finally, Mr. Gurski concluded that a more detailed analyses should be performed, especially concerning the nodalisation of the test facility, as well as open simulations to evaluate the code performance. The last presentation of the session Convective Heat Transfer of an Air Cooled BWR Spent Fuel assembly was given by Christine Partmann (co-authors: C. Schuster, A. Hurtado, Institute of Power Engineering, Chair of Hydrogen and Nuclear Energy, Technische Universität Dresden). At the beginning, different scenarios were introduced, which can lead to boil-off or a partial drain-down. To understand the phenomenology during such scenarios several test series were performed in the ALADIN facility (TU Dresden), which was designed to simulate a full FA inside an SFP taking the heat transfer mechanisms with the surrounding into account. For the experimental campaign presented a power supply of 20 W per rod was used, and the above mentioned scenarios were considered. The results of the experiments showed radial temperature gradients within one bundle, which indicated that the heat transfer inside one fuel assembly was observed, although the cooling at the outer side should be high enough and only axial heat transfer was possible. Furthermore, a blockage at the bottom of the fuel assembly influenced the flow regime, leading to reverse temperature behaviour in the lower and upper part of the fuel assembly, without a significant effect on the maximum temperature. Finally, Mrs. Partmann gave an outlook on future steps, including inserting a grid sensor for combined temperature and flow velocity measurement, as well as the modelling of the fuel assembly structure in original scale to be able to give a better prediction of the cladding temperature, which can be used for code validation. Authors Dr. Thorsten Hollands Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH Abteilung Kühlkreislauf / Cooling Circuit Department Bereich Reaktorsicherheitsforschung / Reactor Safety Research Division Forschungszentrum Boltzmannstr. 14 85748 Garching Germany Dr. Winfried Zwermann Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH Forschungszentrum Boltzmannstraße 14 85748 Garching Germany 759 AMNT 2017 AMNT 2017 Key Topic | Enhanced Safety & Operation Excellence: Technical Session: Operation and Safety of Nuclear Installations, Fuel ı Thorsten Hollands
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