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Tesi etd-04072009-192655

Thesis type
Tesi di dottorato di ricerca
Contribution to the assessment of CFD codes for in-vessel flow investigation
Settore scientifico disciplinare
Corso di studi
Relatore Prof. D'Auria, Francesco
Relatore Prof. Ambrosini, Walter
Parole chiave
  • nuclear reactor safety
  • mixing
  • in-vessel flow
  • CFD
  • boron dilution
  • assessment
  • validation
Data inizio appello
Riassunto analitico
The present research aims at contributing to the CFD code assessment process for<br>nuclear reactor applications, and particularly for the predictive analysis of the fluid dynamic<br>phenomena occurring inside the reactor pressure vessel of a pressurized<br>water reactor. The importance of such phenomena relies, for instance, on the<br>influence that they can have on the spatial and temporal distribution of coolant<br>properties (such as temperature or boron concentration) at the core inlet during<br>certain accident transients involving perturbations of such properties with respect to<br>nominal conditions; furthermore, in-vessel mixing phenomena can also affect the<br>thermal interaction between coolant and pressure vessel during pressurized<br>thermal shock scenarios.<br>The contribution provided by this work consists in the proposal of a general and<br>systematic methodology to be applied in the CFD code assessment for in-vessel<br>flow investigations. Within the proposed approach, the relevant modelling issues<br>are identified and discussed, so as to point out the main capabilities and limitations<br>in the present state-of-the-art tools and methods. Then, the main steps of the code<br>application procedure are described and discussed analytically, thus providing<br>guidance for a quality-oriented use of the codes, and complementing the existing<br>best practice guidelines for this specific problem.<br>Furthermore, the research addresses the problem of the quantification of the<br>accuracy for numerical predictions (both from CFD and integral codes) about<br>coolant properties perturbations at the core inlet. As a result, a methodology is<br>proposed based on a set of accuracy indicators, which can represent a means for<br>judging whether the code results are sufficiently close to experimental data, once<br>acceptance thresholds have been defined and the method has been completely<br>assessed.<br>The work is supported by extensive CFD code validation and application results<br>obtained in the frame of several international research projects and co-operations,<br>and by a continuous interaction with the involved International scientific community.