Motivation and design for an ideal test facility

Sophisticate computational tools exist in nuclear thermal-hydraulics; however, approximations and hypotheses are needed to derive solutions or results applicable for the design and safety analysis of Nuclear Power Plants (NPP). A vast amount of experimental data has been gathered from so-called basic experiments, separate effect and integral effect test facilities. The measured data has been extensively used to prove the validity of computational tools. A number of issues arises when comparing experimental data with the code results (validation process) as well as when attempting to apply the codes to the actual configuration of nuclear reactors. Examples are: a) precision targets are not established; b) in one assigned scenario some measured parameters maybe very well predicted and other at the same time may be mispredicted c) full demonstration of scaling capability cannot be achieved; d) some phenomena, whose importance is recognized within accident analysis in NPP, like two phase critical flow are predicted with large errors also due to the lack of modeling of parameters as density of the nucleation sites (either in the fluid and on the solid wall) and possible void formation following sharp edge cavitation upstream the break location. We propose the design of a virtual (so far) test facility aiming at prioritization of the research in nuclear reactor thermal-hydraulics with respect to the importance on safety and design of NPP. The test facility is entitled as μλ-I4TF (μ=Modular, λ=Large, Advanced, Multi-Basics & discipline apparatus, I4TF=Ideal (four times) Test facility) and has the following key features: • The scaling of the reference configuration is based upon the findings and recommendation of a recently issued NEA/CSNI State-of-Art-Report on Scaling. • The size is the maximum reasonable (even though it remains four times ideal). • Occurring phenomena are expected to cover an entire spectrum of accidents in Light Water Reactors (LWR), including primary system and containment. • Calculated trends are (to be demonstrated) fully consistent with the experimental data base available today. The global strategy behind this idea can be summarized as following: 1) To fix the minimum list of accident scenarios which covers all the phenomena mentioned above with the reasonable ranges of variation of dominating parameters, including their combination; 2) To perform calculation and analysis of each selected scenario (one example is provided in the present paper); 3) To show consistency between the calculated phenomena and parameter ranges with the experimental data; 4) To change features of the μλ-I4TF (e.g. by introducing CFD portions, by changing scaling laws, etc.) and performing new calculation; 5) The comparison between the calculation results at previous step with the reference calculation at step 2) may involve large differences in Safety Margins or in important design features: those differences (following a specific qualification analysis) will support the prioritization of new research in nuclear thermal-hydraulics. The purposes of the present paper are: - to describe the overall pattern of prioritization-driven research using μλ-I4TF facility, - to present the main features of μλ-I4TF, - to perform one reference calculation of the selected accident scenario.