The best estimate plus the uncertainty quantification methods applied to a computer code play a key role in the development of the innovative Generation IV nuclear reactors for the improvement of knowledge and the good evaluation of the safety margins for new phenomena. The aim of this proposal is to validate an uncertainty quantification approach using the RAVEN code. RAVEN, developed at the Idaho National Laboratory, is a multipurpose probabilistic and uncertainty quantification platform, capable to communicate with any system code, implemented with an integrated validation methodology involving several different metrics. In this activity, a coupling calculation RELAP5-3D/RAVEN will be performed to validate the uncertainty quantification approach. The simulations will concern two test conducted on NACIE (NAtural CIrculation Experiment) facility, a non-nuclear loop-type system using Lead-Bismuth Eutectic (LBE) as coolant, realized at the ENEA Brasimone Research Centre (Italy) in order to support the development of the GEN-IV reactors. The experimental test aimed to investigate the phenomena related to the natural and gas enhanced circulation flow regimes of HLMs, and to test and validate the main components in a LBE environment. A numerical 1-D model of the NACIE facility will be realized and the post-test analysis will be carried out using RELAP5-3D© ver. 4.3.4. After that, a statistical analysis will be performed using RAVEN computer code.
In summary, the innovations which this activity aims to achieve are:
1. the validation of the uncertainty quantification methodology using RAVEN code;
2. the verification and validation of RELAP5-3D for HLM application
The uncertainty quantification plays a crucial role on the safety analysis, based on the best estimate calculation. The target of the proposal is to validate an uncertainty quantification methodology based on the exploration of the input space, considering the associated uncertainties, and the analysis of the response through the use of different validation metrics.
Moreover, the best estimate computer code, like RELAP5, was developed to perform safety analysis for LWR. During the last years, improved version of these codes, which includes possibilities to model HLM cooled reactor, are released. The main improvements implemented in RELAP5-3D concern the capability to model the NPP with multi-dimensional components and using innovative fluid as HLM. In addition, our team implemented new thermophysical properties correlations for heavy liquid metal, according to the NEA state-of-the-art data [1] through the application of the soft-sphere model [2]. These improvements need to be validated; at this purpose, the comparison between experimental data and simulations results will support the verification and validation of RELAP5-3D to reproduce phenomena related to the natural and gas enhanced circulation flow regimes.
This activity will be used as reference for the uncertainty quantification for more complex system as CIRCE, for the analysis of the experimental campaign which will be performed during next months [3].
In summary, the innovations that this proposal aims to achieve are:
1. the validation of the uncertainty quantification methodology using RAVEN code;
2. the verification and validation of RELAP5-3D for HLM application
[1] 2015 Handbook on Lead-bismuth Eutectic Alloy and Lead Properties, Materials Compatibility, Thermal- hydraulics and Technologies 647¿730.
[2] Balestra P, Giannetti F, Caruso G and Alfonsi A 2016 New RELAP5-3D lead and LBE thermophysical properties implementation for safety analysis of Gen IV reactors Sci. Technol. Nucl. Install. 2016.
[3] Narcisi V, Giannetti F, Del Nevo A, Tarantino M, Caruso G, 2018, Pre-test analysis of accidental transients for ALFRED SGBT mock-up characterization, Nuc. Eng. And Des. 333 (2018) 181¿195, https://doi.org/10.1016/j.nucengdes.2018.04.015