European research on HLM thermal hydraulics for ADS applications

The objective of the European 6th framework project EUROTRANS, is to demonstrate the technical feasibility of transmutation of high level nuclear waste using Accelerator Driven Systems (ADS). Within this objective the design of a European experimental ADS (XT-ADS) should demonstrate the technical feasibilities to transmute a sizeable amount of waste and to operate an ADS safely. The XT-ADS will be a subcritical reactor system having liquid lead-bismuth eutectic (LBE) as coolant.
This liquid LBE is also intended to serve as target material for the spallation reaction which forms a crucial part to the subcritical reactor core. Since LBE is used as core coolant and spallation material, knowledge of the thermal hydraulic behaviour of LBE is essential.
Within the DEMETRA domain of the EUROTRANS project, basic thermal hydraulic studies in order to support the design and safety analysis of XT-ADS components and the development of measurement techniques have been started. In particular, the work focuses on:
• Characterisation of the free surface flow for the windowless spallation target design.
Validated numerical methods are needed to predict the LBE heat removal capability in the windowless spallation target configuration. For this purpose, computational fluid dynamics (CFD) simulation methods are most appropriate. CFD methods allow to capture the specific three-dimensional local effects of the LBE free surface including the heat deposition.
Various methods are assessed and first promising results have been obtained for the simulation of an isothermal windowless spallation target. For the improvement and validation of the developed numerical models, an experimental campaign has started. This campaign exists of experiments in a water-loop and in an LBE loop.
• The interaction of LBE with water as secondary coolant.
Since the XT-ADS design foresees the presence of steam generator modules placed inside the main vessel in direct contact with the lead-bismuth and the probability of a steam generator tube rupture is not negligible, the consequences of such an accident have to be assessed. Experimental campaigns aim at assessing the physical effects and possible consequences related to the interaction of LBE and water in representative conditions for the XT-ADS design. The experimental data are also used for the validation of the SIMMER code. First experimental campaigns have been performed successfully. Simulation of the experimental data with the SIMMER code showed a good agreement.
• The development of measurement techniques for heavy liquid metal (HLM) flows.
Measurement techniques are developed for different purposes (i.e. thermal-hydraulics experiments and operational techniques for large facilities in relation to the development of the XT-ADS) and tested within the laboratories of FZD (Germany), FZK (Germany), and SCK•CEN (Belgium). The focus is on local velocity meters, integral flow meters, and free surface level sensors. The various methods studied are briefly described.

Finally, the links with the DESIGN domain of the EUROTRANS project, with the European Commission Integrated Infrastructure Initiative VELLA (Virtual European Lead LAboratory), and with the European Commission Specific Targeted Research Project ELSY (European Lead-cooled System) are also addressed.