Contents lists available at ScienceDirect Progress in Nuclear Energy journal homepage: www.elsevier.com/locate/pnucene In-loop oxygen reduction in HLM thermal-hydraulic facility NACIE-UP S. Bassini a,∗ , I. Di Piazza a , A. Antonelli a , M. Angelucci b , V. Sermenghi a , G. Polazzi a , M. Tarantino a a Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), C.R. Brasimone, Italy b University of Pisa, Dipartimento di Ingegneria Civile e Industriale, Italy ARTICLE INFO Keywords: HLM coolant chemistry HLM thermal-hydraulics Oxygen control Potentiometric oxygen sensor ABSTRACT NACIE-UP loop located at the ENEA Brasimone Research Centre is an experimental thermal-hydraulic facility working with liquid lead-bismuth eutectic (LBE). The facility was designed and constructed with the purpose to support the research activity on future nuclear reactors cooled by HLMs (Heavy Liquid Metals). A major problem in the operation of experimental HLM facilities concerns the chemical control of the coolant and, in particular, of the dissolved oxygen. Indeed, a reduction of the oxygen concentration in the HLM must be performed before each experimental thermal-hydraulic campaign in order to prevent the formation of PbO, whose deposition above piping and components may affect the experimental results. The present work describes the conditioning to low oxygen of the LBE inside NACIE-UP facility. The oxygen concentration reduction was performed by injecting Ar-3%H 2 gas mixture in the riser column of the loop for 650 h and by varying the LBE temperature in the range 230–400 °C. The oxygen concentration in the LBE was monitored in the expansion vessel of the loop using a potentiometric Cu/Cu 2 O oxygen sensor. The sensor showed that a deep oxygen reduction in the LBE was successfully obtained, even if the optimal working concentration for the operation of a HLM nuclear system was not achieved. The oxygen concentration was globally reduced from 10 −6 to 10 −12 % in weight at around 250 °C. Furthermore, the sensor revealed the establishment of M/M x O y equilibria in the expansion vessel, indicating that metal impurities dissolving from loop steel walls were here collected and influenced the electric potential of the sensor. 1. Introduction Heavy liquid metals (HLMs) such as liquid lead and lead-bismuth eutectic (LBE) are candidate coolants in future nuclear systems Lead- cooled Fast Reactors (LFRs) and Accelerator Driven System (ADSs) and in their European demonstrator ALFRED and MYRRHA. Their favourable nuclear, chemical and thermo-physical properties make these coolants particularly suitable for this purpose. The high boiling point at atmospheric pressure, high specific heat, density and conductivity allow to obtain a good heat transfer coefficient and to adopt passive system for the decay heat removal. The high mass number allows the adoption of a fast neutron spectrum, while the high atomic number makes the coolant also a good shield for radiation (OECD/NEA, 2015). These features open good perspectives on the ef- ficient use of the fuel and in general to the achievement of the GEN-IV goals (OECD/NEA, 2014). Nevertheless, one of the major issues in the HLM technology con- cerns the HLM chemistry control, which is strongly related to the issue of the dissolved oxygen concentration in the melt. Indeed, oxygen dissolved in the HLM can have both a beneficial and negative effect depending on its concentration (Brissonneau et al., 2011; Li, 2002; Muller et al., 2003; Schroer et al., 2011a,b). Oxygen enables the for- mation of a self-healing Fe-Cr oxide layer above steel surface which acts as a barrier against the HLM and reduces the corrosion of structures and components as well as the release of corrosion products in the HLM. On the other hand, oxygen becomes detrimental when its concentration reaches the solubility level in the HLM. In such conditions coolant oxides may form (mainly PbO) and deposit on the walls of structures and components with degradation of the heat transfer and/or plugging of the circulation. Thus, the oxygen concentration has to be balanced within an optimal range to minimize steel corrosion and to avoid HLM oxidation (Brissonneau et al., 2011; Li, 2002; Muller et al., 2003; Schroer et al., 2011a,b). The control of the oxygen concentration in the HLM requires proper operative procedures and on-line devices aimed to achieve and keep constant the target concentration and restore potential deviations. Experiences done in recent years have shown that the adoption of fil- tering and degassing procedures before the filling of the facility helps in having a HLM with a starting good purity, thus simplifying the oxygen control procedures during the operation (Courouau et al., 2004). The https://doi.org/10.1016/j.pnucene.2018.01.006 Received 5 April 2017; Received in revised form 8 January 2018; Accepted 22 January 2018 ∗ Corresponding author. E-mail address: serena.bassini@enea.it (S. Bassini). Progress in Nuclear Energy 105 (2018) 137–145 Available online 04 February 2018 0149-1970/ © 2018 Elsevier Ltd. All rights reserved. T