Julio Pacio

• SCK CEN - Belgian Nuclear Research Centre

Investigating Fiber Bragg Gratings (FBG) behavior in varied fluid environments for temperature measurements. Analysis includes secondary effects and liquid metal influence on peak spectrum.

Turbulent heat fluxes (THFs) estimation is of paramount importance in the determination of heat transfer in fluids. Numerical models for low Prandtl number fluids are still unreliable and their experimental evaluation is a challenging task since it requires simultaneous measurement of fast velocity and temperature fluctuations. In nuclear applicati...

Heavy-liquid metals (HLMs), such as lead and lead–bismuth eutectic (LBE), are proposed as primary coolants in accelerator driven systems and next-generation fast reactors. In Europe, the reference systems using HLMs are MYRRHA (LBE) and ALFRED (lead). Extensive R&D programs have been established for supporting their detailed design and safety asses...

This work presents the main results of a CFD benchmark exercise completed by partner institutions from Europe and USA aiming to achieve a better understanding of the heat transfer characteristics and flow behavior in fuel assemblies cooled by heavy liquid metals. The selected scenario is a 19-rod bundle with wire spacers representative of the MYRRH...

This two-part paper presents an updated version of the long term MIT-NTHU modeling effort on the hydraulics of hexagonal arrays of wire wrapped fuel pins. It has been stimulated by the emergence of technical licensing considerations from the current development efforts for MYRRHA, the accelerator-driven system cooled by lead–bismuth eutectic being...

This two-part paper presents an updated version of the long term MIT-NTHU modeling effort on the hydraulics of hexagonal arrays of wire wrapped fuel pins. It has been stimulated by the emergence of technical licensing considerations from the current development efforts for MYRRHA, the accelerator-driven system cooled by lead–bismuth eutectic being...

Liquid metals are promising candidates for highly efficient thermal receivers in concentrating solar power plants due to their excellent thermal conductivity. In the SOMMER (SOlar furnace with a Molten MEtal-cooled Receiver) facility at the Karlsruhe Institute of Technology (KIT), the cooling of a 10-kW thermal receiver by a lead–bismuth eutectic f...

For the occasion of celebrating the 40th anniversary of the NURETH conference series, we present a brief overview of our work on the thermal-hydraulics of wire-wrapped rod bundles over these past four decades. In this context, this short technical note presents a personal perspective about this topic in a colloquial narrative. Particular focus is p...

Within the thermal energy storage initiative NADINE (National Demonstrator for IseNtropic Energy storage) three projects have been carried out, each focusing on thermal energy storage (TES) at different temperature levels. This work deals with technical concepts for using liquid metal technology in innovative high temperature TES systems. This appr...

Most liquid metal fast reactor (LMFR) designs consider a regular hexagonal lattice of fuel pins in the core. Detailed thermal-hydraulic analyses of the core are based on an accurate description of the flow in fuel assemblies (FAs), which are arrangements of pins with a specific spacer design, and enclosed in a wrapper tube. Treating them as an isol...

Liquid metal reactors typically employ wire wraps as spacers between the fuel pins. In the past, design and safety calculations were largely one-dimensional and based on experimental data. Nowadays, with modern state-of-the-art computer power and tools, three-dimensional Computational Fluid Dynamics (CFD) simulations allow designers and safety spec...

Liquid metal fast reactors (LMFRs) are foreseen to play an important role in the future of nuclear energy, thanks to their increased fuel utilization and safety features profiting from the optimal heat transfer performance of the metallic coolants. Accurate thermal-hydraulic analysis of their fuel assemblies, typically employed with wire-wraps as s...

In recent years, extensive thermal-hydraulic experimental tests have been performed on the lead-bismuth eutectic (LBE)–cooled, wire-wrapped fuel assembly (FA) of MYRRHA. These thermal-hydraulic tests were performed using FA mock-ups in large-scale LBE experimental test facilities at SCK•CEN (Belgium), ENEA (Italy), and Karlsruhe Institute of Techno...

Liquid metal fast reactors (LMFRs) are foreseen to play an important role in the future of nuclear energy, thanks to their increased fuel utilization and safety features profiting from the optimal heat transfer performance of the metallic coolants. Accurate thermal-hydraulic analysis of their fuel assemblies, typically employed with wire-wraps as s...

The inter-wrapper flow (IWF) between fuel assemblies in an LMFR plays an important role in the reduction of the peak cladding temperature in abnormal scenarios, such as blockages or flow reductions. This paper focusses on the heat transfer through the IWF in a geometry which is representative for the MYRRHA reactor under design by SCK•CEN in Belgiu...

A detailed safety assessment of innovative Generation IV reactor designs with heavy-liquid metal coolants, such as lead and lead-bismuth eutectic (LBE), requires an evaluation of the maximum core temperature in several postulated scenarios. Considering the complex geometry of fuel assemblies (FAs), and the low Prandtl number of the coolants, this f...

Experimental investigations of thermal hydraulic properties of coolant flow in experimental models of fuel assemblies (FA) were performed. FA models with 7, 19 and 37 pins in hexagonal arrangement were used as test sections. Friction loss coefficients of smooth rod bundles are presented and compared. Hydraulic resistance of spacing grids with diffe...

Internal blockages in fuel rod bundles can be rather small and may have a negligible global effect on the flow rate in a fuel assembly, and yet they can still produce significant local hot spots potentially leading to clad failure. Within the European project MAXSIMA the thermal-hydraulic effects of internal flow blockages in a heated rod bundle co...

Heavy liquid metals (HLMs), such as lead-bismuth eutectic (LBE) and pure lead are prominent candidate coolants for many advanced systems based on fast neutrons. In particular, LBE is used in the first-of-its-kind MYRRHA fast reactor, to be built in Mol (Belgium), which can be operated either in critical mode or as a sub-critical accelerator-driven...

Heavy liquid metals, such as Pb and lead–bismuth eutectic (LBE), are fluids of interest for applications in fast reactors and accelerator-driven systems (ADS). For the development of such systems, thermal-hydraulics is a key discipline to be further investigated. The low Prandtl number of these fluids makes this problem particularly challenging and...

Liquid metals have been proposed in the past as high temperature heat transfer media in concentrating solar power (CSP) systems. Until the mid 80s test facilities were operated with liquid sodium-cooled central receivers. After a period of reduced interest in that approach, several new efforts have been reported recently, particularly from the US,...

Within the present work the dataset of experimental points and the heat transfer correlations available in literature for liquid-metal fully-developed, forced-convective heat transfer in pipes are reviewed and critically analyzed. Over 1,100 data points from 21 different sources are considered for constant heat flux, covering a wide range of operat...

To a large extent, the economic viability of CSP projects is influenced by the main parameters characterizing the receiver, such as concentration ratio, heat-flux-intensity and distribution, fluid outlet temperature and, naturally, the receiver efficiency. The design ranges for these parameters are in turn limited by the selection of the heat trans...

Thermal-hydraulics is a key scientific subject to be investigated for the development of innovative reactor systems. For applications using liquid metals as coolants this task is particularly challenging due to their very low Prandtl number (Pr), preventing the application of common analogies between the turbulent transport of momentum and heat. Th...

Concentrated solar power (CSP) systems can play a major role as a renewable energy source with the inherent possibility of including a thermal energy storage subsystem for improving the plant dispatchability. Next-generation CSP systems have to provide an increased overall efficiency at reduced specific costs and they will require higher operating...

To a large extent, the economic viability of CSP projects is influenced by the main parameters characterizing the receiver, such as concentration ratio, heat-flux-intensity and distribution, fluid outlet temperature and, naturally, the receiver efficiency. The design ranges for these parameters are in turn limited by the selection of the heat trans...

Concentrated solar power, and in particular central receiver systems, can play a major role as a renewable energy source with the inherent possibility of including a thermal energy storage subsystem for improving the plant dispatchability. While current commercial projects are dominated by direct steam generation and molten nitrate salt concepts, n...

Concentrated solar power, and in particular central receiver systems, can play a major role as a renewable energy source with the inherent possibility of including a thermal energy storage subsystem for improving the plant dispatchability. Next-generation systems, in an effort for increasing the overall efficiency and reducing specific costs, will...

The solution of heat exchanger models is usually influenced by different parameters related to fluid properties, geometry and flow conditions. This implies that several simulations are usually required for design and optimization purposes. In this work, a sensitivity analysis using perturbative methods is presented as an alternative for reducing th...

Heat exchangers are the main components in cryogenic processes. Thermo-economic considerations set the need for high-effectiveness equipment and accurate models. This situation is challenging due to the complex operating conditions and the fact that some physical effects, such as changes in fluid properties, flow maldistribution, axial conduction a...

Two-phase flow heat exchangers are main components of large cryogenics, power generation, refrigeration and liquefaction of natural gas plants, both in terms of capital cost and technical challenges. A major challenge in their design is the prediction of local heat transfer coefficients and pressure gradients for the evaporating or condensing fluid...

AbstractThe performance of a heat exchanger with parallel channels can be seriously affected by flow maldistribution. In two-phase flow applications, such as evaporators, this situation may lead to local dryout and off-specification products. However, due to the complexity of describing this effect, it is normally not considered in the design proce...