Pre-test CFD analysis of the rod bundle experiment in the Heavy Liquid Metal facility NACIE-UP

In the context of the studies on GEN. IV/ADS nuclear systems, the correct evaluations of the temperature distribution in the fuel pin bundle is of central interest. In particular, the use of lead or lead-bismuth eutectic (LBE) as coolant for the new generation fast reactors is one of the most promising choices. Due to the high density and high conductivity of lead or LBE, a detailed analysis of the thermo-fluid dynamic behavior of the heavy liquid metal (HLM) inside the sub-channels of a fuel rod bundle is necessary in order to support the front-end engineering design (FEED) of GEN. IV/ADS prototypes and demonstrators. In this frame, the synergy between numerical analysis by CFD and data coming from large experimental facilities seems to be crucial to assess the feasibility of the components. At ENEA-Brasimone R.C., large experimental facilities exist to study HLM free, forced and mixed convection in loops and pools: e.g. NACIE-UP is a large scale LBE loop for mixed convection experiments. In the context of the SEARCH FP7 project, an experiment has to be performed in the NACIE-UP facility to assess the coolability of a 19-pin wire-wrapped electrical bundle (Fuel Pin Simulator, FPS), with heat flux up to 1 MW/m^2. The bundle is representative of the one adopted in the MYRRHA concept. The present master thesis is devoted to the Computational Fluid Dynamic (CFD) analysis of Heavy Liquid Metal (HLM) cooled Fuel Bundles to be adopted in the Gen-IV nuclear reactors. The thesis was carried out in collaboration with the ENEA Brasimone research center, where large experimental facilities are operated to investigate HLM technology and thermal hydraulics. In particular liquid Lead or Lead-Bismuth Eutectic (LBE) is considered as working fluid. A CFD analysis of fluid flow and heat transfer was carried out in the heavy liquid metal (LBE) cooled bundle test section of the NACIE-UP facility. The model includes the details of the wire-spacers as well as the entry region of the test section. A turbulence closure approach is adopted for all the simulations with ≈ 3.5∙10^7 nodes and a resolution of y+ = 1 - 4 at the wall in the range of interest. A CFD code validation was carried out on experimental data by ORNL in a similar geometry cooled by sodium. Results showed a global coherence of the results and a correct description of the conjugate heat transfer effects. A good agreement was found between numerical and experimental data, although the RANS approach showed some limitations for the central sub-channel temperature distributions at high mass flow rates. Results are compared with the up-to-date correlations on pressure loss and heat transfer and the experimental range is completely explored by CFD. The thermal structures of the test section are modelled and the role of conjugate heat transfer was assessed. Several highlights emerged from the numerical study for the experimental campaign. In particular, the accuracy in the measurement of heat transfer between rods and fluid was evidenced as weak point of the experimental test matrix. As a consequence the test matrix was modified. A CFD analysis of fluid flow and heat transfer was carried out in the heavy liquid metal (LBE) cooled bundle test section of the NACIE-UP facility. The model includes the details of the wire-spacers as well as the entry region of the test section. A turbulence closure approach is adopted for all the simulations with ≈ 3.5∙10^7 nodes and a resolution of y+ = 1 - 4 at the wall in the range of interest. A CFD code validation was carried out on experimental data by ORNL in a similar geometry cooled by sodium. Results showed a global coherence of the results and a correct description of the conjugate heat transfer effects. A good agreement was found between numerical and experimental data, although the RANS approach showed some limitations for the central sub-channel temperature distributions at high mass flow rates. Results are compared with the up-to-date correlations on pressure loss and heat transfer and the experimental range is completely explored by CFD. The thermal structures of the test section are modelled and the role of conjugate heat transfer was assessed. Several highlights emerged from the numerical study for the experimental campaign. In particular, the accuracy in the measurement of heat transfer between rods and fluid was evidenced as weak point of the experimental test matrix. As a consequence the test matrix was modified

A Numerical Study of Ultrametricity in Finite Dimensional Spin Glasses

We use a constrained Monte Carlo technique to analyze ultrametric features of a 4 dimensional Edwards-Anderson spin glass with quenched couplings J=\pm 1. We find that in the large volume limit an ultrametric structure emerges quite clearly in the overlap of typical equilibrium configurations.Comment: 8 one column pages, latex, 4 figures with epsfig.st

Preliminary Assessment of Radiolysis for the Cooling Water System in the Rotating Target of {SORGENTINA}-{RF}

The SORGENTINA-RF project aims at developing a 14 MeV fusion neutron source featuring an emission rate in the order of 5-7 x 10(13) s(-1). The plant relies on a metallic water-cooled rotating target and a deuterium (50%) and tritium (50%) ion beam. Beyond the main focus of medical radioisotope production, the source may represent a multi-purpose neutron facility by implementing a series of neutron-based techniques. Among the different engineering and technological issues to be addressed, the production of incondensable gases and corrosion product into the rotating target deserves a dedicated investigation. In this study, a preliminary analysis is carried out, considering the general layout of the target and the present choice of the target material

Numerical and experimental characterization of heavy liquid metal cooled bundles

The focus of the present research activity was the experimental and numerical investigation of some thermal-hydraulic phenomena peculiar of the heavy liquid metal cooled systems like Lead Fast Reactors. The two activities were carried out in parallel during the three-year research period and performed mainly at the Experimental Thermo-fluid-dynamic Laboratory of ENEA Brasimone R.C., in the framework of a collaboration between ENEA and the Department of Civil and Industrial Engineering of the University of Pisa. The main thermal-hydraulic aspects investigated were the core coolability during normal conditions in wire-wrap and grid spaced bundles and coolability during a specific accident condition called “flow blockage accident”. The experimental activity had two main focuses: the evaluation of heat transfer coefficients in a grid spaced bundle cooled by heavy liquid metal and the evaluation of the thermal-hydraulic field in a grid-spaced bundle affected by different degrees of internal blockage. The numerical activities concerned pre-test and post-test CFD studies, on three different test sections installed in the two HLM cooled facilities at ENEA Brasimone (NACIE-UP and CIRCE). Pre-test CFD simulations were developed for the Blockage Fuel Pin Simulator test section installed in the NACIE-UP facility for the optimization of TCs position near the blockage. Post-test CFD analyses were developed looking for a preliminary assessment of CFD code capabilities and limitations

CFD Optimization of the Resistivity Meter for the IFMIF-DONES Facility

A detailed study of lithium-related topics in the IFMIF-DONES facility is currently being promoted and supported within the EUROfusion action, paying attention to different pivotal aspects including lithium flow stability and the monitoring and extraction of impurities. The resistivity meter is a device able to monitor online non-metallic impurities (mainly nitrogen) in flowing lithium. It relies on the variation of the electric resistivity produced by dissolved anions: the higher the concentration of impurities in lithium, the higher the resistivity measured. The current configuration of the resistivity meter has shown different measuring issues during its operation. All these issues reduce the accuracy of the measurements performed with this instrument and introduce relevant noise affecting the resistance value. This paper proposes different upgrades, supported by CFD simulations, to optimize lithium flow conditions and to reduce measurement problems. Owing to these upgrades, a new design of the resistivity meter has been achieved, which is simpler and easier to manufacture

Mechanical Behaviour of the Rotating Target SORGENTINA-RF

The SORGENTINA-RF project aims at developing a 14 MeV neutron source based on a deuterium/tritium ion accelerator and a rotating target where fusion reactions take place. Among the different research fields, the most interesting and promising is medical radioisotope production. In this framework, intense research work on the design of the rotating target has been carried out. More in detail, to define the optimal design configuration, a sensitivity analysis on the mechanical performance of the rotating target considering the influence of some relevant parameters, such as material type, thickness, and presence of internal stiffeners, was carried out. Among the materials analyzed, aluminium alloy represents the best compromise to efficiently address all the critical requirements in the design phase. One of the most demanding project requirements that the conceptual design must fulfill is the ability of the target to dissipate a thermal power of 250 kW without precluding its mechanical properties and resistance. To investigate the performance of the rotating target, some thermo-mechanical analyses were undertaken with finite element method under some thermal transients and mechanical loads able to simulate the working conditions of the system. The numerical results emphasise the target’s ability to withstand operating conditions. The main outcomes of the present study have been implemented as engineering solutions in the project design

CFD thermo-hydraulic analysis of the CIRCE fuel bundle

The present paper focuses on the CFD post-test analysis of the experimental campaign performed in the frame of the Integral Circulation Experiment (ICE) configuration of the CIRCulation Eutectic (CIRCE) facility located at the ENEA Brasimone Research Centre (Italy). Experiments were carried out aiming to fully investigate the heat transfer phenomena in grid spaced fuel pin bundles providing experimental data in support of European Lead cooled Fast Reactor development. The fuel pin bundle simulator is composed by 37 electrical pins arranged in a hexagonal lattice cooled by lead bismuth eutectic (LBE). The thermal power is about 1 MW with a uniform linear power up to 25 kW/m. The CFD geometrical domain reproduces an angle of 60° of the FPS and lateral rotational periodic boundary conditions are adopted. High-resolution Reynolds Average Navier Stokes (RANS) simulations were carried out adopting the Ansys CFX commercial code with enhanced wall and the SST k-ω turbulence model. Due to the relatively low molecular Prandtl number of heavy liquid metal, a sensitivity study on the Prt was performed. Numerical results for the pin wall temperature and the coolant temperature in the central subchannel were compared with the experimental data. The Nusselt number was derived for each simulation for the central subchannel and compared both with the experimental results and Nusselt numbers obtained from convective heat transfer correlations available in literature for Heavy Liquid Metals. The good agreement found justifies the use of high quality RANS with a modified turbulent Prandtl number in the investigation of heat transfer in fuel pin bundle at high Re

Heat transfer on HLM cooled wire-spaced fuel pin bundle simulator in the NACIE-UP facility

The NACIE-UP experimental facility at the ENEA Brasimone Research Centre (Italy) allowed to evaluate the heat transfer coefficient of a wire-spaced fuel bundle cooled by lead-bismuth eutectic (LBE). Lead or lead-bismuth eutectic are very attractive as coolants for the GEN-IV fast reactors due to the good thermo-physical properties and the capability to fulfil the GEN-IV goals. Nevertheless, few experimental data on heat transfer with heavy liquid metals (HLM) are available in literature. Furthermore, just a few data can be identified on the specific topic of wire-spaced fuel bundle cooled by HLM. Additional analysis on thermo-fluid dynamic behaviour of the HLM inside the subchannels of a rod bundle is necessary to support the design and safety assessment of GEN. IV/ADS reactors. In this context, a wire-spaced 19-pin fuel bundle was installed inside the NACIE-UP facility. The pin bundle is equipped with 67 thermocouples to monitor temperatures and analyse the heat transfer behaviour in different sub-channels and axial positions. The experimental campaign was part of the SEARCH FP7 EU project to support the development of the MYRRHA irradiation facility (SCK-CEN). Natural and mixed circulation flow regimes were investigated, with subchannel Reynolds number in the range Re = 1000-10,000 and heat flux in the range q″ = 50-500 kW/m2. Local Nusselt numbers were calculated for five sub-channels in different ranks at three axial positions. Section-averaged Nusselt number was also defined and calculated. Local Nusselt data showed good consistency with some of the correlation existing in literature for heat transfer in liquid metals for rod bundles. Local Nusselt numbers in peripheral ranks are lower, due to the presence of the hexagonal external wrap which affects the temperature profile. The good accuracy of the instrumentation and the error analysis implemented in the post-processing routines guaranteed a good reliability of the results. The data set presented can be used also to validate computer codes for HLM-cooled rod bundles

Design of a Prototypical Mock-Up for the Experimental Investigation of WCLL First-Wall Performances

A large research effort is currently ongoing within the framework of the EUROfusion consortium for the study and design of a water-cooled lithium–lead (WCLL) breeding blanket (BB). This concept will be tested in ITER through the installation of a test blanket module (TBM) and it is one of the two candidates adopted as driver BBs in DEMO. In this framework, at the ENEA research centre of Brasimone, the realization of the experimental platform, W-HYDRA, is envisaged. The platform is dedicated to the support of the development of WCLL BB and ITER TBM and the investigation of the DEMO balance of plants. One of the most important experimental infrastructures is the water-loop facility, the aim of which is to provide water at a high pressure and temperature (PWR conditions), with a sufficient mass-flow rate and power for the experimental testing of BB and TBM components. The facility will be equipped with a vacuum chamber and an electron beam gun for the reproduction of high surface heat flux on plasma-facing components. In the present work, the design of a prototypical mock-up (MU) of the WCLL BB first wall is described. The MU is used to investigate the thermal, hydraulic and structural behavior of the current first-wall design under relevant heat loads at the expected operational conditions. The delineation of the main experimental test’s features and the instrumentation needed is assessed in the paper. A preliminary CFD calculation on the prototypical MU and the computational results are also presented

Development of a Steam Generator Mock-Up for EU DEMO Fusion Reactor: Conceptual Design and Code Assessment

Recent R&D activities in nuclear fusion have identified the DEMO reactor as the ITER successor, aiming at demonstrating the technical feasibility of fusion plants, along with their commercial exploitation. However, the pulsed operation of the machine causes an “unconventional” operation of the system, posing unique challenges to the functional feasibility of the steam generator, for which it is necessary to define and qualify a reference configuration for DEMO. In order to facilitate the transitions between different operational regimes, the Once Through Steam Generator (OTSG) is considered to be a suitable choice for the DEMO primary heat transfer systems, being characterized by lower thermal inertia with respect to the most common U-tube steam generators. In this framework, the ENEA has undertaken construction of the STEAM facility at Brasimone R.C., aiming at characterizing the behavior of the DEMO OTSG and related water coolant systems in steady-state and transient conditions. A dedicated OTSG mock-up has been conceived and designed, adopting a scaling procedure, keeping the height 1:1 of the DEMO OTSGs. The conceptual design has been supported by RELAP5/Mod3.3 thermal-hydraulic calculations. CFD and FEM codes have been used for fluid-dynamic analyses and mechanical stress analyses, respectively, in specific parts of the component