Multiscale neutronics/thermal-hydraulics coupling with COBAYA4 code for pin-by-pin PWR transient analysis

• Published in: Nuclear engineering and design 2017-09, Vol.321, p.38-47
• Main Authors: García-Herranz, N., Cuervo, D., Sabater, A., Rucabado, G., Sánchez-Cervera, S., Castro, E.
• Format: Article
• Language: English
• Subjects: Assembly; Channels; COBAYA/COBRA-TF; Computational fluid dynamics; Computer simulation; Computing time; Coupling; Fluid flow; Hydraulics; Legibility; Maintainability; Mapping; MSLB transient; Multi-physics; Multi-scale; Multiscale analysis; Nodal diffusion; Nuclear accidents & safety; Nuclear engineering; Nuclear power plants; Nuclear reactors; Nuclear safety; Physics; Pin-by-pin diffusion; Pressurized water reactors; Reactor safety; Simulation; Steam; Sub-channel thermal-hydraulics; Transient analysis
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2017.03.017

•Multi-scale multi-physics analysis for a MSLB transient benchmark.•Nodal and pin-by-pin diffusion calculations.•Sub-channel thermal-hydraulics.•COBAYA/CTF mapping. At UPM, in-depth modifications of the core simulator COBAYA, able to perform neutronics diffusion calculations at both nodal and pin-by-pin levels, have been accomplished during the 7th Framework EURATOM NURESAFE project. The main goal was to upgrade its integration in the European Platform for Nuclear Reactor Safety Simulation in order to facilitate the coupling with any other code of the platform for multi-physics analysis, focusing also on the code legibility and maintainability. An external and flexible coupling with the thermal-hydraulics code COBRA-TF was designed. As a result, COBAYA4/COBRA-TF allows multiscale coupled calculations, enabling both nodal and pin-by-pin neutronics resolutions using both assembly-based channels and pin-based subchannels at the thermal-hydraulics domain. Flexible mapping schemes also in axial direction can be defined. The coupled system was applied to a Main Steam Line Break transient benchmark. Pin-by-pin 3D simulations using one thermal-hydraulic channel per assembly were carried out in a reasonable computing time, and results compared to nodal solutions demonstrating the multiscale coupling capability for full core transients. Pin-by-pin calculations using thermal-hydraulics subchannels will be performed in a near future to assess the role that a very detailed mapping can play to predict realistic local parameters. While in asymmetric transients the effect can be important, it is expected that in symmetric transients assembly-based thermal-hydraulics channels can provide accurate pin-by-pin solutions in execution times suitable for routine analysis. The performed work will bring the ability to explore in an easy way multiscale effects on safety transient evaluations and give recommendations for the neutronics/thermal-hydraulics mapping depending on the application.