A SUBCHANNEL COARSENING METHOD FOR Serpent2-SUBCHANFLOW APPLIED TO A FULL-CORE VVER PROBLEM Manuel García, Diego Ferraro, Ville Valtavirta, Riku Tuominen, Uwe Imke, Luigi Mercatali, Victor Sanchez-Espinoza and Jaakko Leppänen EPJ Web Conf., 247 (2021) 06018 Published online: 22 February 2021 DOI: 10.1051/epjconf/202124706018