Online optical refractive index measurement in research reactor core Gary Fourneau, Marion Agoyan, Guy Chemol, Ayoub Ladaci, Hicham Maskrot, Christophe Destouches, Damien Fourmentel, Sylvain Girard and Aziz Boukenter EPJ Web Conf., 253 (2021) 04020 Published online: 19 November 2021 DOI: 10.1051/epjconf/202125304020