PT Unknown AU Qvist, S Luley, J Nikitin, E Pivovarov, V Vijayashree, R Rineiski, A Schikorr, M Serkulov, M Tochenyy, L Van Wert, C Vrban, B Baudrand, O Bubelis, E Burgazzi, L Farmer, M Fomin, O Gugio, DE Lamberts, D Lee, JH TI IAEA study on passive shutdown systems for fast reactors: status review PY 2017 LA english ER