[en] Fuel behavior studies in simulated reactivity initiated accident (RIA) conditions have been performed by utilizing Nuclear Safety Research Reactor (NSRR) since October, 1975. This report describes the results obtained from January through December, 1984. A total of 62 tests were carried out during this period; those are 6 fuel design parameter tests (2 long-sized fuel rod tests, 4 pre-irradiated clad fuel rod tests), 3 cooling condition parameter tests (2 forced convection tests and 1 bundle rod test), 4 defected fuel rod tests (4 fretting corroded clad fuel rod tests), 3 severe fuel damage tests, 18 special fuel rod tests (2 HTGR fuel tests, 5 mixed oxide fuel rod tests, 11 Gd₂O₃-UO₂ fuel rod tests), 18 miscellaneous atomspheric pressure capsule tests (mechanical energy measurement tests, fuel rod deformation measurement tests, etc), 4 high temperature high pressure capsule tests, 2 high temperature high pressure loop tests and 4 fuel behavior observation tests. (author)