Abstract: Containment radiation level is one of the most important base for core damage assessment and protective actions recommendation during accidents. Incontainment radio-(active) reading calculations is the precondition of using this kind of method. Importance of individual nuclides were compared during normal coolant release, gap release and core melt. Conclusions are deduced that when the spray is off, the radioactive reading in containment is mainly from iodine and noble gas, and the spray is on, the radioactive reading is mainly from noble gas.