An object is to reduce radiation exposure in a nuclear plant. A nuclear plant 1 is a nuclear power generating plant where steam is generated by thermal energy generated by nuclear fission of a nuclear fuel 2C in a nuclear reactor 2, and a turbine 8 is driven by the steam to generate heat by a power generator 10. After a nuclear plant 1 is newly constructed, when a primary cooling system of the nuclear reactor 2 raises the temperature to around a power operation temperature for the first time, zinc is injected into a primary coolant C1 present in the primary cooling system by a zinc injector 20.