Reactor and reactivity control method thereof

The embodiment of the invention relates to the technical field of nuclear reactors, in particular to a reactor and a reactivity control method thereof, and the reactor comprises a cooling medium pool containing a cooling medium, a fuel assembly arranged in the cooling medium pool, a reflecting layer and a boron injection pipeline. The reflecting layer is arranged in the cooling medium pool, located on the radial outer side of the fuel assembly and used for reflecting neutrons, and at least one closed boron injection hole channel is formed in the reflecting layer. And the boron injection pipeline is communicated with each boron injection pore channel and is used for controllably supplying concentrated boron water to the boron injection pore channels when the reactor is shut down due to an accident. According to the reactor provided by the embodiment of the invention, the boron injection pore channel is formed in the reflecting layer, so that the original structure of the reactor core can be fully utilized, a f