Abstract: A nuclear reactor includes a reactor container, a reactor core, a control drum assembly, a hot channel, a heat exchanger and a main pump. The reactor container contains a coolant; the reactor core is arranged at a lower middle part of the reactor container; the control drum assembly is arranged on an outer periphery of the reactor core, and includes control drums arranged at intervals along a peripheral direction of the reactor core; the hot channel is arranged in the reactor container and located above the reactor core. The hot channel has a bottom hermetically connected to the control drum assembly and a top hermetically connected to an inner top surface of the reactor container. The hot channel has a hot pool passage for the coolant to pass through. The heat exchanger is arranged in the reactor container and located on an outer periphery of the hot channel.