Of the following, which does not belong to a nuclear reactor?

A nuclear reactor consists of a reaction chamber (core) where fission occurs, a heat exchanger to transfer heat to a working fluid, and a turbine driven by steam to generate electricity. Nuclear reactors do not emit CO2 during fission, so they do not require a mechanism to reduce CO2 emissions. Therefore, a 'mechanism to reduce CO2 emission' is not a component of a nuclear reactor.