In a nuclear fission reactor, several components are required to efficiently control and sustain the fission process. These components include a moderator, coolant, control device, and, sometimes, an accelerator.

1) Moderator: The purpose of a moderator is to slow down the fast-moving neutrons produced during fission, enabling them to collide with other atoms and initiate a chain reaction. The moderator is typically made of materials like water, graphite, or heavy water. Its role is important for maintaining a controlled reaction.

2) Coolant: A coolant is essential in a nuclear reactor to remove the excess heat generated during fission. It helps in preventing the reactor from overheating. Common coolants include water, liquid metal, or gas. The coolant absorbs the heat and transfers it to a heat exchanger for further use.

3) Accelerator: This option is incorrect as accelerators are not typically needed in a nuclear fission reactor. Accelerators like particle accelerators are used in nuclear research, but not in traditional fission reactor designs.

4) Control device: A control device, such as control rods, is important in a nuclear reactor to regulate the fission process. By adjusting the position of the control rods, the rate of fission and the reactor`s power output can