The Nuclear Reactor

Series: Elementary Nuclear Series

Year Published: 1954

Creator: McGraw-Hill

Description: This McGraw-Hill film from the Elementary Nuclear Series, "The Nuclear Reactor" (1954) shows basic reactor operation using animation. It shows how uranium-235 undergoes radioactive behavior and nuclear fission, releasing energy and neutrons that can trigger a chain reaction. When a U-235 nucleus absorbs a neutron, it becomes unstable uranium-236, which splits into two fragments, emits additional neutrons, and releases energy as kinetic energy, gamma rays, and beta particles. If enough uranium is present, these neutrons can sustain further fissions, forming a chain reaction that is uncontrolled in an atomic bomb. In a nuclear reactor, the reaction is moderated by materials such as graphite that slow neutrons, and controlled by cadmium or boron rods that absorb them, allowing the reaction to remain stable at a desired level. The text also describes how reactors can produce new fissionable material, such as plutonium-239 from uranium-238, and generate radioactive products that are widely used as tracers in science and medicine.




00:00 Main titles. 0:32 — Uranium-235 is radioactive; its nucleus is in constant motion due to excess energy.

0:59 — Over time, U-235 can release energy by emitting an alpha particle, transforming into thorium-231 while conserving momentum.

1:20 — When U-235 absorbs a neutron, it becomes highly unstable uranium-236.

1:30 — Uranium-236 splits into two fragments of roughly equal mass that fly apart at high speed, releasing energy.

1:44 — Two or three neutrons are emitted during or shortly after fission.

2:00 — Fission fragments release additional energy as gamma radiation and beta particles while becoming stable.

2:26 — Each fission of U-235 emits one to three neutrons.

2:46 — If enough U-235 is present, emitted neutrons can trigger further fissions, creating a chain reaction.

3:00 — An uncontrolled chain reaction is the basis of an atomic bomb.

3:12 — In the presence of a moderator such as graphite, neutrons are slowed, making sustained reactions more likely.

3:51 — If too little uranium or moderator is present, neutrons escape and the reaction dies out.

4:08 — Above a critical size, the uranium–moderator structure sustains the reaction.

4:19 — In a nuclear reactor, moderated fission occurs in a lattice of uranium and graphite surrounded by shielding.

4:34 — Control rods made of cadmium or boron absorb neutrons to regulate the reaction.

4:48 — Withdrawing rods increases activity; inserting them deeper reduces activity.

5:07 — At an intermediate rod position, the chain reaction becomes exactly self-sustaining.

5:14 — A numerical example shows how neutron losses can balance production so the reaction remains steady.

5:49 — Further rod withdrawal increases neutron numbers exponentially, risking loss of control.

6:25 — Reinserting rods restores a stable, self-sustaining reaction at a chosen level.

7:00 — Neutron-absorbing rods allow precise control of reactor activity.

7:17 — A simple reactor (atomic pile) consists of graphite blocks with embedded uranium and movable control rods.

7:46 — Natural uranium is mostly U-238; only a small fraction is fissionable U-235.

8:00 — U-238 can absorb neutrons and decay into plutonium-239, which is itself fissionable.

8:27 — The atomic pile produces both new fissionable material and radioactive fission products.

8:38 — These products are used as tracer elements in biology, chemistry, medicine, and physics.

Online Copy: https://www.youtube.com/watch?v=wLfuDDJuKK8

Metadata Source:YouTube