Nuclear Fission and Fusion

Solution

1. 1

   Fission.

   $\text{Each U-235 nucleus that absorbs a slow neutron fissions, releasing 2–3 new neutrons.}$

2. 2

   Without control.

   $\text{All neutrons would cause more fissions → exponential growth.}$

3. 3

   Control rods.

   $\text{Control rods (boron/cadmium) absorb excess neutrons.}$

4. 4

   Steady state.

   $\text{Exactly one neutron per fission goes on to cause another fission → steady output of heat.}$

Solution

1. 1

   Process.

   $\text{Fission: large nucleus splits; fusion: small nuclei join.}$

2. 2

   Fuel.

   $\text{Fission: U-235 (limited); fusion: H isotopes (abundant from water).}$

3. 3

   Conditions.

   $\text{Fission: slow neutron triggers at near-ambient T; fusion: ~10}^7\text{ K and high P needed.}$

4. 4

   Products.

   $\text{Fission: radioactive daughters (long-lived waste); fusion: mostly helium (low-radioactivity).}$

5. 5

   Status.

   \text{Fission: commercial (UK ~14% electricity); fusion: experimental.}