Chapter 11Nuclear Power

Energy released in combustion reactions comes from changes in the chemical bonds that hold the atom together.

Nuclear Energy involves changes within the nuclei of the atom. Small amounts of matter from the nucleus are converted into large amounts of energy

Fission: Larger atoms of certain elements are split into smaller atoms of certain elements. Power Plants.

Fusion: 2 smaller atoms are combined to make 1 large atom of a different element. Mass of the end product is less than the mass of the starting materials released as energy. The Sun.

Neutron

Proton

Electron

Atomic Number: # of

protons

Atomic Mass: # of protons + # of neutrons

Nucleus

Isotope: forms of a given element with different numbers of neutrons therefore different atomic masses.

ex) Hydrogen has 1 P and no N

Deuterium has 1 P and 1 N

Tritium has 1 P and 2 N

As a radioactive element emits radiation, its nucleus changes into the nucleus of a different element that is more stable…. Radioactive decay.

Each radioisotope has its own characteristic rate of decay.

◦ Half-Life: the period of time required for one half of the total amount of a radioactive substance to change into a different material.

Examples: Iodine- 131 0.02 years ( 8.1 days) Krypton-85 10.4 years Plutonium- 239 24,400 years

◦ U-235: produces a fission chain reaction Critical mass: amount of U-235 required to start a

chain reaction Less than 1% of all uranium is U-235 Known as enriched uranium Half life: 700 million years

◦ U-238 Most common (99.3%) Half life: 4.5 billion years When hit by a neutron it decays into PU-239

◦ PU-239 Produced in breeder reactors from U-238 Half life: 24,000 years Regulated by international inspections because it

can be used in nuclear weapons.

Nuclear Fuel Cycle

1. Mining2. Enrichment

(refining process)

3. Fuel rods4. Fuel assemblies

(200 rods) 5. Reactor

(~ 250 fuel assemblies)

6. Fuel is used7. Fuel is

reprocessed8. Fuel is disposed of

or sent for enrichment.

1. Reactor core- heat produced by nuclear fission is used to produce steam from liquid water.

2. Steam generator- uses steam turn a turbine3. Turbine- generates electricity from steam4. Condenser- cools the steam converting it back to a

liquid.

Above each reactor core is a control rod made of metal alloy capable of absorbing neutrons.

The plant will move this up and down depending on the energy needs throughout the day.

Up = faster rxn Down = slower rxn

SAFETY…The reactor is surrounded by a huge steel pot like structure called a reactor vessel. Reactor vessel & steam generator are placed in a containment building.

1. Primary water circuit (orange in fig 11.5)◦ Heats water using energy produced by the fission rxn.◦ Circulates water under high pressure through the core◦ Superheated water cannot expand stays liquid.

2. Secondary Water Circuit (blue in fig 11.5)◦ Convert the water to steam

3. Tertiary Water Circuit (green in fig 11.5)◦ Provides cool water to the condenser cooling off spent

steam in the secondary water circuit.◦ Water moves to a cooling tower or lake.