Oxidation of Nuclear Graphites

Question 1

Draw a diagram of nuclear fission

Annotate and explain it

Answer 1

• After the impact with slow neutron, the nucleus breaks up into two smaller nuclei and releases 2 or 3 fast neutrons
• There is a mass defect which is converted into kinetic energy
• Fast neutrons must be slowed to create more fissions

Question 2

How is electricity generated from fission

Answer 2

• Kinetic energy from fission fragments heat up surrounding material
• Transferred heat is used to generate steam to drive turbines
• Requires slow neutrons
• Moderated by collisions with foreign nuclei

Question 3

What are 2 moderators for fission

Answer 3

Carbon/graphite or water

Question 4

Why is carbon a good moderator

Answer 4

It is not a finite resource, not flammable, or toxic and light enough to slow neutrons without completely stopping them

Question 5

What is the issue with moderator oxidation

Answer 5

Graphite can be oxidised by CO2 and cause the formation of carbon monoxide, this can be reduced by flushing methane through the reactor so that is oxidised instead

Question 6

What is the effect of oxidation on graphite

Answer 6

• density reduction
• more porees lead to reduced mechanical properties
• reduced mechanical properties increase the probability of cracking in moderator bricks
• very expensive if reactor is shutdown

Question 7

what is the equation for the fractional volume of porosity

Answer 7

(psi) = 1-(pbulk/pcrystal)