Fundamentals of Radiation Damage- Lecture 1

Question 1

PWR vs AGR

Answer 1

Coolant: H2O, CO2
Moderator: H2O, graphite
Temperature: 300C, 650C (roughly)
Pressure: 15MPa, 4MPa
Fuel cladding: zircaloy, stainless steel

Question 2

The 6 designs of generation IV fission reactors

Answer 2

Gas-cooled fast reactor
Lead-cooled reactor
Molten salt reactor
Sodium-cooled fast reactor
Very high temperature reactor
Super critical water-cooled reactor

Question 3

Challenges for materials in fusion reactors

Answer 3

Higher operating temperatures (1000C)
Higher levels of radiation (up to 400dpa)
Higher thermal gradients

Question 4

Sources of radiation damage

Answer 4

Fission fragments (e.g Xe, Sr, 80MeV)
Alpha particles (5MeV)
Alpha-daughter recoil nuclei (e.g Pb, Bi, few 100 keV)
He gas bubbles (transmutation and alpha particles)
Protons (hydrogen)
Neutrons (1-14MeV)
Gamma and beta particles

Question 5

How do fission fragments work?

Answer 5

Neutron capture by 235-U to form 236-U which is unstable. It splits into two nuclides releasing loads (about 200 MeV) of energy. The two nuclides are called fission fragments and have energy roughly 80MeV. Neutrons also released with roughly 2MeV energy.

Question 6

How do alpha particles work?

Answer 6

Radionuclides are produced by fission. They release energy by radioactive decay, e.g by alpha decay. Get a daughter nucleus and a helium nucleus (alpha particle) with energy roughly 5MeV

Question 7

How do alpha-daughter recoil nuclei work?

Answer 7

The daughter nucleus of the radionuclide after alpha decay is heavy and has a few 100keV of energy

Question 8

How are neutrons produced in fission?

Answer 8

Fission of a 236-U nucleus forms two daughter nuclei and maybe 3 neutrons. These neutrons have energy less than 14MeV and an average of 2MeV.

Question 9

How are neutrons produced in fusion?

Answer 9

Fuse together deuterium and tritium so there are two protons and three neutrons. This then forms a helium nucleus and so releases one spare neutron which has 14.1 MeV energy

Question 10

How do gas bubbles work?

Answer 10

Alpha particles are helium nuclei. When electrons are added they form helium atoms. Reactor core temperatures are high (maybe 600C) which allows He atom migration and agglomeration into bubbles

Question 11

What does the type and amount of damage produced in a material depend on?

Answer 11

Nature of particle (gas atom or not)
Mass of particle (heavy fission fragments or light neutron)
Energy of particle (related to velocity, fast fission fragment or slow α-daughter recoils nuclei)
Nature of material (density, mass, composition)

Question 12

Displacement energy

Answer 12

The amount of energy required to displace an atom. Approximately 50eV but depends on electronic bonding in material.

Question 13

Conservation of energy for collision of particle with atom

Answer 13

E0 is energy of particle before collision
E1 is energy of particle after collision
E2 is energy of atom after collision
E1+E2=E0

Question 14

Formula for maximum amount of energy a particle can transfer to an atom

Answer 14

KEmax=E0(4M1M2/(M1+M2)^2))
Where E0 is energy of particle before collision
M1 is mass of particle (in a.m.u)
M2 is mass of atom (in a.m.u)
Uses assumptions

Question 15

Assumptions for formula for maximum energy a particle can transfer to an atom

Answer 15

Non-relativistic effects (no travel near speed of light)
Near head on collisions
Interactions (collisions) are elastic so no energy is lost and momentum and energy are conserved

Question 16

How does the mass of a particle effect how much energy it can transfer to an atom?

Answer 16

When the mass of the particle is much less than the atom the energy it can transfer is much less than its initial energy E0.
When the mass of the particle is much greater than the atom the energy it can transfer is a little less than E0.
When the mass of the particle equals the mass of the atom, the energy it can transfer is all of E0.