---
title: Week 4
allDay: false
startTime: 18:00
endTime: 20:30
date: 2024-09-17
completed: null
type: single
---
# Module 5.1 - Reactor Overview
Classifying Reactors
1. Type of reaction
2. Moderator material
3. Coolant
4. Generation (I-IV)
5. Use
Heat is created from fission. Kinetic energy from the decay products moving around is kind of what we see as "temperature".
# Module 5.2 - Neutron Multiplication
## Criticality Conditions
### Neutron Economy
A successful reactor must
1. Create enough excess neutrons to continue the reaction
2. Not have so many neutrons that it becomes uncontrolled
3. Consider material limits
Letting too many neutrons leak is expensive. This is the gas!
### Neutron Balance
Rate of increase = Production - absorbed - leakage
0 = Critical - Steady State - Static
\> 0 Supercritical - increasing - Kinetic/Dynamic
\< 0 Subcritical - decreasing - Kinetic/Dynamic
### Neutron Life Cycle
1. Birth 
2. Lifetime. Gets scattered around. Sneaky little fella
3. Death 😬 Leaks from the system or is absorbed
### Multiplication factor
$$k = \frac{\text{Number of neutrons in one generation}}{\text{Number of neutrons in preceding generation}}$$
Measures how many neutrons produced by each neutron born.
There are more formulas in the slides. K can be based on material properties
## Energy Dependence and Moderating
Fission is most efficiently caused by thermal neutrons (energy < 1eV), but neutrons from fission are born at something like \>2MeV. 7 orders of magnitude reduction -- usually kinetic losses by neutrons colliding with things.

Different neutron moderators require a different number of collisions to bring the energy down to thermal. The closer the mass is to that of a neutron, the better. Hydrogen is best, then deuterium, then beryllium, then carbon (graphite).
# Module 5.3 - PWR and BWR Reactors
Fuel pellots. Small boys. Stacked into fuel elements 12 feet high. about 300 per rod
14x14 lattice or 17x17. That is one fuel assembly.
Zirconium is used as the cladding. Low neutron absorbtion cross section.
Not all of the rods in the lattice are fuel. Sometimes they are, but also, sometimes they're control rods or instrumentation rods. 
BWRs have smaller assemblies. Have water rods. Can be 'canned'
# Module 5.4 - Criticality Control
No reactor can be constantly critical. Things are dynamic no matter what.
Criticality Impacters:
- Fuel depletion
- Moderator tempeature
- 