---
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
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.