firs - floo
- first charge
- first connection to the grid
- first connection to the mains
- first core
- first core charging
- first core inventory
- first core load
- first core load fuel
- first core loading
- first cost
- first critical experiment
- first criticality
- first divergence
- first dry-out
- first echelon
- first event source
- first flight density
- first fuel charging
- first fuel loading
- first inspection of the plant components
- first inventory
- first law of thermodynamics
- first load
- first phase
- first priority
- first shift
- first start-up
- first test
- first wall
- first wall loading
- first-class personnel-safety hazard
- first-flight flux
- first-line maintenance men
- fisser
- fissibility
- fissible material inventory
- fissile
- fissile atom density
- fissile atoms destroyed
- fissile atoms produced
