- ultraviolet mirror
- uncoupling
- twin magazine
- twisting
- twisting moment
- ultrasonic inspection
- ultraviolet radiation
- underbead crack
- underdevelop
- underexposed picture
- undercool
- undercritical
- underexpose
- underexposure
- underground storage
- underwater housing
- underwater reactor
- uniform light
- underpressure
- underwater camera
- undulation
- undulatory theory
- unenriched uranium
- unexposed film
- unfolding
- unilateral track
- unison
- uninterrupted traffic
- unipotential lens
- universal assembler
- universal attraction
- universal gravitation
- universal manipulator
- universal motion
- universal viewfinder
- unloading rod
- unpaired neutron
- unpaired proton
- unpressurized line
- unpaired electron
- unperiod motion
- unlatching
- unpolarized
- unrectified
- unrefracted
- unsaturated steam
- unscheduled withdrawal
- unshielded source
- unspool
- unstable oscillation
- unvulcanized
- upender
- uplift pressure
- upper plenum
- uranium milling
- uranium scrap
- unstable nucleus
- unwind
- up-quark
- uphand welding
- upper core
- upstream wake
- upward pressure
- uranium compound
- upflow
- upward flow
- uranium black
- uranium concentrate
- uranium dicarbide
- uranium ingot
- uranium nucleus
- uranium refining
- uranium slug
- UV catastrophe
- UV microscope
- UV mirror
- UV photography
- V-number
- vacua
- vacuum
- vacuum casting
- vacuum factor
- vacuum jacket
- valence band
- valence state
- value
- valve
- valve gear
- valve guide
- valve off
- valve travel
- vapor generator
- vapor permeability
- vaporize
- vaporized
- variation
- varied pitchblende
- variometer
- vary
- vector