| large-bore (adj) |
| LERF | large early release frequency |
| large-scale (adj) |
| lat | latitude |
| laydown |
| Pb | lead (element) |
| lead time |
| leakoff (noun or adj), leak off (verb) |
| leakrate |
| leaktight |
| leaktightness |
| letdown (noun or adj), let down (verb) |
| LCV | level control valve |
| LI | level indicator |
| LS | level sensor |
| LT | level transmitter |
| LAR | license amendment request |
| LER | Licensee Event Report |
| LDBAP | Licensing and Design Bases Alignment Program |
| LB | licensing basis |
| LBIE | licensing basis impact evaluation (50.59 evaluation) |
| LIS | Licensing Information Service |
| life-support (adj) |
| LED | light emitting diode |
| LS | limit switch |
| LCO | limiting condition for operation |
| lf | linear feet |
| LVDT | linear variable differential transformer |
| L | liter(s) |
| LL | live load |
| loadout (noun or adj), load out (verb) |
| LLRT | local leak rate test |
| log (ln) | logarithm (natural) |
| long. | longitude |
| LTSP | Long Term Seismic Program |
| long-term (adj) |
| LPMS | Loose Parts Monitor System |
| LOOP | loss of offsite power |
| LOCA | loss-of-coolant accident |
| LPZ | low population zone |
| LPD | low power density |
| LSA | low specific activity |
| LTOP | low temperature overpressure protection |
| LLD | lower limits of detection |
| low-level (adj) |
| LLW | low-level waste (but: very low level waste) |
| low-low |
| LP | low-pressure (adj) |
| lumenlm |
| lm/W | lumens per watt |
| lump-sum (adj) |
