| fab | fabricate |
| F | Fahrenheit |
| FAI | fail-as-is |
| FC | fail-closed |
| FO | fail-open |
| fail-safe |
| FMEA | failure modes and effects analysis |
| f | Farad |
| FEMA | Federal Emergency Management Administration |
| FERC | Federal Energy Regulatory Commission |
| FR | Federal Register |
| FWPCA | Federal Water Pollution Control Act |
| FWQA | Federal Water Quality Act |
| feedwater |
| FLB | feedwater line break |
| ft | feet |
| fpm | feet per minute |
| fps | feet per second |
| FCN | field change notice |
| FCO | field change order |
| FCR | field change request |
| FCT | field change transmittal |
| FCT | field correction transmittal |
| FDR | field deficiency report |
| FIR | field installation request |
| field-fabricated |
| field-routed |
| field-run |
| fig. | figure (capitalize when specified) |
| FES | Final Environmental Statement |
| FSAR | Final Safety Analysis Report |
| FHARE | fire hazards Appendix R evaluations |
| FPP | Fire Protection Program |
| FPS | fire protection system |
| fire water |
| FWST | fire water storage tank |
| first-line (adj) |
| fishplate |
| fixed-fee (adj) |
| FCV | flow control valve |
| FD | flow diagram |
| FI | flow indicator |
| FT | flow transmitter |
| FIT | flow-indicating transmitter |
| flow-induced |
| flowmeter |
| flowpath |
| flowrate |
| follow-up (noun or adj), follow up (verb) |
| ft | foot, feet |
| ft-lb | foot-pound |
| ft-kip | foot-pound (thousands) |
| FMEA | foreign material exclusion area |
| fossil-fueled (preferred over fossil-fired) |
| fdn | foundation |
| FTI | Framatome Technologies, Inc. |
| FOIA | Freedom of Information Act |
| fp | freezing point |
| freq | frequency |
| FM | frequency modulation |
| FHB | fuel handling building |
| fuel-to-cladding |
| full power (noun and adj) |
| full-length (adj) |
| full-scale (adj) |
| full-size (adj) |
| full-time (adj), full time (adverb) |
