| n | nano- (10-9) (prefix) |
| NR | narrow range |
| NBFU | National Board of Fire Underwriters |
| NBS | National Bureau of Standards |
| NEC | National Electric Code |
| NEMA | National Electrical Manufacturer’s Association |
| NEPA | National Environmental Policy Act |
| NFPA | National Fire Protection Association |
| NFPC | National Fire Protection Code |
| NPDES | National Pollutant Discharge Elimination System |
| near-term (adj) |
| NTOL | near-term operating license |
| NPSH | net positive suction head |
| n/cm
2
| neutrons per square centimeter |
| n/cm2-sec | neutrons per square centimeter per second |
| N | newton |
| NDT | nil ductility temperature |
| N | nitrogen |
| NDD | no detectable degradation |
| no-load (condition) |
| nonaccident |
| noncondensable |
| NCR | Nonconformance Report |
| nonconsumable |
| NDE | nondestructive examination |
| NDT | nondestructive testing |
| nonexistent |
| nongaseous |
| nonlinear |
| nonmanual |
| nonmarine |
| nonnuclear |
| non-1E |
| nonpositive |
| non-Q |
| nonradioactive |
| NPTS | nonradiological permit tracking system |
| nonrecurring |
| nonregenerative |
| nonreversing |
| nonsafety-related |
| nonseismic |
| nonstructural |
| nonunion |
| nonvital |
| NOP | normal operating pressure |
| NOT | normal operating temperature |
| N/C | normally closed |
| N/O | normally open |
| N/A | not applicable |
| NTS | not to scale |
| NOD | Notice of Deviation |
| NOV | Notice of Violation |
| NEI | Nuclear Energy Institute |
| NEI-98-XXX | Nuclear Energy Institute Letter |
| NIS | nuclear instrumentation system |
| NUMARC | Nuclear Management and Resources Council |
| NMSS | Nuclear Material Safety and Safeguards (NRC) |
| NPAP | Nuclear Plant Administrative Procedure |
| NPPR | Nuclear Plant Problem Report |
| NPRDS | Nuclear Plant Reliability Data System |
| NPG | Nuclear Power Generation |
| NQS | Nuclear Quality Services |
| keffor keff | nuclear reactivity |
| NRR | Nuclear Reactor Regulation (NRC) |
| NSOC | Nuclear Safety Oversight Committee |
| NSSS | nuclear steam supply system |
| NTS | Nuclear Technical Services |
| NUFPG | Nuclear Utility Fire Protection Group |
| number(s)no. (nos.) |
