| SSE | safe shutdown earthquake |
| SCP | Safeguards Contingency Plan |
| SER | Safety Evaluation Report |
| SFAS | safety feature actuation system |
| SIF | safety identification factor |
| SIS | safety injection system |
| SPDS | safety parameter display system |
| safety-related |
| SRV | safety relief valve |
| SV | (safety)(solonoid)(stop) valve |
| SSFAR | safety system functional audit and review |
| SSFI | safety system functional inspection |
| SSOMI | safety system outage modification inspection |
| saltwater |
| seawater |
| sec | second(s) |
| SLUR | second level undervoltage relay |
| SECY | Secretary (of NRC) papers |
| section (capitalize when specific) |
| SEC | Securities and Exchange Commission |
| SIR | Security Incident Report |
| SSI | security safeguards information |
| SAM | seismic anchor movement |
| SISIP | Seismically Induced Systems Interaction Program |
| self-actuated |
| self-contained |
| SCBA | self-contained breathing apparatus |
| SPPR | Semiannual Plant Performance Review (NRC) |
| semiannually |
| semimonthly |
| SMM | senior management meeting (NRC) |
| SRO | Senior Reactor Operator |
| SW | service water |
| setpoint |
| Severity Level I, II, III, IV, V violation |
| shaker-table |
| G | shear modulus |
| shearwall |
| shelf-life |
| SMAW | shielded metal arc welding |
| SFM | shift foreman |
| STA | Shift Technical Advisor |
| shop-fabricated |
| shoreline |
| short circuit |
| short-term (adj) |
| shutdown (noun or adj), shut down (verb) |
| SDM | shutdown margin |
| shutoff (noun or adj), shut off (verb) |
| sic (so, thus) |
| S | siemens (unit of conductance) |
| SOER | Significant Operating Event Report (INPO) |
| sign-off (noun or adj), sign off (verb) |
| single-degree-of-freedom |
| site-specific |
| small bore |
| small-scale (adj) |
| SFPE | Society of Fire Protection Engineers |
| SSI | soil-structure interaction |
| sole-source (adj) |
| solid-state (adj) |
| SSPS | solid-state protection system |
| SR | Special Report |
| SWP | Special Work Permit |
| sp gr | specific gravity |
| SCN | specification change notice |
| SA | spectral acceleration |
| SFP | spent fuel pool |
| SFPO | Spent Fuel Project Office (NRC) |
| SAT | spray additive tank |
| sq (or2) | square |
| cm2(or sq cm) | square centimeter |
| ft2(or sq ft) | square foot |
| in. 2(or sq in.) | square inch |
| km2
| square kilometer |
| m2
| square meter |
| m2/s | square meter per second |
| mm2
| square millimeter |
| yd2(or sq yd) | square yard |
| SRSS | square-root-of-the-sum-of-squares |
| Staff (use initial cap when referring to NRC) |
| SRM | Staff Requirements Memorandum (NRC) |
| ss | stainless steel |
| std | standard |
| scf | standard cubic feet |
| scfh | standard cubic feet per hour |
| scfm | standard cubic feet per minute |
| scfs | standard cubic feet per second |
| std dev | standard deviation |
| SOP | standard operating procedure |
| SP | Standard Practice |
| SRP | Standard Review Plan |
| STS | Standard Technical Specifications |
| STP | standard temperature and pressure |
| SGTS | standby gas treatment system |
| SU | startup (noun or adj), start up (verb) |
| ES (also OES) | State Office of Emergency Services |
| state-of-the-art (adj) |
| SBO | station blackout |
| SPCS | steam and power conversion system |
| SG or S/G | steam generator |
| SGTR | steam generator tube rupture |
| steam line |
| St | stokes |
| SIF | stress intensification factor |
| strike-slip (adj) |
| SEAOC | Structural Engineering Association of California |
| SSPC | Structural Steel Painting Council |
| SSC | structures, systems, and components |
| sua sponte (voluntarily) |
| sub rosa (privately, in secret) |
| SMM | subcooling margin monitor |
| subsection |
| subsurface |
| subsystem |
| subtidal |
| SSER | Supplement to SER |
| SAFR | Supplier Audit Finding Report |
| SER | Supplier Evaluation Report |
| supra id. | supra idem (the same as above) |
| STP | surveillance test procedure |
| switchgear |
| switchyard |
| SALP | Systematic Assessment of Licensee Performance |
| SVT | systems verification test |
