| rad | radian |
| rad/s | radian per second |
| rad | radiation absorbed dose |
| RCA | radiation control access |
| RCP | radiation control procedure |
| RCV | radiation control valve |
| R(P)M | radiation (process) monitor |
| RMS | radiation monitoring system |
| RC | radiochemical |
| RRS | Radiological and Radwaste Services |
| RCA | radiological controlled area |
| RETS | Radiological Effluent Technical Specifications |
| REMP | Radiological Environmental Monitoring Program |
| r | radius |
| radwaste |
| RAM | random-access memory |
| rarefaction |
| RWSR | raw water storage reservoir |
| RCCW | reactor component cooling water |
| RCL | reactor coolant loop |
| RCPB | reactor coolant pressure boundary |
| RCP | reactor coolant pump |
| RCS | reactor coolant system |
| RCIC | reactor core isolation cooling |
| RPS | reactor protection system |
| RTS | reactor testing system |
| RTB | reactor trip breaker |
| RTS | reactor trip system |
| RVHVS | reactor vessel head vent system |
| RVID | reactor vessel integrity database |
| RVLIS | reactor vessel level instrumentation system |
| RVRLIS | reactor vessel refueling level indication system |
| RATI | Readiness Assessment Team Inspection (NRC) |
| ROM | read-only memory |
| readout |
| real time |
| reanalyze |
| recalibrate |
| RMS | records management system |
| red-line |
| reenergize |
| reevaluate |
| Ref. , Refs. | reference(s) |
| RWST | refueling water storage tank |
| RegionĀ IV (NRC) |
| RWQCB | Regional Water Quality Control Board |
| RG, Reg Guide | Regulatory Guide |
| RRG | Regulatory Review Group (NRC) |
| RS | Regulatory Services |
| RH | relative humidity |
| RAOC | relaxed axial offset control |
| RCM | reliability centered maintenance |
| RPE | replacement parts evaluation |
| RAI | request for additional information (NRC) |
| RFP | request for proposal |
| RRS | required response spectra (equip. testing) |
| reracking |
| rerun |
| RE | Resident Engineer (NRC) |
| RHRS | residual heat removal system |
| RTD | resistance temperature detector |
| RCRA | Resource Conservation Recovery Act |
| RC | responsibility center |
| retrofit |
| rev. | revision |
| rpm | revolutions per minute |
| rps | revolutions per second |
| riprap |
| RCC | rod cluster control |
| RCCA | rod cluster control assembly |
| RPI | rod position indication |
| R | Roentgen |
| Rem | Roentgen equivalent man |
| R/hr | Roentgens per hour |
| R/min | Roentgens per minute |
| rms | root mean square |
| RPC | rotating pancake coil |
| runback |
| runoff |
| runup (wave) |