| half-life |
| HCV | hand control valve |
| hands-on |
| hav | haversine |
| HWMP | Hazardous Waste Minimization Program |
| hdr | header |
| HX | heat exchanger |
| htr | heater |
| HVAC | heating, ventilating, and air conditioning |
| heat-treated |
| heatup (noun or adj), heat up (verb) |
| heavy-duty (adj), heavy duty (noun) |
| H | henry |
| Hz | hertz (cycles per second) |
| HIT | High Impact Team |
| HPCI | high pressure coolant injection |
| HPSI | high pressure safety injection |
| HTR | high temperature resistant |
| HCLPF | high-confidence-of-low-probability-of-failure |
| high-density (adj) |
| HEPA | high-efficiency particulate air (filter) |
| high-energy (adj) |
| HELB | high-energy line break |
| hf | high-frequency (adj) |
| high-level (adj) |
| HP | high-pressure (adj) |
| high-temperature (adj) |
| hv | high-voltage (adj) |
| holddown (noun or adj), hold down (verb) |
| holdup (noun or adj), hold up (verb) |
| HI-STORM | Holtec International Storage and Transfer Operation Reinforced Module |
| HI-STAR | Holtec International Storage, Transport and Repository |
| hp | horsepower |
| HE | Hosgri earthquake |
| HCF | hot channel factor |
| HFT | hot functional test |
| hot leg |
| hotwell |
| hr | hour(s) |
| HPES | human performance evaluation system |
| HBPP | Humboldt Bay Power Plant |
| HBL-98-XXX | Humboldt Bay Letter |
| hydroelectric |
| pH | hydrogen ion concentration |
| hydrotesting |
