| G | SK | PHYSICS |
| G21 | USK | NUCLEONICS |
| G21 | KL | NUCLEAR PHYSICS; NUCLEAR ENGINEERING |
| G21B | UKL | FUSION REACTORS (uncontrolled fusion, applications thereof G21J) |
| G21C | UKL | NUCLEAR REACTORS (fusion reactors, hybrid fission-fusion reactors G21B; nuclear explosives G21J) |
| G21D | UKL | NUCLEAR POWER PLANT |
| G21F | UKL | PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR (radiation protection by pharmaceutical means A61K 8/00, A61Q 17/04; in cosmonautic vehicles B64G 1/54; combined with a reactor G21C 11/00; combined with X-ray tubes H01J 35/16; combined with X-ray apparatus H05G 1/02) |
| G21G | UKL | CONVERSION OF CHEMICAL ELEMENTS; RADIOACTIVE SOURCES [2] |
| G21H | UKL | OBTAINING ENERGY FROM RADIOACTIVE SOURCES; APPLICATIONS OF RADIATION FROM RADIOACTIVE SOURCES, NOT OTHERWISE PROVIDED FOR; UTILISING COSMIC RADIATION (measurement of nuclear or X-radiation G01T; fusion reactors G21B; nuclear reactors G21C; lamps in which a gas filling is excited to luminescence by external corpuscular radiation or by radioactive material structurally associated with the lamp H01J 65/04, H01J 65/06) |
| G21J | UKL | NUCLEAR EXPLOSIVES; APPLICATIONS THEREOF |
| G21K | UKL | TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES [2] |