Radioactive waste is a by-product of various nuclear technology processes. Industries generating radioactive waste include nuclear medicine, nuclear research, nuclear power, manufacturing, construction, coal and rare-earth mining and nuclear weapons reprocessing. Types Of Radioactive Waste. Radioactive wastes are grouped into three categories: high-level waste, low-level waste, and transuranic waste. High-level waste (HLW) is produced by nuclear reactors. After a nuclear fuel rod serves one fuel cycle and is removed from the core, it is considered HLW. Fuel rods contain fission products and transuranic elements generated in the reactor core. Spent fuel is highly radioactive and often hot. Radioactive wastes are stored to (1) allow some radioactive wastes to decay to nonradioactive wastes, (2) reduce transport risks; (3) provide lag storage between waste generator, treatment, and disposal sites; (4) simplify disposal; and (5) manage radioactive wastes until disposal facilities become available. For radioactive wastes containing only radionuclides with half-lives measured in days or weeks, such as some medical and research isotopes, storage for weeks or months eliminates the radioactivityand converts the radioactive waste into a nonradioactive waste. The general rule-of-thumb is that a waste stored for 10 times the half-life of the primary radionuclide is no longer a radioactive waste. Such storage reduces the radioactivity by about a factor of 1000. For other radioactive materials, a period of storage reduces the radioactivity and heat generation and, in turn, reduces transport and disposal site costs and risks. One of the most radioactive wastes is SNF from power reactors. It is universal practice to store SNF for some period of time before transport and disposal to allow the radioactivity and decay heat to decrease. This storage reduces transport and disposal costs and risks. SNF is so radioactive and generates so much heat immediately after discharge that, in most cases, it is stored under water in pools at the reactor site. The water provides radiation shielding to protect the workers from gamma radiation and cools the SNF. Typically, the minimum storage times are 2 to 5 years.