Radioactive waste is any waste that contains radioactive material. Radioactive (or nuclear) waste is a byproduct from nuclear reactors, fuel processing plants, hospitals, various industrial applications and research facilities. Radioactive waste is hazardous to most forms of life and the environment, and is regulated by government agencies in order to protect human health and the environment.
For radioactive waste, this means isolating or diluting it such that the rate or concentration of any radionuclides returned to the biosphere is harmless. A time in this case plays a very important role, since radioactivity naturally decays over time. The radioactive decay of certain number of atoms (mass) is exponential in time. The rate of nuclear decay is also measured in terms of half-lives. The half-life is the amount of time it takes for a given isotope to lose half of its radioactivity. If a radioisotope has a half-life of 14 days, half of its atoms will have decayed within 14 days. In 14 more days, half of that remaining half will decay, and so on. Half lives range from millionths of a second for highly radioactive fission products to billions of years for long-lived materials (such as naturally occurring uranium). Notice that short half lives go with large decay constants. Radioactive material with a short half life is much more radioactive (at the time of production) but will obviously lose its radioactivity rapidly. No matter how long or short the half life is, after seven half lives have passed, there is less than 1 percent of the initial activity remaining.
To achieve this, practically all radioactive waste is contained and managed, with some clearly needing deep and permanent disposal. Current approaches to managing radioactive waste have been segregation and storage for short-lived waste, near-surface disposal for low and some intermediate level waste, and deep burial or partitioning / transmutation for the high-level waste. From nuclear power generation, unlike all other forms of thermal electricity generation, all waste is regulated – none is allowed to cause pollution.
Danger of Radioactive Waste
Radioactive waste dangers are determined by many factors, since it is very important to note that there are many types of radiation. Dangers are usually determined by:
- Type of Radiation. Unstable isotopes decay spontaneously through various radioactive decay pathways, most commonly alpha decay, beta decay, gamma decay or electron capture. We have to take into account to which type of radiation (and its energy) are you exposed. For example, alpha radiation tend to travel only a short distance and do not penetrate very far into tissue if at all. Therefore, alpha radiation is sometimes treated as non-hazardous, since it cannot penetrate surface layers of human skin. This is naturally true, but this is not valid for internal exposure by alpha radionuclides. When inhaled or ingested, alpha radiation is much more dangerous than other types of radiation. In short, the biological damage from high-LET radiation (alpha particles, protons or neutrons) is much greater than that from low-LET radiation (gamma rays).
- Intensity. Intensity of ionizing radiation is a key factor, which determines health effects from being exposed to any radiation. It is similar as being exposed to heat radiation from a fire (in fact, it is also transferred by photons). If you are too close to a fire, the intensity of thermal radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from ionizing radiation sources. We must note that, radiation is all around us. We are continually exposed to natural background radiation and it seems to be without any problem.
- Chemical properties of the radioactive material. Chemical properties are key factor for possible internal exposure. For example, Sr-90, Ra-226 and Pu-239 are radionuclides known as bone-seeking radionuclides. These radionuclides have long biological half-lives and are serious internal hazards. Once deposited in bone, they remain there essentially unchanged in amount during the lifetime of the individual. These radioactive chemical elements have to be isolated from the environment as long as they are radioactive. On the other hand, in case of artificial tritium ingestion or inhalation, a biological half-time of tritium is 10 days for HTO and 40 days for OBT (organically bound tritium) formed from HTO in the body of adults.
As a result, radioactive waste management assumes different approaches for different types of radioactive waste.
See also: Fear of Radiation – Is it rational?