What Is Nuclear Waste?
Radioactive (or nuclear) waste is a byproduct of nuclear reactors, fuel processing plants, hospitals, and research facilities. Radioactive waste is also generated while decommissioning and dismantling nuclear reactors and other nuclear facilities. There are two broad classifications: high-level or low-level waste.
High-level waste is primarily spent fuel removed from reactors after producing electricity. Low-level waste comes from reactor operations and from medical, academic, industrial, and other commercial uses of radioactive materials.
Nuclear waste is much different from what you might think.
When most people talk about nuclear waste, they’re referring to fuel that’s been used in a reactor once. Most of the radioactivity associated with nuclear power remains contained in the fuel in which it was produced.
This is why used fuel is classified as high-level radioactive waste. Nuclear fuel is used to produce electricity for about five years. Then, it’s removed and safely stored until a permanent disposal site becomes available. Nuclear plants also produce low-level radioactive waste which is safely managed and routinely disposed of at various sites around the country.
It is solid. Nuclear fuel is solid when it goes in a reactor and solid when it comes out. It is arranged in fuel assemblies: sets of sealed metal tubes that hold ceramic uranium pellets. The radioactive byproducts of nuclear reactions remain inside the fuel. No green goes anywhere.
There is not that much of it. All of the used fuel ever produced by the commercial nuclear industry since the late 1950s would cover a whole football field to a height of approximately 10 yards. That might seem like a lot, but coal plants generate that same amount of waste every hour.
It can still be used for energy. Used fuel has only exhausted part of the potential energy in the uranium pellets after five years in a reactor. Some countries like France reprocess and recycle nuclear fuel, extracting elements still capable of generating energy for use in new fuel and encasing the radioactive byproducts in solid glass logs for permanent disposal.
The United States currently does not, but some advanced reactor designs in development would be able to run on used fuel.
Types of radioactive waste
Radioactive waste includes any material that is either intrinsically radioactive or has been contaminated by radioactivity, and that is deemed to have no further use. Government policy dictates whether certain materials such as used nuclear fuel and plutonium are categorized as waste.
Every radionuclide has a half-life – the time taken for half of its atoms to decay, and thus for it to lose half of its radioactivity. Radionuclides with long half-lives tend to be alpha and beta emitters making their handling easier while those with short half-lives tend to emit the more penetrating gamma rays.
Eventually, all radioactive waste decays into non-radioactive elements. The more radioactive an isotope is, the faster it decays. Radioactive waste is typically classified as either
- Low-level (LLW),
- Intermediate-level (ILW),
- High-level (HLW),
1. Low-level waste
Low-level waste (LLW) has a radioactive content not exceeding four giga-becquerels per tonne (GBq/t) of the alpha activity or 12 GBq/t beta-gamma activity. LLW does not require shielding during handling and transport and is suitable for disposal in near-surface facilities.
LLW is generated from hospitals and industry, as well as the nuclear fuel cycle. It comprises paper, rags, tools, clothing, filters, etc., which contain small amounts of mostly short-lived radioactivity. To reduce its volume, LLW is often compacted or incinerated before disposal. LLW comprises some 90% of the volume but only 1% of the radioactivity of all radioactive waste.
2. Intermediate-level waste
Intermediate-level waste (ILW) is more radioactive than LLW, but the heat it generates (<2 kW/m3) is not sufficient to be taken into account in the design or selection of storage and disposal facilities. Due to its higher levels of radioactivity, ILW requires some shielding.
ILW typically comprises resins, chemical sludges, and metal fuel cladding, as well as contaminated materials from reactor decommissioning. Smaller items and any non-solids may be solidified in concrete or bitumen for disposal. It makes up some 7% of the volume and has 4% of the radioactivity of all radioactive waste.
3. High-level waste
High-level waste (HLW) is sufficiently radioactive for its decay heat (>2kW/m3) to increase its temperature, and the temperature of its surroundings, significantly. As a result, HLW requires cooling and shielding.
HLW arises from the ‘burning’ of uranium fuel in a nuclear reactor. HLW contains the fission products and transuranic elements generated in the reactor core. HLW accounts for just 3% of the volume, but 95% of the total radioactivity of produced waste. There are two distinct kinds of HLW:
- Used fuel that has been designated as waste.
- Separated waste from reprocessing of used fuel.
HLW has both long-lived and short-lived components, depending on the length of time it will take for the radioactivity of particular radionuclides to decrease to levels that are considered non-hazardous for people and the surrounding environment. If generally short-lived fission products can be separated from long-lived actinides, this distinction becomes important in the management and disposal of HLW.
HLW is the focus of significant attention regarding nuclear power and is managed accordingly.
4. Very low-level waste
Exempt waste and very low-level waste (VLLW) contain radioactive materials at a level that is not considered harmful to people or the surrounding environment. It consists mainly of demolished material (such as concrete, plaster, bricks, metal, valves, piping, etc.) produced during rehabilitation or dismantling operations on nuclear industrial sites.
Other industries, such as food processing, chemical, steel, etc., also produce VLLW as a result of the concentration of natural radioactivity present in certain minerals used in their manufacturing processes (see also information page on Naturally-Occurring Radioactive Materials).
The waste is therefore disposed of with domestic refuse, although countries such as France are currently developing specifically designed VLLW disposal facilities.
Is Nuclear Waste Handled Safely?
Once removed from a reactor, used fuel assemblies initially cool down in a storage pool. The concrete and steel pool and the water shield workers from radioactivity.
When cool enough that it no longer needs to be stored underwater—typically for 2 to 5 years after removal from the reactor—used fuel is transferred and stored in dry casks, which are large steel-reinforced concrete containers.
These casks are designed for long-term storage until a site is available for permanent disposal. They’re safe enough to walk up to and touch.
The U.S. nuclear energy industry routinely transports used fuel. In fact, after 7,000 shipments total of used fuel by the worldwide nuclear industry since 1970, there have been no harmful releases of radioactivity, injuries, or environmental damage.
What Happens to Nuclear Waste?
The nuclear industry handles nuclear waste safely and in compliance with the stringent requirements of the U.S. Nuclear Regulatory Commission, the U.S. Department of Energy, and the U.S. Environmental Protection Agency.
The NRC divides waste from nuclear plants into two categories: high-level and low-level. High-level waste is mostly used as fuel. Low-level waste includes items like gloves, tools or machine parts that have been exposed to radioactive materials and makes up most of the volume of waste produced by plants.
Low-level radioactive waste is collected and transported safely to one of four disposal facilities in South Carolina, Washington, Utah, or Texas. Some low-level waste can be stored at the plant until it stops being radioactive and are safe to be disposed of like normal trash.
A permanent disposal site for high-level waste has been planned for Yucca Mountain, Nevada, since 1987. This proposal has been found to meet NRC’s and EPA’s stringent safety and environmental regulations.
Nevertheless, the project remains stalled by a lack of funding from Congress. Whether it is at Yucca Mountain or some other location, DOE will transport and dispose of all U.S. commercial used fuel. All major nuclear countries in the world are pursuing similar disposal sites.
Finland is in the lead with a site licensed and under construction. Consolidated interim storage sites also have been proposed so that used fuel can be more efficiently managed until a disposal site becomes available.