Radioactive waste is a type of dangerous waste that contains materials that give off radiation. It comes from many activities, such as medical treatments using radiation, research with nuclear materials, power generated by nuclear reactors, shutting down nuclear facilities, mining for rare-earth elements, and processing nuclear weapons. The way this waste is stored and disposed of is controlled by government groups to protect people and the environment.

Radioactive waste is divided into three main groups: low-level waste (LLW), which includes items like paper, cloth, tools, and clothing that have small amounts of radiation that does not last long; intermediate-level waste (ILW), which has more radiation and needs some protection from it; and high-level waste (HLW), which is very radioactive and produces a lot of heat, requiring cooling and strong protection.

Used nuclear fuel can be processed in special plants. About one-third of all used fuel has already been processed. Through reprocessing, 96% of the used fuel can be reused to make new fuels, such as uranium-based or mixed-oxide (MOX) fuels. The remaining 4% includes minor actinides and fission products. Fission products are a mix of elements that are either stable or decay quickly (likely already decayed in storage pools), medium-lived elements like strontium-90 and caesium-137, and seven long-lived elements with half-lives lasting hundreds of thousands to millions of years. Minor actinides are heavy elements other than uranium and plutonium created by neutron capture. These elements have half-lives ranging from years to millions of years and are especially harmful because they emit alpha radiation. Although some of these elements have potential uses, large-scale reprocessing using the PUREX process treats them as waste along with fission products. This waste is then turned into a glass-like material for storage in deep underground facilities.

The time radioactive waste must be stored depends on the type of waste and the radioactive elements it contains. Short-term storage methods include separating waste and keeping it on or near the Earth's surface. For long-term storage of high-level waste, burial in deep underground repositories is a preferred method. Reusing and changing radioactive materials are also considered ways to reduce the amount of high-level waste. However, recycling used nuclear fuel faces challenges such as rules, costs, and the risk of radioactive contamination if chemical processes do not achieve very high purity. Some elements may contain both useful and harmful forms, requiring costly and energy-intensive methods to separate them, which is not currently practical.

A summary of how much radioactive waste exists and the methods used to manage it in most developed countries is reviewed regularly as part of a joint agreement by the International Atomic Energy Agency (IAEA).

Nature and significance

Radioactive waste usually contains several types of radioactive elements, called radionuclides. These elements are unstable and break down over time, releasing ionizing radiation, which can harm humans and the environment. Each radionuclide emits different kinds and amounts of radiation, and these emissions last for different lengths of time.

The radioactivity in all radioactive waste decreases over time. Every radionuclide in the waste has a half-life, which is the time it takes for half of the atoms to change into a different type of atom. Eventually, all radioactive waste turns into non-radioactive elements. Because radioactive decay follows the half-life rule, the faster a substance decays, the more intense its radiation is at first. For example, iodine-129, which has a long half-life, releases less intense radiation than iodine-131, which has a short half-life. Two tables list some major radioactive elements, their half-lives, and how much radiation they produce compared to the radiation from uranium-235.

The energy and type of ionizing radiation a substance emits also affect how dangerous it is to humans. The chemical properties of the radioactive element determine how easily it moves through the environment and how likely it is to spread and contaminate humans. This is further complicated because many radioactive elements do not immediately become stable. Instead, they change into other radioactive elements in a series of steps, called a decay chain, before finally becoming stable.

Exposure to radioactive waste can harm health due to ionizing radiation. A dose of 1 sievert increases the risk of developing cancer by 5.5%. Regulatory agencies assume this risk is directly related to the amount of radiation received, even at low doses. Ionizing radiation can cause changes in chromosomes. If a developing organism, such as a fetus, is exposed to radiation, it may lead to birth defects, but these defects are unlikely to occur in cells that produce gametes (eggs or sperm). The chance of radiation causing genetic changes in humans is small because of natural repair processes in cells, such as fixing damaged DNA, breaking down faulty proteins, and triggering cell death when needed.

The danger from exposure to a radioactive substance depends on how it decays and how the body handles it. For example, iodine-131 is a short-lived substance that emits beta and gamma radiation. It is more harmful than cesium-137 because iodine-131 tends to collect in the thyroid gland, while cesium-137 dissolves in water and is quickly removed from the body through urine. Similarly, alpha radiation from actinides and radium is very harmful because these substances stay in the body for a long time and their radiation causes more damage to tissues than other types of radiation. Because of these differences, the rules for how radiation harms the body vary depending on the radioactive substance, the length of exposure, and the chemical form of the substance.

Classification

The way radioactive waste is classified depends on the country. The IAEA, which created the Radioactive Waste Safety Standards (RADWASS), helps guide this process. In the UK, the types of radioactive waste produced by volume are:

• 94% – low-level waste (LLW)
• About 6% – intermediate-level waste (ILW)
• Less than 1% – high-level waste (HLW)

Uranium tailings are materials left after processing uranium ore. They are not highly radioactive. These materials are sometimes called 11(e)2 wastes, based on a part of the US Atomic Energy Act from 1946. Uranium mill tailings often contain harmful heavy metals like lead and arsenic. Large piles of these tailings remain at old mining sites in places like Colorado, New Mexico, and Utah.

Although mill tailings are not very radioactive, they can stay dangerous for a long time. They often contain radium, thorium, and small amounts of uranium.

Low-level waste (LLW) comes from hospitals, industry, and the nuclear fuel cycle. It includes items like paper, tools, clothing, filters, and other materials with small amounts of short-lived radioactivity. Even materials from non-active areas may be labeled as LLW if there is a chance they might be contaminated. LLW is not more radioactive than similar materials in a normal office. Examples include rags used for cleaning, medical tubes, and lab animal remains. In the UK, LLW makes up 94% of all radioactive waste. It is usually buried in Cumbria, first in trenches and now in concrete vaults with metal containers. A new site in northern Scotland, called Dounreay, is built to survive a 4-meter tsunami.

Some LLW needs shielding during handling and transport, but most can be buried in shallow land. To save space, it is often compacted or burned before disposal. LLW is divided into four classes: A, B, C, and Greater Than Class C (GTCC).

Intermediate-level waste (ILW) has more radioactivity than LLW. It usually needs shielding but not cooling. ILW includes materials like resins, chemical sludge, and metal parts from nuclear reactors. It is often mixed with concrete or bitumen or turned into glass for disposal. Short-lived ILW is buried in shallow areas, while long-lived ILW is stored deep underground. In the US, this category is not officially defined, but it is used in Europe and other places. ILW makes up 6% of all radioactive waste in the UK.

High-level waste (HLW) comes from nuclear reactors and fuel reprocessing. HLW is defined differently in different countries. After nuclear fuel rods are used once, they become HLW. Spent fuel rods contain mostly uranium, along with fission products and transuranic elements. They are highly radioactive and often very hot. HLW makes up over 95% of the radioactivity from nuclear power but less than 1% of the total waste volume in the UK. By 2019, the UK’s 60-year nuclear program had produced 2150 cubic meters of HLW.

HLW from spent fuel rods mainly includes cesium-137 and strontium-90, but may also contain plutonium, a type of transuranic waste. These elements have very different half-lives. Cesium-137 and strontium-90 decay in about 30 years, but plutonium can take up to 24,000 years to decay.

Globally, HLW increases by about 12,000 tons each year. A 1000-megawatt nuclear power plant produces about 27 tons of spent fuel yearly. For comparison, US coal plants produce about 130 million tons of ash yearly, which releases 100 times more radiation than a similar nuclear plant.

In 2010, about 250,000 tons of HLW were stored worldwide, not including waste from accidents or tests. Japan stored about 17,000 tons in 2015, and the US had over 90,000 tons by 2019. Some HLW is sent to other countries for storage or reprocessing, and in some cases, it is returned as fuel.

Disposing of HLW is a major challenge for expanding nuclear power. Scientists suggest deep underground storage as a long-term solution. As of 2019, no large HLW storage site was fully operational. Finland is building the Onkalo repository, planned to open in 2025 at 400–450 meters deep. France and Sweden are also planning similar projects. The only active HLW storage site in the US is the Morris Operation in Grundy County, Illinois.

Transuranic waste (TRUW) is defined in the US as waste contaminated with radioactive elements heavier than uranium, with half-lives longer than 20 years and concentrations above 100 nCi/g. TRUW mainly comes from nuclear weapons production and includes items like clothing, tools, and debris. In the US, TRUW is divided into two groups: contact-handled (CH) and remote-handled (RH), based on radiation levels. CH TRUW has low radiation, while RH TRUW has very high radiation. The US stores TRUW at the Waste Isolation Pilot Plant (WIPP) in New Mexico, deep in a salt layer.

Prevention

A future way to reduce waste is to replace current reactors with Generation IV reactors, which produce less waste for each unit of power they make. Fast reactors, like the BN-800 in Russia, can also use MOX fuel made from recycled spent fuel from older reactors.

In 2014, the UK's Nuclear Decommissioning Authority released a position paper that outlines progress in managing separated plutonium. This paper summarizes the results of the NDA's work with the UK government.

Management

Nuclear waste management involves handling materials that remain radioactive for very long periods. Two important examples are Tc-99 (half-life 220,000 years) and I-129 (half-life 15.7 million years). These materials become the main source of radioactivity in spent nuclear fuel after several thousand years. Other long-lasting radioactive elements include Np-237 (half-life 2 million years) and Pu-239 (half-life 24,000 years). Proper handling of nuclear waste is essential to keep it from harming the environment. This often includes treating the waste and then using long-term strategies like storage, disposal, or changing the waste into a non-harmful form. Many countries are exploring different methods for managing nuclear waste, but progress toward long-term solutions has been slow.

Several methods for disposing of radioactive waste have been studied:

• Storing waste deep underground in stable rock formations.
• Keeping waste in steel containers placed outside of reactors.
• Burying waste in deep holes in the Earth (not used yet).
• Melting rock to mix with waste (not used yet).
• Dumping waste in the ocean (used by some countries before 1993; now banned).
• Placing waste in ice sheets (not allowed under international rules).
• Injecting waste into deep wells (used by some countries).
• Using nuclear reactions to change unstable atoms into less dangerous ones.
• Recycling radioactive materials through processes like PUREX.
• Sending waste into space (too expensive to do).

In the United States, plans for a nuclear waste storage site at Yucca Mountain were stopped. Today, spent fuel is stored at 70 nuclear power plant locations. A group of experts was formed to find better waste management solutions. A deep underground storage facility is currently considered the best option.

Methods like Ducrete, Saltcrete, and Synroc are used to lock nuclear waste into solid forms that do not break down. Rules for moving radioactive waste by ship are set by the INF Code.

Long-term storage of nuclear waste requires making it stable so it does not react with water or break down over time. One method is vitrification, where waste is mixed with glass. At Sellafield, high-level waste is combined with sugar and heated to remove water. This process helps create stable glass. The glass is then placed in steel containers and stored underground. This form of waste is expected to remain stable for thousands of years.

The glass inside the containers is usually black and shiny. In the United Kingdom, this process is done in special heated rooms. Sugar helps control reactions involving radioactive materials. In some countries, borosilicate glass (like Pyrex) is used, while others use phosphate glass. Too much of certain materials in the glass can cause problems, so their amounts are carefully controlled.

Another way to make waste stable is to mix it into a phosphate-based ceramic material. These ceramics are strong and can resist damage from heat, chemicals, and radiation over time.

In the nuclear industry, medium-level waste is often treated to concentrate the radioactivity into smaller amounts. The less radioactive parts are sometimes released after treatment. For example, radioactive metals can be removed from water using a substance called ferric hydroxide. The waste is then mixed with cement to make it solid. Using materials like fly ash or blast furnace slag can make this waste more durable.

Synroc is a special type of synthetic rock used to lock waste into a stable form. It was developed by a scientist named Ted Ringwood. Synroc contains minerals that can hold radioactive materials safely. It was originally designed for waste from nuclear reactors and is now being tested for use in the United States. A facility to process waste using Synroc started construction in 2018.

Radioactive waste must be managed for thousands to millions of years. Studies suggest that health risks from waste over such long times are hard to predict. Most planning focuses on the next 100 years because it is easier to manage costs and plans for that time. Scientists continue to study how radioactive waste behaves over long periods.

Algae has been studied for its ability to remove strontium from water. Unlike other plants, algae can separate strontium from calcium, which is more common in nuclear waste. Strontium-90, which is highly radioactive and has a half-life of about 30 years, is considered high-level waste. Research has shown that certain types of algae, like Scenedesmus spinosus, can absorb strontium from water. Adjusting the amount of barium in water can improve how well algae remove strontium.

Dry cask storage involves moving waste from cooling pools into steel containers filled with an inert gas. These containers are then stored in secure locations.

Accidents

Some problems have happened when radioactive material was not disposed of correctly, when shielding during transport was not working properly, or when it was left behind or stolen from storage. In the Soviet Union, waste stored in Lake Karachay was carried by a dust storm after the lake dried up. In Italy, radioactive waste deposits allowed material to flow into rivers, making the water unsafe for daily use. In France during the summer of 2008, several incidents occurred: at the Areva plant in Tricastin, untreated uranium leaked from a broken tank, and about 75 kilograms of radioactive material seeped into the ground and then into nearby rivers. In another case, over 100 workers were exposed to low levels of radiation. Concerns remain about the condition of the nuclear waste site on Enewetak Atoll in the Marshall Islands and the risk of a radioactive spill.

Scavenging of abandoned radioactive material has caused radiation exposure in many cases, especially in developing countries where there may be fewer rules about dangerous substances, less knowledge about radioactivity, and a market for recycled materials. People who collect or buy the material often do not know it is radioactive and choose it for its appearance or value. Neglect by the owners of radioactive material, such as hospitals, universities, or military groups, and a lack of rules or enforcement about radioactive waste have contributed to radiation exposure. An example of an accident involving radioactive scrap from a hospital is the Goiânia accident.

Transportation accidents involving spent nuclear fuel from power plants are unlikely to cause serious problems because the containers used to transport the fuel are very strong.

On December 15, 2011, a top Japanese government official, Osamu Fujimura, admitted that radioactive materials were found in the waste from Japanese nuclear facilities. Although Japan agreed to inspections with the International Atomic Energy Agency (IAEA) in 1977, the reports were kept private from IAEA inspectors. Japan began discussing with the IAEA the large amounts of enriched uranium and plutonium found in nuclear waste removed by Japanese nuclear operators. At a press conference, Fujimura said, "Based on current investigations, most radioactive materials were properly managed as waste, and from that perspective, there is no safety issue," but he added that the matter was still being studied.

Associated hazard warning signs

• The trefoil symbol, which is a three-leaf design, is used to show the presence of ionizing radiation.
• A radioactivity danger symbol created by the International Organization for Standardization (ISO) in 2007 is used for IAEA Category 1, 2, and 3 sources. These sources are classified as dangerous because they can cause serious injury or death.
• A classification sign used for transporting radioactive materials as dangerous goods.

Cited sources

• Vandenbosch, Robert & Vandenbosch, Susanne E. (2007). Nuclear waste stalemate. Published by the University of Utah Press in Salt Lake City. ISBN 978-0874809039.
• Hecker, Siegfried S. (2000). "The Plutonium Challenge-Environmental Issues." Los Alamos Science (26). Los Alamos National Laboratory, pages 36–47. Accessed on October 1, 2023.