Overview

Nuclear energy is the large-scale energy-producing technology and is considered to be "clean" so far as it does not create greenhouse gas or particulate emissions like fossil fuels. Nuclear fuel is "energy dense" it packs a LOT of energy for every kg. So, it was long heralded as a  wondrous source of energy.

The bad part of it is that once the fuel is spent and has lost most of its ability to generate the heat required for the power plant, it is still radioactive and it is literally impossible to destroy or neutralize. As a result, all the nuclear material that has ever been used and will ever be used on the planet, will be here for ever more. It is kept in protected areas, in ponds to keep it cool. Short of burying it deep in a mountain, which has been proposed, it will remain a threat as it continues to give off radiation.

Nuclear waste

Nuclear waste is the radioactive waste produced by nuclear reactors, or left over from research projects, medical uses, and the manufacture of nuclear weapons.

Waste from a nuclear plant is primarily a solid waste, spent fuel, and some process chemicals, steam, and heated cooling water.  Such waste differs from a fossil fuel plant's waste in that its volume and mass are small relative to the electricity produced. The waste is under the control of the plant operators and subsequent waste owners or managers, including the Department of Energy, until it is disposed.  Nuclear waste also differs from fossil fuels in that spent fuel is radioactive while only a minute share of the waste from a fossil plant is radioactive.  Solid waste from a nuclear plant or from a fossil fuel plant can be toxic or damaging to the environment, often in ways unique to the particular category of plant and fuel.  Waste from the nuclear power plant is managed to the point of disposal, while a substantial part of the fossil fuel waste, especially stack gases and particulates are un-managed after release from the plant. 

 Types and Sources

Methods of Nuclear waste classification can vary somewhat from country to country, but two categories — high-level waste (HLW), and low-level waste (LLW) — are generally recognized, based on radioactivity, source and half-life.

High-level waste consists mainly of spent fuel rods from nuclear reactors. These power plants rely on nuclear fission to generate heat, and the fuel is made into rods that can be moved in and out of the reactor core to control the process. After a time, the rate of fission in a rod will decrease to the point where it is no longer efficient, and the rod will be removed. The removed rods are known as spent fuel rods and are highly radioactive, containing a number of fission products — radioactive elements created by the fission process. These elements decay at different rates, and over time, the rods become less radioactive, but will remain potentially dangerous for many thousands of years.

Common types of radioactive waste

Exempt waste & very low-level waste

Exempt waste and very low-level waste (VLLW) contains radioactive materials at a level which 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. The waste is therefore disposed of with domestic refuse, although countries such as France are currently developing facilities to store VLLW in specifically designed VLLW disposal facilities.

Low-level waste

Low-level waste (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. It does not require shielding during handling and transport and is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal. It comprises some 90% of the volume but only 1% of the radioactivity of all radioactive waste.

Intermediate-level waste

Intermediate-level waste (ILW) contains higher amounts of radioactivity and some requires shielding. It 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 radwaste. By definition, its radioactive decay generates heat of less than about 2 kW/m3 so does not require heating to be taken into account in design of storage or disposal facilities.

Low- and intermediate-level waste is produced as a result of operations, such as the cleaning of reactor cooling systems and fuel storage ponds, and the decontamination of equipment, filters and metal components that have become radioactive as a result of their use in or near the reactor.

High-level waste

High-level waste (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. It is highly radioactive and hot due to decay heat, so requires cooling and shielding. It has thermal power above about 2 kW/m3 and can be considered as the 'ash' from 'burning' uranium. HLW accounts for over 95% of the total radioactivity produced in the process of electricity generation. There are two distinct kinds of HLW:

• Used fuel itself.
• Separated waste from reprocessing the used fuel.

How much waste is produced?

The volume of nuclear waste produced by the nuclear industry is small compared with other wastes generated from industrial activity. Each year, nuclear power generation facilities worldwide produce about 154,000 m3 of LLW and ILW, and about 34,000 m3 of HLW (including used fuel designated as waste)1.

In the OECD countries, some 300 million tonnes of toxic wastes are produced each year, but conditioned radioactive wastes amount to only 81,000 m3 per year.

In the UK, for example, the total amount of radioactive waste (including radioactive waste expected to arise from existing nuclear facilities) is about 4.7 million m3, or around 5 million tonnes. A further 1 million m3 has already been disposed. Of the UK's total radioactive waste, about 94% (i.e. about 4.4 million m3) falls into the LLW category. About 6% (290,000 m3) is in the ILW category, and less than 0.1% (1000 m3) is classed as HLW. Although the volume of HLW is relatively small, it contains about 95% of the total inventory of radioactivity12.

A typical 1000 MWe light water reactor will generate (directly and indirectly) 200-350 m3 of LLW and ILW waste per year. It will also discharge about 20 m3 (27 tonnes) of used fuel per year, which corresponds to a 75 m3 disposal volume following encapsulation if it is treated as waste. Where that used fuel is reprocessed, only 3 m3 of vitrified waste (glass) is produced, which is equivalent to a 28 m3 disposal volume following placement in a disposal canister.

This compares with an average 400,000 tonnes of ash produced from a coal-fired plant of the same power capacity. Today, volume reduction techniques and abatement technologies, as well as continuing good practice within the workforce, all contribute to continuing minimisation of waste produced – a key principle of waste management policy in the nuclear industry. Whilst the volumes of nuclear wastes produced are very small, the most important issue for the nuclear industry is managing their toxic nature in a way that is environmentally sound and presents no hazard to both workers and the general public.

Category wise impact of nuclear waste-summary

The most significant high-level waste from a nuclear reactor is the used nuclear fuel left after it has spent about three years in the reactor generating heat for electricity. Low-level waste is made up of lightly-contaminated items like tools and work clothing from power plant operation and makes up the bulk of radioactive wastes. Items disposed of as intermediate-level wastes might include used filters, steel components from within the reactor and some effluents from reprocessing.

Generating enough electricity for one person produces just 30 grams of used fuel each year.

High-level wastes make just 3% of the total volume of waste arising from nuclear generation, but they contain 95% of the radioactivity arising from nuclear power. Low-level wastes represent 90% of the total volume of radioactive wastes, but contain only 1% of the radioactivity.

The Risk Posed by Nuclear Waste

Nuclear waste is potentially dangerous because it emits ionizing radiation, which can damage or kill cells, produce mutations and birth defects, and cause cancer. The degree of risk depends upon the level, and type, of radioactivity, with some materials being very hazardous in raw form, and others posing little threat in most circumstances.

High levels of ionizing radiation kill cells and can cause immediate life-threatening effects, while lower levels can cause genetic damage and cancer. To put things in perspective, however, nuclear waste is not necessarily more dangerous than chemical poisons, which are produced in much larger quantities. It has been estimated that public exposure to cancer-causing agents from coal-fired power stations is much greater than from nuclear waste, due to chemicals, and natural radioactive elements, released into the atmosphere from the burning of coal.

Unlike other industrial wastes, the level of hazard of all nuclear waste – its radioactivity – diminishes with time. Each radionuclidea contained in the waste 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 wastes decay into non-radioactive elements. The more radioactive an isotope is, the faster it decays.

Environmental impacts of Nuclear waste

Nuclear power provides an environmental benefit by almost entirely eliminating airborne wastes and particulates generated during power generation.  Nuclear power creates a cost in the form of relatively small volumes of radioactive wastes that are produced that must be managed prior to ultimate disposal. 

Nuclear power has been presented as providing net environmental benefits.  Specifically, nuclear power makes no contribution to global warming through the emission of carbon dioxide.  Nuclear power also produces no notable sulphur oxides, nitrogen oxides, or particulates.  When nuclear power is produced, nothing is burned in a conventional sense.  Heat is produced through nuclear fission, not oxidation. Nuclear power does produce spent fuels of roughly the same mass and volume as the fuel that the reactor takes in.  These spent fuels are kept within the reactor's fuel assemblies, thus unlike fossil fuels, which emit stack gasses to the ambient environment, solid wastes at nuclear power plants are contained throughout the generation process. No particulates or ash are emitted.

When handled properly, nuclear waste doesn't harm the environment. The small amounts that do reach the environment are insignificant compared to the large amounts of naturally occurring radioactive materials already in the environment: uranium, thorium, potassium-40, carbon-14, radon, etc.

An advantage of nuclear waste is that it will eventually decay to harmless materials. Most industrial and lab nuclear waste is harmless in a decade. Waste from a nuclear reactor will decay to the level of the original uranium in about 500 years. That's important in 500 years it is about as dangerous as it was when it was just sitting in the ground originally. After a few thousand years it's barely detectable so it is less dangerous than when it was dug up. Some other kinds of waste are dangerous literally forever: lead, arsenic, etc.

Nuclear is the safest, cleanest source of energy, and cheapest with Thorium. If disposed of properly, it does not affect the environment at all.

Sources/References:

http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-wastes/radioactive-waste-management.aspx

http://www.world-nuclear.org/nuclear-basics/what-are-nuclear-wastes.aspx

http://www.wisegeek.org/what-is-nuclear-waste.htm

http://nuclearfiles.org/menu/key-issues/nuclear-energy/issues/health-environment/moens_nuclear_power_environment.html

Book "Power to Save the World, The Truth About Nuclear Energy" by a formerly anti-nuclear author, Gwyneth Cravens, ISBN 978𔂾��𔃇.