Nuclear power has three main problems: safety, economics and waste disposal. Half a million tonnes of highly dangerous radioactive waste has been produced by the nuclear industry, and no foolproof solution to its disposal has been found.
Nuclear waste is radioactive material which is dangerous for human health and the environment, and is subject to special laws and regulations with regards its disposal, transport and storage. Half a million tonnes of high-level nuclear waste has been generated in the world's 500 nuclear power stations. After more than half a century of nuclear power, a corresponding stockpile of political, economic and environmental liabilities have accumulated to mountainous dimensions.
The optimism of the 1950s in nuclear power foresaw two things:
- Nuclear power would provide nearly limitless, inexpensive energy, and
- Technological advances would solve the problem of nuclear waste and other risks.
Needless to say, neither of these has been achieved - far from it:
- Nuclear power never produced more than 5% of world electricity, and is one of the most expensive forms of energy, and
- Technology has not found a definitive solution for the safe disposal of half a million tonnes of useless waste, leaving the world with a dangerous, hard to manage legacy for tens of thousands of years.
Two systems are proposed for handling waste from nuclear fission in reactors: geological storage and transmutation.
The fuel in a nuclear reactor core generates heat from the chain reaction of neutrons from one fission event striking other nuclei, which in turn undergo fission, generating neutrons, which strike other nuclei... and so on, millions of times per second.
When a nuclear reactor is shut down, the fuel rods are removed and placed in a temporary storage tank, under water. The water cools the rods and absorbs the neutrons which are still leaving the uranium or plutonium fuel. Although the chain reaction has ceased, since most of the neutrons are being absorbed by the water, and not reaching the nuclei of other uranium atoms, there is still a fair amount of heat being produced by the beta decay of the fission products in the fuel. This heat generation continues until the unstable isotopes have all been transmuted to stable isotopes, which do not decay.
This decay heat is initially 7% of the chain reaction energy, and within a day is only 4%. The rate of heat generation slowly decreases over time. Although this rate is small compared to the reactor chain reaction heat, the fuel rods need to be kept for a matter of years before they are ready to be placed in more permanent storage.
According to the IAEA, by 2020 there will be worldwide a total of 445 kt (approx. 20 000 m3) of spent fuel, for which the only solution is long-term deep geological depository. Storage is so far only in temporary water tanks, but storage capacity is close to exhaustion.
Transmutation is the conversion of radioactive isotopes to less dangerous isotopes, usually through bombardment with neutrons. An example of transmutation is the conversion of technetium-99c. The target is bombarded with neutrons to create the isotope technetium-100Tc, which has a very short half-life, decaying to the non-radioactive ruthenium-100. So far, transmutation is not a viable solution to uranium and plutonium waste.
Vienna Joint Convention on Radioactive Waste
The Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management (Vienna, 1997) is an IAEA global treaty covering the transport and storage of radioactive waste. It currently has 71 state parties.
Download: Vienna Joint Convention - English (pdf 67 kB)
Full name: Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management
Radioactive wastes are divided into three classifications: high-level (over 1015 Bq m-3), medium-level (1010 to 1015 Bq m-3), and low-level (less than 1010 Bq m-3). High-level wastes generate high levels of heat through ongoing decay processes, typically in the range 2-20 kW m-3.
There are 7 long-lived radio-isotopes in spent nuclear fuel: selenium-79, zirconium-93, technetium-99, palladium-107, tin-126, iodine-129, and caesium-135.
Isotope Half-life /My Decay mode Decay energy /MeV Decay product Yield (U-235) /% Note 7934Se 0.327 *1 β- 0.15 7935Br 0.045 bio-accumulating with nitrate 9340Zr 1.53 β- γ 0.091 9341Nb 5.46 low soil mobility, suitable for geological storage 9943Tc 0.211 β- 0.294 9944Ru 6.14 environmentally mobile, significant component of nuclear waste, may be transmuted artificially 10746Pd 6.5 β- 0.033 10747Ag 1.25 not amenable to disposal by nuclear transmutation, less environmentally mobile I and Tc 12650Sn 0.230 β- γ 4.050 12651Sb 0.108 gamma emitted from decay product (antinomy-126) 12953I 15.7 β- γ 0.194 12954Xe 0.841 high long-term risk since environmentally mobile and long-lived, potential for transmutation (neutron bombardment or lasers) under study 13555Cs 2.3 β- 0.269 13556Ba 6.911 disposal by nuclear transmutation difficult, intense medium-term radiation
*1 Uncertainty in the half-life of Selenium-79 gives measurements/estimates in the range 6.5 × 104 to 1.13 × 106 years.
The half-life is a measure of the activity of a radioactive substance. Since nucleus decay rates are exponentially decreasing over time, a mass will theoretically never lose all of its radioactivity. Statistically, the decay rate is best described by the period of time it takes for half of the original population to decay - the half-life.
For any mass of a radioactive substance, there is an exponentially decreasing number of decay events through time. After one half-life, half of the isotopes have decayed. After a second half-life has elapsed, half of the remaining isotopes (i.e. one-quarter of the original amount) will have decayed (leaving only 1/4). After a third half-life, one-eighth remain. Four half-lives: 1/16, and so on.
The most abundant isotope of uranium is U-238. This isotope has 92 protons and 146 neutrons, and accounts for 99.274% of all naturally-occurring uranium. The next most abundant isotope is U-235, with only 0.720% abundance. The difference in abundances can be understood by comparing the half-lives: the half-life of U-238 is 4.47 x 109 years, while that of U-235 is 7.04 x 108 years.
Nuclear Waste Depositories
The Atomgesetz is the German law governing the peaceful use of atomic energy and the protection against its dangers sets clear regulations concerning the handling, transport, and storage of nuclear waste.
German National Disposal Programme
The German Federal Disposal Programme (§ 2c) is based on the following principles:
- the production of radioactive waste is limited by means of appropriate design, and operating and decommissioning procedures, including the further use and reuse of materials, to the extent that is reasonably feasible in terms of activity and volume of radioactive waste;
- interdependencies of the different steps in the occurrence and in the management of spent fuel and radioactive waste are considered;
- spent fuel and radioactive waste is safely managed, taking into account aspects of passive safety and long-term safety;
- the implementation of measures shall follow a step-by-step approach;
- the costs of the management of spent fuel and radioactive waste shall be borne by the waste producers;
- relating to all stages of spent fuel and radioactive waste, an evidence based and documented decision-making process is applied.
The Yucca Mountain Nuclear Waste Depository, Nevada USA, was approved by the US Congress in 2002 as a deep geological repository for high level radioactive waste. The project was heavily criticised and opposed by the general public and many politicians, and was cancelled in 2011.
The site is next to the Nevada Test Site in Nye County, Nevada. The cancellation of the project was officially for political reasons rather than technical or safety concerns.
Nuclear waste (70 thousand tonnes in the USA as of 2015) is currently being held in temporary storage facilities around the country, mostly at or close to the reactors producing the waste.
The prime candidate to supersede Yucca Mountain is WIPP (Waste Isolation Pilot Plant), a deep geological repository in New Mexico.
Nuclear energy problems
Countries like Germany and Switzerland are abolishing their nuclear energy industries, for three main reasons.
1. Nuclear Waste
We do not really have a guaranteed long-term system to store the used uranium for the tens of thousands of years necessary before it is sufficiently less dangerous (it will never be completely safe).
For issues concerning nuclear waste management see the article on 'Nuclear Waste' (click and follow link).
2. Nuclear Accidents
Plant safety has not had a clean record. There have been many accidents involving reactor operations and waste management. The radioactive materials from reactors can cause ionising radiation, which is dangerous for health and the environment. Radioactive fall-out plays very much into a primeval fear. There are also the problems of nuclear terrorism and proliferation of nuclear materials and technology, making the world a less safe place.
For accidents and proliferation issues see the article on 'Nuclear Safety' (click and follow link).
On the plus side, nuclear power generation requires the least space of all the energy sources: 0.5 km2/TWh, compared to, say, wind power, 72 km2/TWh.
Energy Returned on Energy Invested, ERoEI: Nuclear = 5-15 (optimised plants up to 24), Photovoltaic (P/V) 3-7, Wind 16-25, Hydro = 10-270 (very dependent on location). Some reports claim the ERoEI for a new generation of nuclear power plant could be in the hundreds, but for now this remains theoretical.
Uranium supply and economic efficiency: far from being 'almost free', as was first touted in the 1950s, the costs of the nuclear industry still outweigh most other forms of electricity production. The high costs of decommissioning aged plants were typically grossly underestimated in original planning, if they were accounted for at all. As Germany is experiencing, there is no way to have the nuclear industry balance its books without the public purse picking up a large part of the tab.
Insight EU provides the following breakdown of energy subsidies in Europe in 2011: Nuclear = 35 billion Euro, Renewable energy = 30 billion Euro, Fossil fuels = 26 billion Euro, Efficiency measures = 15 billion euro. A large part of the subsidies for nuclear power is in the form of liability insurance, which guarantees the state pays for the costs following severe reactor incidents.
The German federal and Länder governments spent between 1956 and 2006 of the order of 50 billion euro on nuclear energy research and technology. This does not include decommissioning costs for installations, which amounted to 2.5 billion Euro, and 6.6 billion Euro for uranium mining redevelopment. Nuclear power stations in Germany in 2009 had an average operational availability of 74.2%.
Nuclear power is expensive and its waste product, depleted uranium fuel, must be stored for tens of thousands of years till it is 'safe'. Accidents can cause leaks of radiative material which leave large areas of land uninhabitable due to contamination, as well as spreading through the groundwater and sea, entering the human foodchain through fish.
Ticino, Switzerland, received a lot of radiation from the Chernobyl nuclear accident in 1986, from a contaminated raincloud. Japan, Russia, Ukraine, and the USA have all suffered serious nuclear accidents, releasing deadly radiation which will contaminate land, water, and food for thousands of years.
It is being phased out in Germany and Switzerland, but France still makes 75% of its electricity from nuclear power. Italy does not use nuclear power at all. Nuclear reactors in 2015 produced 13% of the world's electricity.