Воробева Нуцлеар Реацтор Тыпес (Леарн то реад бы реадинг) 2010

through a millimetre-high gold cone inside the compressed fuel, and timed to coincide with the peak compression. This technique means that fuel compression is separated from hot spot generation with ignition, making the process more practical.

So far most inertial confinement work has involved lasers, although their low energy makes it unlikely that they would be used in an actual fusion reactor. The world's most powerful laser fusion facility is the NOVA at Lawrence Livermore Laboratory in the US, and declassified results show compressions to densities of up to 600 times that of the D- T liquid. Various light and heavy ion accelerator systems are also being studied, with a view to obtaining high particle densities.

Cold fusion

In 1989, spectacular claims were made for another approach, when two researchers, in USA and UK, claimed to have achieved fusion in a simple tabletop apparatus working at room temperature. Other experimenters failed to replicate this "cold fusion", however, and most of the scientific community no longer considers it a real phenomenon. Nevertheless, research continues. Cold fusion involves the electrolysis of heavy water using palladium electrodes on which deuterium nuclei are said to concentrate at very high densities.

Fusion history

Today, many countries take part in fusion research to some extent, led by the European Union, the USA, Russia and Japan, with vigorous programs also under way in China, Brazil, Canada, and Korea. Initially, fusion research in the USA and USSR was linked to atomic weapons development, and it remained classified until the 1958 Atoms for Peace conference in Geneva. Following a breakthrough at the Soviet tokamak, fusion research became big science in the 1970s. But the cost and complexity of the devices involved increased to the point where international co-operation was the only way forward.

In 1978, the European Community (with Sweden and Switzerland) launched the JET project in the UK. JET produced its first plasma in 1983, and saw successful experiments using a D-T fuel mix in 1991. In the USA, the PLT tokamak at Princeton produced a plasma temperature of more than 60 million degrees in 1978 and D-T experiments began on the Tokamak Fusion Test Reactor (TFTR) there in 1993. In Japan, experiments have been carried out since 1988 on the JT-60 Tokamak.

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JET

JET is the largest tokamak operating in the world today. Up to 16 MW of fusion power for one second has been achieved in D-T plasmas using the device and many experiments are conducted to study different heating schemes and other techniques. JET has been very successful in operating remote handling techniques in a radioactive environment to modify the interior of the device and has shown that the remote handling maintenance of fusion devices is realistic.

In 2001 the US Department of Energy (DOE) and the EU agreed to conduct joint research in fusion energy extending an umbrella fusion agreement signed in 1986 between Europe and the DOE. Areas of cooperation include tokamaks, alternatives to tokamaks, magnetic fusion energy technology, plasma theory and applied plasma physics.

ITER

In 1985, the Soviet Union suggested building a next generation tokamak with Europe, Japan and the USA. Collaboration was established under the auspices of the International Atomic Energy Agency (IAEA). Between 1988 and 1990, the initial designs were drawn up for an International Thermonuclear Experimental Reactor (ITER) with the aim of proving that fusion could produce useful energy. The four parties agreed in 1992 to collaborate further on Engineering Design Activities for ITER (ITER is both an acronym, and means 'a path' or 'journey' in Latin). Canada and Kazakhstan are also involved through Euratom and Russia respectively.

Six years later, the ITER Council approved the first comprehensive design of a fusion reactor based on well-established physics and technology with a price tag of US$ 6 billion. Then the USA decided pull out of the project, forcing a 50 % reduction in costs and a redesign. The result was the ITER — Fusion Energy Advanced Tokomak (ITERFEAT) — expected to cost $3 billion but still achieve the targets of a self-sustaining reaction and a net energy gain. The energy gain is unlikely to be enough for a power plant, but it will demonstrate feasibility.

In 2003 the USA rejoined the project and China also announced it would do so. After deadlocked discussion, the six partners agreed in mid 2005 to site ITER at Cadarache, in southern France. The deal involved major concessions to Japan, which had put forward Rokkasho as a preferred site. The EU and France will contribute half of the EUR 12.8 billion total cost, with the other partners — Japan, China, South Korea, USA and Russia — putting in 10 % each. Japan will provide a lot of the high-tech components, will host an EUR 1 billion materials testing facility and will have the right to host a subsequent demonstration fusion reactor. The total cost of the 500 MWt ITER comprises about half for the ten-year construction and half for 20 years of operation.

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In November 2006 China, India, Japan, Russia, South Korea, the USA and the European Union — signed the ITER implementing agreement. The French President praised the attempt to "tame solar fire to meet the challenge of ecological energy."

Assessing fusion power

The use of fusion power plants could substantially reduce the environmental impacts of increasing world electricity demands since, like nuclear fission power, they would not contribute to acid rain or the greenhouse effect. Fusion power could easily satisfy the energy needs associated with continued economic growth, given the ready availability of fuels. There would be no danger of a runaway fusion reaction as this is intrinsically impossible and any malfunction would result in a rapid shutdown of the plant.

However, although fusion generates no radioactive fission products or transuranic elements and the unburned gases can be treated on site, there would a short-term radioactive waste problem due to activation products. Some component materials will become radioactive during the lifetime of a reactor, due to bombardment with high-energy neutrons, and will eventually become radioactive waste. The volume of such waste would be similar to that due to activation products from a fission reactor. The radio toxicity of these wastes would be relatively shortlived compared with the actinides (long-lived alpha-emitting transuranic isotopes) from a fission reactor.

There are also other concerns, principally regarding the possible release of tritium into the environment. It is radioactive and very difficult to contain since it can penetrate concrete, rubber and some grades of steel. As an isotope of hydrogen, it is easily incorporated into water, making the water itself weakly radioactive. With a half-life of 12.4 years, tritium remains a threat to health for about 125 years after it is created, as a gas or in water. It can be inhaled, absorbed through the skin or ingested. Inhaled tritium spreads throughout the soft tissues and triturated water mixes quickly with all the water in the body. Each fusion reactor could release significant quantities of tritium during operation through routine leaks, assuming the best containment systems. An accident could release even more. This is one reason why long-term hopes are for the deuterium-deuterium fusion process, dispensing with tritium.

While fusion power clearly has much to offer when the technology is eventually developed, the problems associated with it also need to be addressed if is to become a widely used future energy source. Much will change before fusion power is commercialized, including the development of new materials.

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Annex 19

A look at the future of nuclear power

Younger people have revealed visions

of a 21st century nuclear power plant, at ease in its environment

Nuclear power plants should have their features blended into the environment as much as possible, while boasting strong, hi-tech design for the components that remain on view. Placing reactors underground was a popular suggestion, as was improving materials used for large highly visible structures like containment domes and cooling towers.

Many thanks to those readers that submitted their own ideas of the way nuclear power plants should be designed in the modern era. Some of the best are reproduced below.

Aleš Buršič blends power plant features with the environment through the use of earth coverings. A hybrid cooling tower is sunken to reduce its visual impact and the 'green barrier' also helps in protection from external hazards.

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Spain-based architecture firm with nuclear experience IDOM-ACXT proposes a living skin sustained by rainwater to cover the main plant structures. Left, making a natural feature from an artifice, its appearance would change through the seasons.

Another IDOM ACTX design sees an second skin erected which would be opaque in sunlight and translucent at night. Night-time lighting transforms the power plant into a new landmark.

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Christian Raetzke's hand drawings show a modern nuclear power plant benefiting from eccentric and modern superstructures that give a new outline to familiar technology. Left, a traditional nuclear plant gets retro treatment, including a Greco-Roman facade.

Carlton Stoiber proposes specialised designs as approved by senior nuclear industry figures. An undersea unit boasts a reliable source of cooling water, while a pyramid superstructure has the advantages of operating experience and seismic safety.

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BASIC GLOSSARY

A

Actinide: An element with atomic number of 89 (actinium) to 102. Usually applied to those above uranium — 93 up (also called transuranics). Actinides are radioactive and typically have long half-lives. They are therefore significant in wastes arising from nuclear fission, e.g. used fuel. They are fissionable in a fast reactor.

Activation product: A radioactive isotope of an element (e.g. in the steel of a reactor core) which has been created by neutron bombardment.

Activity: The number of disintegrations per unit time inside a radioactive source. Expressed in becquerels.

ALARA: As Low As Reasonably Achievable, economic and social factors being taken into account. This is the optimisation principle of radiation protection.

B

Base load: That part of electricity demand which is continuous, and does not vary over a 24-hour period. Approximately equivalent to the minimum daily load.

Biological shield: A mass of absorbing material (eg thick concrete walls) placed around a reactor or radioactive material to reduce the radiation (especially neutrons and gamma rays respectively) to a level safe for humans.

Boiling water reactor (BWR): A common type of light water reactor (LWR), where water is allowed to boil in the core thus generating steam directly in the reactor vessel.

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Breed: To form fissile nuclei, usually as a result of neutron capture, possibly followed by radioactive decay.

Breeder reactor: see Fast Breeder Reactor and Fast Neutron Reactor.

Burn: cause to fission.

Burnable poison: A neutron absorber included in the fuel which progressively disappears and compensates for the loss of reactivity as the fuel is consumed. Gadolinium is commonly used.

Burnup: Measure of thermal energy released by nuclear fuel relative to its mass, typically Gigawatt days per tonne (GWd/tU).

C

Calandria: (in a CANDU reactor) a cylindrical reactor vessel which contains the heavy water moderator. It is penetrated from end to end by hundreds of calandria tubes which accommodate the pressure tubes containing the fuel and coolant.

CANDU: Canadian deuterium uranium reactor, moderated and (usually) cooled by heavy water.

Cladding: The metal tubes containing oxide fuel pellets in a reactor core.

Control rods: Devices to absorb neutrons so that the chain reaction in a reactor core may be slowed or stopped by inserting them further, or accelerated by withdrawing them.

Conversion: Chemical process turning U3O8 into UF6 preparatory to enrichment.

Coolant: The liquid or gas used to transfer heat from the reactor core to the steam generators or directly to the turbines.

Core: The central part of a nuclear reactor containing the fuel elements and any moderator.

Critical mass: The smallest mass of fissile material that will support a self-sustaining chain reaction under specified conditions.

Criticality: Condition of being able to sustain a nuclear chain reaction.

D

Decommissioning: Removal of a facility (eg reactor) from service, also the subsequent actions of safe storage, dismantling and making the site available for unrestricted use.

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Delayed neutrons: neutrons released by fission products up to several seconds after fission. These enable control of the fission in a nuclear reactor.

Depleted uranium: Uranium having less than the natural 0.7 % U-235. As a by-product of enrichment in the fuel cycle it generally has 0.25 — 0.30 % U-235, the rest being U-238. Can be blended with highly-enriched uranium (eg from weapons) to make reactor fuel.

Deuterium: "Heavy hydrogen", a stable isotope having one proton and one neutron in the nucleus. It occurs in nature as 1 atom to 6500 atoms of normal hydrogen, (Hydrogen atoms contain one proton and no neutrons).

Dose: The energy absorbed by tissue from ionising radiation. One gray is one joule per kg, but this is adjusted for the effect of different kinds of radiation, and thus the sievert is the unit of dose equivalent used in setting exposure standards.

E

Enriched uranium: Uranium in which the proportion of U-235 (to U-238) has been increased above the natural 0.7 %. Reactor-grade uranium is usually enriched to about 3.5 % U-235, weapons-grade uranium is more than 90 % U-235.

F

Fast breeder reactor (FBR): A fast neutron reactor (qv) configured to produce more fissile material than it consumes, using fertile material such as depleted uranium in a blanket around the core.

Fast neutron: neutron released during fission, travelling at very high velocity (20 000 km/s) and having high energy (c 2 MeV).

Fast neutron reactor: A reactor with no moderator and hence utilising fast neutrons. It normally burns plutonium while producing fissile isotopes in fertile material such as depleted uranium (or thorium).

Fossil fuel: A fuel based on carbon presumed to be originally from living matter, eg coal, oil, gas. Burned with oxygen to yield energy.

Fuel assembly: Structured collection of fuel rods or elements, the unit of fuel in a reactor.

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Fuel fabrication: Making reactor fuel assemblies, usually from sintered UO2 pellets which are inserted into zircalloy tubes, comprising the fuel rods or elements.

G

Giga: One billion units (eg gigawatt = 109 watts or million kW). Graphite: Crystalline carbon used in very pure form as a moderator,

principally in gas-cooled reactors, but also in Soviet-designed RBMK reactors.

Gray: The SI unit of absorbed radiation dose, one joule per kilogram of tissue.

Greenhouse gases: Radiative gases in the earth's atmosphere which absorb long-wave heat radiation from the earth's surface and re-radiate it, thereby warming the earth. Carbon dioxide and water vapour are the main ones.

H

Heavy water: Water containing an elevated concentration of molecules with deuterium ("heavy hydrogen") atoms.

Heavy water reactor (HWR): A reactor which uses heavy water as its moderator, eg Canadian CANDU (pressurised HWR or PHWR).

High-level wastes: Extremely radioactive fission products and transuranic elements (usually other than plutonium) in used nuclear fuel. They may be separated by reprocessing the used fuel, or the spent fuel containing them may be regarded as high-level waste.

Highly (or High)-enriched uranium (HEU): Uranium enriched to at least 20 % U-235. (That in weapons is about 90 % U-235.)

I

Ionising radiation: Radiation (including alpha particles) capable of breaking chemical bonds, thus causing ionisation of the matter through which it passes and damage to living tissue.

Irradiate: Subject material to ionising radiation. Irradiated reactor fuel and components have been subject to neutron irradiation and hence become radioactive themselves.

Isotope: An atomic form of an element having a particular number of neutrons. Different isotopes of an element have the same number of protons but different numbers of neutrons and hence different atomic mass,

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