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

in using this form of gauging or measurement is that there is no contact with the material being gauged.

Many process industries utilise fixed gauges to monitor and control the flow of materials in pipes, distillation columns, etc, usually with gamma rays.

The height of the coal in a hopper can be determined by placing high energy gamma sources at various heights along one side with focusing collimators directing beams across the load. Detectors placed opposite the sources register the breaking of the beam and hence the level of coal in the hopper. Such level gauges are among the most common industrial uses of radioisotopes.

Some machines which manufacture plastic film use radioisotope gauging with beta particles to measure the thickness of the plastic film. The film runs at high speed between a radioactive source and a detector. The detector signal strength is used to control the plastic film thickness.

In paper manufacturing, beta gauges are used to monitor the thickness of the paper at speeds of up to 400 m/s.

When the intensity of radiation from a radioisotope is being reduced by matter in the beam, some radiation is scattered back towards the radiation source. The amount of 'backscattered' radiation is related to the amount of material in the beam, and this can be used to measure characteristics of the material. This principle is used to measure different types of coating thicknesses.

READING 16-C

Gamma Sterilization

Gamma irradiation is widely used for sterilizing medical products, for other products such as wool, and for food. Cobalt-60 is the main isotope used, since it is an energetic gamma emitter. It is produced in nuclear reactors, sometimes as a by-product of power generation.

Large-scale irradiation facilities for gamma sterilization are used for disposable medical supplies such as syringes, gloves, clothing and instruments, many of which would be damaged by heat sterilization. Such facilities also process bulk products such as raw wool for export from Australia, archival documents and even wood, to kill parasites. Currently Australia sterilizes up to 25 million Queensland fruit fly pupae per week by gamma irradiation.

Smaller gamma irradiators are used for treating blood for transfusions and for other medical applications.

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Food preservation is an increasingly important application, and has been used since the 1960s. In 1997 the irradiation of red meat was approved in USA. Some 41 countries have approved irradiation of more than 220 different foods, to extend shelf life and to reduce the risk of food-borne diseases.

READING 16-D

Scientific Uses

Radioisotopes are used as tracers in many research areas. Most physical, chemical and biological systems treat radioactive and non-radioactive forms of an element in exactly the same way, so a system can be investigated with the assurance that the method used for investigation does not itself affect the system. An extensive range of organic chemicals can be produced with a particular atom or atoms in their structure replaced with an appropriate radioactive equivalent.

Using tracing techniques, research is conducted with various radioisotopes which occur broadly in the environment, to examine the impact of human activities. The age of water obtained from underground bores can be estimated from the level of naturally occurring radioisotopes in the water. This information can indicate if groundwater is being used faster than the rate of replenishment. Trace levels of radioactive fallout from nuclear weapons testing in the 1950s and 60s is now being used to measure soil movement and degradation. This is assuming greater importance in environmental studies of the impact of agriculture.

Tracing/Mixing Uses

Even very small quantities of radioactive material can be detected easily. This property can be used to trace the progress of some radioactive material through a complex path, or through events which greatly dilute the original material. In all these tracing investigations, the half-life of the tracer radioisotope is chosen to be just long enough to obtain the information required. No long-term residual radioactivity remains after the process.

Sewage from ocean outfalls can be traced in order to study its dispersion. Small leaks can be detected in complex systems such as power station heat exchangers. Flow rates of liquids and gasses in pipelines can be measured accurately, as can the flow rates of large rivers.

Mixing efficiency of industrial blenders can be measured and the internal flow of materials in a blast furnace examined. The extent of termite infestation in a structure can be found by feeding the insects radioactive

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wood substitute, then measuring the extent of the radioactivity spread by the insects. This measurement can be made without damaging any structure as the radiation is easily detected through building materials.

UNIT XVII

INDUSTRIAL USE

READING 17-A

Process Heat for Industry

• Nuclear energy is an excellent source of process heat for various industrial applications including desalination, synthetic and unconventional oil production, and in the future: hydrogen production.

It is. suggested that a single CANDU 6 reactor (about 1800 MWt) configured to produce 75 % steam and 25 % electricity would replace 6 million cubic metres per day of natural gas and support production of 175 — 200,000 barrels per day of oil. It would also save the emission of CO2.

The potential application of nuclear heat depends mainly on the temperature required. With reactor output temperatures (ROT) of up to 700 °C there is a wide range of possibilities, at 900 °C there are further possibilities, and at 950 °C an important future application to hydrogen production opens up.

Recovery of oil from tar sands

From about 2003 various proposals have been made to use nuclear power to produce steam for extraction of oil from northern oilsand (tar

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sand) deposits and electricity also for the major infrastructure involved. At present a lot of natural gas is used — up to 30 cubic metres per barrel of oil, the cost exposure increasing dramatically. In fact, natural gas is inadequate to supply the anticipated expansion in oil sands output and its use has major CO2 implications which are creating public concern — about 20 % of the energy in the oil is required to produce it and about 80 kg of CO2 per barrel is released.

The main difference between natural gas and nuclear steam generation is that a fuel-intensive process is replaced by a capital-intensive one.

Oil refining

Natural gas is a raw material for hydrogen to break down the longchain hydrocarbons to yield synthetic crude oil (about 5 kg is used per barrel). This hydrogenation of heavy crude oil is a major use of hydrogen today.

Hydrogen production is by steam reforming of the natural gas. Nuclear power could make steam and electricity and use some of the electricity for high-temperature electrolysis for hydrogen production. (Heavy water and oxygen could be a valuable by-products of electrolysis.)

Coal to liquids

The Fischer-Tropsch process was originally developed in Germany in the 1920s, and provided much of the fuel for Germany during the Second World War. It then became the basis for much oil production in South Africa. However, it is a significant user of hydrogen which is now produced by coal gasification with the water shift reaction. A nuclear source of hydrogen coupled with nuclear process heat would double the amount of liquid hydrocarbons from the coal and eliminate most CO2 emissions from the process.

Nuclear energy for hydrogen production

Nuclear power already produces electricity as a major energy carrier. It is well placed to produce hydrogen if this becomes a major energy carrier also.

The evolution of nuclear energy's role in hydrogen production over perhaps three decades is seen to be:

•electrolysis of water, using off-peak capacity,

•use of nuclear heat to assist steam reforming of natural gas,

•high-temperature electrolysis of steam, using heat and electricity from nuclear reactors, then

•high-temperature thermo chemical production using nuclear

heat.

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Steam reforming of methane requires temperatures of over 800 °C to combine methane and steam to produce hydrogen and carbon monoxide. A nuclear heat source would reduce natural gas consumption by about 30 % (i.e. that portion of feed which would simply be for heat), and eliminate CO2 emissions. Apart from this, the efficiency of the whole process (primary heat to hydrogen) moves from from about 25 % with today's reactors

The chemical plant needs to be isolated from the nearby reactor, for safety reasons, possibly using an intermediate helium or molten fluoride loop.

Three potentially-suitable reactor concepts have been identified, though only the first is sufficiently well developed to move forward with:

•High-temperature gas-cooled reactor (HTGR), either the pebble bed or hexagonal fuel block type. Modules of up to 285 MWe will operate at 950 °C but can be hotter.

•Advanced high-temperature reactor (AHTR), a modular reactor using a coated-particle graphite-matrix fuel and with molten fluoride salt as primary coolant. This is similar to the HTGR but operates at low pressure

•Lead-cooled fast reactor, though these operate at lower temperatures than the HTGRs - the best developed is the Russian BREST reactor which runs at only 540 °C. A US project is the STAR-H2 which will deliver 780 °C for hydrogen production and lower temperatures for desalination.

UNIT XVIII

NUCLEAR RENAISSANCE

READING 18-A

Reasons for the Nuclear Renaissance

Since about 2001 there has been much talk about an imminent nuclear revival or "renaissance" which implies that the nuclear industry has been dormant or in decline for some time. Whereas this may generally be the case for the Western world, nuclear capacity has been expanding in Eastern Europe and Asia. Indeed, globally, the share of nu-

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•Insurance against future price exposure

A longer-term advantage of uranium over fossil fuels is the low impact that increased fuel prices will have on the final electricity production costs, since a large proportion of those costs is in the capital cost of the plant. This insensitivity to fuel price fluctuations offers a way to stabilize power prices in deregulated markets.

•Security of Supply

A re-emerging topic on many political agendas is security of supply, as countries realize how vulnerable they are to interrupted deliveries of oil and gas. The abundance of naturally occurring uranium makes nuclear power attractive from an energy security standpoint.

As the nuclear industry is moving away from small national programmes towards global cooperative schemes, serial production of new plants will drive construction costs down and further increase the competitiveness of nuclear energy.

In practice, is a rapid expansion of nuclear power capacity possible? Most reactors today are built in under five years (first concrete to

first power), with four years being state of the art and three years being the aim with prefabrication. Several years are required for preliminary approvals before construction.

It is noteworthy that in the 1980s, 218 power reactors started up, an average of one every 17 days. These included 47 in USA, 42 in France and 18 in Japan. The average power was 923.5 MWe. So it is not hard to imagine a similar number being commissioned in a decade after about 2015. But with China and India getting up to speed with nuclear energy and a world energy demand double the 1980 level in 2015, a realistic estimate of what is possible might be the equivalent of one 1000 MWe unit worldwide every 5 days.

A relevant historical benchmark is that from 1941 to 1945, 18 US shipyards built over 2700 Liberty Ships. These were standardised 10 800 dwt cargo ships of a very basic British design but they became symbolic of US industrial wartime productivity and were vital to the war effort. Average construction time was 42 days in the shipyard, often using prefabricated modules1. In 1943, three were being completed every day. They were 135 metres long and could carry 9100 tonnes of cargo.

1As a publicity stunt, and using a lot of prefabrication, in 1942 the Robert G. Peary was launched in under five days and ready for sea three days later.

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Public acceptance

During the early years of nuclear power, there was a greater tendency amongst the public to respect the decisions of authorities licensing the plants, but this changed for a variety of reasons. No revival of nuclear power is possible without the acceptance of communities living next to facilities and the public at large as well as the politicians they elect.

The Chernobyl disaster marked the nadir of public support for nuclear power. However, this tragedy underscored the reason for high standards of design and construction required in the West. It could never have been licensed outside the Soviet Union, incompetent plant operators exacerbated the problem, and partly through Cold War isolation, there was no real safety culture. The global cooperation in sharing operating experience and best practices in safety culture as a result of the accident has been of benefit worldwide. The nuclear industry's safety record over the last 20 years is unrivalled and has helped restore public faith in nuclear power. Over this period, operating experience has tripled, from about 4000 reactor-years to more than 12,500 reactor years.

Another factor in public reassurance is the much smaller than anticipated public health effects of the Chernobyl accident. At the time many scientists predicted that tens of thousands would die as a result of the dispersal of radioactive material. In fact, according to the UN's Chernobyl Forum report, as of mid 2005, fewer than 60 deaths had been directly attributed to radiation from the disaster, and further deaths from cancer are uncertain.

One of the criticisms often levelled against nuclear power is the alleged lack of strategy and provision for its long-lived wastes. It is argued that local communities would never be prepared to host a repository for such waste. However, experience has shown in Sweden and Finland, that with proper consultation and compensation mostly in the form of long-term job prospects, communities are quite prepared to host repositories. Indeed in Sweden, two communities are currently competing to be selected for the siting of the final repository.

•New nuclear power capacity

With 30 reactors being built around the world today, another 35 or more planned to come online during the next 10 years, and over two hundred further back in the pipeline, the global nuclear industry is clearly going forward strongly. Countries with established programmes are seeking to replace old reactors as well as expand capacity, and an

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additional 25 countries are either considering or have already decided to make nuclear energy part of their power generation capacity. All parts of the world are involved in this development.

UNIT XIX

THE NUCLEAR RENAISSANCE EXAMPLES

READING 19-A

China

The Chinese government plans to increase nuclear generating capacity to 40 GWe by 2020. China has completed construction and commenced operation of eight nuclear power plants within the last five years, and there are currently eight more units under construction or about to start construction and that are planned to be connected to the grid within five years. At least eight more reactors will start construction within the next few years, and an additional 75 reactors are proposed in recent projections.

China started its nuclear power program in the 1970s and the industry has now moved to a steady development period as electricity consumption grows very rapidly.

China has 11 nuclear power reactors in operation, giving 8.6 GWe capacity, and 12 more under construction or about to start construction, taking the total to 22 GWe capacity. Another 19 are expected to start construction, which will give 40 GWe total by 2020.

Its operational reactors generated 52 billion kWh of electricity to the national grid in 2006, representing 1.9 % of total electricity generation in the country.

Most electricity produced in China is supplied by fossil fuels (about 80 %, mainly coal) and hydro power (about 18 %). Nuclear power has an important role, especially in the coastal areas remote from the coalfields and where the economy is developing rapidly.

China has set the following points as key elements of its nuclear energy policy:

•PWRs will be the mainstream but not sole reactor type;

•nuclear fuel assemblies are fabricated and supplied indige-

nously;

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•domestic manufacturing of plant and equipment will be maximised, with self-reliance in design and project management;

•international cooperation is nevertheless encouraged.

India

India's target is to construct 20 to 30 new reactors by 2020 as part of its national energy policy. These reactors include lightand heavy water reactors as well as fast reactors. Seven power reactors are under construction, of both indigenous and foreign design, and including a 500 MWe prototype fast breeder reactor. This will take India's ambitious thorium programme to stage 2, and set the scene for eventual utilization of the country's abundant thorium to fuel reactors.

Russia

Russia plans to build 40 GWe of new nuclear power by 2025, using domestically designed light water reactors. Construction of a large fast breeder unit has been prioritised, and development proceeds on others, aiming for significant exports. An initial floating power plant is under construction, with delivery in 2010.

EUROPE

Finland and France

Are both expanding their fleets of nuclear power plants with the 1600 MWe EPR from Areva, 40 of which will eventually replace all present French units. Several countries in Eastern Europe are currently constructing (Romania) or have firm plans to build new nuclear power plants (Bulgaria, Czech Republic, Romania, Slovakia, Slovenia and Turkey). Italy is considering a revival of its scrapped nuclear program, and has already invested in reactors in Slovakia and sought to do so in France.

A UK government energy paper in mid 2006 endorsed the replacement of the country's ageing fleet of nuclear reactors with new nuclear build. Sweden has abandoned its plans to prematurely decommission its nuclear power, and is now investing heavily in life extensions and uprates. Hungary, Slovakia and Spain are all planning for life extensions on existing plants.

A number of countries are considering developing nuclear programmes, among them Poland with Estonia and Latvia, who are looking into a joint project with established nuclear power producer Lithuania.

NORTH AMERICA

Canada

The Ontario government has decided to refurbish and restart four reactors adding 25 years to operating lifetime as a step in its plan to expand its nuclear fleet. Two more reactors will be needed for Ontario under mid 2006 policy.

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