Course Objectives• Understand what is radioactivity

• How does radio activity produce energy E=MC^2

• Model of nucleus Liquid drop model

• Isotopes, binding energy

• What is fusion and fission

• How does a fission reactor work

• Uranium and safety

So you have always wanted to be a Nuclear Physicist

• Lets look at the physics first

Nuclear Nomenclature

Nucleon A proton or neutron.

Atomic Number, Z: The number of protons in a nucleus.

Atomic Mass number, A: The number of nucleons in a nucleus.

Nuclide A nucleus with a specified value of A and Z.

Ni means Nickel with 28 protons and

a further 28 neutrons.

Isotope Nucleus with a given atomic number but different atomic mass number i.e. different number of neutrons.

Isotopes have very similar atomic and

chemical behaviour but may have very

different nuclear properties.

Isotone Nulceus with a given number

of neutrons but a different number of

protons (fixed (A-Z)).

Isobar Nucleus with a given A but a

different Z.

Mirror Nuclei Two nuclei with odd A in

which the number of protons in one

nucleus is equal to the number of

neutrons in the other and vice versa.

Binding Energy Liquid Drop Model

The mass of a nuclide is given by

Mn = Z Mp + (A-Z) Mn + B(A,Z)/c2

where B(A,Z) is the binding energy of the nucleons and depends on both Z and A.

The binding energy is due to the strong short-range nuclear forces that bind the nucleons together.

Unlike Coulomb binding these cannot even in principle be calculated analytically as the strong forces are much less well understood than electromagnetism.

Binding energies per nucleon increase sharply as A increases, peaking at iron (Fe) and then decreasing slowly for the more massive nuclei.

Semi-Empirical Mass Formula

For most nuclei (nuclides) with A > 20 the binding energy is well reproduced by a semi-empirical formula based on the idea the the nucleus can be thought of as a liquid drop.

1. Volume term: Each nucleon has a binding energy which binds it to the nucleus.

Therefore we get a term proportional to the volume

i.e. proportional to Av * A

This term reflects the short-range nature of the strong forces. If a nucleon interacted with all other nucleons we would expect an energy term of proportional to A(A-1), but the fact that it turns out to be proportional to A indicates that a nucleon only interact with its nearest neighbours.

Liquid drop

Surface term: The nucleons at the surface of the `liquid drop' only interact with other nucleons inside the nucleus, so that their binding energy is reduced. This leads to a reduction of the binding energy proportional to the surface area of the drop, i.e. proportional to A2/3

= As * A2/3

Liquid Drop - Coulomb term

Coulomb term: Although the binding energy is mainly due to the strong nuclear

force, the binding energy is reduced owing to the Coulomb repulsion between the

protons. We expect this to be proportional to the square of the nuclear charge, Z,

( the electromagnetic force is long-range so each proton interacts with all the others),

and by Coulomb's law it is expected to be inversely proportional to the nuclear radius,

(the Coulomb energy of a charged sphere of radius R and charge Q is 3Q2/(20πε0R)

The Coulomb term is therefore proportional to 1/A1/3

= Ac * Z2 / A1/3

Liquid Drop - Asymmetry term

This is a quantum effect arising from the Pauli exclusion principle which only allows two protons or two neutrons (with opposite spin direction) in each energy state. If a nucleus contains the same number of protons and neutrons then for each type the protons and neutrons fill to the same maximum energy level (the `Fermi level'). If, on the other hand, we exchange one of the neutrons by a proton then that proton would be required by the exclusion principle to occupy a higher energy state, since all the ones below it are already occupied.

The upshot of this is that nuclides with Z = N = (A-Z) have a higher binding energy, whereas for nuclei with different numbers of protons and neutrons (for fixed A) the binding energy decreases as the square of the number difference. The spacing between energy levels is inversely proportional to the volume of the nucleus - this can be seen by treating the nucleus as a three-dimensional potential well- and therefore inversely proportional to A. Thus we get a term

= Aa * (Z - N)2 / A

Liquid Drop - Pairing term

Pairing term: It is found experimentally that two protons or two neutrons bind more strongly than one proton and one neutron.

In order to account for this experimentally observed phenomenon we add a term to the binding energy if number of protons and number of neutrons are both even, we subtract the same term if these are both odd, and do nothing if one is odd and the other is even.

Bohr and Mottelson showed that this term was inversely proportional to the square root of the atomic mass number.

We therefore have a term

= Ap ( (-1)Z + (-1)N) / ( 2 A1/2)

Full model

B( A, Z ) = Av * A + As * A2/3 + Ac * Z2 / A1/3 + Aa * (Z - N)2 / A +

Ap ( (-1)Z + (-1)N) / ( 2 A1/2)

From fitting to the measured nuclear binding energies, the values of the parameters are

Av = 15:56 MeV

As = 17:23 MeV

Ac = 0:697 MeV

Aa = 23:285 MeV

Ap = 12:0 MeV

For most nuclei with A > 20 this simple formula does a very good job of determining the binding energies - usually better than 0.5%.

Most stable Isotopes from liquid model

Nuclear decay

Alpha decay

Beta decay

Gamma decay

Positron emission

Electron capture

Nuclear Decay are important if you are interested in blowing up large parts of the world,

If you want to make huge quantities of energy without creating huge quantities of pollution,

and they’re important if you’re a doctor who wants to use radiation to treat various diseases.

Alpha Decay

Alpha decay

Alpha decay occurs when helium nuclei come flying off of the nucleus of a larger isotope, forming an isotope with a smaller mass. These helium nuclei are called alpha particles, and are the same things that Rutherford busily shot at a sheet of goldfoil during his experiment where he discovered the nucleus. When an atom undergoes alpha decay, the atomic number of the atom decreases by two and the atomic mass decreases by four. An example of alpha decay is shown below:

Beta decay

Beta decay is when an electron (called in this context a “beta particle”) is emitted from the nucleus of an atom, essentially turning a neutron into a proton. As a result, the atomic number of the element increases by one, while the mass stays virtually unchanged. An example of a beta decay is shown. A neutrino is also released and carries away energy.

Gamma decay

Gamma decay is when very high energy light called a gamma ray is emitted from a nucleus to bring it to a lower energy state. Gamma decay generally takes place at the same time as other nuclear reactions:

Positron emission

Positron emission is when a positron is given off by a nucleus. Positrons are the antimatter equivalent to electrons, so they have very little mass and a charge of +1. Positron emission causes the atomic number of the element to decrease and the atomic mass to stay unchanged. A neutrino is also released.

Electron capture

Electron capture is when an electron is absorbed by the nucleus of an atom, causing the atomic number to decrease by one and the atomic mass to stay unchanged. An example of an electron capture is shown below:

Usually unstable nuclides are clearly either

"neutron rich" or "proton rich", with the former

undergoing beta decay and the latter undergoing

electron capture (or more rarely, due to the higher

energy requirements, positron decay). However, in

a few cases of odd-proton, odd-neutron

radionuclides, it may be energetically favourable

for the radionuclide to decay to an even-proton,

even-neutron isobar either by undergoing beta-

positive or beta-negative decay. An often-cited

example is 6429Cu, which decays by positron

emission 61% of the time to 6428Ni, and 39% of the

time by (negative) beta decay to 6430Zn.

A beta-stable nucleus may undergo other kinds of

radioactive decay (alpha decay, for example). In

nature, most isotopes are beta stable, but a few

exceptions exist with half-lives so long that they

have not had enough time to decay since the

moment of their nucleosynthesis. One example is

the odd-proton odd-neutron nuclide 4019K, which

undergoes all three types of beta decay (β−, β+and

electron capture) with a half-life

of 1.277×109 years.

Half-Life wikipedia

• Half-life (t½) is the time required for a quantity to fall to half its value as measured at the beginning of the time period. In physics, it is typically used to describe a property of radioactive decay, but may be used to describe any quantity which follows an exponential decay.

• The original term, dating to Ernest Rutherford's discovery of the principle in 1907, was "half-life period", which was shortened to "half-life" in the early 1950s.

• Half-life is used to describe a quantity undergoing exponential decay, and is constant over the lifetime of the decaying quantity. It is a characteristic unit for the exponential decay equation. The term "half-life" may generically be used to refer to any period of time in which a quantity falls by half, even if the decay is not exponential. For a general introduction and description of exponential decay, see exponential decay. For a general introduction and description of non-exponential decay, see rate law.

• The converse of half-life is doubling time.

• The table on the right shows the reduction of a quantity in terms of the number of half-lives elapsed.

Number of

half-lives

elapsed Fraction

remaining Percentage

remaining

0 1/1 100

1 1/2 50

2 1/4 25

3 1/8 12.5

4 1/16 6.25

5 1/32 3.125

6 1/64 1.563

7 1/128 0.781

... ... ...

n 1/2n 100/(2n)

http://www.world-nuclear.org/Nuclear-Basics/

• Nuclear energy is used to generate around 13% of the world's

electricity, with almost no greenhouse gas emissions.

• A single uranium fuel pellet contains as much energy as 480 cubic

metres of natural gas, 807 kilos of coal or 149 gallons of oil.

What is radiation?Radiation is energy travelling through space in the form of alpha, beta, gamma, neutrino, light (hard soft).Sunshine is one of the most familiar forms of radiation. It delivers light, heat and suntans. While enjoying and depending onit, we control our exposure to it.

Beyond ultraviolet radiation from the sun are higher-energy kinds of radiation which are used in medicine and which we all get in low doses from space, from the air, and from the earth and rocks. Radiation with enough energy to knock of an electron from a gas atom is called ionizing radiation. Neutrinos and red light are not ionizing.

Ionizing radiation can cause damage to matter, particularly living tissue. At high levels it is therefore dangerous, so it is necessary to control our exposure. Living things have evolved in an environment which has significant levels of ionizing radiation.

Furthermore, many people owe their lives and health to such radiation produced artificially. Medical and dental X-rays discern hidden problems. Other kinds of ionizing radiation are used to diagnose ailments, and some people are treated with radiation to cure disease.

Ionizing radiation, such as occurs from uranium ores and nuclear wastes, is part of our human environment, and always has been so. At high levels it is hazardous, but at low levels such as we all experience naturally, it is harmless. Considerable effort is devoted to ensuring that those working with nuclear power are not exposed to harmful levels of radiation from it. Standards for the general public are set about 20 times lower still, well below the levels normally experienced by any of us from natural sources.

How much do radiation do we get from nuclear power industry

Background radiation is that ionizing radiation which is naturally and inevitably present in our environment. Levels of this can vary greatly. People living in granite areas or on mineralised sands receive more terrestrial radiation than others, while people living or working at high altitudes receive more cosmic radiation. A lot of our natural exposure is due to radon, a gas which seeps from the Earth's crust and is present in the air we breathe.

Radioactivity in materialApart from the normal measures of mass and volume, the amount of radioactive material is measured in Becquerel (Bq), which enables us to compare the typical radioactivity of some natural and other materials. A Becquerel is one atomic decay per second, so a household smoke detector with 30,000 Bq contains enough americium to produce that much disintegration per second. A kilogram of coffee or granite might have 1000 Bq of activity and an adult human 7000 Bq. Each atomic disintegration produces some ionizing radiation.all experience radiation from natural sources every dayAlpha particles Because of their relatively large size, alpha particles collide readily with matter and lose their energy quickly. They therefore have little penetrating power and can be stopped by the first layer of skin or a sheet of paper. But inside the body they can inflict more severe biological damage than other types of radiation.

Beta particles are much smaller than alpha particles and can penetrate up to 1 to 2 centimetres of water or human flesh. They can be stopped by a sheet of aluminium a few millimetres thick.

Gamma rays, like light, represent energy transmitted in a wave without the movement of material, just like heat and light. Gamma rays and X-rays are virtually identical except that X-rays are generally produced artificially rather than coming from the atomic nucleus. But unlike light, these rays have great penetrating power and can pass through the human body. Mass in the form of concrete, lead or water is used to shield us from them.

The effective dose of all these kinds of radiation is measured in a unit called the Sievert, although most doses experienced are much lower than a Sievert, so figures are given in millisieverts (mSv), which are one-thousandth of a Sievert.

Neutrinos Do not interact with matter. They travel through material and have little or no impact. They are not referred to as ionizing radiation.

The Nuclear Industry

Number of Reactors

• Number of nuclear reactors operable and under construction

• There are currently 435 operable civil nuclear power nuclear

reactors around the world, with a further 67 under construction. (This under construction total includes V.C. Summer 2 and Vogtle 3).

• A list of reactors operable, under construction, planned and proposed can be found in this information paper World Nuclear Power Reactors and Uranium Requirements (IAEA).

• Details of individual reactors operable and under construction can be found in our Nuclear Reactor Database, which uses information supplied by the International Atomic Energy Agency.

Percentage share Electricity Supplied TWh

Argentina 5 5.9

Armenia 33.2 2.4

Belgium 54 45.9

Brazil 3.2 14.8

Bulgaria 32.6 15.3

Canada 15.3 88.3

China Mainland 1.8 82.6

Czech Rep 33 26.7

Finland 31.6 31.6

France 77.7 423.5

Germany 17.8 102.3

Hungary 43.2 14.7

India 3.7 28.9

Japan 18.1 156.2

Mexico 3.6 9.3

Netherlands 3.6 3.9

Pakistan 3.8 3.8

Romania 19 10.8

Russia 17.6 162.0

Slovakia 54 14.3

Slovenia 41.7 5.9

South Africa 5.2 12.9

South Korea 34.6 147.8

Spain 19.5 55.1

Sweden 39.6 58.1

Switzerland 40.8 25.7

Taiwan 19 40.4

UK 17.8 62.7

Ukraine 47.2 84.9

USA 19.2 790.4

Percentage share Electricity Supplied TWh

Uranium is a key fuel for the Nuclear Industry

27 tonnes of fresh fuel is required each year by a 1000 MWe nuclear reactor. In contrast, a coal power station requires more than two and a half million tonnes of coal to produce as much electricity. (1)

Neutron induced decay

Example fission reaction

How uranium ore is made into nuclear fuelHow uranium ore is made into nuclear fuelHow uranium ore is made into nuclear fuelHow uranium ore is made into nuclear fuelUranium is a naturally-occurring element in the Earth's crust. Traces of it occur almost everywhere, although mining takes place in locations where it is naturally concentrated. To make nuclear fuel from the uranium ore requires first for the uranium to be extracted from the rock in which it is found, then enriched in the uranium-235 isotope, before being made into pellets that are loaded into the nuclear fuel assembly.

Mining

Uranium mines operate in some twenty countries, though about half of world production comes from just ten mines in six countries, in Canada, Australia, Niger, Kazakhstan, Russia and Namibia.

At conventional mines, the ore goes through a mill where it is first crushed. It is then ground in water to produce a slurry of fine ore particles suspended in the water. The slurry is leached with sulphuric acid to dissolve the uranium oxides, leaving the remaining rock and other minerals undissolved.

However, nearly half the world's mines now use a mining method called in-situ leaching (ISL). This means that the mining is accomplished without any major ground disturbance. Groundwater with a lot of oxygen injected into it is circulated through the uranium ore, extracting the uranium. The solution with dissolved uranium is pumped to the surface.

Both mining methods produce a liquid with uranium dissolved in it. This is filtered and the uranium then separated by ion exchange, precipitated from the solution, filtered and dried to produce a uranium oxide concentrate (U3O8), which is then sealed in drums. This concentrate is a bright yellow colour, and is known as 'yellowcake'.

The U3O8 is only mildly radioactive. (The radiation level one metre from a drum of freshly-processed U3O8 is about half that - experienced from cosmic rays - on a commercial jet flight.)

Raw uranium ore and finished reactor rods

EnrichmentEnrichmentEnrichmentEnrichmentThe vast majority of all nuclear power reactors require 'enriched' uranium fuel in which the proportion of the uranium-235 isotope has been raised from the natural level of 0.7% to about 3.5% to 5%. The enrichment process needs to have the uranium in gaseous form, so on the way from the mine it goes through a conversion plant which turns the uranium oxide into uranium hexafluoride (UF6).

The enrichment plant removes about 85% of the uranium by separating gaseous uranium hexafluoride into two streams: One stream is enriched to the required level and then passes to the next stage of the fuel cycle. The other stream is depleted in U-235 and is called 'tails'. It is mostly uranium-238 and has little immediate use.

Today's enrichment plants use the centrifuge process, with thousands of rapidly-spinning vertical tubes. Research is being conducted into laser enrichment, which appears to be a promising new technology.

A small number of reactors, notably the Canadian CANDU reactors, do not require uranium to be enriched.

Fuel fabrication

27 tonnes of fresh fuel is required each year by a 1000 MWe nuclear reactor. In contrast, a coal power station requires more than two and a half million tonnes of coal to produce as much electricity. (1)Enriched UF6 is transported to a fuel fabrication plant where it is converted to uranium dioxide (UO2) powder. This powder is then pressed to form small fuel pellets, which are then heated to make a hard ceramic material. The pellets are then inserted into thin tubes to form fuel rods. These fuel rods are then grouped together to form fuel assemblies, which are several meters long.

The number of fuel rods used to make each fuel assembly depends on the type of reactor. A PWR (pressurised water reactor) may use between 121-193 fuel assemblies, each consisting of between 179-264 fuel rods. A BWR (boiling water reactor) has between 91-96 fuel rods per assembly, with between 350-800 fuel assemblies per reactor.

How a nuclear reactor makes electricityHow a nuclear reactor makes electricityHow a nuclear reactor makes electricityHow a nuclear reactor makes electricityA nuclear reactor produces and controls the release of energy from splitting the atoms of uranium.

Uranium-fuelled nuclear power is a clean and efficient way of boiling water to make steam which drives turbine generators. Except for the reactor itself, a nuclear power station works like most coal or gas-fired power stations.

The Reactor Core

Several hundred fuel assemblies containing thousands of small pellets of ceramic uranium oxide fuel make up the core of a reactor. For a reactor with an output of 1000 megawatts (MWe), the core would contain about 75 tonnes of enriched uranium.

In the reactor core the U-235 isotope fissions or splits, producing a lot of heat in a continuous process called a chain reaction. The process depends on the presence of a moderator such as water or graphite, and is fully controlled.

The moderator slows down the neutrons produced by fission of the uranium nuclei so that they go on to produce more fissions.

Fission reactions with different daughter products

Two examples of fission of a Uranium-235 atom

Fission Reactor

Some of the U-238 in the reactor core is turned into plutonium and about half of this is also fissioned similarly, providing about one third of the reactor's energy output.

The fission products remain in the ceramic fuel and undergo radioactive decay, releasing a bit more heat. They are the main wastes from the process.

The reactor core sits inside a steel pressure vessel, so that water around it remains liquid even at the operating temperature of over 320°C. Steam is formed either above the reactor core or in separate pressure vessels, and this drives the turbine to produce electricity. The steam is then condensed and the water recycled.

PWRs and BWRs

The main design is the pressurised water reactor (PWR) which has water in its primary cooling/heat transfer circuit, and generates steam in a secondary circuit. The less popular boiling water reactor (BWR) makes steam in the primary circuit above the reactor core, though it is still under considerable pressure. Both types use water as both coolant and moderator, to slow neutrons.

Diagram of Pressurised Water Reactor

Fuelling the reactorTo maintain efficient reactor performance, about one-third or half of the used fuel is removed every year or two, to be replaced with fresh fuel.

The pressure vessel and any steam generators are housed in a massive containment structure with reinforced concrete about 1.2 metres thick. This is to protect neighbours if there is a major problem inside the reactor, and to protect the reactor from external assaults.

Because some heat is generated from radioactive decay even after the reactor is shut down, cooling systems are provided to remove this heat as well as the main operational heat output.

Natural Prehistoric Reactors

The world's first nuclear reactors operated naturally in a uranium deposit about two billion years ago in what is now Gabon. The energy was not harnessed, since these were in rich uranium orebodies in the Earth's crust and moderated by percolating rainwater.

Nuclear energy's contribution to global electricity supply

Nuclear energy supplies some 14% of the world's electricity. Today 31 countries use nuclear energy to generate up to three quarters of their electricity, and a substantial number of these depend on it for one quarter to one half of their supply. Almost 15,000 reactor-years of operational experience have been accumulated since the 1950s by the world's 440 nuclear power reactors (and nuclear reactors powering naval vessels have clocked up a similar amount).

What are nuclear wastes and how are they managed?What are nuclear wastes and how are they managed?What are nuclear wastes and how are they managed?What are nuclear wastes and how are they managed?

The most significant high-level waste from a nuclear reactor is the used nuclear fuel left after it has spent 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.

Grading of waste

By Volume By Radioactive Content

High Level

Waste

3% 95%

Intermediate

Level Waste

7% 4%

Low Level

Waste

90% 1%

Grading waste

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

Managing used fuel

Used nuclear fuel is very hot and radioactive. Handling and storing it safely can be done as long as it is cooled and people are shielded from the radiation it produces by a dense material like concrete or steel.

Water can conveniently provide both cooling and shielding, so a typical reactor will have its fuel removed underwater and transferred to a storage pool. After about five years it can be transferred into dry ventilated concrete containers, but otherwise it can safely remain in the pool for up to 50 years.

Cooling ponds

RecyclingUsed fuel is also a valuable resource, and 96% of it can be recycled. Currently, this means that the sustainability of nuclear power is enhanced. In this case about 1% of the fuel is recycled promptly into mixed oxide fuel (MOX), the rest is usually stored for the future while about 3% of the original mass remains as waste to be disposed of.

The high-level wastes (whether used as fuel after 50 years cooling, or the separated 3% of such fuel) will be disposed of deep underground in geological repositories.

Intermediate and low-level wastes

Intermediate- and low-level wastes are disposed of closer to the surface, in many established repositories. Low-level waste disposal sites are purpose built, but are not much different from normal municipal waste sites.

Nuclear power is not the only industry that creates radioactive wastes. Other industries include medicine, particle and space research, oil and gas, and mining - to name just a few. Most of these are not produced inside a reactor, but rather are concentrated forms of naturally occurring radioactive material.

Civil nuclear wastes have never caused any harm, nor posed an environmental hazard, in over 50 years of the nuclear power industry. Their management and eventual disposal is straightforward.

Low level storage - finland

Half life and storageOne characteristic of all radioactive wastes which distinguishes them from the very much larger amount of other toxic industrial wastes is that their radioactivity progressively decays and diminishes. For instance, after 40 years, the used fuel removed from a reactor has only one thousandth of its initial radioactivity remaining, making it very much easier to handle and dispose of.

Disposal

The categorization - high, intermediate, low - helps determine how wastes are treated and where they end up. All radioactive waste facilities are designed with numerous layers of protection to make sure that the environment remains protected for as long as it takes for radioactivity to reduce to background levels. Low-level and intermediate wastes are buried close to the surface. For low-level wastes disposal is not much different from a normal municipal landfill. High-level wastes can remain highly radioactive for thousands of years. They need to be disposed of hundreds of metres underground in heavily engineered facilities built in stable geological formations. While no such facilities currently exist, there have been feasibility studies and there are several countries now in the process of designing them.

Ireland first Nuclear reactorPapers Today

// UCC keeping 2.5 tonnes of uranium in basement store

Uranium stored in a basement in University College Cork is to remain there in the absence of a national waste repository or the Government paying for it to be taken away, a radiation protection officer said yesterday.

The 2.5 tonnes of uranium rods have been kept in a secured store in the basement of the university's physics department since1986. Yesterday, UCC's radiation protection officer, Dr William Reville, said: "We're not storing nuclear waste or the remnants of a nuclear reactor." He said he inquired some years ago about having the uranium taken away but it would have cost something like £4 million (€6 million) at the time. "The ideal solution would be if the Government had a national waste repository which would hold unwanted substances. "In the absence of that and in the absence of the Government coming up with the money to export it,it will have to sit where it is," he said. The uranium was classified as sensitive material but it was natural uranium, the type that was found in the earth, he said. It was not a hazard as it sat in the store. It was in a very safe place. It was part of a student training reactor, now dismantled, and it had generated no power. It was not a commercial reactor. "It bore as much relation to acommercial reactor as a lighted match does to the sun. The uranium is not nuclear waste," Dr Reville said. The senior scientific officer in the Regulatory Service of the Radiological Protection Institute of Ireland (RPII), Dr John O'Grady, said they had been licensing the uranium since 1977 and its storage conditions met all safety requirements. It was inspected annually by the European Atomic Energy Community (EURATOM), and by the RPII on a periodic basis. "There are all sorts of checks and monitoring and there is never the least danger of radiation being produced," he said. It was uranium for a small research reactor and was far from being the material needed for a satisfactory power generator. Dr O'Grady said there might be a route for disposal but it was very expensive. "Until there is both the will and the money, it will just lie there," Dr O'Grady said. Cork people knew all about it over the years and if anybody wanted information they could contact the RPII or Dr Reville, he said. "We've never hesitated to licence it," he said. The reactor was given to Ireland by the US under the Atoms for Peace Programme in 1974.In the 1980s, it was decommissioned and taken apart.

UraniumUraniumUraniumUraniumThe International Atomic Energy Agency (IAEA) defines uranium as a Low Specific Activity material. In its natural state, it consists of three isotopes (U-234, U-235 and U-238). Other isotopes that cannot be found in natural uranium are U-232, U-233, U-236 and U-237. The table below shows the fraction by weight of the three isotopes in any quantity of natural uranium, their half lives, and specific activity. The half life of a radioactive isotope is the time taken for it to decay to half of its original amount of radioactivity. The specific activity is the activity per unit mass of a particular radionuclide and is used as a measure of how radioactive a radionuclide is. It is expressed in the table in becquerels (Bq) per milligram (1 milligram, mg, = 0.001 grams). An activity of one becquerel (Bq) means that on average one disintegration takes place every second.

Safety

Isotope Relative abundance by weight Half life (years) Specific activity (Bq mg-1)

U-238 99.28% 4,510,000,000 12.4

U-235 0.72% 710,000,000 80

U-234 0.0057% 247,000 231000

How dangerous is uranium

The average concentration of natural uranium in soil is about 2 parts per million, which is equivalent to 2 grams of uranium in 1000 kg of soil. This means that the top metre of soil in a typical 10 m by 40 m garden contains about 2 kg of uranium (corresponding to about 50,000,000 Bq of activity just from the decay of the uranium isotopes and ignoring the considerable activity associated with the decay of the progeny. Concentrations of uranium in granite range from 2 parts per million to 20 parts per million. Uranium in higher concentrations (50 - 1000 mg per kg of soil) can be found in soil associated with phosphate deposits. In air, uranium exists as dust. Very small, dust-like particles of uranium in the air are deposited onto surface water, plant surfaces, and soil. These particles of uranium eventually end up back in the soil or in the bottom of lakes, rivers, and ponds, where they mix with the natural uranium that is already there. Typical activity concentrations of uranium in air are around 2 µBq per cubic metre. (UNSCEAR 2000).

How does it harm us?Uranium is introduced into the body mainly through ingestion of food and water and inhalation of air.

When inhaled, uranium is attached to particles of different sizes. The size of the uranium aerosols and the solubility of the uranium compounds in the lungs and gut influence the transport of uranium inside the body. Coarse particles are caught in the upper part of the respiratory system (nose, sinuses, and upper part of the lungs) from where they are exhaled or transferred to the throat and then swallowed. Fine particles reach the lower part of the lungs (alveolar region). If the uranium compounds are not easily soluble, the uranium aerosols will tend to remain in the lungs for a longer period of time (up to 16 years), and deliver most of the radiation dose to the lungs. They will gradually dissolve and be transported into the blood stream. For more soluble compounds, uranium is absorbed more quickly from the lungs into the blood stream. About 10% of it will initially concentrate in the kidneys.

Most of the uranium ingested is excreted in faeces within a few days and never reaches the blood stream. The remaining fraction will be transferred into the blood stream. Most of the uranium in the blood stream is excreted through urine in a few days, but a small fraction remains in the kidneys and bones and other soft tissue.

Toxicity

In sufficient amounts, uranium that is ingested or inhaled can be harmful because of its chemical toxicity. Like mercury, cadmium, and other heavy-metal ions, excess uranyl ions depress renal function (i.e., affect the kidneys). High concentrations in the kidney can cause damage and, in extreme cases, renal failure. The general medical and scientific consensus is that in cases of high intake, uranium is likely to become a chemical toxicology problem before it is a radiological problem. Since uranium is mildly radioactive, once inside the body it also irradiates the organs, but the primary health effect is associated with its chemical action on body functions.

In many countries, current occupational exposure limits for soluble uranium compounds are related to a maximum concentration of 3 µg uranium per gram of kidney tissue. Any effects caused by exposure of the kidneys at these levels are considered to be minor and transient. Current practices, based on these limits, appear to protect workers in the uranium industry adequately. In order to ensure that this kidney concentration is not exceeded, legislation restricts long term (8 hour) workplace air concentrations of soluble uranium to 0.2 mg per cubic metre and short term (15 minute) to 0.6 mg per cubic metre.

Like any radioactive material, there is a risk of developing cancer from exposure to radiation emitted by natural and depleted uranium. This risk is assumed to be proportional to the dose received. Limits for radiation exposure are recommended by the International Commission on Radiological Protection (ICRP) and have been adopted in the IAEA's Basic Safety Standards. The annual dose limit for a member of the public is 1 mSv, while the corresponding limit for a radiation worker is 20 mSv. The additional risk of fatal cancer associated with a dose of 1 mSv is assumed to be about 1 in 20,000. This small increase in lifetime risk should be considered in light of the risk of 1 in 5 that everyone has of developing a fatal cancer . It must also be noted that cancer may not become apparent until many years after exposure to a radioactive material.

IAEA

Uranium and Thorium in coalIn a 1978 paper for Science, J. P. McBride at Oak Ridge National Laboratory (ORNL) and his colleagues looked at the uranium and thorium content of fly ash from coal-fired power plants in Tennessee and Alabama. To answer the question of just how harmful leaching could be, the scientists estimated radiation exposure around the coal plants and compared it with exposure levels around boiling-water reactor and pressurized-water nuclear power plants.

The result: estimated radiation doses ingested by people living near the coal plants were equal to or higher than doses for people living around the nuclear facilities. At one extreme, the scientists estimated fly ash radiation in individuals' bones at around 18 millirems (thousandths of a rem, a unit for measuring doses of ionizing radiation) a year. Doses for the two nuclear plants, by contrast, ranged from between three and six milliremsfor the same period. And when all food was grown in the area, radiation doses were 50 to 200 percent higher around the coal plants.

McBride and his co-authors estimated that individuals living near coal-fired installations are exposed to a maximum of 1.9 millirems of fly ash radiation yearly. To put these numbers in perspective, the average person encounters 360 millirems of annual "background radiation" from natural and man-made sources, including substances in Earth's crust, cosmic rays, residue from nuclear tests and smoke detectors.

Sci American December 13, 2007

Uranium decays to form a gas Radon56% of radioactive risk in Ireland is from Radon100 – 150 deaths a year from lung cancer

Radon is a radioactive gas which is naturally produced in the ground from uranium present in small quantities in all rocks and soils

You cannot see, smell or taste radon

Radon can only be measured by a simple test.

Radon is a radioactive gas which produces tiny radioactive particles. When inhaled, these particles are deposited in the airways and on the tissue of the lung. This results in a radiation dose that can cause lung cancer

Your risk of contracting lung cancer from exposure to radon depends on how much radon you have been exposed to, how long you have been exposed and whether or not you smoke

When you are exposed for a long period of time to high levels of radon, you increase your risk of developing lung cancer. For more information on this read the RPII-HSE Joint Position Statement on Radon

Radon is in the same group of carcinogens as asbestos and tobacco smoke

Radon is not linked to any other types of respiratory illnesses or other types of cancer

IrelandIrelandIrelandIreland has the sixth highest radonradonradonradon levels in the world RPIIworld RPIIworld RPIIworld RPII

Risk from Radon

Based upon current epidemiological evidence, it is estimated that in Ireland, for the population as a whole, a lifetime exposure to radon in the home at the Reference Level of 200 Bq/m3 carries a risk of about 1 in 50 (2%) of contracting fatal lung cancer.

The risk is much lower for non-smokers and far greater, than this average value, for smokers

World consumption of primary energy by energy type in terawatts(TW), 1965-2005.(Green-Oil; Black-Coal; Red-Gas; Purple- Nuclear; Blue-Hydro)

An appraisal of nuclear power by a team at MIT in 2003, and updated in 2009, have stated that:

Most commentators conclude that a half century of unimpeded growth is possible, especially since resources costing several hundred dollars per kilogram (not estimated in the Red Book) would also be economically usable...We believe that the world-wide supply of uranium ore is sufficient to fuel the deployment of 1000 reactors over the next half century.

Mining companies usually consider concentrations greater than 0.075% (750 ppm) as ore, or rock economical to mine at current uranium market prices.[34] There is around 40 trillion tons of uranium in Earth's crust, but most is distributed at low parts per million trace concentration over its 3 * 1019 ton mass.[35][36] Estimates of the amount concentrated into ores affordable to extract for under $130 per kg can be less than a millionth of that total.[12]

World reserves of uranium

Uranium deposits world wide