Radiation and Safety
Nuclear fission creates hazardous radiation that can harm human health and the environment. There have been many incidents in nuclear reactors and in handling radiative materials, with serious consequences involving the release of radiation.
Ionisation occurs when electrons are stripped off or added to an atom, leaving a net charge. Ionising radiation is radiation with the energy to achieve the charging of atoms or molecules, such as air.
Ionisation: these radiations strip electrons off molecules in the air, or any media they pass through, so are referred to as ionising radiation. Although short-lived, alpha particles are much more ionising than beta particles, which in turn are much more ionising than gamma radiation.
International Atomic Energy Agency
IAEA, the International Atomic Energy Agency. Founded in 1957. It is independent of the UNO, and has its own international treaty (the IAEA Statute), but reports to the UNGA (United Nations General Assembly) and the Security Council.
The IAEA has its headquarter in Vienna, and two offices (Regional Safeguards offices) in Toronto and Tokyo, as well as 2 liaison offices in New York and Geneva.
The function of the IAEA is international forum for scientific and technical cooperation, and watchdog for the peaceful use of nuclear technology and materials. It publishes standards for nuclear safety, radiation protection and security. The IAEA was awarded the Nobel Prize for Peace, jointly with its former Director General, Mohamed ElBaradei, in 2005.
International Nuclear and Radiological Event Scale
The IAEA (International Atomic Energy Agency) introduced a logarithmic scale in 1990: the International Nuclear and Radiological Event Scale (INES), which ranks severity of incident or accident from one to seven, where seven is the most severe.
Level 7: Major Accident
Major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures. Only two accidents are classed as the highest level accident:
Fukushima Daiichi nuclear disaster
Japan, 11 March 2011
Ukraine (formally Soviet Union), 26 April 1986
Level 6: Serious Accident
Significant release of radioactive material likely to require implementation of planned countermeasures. There has been only one Level 6 event:
Soviet Union, 29 September 1957. At the military nuclear waste reprocessing facility, Mayak Chemical Combine (MCC), there was an explosion, which released as much as 80 tonnes of highly radioactive material into the environment. The cause of the explosion was a cooling system malfunction. Due to secrecy around military operations in the Soviet Union, the consequences for the workers at the plant, and inhabitants of the surrounding area, are unknown, but were in all likelihood very serious.
Level 5: Accident with wider consequences
Limited but dangerous release of radioactive material, and several deaths. The reactor core is likely to have been damaged severely.
There have been at least five such incidents, including 3-Mile Island (1979).
Nuclear safety treaties
The very serious, long-range and long-term nature of nuclear accidents makes radioactive fallout and radioactive waste management a global rather than a local issue.
Nuclear Safety Treaties
- Comprehensive Test Ban Treaty (CTBT) 1996
- Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency (Assistance Convention), Vienna, 1986.
- Convention on Early Notification of a Nuclear Accident (Notification Convention), Vienna, 1986.
- Convention on Nuclear Safety, Vienna, 1994.
- Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space, and Under Water
- Vienna Convention on Civil Liability for Nuclear Damage, Vienna, 1963.
Isotopes are variations of atoms of the same element. The element is defined as the number of protons (atomic number), which is invariable, but the number of neutrons, the mass number or atomic weight, can vary.
From Greek [isos = 'the same', topos = 'location'], isotopes are listed on the Periodic Table as the one element (same location, whole number atomic number), and the relative proportions of the varying atomic weights is usually expressed as a single average.
Some isotopes are radioactive. They can be used as fissile material in nuclear reactors to generate electricity because they can be induced to decay at a rate far greater than the natural decay rate by bombardment with neutrons.
Isotopes are also used as radiation sources in applications such as medicine and research, and they make useful markers for radiometric dating of substances. An example is carbon-14.
Isotopes should not be confused with allotropes, which are different shapes or bond combinations of the same element. An example of allotropes are graphite and diamond.
The Flower's Report (actual title: Nuclear Power and the Environment) was the 6th report, issued September 1976, of the UK Royal Commission on Environmental Pollution, so-called after its chairman, Sir Brian Flowers.
The report is seen as a landmark change in the UK government's policies regarding nuclear power. Following the leak at Windscale in 1973, in 1975, there was a proposal to develop a nuclear fuel reprocessing plant in Cumbria at the same site (now Sellafield), also as an international service.
Fuel had to date been managed without sufficient regard to the disposal of waste. Spent nuclear fuel was reprocessed, the usable uranium and plutonium returned to the client, but the useless, and highly dangerous, waste that remained was simply dumped in a temporary storage tank.
The Flowers Report forced the reprocessing industry to take responsibility for nuclear waste, and to plan for long-term disposal. The Windscale proposal was consequently cancelled, obliging waste exporting countries, such as Switzerland to take responsibility for the waste they produced in their nuclear reactors.
Beta (β) radiation consists of a stream of fast electrons (charge -e).
During the decay of an atomic nucleus, three types of radiation are emitted. When they were discovered, it was not known what they were, so they were called 'A', 'B', and 'C' radiations, but scientists being scientists they used Greek letters: α (alpha), β (beta), and γ (gamma).
In 1897, J.J. Thomson ran an experiment which demonstrated the ratio of charge to mass. This was used to identify the -e charge and very low mass of the beta particles. When a neutron decays into a proton, an electron is released. Beta radiation is a stream of fast-moving, and therefore very energetic, electrons.
Electrons are in the lepton class of sub-atomic particles, along with neutrinos and muons. Example of a beta radiation equation:
Thorium-Protactinium β-decay: 23490Th → 23491Pa + 0-1e + 00νe-,
where νe- is the electron antineutrino.
Alpha radiation is a stream of particles. These particles consist of two protons and two neutrons - which is the nucleus of a helium atom. Alpha particles therefore have a charge of +2e, and are detectable because their flightpath is curved by a magnetic field.
Alpha particles ionise the material they passes through, and interact with it. After a short distance, called the range, which depends on its energy, an alpha particle will be absorbed by the medium (e.g. air).
Alpha Beta Gamma Mass 6.64 × 10-27 kg 9.1 × 10-31 kg 0 Charge +2e -e 0 Particle He nucleus electron (fast) photon Shielding required A few cm of air 1-2 cm of paper, thin metal Thick lead Ions per mm of air for 2MeV 104 102 1
Gamma radiation (γ-rays) is the frequency band of the electromagnetic spectrum with the highest frequency (>1019 Hz), and shortest wavelengths (<10-12 m), and particularly high penetrating power. Gamma radiation is high energy (>105 keV), and ionising, so very destructive to living tissue, and requires many centimetres of lead shielding to absorb.
Gamma radiation was discovered by Paul Villard in 1900, who observed them being emitted from radium, and named by Ernest Rutherford in 1903.
The becquerel (Bq, after the French physicist Henri Becquerel, 1852 - 1908) is the S.I. derived unit for radiative activity, and is equal to one nucleus decay per second.
The first nuclear bomb was exploded in July 1945 in New Mexiko, USA. Since then the world has added a new nuclear-armed state on average every 9 years, and a nuclear weapon technology-capable state every 5 years.
Nuclear weapons are regulated by the Treaty on the Nonproliferation of Nuclear Weapons (NPT). Under this treaty, states possessing nuclear arsenals prior to 1968 are entitled to maintain their capabilities. Four states have challenged the legitimacy of this principle, and proceeded to acquire weapons. They are not party to the NPL. Another group of countries have developed or inherited (Soviet Bloc) nuclear weapon capabilities.
5 NPL recognised nuclear states: USA, Russia, China, France, UK.
Other states possessing nuclear weapons (not party to the NPL): North Korea, India, Pakistan, Israel.
States possessing weapons technology or formerly possessed weapons: Iran, Saudi Arabia, South Africa, Ukraine, Poland, Kazakhstan. The ex-Soviet bloc nations have returned their stockpiles to Russia, and are now officially non-nuclear.
Japan and Iran, and probably several other states, possess what is termed 'breakout capability', meaning they have stockpiled sufficient plutonium and technical capability to fabricate weapons quickly.