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Basic Terminology


Basic Terminology

An atom consists of a central nucleus which is surrounded with negatively charged electrons travel in distinct orbits. The number of protons in the nucleus is matched by the same number of orbital electrons so that the entire atom has no net electrical charge.

The medium (liquid or gas) used to transfer heat from the reactor core to the steam generators or directly to the turbines.


Condition of being able to sustain a nuclear chain reaction.

To clean up or reduce the radiological contamination.
A process of splitting the heavy nucleus into two or more fission fragments.
One of a group of nuclides with the same number of protons but different numbers of neutrons. (e.g. 11H, 21H, 31H are isotopes of hydrogen. 11H is called protium or light hydrogen , 21H is called deuterium (D2) or heavy hydrogen, 31H is called tritium ; U-238 (consists of 92 protons and 146 neutrons) and U-235 (consists of 92 protons and 143 neutrons) are isotopes of Uranium).
A material or medium used to slow down the fast neutrons (with high energy) released from fission to low energy neutrons known as thermal neutrons to induce more fissions. Ordinary water, heavy water and graphite are commonly used as moderator in nuclear reactors).
Nuclear Safety
The achievement of proper operating conditions, prevention of accident or mitigation of accident consequences, resulting in protection of workers, the public and environment from undue radiation hazard.
A small, massive, positively charged structure at the centre of an atom composed of subatomic particles namely the protons and neutrons. Protons are positively charged whereas neutrons have no charge at all.
A term used to specify a type of nucleus or an atom with reference to its nuclear properties. A nuclide is often represented by the symbol AZX, or X - A where A is the mass number equal to the numbers of protons plus the number of neutrons in the nucleus, Z is the atomic number equal to the number of protons in the nucleus, X is the chemical symbol of the atom.
Any other areas outside On-site boundary of the Nuclear Power Station.
An area under the management of the Nuclear Power Station.
A continuous radiological gaseous discharge from the chimney or discharge outlets of a nuclear power station in the form of a stream of smoke or cloud and the mass of it shaped like a feather and therefore known as the plume.
Refuelling outage
A temporary shutdown of the nuclear reactor unit for carrying out maintenance and overhaul of plant and equipment including the replacement of a portion of used fuel with new one.
A process or operation to extract radioactive isotopes from spent fuel for further use.
The rapid and automatic shutting down of a nuclear reactor.
A means of emergency protective countermeasures, which requires personnel to enter or stay inside a structure; close all windows and shutdown ventilation system for the purpose of providing shielding against external exposure and to reduce the intake of airborne radioactive nuclides by inhalation due to the passing of the plume, and also reducing the external exposure due to the deposited radioactive nuclides.
Single Failure
A failure which results in the loss of capability of a component to perform its intended safety function(s), and any consequential failure(s) which result from it.
Spent Fuel
Fuel assemblies removed from a reactor after use. Spent fuel contains a number of highly radioactive nuclides.
Thermal neutron
A low energy neutron formed as a result of scattering reactions of fast neutrons with moderator. It is called thermal neutron because the average kinetic energy of the neutron is directly proportional to the temperature.
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