The International Radiation Protection Association (IRPA) is an independent non-profit association of national and regional radiation protection societies, and its mission is to advance radiation protection throughout the world.

The International Panel on Fissile Materials (IPFM), established in 2006, is a group of independent nuclear experts from 17 countriesthat aims to advance international initiatives to “secure and to sharply reduce all stocks of highly enriched uranium and separated plutonium, the key materials in nuclear weapons, and to limit any further production”.

The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations.

The International Hydropower Association (IHA) is a non-profit, international organisation and membership association representing the global hydropower sector.

The International Geothermal Association (IGA) is an international non-profit, non-political, non-governmental association representing the geothermal power sector worldwide. The organisation works for the promotion and worldwide deployment of geothermal energy technology and advocates a future energy system based on renewable energy.

The International Energy Agency is a Paris-based autonomous intergovernmental organisation established in the framework of the Organisation for Economic Co-operation and Development (OECD) in 1974 in the wake of the 1973 oil crisis.

An international standards organization that prepares and publishes international standards for all electrical, electronic and related technologies

The International Commission on Radiological Protection (ICRP) is an independent, international, non-governmental organization, with the mission to protect people, animals, and the environment from the harmful effects of ionising radiation.

The International Commission on Radiation Units and Measurements (ICRU) is a standardization body set up by the International Congress of Radiology.

An international non-governmental organization dedicated to the sharing of professional information and knowledge of the design, construction, maintenance, and impact of large dams.

An international organization that seeks to promote the peaceful use of nuclear energy, and to inhibit its use for any military purpose, including nuclear weapons.

A practical electrical power source which is a linear electric circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance.

Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.

Internal erosion is the formation of voids within a soil caused by the removal of material by seepage. It is the second most common cause of failure in levees and one of the leading causes of failures in earth dams.

The internal energy of a thermodynamic system is the energy contained within it. It is the energy necessary to create or prepare the system in any given internal state.

Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine.

Is a heat engine where combustion takes place in a combustion chamber producing force on pistons which in turn produces usable work usually by turning a shaft which can, for example, be coupled to a generator to produce electricity.

Resources that are on occasion not available such as the solar, wind or wave energy.

The frequency a power source is unintentionally stopped or partially unavailable.

Intermediate-level waste (ILW) contains higher amounts of radioactivity compared to low-level waste.