Primary energy is an energy form found in nature that has not been subjected to any human engineered conversion process.

The primary containment system usually consists of a large metal and/or concrete structure (often cylindrical or bulb shaped) that contains the reactor vessel. The primary containment system is designed to withstand strong internal pressures resulting from a leak or intentional depressurization of the reactor vessel.

A battery (galvanic cell) that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell (rechargeable battery).

Preventive maintenance (PM) is a routine for periodically inspecting with the goal of noticing small problems and fixing them before major ones develop.

The most common direction or directions that the wind comes from at a location.

A pressurized water reactor (PWR) is a type of light-water nuclear reactor.

A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator.

A pressure sensor is a device for pressure measurement of gases or liquids.

The yield strength or yield stress is a material property and is the stress corresponding to the yield point at which the material begins to deform plastically.

Yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior.

Yellowcake is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores.

A yaw motor powers the yaw drive.

To ensure the wind turbine is producing the maximum amount of electric energy at all times, the yaw drive is used to keep the rotor facing into the wind as the wind direction changes.

The angle between a line in the direction of wind and a plane through the longitudinal and vertical axes of a turbine.

The movement of the tower top turbine that allows the turbine to stay into the wind.

The World Wind Energy Association (WWEA) is an international non-profit association representing the wind power sector worldwide, with members in 100 countries, amongst them the leading national and regional wind energy associations.

The World Resources Institute (WRI) is a global research non-profit organization established in 1982 with activities are focused on seven areas: food, forests, water, energy, cities, climate and ocean.

World Nuclear Association is the international organization that promotes nuclear power and supports the companies that comprise the global nuclear industry.

The World Forum on Energy Regulation (WFER) is the leading international conference on energy regulation, held once every three years.

The World Energy Council is a global forum for thought-leadership and tangible engagement with headquarters in London.