Phenomenon that results in the aggregation of hydrogen with another element and wherein the hydrogen atom plays an electronegative role, i.e. it accepts an electron and is negatively polarised. This concerns most metal hydrides such as lithium hydride, sodium hydride and magnesium hydride, as well as several non-metallic elements such as boranes, silanes and germanes.

High Temperature Reactor. High-temperature gas-cooled reactors (HTGRs), also known as very-high-temperature reactors (VHTR), are Generation IV reactors that operate at very high temperatures and use a graphite-moderated gas-cooled nuclear reactor with a once-through uranium fuel cycle.

A gradient operates on a scalar function to produce a vector whose scale is the maximum rate of change of the function at the point of the gradient and which is pointed in the direction of that utmost rate of change. In brief, it tells you how much something (a physical quantity) changes as you move from one point to another. In practical terms, the spatial derivative of this physical quantity is calculated according the directions chosen.