10k Coolant Cells are used in Nuclear Reactors but also extends to IC2 Upgrades. They absorb up to 10.000 heat points from adjacent sources in the reactor. There are many different types of Coolant cells in IC2, of which include the 10k Coolant Cell, 30k Coolant Cell, and the 60k Coolant Cell. GregTech, also included in FTB, adds Helium Coolant Cells and NaK (Sodium Potassium) Coolant Cells, of which include the 60k Helium/NaK Coolant Cells, the 180k Helium/NaK Coolant Cells, and the 360k Helium/NaK Coolant Cells.
To restore the coolant it requires to be placed next to a Component Heat Vent.