Plutonium cells are one of the cell types found in GregTech.
While plutonium cells can also be produced by adding a piece of UU-Matter to Uranium Cell, it's not recommended as the amount of energy required to produce UU-matter far outweighs the EU produced by plutonium cell.
Plutonium cell is used in Nuclear Reactors to produce energy. Without proper cooling it will cause the reactor to go into a meltdown stage where it explodes, leaving a huge crater for you to fill in assuming you survive.
Plutonium Cells produce twice as much energy and heat as Uranium cells (making it 10 EU/heat per tick, 20 EU 30heat if next to 1 other Plutonium Cell, 30 EU/ 60heat if next to 2 other Plutonium Cells, etc.) and they last twice as long. (This behaviour can be customized inside the config files) This results power generation of 8-40 million EU per cycle (5 hours and 34 minutes real time).
As plutonium cells generate a lot of heat, managing reactors containing plutonium is a bit tricky as it's harder to maximise the energy potential of each cell while trying to keep the reactor running for as long as possible.
Dual Plutonium Cell