Pressurised Water Reactors

Fuel – Uranium Dioxide with 2.5% 235U enrichment
Cladding – zircaloy, an alloy of zirconium with low concentrations of tin, iron, chromium, and nickel
Moderator – light water – H2O
Coolant – light water – H2O
Control – control rods plus boric acid
Shield – reinforced concrete

Steam has a lower neutron absorption cross section than water. Maintaining a high pressure keeps the water liquid. An increase in temperature will slow down the rate of fission resulting in the temperature decreasing.

UK PWR Reactor 

Sizewell B in Suffolk connected in 1995, 1188 MWe