All nuclear power stations are equipped to handle gaseous and liquid wastes in conformity with regulatory requirements. The gaseous waste originates primarily from gases dissolved in the coolant, radiolytic decomposition of water into hydrogen (H2) and oxygen (O2), and added gases such as H2 and nitrogen (N2).
Designs of waste gas systems often differ considerably from plant to plant, regardless of manufacturer or type of unit (PWR, BWR, etc.), although some main features remain common. In PWR's where gas volumes are rather small because the primary system is sealed, the gases are typically compressed and stored in decay tanks for 30–45 days before being released to the environment in a controlled manner. In the case of BWR's, released gas volume is much larger because the feed water is continuously deaerated and the gas produced at the deaerator must be treated as radioactive since it was in direct contact with the fuel. BWR gases are held for a short time (often around 30 minutes) and then diluted with air and released to the atmosphere.