The main sources of radioactive waste are shown in Fig 3.56 and are made up of gases, liquids and solids. The most active of these wastes is the spent irra­diated fuel which is returned to the BNFL plant at Sella field, Cumbria. At Sellafield, the radioactive con­stituents are chemically separated from the bulk of the material (uranium) and are stored in solution in cooled vtainless steel tubes. The remaining waste materials arc dealt with on site.

The gaseous wastes are solely derived from the dis­charge or leakage of the carbon dioxide coolant gas. Generally gas leaks arise from leakage past seals. The Co is collected by ventilation systems and after pass — ,nt through absolute filters to remove particulate mat — tcr 11 о discharged to the atmosphere. The volume afid activity of these discharges are carefully moni­tored to control the activity release and to detect any unusual increase in levels which would demand an immediate investigation as to the source and cause. There is also some controlled discharge of gas from the blowdown of reactor gas, either from a require­ment to depressurise the reactor or for control of gas composition, and from the necessity to depressurise the fuelling machine at the end of its cycle prior to the discharge of fuel. In either case strict controls are enforced to ensure that the discharge conforms to statutory regulations.

The liquid wastes are largely derived from the cool­ing pond water treatment plant, and via drains from change room and laundry wash-water facilities. These are collected in the active effluent plant and after treatment, which is usually pH adjustment, it is passed to a final delay tank for analysis before disposal. If necessary, a time delay may be employed for radio­activity decay or water dilution to control activity release to the environment.

The bulk of the solid wastes is derived from the fuel elements in the form of magnox, steel and graph­ite. This material is stored on site in specially-con­structed above or below ground vaults. Similar vaults are used to contain solid wastes derived from main­tenance procedures on active or contaminated equip­ment. Spent resins and sludges from the active water treatment plant are stored in shielded tanks. A start has been made to contain some of these solid wastes in approved packages and to dispatch them to the BNFL sites at Drigg, Cumbria for trench burial.