Section Ю.7 has described the operation of a PWR primary coolant system (reactor coolant system), and has emphasised the importance of an optimised chemical control regime.

Most of the technical issues discussed have been and will continue to be subjected to continuous re­search and re-assessment, particularly in response to changes in design and operation of PWR systems, improved monitoring techniques, the desirability of further reducing dose rates, and the emergence of new materials.

An attempt has been made to cover all the features that are included in current PWR primary circuit op­eration and to indicate either specific or general fea­tures that may be incorporated in future reactor de­signs following successful research and development.

10.8 Behaviour of magnox fuel in storage After discharge from a magnox reactor, fuel elements are stored to allow decay of radioactivity, particularly iodine, and of their heat content before they are transported to Sellafield for reprocessing. At all mag­nox stations (except Wylfa), the storage medium is water, the elements generally being stored horizontally in skips in ponds deep enough for adequate shield­ing purposes. At Wylfa, the fuel elements from the reactor are transferred to a dry store in which they are held in carbon dioxide and then, after a period to allow thermal decay, moved either to an air-filled dry store on site, or transported directly to Sellafield.