After removal from the reactor, the spent fuel ele­ments are stored for a period in order to allow some of the short-lived radioactivity to decay prior to their transport off site for reprocessing.

Of the CEGB’s eight magnox power stations, seven employ water filled ponds for fuel storage, the eighth station, Wylfa, uses dry storage facilities. All the AGR stations operating or under construction also have ponds.

The pond water provides shielding against radiation from the fuel and also allows the heat generated by the decay of the radioactive fission products to be safely removed.

On receipt in the pond, the fuel elements are placed into open-topped skips and transferred to the main pond storage area. The skips have holes in the sides and base to allow water circulation. Most of the fuel is stored wet, i. e., the elements are in contact with water. However, a small number of elements for post­irradiation examination (PIE) are placed into dry sealed bottles before pond storage.

At the end of its storage period, each skip of fuel is prepared for transfer to the flask loading area for loading into the fuel transport flask. Magnox fuel is normally desplittered (or delugged) at or before this stage in order to utilise transport skip capacity to the full. At most magnox stations and all AGR stations flask loading is carried out in the pond itself. How­ever, at two magnox stations, the flask is ‘dry loaded’ in a shielded area outside the pond.

The main safety aspects to be considered in respect of cooling ponds are those of radiation and contami­nation control, containment and nuclear criticality.