The public has become increasingly anxious about what the nuclear industry intends to do with all the accumulating nuclear waste. Various options have been put forward, and they range from dispatching the waste into space on the back of a rocket to dropping it judiciously into the Mid-Atlantic trench and leaving movements of the earth's crust to take the waste ever deeper. Other choices include drilling bore holes several thousands of meters deep either into rock or on land or out at sea, digging out caverns, again either on land or at sea (with a tunnel to the land) or building mausoleum-like structures on the surface of the land.

The industry believes that different kinds of nuclear wastes need different kinds of disposal. The most radioactive obviously needs the greatest care - and the deepest disposal - whereas low-level waste requires little more than sub-surface disposal, not very different from modern methods of landfill.

If spent fuel has been reprocessed, the disposal of waste requires a somewhat different approach than if the fuel has been left intact, as is now the practice in countries such as the United States and to an increasing extent in Sweden. In the United States the concensus both within the nuclear industry and the environmental movement is that the spent fuel should be stored in special self-cooling structures, designed to draw in a natural circulation of air.

Nevertheless, spent fuel is accumulating at a considerable rate, threatening to clog the system before sufficient facilities can be built. More than 20,000 spent fuel assemblies - the product of little more than 20 years of reactor operation - are now stored temporarily in spent fuel ponds throughout the United States, and the number is increasing by some 4,000 each year. By the end of this year the number could be 300,000.

What happened at Chernoble