There are many reasons why improvements to AGR fuel design are constantly being sought. Despite the success so far achieved, the optimum design to meet the longer term requirements of AGR operation has yet to be achieved. We have already seen how large savings in fuel cycle costs can materialise through the attainment of longer fuel life, i. e., higher burn-up. Consequently much effort is being devoted towards this fundamental objective in the hope that AGR fuel will be capable of reaching 21, 24 or even 30 GWd/t at discharge, by the incorporation of burnable poi­son cables or ‘toroids’ within the grid and brace sup­port grooves of more highly-enriched elements. The achievement of greater burn-up, however, must not be realised at the expense of fuel integrity. Therefore, in parallel with any related fuel element modifications, future fuel design and manufacturing objectives will need to make allowances for the implications of in­creased burn-up on the safety and performance aspects of the fuel pins.

Currently, the AGRs w’ithin the UK have not achi­eved their design objective of continuous on-load re­fuelling at full reactor power. The need to regularly reduce reactor power in order to refuel is obviously costly. It is considered that the potential for refuelling at higher reactor powers can only be realised by the development and use of a stronger single-sleeve design of fuel element, which would be capable of with­standing the forces exerted on it by the reactor coolant under conditions of high mass flow. This type of fuel element is known as the Stage 2 (single sleeve) design, as different from the Stage 1 (double sleeve) current design, and its development will undoubtedly be ac­companied by the inclusion of many other age, safety and performance improvements currently under in­vestigation (see Chapter 2).