Historically, average discharge burn-ups in light water reactors (LWRs) have steadily increased with time as experience has accumulated and technological developments have progressed. The main benefits are to decrease fuel cycle cost and increase the operational flexibility that high burn-ups allow.
Average discharges are currently in the region of 50-60 GWd/t and for burn-ups up to and at least a little beyond this figure, there is a clear economic incentive to continue the trend. But the question for which there is no definitive answer at present is whether this historic trend will continue indefinitely or whether there will be a technological limit to pressurised water reactor (PWR) burn-ups. The question is very important for utilities and fuel fabricators, as it is probably the single most important technical unknown affecting the future LWR fuel cycle.
Will the almost constant rate of increase of historical region average discharge burn-ups will continue in the future? It is conceivable that there may be a lack of incentive for increasing burn-ups much beyond 60 GWd/t (for instance, due to the need for enrichments higher than the current 5.0 w/o criticality limit) or that technological barriers may intervene. The incentives may differ between countries and individual utilities such that even if there are no technological limitations not all utilities may choose to adopt very high burn-ups.
