Design considerations for nuclear fuel elements to suit reactor operating in small electrical grids

The 220 MWe Candu-PHW unit of the Rajasthan Atomic Power Station (RAPS) has experienced to-date over 130 reactor trips, shut downs or power cut-backs, as against a total of 100 planned and unplanned outages specified in the fuel design specification. Majority of these power cycles are ascribed to either class IV power failures or severe grid frequency swings. To overcome these problems, consideration is also being given for replacing existing turbine-follow-reactor philosophy by a modified reactor-follow-turbine control scheme. As such, in addition to power cycles associated with outages, the reactor is likely to experience daily cycling of some power level. The objectives set out for the study were (i) to examine, whether or not, the current fuel of the wire-wrap design will survive power cycles (which may exceed 300 for the start-up charge) and (ii) to evolve fuel design modifications, so that power cycling does not become a performance limitation. (Auth.)