Balance of power in ADS operation and safety

Subcritical, accelerator driven systems (ADS) are viewed in recent years wi th increasing interest for their possible role in perspective future nuclea r energy scenarios, as actinide incinerators, and/or claimed energy plants with potential enhanced safety characteristics. Important research programs and in particular extensive studies on their behavior under incidental con ditions are made, for verifying their claimed advantage with respect to the corresponding fast critical reactors. An extensive, effective safety analy sis of these latter systems was made in the late 80's at the Argonne Nation al Laboratory, specifically with respect to the Integrated Fast Reactor (IF R). A synthetic, quite effective deterministic method was used based on a " balance of reactivity" approach. In the present paper an attempt is made to redefine a similar methodology in relation to the ADS, making rather use o f a "balance of power" approach. This would allow to estimate the peculiari ties of the ADS systems, in particular with respect to the corresponding cr itical ones. A number of important incidental events have been considered, such as TOC (transient of power following a current increase, in particular the current reserve for compensating burnup), LOF (loss of coolant how), H TWS (heat transfer without sink), CIT (chilled inlet temperature) events. A s an example of application of this methodology, the Russian lead cooled BR EST fast reactor project has been considered. The results obtained for this system, and for the corresponding ADS at various levels of subcriticality, are given. (C) 1999 Elsevier Science Ltd. All rights reserved.