Improvements in the decay heat model in the thermalhydraulic code TRAC-BF1

Abstract

The implemented models in TRAC-BF1 for the decay heat calculations are based on the 1971 American Nuclear Society (ANS) Standard or the 1979 ANS Standard if selected by the user. With the entry into force of the 1994 ANS Standard and the subsequent review, the TRAC-BF1 models were made completely obsolete, so a revision of the older models and the implementation of ANSI/ANS-5.1-2005 Standard in the code are required. In this paper, a novel numerical study is presented based on the analytical resolution of the decay heat equation which takes into account the number of reactor operation histories, the number of fissionable nuclides, and the number of groups per fissile. Moreover, this paper describes the influence of the short-term power histories on the total decay heat power calculation due to the high interest in the simulation of severe transients, such as Anticipated Transients without SCRAM, which cannot be ignored in nuclear safety analysis.