Abstract
For the existing French Magnox type reactors, two computer codes have been developed to analyze the transient after reactor shutdown: The first one, ''GITA'', is representative of the short term evolution (less than 2 days) and it includes a refined representation of all the reactor components. The second one, ''LOTE'', has been developed to represent the long term evolution (from 2 days to several months) with a simplified representation of the main components of the reactor. One example of accident simulation is presented for existing Magnox reactor. Moreover, as a part of the French program on the future reactors, an analysis of the modular high temperature has been initiated. 2D and 3D general flow and conduction codes are used for this analysis: DELFINE is a 2D conduction code including a 1D thermosyphon model. It has been used for decay heat removal analysis. TRIO is a 3D flow code including 3D radiation, conduction and convection heat transfer. It is used for detailed thermal analysis during accidental conditions.
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