Integrated safety analysis code system (ISAS) application for accident sequence analyses

In the frame of the ITER Task 'Reference Accident Sequences', two accident sequences have been assessed to demonstrate the effectiveness of the use of integrated safety analysis code system (ISAS). The first one is a loss of coolant event in the divertor primary heat transfer system (DV PHTS) toward s the vacuum Vessel containment during normal plasma burn; the second one i s a loss of coolant event in the DV PHTS towards the lower vault during bak ing conditions. The comparison of the results obtained in standalone and co upled modes was performed. The codes used for the analyses are ATHENA for t hermal-hydraulic simulation, INTRA for containment studies and NAUA for aer osol transportation. The three codes are linked together in the ISAS chain by means of files written in the Gibiane language. The ISAS application see ms to be promising in order to have a powerful tool in the fusion plant acc ident analysis. It is able to treat different codes, developed for differen t fields of applications, as a unique code simulating the complete evolutio n of an accident sequence. ISAS permits a detailed exchange of data between the codes, otherwise impossible in standalone mode. It reduces the errors in typing exchange data and takes into account the feedback effects during the calculation. The coupling of the codes makes possible to compensate the lack of some phenomenon models in one code if they are treated in another code of the chain (i.e. radiative heat exchange between heat structures tha t is missing in ATHENA and foreseen in INTRA). The results obtained in the two accident analyses demonstrate that ISAS can be very useful to represent in a more coherent way the trend of an accident respecting the correct bal ance of the inventories. In the paper the whole evolution of a typical fusi on power plant accident is analysed starting from the break in the cooling loop system, studying the effects of the loss of coolant in the containment and simulating the leakage of the aerosols outside vacuum vessel and vault s. (C) 2000 Elsevier Science B.V. All rights reserved.