In this document are presented the results, analyses and conclusions from first simulation runs of selected Loss Of Coolants Accidents (LOCA) and Steam Generator Tube Ruptures (SGTR) in different kinds of LWRs (PWRs, BWR, VVERs and EPR) within DBA and DEC-A conditions. These transients, being by nature completely different and involving different physical phenomena, have been selected at the very beginning of the project as representative bounding scenarios to quantify the gains obtained by code and methodology improvements planned during the project. This first run of simulations of the reactor cases has been performed using existing simulation tools of various details at different scales in various calculation schemes. These calculations have provided a large range of results that were post-processed and analysed. Mostly modelling tools currently used for the reactor accident calculations in each partner's country were used without sometimes going into detailed modelling of all the processes occurring from the reactor core to the environmental releases during the transients. For the non-modelled processes in some cases decoupling factors and arbitrary assumptions usually conservative assumptions were used. The results of these calculations allowed to highlight where improvements in the simulation tools and calculation schemes could be made to better estimate the environmental releases during LOCA and SGTR transients under DBA and DEC-A conditions.