Abstract: STCP Mod1.1 is developed by BCL for estimating the release of radioactivematerials to the environment in severa accidents of nuclear power plant. It is thestate-of-the-art version of STCP which has been released. The STCP Mod1.1 corrects a number of errors discovered in Mod1. 1. TheMod1.1 has already been successfully installed on CDC-825 computer at the IAE. Using this code package, the radionuclide release for four selected severeaccident scenarios were calculated and analysed.