The COCOSYS computer code for simulations of major accidents in nuclear power plant containments

Simulations of major accidents in containments of nuclear power plants are needed for analyses of potential consequences and for evaluating possible countermeasures. Such analyses must be carried out as realistically as possible. For this reason, GRS is developing the containment code system (COCOSYS). Its purpose is to offer a code system based on mechanistic models, as far as possible, of the comprehensive simulation of all relevant phenomena occurring in the course of major accident sequences in light water reactors; also design basis accidents are to be included. Special tools have been developed for handling the code system, for instance. for establishing the datasets, including on-line documentation, and an interface with the ATLAS code has been created far dynamic visualization of the results. The code system has been validated against various experiments for verification. The example cited in the article refers to calculations of specific KAEVER experiments. COCOSYS is currently used in the investigation by expert consultants of the installation of catalytic recombiner systems in German nuclear power plants. For realistic calculation of local hydrogen concentrations, especially detailed nodalization and comprehensive modeling of the technical systems is required.