[en] Typical Code Categories for Deterministic Safety Analysis is carried out through Simulated Phenomena as reactor physics, fuel behaviour, thermal hydraulics, structure dynamics, and radiological dose calculations. Other criterion is Depth of Simulation concerning detailed mechanistic models and simplified modelling. And last criteria is the Scope of Simulation, concerning core (square, hexagonal etc.), reactor coolant system, dry containment, pressure suppression systems. Verification: The code behaves as intended (proper mathematical representation of the conceptual model, equations are correctly encoded and solved). Verification may include demonstration of convergence of calculated results while reducing time steps and size of nodes, comparison with exact mathematical solutions, benchmark comparison with other codes, and check of plausibility. Validation: Comparison of calculated results with measured values. As an example, the verification matrix for RELAP5/MOD3, partly repetitions of calculations already performed before with RELAP5/MOD2, contains phenomenological problems like for instance gravitation head effect of falling liquid into a steam atmosphere, non-condensable state oscillatory flow (U-tube oscillations), and several workshop problems simulating a hypothetical two-loop PWR system. US NRC has approved ANF-RELAP - an SPC-modified version of RELAP5/MOD2, Version 36.02 - for SBLOCA, steam line break, and non-LOCA transient licensing analyses. The improvements and modifications included are those required to provide congruency with the unmodified literature correlations and those required to obtain adequate simulation of key LBLOCA experiments. The developmental verification problems performed for RELAP5/MOD2 and MOD3 can also be considered as applicable for S-RELAP5. The validation of single physical models and the entire computer code ATHLET is performed systematically by pre- and post-calculations of experiments on reactor safety as well as by confirmatory calculations of transients in reactor plants. On the basis of the international OECD/NEA validations matrix, an overall validation matrix was derived for ATHLET extended by the experiments, which are specific for reactors of German design. The ATHLET overall validation matrix contains 93 single-effects experiments (PWR, BWR), 101 integral experiments (PWR, BWR), and 24 integral experiments for WWER-reactors