More mechanistic codes have been developed to model in detail, the various phases of a severe accident. They include SCDAP/RELAP5 (Allison et al.) for the in-vessel core

melt-down phase, VICTORIA (NUREG/CR-5545, 1992) for fission product effects including transport in the primary circuit and CONTAIN (NUREG/CR-6533, 1997), a containment phenomenology code.

The development of severe accident LWR codes (and supporting experimental programmes) has attracted significant research and development investment, much greater than that invested in other reactor types. The work have resulted in the development of improved accident management guidelines for the existing plants and improved robustness against severe accident challenges in the design of evolutionary plant.