A level 2 PRA includes the postaccident phenomenology necessary to estimate the amount of material or energy released from the facility in question, but does not assess the off-site consequences that would result. For example, a level 2 PRA of a nuclear power plant would include analyses of potential postcore melt phenomena such as core/concrete interactions or hydrogen explosions in order to assess the structural response of the containment building and the amount of radioactivity released from the plant as a result of different types of accidents (corresponding to different plant damage states). Similarly, at a chemical facility, a level 2 PRA could include analyses of exothermic chemical reactions occurring due to unintended chemical mixtures. (Note that level 2 PRAs may not be meaningful for some types of facilities, such as holding tanks whose only failure mode is leakage.) A level 3 PRA includes a model of how material released from the facility disperses in the environment, as well as models for public health impact and off-site property damage.
