IMPAIR/3: a computer program to analyze the iodine behaviour in multi-compartments of a LWR containment

This publication describes the second version of the Iodine Severe Accident Code (IMPAIR 3) for multi-compartments and constitutes the revision on the first version code (IMPAIR 2/M). This code models postulated conditions of iodine chemistry present in a compartment (sump, deposition and atmosphere) during a hypothetical LWR severe accident and the transport of species by simulated connections to other compartments or to the environment. The number of species modelled is extended from 18 to 28. The revised chemical basis is described in PSI-Bericht Nr. 114. The code is now written in FORTRAN double precision. This code aims to simulate iodine behavior in multiple compartments of any type of reactor containment starting with reactor core release until the postulated end of accident time. The code boundary conditions are set by the required thermalhydraulic conditions for the transport of airborne iodine species. Since no high temperature iodine reactions relevant to the reactions occurring in the reactor vessel are included to calculate the initial physical and chemical forms of the iodine species, the initial iodine forms must be provided by the user. Two sets of reaction rate and activation energy constants are available. User may assign one or the other to the compartments. Currently both data sets have the same values. However, a user may apply his own data set via the input file. (author) 5 figs., 22 tabs., 22 refs