Analysis of iodine source term from a small BWR during a postulated severe accident using IMPAIR 2/M code

The iodine source term expected to occur during a postulated severe accident is analyzed for a small (1000 MWt) Boiling Water Reactor. The accident was assumed to be initiated as a result of an anticipated transient with scram. The IMPAIR 2/M code which essentially employs the IMPAIR 2 code chemistry to the LWR containments modelled with multiple compartments is used for the analyses. The thermal-hydraulics, aerosol behavior, source term of various iodine species and the dose rates required for the IMPAIR 2/M analyses are calculated with other computer programs. This paper introduces IMPAIR 2/M code and presents the capabilities of the code in predicting iodine behavior in postulated severe accident in a BWR, especially in the wet-well. In summary: IMPAIR 2/M code is written to apply the IMPAIR 2 to multiple compartment applications with the boundary conditions taken from other thermal-hydraulic, aerosol and dose rate calculations. The code has the strength of calculating iodine species behavior in dry compartments and compartments containing water pool, as well as the transport of airborne iodine species into the environment. (authors)