SMART: a Simple Model for Activity Removal and Transport

Abstract

SMART is a computer program designed to predict the radionuclide behaviour in containment following a loss-of-coolant accident, including the time-dependant source term from the break and the subsequent transport, removal and releases to the atmosphere. The SMART code uses containment thermal-hydraulic data generated by a containment thermal-hydraulic code. The node-link structure of SMART is set by the containment thermal- hydraulic code, using a data transfer file. Other relevant information, such as the location and type of holes in containment, cooler characteristics, surf ace areas, etc., is also directly transferred between the two codes. Transient thermal-hydraulic data transfer between these two codes includes link flow rates, nodal temperatures, nodal pressures , the node mass, the flow through holes etc. The SMART program considers the build-up of radionuclides due to the decay of their precursor(s). Decay chains of two levels can be considered. It also simulates the production of penetrating (organic) iodine and its partitioning from the water pools if the airborne fraction of the penetrating iodine falls below a specified equilibrium level. The philosophy of the radionuclide treatment is based on combining the unit processes to define the behavioral models, and combining the behavioral models to define a radionuclide model. A unit process is the representation of a specific phenomenon such as sedimentation, washout by liquid drops etc. A behavioral model is a collection of relevant unit processes to define the behaviour of a given physical and chemical form of a chemical specie such as gaseous molecular iodine. Other than the user defined behavioral model, the predefined behavioral models available in SMART are; stable gas, noble gas, fog, liquid aerosol, molecular iodine, drop, penetrating iodine and non-mobile form. Even when the user selects a predefined behavioral model, he has a choice to deselect some non-critical unit processes; for example using molecular iodine model, the user can deselect the following unit processes: decay, build-up, washout by dousing-spray, and washout by break spray.