Chemical reactions in LWR reactor vessels during core melt accidents analyzed with the CELSOL computer code

A computer code CELSOL for calculation of chemical equilibria in reactor accidents as function of time and space was developed as a part of a common nordic safety study. The CELSOL code was used together with the codes MARCH 3l0, RELCON and TRAP-MELT 3 to evaluate the amount and to describe the chemical behavior of elements released from reactor fuel during core melt accidents in LWR reactors. It appears from a number of calculations with these codes on different accident sequences that the chemical behavior of Cs, I, Te, B and C varies considerably from one accident sequence to another. The CELSOL code keeps track of the physical form of the different compounds, whether they are in gaseous, liquid or solid state. The chemical environment changes, if the liquid and solid parts of the compounds are removed from the gas stream due to aerosol sedimentation. A sensitivity study was carried out in order to study the effect of sedimentation on the gas phase chemistry