Thermodynamic modeling of the processes in a boiling water reactor to buildup the magnetic corrosion product deposits

The buildup of corrosion product deposits (CRUD) on the fuel cladding of the boiling water reactor (BWR) before and after zinc injection has been investigated by using Gibbs Energy Minimization (GEM-Selector code) calculations of thermodynamic equilibrium at in situ temperatures and pressures. Under the BWR water chemistry conditions, Zn addition together with the presence of Ni and Mn induce the formation of (Zn,Ni,Mn)[Fe2O4] spinel solid solutions. GEM calculations applied to the boiling zone match with the electron probe microanalysis (EPMA) and Extended X-ray Absorption Fine Structure (EXAFS) findings, indicating that zinc-rich ferrite spinels are formed on BWR fuel cladding mainly at lower pin elevations under Zn water chemistry conditions. GEM results have helped to explain the existence of magnetic product deposits on the surface of the fuel element and the processes that take place in the reactor.

► Buildup of corrosion product deposits on fuel claddings of a boiling water reactor (BWR) are investigated.
► Under BWR water conditions, Zn addition with Ni and Mn induced formation of (Zn,Ni,Mn)[Fe2O4].
► GEM calculations applied to the boiling zone match with the EPMA and EXAFS findings.
► Zinc-rich ferrite spinels are formed on BWR fuel cladding mainly at lower pin elevations.