Experimental and Modeling Investigation of Factors Affecting Crud Deposition in PWRs: Role of Zn, Ni, and Redox Potential

Corrosion products such as nickel-iron spinel oxides (known as crud) in the coolant circuits of pressurized water (PWR) reactors may lead to particulate fouling, negatively impacting power distribution and changing local chemistry. The transport and deposition of particles depend in part on the surface charge of the particles and the nearby surfaces. Tuning coolant chemistry and the composition of the primary circuit materials has been used as an empirical lever for crud mitigation, but experimentation is limited by a variety of other constraints in a working reactor. To simulate the transport and deposition process of crud particles, a multiscale multi-physics model was designed for a simple geometry representing hot/cold leg piping with fluid properties reflecting a PWR environment. A macro-scale model solves the fluid flow and particle trajectories and is later coupled with a fine-scale particle adhesion model. To ensure the relevance of the fine-scale model, surface properties of synthetic crud particles covering a range of compositions and water chemistry (Zn addition and reducing environment) were measured and incorporated into the simulations. Preliminary results of the fine-scale simulations examining the effect of the surface potential of the crud particles and the pipe surface are consistent with expectations from DLVO (Derjaguin, Landau, Verwey and Overbeek) theory and support observations from test loop experiments.