Generic zinc corrosion studies at PWR LOCA conditions

During the sump recirculation phase after loss-of-coolant accidents (LOCA) in pressurized water reactors (PWR), coolant spilling out of the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps. The long-term contact of the boric acid containing coolant with hot-dip galvanized containment internals (e.g. grating treads, supporting grids of sump strainers) may cause corrosion of the corresponding materials influencing the cooling water chemistry.
Generic investigations regarding such zinc corrosion processes, changes of the coolant chemistry and possible resulting in-core effects are subject of joint research projects of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Dresden (TUD) and Zittau/Görlitz University of Applied Sciences (HSZG). Lab-scale experiments at HZDR and TUD were focused on elucidation of physico-chemical corrosion and precipitation processes as well as resulting clogging effects [1-2].
Recent results of generic experiments in a lab-scale corrosion test facility led to further information regarding the main parameters determining the zinc corrosion rates and the whole corrosion process in such scenarios.
Main influences on the zinc corrosion rates were identified as the impact of the coolant jet onto the corroding surface and the particular flow conditions around submerged zinc surfaces.
In contrast, variations of the coolant temperature in the range between 25 °C and 70 °C as well as small changes in the boric acid concentration have no significant influence on the corrosion rates during the first stage of the corrosion process.
Further lab-scale experiments at realistic time-dependent LOCA parameters like calculated temperature courses in the sump and inside the reactor core are planned to evaluate, if zinc corrosion processes with subsequent zinc borate precipitations could lead to considerable clogging effects inside the reactor core.
The results obtained at lab-scale were complemented by corresponding experiments in semi-technical test facilities of the project partner HSZG.

[1] Seeliger, A.; Alt, S.; Kästner, W.; Renger, S.; Kryk, H., Harm, U. : Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - thermo- and fluid-dynamic effects. Nuclear Engineering and Design, 2016, 305, 489-502
[2] Hoffmann, W.; Kryk, H.; Seeliger, A.; Kästner, W.; Alt, S. & Renger, S.: Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - physicochemical effects. Nuclear Engineering and Design, 2014, 280, 570-578