Potential Impairment of Core Coolability during LOCA due to Precipitation of Zinc Borate


Potential Impairment of Core Coolability during LOCA due to Precipitation of Zinc Borate

Pointner, W.; Kryk, H.; Kästner, W.; Austregesilo, H.

Within the framework of German nuclear safety research, generic experimental investigations were carried out at HZDR and the Hochschule Zittau/Görlitz aiming at the elucidation of physicochemical and thermo hydraulic mechanism of corrosion product formation, which may occur during the sump circulation operation after loss-of-coolant accidents in pressurized water reactors.
The contact of the boric acid containing coolant with hot-dip galvanized steel containment internals causes corrosion of the corresponding materials resulting in dissolution of the zinc coating. As main result of batch experiments, decreasing solubility of zinc corrosion products in boric acid solutions with increasing temperature was found. Thus, the formation and deposition of solid corrosion products cannot be ruled out if zinc containing coolant is heated up due to its recirculation into hot regions within the cooling circuit. Generic corrosion and deposition experiments at a lab-scale test facility proved that dissolved zinc, formed at low temperatures in boric acid solution by zinc corrosion, may turn into solid deposits of zinc borates when contacting heated zircaloy surfaces during the heating of the coolant. The results obtained at lab-scale were confirmed by generic experiments at semi-technical scale using a 3x3 heating rod configuration including spacer segments as well as a 16x16 (8x8 heated) fuel rod dummy.
Experiments regarding the corrosion kinetics of zinc-coated components were not subject of the study. Therefore, a quantitative transferability of the results to postulated PWR-LOCA is not given so far.

Keywords: pressurized water reactor; loss-off-coolant accident; corrosion; zinc; boric acid; in-vessel effects

  • Lecture (Conference)
    17th WGAMA Meeting, 23.-26.09.2014, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-20986
Publ.-Id: 20986