Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

In a joint research project of the Zittau/Goerlitz University of Applied Sciences (HSZG), the Technische Universitaet Dresden (TUD) and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the main emphasis is the time-related assignment of simultaneous and interacting mechanisms at zinc sources and zinc sinks at boundary conditions of a loss-of-coolant accident (LOCA) in German pressurized water reactors (PWR). The according experiments are carried out at semi-technical as well as at laboratory scale.
Zinc is used as a protective coating, e.g. for gratings in the containment, showing high corrosion resistance due to a gradual formation of passivating layers. In contrast, its long-term behaviour during LOCA changes significantly under the influence of the coolant chemistry of German PWR. As a consequence, according installations in the containment act as zinc sources due to corrosion. Released zinc ions change the chemical properties of the coolant and could e.g. lead to layer-forming depositions of zinc borates in the core, which increase the possibility of a hindered heat dissipation. For experimental and methodical investigations of these phenomena, the test rig “Zittau Flow Tray” (ZFT), a scaled sump model of a German PWR, was equipped with a full-length 3×3 fuel assembly (FA) dummy acting as core model, a preheater and a cooler component. Nine 4.4 m long fuel rod dummies simulate the decay heat by internal heating cartridges. This rig design enables experimental investigation of physico-chemical mechanisms considering coolant containing boric acid and zinc and their influence on the thermo-hydraulic processes in the reactor core at post-LOCA boundary conditions.
The time depending zinc release at hot-dip galvanized gratings (HGG) was investigated regarding their position (e.g. inside or near the leaking jet, freely suspended or submerged in the coolant) and their surface area as well as temperature and flow rate of the coolant. The experimental database allows the approximation of corrosion rates in dependence of HGG position and the accident-specific coolant leakage rate as well as the development of first mathematical approaches for the modelling of zinc sources.