Chemical long-term effects during loss-of-coolant accidents in pressurized water reactors
Motivation and aim
To ensure the core cooling in case of loss-of-coolant accidents (LOCA) in pressurized water reactors (PWR), the cooling water spilling out of the leak is collected in the reactor sump and recirculated into the primary cooling circuit by emergency cooling pumps. During the LOCA, coolant impurities may affect both, the clogging of retaining components and the water chemistry. Especially, the long-term contact of the water jet from the leak with hot-dip galvanized steel internals (e.g. grating treads) installed in the containment may cause corrosion of the corresponding materials. Therefore, research activities are focused on studying transport and clogging processes of particles in the sump and on retaining components, respectively. Within a joint research project, the influences of corrosion processes on the water chemistry as well as on the formation of particulate products are investigated in co-operation with the Hochschule Zittau/Görlitz (institute IPM). The experimental and methodic studies are aimed to support the development of methodologies for improved analytical evaluation of the operation of emergency cooling systems during the late stage of a LOCA as well as for evaluation of the fuel rod integrity.
Due to the complex corrosion chemistry and the specific PWR cooling water chemistry, corrosion and subsequent deposition of products are highly complex processes wherein electrochemical reactions are associated with mass transfer and solubility processes, hydrodynamics as well as material properties.
To study the complex corrosion processes in detail, separate investigations of influencing factors are necessary, which is realized by single-effect experiments where basic experiments regarding the corrosion chemistry are carried out in a stirred tank reactor. The results of the batch experiments form the basis for long-term corrosion studies at LOCA-specific process conditions in a lab-scale corrosion test facility. Based on the experimental results, mechanistic models regarding the zinc and the subsequent steel corrosion, which are valid for PWR-specific post-LOCA conditions, were developed.
|Experimental strategy - schematic representation|
|Corrosion of hot-dip galvanized steel in boric acid containing leakage jet|
|Zinc corrosion products and their interactions in boric acid solution|
- Alt, S.; Hampel, R.; Kästner, W.; Kratzsch, A.; Renger, S.; Seeliger, A.; Zacharias, F.; Cartland-Glover, G.; Grahn, A.; Hoffmann, W.; Krepper, E.; Kryk, H.; Generic experiments at the sump model “Zittauer Strömungswanne” (ZSW) for the behaviour of mineral wool in the sump and the reactor core; Kerntechnik 76(2011)1, 20-29
- Kryk, H.; Hoffmann, W.; Waas, U.; Influence of corrosion processes on the head loss across ECCS sump strainers; Kerntechnik 76(2011)1, 46-53
- Kryk, H.; Cartland-Glover, G.; Grahn, A.; Hoffmann, W.; Lecrivain, G.; Isolationsmaterialbelastete Kühlmittelströmung im Kern – CFD-Modellentwicklung und Untersuchung von Korrosionsprozessen; Abschlussbericht zum BMWi-Vorhaben 150 1363; Dresden: HZDR\FWD\2012\01, 2012
German Federal Ministry of Economics and Technology (BMWi): „Particle formation and transport inside the core of Pressurized Water Reactors; physicochemical mechanisms“ (Contract No.: 150 1363, 150 1430), term: 10/2008 – 03/2014
- Hochschule Zittau/Görlitz, Institute of Process Technology, Process Automation and Measuring Technology (IPM)
- HZDR, Institute of Resource Ecology, Surface Processes Division
- HZDR, Institute of Ion Beam Physics and Materials Research, Structural Materials Division