Local effects in pressurized water reactors core caused by zinc borate deposition in a loss-off-coolant accident
Motivation:
In the case of a leak in the primary circuit of a pressurized water reactor (LOCA) large amounts of boric acid coolant will get in the containment of a nuclear power plant. Zinc corrosion of various hot-dip galvanized fittings will then cause the formation of (solved) zinc borates. During the management of such a LOCA, first the reactor will be rapidly shut down and later different emergency cooling systems for the reactor core will be started to ensure the permanent further cooling of the fuel rods (removal of decay heat). During this time, the sump recirculation will be started using the collected liquids in the containment.
Because the water solubility of the formed zinc borates decreases at higher temperatures, it is possible that these compounds will precipitate later in the hot regions of the reactor core. This could cause a reduction of the heat removal from the reactor core with all the subsequent problems.
Objectives:
The main task of the project is to simulate the assumed zinc corrosion process in the containment and the later precipitation of the formed zinc borates (ZnB) in the reactor core by using laboratory scale experiments (PETrA-facility). Particularly, it needs to be investigated, if a significant or even critical zinc borate precipitation will take place in the reactor core in the later phase of a LOCA scenario under realistic boundary conditions. The data for such an incident can be obtained by the usage of special software, which had been developed in the past to simulate different accidents in pressurized water reactors. Furthermore as needed, strategies should be developed to avoid a zinc borate precipitation under LOCA conditions.
Methods and results:
With the lab-scale facility (PETrA), experiments are carried out to examine the zinc corrosion process in the boric acid containing coolant and also to investigate under which conditions a precipitation of the formed zinc borates will occur. Among other things, these investigations include chemical analysis as well as conductivity measurements (coolant solutions), temperatures, flow rates and pressure values of the coolant. So far the dependence of the corrosion rate from coolant temperature, changes of the coolant chemistry or different flow conditions could be examined for some estimated LOCA conditions.
Operational scheme of the PETrA facility (laboratory scale) to simulate the zinc dissolution and subsequent zinc borate precipitation in hot spots of the reactor core.
Zinc borate precipitations at a heated cladding tube (up to 90° C).
Publications:
H. Kryk, U. Harm, U. Hampel
Reducing in-core zinc borate precipitation after LOCA in pressurized water reactors
47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Germany
H. Kryk, U. Harm, U. Hampel
Corrosion of hot-dip galvanized containment installations - A potential cause for thermal-hydraulic effects after LOCA in PWR?
ICONE 24 - International Conference on Nuclear Engineering, 26.-30.06.2016, Charlotte, USA
A. Seeliger, S. Alt, W. Kästner, S. Renger, H. Kryk, U. Harm
Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - Thermo- and Fluid-dynamic effects
Nucl. Eng. Des. 305 (2016), 489-502