An important accident management measure for controlling severe accident transients in light water reactors (LWRs) is the injection of water to cool the degrading core. Flooding of the overheated core, which causes quenching of the fuel rods, is considered a worst-case scenario regarding hydrogen generation rates which should not exceed safety-relevant critical values. Before the water succeeds in cooling the uncovered core, there could be an enhanced oxidation of the Zircaloy cladding and other core materials that in turn causes a sharp increase in temperature, hydrogen production, and fission product release.
The complex physico-chemical processes during quenching and their mutual influence are the subject of the QUENCH program at KIT. The OECD/NEA International Standard Problem ISP-45 on QUENCH-06 as well as subsequent code activities have shown that the codes still have difficulties to calculate correctly the bundle behavior during reflood; especially thermal runaway is usually not predicted. Coolability of a degraded core is still a matter of high priority as was confirmed by the SARNET-SARP group as well as by OECD-GAMA reports. ... mehrThe outcomes of the OECD SFP program as well as of the SARNET2 benchmarks on the bundle tests QUENCH-10 and QUENCH-16 with air ingress indicated a strong need for more experiments and modelling work to better understand the effect of nitrogen on cladding degradation. Furthermore, after the Fukushima accidents new activities on accident tolerant fuels (ATF) have started worldwide. Design basis accidents are also investigated in the framework of the QUENCH program to support German authorities and utilities.
Topics of the 22nd International QUENCH Workshop have been the discussion of the available experimental data base and the status of the modelling activities on quenching in various countries. Sessions on the current status of the QUENCH program with the focus on the VGB sponsored LOCA experiments as well as on Accident Tolerant Fuels took place at the first day of the workshop. Modelling and application of QUENCH tests for code validation were the main topics at the second day. Additionally, two overview presentations on the outcomes of two international programs were presented. Most of the presentations on the third day of the workshop have been devoted to recent studies on zirconium alloy oxidation and chemical interactions of core materials under severe accident conditions with the focus on air oxidation and hydrogen behavior.
63 scientists from 13 countries took part in the workshop.