Image: QUENCH facility at KIT. Court. KIT.
The purpose of the QUENCH-ATF project is to investigate the chemical, mechanical and thermal-hydraulics behaviour of ATF claddings in Design Basis Accidents and Beyond Design Basis Accidents scenarios. This will be achieved through a series of three bundle tests at the QUENCH facility at the Karlsruhe Institute of Technology, Germany. Such ATF designs represent an alternative to the standard UO2/Zry system, focusing on the reduction of hydrogen and heat release during severe accident scenarios, and thus increasing coping time for accident management measures, while maintaining or even improving the fuel assembly properties and performance during normal operation. Further requirements include reasonable costs, licensing as well as front end and back end performance. Prior commercial use, extensive testing of the new designs is paramount to demonstrate the advanced safety features; and the NEA QUENCH-ATF project contributes to this effort.
The QUENCH facility is dedicated to DBA-LOCA experiments with pressurised fuel rod simulators and early in-vessel severe accident scenarios with reflood occurring from high temperatures. For both types of tests, a number of reference experiments with zirconium alloys would be available. An initial LOCA test evolving towards severe accident scenario should also be possible.
Following the discussions during the first Technical Meeting held at the NEA on February 14, 2020, three experiments with cladding materials under research worldwide are proposed. The focus of the first two tests will be on Cr-coated Zr alloys, a technology with a higher technology readiness level.
The decision about the third test will be made by the Management Board depending on the outcome of the first two tests and the availability of SiC CMC (ceramic matrix composite) rods with 2.3 m length. The third test may be:
The detailed test scenarios for the first two tests are still under discussion, i.e. LB (large break) or SB (small break) DBA LOCA scenarios, which will result in different temperature-time histories of the corresponding tests. Another criterion for both types of tests (DBA, DEC) is also the availability of reference test data from experiments with uncoated Zr alloys.
The decision for the third test, and therefore the Go/No-go decision for SiC cladding, should be made latest end 2022.