Confirmation of the Design Characteristics of the TVS-K Design After Operation in the PWR Reactor at Ringhals-3 NPP

Abstract

In 2020, four TVS-K fuel assemblies were unloaded from Ringhals-3 NPP after completion of pilot operation. During four fuel cycles, the TVS-K reached a burnup of 54.3 MWday/kgU. To confirm the design characteristics and justification the reliability and performance of TVS-K materials, six fuel rods and the skeleton were delivered to the Studsvik Hot Cell Laboratories for post-irradiation examinations. This paper presents the results of the following studies:

• Examinations of the Skeleton and the Top Nozzle;

• Non-destructive examination of Guide Thimbles (GT), Instrumental Tube (IT) and Spacer grids (SG);

• SEM studies of SG including welds;

• Metallographic studies and determination of hydrogen content of GT and IT;

• TEM and EDX investigation of structural-phase state and element composition of GT and IT;

• Non-destructive examination of fuel rod claddings (E110opt);

• Metallographic studies and microhardness measurements of the top and bottom welds and fuel rod claddings and measurement of the gap;

• Fuel density measurement with fuel swelling assessment. SEM and EDX of fuel;

• Mechanical tests of fuel rod claddings and fuel rod springs relaxation;

The presented experimental data confirm the design characteristics and the high performance properties of the materials and TVS-K components and provide information on their corrosion resistance, strength, and dimensional stability under irradiation in the water-chemical regime of the PWR.