The evolution of endurance tests for development of fast reactor core sub-assemblies

Flow induced vibration is a potential cause of high-frequency fatigue, fretting, wear and fretting-fatigue damage to core sub-assemblies of sodium-cooled fast reactors. These damage mechanisms could possibly lead to premature failure of fuel pins or components so it is necessary to confirm that such failures are very unlikely before committing a significant number of sub-assemblies of a given design for irradiation. To do this it is necessary to show that there is a reasonable margin between the conditions to which the sub-assembly will be exposed in service and those needed to cause significant wear or fatigue damage. Endurance tests using water flow instead of sodium have been found to give a practical and timely route for sub-assembly evaluation with respect to flow induced wear and fatigue. Experience gained in the development of the test method is reviewed in order to show that tests, at increased flow rate in water, cause wear to take place at the same, more vulnerable sites, but in a sorter time. (author)