Year
2010
File Attachment
Abstract
TN International and International Nuclear Services (INS) started in early 2000s a joint project, the Fuel Integrity Project (FIP), in order to develop a methodology to assess the response of Light Water Reactor (LWR) fuel assemblies (FA) during 9 meters regulatory drops. To this end, several series of mechanical tests were carried out on fresh and used fuel rods samples, including intergrid bending tests on samples of used fuel rods with average burn-up of 50 GW.d/tU. In this framework, a preliminary analysis of the commissioning test (test 11.1) results was presented during Patram 2004; in complement, the analysis of the whole test series 11 (tests 11.1 to 11.6) is now presented. The used test span matches a typical intergrid length of LWR FA. The load is applied at mid-span of the fuel rods samples by a pulley wheel. This test series leads to failures starting at a net lateral deflection of about 35 mm at room temperature and 60 mm at 500 °C, and with few percent high total elongations. Calculation of the whole tests series was carried out with the ANSYS code using a shell and brick model. The different mechanical phenomena occurring during the tests were distinguished and the adequate fuel rods material parameters were determined. The determination of these phenomena by preliminary calculations and the models validation were followed by a sensitivity study of the parameters values in the material constitutive laws to insure a good agreement between the obtained strength / deflection curves and the actual tests curves. This sensitivity study was all the more efficient and reliable as the effects of each material parameter appeared almost sequentially and cumulatively during the loading of the fuel rods samples. Even though models improvements might be possible, the guidelines of the retained approach lead to reference maximum elongations at rupture in consistency with literature values for used fuel rods. The methodology to apply these Finite Element Analysis (FEA) results of bending test series 11 to an actual used FA during a 9 m lateral drop test is finally presented.