Ballooning & relocation during - Models and developments

One of the major issues after a (postulated) design basis accident in a nuclear power plant is to ensure the long term coolability of the core and the handling of the fuel assemblies after such an accident. Regulatory criteria have been established for designing and dimensioning the emergency core cooling system. These criteria are well established for many years; still, in view of recent experiments performed at Halden – IFA‐650 series – where extended relocation in the balloon region is observed at (very) high burnup, the issue of clad ballooning, as well as that of fuel fragmentation and relocation, have regained attention of the nuclear community. This report describes supporting material to the computational analysis of the FCA-2013 project: - an analytical approach to characterize the high temperature steady‐state in presence of ballooning and relocation - a model to evaluate the extent of fuel relocation as a function of the cladding deformation - a methodology to simulate the tests of the Halden IFA‐650 series with FRAPTRAN - an overview of the corrections brought to the FRAPTRAN code and the assessment of the FRAPTRAN‐SCK version on the basis of the Halden IFA‐650.2 test.