A state-of-the-art review of past programs devoted to fuel behaviour under LOCA conditions - part1 Clad Swelling and Rupture Assembly Flow Blockage
Note technique SEMCA-2005-313 - Décembre 2005
This report reviews the main experimental LOCA programs performed in the 70s and 80s devoted to the aspects of clad ballooning and burst as well as resulting flow blockage. For out-of-pile experimental programs, focus has been put on bundle experiments, essentially the REBEKA, ORNL and JAERI tests. For in-pile programs, single rod tests with irradiated fuel from FR2 and PBF programs have mainly been examined, with particular attention paid to the PHEBUS-LOCA bundle experiments, which are the only tests with a fully integral character.
Among the main lessons drawn from the results of these programs that were performed under various experimental conditions, it is worth pointing out the importance of thermal and mechanical interactions between rods as observed on bundle tests on the one hand, and the significant influence of rod pre-irradiation, as observed on PBF tests with single rods on the other hand. The superposition of these two aspects reveals the complete lack of results related to the bundle behavior of irradiated fuel rods, as was already pointed out in a previous recommendation raised in 1983.
A review of analytical work associated with these test results has been limited to a selection of summary reports, namely 1) the NUREG-630 report that recommended a set of correlations for clad rupture, burst strain and the flow blockage ratio , 2) the final comparison reports of the International Standard Problems on REBEKA and PHEBUS and 3) the summary report of LOCA studies related to the EDGAR and PHEBUS programs provided by IPSN. This review highlights the need to both revise the NUREG-630 correlations still used in most of current codes and further develop these LOCA calculation tools so as to take into account the two-dimensional aspects related to fuel-clad eccentricity and thermal & mechanical interactions between neighboring rods.