Provision of Research Support on the Review of the Established Good Practices in Development of Clad Ballooning and Embrittlement Models for Higher Burnup PWR Fuel

Collect and analyse information for the experiments conducted to simulate ballooning behaviour and to investigate flow area blockage in the following three conditions:  LBLOCA refill phase;  LBLOCA reflood phase;  SBLOCA boildown phase.

This analysis should also consider the PAKS event and should make judgements on the influence of bundle size and radial constraint when drawing conclusions for the reactor.

Identify the modelling methods and computer codes that are currently used to predict flow area blockage and subsequent effect on heat transfer of fuel at higher (50 – 80 GWd/tU) burnup PWR fuel in accident conditions; Select three sets of modelling methods and related computer codes as representative for established good practice in terms of:  representation of the most important phenomena to mechanistically model the failure of individual pins across the range of LOCA sizes (and azimuthal temperature gradients);  realistically translate pin failure strain to flow blockage in the fuel assembly;  realistically represent the two-phase flow in ballooned fuel in order to provide a reliable prediction of peak-cladding temperature;  verification and validation status.

Estimate the accessibility and implementation cost for each of the selected sets.

Provide conclusions and recommendations