This paper presents 3D simulations of power ramps in pressurized water reactors with the fuel performance code ALCYONE, which is part of the computing environment PLEIADES. The code has been upgraded to couple the description of irradiated fuel thermochemistry already available with oxygen transport taking into account thermodiffusion. The impact of oxygen redistribution during a power transient on irradiated fuel thermochemistry in the fuel and on chemically reactive gas release from the fuel (I (g) , I 2(g) , CsI (g) , TeI 2(g) , Cs (g) , Cs 2(g) ) is studied. The simulations show that oxygen redistribution, even if moderate in magnitude, leads to the reduction of metallic oxides (molybdenum dioxide, cesium molybdates, chromium oxide) at the fuel pellet center and consequently to the release of a much greater quantity of gaseous cesium. Pellet-Cladding Interaction failure propensity is shown to decrease in consequence of the thermodynamically favourable reaction of iodine with released cesium in the free volume of the rod.

The role of dry storage in spent nuclear fuel management becomes more and more important. Originally intended to serve as a temporary solution for a few decades until final disposal, now dry storage period is to be extended to 100 years and beyond. It has to be proven for licensing that the fuel rod integrity during dry storage is ensured. Since it is difficult to provide experimental support, the licensing process has to rely largely on numerical simulations. This paper reviews the literature associated with the modeling of spent nuclear fuel under dry storage conditions. The main phenomena threatening the fuel rod integrity and the numerical models representing them are described here. Moreover, the most recent or currently ongoing experimental efforts that could support the modeling of nuclear fuel in dry storage in the future are discussed. Finally, this paper reviews approaches to dry storage modeling chosen by different countries. In general, these approaches are similar and can be described as a calculation chain consisting of neutronics-thermo-hydraulics-fuel performance computations where sensitivity and uncertainty studies are crucial elements.

According to the Swiss waste management policy, spent nuclear fuel is planned to be disposed in a deep underground repository. Prior to final disposal, spent nuclear fuel is stored at reactor sites and in a centralized dry storage facility. Since the operation dates of the final repository are unknown, extended periods of interim storage have to be considered. A research program to investigate the fuel rod integrity during long-term dry storage has recently been launched at Paul Scherrer Institute. In the context of the project, fuel rod performance simulations will be carried out with the code Falcon. Until now, an extensive literature survey concerning current trends in dry storage modelling has been written and first developments of Falcon’s capabilities towards dry storage modeling have been made. In this work, Falcon has been modified by implementing a long-term cladding creep model. The original and upgraded versions of Falcon have been used to simulate a demonstration case consisting of the base irradiation, wet storage, drying and dry storage. Results obtained with both versions have shown an important difference in the cladding hoop creep which justifies implementation of the new creep model.