PSI Center for Nuclear Engineering and Sciences

For water-cooled nuclear reactors, a loss of coolant accident constitutes one of the key scenarios to be evaluated for the design of the plant and associated safety systems. Even if these accidents are not expected to occur at all during reactor lifetime, their potential consequences include the heat up of the fuel in the reactor core. For the recovery of the plant to safe conditions, safety systems are in place to inject water in order to reflood the core and to quench the high temperature fuel. The two-phase flow behaviour during this reflooding phase is extremely complex. In particular, the prediction of the behaviour of small liquid droplets generated as the quench front propagates upwards has a significant effect on the fuel temperatures in the upper regions of the reactor core. In collaboration with the US Nuclear Regulatory Commission (NRC), we have been working to improve our modelling of the droplet behaviour and their impact on key safety parameters.

The European aviation sector stands at a pivotal juncture in its quest to achieve net-zero climate impacts. Focusing on flight CO₂ emissions overlooks up to 80% of the sector's climate repercussions.

Our research delves deep into the role of electricity-based synthetic jet fuels and direct air carbon capture and storage (DACCS) as potential game-changers. These solutions promise climate-neutral aviation, but there's a catch: the relentless rise in air traffic. Relying solely on renewables-derived synthetic fuels may strain both economic and natural resources. On the flip side, offsetting fossil jet fuel impacts via DACCS poses its own set of challenges. Our findings underscore one clear message: for a genuinely climate-neutral European aviation, we must reconsider the scale of air traffic.

The objective of this project was to determine the contribution from a variety of obstacles to moving dislocations to the nano-indentation stress necessary to initiate plastic flow. The obstacles are characterized by different length scales. Among these characteristic lengths, there are those associated with the material microstructure such as grain size, dislocations density, irradiation-induced defects, and those related to the size of the plastic zone beneath the indenter, or equivalently to the size of the indent. Thus, we can classify the size effects into two categories: structural size effect and indentation size effect (ISE). The underlying idea is to quantify and separate these two effects on the unirradiated material first to be able to properly isolate the contribution of the irradiation defect on the measured hardness from the tests on irradiated materials.