Prompt reactivity determination in a subcritical assembly through the response to a Dirac pulse

The full understanding of the kinetics of a subcritical assembly is a key issue for its online reactivity control. Point kinetics is not sufficient to determine the prompt reactivity of a subcritical assembly through the response to a dirac pulse, in particular in the cases of a large reflector, a small reactor, or a large subcriticality.Taking into account the distribution of intergeneration times, which appears as a robust characteristic of each type of reactor, helps to understand this behaviour.Eventually, a method is proposed for the determination of the prompt reactivity. It provides a decrease rate function depending on the prompt multiplication coefficient Keffp. Fitting a measured decrease rate with this function, calculated once for the reactor, gives the true value of keffp. The robustness of the method is tested. (Elsevier

Potential of thorium molten salt reactors : detailed calculations and concept evolution with a view to large scale energy production

PAC

Molten salt reactors and possible scenarios for future nuclear power deployment

PAC

Failure analysis of micro-heating elements suspended on thin membranes

We report on the degradation of platinum micro-heating elements operating at high temperatures. Devices with platinum heaters suspended on micro-machined dielectric membranes were self-heated at high temperature until failure. Optical and SEM observations combined with mechanical deformation measurements and Thermal Laser Stimulation techniques were used to analyze the failure mechanisms of the micro-heating elements. Platinum atoms migration and breaking of the membrane were two failure modes observed. At high temperature, the migration of the platinum atoms was linked to the mechanical stress in the dielectric membrane. The Thermal Laser Stimulation technique revealed the formation of vertical as well as lateral thermocouples at mechanically deformed areas. One explanation proposed is that those thermocouples are the result of Si diffusion from the Si3N4 membrane into the platinum heater as well as electro-stress migration of platinum atoms