Validation of Load History on Fracture

5 November 2014, 1.00 PM - 5 November 2014, 1.00 PM

Venue: Room 3.27, School of Physics,University of Bristol. Speakers: Derreck van Gelderen, Department of Mechanical Engineering and Ventao Liu, Interface Analysis Centre, School of Physics

Validation of Load History on Fracture

Ferritic steels used in Reactor Pressure Vessels exhibit a ductile to brittle fracture transition with temperature. Nuclear Reactor components may be faced with loss-of-coolant accidents, causing pressurised thermal shocks (PTS). Warm pre-stressing (WPS) is an idealisation of PTS and is the process of subjecting a pre-cracked component to a load cycle at a temperature higher than subsequent operating temperatures.

This process is widely acknowledged as being able to enhance the load to fracture. A WPS model developed by Chell and co-workers is reformulated to create a method of undertaking Monte Carlo simulations to study the effects of WPS on brittle fracture. It can be argued that the experiments conducted to date are contrived to show that the WPS enhancement is always successful, however there are circumstances when a specimen might fail prematurely during the WPS path. In this instance, the modified Chell model will be used proactively, incorporating all known errors associated with performing a WPS experiment, to predict the number of prematurely failed specimens at different temperatures and pre-load levels.

Fabrication of UO2 thin films for electronic devices

Uranium dioxide has electrical and electronic properties equivalent to or better than those of conventional Si, Ge, and GaAs semiconductor materials. Thus, it is possible that a new, higher performance class of semiconductors are possible: uranium oxide-based semiconductors. Uranium oxides have characteristics that could give them significantly better performance than conventional materials: operation at substantially higher temperatures and greater radiation and electromotive force resistance implying they may be better suited for use in hazardous environments e.g. space. If depleted uranium instead of silicon was used in the fabrication of semiconductors, it would consume the annual production rate of depleted uranium from uranium enrichment facilities – effective recycling an unwanted waste. In the current project the UO2 thin films were prepared from uranyl

nitrate solution using an electodeposition technique. The UO2 thin films deposited on Ni-layer and Ni-foil exhibited unexpected columnar growth morphology, and have the potential to be a very promising material for solar cells applications.

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