The behavior of PWR fuel rod cladding under LOCA conditions strongly depends on the interactions between the metallurgical evolution (phase transformation) and the thermomechanical behavior at high temperature. FRAMATOME needs for the qualification of advanced zirconium alloys have motivated an extensive study of the phase transformation kinetics and the development of a new test facility, EDGAR-2, to perform thermomechanical tests. The first part of the paper deals with an experimental study and modeling of the α↔β phase transformation kinetics. High-temperature/high-sensitivity calorimeter and fast dilatometer facilities have been used to measure the on-heating α⃗β and on cooling β⃗α phase transformations from near equilibrium conditions up to LOCA conditions (heating-cooling rates up to 100°C/s). The equilibrium fraction of α/β phase as a function of temperature is derived from calorimetric measurements using the Zhu and Devletian model and described using a modified Johnson-Mehl-Avrami equation. Modeling of the α↔β kinetics is given by the differential Holt equation. The present results show that the Holt model gives a good description of the α⃗β kinetics upon heating but is not able to describe accurately the β⃗α phase transformation upon cooling, probably because it does not take into account the occurrence of the partial martensitic transformation during cooling, especially for the higher cooling rates. An important feature of the current study is that, despite the α/β equilibrium temperatures for M4 (ZrSnFeV) and M5 (ZrNbO) alloys being lower than that of Zy-4, for kinetic reasons the α to β phase transformation occurs in the same temperature range for the three alloys in the case of fast thermal transients (i.e., 10°C/s). This observation could be related to the slower thermal diffusion of Nb and V atoms compared to that of Fe and Cr. This slower diffusion explains why the thermalmechanical behavior of new M4 and M5 alloys is quite equivalent to Zy-4 in LOCA conditions. The second part of this paper deals with the thermomechanical tests. The EDGAR-2 test facility performs single rod tests under any internal pressure and clad temperature transients in steam environment. The advanced zirconium alloys M4 and M5 have been tested under steady-state conditions of pressure and temperature, continuous-heating and constant-pressure conditions for various heating rates and pressure, and some LOCA representative pressure temperature transients. The experimental program covers the LOCA conditions, and the rupture occurs from a few seconds up to 2000 seconds. The results are compared with those of the SRA optimized Zy-4 clad using the Monkman-Grant correlation, rupture ductility versus burst temperature, and burst criteria. EDGAR models for the prediction of the evolution of the transformed β-phase volume fraction and of the diametral deformation, time to rupture, and uniform diametral rupture elongation in typical LOCA conditions are derived for advanced alloys from the two parts of this study. These models may easily be implemented in most accident simulation computerized codes for safety analysis.

Human chorionic gonadotropin (hCG), a 37 kDa glycoprotein hormone, is a key diagnostic marker of pregnancy and has been cited as an important biomarker in relation to cancerous tumors found in the prostate, ovaries and bladder.A novel chemically-modified epitaxial graphene diagnostic sensor has been developed for ultrasensitive detection of the biomarker hCG. Multi-layer epitaxial graphene (MEG), grown on silicon carbide substrates, was patterned using electron beam lithography to produce channel based devices. The MEG channels have been amine terminated using 3-Aminopropyl-triethoxysilane (APTES) in order to attach the anti-hCG antibody to the channel.Detection of binding of hCG with its graphene-bound antibody was monitored by measuring reduction of the channel current of the graphene biosensor. The sensitivity of the sensor device was investigated using varying concentrations of hCG, with changes in the channel resistance of the sensor observed upon exposure to hCG. The detection limit of the sensor was 0.62 ng/mL and the sensor showed a linear response to hCG in the range 0.62 to 5.62 ng/mL with a response of 142 Ω/ng/mL. At concentrations above 5.62 ng/mL the sensor begins to saturate.

A generic electrochemical method of "bioreceptor" antibody attachment to phenyl amine functionalised graphitic surfaces is demonstrated. Micro-channels of chemically modified multi-layer epitaxial graphene (MLEG) have been used to provide a repeatable and reliable response to nano molar (nM) concentrations of the cancer risk (oxidative stress) biomarker 8hydroxydeoxyguanosine (8-OHdG). X-ray photoelectron spectroscopy, Raman spectroscopy are used to characterize the functionalised MLEG. Confocal fluorescence microscopy using fluorescent-labelled antibodies indicates that the anti-8-OHdG antibody selectively binds to the phenyl amine-functionalised MLEG's channel. Current-voltage measurements on functionalised channels showed repeatable current responses from antibody-biomarker binding events. This technique is scalable, reliable, and capable of providing a rapid, quantitative, label-free assessment of biomarkers at nano-Molar (less than 20 nM) concentrations in analyte solutions. The sensitivity of the sensor device was investigated using varying concentrations of 8-OHdG, with changes in the sensor's channel resistance observed upon exposure to 8-OHdG. Detection of 8-OHdG concentrations as low as 0.1ng/ml

No abstract

No abstract

No abstract

The high density of interface states of thermally grown oxides on silicon carbide has prompted research into alternative oxidation methods and post oxidation anneals. One such alternative is oxidation of a deposited sacrificial silicon layer. A recent variation of this technique is a partial oxidation of the deposited Si layer, so that a thin Si layer remains between the SiO2 and SiC layers. If the SiO2/Si interface has lower interface state densities than the SiO2/SiC interface, the SiO2/Si/SiC hetero-structure could yield improved channel mobilities in MOS devices. Moreover, by correct optimization of the MOSFET device structure, breakdown can be designed to occur in the bulk SiC layer, thus maintaining a high blocking voltage. Post oxidation annealing in N2O is another technique often used to reduce interface state densities. However, little is known about the chemical and physical nature of these N2O oxidized dielectrics. Ellipsometric and Medium Energy Ion Scattering (MEIS) investigations of conventional SiO2/SiC interfaces compared with SiO2/Si/SiC hetero-junction structures and N2O oxidized samples are reported.

No abstract