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The fuel rod claddings in nuclear light water reactors are made of zirconium alloys. Corrosion of these alloys during operation and in particular high temperature oxidation during nuclear accidents results in the production of free hydrogen. The cladding can absorb this hydrogen. It affects the mechanical properties of the cladding material. Hydrogen embrittlement of these materials provides the risk of brittle fracture of the cladding by thermo-shock during emergency cooling. At KIT the behaviour of cladding materials under different hypothetical nuclear accident scenarios was investigated. One focus was on hydrogen absorption and distribution/re-distribution in the alloys. The hydrogen distribution was determined mainly by neutron tomography. Examples for the determination of the 3D hydrogen distribution in cladding tubes after loss of coolant accident simulation tests are given and discussed.

High‐speed neutron tomographies (1‐min acquisition) have been acquired during water invasion into air‐filled samples of both intact and deformed (ex situ) Vosges sandstone. Three‐dimensional volume images have been processed to detect and track the evolution of the waterfront and to calculate full‐field measurement of its speed of advance. The flow process correlates well with known rock properties and is especially sensitive to the distribution of the altered properties associated with observed localized deformation, which is independently characterized by Digital Volume Correlation of X‐ray tomographies acquired before and after the mechanical test. The successful results presented herein open the possibility of in situ analysis of the local evolution of hydraulic properties of rocks due to mechanical deformation. Full 3‐D fluid front velocity map can be obtained from high‐speed (1 min per tomography) neutron tomography during water invasion into dry samplesQuantitative measurements are validated by comparing experimental results to 1‐D analytical solution of pressure‐driven flowDuring imbibition, compactant shear bands result in locally higher fluid flow velocity due to decreased pore size in the bands

Absorbed hydrogen degrades the mechanical properties of zirconium alloys used for nuclear fuel claddings. Not only the total amount of hydrogen absorbed in the cladding tube but also the zirconium hydride orientation and its distribution influence the toughness of the material. For instance, the so-called delayed hydride cracking is caused by the diffusive re-distribution of hydrogen into the dilative elastic strain field ahead of crack tips. The paper presents in-situ and ex-situ neutron imaging investigations of hydrogen uptake, diffusion and distribution in zirconium alloys used for claddings. An overview about results of in-situ experiments studying the hydrogen uptake in strained Zircaloy-4, as well as ex-situ investigations of the diffusion of hydrogen in cold rolled Zircaloy-2 and Zr-2.5 % Nb alloy depending on temperature, rolling direction and thermal treatment and of the hydrogen re-distribution in the ß-phase of Zircaloy-4 during a Three-Point-Bending-Test at 600 °C are presented.

In this work, neutron imaging was used to visualize and study invasion phenomena in fibrous porous transport layers (PTLs) of titanium felt under different flow conditions of gas and liquid phase. The experiments were realized with flow cells that contained a gas and a liquid flow channel separated by PTLs with different thicknesses and pore size distributions. The invasion can be characterized by counter-current flow of water and air with joint imbibition and drainage processes. The dynamics were visualized with neutron radiography with a local resolution of 6.5 μm and a temporal resolution of 0.1 s. Individual static gas-liquid distributions were additionally studied by neutron tomography, with a local resolution of 22 μm and an exposure time of 1.5 s per image (projections: 800/360°). It is shown and discussed that the invasion occurred in continuously repeated imbibition/drainage cycles with frequencies depending on the flow conditions and the PTL structure as well. The change of the PTL saturation with air or water appeared almost independent from the specific PTL structure and the breakthrough of the gas phase occurred at almost constant positions.

A state-of-the-art neutron tomography imaging system was set up at the neutron radiography beam tube at the Egypt Second Research Reactor (ETRR-2) and was successfully commissioned in 2013. This study presents a set of tomographic experiments that demonstrate a high quality tomographic image formation. A computer technique for data processing and 3D image reconstruction was used to see inside a copy module of an ancient clay article provided by the International Atomic Energy Agency (IAEA). The technique was also able to uncover tomographic imaging details of a mummified fish and provided a high resolution tomographic image of a defective fire valve.

The investigations presented here show the results of an epigraphic analysis on ancient Roman lead ingots rescued from shipwrecks along the coast of Sicily (Italy) by means of Neutron Tomography (NT). The artefacts, including a lead horn, can be dated back to a period between the 3rdand 1stcentury BC. The three dimensional NT reconstructions helped the decipherment of hidden signs and partially visible details on the severely damaged objects. The findings obtained using the non-destructive procedure allowed us also to reach plausible conclusions in the context of the known commercial routes.

Water transport in an operating PEM fuel cell was investigated with synchrotron X‐ray radiography with a spatial resolution of 3 μm and a temporal resolution of 5 s. This method allows for the detection of water accumulations with less than 10 μm diameter. We demonstrate that synchrotron X‐ray imaging can dramatically expand the possibilities of imaging with high spatial and time resolution, especially as a complement to neutron radiography. Water transport processes from the first appearance of small water accumulations in the gas diffusion layer to their transport into the channel system were analysed in situ. Correlations between local effects such as water formation and operating conditions of the whole system, e.g. power variations, were found. A recently described eruptive water transport mechanism is analysed in detail.

Der Funktionalisierung von meso‐ und nanoporösen Werkstoffen durch Beschichtungen kommt zunehmend größere Bedeutung zu. So kann z.B. deren Porenoberfläche hinsichtlich der Biokompatibilität oder dem katalytischen Verhalten modifiziert werden. Derzeit sind dafür vor allem CVD‐Verfahren im Einsatz. Die vorliegende Arbeit zeigt jedoch am Beispiel der Pulslaserbeschichtung (PLD)‐‐ einem PVD‐Verfahren —, dass nanoporöse Membranen auf Ni3Al‐Basis und Porendimensionen von etwa 200 nm mit hoher Schichtdicken‐Homogenität und Schichthaftung von diamantähnlichen Kohlenstoffschichten bei geringen Membrandicken beschichtet werden können.

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This work describes the effects of catalyst layers (CLs) consisting of hydrophobic PTFE on the performance and water management of PEM fuel cells. Catalyst inks with various PTFE contents were coated on Nafion membranes and characterized using contact angle measurements, SEX-EDX, and mercury porosimetry. Fuel cell tests and electrochemical impedance spectroscopy (EIS) were conducted under varying operating conditions for the prepared materials. At dry conditions, CLs with 5 wt.% PTFE were advantageous for cell performance due to improved membrane hydration, whereas under humid conditions and high air flow rates CLs with 10 wt.% PTFE improved the performance in high current density region. Higher PTFE contents (?20 wt.%) increased the mass transport resistance due to reduced porosity of the CLs structure. Operando neutron radiography was utilized to study the effects of hydrophobicity gradients within CLs and cathode microporous layer (MPLC) on liquid water distribution. More hydrophobic CLs increased the water content in adjacent layers and improved performance, especially at dry conditions. MPLCwith higher PTFE contents increased the overall liquid water within the CLs and GDLs and escalated the water transfer to the anode side. Furthermore, the role of back-diffusion transport mechanism on water distribution was identified for the investigated cells.