Future fossil power generation plant will have to operate at higher temperatures to increase its thermal efficiency and reduce its carbon footprint. High-chromium martensitic steels (such as P91, P92) have been developed for elevated temperature applications and are being used increasingly in supercritical power stations, but there are early signs of cracking around weldments in service. The underlying physics and micro-mechanisms contributing these failures needs to be understood and quantified so that new design and life assessment methods can be developed. The aim of this training research proposal is to exploit the potential of neutron and synchrotron radiation measurement techniques at Central Facilities. The techniques will be applied to measure fabrication residual stresses at multiple length-scales in high Cr weldments and quantify how they relax during service high temperature exposure, to measure and spatially resolve plastic and creep deformation across weldments, and to quantify volumetrically the evolution of creep cavitation leading to cracking. The project will use ENGIN-X, LOQ and SANS_2D instruments at ISIS and JEEP at Diamond and involve the student spending four training placements these instruments. The project fits closely with a programme of high temperature materials for energy research at the Open University where the student will have access to complementary test facilities. Welded test specimens will provided by European Technology Development Ltd whose involvement will facilitate dissemination of the results and capabilities of advanced measurement techniques to the power generation industry worldwide.