The UK's new build nuclear research programme involves construction of components such as reactor pressure vessels (RPV), by conventional and candidate advanced joining processes. Candidate joining processes must demonstrate reliability for long-term safe operation. In comparison with conventional methods, advanced joining processes including narrow-groove submerged-arc and gas-tungsten arc welding, laser-beam and electron-beam, aim to improve weldment materials properties and reduce damaging welding residual stresses. This is achieved by decreasing heat-input and weld passes, thus reducing total heat energy. However, post-weld heat-treatments (PWHT) must be adopted after welding to minimise damaging residual stresses. In the proposed work, residual stresses in RPV steel welds produced by conventional and advanced welding processes will be quantified and compared, enabling a understanding of the process-dependency on stress evolution; determine effectiveness of PWHT and degree to which stresses are minimised for each method; and provide data for numerical predictive models. This work is integral in choosing the best welding processes for manufacture of future nuclear components.