In systems modelling for fusion power plants, it is essential to robustly predict the performance of a given machine design (including its respective operating scenario). One measure of machine performance is the energy confinement time tau(E) that is typically predicted from experimentally derived confinement scaling laws (e.g. IPB98(y, 2)). However, the conventionally used scaling laws have been derived for ITER which-unlike a fusion power plant-will not have significant radiation inside the separatrix. In the absence of a new high core radiation relevant confinement scaling, we propose an ad hoc correction to the loss power P-L used in the ITER confinement scaling and the calculation of the stored energy W-th by the radiation losses from the 'core' of the plasma P-rad,P- core. Using detailed ASTRA/TGLF simulations, we find that an appropriate definition of P-rad,P-core is given by 60% of all radiative losses inside a normalised minor radius rho(core) = 0.75. We consider this an improvement for current design predictions, but it is far from an ideal solution. We therefore encourage more detailed experimental and theoretical work on this issue.