Faults caused by ionising radiation have become a significant reliability issue in modern ICs. However, the Radiation Hardening (RADHARD) design flow differs from the standard design flow. Thus, there is not sufficient support from industrial EDA tools. In this work, we present a Triple Modular Redundancy (TMR) Radiation Hardening (RADHARD) methodology, based on the replacement of Flip-Flops (FFs) to a TMR structure, consisting of a FF triplet and a majority voter, as well as a custom, Displacement-driven legalisation algorithm, called R-Abax, able to satisfy user-specified, minimum distances between the FFs of each triplet. Our RADHARD legalisation algorithm is fully compatible with existing EDA tools. By ensuring a minimum spacing between triplet FFs of each TMR structure, we reduce the probability of a particle strike affecting more than one triplet instances. We present the impact of our RADHARD flow, for a set of spacing constraints, to Power, Performance and Area (PPA) on a set of 11 OpenCores benchmarks. On average, a larger spacing between FF triplets worsens a design's Quality-of-Results (QoR), but not significantly, making our RADHARD flow attractive for reducing radiation faults.