Antineutrinos offer new possibilities for nuclear safeguards. Their abundant production in on-line fission reactors and the near impossibility of shielding them presents an opportunity for non-invasive on-line reactor monitoring. In support of this there have been numerous predictions of reactor antineutrino emissions, both based on the work of Schreckenbach et al and ab initio methods using fission fractions and known $\beta$-decay spectra. \
This work discusses an ab initio generation of reactor antineutrino spectra using nuclide inventories taken from reactor modelling software. The resulting spectra are compared to the work of Schreckenbach et al and to other predictions. To put the work in a safeguards monitoring context, the daily antinuetrino flux density at the VIDARR detector during its proof of concept demonstration at Wylfa power station is calculated, using reactor data provided by Wylfa operators and FISPIN calculations by Robert Mills at the National Nuclear Laboratory. Also discussed is an application of the work to predict antineutrino flux densities from the Hartlepool Advanced Gas-cooled Reactor (AGR) at the WATCHMAN detector.