Monte Carlo radiation transport calculations have been performed in order to determine the factors affecting predicted neutron dose rates to steel reactor pressure vessels (RPV) of Magnox reactors. The AEA Technology Monte Carlo radiation transport code MCBEND has been used to create a model of a notional Magnox reactor representing the main features of the presently operating Magnox reactors with steel RPVs. It was developed with the single purpose of improving understanding and was created so as to facilitate making the perturbations required in sensitivity calculations. A comprehensive series of sensitivity studies has been performed identifying influential factors and investigating the dominant pathways for the transmission of neutrons between the active core and RPV.

This study has confirmed the current calculational methodology for the provision of Magnox RPV doses. It has increased understanding of the neutron transport mechanisms and now provides a sound basis for the assessment of modelling uncertainties.