EDF Energy operates one pressurized water reactor in the UK at the Sizewell B Nuclear Power Plant (NPP) in Suffolk, which has been generating since 1995. The recent Refueling Outage RO14, in April 2016, saw the removal of the last of the eight original surveillance dosimetry capsules that were installed when the reactor was commissioned. An in-depth review was conducted of the existing MCBEND Monte Carlo methodology for determining calculation to measurement ratios of dosimeter activities, which has been in use since the first surveillance capsule analysis was conducted. Sensitivity calculations were then undertaken to identify areas of the methodology that could be developed to further improve the accuracy of the surveillance calculations for Sizewell B. This resulted in a new, more complex, MCBEND model that makes better use of modern computing resources with a revised geometry and a whole core neutron source definition that takes into account NPP load variations by using high time resolution plant data. This paper presents a complete “set” of all the surveillance dosimeter activities, which span 21 years of NPP operation, and the potential improvements that could be possible with a refined MCBEND model. Examples of the use of the MCBEND Monte Carlo model as a tool for performing surveys of the incident fluence on reactor pressure vessel component surfaces are also presented.