Justin has over 25 years' experience in developing and maintaining computer based models to predict the transfer of radionuclides through the environment following accidental and routine releases. He is the lead developer of PC-CREAM 08, which is an application for performing radiological impact assessments of routine, continuous discharges of radionuclides to the environment. He is a contributor to Working Group 3 (Assessments and control of exposures to public and biota for planned releases) of the IAEA's Modelling and Data for Radiological Impact Assessments (MODARIA II) programme and provides secretariat support to the UK's Atmospheric Dispersion Modelling Liaison Committee.