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Activity name

EPHSOGAM: Early Phase Source Term Estimation From Gamma Spectra 

NKS-B Research Area Emergency preparedness
Project summary

As evidenced by the Fukushima Accident, estimation of the release term in the early phases of a nuclear accident is fraught with difficulties despite such an estimate being one of the more critical pieces of information in effective handling of an accident. The ability to provide an early estimate of quantitative and qualitative information regarding a release establishes a firm foundation for early actions on the part of a responding authority and underpins the ultimate response measures implemented. Monitoring data in the early phase facilitates the drawing of some conclusions in relation to the nature of a release, its duration, possible location etc. As has been experienced in earlier accidents, the availability of information in the days following or during the release can be relatively poor. Initial estimates of releases are often based on knowledge of the facility involved, measured dose rates and air concentration measurements combined with various inverse modelling techniques. By combining information as to air concentrations at various spatio-temporal points and tools for the estimation of atmospheric dispersion, it is possible to arrive at an estimate of a release and possible locations and times at which that release occurred.


The EPHSOGAM activity is aimed at the provision of a high quality, robust and comprehensive virtual exercise for personnel involved in early phase response. The exercise will involve the dissemination of technical materials, derived from a simulated incident, from which participants will be tasked with the generation of an estimate of the amount of activity released, its location and any other information they are fit to provide. The technical data will include meteorological and gamma spectrometric data that would typically be available in the aftermath of an incident and the activity will therefore test various aspects of the abilities of the participant organisations. EPHSOGAM will conclude with a final workshop facilitating discussion of the exercise and its results and allow for experience exchange and elucidation of possible developmental trajectories in the years to come.
Lead Organization Norwegian Radiation Protection Authority (NRPA), Norway
Contact Person Mark Dowdall
phone number: +47 67162546


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