Theoretical determination of the size of the emergency planning zones pertinent to a postulated severe accident of the SAFARI-1 research reactor at NECSA due to gaseous releases

Abstract

In South Africa the requirement for emergency planning at nuclear installations is a statutory requirement. Emergency planning consists of two distinct functions, preparedness and response. The preparedness functions deals proactively with issues such as threat quantification, the infrastructure and resources to manage the threat, and aspects of mitigating the consequences to the worker, public and environment. The response function , on the other hand, deals with actions and organisations implemented during the event. Preparedness therefore is the planning and preparation function and response is the actual implementation of all the planned activities. Due to the public sensitivity to effects of radiological and nuclear emergencies, it is of the utmost importance to be appropriately prepared to manage any unplanned event, even those of very low probabilities, before it manifests. Preparedness commences with threat identification and threat quantification. The design of the facility should eliminate most of the threats. However, those of very low frequencies would not be accounted for by design. It is for these events that the emergency plan must be in place. At SAFARl-1 , the research reactor at Necsa, changes were made to the composition of the fuel elements. These changes would affect on the quantities of radioactive material that could be released under remote circumstances. That necessitated a recalculation of the extent of planning and the size of the zone for which this planning is performed. The emergency planning zone at question is that in which urgent protective actions may require implementation. Off-site consequences are included. The perimeter of the radial zone was derived to be at the level at which sheltering, as a protective action, is to be implemented. Calculation of the zone size was performed with acceptable codes, PC COSYMA and lnterras. The input data required for the use of the code, include amongst other, the source term and meteorological information. The outputs of the codes were compared with work done previously on fuel elements containing 200g U-235. It was concluded, from the results of this work, that the size of the urgent protective may be reduced to less than one kilometre from the point of release, if all the assumptions that were made are valid and all the uncertainties regarding the source term and dispersion modelling are acceptable. However more work is required on the validation of the model, the verification of assumptions and uncertainties regarding the source term.