Methodology to Calculate Gamma Dose Contours for a Postulated Criticality Accident

Abstract

Dose contour maps resulting from a postulated criticality accident need to be calculated to support emergency planning work, including establishing immediate evacuation zones and the maximum acceptable absorbed dose. This paper presents the analysis steps developed to calculate the gamma dose contour map for a postulated criticality accident. Neutron doses are not considered in this analysis since the postulated accidents are thermal systems (average lethargy of neutron causing fission for the postulated systems is between 0.033 eV and 0.082 eV), and the neutrons will be stopped by the water reflector, surrounding equipment and/or building concrete walls. The methodology is demonstrated using a conceptual facility, referred to as 'Building A', whose operations primarily involve the use of ²³⁵U as the fissile material of interest. The results obtained provide useful insight into the spread of gamma radiation in a 30 m area surrounding 'Building A', and can be used for emergency planning purposes.