Dosimetry for criticality accident

A. Rannou and P. Gourmelon. The International Symposium on Criticality Accident in Tokaimura : Medical Aspects of Radiation Emergency. Chiba, Japan, 14-15 Dec. 2000

In the event of any overexposure accident, every effort should be made to evaluate doses as accurately and as soon as possible. It is stated that the physician must treat injured patients according to clinical grounds before any other consideration. However, results of dosimetry systems or estimates of dose will give valuable support to those who have to take care of the victims from the first moments following the radiation accident, and then when assessing the degree of injury through clinical observations or medical laboratory tests. Dosimetry may also give reassurance to the physicians about the probability of occurrence of certain symptoms. Despite the availability of highly sophisticated physical dosimetry systems for nuclear accidents, past cases involving serious exposure like the last one in Tokaimura in September 1999 often occurred in the absence of adequate dosimetry systems. Alternative approaches based on biological techniques (e.g. chromosome analysis or changes in components of the blood) and activation techniques (activity of 24Na in the blood or in the whole body) are then used to estimate doses received by the victims. However, most of these dosimetric approaches and systems only provide an evaluation of the maximum or average dose in the body when it is known that the radiation field during a criticality accident generally gives rise to a huge heterogeneity of the dose in the victim’s body. Experiences reported in connection with dosimetry of past nuclear accidents, together with findings from studies and experimental researches, make it possible to outline some general rules on which dosimetry must be based for any future criticality accident.