Improvement of Risk Assessment for a Severe Accident with Radioactive Materials Inside a Closed Workplace

Severe accidents, like an explosion or a fire of radioactive materials inside closed workplaces, have a potential of significant internal exposure risk to workers and emergency staff (like firefighters, etc.). Regular risk assessments that are conducted for these cases use some assumptions that might lead to an underestimation of internal dose to these workers, according to the following details:

1. Only aerosols below 10 micron aerodynamic diameter are being considered. For these aerosols, a distribution with a 1 micron aerosol median aerodynamic diameter (AMAD) is assumed.
2. A breathing rate of a "light worker", as defined by the International Commission on Radiological Protection (ICRP), is assumed.
3. Internal dose is calculated using the general available data of committed effective dose per intake (Sv/Bq) for a 1 micron AMAD and for "light worker".

Improved computerized codes were developed and used at the Internal Dose Assessment Department at the NRCN, which improve substantially the risk assessment for severe accidents inside closed work[laces, according to the following details:

1. All aerosols, including those above 10 micron aerodynamic diameter, are being considered.
2. A breathing rate of a "heavy worker", which is more appropriate for these scenarios, may be used.
3. Sv/Bq values for any required AMAD may be used.

Estimation was made of the internal doses to workers and firefighters in an explosion and fire accidents with uranium, using these improved codes. The calculated doses were about three times higher for a fire accident and two times higher for an explosion accident, as compared to the "regular" estimation.