Design study of a real time radiation monitoring system for severe accident conditions

Radiation monitoring methods for nuclear reactor accident conditions should serve to determine airborne radioactivity and ambient dose rate in the reactor building even in locations with high gamma fields and high activity concentrations. The assessment of the radiological conditions inside containment should also provide sufficient characterization of releases in terms of the beta activity of radioactive gases and fission products to enable real-time updates on the type and extent of the accident, so enabling rapid response decisions concerning re-entering affected locations. This work describes the design and implementation process of a prototype dosimetric system that will be robust and capable of measuring accurately, over a wide response range, both the ambient gamma ray dose rate and the β and γ gas-aerosol activity. The prototype design consists of paired flow and non-flow ionization chambers with identical dimensions. The non-flow ionization chamber will be sensitive to ambient gamma radiation only. The flow through chamber will be sensitive to both ambient gammas and airborne γ and β emitters transported through the chamber with the airflow. (author)