An International Intercomparison of National Network Systems used to Provide Early Warning of a Nuclear Accident Having Transboundary Implications

Abstract

Since the Chernobyl accident many countries now operate large national networks of radiation detectors that continuously monitor radiation levels in order to give early warning of nuclear accidents having transboundary implications. The networks are used to provide data to assist in determining the action that should be implemented in that country. However, each country has its own unique system of detection. These are based either on Geiger-Müller counters, high pressure ionisation chambers, scintillation detectors, proportional counters, passive detectors or spectrometry systems; or mixtures of these detectors are used. During an accident the data produced by such systems will be exchanged between countries within the European Communities, (EC) and as required by the IAEA's Early Warning Convention between the rest of the world and Europe. It is therefore important to ensure that such data should be harmonised so that it can be accurately interpreted by other countries and by international organisations. To assist with such harmonisation an intercomparison was held during May/June 1999 at the Risø Natural Environmental Radiation Measurement Station in Denmark and at the PTB underground laboratory for dosimetry and spectrometry (UDO) in Germany. The main aim of the intercomparison was to help ensure that results reported by different countries during a nuclear accident will be consistent and comparable. It is important that during an emergency the measurements of the plume doses or contamination levels reported from network systems will not show significant increments or decrements at national boundaries that are due to inadequate calibration, or to different measurement quantities being used for different systems. Seven countries participated in the intercomparison with detectors used in their national network system as well as with other detectors being developed for future use. This report summarises the important results arising from the intercomparison.