Determination of 137Cs contamination depth distribution in building structures using geostatistical modeling of ISOCS measurements

• 137Cs depth contamination was determined using the multiple photo peak method.
• Geostatistical modeling was used to determine treatment depth areas and perform risk analysis.
• Results were evaluated using laser scanning and long term gamma-ray spectroscopy.
• Waste volume reduction of about 1/3 compared to a more traditional approach.

Decommissioning of nuclear building structures usually leads to large amounts of low level radioactive waste. Using a reliable method to determine the contamination depth is indispensable prior to the start of decontamination works and also for minimizing the radioactive waste volume and the total workload. The method described in this paper is based on geostatistical modeling of in situ gamma-ray spectroscopy measurements using the multiple photo peak method. The method has been tested on the floor of the waste gas surge tank room within the BR3 (Belgian Reactor 3) decommissioning project and has delivered adequate results.