Radiological Characterisation of Waste in Interim Storage Building of COVRA

At COVRA spatial dose rate distribution measurements were performed in December 2004 and December 2006 in the interim L/ILW storage building (LOG). This storage facility consists out of four large storage halls (height * width * depth; 7m * 40m * 70m) each with a volume of about 20000 m3 (see photo 1). The scope of this study is to investigate the benefits of the waste storage strategy (see figure 1) and procedures for minimization of the dose to the workers and the public. The main aim of the measurements in 2004 was: - to validate the applied L/ILW storage strategy; - to examine, if spatial collected data can be used to detect unforeseen differences in radiation level. The results of these measurements of spatial dose showed a number of unforeseen hotspots at different locations, so that it could be concluded that the applied storage strategy and procedures has to be improved. Further the dose rate at the height of 6 m, mainly responsible for the sky-shine dose rate, being an important part of the dose rate to the public at the site boundary, has to be reduced by more shielding (1). In December 2006 a second serial of spatial radiological and non-radiological data have been collected. The applied nondestructive INDSS-R (INDoor Survey System-Radiation) method has been improved, so that the following 3-dimensional data could be collected between 0.5 m and 5.5 m: - dose rate (by pressurized ionisation chamber). - nuclide depended gamma photon flux (3 * 3 NaI). - temperature and relative humidity. These last two non-radiological parameters were measured to verify the storage conditions of the waste. The main aim of these 3 dimensional collection was to verify the second stated aim of 2004.