Gamma dose rate mapping of APSARA structural components for decommissioning

APSARA was a swimming pool type research reactor operated using Highly Enriched Uranium fuel. The reactor pool water was used as coolant, moderator, reflector and radiological shielding. Graphite and beryllium oxide encased in aluminum boxes were used as in-core reflector. The reactor had a maximum power level of 1 MW and was mostly operated up to 400 KW. APSARA was shut down for major refurbishment in 2009. Defuelling and partial decommissioning of reactor was carried out. The core structure and other reactor components were dismantled and shifted to Waste Management site. 'Second stage decommissioning' planned further consists of dismantling and disposal of various components like thermal column, shielding racks, graphite blocks, stainless steel liner of pool and the pool block itself. Detailed gamma dose rate mapping study served in localizing and identifying hotspots of activation product activity in structural components of the APSARA reactor in order to plan the strategy for dismantling of the pool structure. In-situ gamma spectrometry of the structural components was carried out for qualitative and semi quantitative characterization of the bulk structural materials in pool walls, SS and aluminum liners, shield racks, graphite blocks etc., to plan the dismantling and demolition of large structures. This study has also served in comparing the performance of different radiation measuring instruments used for such large area insitu dose rate measurements and mapping