Monte Carlo integrated approach to radiological characterization for nuclear facilities decommissioning

Abstract

Monte Carlo integrated approach to radiological characterization for nuclear facilities decommissioning In the last decades, hundreds of nuclear reactors have been shutdown and have experienced decommissioning. This is also the case of L-54M Politecnico di Milano nuclear research reactor. Since shutdown in 1979, the plant has been managed following deferred dismantling strategy. Recently, preliminary radiological characterizations have been launched, even though a more extended campaign is necessary to implement facility decommissioning and restore unrestricted reuse status. In the framework of the IAEA collaborative research project on irradiated GRAphite Processing Approaches (GRAPA), a general radiochemistry and Monte Carlo integrated approach has been developed to study materials activation and support radiological characterization campaign. This integrated method, thanks to its general principles, could be applied to any nuclear reactor or facility undergoing decommissioning, thus helping to reduce the characterization efforts and, possibly, the associated costs.

MCNP model of L-54M nuclear research reactor: validation by preliminary graphite radiological characterization

“…The development of L-54M reactor neutronic model has already been satisfactorily achieved, even if some knowledge gaps could not be overcome [15]. As well, the simulated criticality and neutron fluence data within the core have already been satisfactorily compared with the available experimental ones [14].…”

“…Several points had been identified as relevant on two accessible parts of the graphite stack: 7 samples were picked-up from the western surface of the stack (top) and other 10 along two (Top, Bottom) east side removable rods (center and bottom) of the at different axial and radial positions with respect to the core. and on the two east surface rods (center, bottom) [14] [15] The sampling activities took place in the Reactor Hall, inside an operative area continuously kept in a negative pressure status also during the L-54M CeSNEF Safe Enclosure Condition: the primary air pipes system continuously supplies ventilation in the Reactor Building with the exit pipe lines connected to absolute particulate HEPA filters (ε = 99.98%; d= 0.3 µm).…”

“…It has already been accomplished [14] [15]. As elsewhere described, all structural components were implemented in dedicated input sections, namely: cell, surface and material cards [15]. Several preliminary debugging experiments were carried out to identify potential mistakes.…”

“…The neutron fluences (expressed in cm -2 ) were obtained with F2 and F4 tallies and processed as elsewhere described to obtain the most common flux formulations (expressed in n cm -2 J -1 or n cm -2 s -1 ) [15]. In order to gather detailed activation maps of irradiated graphite, these calculations were performed on a dense mesh (1 cm 3 single element volumes) covering the whole graphite stack.…”

Column Leaching Tests to Valorize a Solid Waste from the Decommissioning of Coal-Fired Power Plants

“…Although the decommissioning of nuclear power plants has been extensively studied [6][7][8][9][10][11][12][13], far less research has been done to examine the decommissioning of coal, oil, and natural gas-burning plants [4,14].…”