Sensing and Monitoring of Radwaste Storage: A Realtime Online Demonstrator
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Sensing and Monitoring of Radwaste Storage: A Realtime Online Demonstrator Luigi Cosentino, Claudio Calì, Giovanni De Luca, Paolo Finocchiaro, Pietro Litrico, Alfio Pappalardo, Massimo Piscopo, Carlotta Scirè, Sergio Scirè INFN Laboratori Nazionali del Sud, via S. Sofia 62, 95125 Catania, Italy ABSTRACT At INFN-LNS we have developed a new kind of gamma mini-sensor, which allowed to implement a prototype array of modular sensors for online monitoring of radioactive waste. The sensors are based on Silicon PhotoMultipliers and scintillating fibers sensitive to gamma radiation, that have to be placed in a repository in shape of a fine grid, around each single waste drum. We simulated the counting response of thin scintillating fibers and verified the results with measurements using radioactive sources. Front-end electronics and an FPGA-based counting system were developed to handle the field data, also implementing data transmission, a graphical user interface and a data storage system. Moreover a test of four sensors in a real radwaste storage site was performed with promising results. INTRODUCTION One of the main topics in decommissioning and storage of radioactive waste is its monitoring in the short, medium and long term. Whereas for the long term waste the geological disposal is foreseen, the short and medium term waste is currently packed into drums and either kept inside the production site or transported to dedicated storage sites. Special care must be devoted to the prompt detection of possible leaks due to structural weakness or accident [1]. Detector Mesh for Nuclear Repositories (DMNR) is a project for a prototype demonstrator of the online monitoring of short-medium term radioactive waste, currently under development at INFN-LNS (Italy) [2]. Such a system is planned to be distributed, finegrained, robust, reliable, and based on low-cost components. Its goal would be measuring the radioactivity around each single drum containing the radioactive waste. Under these conditions it could be possible to achieve a realtime three-dimensional radioactivity map, capable of monitoring the expected decrease of radioactivity over time on a drum-by-drum basis, figure 1. The activity is measured by counting gamma radiation, making use of a new kind of minidetector that behaves like a scintillating Geiger-Muller counter and that can be arranged in shape of a grid around each single waste drum, interconnected with an overall transmission and control system. Each detector is made of a cheap scintillating fibre, readout by means of SiPM (Silicon PhotoMultiplier) photosensors capable of detecting the tiny light signals of a few photons ([3], [4] and references therein). This way one can easily place grids of 5-10 radiation sensors around each waste drum, and record continuously the measured activity in order to know its instant rate as well as its history. In order to find the most suitable SiPM detectors, a depth characterization of the photosensors has been carried out for several families of SiPM, in terms of gain, photon r
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