The proposed doctoral work is dedicated to optimizing non-destructive characterization methods for the quantity of plutonium in radioactive waste packages. One of the primary nuclear measurement methods to achieve this goal is based on the passive counting of coincidences between spontaneously fissioned neutrons. Most neutron measurement stations are equipped with 3He counters, which have the advantage of good detection efficiency while being less influenced by gamma radiation.
However, the price of these detectors has significantly increased in recent years, and they are relatively slow as they require prior thermalization of the neutrons to be detected. Plastic scintillators offer a 5 to 10 times less expensive alternative with equivalent detection efficiency, making them attractive for implementation in industrial stations. In exchange, they are highly sensitive to gamma radiation and the phenomenon of crosstalk (parasitic coincidences due to interactions between neighboring detectors). An innovative method for discriminating between useful and parasitic coincidences by differentiating the time of flight between neutrons and gamma radiation has been developed and validated in previous work.
There are still significant practical challenges addressed by this thesis in order to move towards an industrial neutron measurement station equipped with these scintillators, particularly for technological waste (ORANO La Hague, MELOX Cadarache). The primary objective in passive neutron measurement will be to advance in detection efficiency, data processing, and reducing uncertainties related to matrix effects and nuclear material localization, closely integrating experiments and modeling. A secondary objective of the thesis will be to demonstrate the feasibility of active neutron measurement in terms of data processing and resilience to high counting rates for quantifying the mass of nuclear material (detection of neutrons induced by a neutron generator).
The proposed doctoral work is dedicated to optimizing non-destructive characterization methods for the quantity of plutonium in radioactive waste packages. One of the primary nuclear measurement methods to achieve this goal is based on the passive counting of coincidences between spontaneously fissioned neutrons. Most neutron measurement stations are equipped with 3He counters, which have the advantage of good detection efficiency while being less influenced by gamma radiation.
However, the price of these detectors has significantly increased in recent years, and they are relatively slow as they require prior thermalization of the neutrons to be detected. Plastic scintillators offer a 5 to 10 times less expensive alternative with equivalent detection efficiency, making them attractive for implementation in industrial stations. In exchange, they are highly sensitive to gamma radiation and the phenomenon of crosstalk (parasitic coincidences due to interactions between neighboring detectors). An innovative method for discriminating between useful and parasitic coincidences by differentiating the time of flight between neutrons and gamma radiation has been developed and validated in previous work.
There are still significant practical challenges addressed by this thesis in order to move towards an industrial neutron measurement station equipped with these scintillators, particularly for technological waste (ORANO La Hague, MELOX Cadarache). The primary objective in passive neutron measurement will be to advance in detection efficiency, data processing, and reducing uncertainties related to matrix effects and nuclear material localization, closely integrating experiments and modeling. A secondary objective of the thesis will be to demonstrate the feasibility of active neutron measurement in terms of data processing and resilience to high counting rates for quantifying the mass of nuclear material (detection of neutrons induced by a neutron generator).
This work opens up career prospects particularly in research centers and R&D departments in industry.
A master internship is proposed by the team in addition to the thesis.