Design of MICADO advanced passive and active neutron measurement system for radioactive waste drums

Abstract

In the frame of the MICADO H2020 project, a passive and active neutron measurement system is being developed to estimate the nuclear material mass inside legacy waste drums of low and intermediate radioactivity levels. Monte-Carlo simulations have been performed to design a new modular and transportable neutron system, with the main objective to reach a good tradeoff between the performances in passive mode, i.e. neutron coincidence counting, and in active interrogation mode with the Differential Die-away Technique. Different designs are compared, which mainly differ in their moderation materials, graphite and polyethylene. This parametric study allowed us to define a prototype taking into account practical constraints in view of its final implementation in a wide range of in-situ locations and nuclear facilities. The total neutron detection efficiency of the prototype is 6.75%, as calculated for an empty drum, i.e. without waste matrix. The detection limit in terms of nuclear material equivalent mass have also been estimated based on assumptions for a homogeneous distribution of nuclear materials inside the drum, filled with four types of matrices covering the range of nuclear waste drums defined in the frame of the project. The most favorable matrix is made of stainless steel in passive mode and of polyethylene in active mode, with an apparent density of 0.7 g.cm -3 and 0.1 g.cm -3 , respectively. The calculated mass detection limits are respectively 68 mg of 240 Pu, 62 mg of 235 U and 39 mg of 239 Pu. The most penalizing matrix is made of polyethylene with an apparent density of 0.7 g.cm -3 , which leads to a mass detection limit of 519 mg of 240 Pu in passive mode, and 564 mg of 235 U or 349 mg of 239 Pu in active mode. Measurement time is 30 min for both passive and active modes. Next steps will be a complete investigation of matrix effects based on intensive Monte-Carlo calculations and an experimental design to figure out the appropriate corrections. Experiments will also be conducted at CEA Cadarache Nuclear Measurement Laboratory with the construction and the assembly of the neutron system prototype, and the measurement of mock-up drums filled with different matrices. I.

Developments and experiences of the CHANCE, MICADO and PREDIS projects in radioactive waste characterization

“…The structure is mobile and can process packages of different sizes up to 220 l. Moreover, this technique is combined with data analysis based on matrix characteristics (material, density, filling) using artificial intelligence with trained data (based on many MCNP simulations) to apply signal attenuation corrections (also called "matrix effect" corrections) based on internal monitors and neutron transmission measurements to characterize the matrix. Monte Carlo simulations [18] were performed to optimize the design. In order to achieve a good compromise between the performances in passive mode and active interrogation mode, the differential die-away technique was used.…”

Neutron coincidence counters for disarmament verification: Experiments and modeling

“…If the geometry or chemical composition of the assayed samples differ from the ones of the reference materials correction factors need to be introduced, for example to account for the multiplication or hydrogen content [13]. The calibration coefficient can also be obtained from Monte Carlo simulations as explained in [8,14]. One of the main advantages of this approach is that the impact of the geometry of the sample, the gate occupation factor f and, if the mass is known, the multiplication factor are accounted for in the simulations.…”

Novel flexible and conformable composite neutron scintillator based on fully enriched lithium tetraborate

“…Its characteristics make it suitable to be employed in scenarios where nonstandard geometries are needed, for example, to optimize the detector performance and/or maximize the detection efficiency. Finally, the response of a hybrid detector made of a plastic scintillator, wrapped with the proposed scintillator, coupled to a silicon photomultiplier array is described, and the excellent discrimination between γ-rays, fast and thermal neutrons resulting from data processing is demonstrated.Nowadays, neutron detection is a subject of steadily growing interest in nuclear and particle physics research, but also it is fundamental in a wide variety of applications such as homeland security 1-3 , neutron monitoring (in power plants and radioactive waste repositories [4][5][6] ), material analysis 7 , hydrology 8 , radiation protection 9 , industrial procedures, nuclear medicine 10 , etc. Presently, the increasing interest in the development of new nuclear power plants, pushed forward by the current, dramatic energy crisis, demands modern safeguards equipment to ensure that nuclear material is not diverted from peaceful uses.…”

“…Nowadays, neutron detection is a subject of steadily growing interest in nuclear and particle physics research, but also it is fundamental in a wide variety of applications such as homeland security 1-3 , neutron monitoring (in power plants and radioactive waste repositories [4][5][6] ), material analysis 7 , hydrology 8 , radiation protection 9 , industrial procedures, nuclear medicine 10 , etc. Presently, the increasing interest in the development of new nuclear power plants, pushed forward by the current, dramatic energy crisis, demands modern safeguards equipment to ensure that nuclear material is not diverted from peaceful uses.…”

“…On the other hand, simultaneous real-time discrimination of γ-rays and neutrons is of interest for several homeland security applications, and for nuclear safety and waste management operations 4,18,19 . In this respect, there are recent scintillation compounds (e.g.…”