G. Jonkmans

Nuclear waste imaging and spent fuel verification by muon tomography

This paper explores the use of cosmic ray muons to image the contents of shielded containers and detect high-Z special nuclear materials inside them. Cosmic ray muons are a naturally occurring form of radiation, are highly penetrating and exhibit large scattering angles on high Z materials. Specifically, we investigated how radiographic and tomographic techniques can be effective for non-invasive nuclear waste characterization and for nuclear material accountancy of spent fuel inside dry storage containers. We show that the tracking of individual muons, as they enter and exit a structure, can potentially improve the accuracy and availability of data on nuclear waste and the contents of Dry Storage Containers (DSC) used for spent fuel storage at CANDU ® plants. This could be achieved in near real time, with the potential for unattended and remotely monitored operations. We show that the expected sensitivity, in the case of the DSC, exceeds the IAEA detection target for nuclear material accountancy.

Cosmic Ray Inspection and Passive Tomography for SNM Detection

The Cosmic Ray Inspection and Passive Tomography (CRIPT) project has recently started investigating the detection of illicit Special Nuclear Material in cargo using cosmic ray muon tomography and complementary neutron detectors. We are currently performing simulation studies to help with the design of small scale prototypes. Based on the prototype tests and refined simulations, we will determine whether the muon tracking system for the full scale prototype will be based on drift chambers or extruded scintillator trackers. An analysis of the operations of the Port of Montreal has determined how long muon scan times should take if all or a subset of the cargo is to be screened. As long as the throughput of the muon system(s) is equal to the rate at which containers are unloaded from ships, the impact on port operations would not be great if a muon scanning stage were required for all cargo. We also show preliminary simulation results indicating that excellent separation between Al, Fe and Pb is possible under ideal conditions. The discrimination power is reduced but still significant when realistic momentum resolution measurements are considered.

Prototype testing and algorithm development for the Cosmic Ray Inspection and Passive Tomography (CRIPT) project

The Cosmic Ray Inspection and Passive Tomography (CRIPT) collaboration has completed the testing of small muon detector prototypes and has commenced construction of a 12 layer, 4m2 prototype muon scattering tomography system. Three areas of CRIPTs progress are reported: (1) results from the testing of one of drift chamber muon detector prototypes; (2) algorithms for muon momentum estimation and tomographic image reconstruction; and (3) the status of the large prototype construction. The intrinsic resolution of the 2.4 m long, 1.2 m wide drift chamber muon detector prototype has been measured to be 1.73 mm perpendicular to the anode wire, and 2.9 mm parallel to the anode. A Bayesian estimator algorithm has been developed for muon momentum estimation. From simulations, the momentum resolution is expected to be highly asymmetric, varying from −18% to +92% integrated across the cosmic ray muon spectrum. A novel Point-of-Closest-Approach (PoCA) algorithm has also been developed for tomographic imaging. Multiple possible muon trajectories are assumed for each muon. The expected completion date for the construction is summer 2012, with first tomographic data following soon afterward.

Construction, commissioning and first data from the CRIPT muon tomography project

The Cosmic Ray Inspection and Passive Tomography (CRIPT) project is investigating muon scattering tomography (MST) for applications in border security, nuclear non-proliferation, and nuclear waste characterization. The construction of the full-scale prototype MST system began in the Summer of 2011 and was completed in September 2012. The CRIPT detector employs 12 layers of scintillator to track atmospheric muons before and after passage through a volume of interest, and to estimate each muons momentum. The total height of the system is 5.5 m and its weight is 20 tonnes. Details of its construction are presented. After the integration of the custom data acquisition electronics, the commissioning of the CRIPT detector began. The first tomographic images were obtained in October 2012 and are presented here.

FIRST IMAGES FROM THE CRIPT MUON TOMOGRAPHY SYSTEM

The CRIPT Cosmic Ray Imaging and Passive Tomography system began data taking in September 2012. CRIPT is a “proof of principle” muon tomography system originally proposed to inspect cargo in shipping containers and to determine the presence of special nuclear materials. CRIPT uses 4 layers of 2 m x 2 m scintillation counter trackers, each layer measuring two coordinates. Two layers are used to track the incoming muon and two for the outgoing muon allowing the trajectories of the muon to be determined. The target volume is divided into voxels, and a Point of Closest Approach algorithm is used to determine the number of scattering events in each voxel, producing a 3D image. The system has been tested with various targets of depleted uranium, lead bricks, and tungsten rods. Data on the positional resolution has been taken and the intrinsic resolution is unfolded with the help of a simulation using GEANT4. The next steps include incorporation of data from the spectrometer section, which will assist in determining the muons momentum and improve the determination of the density of the target.

Machine learning for the cosmic ray inspection and passive tomography project (CRIPT)

Muons, which are produced naturally in the upper atmosphere, can be used to scan cargo for special nuclear materials (SNM). Preliminary simulated results show that detecting the presence of these materials can be accomplished by measuring the scattering of cosmic ray muons. Machine learning tools have been used on these data to classify it as SNM or not. The muon exists long enough, and is penetrating enough, that it can be used to passively scan cargo to detect SNM. By measuring the deflection angles of muons after they exit a container, one can determine whether or not SNM are present. Different detector approaches have been evaluated by considering the performance, cost, and robustness of several technologies. Simulations have been performed to help design the detectors and to determine the effectiveness of the proposed techniques. Realistic cargo containers have been simulated. Two types of techniques can be used to determine whether the cargo containers contain SNM. More traditional methods use an expert system which uses knowledge of physics to compute physical information about the cargo. The other approach is to use Machine Learning classifiers, which can be used to determine if the cargo contains SNM. These techniques include the following algorithms: decision trees, neural networks, special vector machines, and k nearest neighbours. Preliminary results from the two approaches to classification have been obtained and will be discussed in the paper.

G4-STORK: A Monte Carlo Reactor Kinetics Simulation Code

Abstract G4-STORK (Geant4 Stochastic Reactor Kinetics) is a time-dependent Monte Carlo particle physics code for reactor physics applications. G4-STORK was built using the Geant4 Monte Carlo toolkit and is designed to model the continuous evolution of a population of neutrons in space and time. From this evolution, various important reactor physics quantities can be calculated, including the reactivity of the system and the entropy of the neutron spatial distribution. System properties, such as the temperature of a material, can be changed incrementally to approximate time dependence. Thus, G4-STORK can be used to model reactor kinetics and was used to simulate a system that underwent an instantaneous increase in temperature.

Nuclear Industry Applications of Si-Diode Based High Gamma Dose Rate Detectors

AECL has developed and deployed several high gamma radiation field measurement and profiling systems based on commercial off-the-shelf (COTS) silicon diode sensors and components. These systems have been useful in a number of applications including radiation survey of a medical radioisotope production hot-cell, liquid level measurement in a highly radioactive tank, identification of waste location inside nuclear waste storage structures, imaging of reactivity devices inside a shut-down nuclear reactor, and for scanning and imaging highly radioactive reactor components inside a hot-cell in support of an industrial surveillance project. The measurements ranged from 100 uGy/h (10 mRad/h) to 10 kGy/h (1MRad/h), which covers typical radiation fields in hazardous nuclear facilities. This paper summarizes the development and characterization of the Si-diode based detector system, and describes its performance in a variety of applications.Copyright