A Compact PC Cluster for Monte Carlo Simulations at JRC-Ispra

At the JRC Ispra, Monte Carlo simulation programs like MCNP and MCNP-PTA are becoming more and more a fundamental tool in the design of new neutron coincidence counters and neutron multiplicity counters. These programs also provide an alternative way for the calibration of these neutron counters for the assay of new sample materials, without the need of new nuclear reference materials. A new PC Cluster has been built to satisfy the increasing demand of computing power, which had the following design requirements: high speed processors, large memory size per node, compact dimensions, high reliability, easy to use, and provide ways for future expansions/upgrades. This paper reports on the design, realisation and performances of the new cluster. Also discussed are the choice of the Operating System (Linux) and various aspects of the software required for running MCNP and MCNP-PTA in parallel with Parallel Virtual Machine (PVM).JRC.G.8-Nuclear safeguard

Towards the ideal 241Am Li(a,n)10B Neutron Energy Spectrum for an ISO Recommendation

Following recent measurements [1,2] of the neutron and photon spectra of two different 241Am Li(a,n)10B source, this paper preliminarily reports on a method based on Monte Carlo simulation in order to obtain the pure and unperturbed 241Am-Li spectrum, hereafter called ideal, one that started within the source material, using the neutron spectrum measured outside the source encapsulations. Various parameters that affect the photon and neutron yields and the energy distributions of these sources were investigated and the theoretical spectrum was calculated and compared to that of Geiger and Van der Zwan [3]. Further work is in progress.JRC.G.8-Nuclear safeguard

Real-Time Simulation of Neutron Counters

In this paper we discuss the long-term perspective of the application of numerical modelling to neutron (coincidence or multiplicity) counting. The advantage of this technique for nuclear safeguards is discussed with particular emphasis to the numerical calibration of detectors. As a particular case of numerical modelling, real-time simulation would allow overcoming some problems related to pre-calibration of neutron counters, especially in all those cases when the sample characteristics deviate from the calibration conditions. Nevertheless it requires a significant increase in computing capabilities. The requirements for real-time simulations deriving from inspection needs are discussed and compared to current (and possible future) computing capabilities.JRC.G.8-Nuclear safeguard

Monte Carlo Techniques Applied to NDA: the JRC Ispra Experience

Since the 1970's, the Non Destructive Assay (NDA) group of the Joint Research Centre (JRC) at Ispra (Italy) has been in the forefront for developing nuclear radiation detection technologies and Monte Carlo methods in the field of Nuclear Safeguards. This paper reports on this experience in general and specifically on the application of the Monte Carlo methods of radiation transport and electronics simulation for the design, modelling and calibration of instruments as well as for the verification of nuclear materials. A number of applications and systems will be presented and reviewed.JRC.G.8-Nuclear safeguard

Simulations of Neutron Multiplicity Counters with MCNP-PTA

The paper is about the improvements and new features related to simulation of neutron multiplicity counters with the MCNP-PTA (Pulse Train Analysis) code developed at JRC Ispra. Simulation models of multiplicity counting electronics, like the JSR-14, AMSR-150, and MI-PTA have been added, paying extra attention to model faithfully all of their characteristics (de-randomising input buffer, pulse pair resolution, clock frequency and direction in time of the gates). Moreover simulation models of several de-randomising mixer circuits have also been added to the PTA program. This is especially important for the correct simulation of measurements with large Pu samples, which involve very high-count rates. In the case of multiplicity counting accurate modelling is mandatory, as will be shown for an Active Well Coincidence Counter. Attention will also be given to the importance and limitations of the nuclear data used in the simulation.JRC.G.8-Nuclear safeguard

Performances of the Scrap Neutron Multiplicity Counter

JRC has developed the SNMC: an advanced neutron multiplicity counter for the verification of inhomogeneous plutonium samples, such as scrap material in MOX fuel fabrication plants. The innovative features of this counter with respect to existing ones rely on two aspects: (i) an optimised design using a large number of Monte Carlo calculations in order to select the most appropriate materials, geometry and detector disposition for maximum efficiency and (ii) the development of a novel electronic based on DSP (digital signal processing) in order to reduce the dead time. The paper will briefly recall the design process, the electronic development, the construction and assembly of the counter. Then the results of the first experimental tests will be reported. We will show the characterisation of the main physical parameters of the counter, the calibration and the verification of a wide variety of plutonium bearing samples available in the PERLA laboratory. This will include pure homogeneous samples (plutonium dioxide powders, metal Pu, MOX powders and pellets) and some tests on heterogeneous samples representative of clean and dirty scraps.JRC.G.8-Nuclear safeguard

Design and Performances of the Scrap Neutron Multiciplicity Counter

JRC has developed the SNMC: an advanced neutron multiplicity counter for the verification of inhomogeneous plutonium samples, such as scrap material in MOX fuel fabrication plants. The innovative features of this counter with respect to existing ones rely on two aspects: (i) an optimised design using a large number of Monte Carlo calculations in order to select the most appropriate materials, geometry and detector disposition for maximum efficiency and (ii) the development of a novel electronic based on DSP (digital signal processing) in order to reduce the dead time. The paper will briefly recall the design process, the electronic development, the construction and assembly of the counter. Then the results of the first experimental tests will be reported. We will show the characterisation of the main physical parameters of the counter, the calibration and the verification of a wide variety of plutonium bearing samples available in the PERLA laboratory. This will include pure homogeneous samples (plutonium dioxide powders, metal Pu, MOX powders and pellets) and some tests on heterogeneous samples representative of scrap material.JRC.G.8-Nuclear safeguard

New Trends in Neutron Coincidence Counting: Digital Signal Processing

Neutron coincidence counting is the reference NDA technique used in nuclear safeguards to measure the fissile mass in nuclear material samples. Nowadays most of the neutron counting systems are based on the original shift register technology, like the (ordinary or Multiplicity) Shift Register Analyser. The analogue signal from the He-3 tubes is processed by amplifier/SCA producing a train of logical TTL pulses that are fed into a neutron analyser performing the time correlation analysis. In the future these systems could be replaced by high-speed PC’s equipped with pulse acquisition cards, providing a time stamp (LIST mode acquisition) for every digital pulse. The time stamp data can be processed directly during acquisition or saved on a hard disk. The latter method has the advantage that measurement parameters, like for instance the pre-delay and gate-width, can be modified without repeating the acquisition. The use of PC based instruments, also called virtual instruments, could be the future major development in practical neutron correlation analysis. Under a push from the main inspection authorities (IAEA, Euratom and French Ministry of Industry) several research laboratories have started to study and develop prototypes of neutron counting systems with PC-based processing. A collaboration in this field among JRC, IRSN and LANL has been established within the framework of the ESARDA-NDA working group. Joint testing campaigns have been performed in the JRC PERLA laboratory, using different equipment provided by the three partners. The paper will describe the rationale for changing to the new technology, give an overview of the hardware and software tools available today and a feedback of the experience gained in the first tests. Associated to the experimental tests, the ESARDA-NDA working group is also performing an inter-comparison benchmark exercise on the analysis software for pulse processing.JRC.G.8-Nuclear safeguard

A Segmented Gamma Scanner for the Verification of LEU Oxide Powders

The verification of the amount of U oxide powder and the 235U/U abundance in typical fuel fabrication plant containers is described. Only gamma spectroscopy and direct calibration with standards are used. The measurements are performed scanning the container axis with a collimated detector. The spectrum energy considered covers the 1001 keV region to estimate the 238U mass and the 185.7 keV region to determine the 235U/U abundance. The gamma spectra taken at different axial positions of the container verify the homogeneity level of the sample.JRC.G.8-Nuclear safeguard

Characterisation of 3HE Proportional Counters

This paper describes the characterisation of a set of 3He proportional counters differing in gas composition and pressure. Each step of the signal generation in the detector is analysed. Optimal working conditions are defined in order to choose the high voltage to be applied. Dead time with short shaping time is measured in such optimal conditions. In addition the overall neutron efficiency and the gamma sensitivity are reported. Such characterisation is required for a correct choice of the associated counting electronics and the applications of the counters. A complete pulse processing modular system, consisting of a pulse height analysis system and a pulse correlation analysis system equipped with a time of arrival recorder, is used for the characterisation.JRC.G.8-Nuclear safeguard