Active-Interrogation Measurements of Induced-Fission Neutrons from Low-Enriched Uranium
Active-Interrogation Measurements of Induced-Fission Neutrons from Low-Enriched Uranium

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Published: 2012

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Protection and control of nuclear fuels is paramount for nuclear security and safeguards; therefore, it is important to develop fast and robust controlling mechanisms to ensure the safety of nuclear fuels. Through both passive- and active-interrogation methods we can use fast-neutron detection to perform real-time measurements of fission neutrons for process monitoring. Active interrogation allows us to use different ranges of incident neutron energy to probe for different isotopes of uranium. With fast-neutron detectors, such as organic liquid scintillation detectors, we can detect the induced-fission neutrons and photons and work towards quantifying a sample's mass and enrichment. Using MCNPX-PoliMi, a system was designed to measure induced-fission neutrons from U-235 and U-238. Measurements were then performed in the summer of 2010 at the Joint Research Centre in Ispra, Italy. Fissions were induced with an associated particle D-T generator and an isotopic Am-Li source. The fission neutrons, as well as neutrons from (n, 2n) and (n, 3n) reactions, were measured with five 5? by 5? EJ-309 organic liquid scintillators. The D-T neutron generator was available as part of a measurement campaign in place by Padova University. The measurement and data-acquisition systems were developed at the University of Michigan utilizing a CAEN V1720 digitizer and pulse-shape discrimination algorithms to differentiate neutron and photon detections. Low-enriched uranium samples of varying mass and enrichment were interrogated. Acquired time-of-flight curves and cross-correlation curves are currently analyzed to draw relationships between detected neutrons and sample mass and enrichment. In the full paper, the promise of active-interrogation measurements and fast-neutron detection will be assessed through the example of this proof-of-concept measurement campaign. Additionally, MCNPX-PoliMi simulation results will be compared to the measured data to validate the MCNPX-PoliMi code when used for active-interrogation simulations.

Determining 235U Enrichment Using a Dual-energy Approach for Delayed Neutron Measurements
Determining 235U Enrichment Using a Dual-energy Approach for Delayed Neutron Measurements

Author: Angela Lynn Lousteau

Publisher:

Published: 2017

Total Pages: 252

ISBN-13:

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Bulk uranium items are often measured using active neutron interrogation systems to take advantage of the relatively high penetrability of neutrons, providing the ability to quickly and accurately measure uranium masses in large, dense configurations. Active techniques employ an external neutron source to induce fission in the uranium and subsequently measure emitted prompt fission or delayed neutrons. Unfortunately, the emitted neutrons from 235U [uranium-235] and 238U [uranium-238] are, for all practical purposes, indistinguishable; therefore, commonly used systems such as the Active Well Coincidence Counter, the 252Cf [californium-252] Shuffler, and other systems based on measurement of prompt or delayed fission neutrons require many representative calibration standards and/or well-known isotopic information to interpret the results (i.e., extract an isotopic mass from the effective fissionable mass), thus limiting these techniques for safeguards applications. The primary objective of this research was to develop and demonstrate a dual-energy neutron interrogation technique using a 252Cf Shuffler measurement chamber for determination of uranium enrichment, thus eliminating the need for a (traditionally separate) gamma isotopic measurement. This new technique exploits the change in fission rates as a function of interrogating neutron energy to independently determine the 235U and 238U content in the measurement item. Dual neutron interrogation energies were achieved by adding a deuterium- tritium (D-T) neutron generator into the measurement chamber of the Oak Ridge National Laboratory 252Cf Shuffler. Results from traditional 252Cf measurements and the new D-T measurements were then used to develop a relationship between uranium enrichment and the ratio of the two delayed neutron count rates. Parameter studies were performed to optimize the measurements for each source using a combination of modeling/simulation and experimental measurements. This dissertation presents the detailed development of this novel dual-energy neutron interrogation technique. The results are promising and with engineering refinements could be deployed for routine assay of certain types of materials.

Active Interrogation of Fresh Nuclear Fuel in Shipping Containers
Active Interrogation of Fresh Nuclear Fuel in Shipping Containers

Author: Sarah Elizabeth Sarnoski

Publisher:

Published: 2019

Total Pages:

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Currently available techniques are intrusive, requiring removal of fuel assemblies from shipping containers to assay them. It is a goal of the International Atomic Energy Agency (IAEA) to have a technique to assay assemblies without removal from shipping containers. A new technique for the assay of fresh nuclear fuel in shipping containers has been developed and benchmarking experiments performed to validate the method. The technique utilizes a tuned energy spectrum neutron source to preferentially fission U-235 and high purity germanium (HPGe) spectrometry to quantify short-lived fission products resulting from the fission process, selecting fission products that provide the greatest differentiation between U-235 and U-238 fission. An experiment was designed to validate the proposed technique by interrogating bare fuel assemblies of Low Enriched Uranium (LEU), Depleted Uranium (DU), and a challenge assembly comprised of an unknown combination of LEU and DU fuel rods. Seventeen unique fission product gamma rays were identified in the LEU fuel. Isotope ratios were calculated for each fuel type and a 2 analysis used to determine the statistical differences between the fuel types. In a blind analysis, the composition of the challenge fuel assembly was postulated to be LEU around the perimeter with DU rods in the center of the assembly, which was revealed to be the true configuration. Monte Carlo N-Particle (MNCP) was used to predict the measured gamma-ray spectrum and the model benchmarked with the experimental data. The simulation was then extended to model a fresh fuel assembly inside a shipping container on a semi-trailer. The results indicate that the fission product gamma rays used in the analysis of the experimental data are expected to be distinguishable above backgrounds, indicating that the proposed technique can be used to measure induced short-lived fission products through a shipping container and verify a fresh nuclear fuel assembly.

A Kinematically Beamed, Low Energy Pulsed Neutron Source for Active Interrogation
A Kinematically Beamed, Low Energy Pulsed Neutron Source for Active Interrogation

Author: P. Kerr

Publisher:

Published: 2004

Total Pages:

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We are developing a new active interrogation system based on a kinematically focused low energy neutron beam. The key idea is that one of the defining characteristics of SNM (Special Nuclear Materials) is the ability for low energy or thermal neutrons to induce fission. Thus by using low energy neutrons for the interrogation source we can accomplish three goals, (1) Energy discrimination allows us to measure the prompt fast fission neutrons produced while the interrogation beam is on; (2) Neutrons with an energy of approximately 60 to 100 keV do not fission 238U and Thorium, but penetrate bulk material nearly as far as high energy neutrons do and (3) below about 100keV neutrons lose their energy by kinematical collisions rather than via the nuclear (n,2n) or (n, n') processes thus further simplifying the prompt neutron induced background. 60 keV neutrons create a low radiation dose and readily thermal capture in normal materials, thus providing a clean spectroscopic signature of the intervening materials. The kinematically beamed source also eliminates the need for heavy backward and sideway neutron shielding. We have designed and built a very compact pulsed neutron source, based on an RFQ proton accelerator and a lithium target. We are developing fast neutron detectors that are nearly insensitive to the ever-present thermal neutron and neutron capture induced gamma ray background. The detection of only a few high energy fission neutrons in time correlation with the linac pulse will be a clear indication of the presence of SNM.

Determination of the 235U Enrichment of Bulk Uranium Samples Using Delayed Neutrons
Determination of the 235U Enrichment of Bulk Uranium Samples Using Delayed Neutrons

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Published: 2006

Total Pages: 11

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A technique for utilizing the physics of the delayed neutron re-interrogation method to determine uranium enrichment is presented in this paper. A series of active interrogation measurements was performed using pulsed 14-MeV neutrons and a polyethylene moderated 3He based neutron detection system. Proof of principle measurements were performed on a set of bulk uranium oxide standards of differing enrichments. A series of measurements was performed on a set of uranium 'unknowns' with and without high-Z gamma-ray shielding (lead) present. Uranium enrichment estimates were obtained for all cases including the bulk uranium samples shielded by lead. Further refinement of this technique is needed to make it a more powerful tool for non-destructive assay of bulk uranium samples.

INL Active Interrogation Testing In Support of the GNEP Safeguards Campaign
INL Active Interrogation Testing In Support of the GNEP Safeguards Campaign

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Published: 2008

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Active interrogation, a measurement technique which uses a radiation source to probe materials and generate unique signatures useful for characterizing those materials, is a powerful tool for assaying special nuclear material. Work at Idaho National Laboratory (INL) in the area of active interrogation, using neutron and photon sources, has been under way for many years to develop methods for detecting and quantifying nuclear material for national and homeland security research areas. This research knowledge base is now being extended to address nuclear safeguards and process monitoring issues related to the Global Nuclear Energy Partnership (GNEP). As a first step in this area preliminary scoping studies have been performed to investigate the usefulness of using active neutron interrogation, with a low-power electronic neutron generator, to assay Department of Transportation 6M shipping drums containing uranium oxide fuel rodlets from INL's zero power physics reactor. Using the paired-counting technique during the die-away time period of interrogation, a lower detection limit of approximately 4.2 grams of enriched uranium (40% 235U) was calculated for a 40 minute measurement using a field portable 2.5 MeV neutron source and an array of 16 moderated helium-3 neutron tubes. Future work in this area, including the use of a more powerful neutron source and a better tailored detector array, would likely improve this limit to a much lower level. Further development work at INL will explore the applicability of active interrogation in association with the nuclear safeguards and process monitoring needs of the advanced GNEP facilities under consideration. This work, which will include both analyses and field demonstrations, will be performed in collaboration with colleagues at INL and elsewhere that have expertise in nuclear fuel reprocessing as well as active interrogation and its use for nuclear material analyses.

Active Interrogation of Highly Enriched Uranium
Active Interrogation of Highly Enriched Uranium

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Published: 2004

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Active interrogation techniques provide reliable detection of highly enriched uranium (HEU) even when passive detection is difficult. We use 50-Hz pulsed beams of bremsstrahlung photons from a 10-MeV linac or 14-MeV neutrons from a neutron generator for interrogation, thus activating the HEU. Detection of neutrons between pulses is a positive indicator of the presence of fissionable material. We detect the neutrons with three neutron detector designs based on 3He tubes. This report shows examples of the responses in these three detectors, for unshielded and shielded kilogram quantities of HEU, in containers as large as cargo containers.

Neutron Generators for Analytical Purposes
Neutron Generators for Analytical Purposes

Author: International Atomic Energy Agency

Publisher: IAEA Radiation Technology Repo

Published: 2012

Total Pages: 145

ISBN-13: 9789201251107

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This publication addresses recent developments in neutron generator (NG) technology. It presents information on compact instruments with high neutron yield to be used for neutron activation analysis (NAA) and prompt gamma neutron activation analysis in combination with high count rate spectrometers. Traditional NGs have been shown to be effective for applications including borehole logging, homeland security, nuclear medicine and the on-line analysis of aluminium, coal and cement. Pulsed fast thermal neutron analysis, as well as tagged and timed neutron analysis, are additional techniques which can be applied using NG. Furthermore, NG can effectively be used for elemental analysis and is also effective for analysis of hidden materials by neutron radiography. Useful guidelines for developing NG based research laboratories are also provided in this publication.