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The potential for gamma emission tomography (GET) to detect partial defectswithin a spent nuclear fuel assembly has been assessed within the IAEA SupportProgram project JNT 1955, phase I, which was completed and reported to theIAEA in October 2016. Two safeguards verification objectives were identified inthe project; (1) independent determination of the number of active pins that arepresent in a measured assembly, in the absence of a priori information about theassembly, and; (2) quantitative assessment of pin-by-pin properties, for examplethe activity of key isotopes or pin attributes such as cooling time and relativeburnup, under the assumption that basic fuel parameters (e.g., assembly typeand nominal fuel composition) are known. The efficacy of GET to meet these twoverification objectives was evaluated across a range of fuel types, burnups andcooling times, while targeting a total interrogation time of less than 60 minutes.The evaluations were founded on a modelling and analysis framework applied toexisting and emerging GET instrument designs. Monte Carlo models of differentfuel types were used to produce simulated tomographer responses to largepopulations of “virtual” fuel assemblies. The simulated instrument response datawere then processed using a variety of tomographic-reconstruction and image-processing methods, and scoring metrics were defined and used to evaluate theperformance of the methods. This paper describes the analysis framework and metrics used to predicttomographer performance. It also presents the design of a “universal” GET(UGET) instrument intended to support the full range of verification scenariosenvisioned by the IAEA. Finally, it gives examples of the expected partial-defectdetection capabilities for some fuels and diversion scenarios, and it provides acomparison of predicted performance for the notional UGET design and anoptimized variant of an existing IAEA instrument.

The potential for gamma emission tomography (GET) to detect partial defects within a spent nuclearfuel assembly is being assessed through a collaboration of Support Programs to the InternationalAtomic Energy Agency (IAEA). In the first phase of this study, two safeguards verification objectiveshave been identified. The first is the independent determination of the number of active pins that arepresent in the assembly, in the absence of a priori information. The second objective is to providequantitative measures of pin-by-pin properties, e.g. activity of key isotopes or pin attributes such ascooling time and relative burnup, for the detection of anomalies and/or verification of operator-declareddata. The efficacy of GET to meet these two verification objectives will be evaluated across a range offuel types, burnups, and cooling times, and with a target interrogation time of less than 60 minutes. The evaluation of GET viability for safeguards applications is founded on a modelling and analysisframework applied to existing and emerging GET instrument designs. Monte Carlo models of differentfuel types are used to produce simulated tomographer responses to large populations of “virtual” fuelassemblies. Instrument response data are processed by a variety of tomographic-reconstruction andimage-processing methods, and scoring metrics specific to each of the verification objectives aredefined and used to evaluate the performance of the methods. This paper will provide a description ofthe analysis framework and evaluation metrics, example performance-prediction results, and describethe design of a “universal” GET instrument intended to support the full range of verification scenariosenvisioned by the IAEA.

The IAEA has initiated Member States’ Support Program project JNT A 1955 to assess the partial defect detection capabilities of gamma emission tomography (GET) for spent nuclear fuel assembly verification. The GET technique is based on measurements of the gamma-ray flux distribution around a spent fuel assembly using dedicated, tomographic equipment and subsequent reconstruction of the internal source distribution using tomographic algorithms applied on the recorded data. One of the verification objectives identified for the project is the quantitative measurement of pin-by-pin properties, e.g. burnup and/or cooling time, for the detection of anomalies and/or verification of operator-declared data. For this objective, reconstruction algorithms that return quantitative, isotopic pin-by-pin data are applied. Previously, GET measurements performed on commercial nuclear fuel assemblies in Sweden have proven capable of determining the relative pin-by-pin power distribution with high precision in BWR fuel with short cooling time, based on the measured distribution of the gamma-ray emitting fission product 140Ba/La in the fuel. In the current project, the capabilities of GET to determine additional pin-wise fuel parameters in additional fuel types are being assessed. The evaluations are based on Monte Carlo simulations of the emission of gamma-rays from the fuel and their detection in a tomographic measurement device. This paper describes the algorithms used for reconstructing quantitative pin-wise data and the results that are anticipated with this technique. It is argued that detailed modelling of the gamma-ray attenuation through the highly inhomogeneous mix of strongly-attenuating fuel rods and less-attenuating surrounding water (wet storage) or air (dry storage) is required to yield high precision in the reconstructed data. The burnup distribution assessment would be based on the recording of 662-keV gamma radiation from 137Cs, whereas the assessment of both burnup an, UGET

A promising non-destructive assay method for verification of irradiated nuclear fuel is gammatomography, i.e. the use of measurements of the gamma radiation field around a nuclear fuel assembly to reconstruct detailed information about the internal source distribution. Typically, tomographic reconstructions result in two-dimensional images of cross sections of the fuel. We demonstrate how such images can be searched for fuel rods using a template matching technique, which is a method commonly used in the field of image analysis. In this case, a template or mask corresponding to the size and shape of a fuel rod is translated across the image in order to find the region with the highest reconstructed activity, which is assumed to correspond to the location of a fuel rod in the image. This is done iteratively, allowing no overlap of the rods. By defining the threshold between background and fuel rod objects in the image, we can identify and count the fuel rods using no other assumptions than the rod radius. Thus the rod identification procedure provides a possible means to verify whether all fuel rods arepresent, and it may also be implemented to identify the fuel type of the measured assembly. Theprocedure is robust in cases of irregularities, such as assembly bow or torsion, or the dislocation ofindividual fuel rods in the measured cross section. Here we demonstrate fuel rod identification procedure, using authentic images collected with a tomographic measurement device on commercial fuel assemblies. The results show that image analysis can support tomographic partial defect verification of irradiated nuclear fuel assemblies, even on the single fuel rod level., UGET

Assessment of gamma emission tomography (GET) for spent nuclear fuel verification is the task in IAEA MSP project JNT1955. In line with IAEA Safeguards R&D plan 2012-2023, the aim of this effort is to “develop more sensitive and less intrusive alternatives to existing NDA instruments to perform partial defect tests on spent fuel assemblies prior to transfer to difficult to access storage". The current viability study constitutes the first phase of three, with evaluation and decision points between each phase. Two verification objectives have been identified; (1) counting of fuel pins in tomographic images without any a priori knowledge of the fuel assembly under study, and (2) quantitative measurements of pin-by-pin properties, e.g. burnup, for the detection of anomalies and/or verification of operator-declared data. Previous measurements performed in Sweden and Finland have proven GET highly promising for detecting removed or substituted fuel pins (i.e. partial defects) in BWR and VVER-440 fuel assemblies even down to the individual fuel pin level. The current project adds to previous experiences by pursuing a quantitative assessment of the capabilities of GET for partial defect detection, across a broad range of potential IAEA applications, fuel types, and fuel parameters. A modelling and performance-evaluation framework has been developed to provide quantitative GET performance predictions, incorporating burn-up and cooling-time calculations, Monte Carlo radiation-transport and detector-response modelling, GET instrument definitions (existing and notional) and tomographic reconstruction algorithms, which use recorded gamma-ray intensities to produce cross-sectional images of the source distribution in the fuel assembly or conclusive pin-by-pin data. The framework also comprises image-processing algorithms and performance metrics that recognize the inherent trade-off between the probability of detecting missing pins and the false-alarm rate. Here, the modellin

The unattended gamma emission tomography (UGET) for spent nuclear fuel verification is an on-going project in the IAEA member states’ support program. In line with the long term R&D plan of the IAEA Department of Safeguards, it is anticipated that this effort will help develop “more sensitive and less intrusive alternatives to existing NDA instruments to perform partial defect test on spent fuel assembly prior to transfer to difficult to access storage”. In the first phase of the project, gamma transport calculations and modelling of exist- ing and proposed new designs of tomographic instruments is performed. In this paper, a set of Monte Carlo calculations regarding modelling of various tomographic devices are presented, including two existing tomographic instruments previously used for spent fuel measurements; one instrument based on scintillator detectors, developed by Uppsala University, and another based on CdTe detector arrays, developed by the JNT 1510 col- laborative effort (Hungary, Finland). Detailed models of the tomographic instruments, including structural materials, and the measured fuel assemblies are used in the simula- tions. The calculated results are compared to the experimentally measured data to provide a benchmark for the simulation procedure. The developed modelling capabilities are also used for evaluation of the partial-defect detection capabilities of the tomographic technique based on a proposed GET instrument design.

Using the neutrino telescope AMANDA-II, we have conducted two analyses searching for neutrino-induced cascades from gamma-ray bursts. No evidence of astrophysical neutrinos was found, and limits are presented for several models. We also present neutrino effective areas which allow the calculation of limits for any neutrino production model. The first analysis looked for a statistical excess of events within a sliding window of 1 or 100 s (for short and long burst classes, respectively) during the years 2001-2003. The resulting upper limit on the diffuse flux normalization times E2 for the Waxman-Bahcall model at 1 PeV is 1.6×10-6 GeV cm-2 s-1 sr-1 (a factor of 120 above the theoretical prediction). For this search 90% of the neutrinos would fall in the energy range 50 TeV to 7 PeV. The second analysis looked for neutrino-induced cascades in coincidence with 73 bursts detected by BATSE in the year 2000. The resulting upper limit on the diffuse flux normalization times E2, also at 1 PeV, is 1.5×10-6 GeV cm-2 s-1 sr-1 (a factor of 110 above the theoretical prediction) for the same energy range. The neutrino-induced cascade channel is complementary to the up-going muon channel. We comment on its advantages for searches of neutrinos from GRBs and its future use with IceCube.

We report the results of a five-year survey of the northern sky to search for point sources of high energy neutrinos. The search was performed on the data collected with the AMANDA-II neutrino telescope in the years 2000 to 2004, with a live time of 1001 days. The sample of selected events consists of 4282 upward going muon tracks with high reconstruction quality and an energy larger than about 100 GeV. We found no indication of point sources of neutrinos and set 90% confidence level flux upper limits for an all-sky search and also for a catalog of 32 selected sources. For the all-sky search, our average (over declination and right ascension) experimentally observed upper limit Phi0=((E/(1 TeV)))gamma·((d Phi)/dE) to a point source flux of muon and tau neutrino (detected as muons arising from taus) is Phinu[sub mu] + [overline nu ][sub mu]0+Phinu[sub tau] + [overline nu ][sub tau]0=11.1× 10-11 TeV-1 cm-2 s-1, in the energy range between 1.6 TeV and 2.5 PeV for a flavor ratio Phinu[sub mu] + [overline nu ][sub mu]0/Phinu[sub tau] + [overline nu ][sub tau]0=1 and assuming a spectral index gamma=2. It should be noticed that this is the first time we set upper limits to the flux of muon and tau neutrinos. In previous papers we provided muon neutrino upper limits only neglecting the sensitivity to a signal from tau neutrinos, which improves the limits by 10% to 16%. The value of the average upper limit presented in this work corresponds to twice the limit on the muon neutrino flux Phinu[sub mu] + [overline nu ][sub mu]0=5.5×10-11 TeV-1 cm-2 s-1. A stacking analysis for preselected active galactic nuclei and a search based on the angular separation of the events were also performed. We report the most stringent flux upper limits to date, including the results of a detailed assessment of systematic uncertainties.

A search has been performed for nearly vertically upgoing neutrino-induced muons with the Antarctic Muon And Neutrino Detector Array (AMANDA), using data taken over the three year period 1997-99. No excess above the expected atmospheric neutrino background has been found. Upper limits at 90% confidence level have been set on the annihilation rate of neutralinos at the center of the Earth, as well as on the muon flux at AMANDA induced by neutrinos created by the annihilation products.

The first sensors of the IceCube neutrino observatory were deployed at the South Pole during the austral summer of 2004-2005 and have been producing data since February 2005. One string of 60 sensors buried in the ice and a surface array of eight ice Cherenkov tanks took data until December 2005 when deployment of the next set of strings and tanks began. We have analyzed these data, demonstrating that the performance of the system meets or exceeds design requirements. Times are determined across the whole array to a relative precision of better than 3 ns, allowing reconstruction of muon tracks and light bursts in the ice, of air-showers in the surface array and of events seen in coincidence by surface and deep-ice detectors separated by up to 2.5 km.

The sensitivity of a search for sources of TeV neutrinos can be improved by grouping potential sources together into generic classes in a procedure that is known as source stacking. In this paper, we define catalogs of Active Galactic Nuclei (AGN) and use them to perform a source stacking analysis. The grouping of AGN into classes is done in two steps: first, AGN classes are defined, then, sources to be stacked are selected assuming that a potential neutrino flux is linearly correlated with the photon luminosity in a certain energy band (radio, IR, optical, keV, GeV, TeV). Lacking any secure detailed knowledge on neutrino production in AGN, this correlation is motivated by hadronic AGN models, as briefly reviewed in this paper.The source stacking search for neutrinos from generic AGN classes is illustrated using the data collected by the AMANDA-II highenergy neutrino detector during the year 2000. No significant excess for any of the suggested groups was found.

On 27 December 2004, a giant gamma flare from the Soft Gamma-Ray Repeater 1806-20 saturated many satellite gamma-ray detectors, being the brightest transient event ever observed in the Galaxy. AMANDA-II was used to search for down-going muons indicative of high-energy gammas and/or neutrinos from this object. The data revealed no significant signal, so upper limits (at 90% C.L.) on the normalization constant were set: 0.05(0.5) TeV-1 m(-2) s(-1) for gamma=-1.47 (-2) in the gamma flux and 0.4(6.1) TeV-1 m(-2) s(-1) for gamma=-1.47 (-2) in the high-energy neutrino flux.

[ 1] We have remotely mapped optical scattering and absorption in glacial ice at the South Pole for wavelengths between 313 and 560 nm and depths between 1100 and 2350 m. We used pulsed and continuous light sources embedded with the AMANDA neutrino telescope, an array of more than six hundred photomultiplier tubes buried deep in the ice. At depths greater than 1300 m, both the scattering coefficient and absorptivity follow vertical variations in concentration of dust impurities, which are seen in ice cores from other Antarctic sites and which track climatological changes. The scattering coefficient varies by a factor of seven, and absorptivity ( for wavelengths less than similar to 450 nm) varies by a factor of three in the depth range between 1300 and 2300 m, where four dust peaks due to stadials in the late Pleistocene have been identified. In our absorption data, we also identify a broad peak due to the Last Glacial Maximum around 1300 m. In the scattering data, this peak is partially masked by scattering on residual air bubbles, whose contribution dominates the scattering coefficient in shallower ice but vanishes at similar to 1350 m where all bubbles have converted to nonscattering air hydrates. The wavelength dependence of scattering by dust is described by a power law with exponent - 0.90 +/- 0.03, independent of depth. The wavelength dependence of absorptivity in the studied wavelength range is described by the sum of two components: a power law due to absorption by dust, with exponent - 1.08 +/- 0.01 and a normalization proportional to dust concentration that varies with depth; and a rising exponential due to intrinsic ice absorption which dominates at wavelengths greater than similar to 500 nm.