Physics prospects of the JUNO experiment Sisti, Monica
Journal of physics. Conference series,
02/2020, Volume:
1468, Issue:
1
Journal Article, Conference Proceeding
Peer reviewed
Open access
Abstract
JUNO is a 20 kton multi-purpose liquid scintillator detector currently being built in China in a dedicated underground laboratory and expected to complete the detector construction in 2021. ...JUNO primary physics goal is the determination of the neutrino mass ordering, with a significance of 3-4 sigma in six years of data taking, by measuring the oscillation pattern of electron antineutrinos coming from two nuclear power plants at a baseline of about 53 km. Besides this fundamental aim, its large target mass, unprecedented energy resolution of 3% at 1 MeV, and vertex reconstruction capability will provide vast opportunities in particle physics and astrophysics. JUNO will have a very rich physics program, which includes the precise measurement at a sub-percent level of the solar neutrino oscillation parameters, the detection of low-energy neutrinos coming from galactic core-collapse supernova, the measurement of the diffuse supernova neutrino background, the detection of neutrinos coming from the Sun and the Earth (geo-neutrinos). In this paper I will give an overview on the JUNO physics potential and discuss the performance of the JUNO detector for the various proposed measurements.
The Jiangmen Underground Neutrino Observatory is constructing the world’s largest liquid scintillator detector, with a 20 kt target mass and approximately 700 m of overburden. The total underground ...space of civil construction is around 300,000 m
3
, with the main hall comprising about 120,000 m
3
, making it the largest experimental hall in the world. Maintaining a low radon concentration in the underground air is crucial for both human health and the accuracy of experiments involving rare decay detection, such as neutrino and dark matter experiments. To ensure human health and the integrity of neutrino physics experiments, the nominal radon concentration in the main hall must be kept below 200 Bq/m
3
with a maximum value below 400 Bq/m
3
. Introduction of fresh air from above ground can significantly lower radon concentration. A benchmark experiment conducted in the refuge room near the main hall revealed that the radon emanating from underground water is a significant source of radon in the underground air. The total underground ventilation rate is approximately 160,000 m
3
/h of fresh air with about 30 Bq/m
3
222
Rn from the bottom of the vertical tunnel after the installation of powerful fans. Of this, 55,000 m
3
/h is used for ventilation in the main hall. As a result of these measures, the radon concentration inside the main hall has decreased from 1600 Bq/m
3
to below 200 Bq/m
3
under stable working conditions, with exceptions during rare adverse weather events or fan failures. The employed strategies to control radon concentration in the underground air are described in this paper.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This work describes the most complete and up-to-date thermal-hydraulics CFD model for studying the natural circulation regime within the entire TRIGA Mark II reactor at the University of Pavia. ...Building on preliminary works, this paper tackles the treatment and investigation of natural circulation in the reactor core and pool, highlighting the coupling between the two components. Despite the assumptions behind the model – such as the use of an unsteady RANS turbulence model and the treatment of the supporting grids as a porous media – the validation compared to experimental data shows quite a good agreement. The model is thus accurate enough to describe the natural convection regime within the core and the pool and highlight local phenomena, such as localised sub-cooled boiling and recirculation.
•Development of a thermal-hydraulics CFD model for the TRIGA Mark II reactor.•Detailed study of the natural circulation regime in both reactor core and pool.•Sensitivity analysis over mesh resolution and presence of the measurement rod.•Validation of both core and pool using experimental data.•Identification of core recirculation zones and localised sub-cooled boiling phenomena.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Soil mobilization has been investigated by means of fallout radionuclides (FRN) in a first‐order catchment of the Eastern Alps. Caesium‐137,
210
Pb
xs.
(
210
Pb excess or unsupported ...fraction), and
241
Am have been measured in soil samples collected from a pasture at about 2150 m above sea level. Combining pedological and radioactivity data, including mineral‐related radionuclides (primordial
40
K and nuclides belonging to the
232
Th and
238
U decay chains), the distribution of FRNs, their spatial variability, vertical distribution, and relationships with pedological and topographical variables were assessed. Because of low activity concentration, it was not possible to use artificial long‐lived
241
Am as a soil tracer, but preliminary results are encouraging. Inventories of
210
Pb
xs.
and
137
Cs have been converted into soil mobilization rates applying the MODERN model. Despite the gentle steepness and the absence of evident signs of erosion, the slopes of the considered catchment are affected by erosion at a rate up to 6 t ha
−1
yr
−1
, likely related to grazing. A comparison between
210
Pb
xs.
and
137
Cs has revealed that at this site
137
Cs, the most used FRN for estimating soil redistribution, is not suitable for this purpose, probably due to its irregular spatial distribution on snow‐covered ground after the Chernobyl accident. Conversely,
210
Pb
xs.
, owing to its continuous input, has provided reliable estimates of soil redistribution rates, in accordance with local morphology. The latter has in fact been related to morphometric variables in a regression model to provide an overview of soil erosion/sedimentation across the entire catchment, confirming that
210
Pb
xs.
is a viable alternative to trace soil erosion and deposition where the Chernobyl fallout occurred on snow‐covered ground.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Soil mobilization has been investigated by means of fallout radionuclides (FRN) in a first‐order catchment of the Eastern Alps. Caesium‐137, 210Pbxs. (210Pb excess or unsupported fraction), and 241Am ...have been measured in soil samples collected from a pasture at about 2150 m above sea level. Combining pedological and radioactivity data, including mineral‐related radionuclides (primordial 40K and nuclides belonging to the 232Th and 238U decay chains), the distribution of FRNs, their spatial variability, vertical distribution, and relationships with pedological and topographical variables were assessed. Because of low activity concentration, it was not possible to use artificial long‐lived 241Am as a soil tracer, but preliminary results are encouraging. Inventories of 210Pbxs. and 137Cs have been converted into soil mobilization rates applying the MODERN model. Despite the gentle steepness and the absence of evident signs of erosion, the slopes of the considered catchment are affected by erosion at a rate up to 6 t ha−1 yr−1, likely related to grazing. A comparison between 210Pbxs. and 137Cs has revealed that at this site 137Cs, the most used FRN for estimating soil redistribution, is not suitable for this purpose, probably due to its irregular spatial distribution on snow‐covered ground after the Chernobyl accident. Conversely, 210Pbxs., owing to its continuous input, has provided reliable estimates of soil redistribution rates, in accordance with local morphology. The latter has in fact been related to morphometric variables in a regression model to provide an overview of soil erosion/sedimentation across the entire catchment, confirming that 210Pbxs. is a viable alternative to trace soil erosion and deposition where the Chernobyl fallout occurred on snow‐covered ground.
This work deals with the application of fallout radionuclides to trace soil erosion and deposition at a high‐elevation pasture in the Eastern Alps. Artificial 137Cs, the radionuclide most used for this purpose, is not suitable because of its irregular distribution on snow‐covered ground after the Chernobyl accident. In such contexts natural 210Pbxs. provides reliable estimates of soil redistribution rates, being less affected by snow‐related processes. The possibility of exploiting artificial 241Am has also been explored, with encouraging preliminary results.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Glaciers are recognized as repositories for atmospheric pollutants, however, due to climate change and enhanced melting rates, they are rapidly transitioning from being repositories to secondary ...sources of such pollutants. Artificial radionuclides are one of the pollutants found on glaciers that efficiently accumulate onto glacier surfaces within cryoconite deposits; a dark, often biogenic sediment. This work provides information about the accumulation, distribution and sources of plutonium (Pu) isotopes in cryoconite samples from glaciers worldwide. Plutonium is an artificial radionuclide spread into the environment in the last decades as a consequence of nuclear test explosions, accidents and nuclear fuel re-processing. Samples collected from 49 glaciers across nine regions of Earth are considered. Activity concentrations of plutonium in cryoconite are orders of magnitude higher than in other environmental matrices typically used for environmental monitoring (e.g. lichens, mosses, soils and sediments), particularly in the Northern Hemisphere. Isotopic ratios indicate that plutonium contamination of cryoconite is dominated by the global signal of stratospheric fallout related to atmospheric nuclear tests. However, specific glaciers in Svalbard reveal a signature compatible with a contribution from the re-entry of the SNAP-9A satellite in 1964, which was equipped with a 238Pu radioisotope thermoelectric generator as well. Similarly, an excess of 238Pu is observed in cryoconite from the Exploradores Glacier (Chile). This could be associated with the November 1996 crash of the automatic Interplanetary Station "Mars '96" which was carrying a 238Pu thermoelectric generator. This is the first time ever that an isotopic evidence for this event is reported. These findings highlight the role that cryoconite can play in reconstructing the radioactive contamination history of different glaciated regions of the Earth.Glaciers are recognized as repositories for atmospheric pollutants, however, due to climate change and enhanced melting rates, they are rapidly transitioning from being repositories to secondary sources of such pollutants. Artificial radionuclides are one of the pollutants found on glaciers that efficiently accumulate onto glacier surfaces within cryoconite deposits; a dark, often biogenic sediment. This work provides information about the accumulation, distribution and sources of plutonium (Pu) isotopes in cryoconite samples from glaciers worldwide. Plutonium is an artificial radionuclide spread into the environment in the last decades as a consequence of nuclear test explosions, accidents and nuclear fuel re-processing. Samples collected from 49 glaciers across nine regions of Earth are considered. Activity concentrations of plutonium in cryoconite are orders of magnitude higher than in other environmental matrices typically used for environmental monitoring (e.g. lichens, mosses, soils and sediments), particularly in the Northern Hemisphere. Isotopic ratios indicate that plutonium contamination of cryoconite is dominated by the global signal of stratospheric fallout related to atmospheric nuclear tests. However, specific glaciers in Svalbard reveal a signature compatible with a contribution from the re-entry of the SNAP-9A satellite in 1964, which was equipped with a 238Pu radioisotope thermoelectric generator as well. Similarly, an excess of 238Pu is observed in cryoconite from the Exploradores Glacier (Chile). This could be associated with the November 1996 crash of the automatic Interplanetary Station "Mars '96" which was carrying a 238Pu thermoelectric generator. This is the first time ever that an isotopic evidence for this event is reported. These findings highlight the role that cryoconite can play in reconstructing the radioactive contamination history of different glaciated regions of the Earth.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
CUORE is the only fully approved 1-ton size neutrinoless double beta decay experiment to date, with the goal of scrutinazing the inverted hierachy region for the effective Majorana mass. CUORE, ...presently being built in Gran Sasso Underground Laboratory, is an array of 988 TeO2 cryogenic detectors containing 200kg of 130Te, the neutrinoless double beta decay candidate. CUORE is due to start data taking in 2012. The feasibility of the project has been proved by Cuoricino, the pilot experiment that took data until 2008, for about five years, with 62 TeO2 cryogenic detectors. Cuoricino will be superseded in 2010 by CUORE-0, the first CUORE tower to be installed in Cuoricino cryogenic facility, which will take data until CUORE start. In this paper the final results of Cuoricino are reported, and CUORE-0 and CUORE potential and state of the art are discussed.
•Low fidelity models for CFD may not be accurate enough for nuclear applications.•They can be improved using data assimilation algorithms with experimental data.•We propose the integration of the ...Kalman filter within CFD algorithms in OpenFOAM.•We validate the code on a real world test case (TRIGA Mark II reactor channel).
The main limitation of Computational Fluid Dynamics (CFD) lies in the unacceptable computational capability needed for performing accurate simulations for most real-time applications, and in the reduced accuracy of computationally more efficient low fidelity models for security-related applications. One example is the treatment of complex turbulent flows, where low-fidelity models introduce simplifications and source of uncertainties. A promising solution to improve accuracy is to use additional information about the actual flow field, such as experimental data taken on the system. The dynamic data-driven paradigm allows the direct incorporation of the knowledge coming from the measurements within the simulation, thus improving the model estimate itself by minimising its misfit with the data. In this work, the Kalman filter algorithm for data assimilation is combined with the segregated method for CFD modelling to get an integrated algorithm for resolving the incompressible Navier-Stokes equations along with the temperature one. The main novelty lies because such an integrated approach allows preserving mass conservation. This algorithm is herein validated regarding an instrumented cooling channel of the TRIGA Mark II reactor at the University of Pavia, using experimental data on temperature. The main takeaway of this validation is that, despite having only measurements on one quantity, also the prediction on velocity is improved regarding the standard segregated CFD algorithm. The prediction of the state also improves in domain locations where experimental data are not available. The increase in computational time is still lower than the one needed for a more accurate simulation.
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•Bayesian statistics to analyze the neutron flux spectrum from activation data.•Rigorous statistical approach for accurate evaluation of the neutron flux groups.•Cross section and activation data ...uncertainties included for the problem solution.•Flexible methodology applied to analyze different nuclear reactor flux spectra.•The results are in good agreement with the MCNP simulations of neutron fluxes.
In this paper, we present a statistical method, based on Bayesian statistics, to analyze the neutron flux spectrum from the activation data of different isotopes. The experimental data were acquired during a neutron activation experiment performed at the TRIGA Mark II reactor of Pavia University (Italy) in four irradiation positions characterized by different neutron spectra.
In order to evaluate the neutron flux spectrum, subdivided in energy groups, a system of linear equations, containing the group effective cross sections and the activation rate data, has to be solved. However, since the system’s coefficients are experimental data affected by uncertainties, a rigorous statistical approach is fundamental for an accurate evaluation of the neutron flux groups.
For this purpose, we applied the Bayesian statistical analysis, that allows to include the uncertainties of the coefficients and the a priori information about the neutron flux. A program for the analysis of Bayesian hierarchical models, based on Markov Chain Monte Carlo (MCMC) simulations, was used to define the problem statistical model and solve it.
The first analysis involved the determination of the thermal, resonance-intermediate and fast flux components and the dependence of the results on the Prior distribution choice was investigated to confirm the reliability of the Bayesian analysis. After that, the main resonances of the activation cross sections were analyzed to implement multi-group models with finer energy subdivisions that would allow to determine the neutron flux groups, their uncertainties and correlations with good accuracy. The results were then compared with the ones obtained from the Monte Carlo simulations of the reactor fluxes performed with the MCNP code, finding in general a good agreement.
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GEOZS, IJS, KILJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The accumulation of fallout radionuclides (FRNs) from nuclear weapons testing and nuclear accidents has been evaluated for over half a century in natural environments; however, until recently their ...distribution and abundance within glaciers have been poorly understood. Following a series of individual studies of FRNs, specifically 137Cs, 241Am and 210Pb, deposited on the surface of glaciers, we now understand that cryoconite, a material commonly found in the supraglacial environment, is a highly efficient accumulator of FRNs, both artificial and natural. However, the variability of FRN activity concentrations in cryoconite across the global cryosphere has never been assessed. This study thus aims to both synthesize current knowledge on FRNs in cryoconite and assess the controls on variability of activity concentrations. We present a global database of new and previously published data based on gamma spectrometry of cryoconite and proglacial sediments, and assess the extent to which a suite of environmental and physical factors can explain spatial variability in FRN activity concentrations in cryoconite. We show that FRNs are not only found in cryoconite on glaciers within close proximity to specific sources of radioactivity, but across the global cryosphere, and at activity concentrations up to three orders of magnitude higher than those found in soils and sediments in the surrounding environment. We also show that the organic content of cryoconite exerts a strong control on accumulation of FRNs, and that activity concentrations in cryoconite are some of the highest ever described in environmental matrices outside of nuclear exclusion zones, occasionally in excess of 10,000 Bq kg−1. These findings highlight a need for significant improvements in the understanding of the fate of legacy contaminants within glaciated catchments. Future interdisciplinary research is required on the mechanisms governing their accumulation, storage, and mobility, and their potential to create time-dependent impacts on downstream water quality and ecosystem sustainability.
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•Accumulation of fallout radionuclides is commonplace in cryoconite on glaciers around the world.•There is large inter-regional variability in fallout radionuclide activity concentrations in cryoconite.•Fallout radionuclides concentrations can be orders of magnitude higher than found in other environmental matrices.•The organic content of cryoconite plays a central role in its ability to accumulate fallout radionuclides.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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