1,720,997 research outputs found
Modelling of radionuclide transport in groundwater and subsoil for Safety Assessment studies
No full textRadioactive waste management is an international techno-scientific and socio-politic problem. Countries that use radioactivity must manage radioactive waste in safety way in order to safeguard population and environment from radiological risks. Safety assessment techniques are used to evaluate the performance of the disposal facility and its impact on human health and environment, during the lifetime of the facility. The final goal is a qualitative and quantitative estimation of the possible radiological risk due to a radioactive source. Safety assessment studies need continue improvements to be able to manage all involved aspects and the evolution of technological and scientific innovation. For this reason, safety case and safety assessment studies are discussed by the international nuclear scientific and research community. The research activity performed during 2013-2016 PhD years can be included in this context. It was developed in collaboration with ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development), coupling different background knowledge necessary to analyze these multidisciplinary topics. Methodological approaches to study the radionuclide transport in environment were investigated. In particular, the modelling of radionuclide transport in groundwater and subsoil was carried out to predict possible accidental leakage of radionuclides from a nuclear facility into the environment. The thesis is divided in four main topics: the investigation of unsaturated zone (part of the subsoil above the water table level); the analysis of the saturated zone (part of the subsoil below the water table level); the coupling of unsaturated zone and saturated zone models; the introduction of some geochemical aspects. The unsaturated zone is characterized by complex physico-chemical phenomena, that strongly influence water flow and radionuclide transport dynamic. The integration of different techniques, such as isotopic analysis, tracer test, and modelling allowed to estimate the barrier effect of the unsaturated zone, which delays the radionuclide transport towards groundwater. The saturated zone can host aquifers where water is collected for human purposes. For this reason, it must be strictly safeguarded. A step-by-step approach focused on the investigation of groundwater dynamics and radiological source terms was applied and different scenarios were analyzed in order to identify the areas that can be involved by radiological risks. The coupling of unsaturated zone and saturated zone was assessed to be fundamental in the development of safety assessment studies that investigate radionuclide transport into the environment. A methodological approach was proposed and promising results were obtained to spend future effort on this topic. Finally, geochemical aspects were introduced and preliminary information on the interaction between radionuclide and environment were estimated. The applied methodological approaches can be introduced in safety assessment studies of disposal facility to estimate how perform mitigation actions in accident case or how plan radiological and environmental monitoring networ
Tritium release scenarios in the IRPR system of DEMO: Safety assessment and mitigation strategies
Full text linkThis study investigates potential tritium release scenarios in the Isotope Rebalancing and Protium Removal (IRPR) system of DEMO fuel cycle, focusing on failures in the Temperature Swing Absorption (TSA) unit, including its feed tank. Two accident cases are considered, based on the postulated initiating events identified by the FFMEA: (1) a guillotine break in the pipeline supplying the IRPR system and (2) a pipe rupture in the TSA unit. MELCOR 1.8.6 for fusion is used to simulate the dynamics of the gases (hydrogen, air, inert gases), the resulting pressurization of the enclosure volumes, and the accumulation of hydrogen isotopes. A parametric study evaluates the impact of design choices like feed tank configuration and glovebox volume, informing the design of the system to enhance safety. The analysis includes cases where safety systems such as detritiation or isolation fail to operate correctly. The findings support ongoing safety assessments for DEMO and inform strategies to improve safety in fusion power plants
TOXICITY AND HEALTH EFFECTS OF ORTHOCHLORO-BENZYLIDENE-MALONONITRILE (CS GAS)
No full textThe CS gas has repeatedly been used as a tear gas by police forces during manifestations and riots, in Europe, in the United States and elsewhere. Our study is aimed to examine toxicity and health effects on humans of CS gas, following the people exposure to CS gas in Valsusa (Italy), during the 2011-2015 period. The claims that the CS gas is not toxic are counterbalanced by many findings by recent studies, showing many toxic effects, especially in case of misuse of the gas, or in weak and sensitive subjects. Adoption of the precaution principle seems, in this case, recommendable. The use of CS gas by police forces for riot control should therefore be abandoned, substituted by other countermeasures
Energy: a study for advanced solutions including low-neutron nuclear fusion
No full textThis paper illustrates an interdisciplinary approach to help solve the energy problem in the Twenty-First Century, and how innovative nuclear energy sources can be a solution. The situation of the world energy issue is demonstrating how an interdisciplinary approach is probably necessary to sketch out a solution. Most of the studies and experiments on nuclear fusion are currently devoted to the Deuterium-Tritium (DT) fuel cycle, however proposed experimental tokamaks based on "advanced' reactions, such as Deuterium-Helium-3 (DHe3), show a much more marked difference with fission reactors. The "zero-waste" option is a clear advantage of DHe3 fusion power versus fission, in view of its ultimate safety and public acceptance. Fusion reactors with advanced DHe3 fuel cycle turn out to have quite outstanding environmental advantages
Radionuclide transport in shallow groundwater
Full text linkAbstract Radioactive waste management is a strategic activity that is adopted in the nuclear field to safeguard the operating staff, the population and the environment from radiological risks. Studies that support the environmental assessment of a nuclear site offer insight into the understanding of the transport of radionuclides in environmental matrices (e.g. soil, groundwater, surface water, etc.). These studies, that involve the migration of a radiological source in the environment, are conducted to identify how to approach the safety assessment of current or future nuclear facilities. This work analyzes the source term as the key point in the modeling of the transport of radionuclides in groundwater and soil. A methodological approach, which focuses on the dynamic of the source term in space and time, was applied to model the transport of radionuclides. This approach can be used to plan reliable environmental monitoring networks. The analysis was performed at the nuclear site of Saluggia, Vercelli (Italy
Assessment of structural materials in compact fusion reactor design
Full text linkThe development of fusion energy systems demands structural components capable of withstanding extreme operational conditions, including intense neutron fluxes, high thermal and mechanical loads, and stringent requirements on neutron activation. Several structural materials have been proposed, such as nickel-based superalloys, reduced activation ferritic/martensitic steels, oxide-dispersion-strengthened alloys, SiC/SiC ceramic matrix composites, and vanadium-based alloys. While those materials have been extensively analysed for large tokamaks, no comparative studies exist on compact tokamaks. This work addresses this gap by considering an ARC-class tokamak as representative of compact design. The materials are evaluated based on the following criteria: power density deposition, absorption rate, TBR, energy multiplication factor within the breeding blanket, and displacement per atom. Numerical simulations were performed using the OpenMC Monte Carlo particle transport code to evaluate the neutronic behavior and activation characteristics of the selected structural materials. A simplified compact reactor model was developed using Constructive Solid Geometry (CSG) to enable consistent and reproducible comparisons. ODS steels and vanadium-based alloys emerged as the most promising candidates for application in compact, high-temperature fusion devices. ODS steels combine low activation with favorable performance across all evaluated metrics, offering a balanced tritium breeding capability alongside good resistance to radiation damage. Vanadium-based alloys, in turn, exhibit very low hydrogen and helium production, minimal power density deposition, facilitating heat removal from the structural material, and activation levels significantly lower than those of conventional austenitic steels. Across all materials, the simulations predict TBR values in the range of 0.90–1.25, energy multiplication factors of between 1.12 and 1.18, and first structural layer power densities of over 7 MW/m3. In the most favourable cases, the shutdown dose rates fall below natural background levels in less than 50 years
Coupling of unsaturated zone and saturated zone in radionuclide transport simulations
Full text linkIn the management of radionuclide release in the environment, the unsaturated zone could be a natural barrier to delay or to stop the radionuclide migration through the environment and to protect the groundwater from radiological risks. Thus, a suitable scientific evaluation of any radionuclide transport problems related to groundwater may to take into account the processes affecting flow through the unsaturated zone. In this work, an approach that involves the interactions between unsaturated zone and saturated zone both from hydrogeological and radionuclide transport point of view is proposed. This approach was tested developing a case study on an Italian nuclear site. The behavior of unsaturated zone as protective barrier for the groundwater was highlighted and identified as a fundamental aspect in the development of environmental analysis concerning the radionuclide transport into the environment. Promising results were found to improve the design of a radiological monitoring network
Groundwater system characterisation in support of safety assessment for radioactive waste disposal
No full textRadioactive waste disposal is a strategic activity in the nuclear field to safeguard the population and the environment from radiological risks. In the radioactive waste disposal field, safety assessment aims to foresee and manage the environmental and radiological impact of possible radionuclide releases. One of the main radionuclide transport pathways in the environment is through groundwater. This paper deals with an assessment process applied to a characterisation of a groundwater system and its relations with surface water, in order to foresee critical scenarios of possible radionuclide migration in environmental matrices (e.g., groundwater, surface water, soil, etc.). The study examines in depth the groundwater system of a nuclear site in Ital
A preliminary CFD and Tritium transport analysis for ARC blanket
Full text linkThe Affordable, Robust, Compact (ARC) fusion reactor is a preconceptual design proposed by the Plasma Science and Fusion Center at the Massachusetts Institute of Technology that will be developed by Commonwealth Fusion Systems. ARC features a Li2BeF4 (FLiBe) molten salt liquid blanket that provides reactor cooling, neutron shielding, and tritium breeding. This work aims to develop a preliminary coupled computational fluid dynamics (CFD) and tritium transport model to describe FLiBe flow inside the tank and to assess ARC tritium inventory in the vacuum vessel and blanket. Both models are built by taking advantage of COMSOL® Multiphysics. FLiBe velocity and temperature fields are evaluated by the CFD models, and they are passed as input to the tritium transport model. The tritium transport model computes tritium concentration inside solid materials and FLiBe. An auxiliary FLiBe inlet has been moved from the original position in the ARC preconceptual design to improve blanket cooling and to reduce the size of flow eddies. Results show that many recirculation zones generate inside the tank for the chosen tank geometry, size, and inlet-outlet conditions. Larger FLiBe temperature and tritium concentration are found in these zones. The high FLiBe temperature in recirculation areas may not allow for effective cooling, and Inconel 718 reaches critical temperatures. The largest tritium concentration for a steady-state model with continuity of tritium partial pressure at the interfaces is found in Inconel 718 while the second-highest concentration is reached in FLiBe. The total tritium inventory in the ARC blanket with the assumed model is quantified as 3.16 g
The lifetime determination of ARC reactor as a load-following plant in the energy framework
Full text linkEnergy studies are interdisciplinary studies. They involve not just technical aspects, but also environmental, social and political aspects. In this framework, an advanced technological innovation as a part of simple solution for the energy problem is considered. The role of the fusion energy as new energy source and in particular the project Affordable Robust Compact (ARC) fusion reactor as new technology is presented as part of energy policy. The most innovative characteristics of ARC is its integration in the energy grid as load-following power plant. In particular, the proposed study investigates the stresses induced in the vacuum vessel, the closest component to the plasma. The performed analysis has been focused on the quantification of time in which the vessel would fail due to repeated thermal stress when it works as load-following. It has been demonstrated that the vacuum vessel lifetime can be quantified from three to five years on the basis of the thermal cycles considered (i.e. 3, 10 and 20 cycles per day)
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