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Papers by Melina Varvayianni

Research paper thumbnail of Preliminary Selection of Device Materials to Locally Transform Thermal into SFR Neutron Spectrum

Science and Technology of Nuclear Installations, 2018

The safe introduction of Generation IV (Gen IV) reactor concepts into operation will require exte... more The safe introduction of Generation IV (Gen IV) reactor concepts into operation will require extensive testing of their components. This must be performed under neutronic conditions representative of those expected to prevail inside the new reactor cores when in operation. In a thermal Material Testing Reactor (MTR) such neutronic conditions can be achieved by tailoring the prevailing neutron spectrum with the utilization of a device containing appropriate materials. In this work various materials are investigated as candidate components of a device that will be required in case that a thermal MTR neutron energy spectrum must be locally transformed, so as to imitate Sodium cooled Fast Reactor (SFR). Many nuclides have been examined with respect to only their neutronic behavior, providing thus a pool of neutronically appropriate materials for consideration in further investigation, such as regarding reactor safety and fabrication issues. The nuclides have been studied using the neutr...

Research paper thumbnail of Sea Breeze Wind Field Predictions in Atmospheric Dispersion Modelling

Research paper thumbnail of Photochemical Modelling Exercise over Greater Athens Area

Research paper thumbnail of A Computer System for Simulating the Transfer of Pollutants over Complex Terrain - Some Recent Applications

Radiation Protection Dosimetry, 1993

ABSTRACT

Research paper thumbnail of Experimental study of the flux trap effect in a sub-critical assembly

HNPS Proceedings, 2019

The neutron flux trap effect was experimentally studied in the sub-critical assembly of the Atomi... more The neutron flux trap effect was experimentally studied in the sub-critical assembly of the Atomic and Nuclear Physics Laboratory of the Aristotle University of Thessaloniki, using delayed gamma neutron activation analysis (DGNAA). Measurements were taken within the fuel grid, in vertical levels symmetrical to the Am-Be neutron source, before and after the removal of fuel elements, also permitting a basic study of the vertical flux profile. Three identical flux traps of diamond shape and an area of 96 cm2 were created by removing four fuel rods for each one. Two (n,γ) reactions and one (n,p) threshold reaction were selected for thermal, epithermal and fast flux study. For the thermal and epithermal flux, results obtained through the 197Au(n,γ)198Au, and 186W(n,γ)187W reactions were used, with and without Cd covers, to differentiate between the two flux regions. For the fast flux, the 58Ni(n,p)58Co reaction was used.All measurements were taken in a HPGe detector of 42% relative effic...

Research paper thumbnail of Sea Breeze Wind Field Prediction in Atmospheric Dispersion Modelling

Reliability of Radioactive Transfer Models, 1988

The estimation of the dispersion of an airborne radioactive release presupposes the knowledge of ... more The estimation of the dispersion of an airborne radioactive release presupposes the knowledge of the windfield and the level of diffusion in the region under consideration.

Research paper thumbnail of Compilation of Existing Neutron Screen Technology

Science and Technology of Nuclear Installations, 2014

The presence of fast neutron spectra in new reactors is expected to induce a strong impact on the... more The presence of fast neutron spectra in new reactors is expected to induce a strong impact on the contained materials, including structural materials, nuclear fuels, neutron reflecting materials, and tritium breeding materials. Therefore, introduction of these reactors into operation will require extensive testing of their components, which must be performed under neutronic conditions representative of those expected to prevail inside the reactor cores when in operation. Due to limited availability of fast reactors, testing of future reactor materials will mostly take place in water cooled material test reactors (MTRs) by tailoring the neutron spectrum via neutron screens. The latter rely on the utilization of materials capable of absorbing neutrons at specific energy. A large but fragmented experience is available on that topic. In this work a comprehensive compilation of the existing neutron screen technology is attempted, focusing on neutron screens developed in order to locally ...

Research paper thumbnail of Criticality Search of an Accelerator Driven System Using the ANET Code

World Journal of Nuclear Science and Technology

Research paper thumbnail of Developing a Monte-Carlo solver for the simulation of the reactor core dynamics

Research paper thumbnail of Qualification of the ANET Code for Spallation Neutron Yield and Core Criticality in the KUCA ADS

World Journal of Nuclear Science and Technology

Research paper thumbnail of Testing the new stochastic neutronic code ANET in simulating safety important parameters

Research paper thumbnail of Developing and investigating a pure Monte-Carlo module for transient neutron transport analysis

Research paper thumbnail of Optimized Flux Trap Dimensions in a Research Reactor Core

Research paper thumbnail of A Newton-based Jacobian-free approach for neutronic-Monte Carlo/thermal-hydraulic static coupled analysis

Research paper thumbnail of ADREA-I: A Three-Dimensional Transient Transport Code for Complex Terrain and Other Applications

Nuclear Technology

ABSTRACT The ADREA-I code is a three-dimensional transient analytical tool that can provide atmos... more ABSTRACT The ADREA-I code is a three-dimensional transient analytical tool that can provide atmospheric boundary layer and dispersion analysis at the mesoscale and microscale levels, under any atmospheric stability conditions and with any ground complexity, and it is particularly suitable for large topographical disturbances and consequently large atmospheric altitudes. The code, in response to the need to treat large topographical disturbances with the highest spatial and temporal numerical resolution possible, introduces new features in the description of anomalous topography, turbulent diffusion coefficients, and numerical approach. This paper reports on applications carried out within the framework of validation and demonstration studies of ADREA-I which give reasonable results.

Research paper thumbnail of Wind field and dispersion modelling in complex terrain

Research paper thumbnail of The TRANSALP experiment Tracer Release and Transport Simulation

Research paper thumbnail of Mesoscale numerical modelling with ADREA I main features and results

Research paper thumbnail of An observational study of the sea breeze circulation at Eastern Attica in light background winds

Research paper thumbnail of Transport of the Chernobyl radioactive plume to Greece

Research paper thumbnail of Preliminary Selection of Device Materials to Locally Transform Thermal into SFR Neutron Spectrum

Science and Technology of Nuclear Installations, 2018

The safe introduction of Generation IV (Gen IV) reactor concepts into operation will require exte... more The safe introduction of Generation IV (Gen IV) reactor concepts into operation will require extensive testing of their components. This must be performed under neutronic conditions representative of those expected to prevail inside the new reactor cores when in operation. In a thermal Material Testing Reactor (MTR) such neutronic conditions can be achieved by tailoring the prevailing neutron spectrum with the utilization of a device containing appropriate materials. In this work various materials are investigated as candidate components of a device that will be required in case that a thermal MTR neutron energy spectrum must be locally transformed, so as to imitate Sodium cooled Fast Reactor (SFR). Many nuclides have been examined with respect to only their neutronic behavior, providing thus a pool of neutronically appropriate materials for consideration in further investigation, such as regarding reactor safety and fabrication issues. The nuclides have been studied using the neutr...

Research paper thumbnail of Sea Breeze Wind Field Predictions in Atmospheric Dispersion Modelling

Research paper thumbnail of Photochemical Modelling Exercise over Greater Athens Area

Research paper thumbnail of A Computer System for Simulating the Transfer of Pollutants over Complex Terrain - Some Recent Applications

Radiation Protection Dosimetry, 1993

ABSTRACT

Research paper thumbnail of Experimental study of the flux trap effect in a sub-critical assembly

HNPS Proceedings, 2019

The neutron flux trap effect was experimentally studied in the sub-critical assembly of the Atomi... more The neutron flux trap effect was experimentally studied in the sub-critical assembly of the Atomic and Nuclear Physics Laboratory of the Aristotle University of Thessaloniki, using delayed gamma neutron activation analysis (DGNAA). Measurements were taken within the fuel grid, in vertical levels symmetrical to the Am-Be neutron source, before and after the removal of fuel elements, also permitting a basic study of the vertical flux profile. Three identical flux traps of diamond shape and an area of 96 cm2 were created by removing four fuel rods for each one. Two (n,γ) reactions and one (n,p) threshold reaction were selected for thermal, epithermal and fast flux study. For the thermal and epithermal flux, results obtained through the 197Au(n,γ)198Au, and 186W(n,γ)187W reactions were used, with and without Cd covers, to differentiate between the two flux regions. For the fast flux, the 58Ni(n,p)58Co reaction was used.All measurements were taken in a HPGe detector of 42% relative effic...

Research paper thumbnail of Sea Breeze Wind Field Prediction in Atmospheric Dispersion Modelling

Reliability of Radioactive Transfer Models, 1988

The estimation of the dispersion of an airborne radioactive release presupposes the knowledge of ... more The estimation of the dispersion of an airborne radioactive release presupposes the knowledge of the windfield and the level of diffusion in the region under consideration.

Research paper thumbnail of Compilation of Existing Neutron Screen Technology

Science and Technology of Nuclear Installations, 2014

The presence of fast neutron spectra in new reactors is expected to induce a strong impact on the... more The presence of fast neutron spectra in new reactors is expected to induce a strong impact on the contained materials, including structural materials, nuclear fuels, neutron reflecting materials, and tritium breeding materials. Therefore, introduction of these reactors into operation will require extensive testing of their components, which must be performed under neutronic conditions representative of those expected to prevail inside the reactor cores when in operation. Due to limited availability of fast reactors, testing of future reactor materials will mostly take place in water cooled material test reactors (MTRs) by tailoring the neutron spectrum via neutron screens. The latter rely on the utilization of materials capable of absorbing neutrons at specific energy. A large but fragmented experience is available on that topic. In this work a comprehensive compilation of the existing neutron screen technology is attempted, focusing on neutron screens developed in order to locally ...

Research paper thumbnail of Criticality Search of an Accelerator Driven System Using the ANET Code

World Journal of Nuclear Science and Technology

Research paper thumbnail of Developing a Monte-Carlo solver for the simulation of the reactor core dynamics

Research paper thumbnail of Qualification of the ANET Code for Spallation Neutron Yield and Core Criticality in the KUCA ADS

World Journal of Nuclear Science and Technology

Research paper thumbnail of Testing the new stochastic neutronic code ANET in simulating safety important parameters

Research paper thumbnail of Developing and investigating a pure Monte-Carlo module for transient neutron transport analysis

Research paper thumbnail of Optimized Flux Trap Dimensions in a Research Reactor Core

Research paper thumbnail of A Newton-based Jacobian-free approach for neutronic-Monte Carlo/thermal-hydraulic static coupled analysis

Research paper thumbnail of ADREA-I: A Three-Dimensional Transient Transport Code for Complex Terrain and Other Applications

Nuclear Technology

ABSTRACT The ADREA-I code is a three-dimensional transient analytical tool that can provide atmos... more ABSTRACT The ADREA-I code is a three-dimensional transient analytical tool that can provide atmospheric boundary layer and dispersion analysis at the mesoscale and microscale levels, under any atmospheric stability conditions and with any ground complexity, and it is particularly suitable for large topographical disturbances and consequently large atmospheric altitudes. The code, in response to the need to treat large topographical disturbances with the highest spatial and temporal numerical resolution possible, introduces new features in the description of anomalous topography, turbulent diffusion coefficients, and numerical approach. This paper reports on applications carried out within the framework of validation and demonstration studies of ADREA-I which give reasonable results.

Research paper thumbnail of Wind field and dispersion modelling in complex terrain

Research paper thumbnail of The TRANSALP experiment Tracer Release and Transport Simulation

Research paper thumbnail of Mesoscale numerical modelling with ADREA I main features and results

Research paper thumbnail of An observational study of the sea breeze circulation at Eastern Attica in light background winds

Research paper thumbnail of Transport of the Chernobyl radioactive plume to Greece