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Papers by Melina Varvayianni
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...
Radiation Protection Dosimetry, 1993
ABSTRACT
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...
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.
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 ...
World Journal of Nuclear Science and Technology
World Journal of Nuclear Science and Technology
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.
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...
Radiation Protection Dosimetry, 1993
ABSTRACT
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...
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.
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 ...
World Journal of Nuclear Science and Technology
World Journal of Nuclear Science and Technology
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.