In the framework of research on generation-IV reactors, it is very important to have infrastructu... more In the framework of research on generation-IV reactors, it is very important to have infrastructures specifically dedicated to the study of fundamental parameters in dynamics and kinetics of future fast-neutron reactors. Among various options pursued by international groups, Italy focused on lead-cooled reactors, which guarantee minimal neutron slowdown and capture and efficient cooling. In this paper it is described the design of a the low-power prototype generator, LEADS, that could be used within research facilities such as the National Laboratory of Legnaro of the INFN. The LEADS has a high safety standard in order to be used as a training facility, but it has also a good flexibility so as to allow a wide range of measurements and experiments. A high safety standard is achieved by limiting the reactor power to less than few hundred kW and the neutron multiplication factor k eff to less than 0.95 (a limiting value for spent fuel pool), by using a pure-uranium fuel (no plutonium) and by using solid lead as a diffuser. The proposed core is therefore intrinsically subcritical and has to be driven by an external neutron source generated by a proton beam impinging in a target. Preliminary simulations, performed with the MCNPX code indicated, for a 0.75 mA continuous proton beam current at 70 MeV proton energy, a reactor power of about 190 kW when using a beryllium converter. The enriched-uranium fuel elements are immersed in a solid-lead matrix and contained within a steel vessel. The system is cooled by helium gas, which is transparent to neutrons and does not undergo activation. The gas is pumped by a compressor through specific holes at the entrance of the active volume with a temperature which varies according to the operating conditions and a pressure of about 1.1 MPa. The hot gas coming out of the vessel is cooled by an external helium-water heat exchanger. The beryllium converter is cooled by its dedicated helium gas cooling system. After shutdown, the decay is completely dissipated by conduction through the lead reflector and steel vessel, and then evacuated by irradiation from the vessel surface to the external ambient air.
In this paper we simulated the behavior of a simple ADS model, based on MOX fuel embedded in soli... more In this paper we simulated the behavior of a simple ADS model, based on MOX fuel embedded in solid lead, in terms of multiplication coefficient k ef f , thermal power and absolute neutron spectra. In the first part of the paper, we report on the results obtained when modifying the reflector surrounding the fission core, by replacing pure lead with a layered graphite/lead structure. We found that, by appropriately choosing position and thickness of the graphite and lead layers, it is possible to obtain a "hybrid" system where the neutron spectrum in the core still exhibits a fast character, while the spectrum in the graphite layer is considerably softer, becoming thermal in the most peripheral positions. In order to obtain such a modulation of the neutron spectra from the center of the system to the periphery, a careful choice of the materials has to be made in order to avoid large variations of the local power at the core boundary. However, the smoothness of the power distribution is obtained at the expense of lower values of k ef f and the total power of the system. In the second part of the paper, we explored the option of adopting light water as coolant, instead of the helium gas assumed in the initial design. We found that this produces an increase in k ef f and thermal power, without significantly perturbing the fast character of the system and without introducing spatial power excursions in any place within the core. The characteristics obtained may allow to design a system where fast, mixed and thermal spectra can be used to expand the use of the ADS as an irradiation facility.
Within European Partitioning & Transmutation research programs, infrastructures specifically dedi... more Within European Partitioning & Transmutation research programs, infrastructures specifically dedicated to the study of fundamental reactor physics and engineering parameters of future fast-neutron-based reactors are very important, being some of these features not available in present zero-power prototypes. This presentation will
The differential cross section, dσ/dt, for ρ 0 meson photoproduction on the proton above the reso... more The differential cross section, dσ/dt, for ρ 0 meson photoproduction on the proton above the resonance region was measured up to a momentum transfer -t = 5 GeV 2 using the CLAS detector at the Thomas Jefferson National Accelerator ...
The spin structure functions $g_1$ for the proton and the deuteron have been measured over a wide... more The spin structure functions $g_1$ for the proton and the deuteron have been measured over a wide kinematic range in $x$ and \Q2 using 1.6 and 5.7 GeV longitudinally polarized electrons incident upon polarized NH$_3$ and ND$_3$ targets at Jefferson Lab. Scattered ...
Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual ... more Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q 2 ...
Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual ... more Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q 2 ...
The results of an experiment on inclusive electron scattering from an oxygen jet target, performe... more The results of an experiment on inclusive electron scattering from an oxygen jet target, performed in a wide range of energy and momentum transfer covering both quasi-elastic and �(1232) resonance regions, are reported. In the former region the theoretical predictions, obtained including effects of nucleon-nucleon correlations in both initial and final states, give a good description of the experimental data.
In this paper the current status of the study of the dynamical behaviour of the proposed ADS is p... more In this paper the current status of the study of the dynamical behaviour of the proposed ADS is presented; it is a complex multi-physics problem which, in the present case of a very low k eff system, is conveniently analyzed because the characteristic time scales of the problem are well separated. To be more specific, time scales of the neutronic (prompt) response of the system are so short to be negligible when studying thermal, mechanical and hydraulic aspects.
The neutron multiplication factor k-eff is a key quantity to characterize subcritical neutron mul... more The neutron multiplication factor k-eff is a key quantity to characterize subcritical neutron multiplying devices and for understanting their physical behaviour, being related to the fundamental eigenvalue of Boltzmann transport equation. Both the maximum available power-and all quantities related to it, like, e.g. the effectiveness in burning nuclear wastes-as well as reactor kinetics and dynamics depend on k-eff. Nevertheless , k-eff is not directly measurable and its determination results from the solution of an inverse problem: minimizing model dependence of the solution for k-eff then becomes a critical issue, relevant both for practical and theoretical reasons.
In this work we report initial studies on a low power Accelerator-Driven System as a possible exp... more In this work we report initial studies on a low power Accelerator-Driven System as a possible experimental facility for the measurement of relevant integral nuclear quantities. In particular, we performed Monte Carlo simulations of minor actinides and fission products irradiation and estimated the fission rate within fission chambers in the reactor core and the reflector, in order to evaluate the transmutation rates and the measurement sensitivity. We also performed a photo-peak analysis of available experimental data from a research reactor, in order to estimate the expected sensitivity of this analysis method on the irradiation of samples in the ADS considered.
We present new S beam asymmetry data for h meson photoproduction on the proton, using a novel tag... more We present new S beam asymmetry data for h meson photoproduction on the proton, using a novel tagged, laser backscattered, linearly polarized photon beam up to 1.1 GeV. The data show large, positive asymmetries, at all incident photon energies. In addition to the S 11 ͑1535͒ and D 13 ͑1520͒ resonances necessary to reproduce the cross sections, P 13 ͑1720͒ and D 15 ͑1675͒ "four stars" resonances contribute to the S observable, but cannot reproduce the strong forward asymmetries measured at energies higher than 900 MeV. [S0031-9007(98)06957-9] PACS numbers: 13.60. Le, 13.88. + e, 14.40.Aq The underlying substructure of the nucleon gives rise to a rich spectrum of excited states, many of which have been associated with the baryon resonances seen in pN scattering [1] and p photoproduction. These baryon resonances and their associated gNN ء electromagnetic couplings form bench marks for models of hadron structure. Quark models have been quite successful in accounting for the masses of most observed resonances, although in some cases the electromagnetic couplings have presented more of a challenge [2].
The GRAAL facility produces a highly polarized gamma-ray beam by Compton scattering of laser phot... more The GRAAL facility produces a highly polarized gamma-ray beam by Compton scattering of laser photons on the electrons of the European Synchrotron Radiation Facility (ESRF) at Grenoble. Preliminary results have been obtained with the LAGRANGE detector showing its excellent performances. 0375-9474/97/$17.00 1997 -Elsevier Science B.V.
In the framework of research on generation-IV reactors, it is very important to have infrastructu... more In the framework of research on generation-IV reactors, it is very important to have infrastructures specifically dedicated to the study of fundamental parameters in dynamics and kinetics of future fast-neutron reactors. Among various options pursued by international groups, Italy focused on lead-cooled reactors, which guarantee minimal neutron slowdown and capture and efficient cooling. In this paper it is described the design of a the low-power prototype generator, LEADS, that could be used within research facilities such as the National Laboratory of Legnaro of the INFN. The LEADS has a high safety standard in order to be used as a training facility, but it has also a good flexibility so as to allow a wide range of measurements and experiments. A high safety standard is achieved by limiting the reactor power to less than few hundred kW and the neutron multiplication factor k eff to less than 0.95 (a limiting value for spent fuel pool), by using a pure-uranium fuel (no plutonium) and by using solid lead as a diffuser. The proposed core is therefore intrinsically subcritical and has to be driven by an external neutron source generated by a proton beam impinging in a target. Preliminary simulations, performed with the MCNPX code indicated, for a 0.75 mA continuous proton beam current at 70 MeV proton energy, a reactor power of about 190 kW when using a beryllium converter. The enriched-uranium fuel elements are immersed in a solid-lead matrix and contained within a steel vessel. The system is cooled by helium gas, which is transparent to neutrons and does not undergo activation. The gas is pumped by a compressor through specific holes at the entrance of the active volume with a temperature which varies according to the operating conditions and a pressure of about 1.1 MPa. The hot gas coming out of the vessel is cooled by an external helium-water heat exchanger. The beryllium converter is cooled by its dedicated helium gas cooling system. After shutdown, the decay is completely dissipated by conduction through the lead reflector and steel vessel, and then evacuated by irradiation from the vessel surface to the external ambient air.
In this paper we simulated the behavior of a simple ADS model, based on MOX fuel embedded in soli... more In this paper we simulated the behavior of a simple ADS model, based on MOX fuel embedded in solid lead, in terms of multiplication coefficient k ef f , thermal power and absolute neutron spectra. In the first part of the paper, we report on the results obtained when modifying the reflector surrounding the fission core, by replacing pure lead with a layered graphite/lead structure. We found that, by appropriately choosing position and thickness of the graphite and lead layers, it is possible to obtain a "hybrid" system where the neutron spectrum in the core still exhibits a fast character, while the spectrum in the graphite layer is considerably softer, becoming thermal in the most peripheral positions. In order to obtain such a modulation of the neutron spectra from the center of the system to the periphery, a careful choice of the materials has to be made in order to avoid large variations of the local power at the core boundary. However, the smoothness of the power distribution is obtained at the expense of lower values of k ef f and the total power of the system. In the second part of the paper, we explored the option of adopting light water as coolant, instead of the helium gas assumed in the initial design. We found that this produces an increase in k ef f and thermal power, without significantly perturbing the fast character of the system and without introducing spatial power excursions in any place within the core. The characteristics obtained may allow to design a system where fast, mixed and thermal spectra can be used to expand the use of the ADS as an irradiation facility.
Within European Partitioning & Transmutation research programs, infrastructures specifically dedi... more Within European Partitioning & Transmutation research programs, infrastructures specifically dedicated to the study of fundamental reactor physics and engineering parameters of future fast-neutron-based reactors are very important, being some of these features not available in present zero-power prototypes. This presentation will
The differential cross section, dσ/dt, for ρ 0 meson photoproduction on the proton above the reso... more The differential cross section, dσ/dt, for ρ 0 meson photoproduction on the proton above the resonance region was measured up to a momentum transfer -t = 5 GeV 2 using the CLAS detector at the Thomas Jefferson National Accelerator ...
The spin structure functions $g_1$ for the proton and the deuteron have been measured over a wide... more The spin structure functions $g_1$ for the proton and the deuteron have been measured over a wide kinematic range in $x$ and \Q2 using 1.6 and 5.7 GeV longitudinally polarized electrons incident upon polarized NH$_3$ and ND$_3$ targets at Jefferson Lab. Scattered ...
Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual ... more Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q 2 ...
Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual ... more Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q 2 ...
The results of an experiment on inclusive electron scattering from an oxygen jet target, performe... more The results of an experiment on inclusive electron scattering from an oxygen jet target, performed in a wide range of energy and momentum transfer covering both quasi-elastic and �(1232) resonance regions, are reported. In the former region the theoretical predictions, obtained including effects of nucleon-nucleon correlations in both initial and final states, give a good description of the experimental data.
In this paper the current status of the study of the dynamical behaviour of the proposed ADS is p... more In this paper the current status of the study of the dynamical behaviour of the proposed ADS is presented; it is a complex multi-physics problem which, in the present case of a very low k eff system, is conveniently analyzed because the characteristic time scales of the problem are well separated. To be more specific, time scales of the neutronic (prompt) response of the system are so short to be negligible when studying thermal, mechanical and hydraulic aspects.
The neutron multiplication factor k-eff is a key quantity to characterize subcritical neutron mul... more The neutron multiplication factor k-eff is a key quantity to characterize subcritical neutron multiplying devices and for understanting their physical behaviour, being related to the fundamental eigenvalue of Boltzmann transport equation. Both the maximum available power-and all quantities related to it, like, e.g. the effectiveness in burning nuclear wastes-as well as reactor kinetics and dynamics depend on k-eff. Nevertheless , k-eff is not directly measurable and its determination results from the solution of an inverse problem: minimizing model dependence of the solution for k-eff then becomes a critical issue, relevant both for practical and theoretical reasons.
In this work we report initial studies on a low power Accelerator-Driven System as a possible exp... more In this work we report initial studies on a low power Accelerator-Driven System as a possible experimental facility for the measurement of relevant integral nuclear quantities. In particular, we performed Monte Carlo simulations of minor actinides and fission products irradiation and estimated the fission rate within fission chambers in the reactor core and the reflector, in order to evaluate the transmutation rates and the measurement sensitivity. We also performed a photo-peak analysis of available experimental data from a research reactor, in order to estimate the expected sensitivity of this analysis method on the irradiation of samples in the ADS considered.
We present new S beam asymmetry data for h meson photoproduction on the proton, using a novel tag... more We present new S beam asymmetry data for h meson photoproduction on the proton, using a novel tagged, laser backscattered, linearly polarized photon beam up to 1.1 GeV. The data show large, positive asymmetries, at all incident photon energies. In addition to the S 11 ͑1535͒ and D 13 ͑1520͒ resonances necessary to reproduce the cross sections, P 13 ͑1720͒ and D 15 ͑1675͒ "four stars" resonances contribute to the S observable, but cannot reproduce the strong forward asymmetries measured at energies higher than 900 MeV. [S0031-9007(98)06957-9] PACS numbers: 13.60. Le, 13.88. + e, 14.40.Aq The underlying substructure of the nucleon gives rise to a rich spectrum of excited states, many of which have been associated with the baryon resonances seen in pN scattering [1] and p photoproduction. These baryon resonances and their associated gNN ء electromagnetic couplings form bench marks for models of hadron structure. Quark models have been quite successful in accounting for the masses of most observed resonances, although in some cases the electromagnetic couplings have presented more of a challenge [2].
The GRAAL facility produces a highly polarized gamma-ray beam by Compton scattering of laser phot... more The GRAAL facility produces a highly polarized gamma-ray beam by Compton scattering of laser photons on the electrons of the European Synchrotron Radiation Facility (ESRF) at Grenoble. Preliminary results have been obtained with the LAGRANGE detector showing its excellent performances. 0375-9474/97/$17.00 1997 -Elsevier Science B.V.
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Papers by Marco Ripani