Shadi Ghrayeb - Academia.edu (original) (raw)

Papers by Shadi Ghrayeb

PhDT, Jul 2, 2013

The principal physical phenomenon underlying the computation of neutron spectra is the nuclear re... more The principal physical phenomenon underlying the computation of neutron spectra is the nuclear reaction in which neutrons lose or gain energy, i.e., the neutron scattering process. As long as neutrons only lose energy they are "slowing down". The loss of energy by the neutrons is the dominant energy exchange mechanism for very fast (and hence very energetic) neutrons. In the past this fact led to the use of approximations in which the gain of energy by the neutron in collisions with the fuel lattice atoms or other materials, such as surrounding moderator, was assumed negligible in the energy range above thermal. This assumption was demonstrated to be inaccurate and unacceptable when scattering resonances are present at intermediate energies (the lower energy domain within the slowing down range). The purpose of this thesis is to contribute a method that allows the relaxation of the incorrect assumption. Namely, a method is developed that accounts for up-scattering by heavy nuclides in the resonance energy range. A multigroup formulation for the exact neutron elastic scattering kernel, taking into account up-scattering events, has been developed and verified. The formulation has been applied to elastic scattering cross section data of heavy nuclides for a very fine energy group structure and then supplied to a deterministic lattice physics code demonstrating its effects. Such resonance treatment provides a more accurate representation of the interaction between neutrons and nuclei and results in more realistic and higher fidelity neutron fluxes that reflect the effect of the temperature of the lattice. The correct accounting for the lattice effects influences the estimated values for the probability of neutron absorption and scattering, which in turn determine the core reactivity and consequent burnup characteristics. The slowing down process is important in thermal reactors because it results in the neutrons entering the thermal energy range in which the majority of fission events occur. Correctly modeling the slowing down and hence slowing down source into the thermal energy range and consequently allowing the correct modeling of iii Chapter 6 Conclusion 6.

In this project a comprehensive study was performed with a state-of-the-art multiphysics code sys... more In this project a comprehensive study was performed with a state-of-the-art multiphysics code system to examine the technical issues of a thorium-based matrix with fast reactors. The utilization of thorium-based fuels has been less developed than other fuels. The characteristics of thorium-based fuels in terms of their potential role in assisting the reduction of current plutonium stockpiles and proliferation resistance aspects are promising. The next generation nuclear reactor systems should reduce the inventory of longlived radioactive species, the radio-toxicity of discharged fuel elements, and the overall heat load on the final disposal systems, thus making nuclear power more sustainable. To achieve this goal, advanced technologies in recycling fuel and converting long-lived actinides into energy must be further investigated. There has been a renewed interest in sodium cooled fast reactors and thorium based fuels. Since advanced fast reactors are very effective at transmutation, their use will help to reduce such inventory by burning transuranics from Light Water Reactor (LWR) spent fuel. Improving the utilization of fertile material in fast reactors is vital. In order to ensure the projected expansion of nuclear power in conjunction with a reduced risk of nuclear weapons proliferation, new conventional sources of fuel will have to be made available. Thorium-based fuel is an attractive option due to the fact that fewer transuranics (TRU) are produced compared to uranium-based fuels. Fast spectrum reactors with plutonium-thorium or TRU-thorium fuel suggest that thorium-based iv fuels can efficiently reduce the plutonium stockpile while maintaining acceptable safety and control characteristics of the reactor system. A thorium-based fuel matrix allows effective burning of plutonium and minor actinides (Am, Cm, Np) since no plutonium and minor actinides (MA) are generated from the thorium.

Procedia - Social and Behavioral Sciences, 2010

When a vehicle equipped with tire is manoeuvred on the ground, the tires are submitted to a numbe... more When a vehicle equipped with tire is manoeuvred on the ground, the tires are submitted to a number of forces-longitudinal force when driving or braking torque is applied to the wheel and/or lateral force when the wheel is steered to turn at a corner. Pacejka model describes these forces that represent the reaction of the road onto the tire. This nonlinear model depends on correlated parameters such as the friction coefficient, the vertical load, the cornering stiffness,. .. which have to be identified from some measurements. The sensitivity of Pacejka model to these correlated parameters are studied using an approach based on polynomial chaos. It consists in decorrelating the parameters using the Nataf transformation and then, in expanding the model output onto polynomial chaos. The sensitivity indices are then obtained straightforwardly from the algebraic expression of the coefficients of the polynomial expansion.

In this project a comprehensive study was performed with a state-of-the-art multiphysics code sys... more In this project a comprehensive study was performed with a state-of-the-art multiphysics code system to examine the technical issues of a thorium-based matrix with fast reactors. The utilization of thorium-based fuels has been less developed than other fuels. The characteristics of thorium-based fuels in terms of their potential role in assisting the reduction of current plutonium stockpiles and proliferation resistance aspects are promising. The next generation nuclear reactor systems should reduce the inventory of longlived radioactive species, the radio-toxicity of discharged fuel elements, and the overall heat load on the final disposal systems, thus making nuclear power more sustainable. To achieve this goal, advanced technologies in recycling fuel and converting long-lived actinides into energy must be further investigated. There has been a renewed interest in sodium cooled fast reactors and thorium based fuels. Since advanced fast reactors are very effective at transmutation, their use will help to reduce such inventory by burning transuranics from Light Water Reactor (LWR) spent fuel. Improving the utilization of fertile material in fast reactors is vital. In order to ensure the projected expansion of nuclear power in conjunction with a reduced risk of nuclear weapons proliferation, new conventional sources of fuel will have to be made available. Thorium-based fuel is an attractive option due to the fact that fewer transuranics (TRU) are produced compared to uranium-based fuels. Fast spectrum reactors with plutonium-thorium or TRU-thorium fuel suggest that thorium-based iv fuels can efficiently reduce the plutonium stockpile while maintaining acceptable safety and control characteristics of the reactor system. A thorium-based fuel matrix allows effective burning of plutonium and minor actinides (Am, Cm, Np) since no plutonium and minor actinides (MA) are generated from the thorium.

Transactions of the American Nuclear Society, 2008

To study the improvement of fuel burnup for fast reactors, thorium based fuels are investigated. ... more To study the improvement of fuel burnup for fast reactors, thorium based fuels are investigated. In order to ensure the projected expansion of nuclear power is achieved in conjunction with reduced risk of nuclear weapons proliferation, new conventional sources of fuel will have to be made available. Thorium fuel cycles have many incentives such as the reduction of plutonium generation and consumption of LWR actinides, the provision of high performance burnup, and the conservation of 235 U resources. This work examined the burnup reactivity loss and depletion analysis of thorium versus uranium based metal fuels. When compared the thorium based metallic fuel outperformed uranium based fuel with respect to higher actinide burnup and higher depletion rate of plutonium isotopes.

Transactions of the American Nuclear Society, 2010

Models of varying complexity are developed to approximate or mimic systems and processes in diffe... more Models of varying complexity are developed to approximate or mimic systems and processes in different aspects of the real world (e.g. physical, environmental, social, or economic). Applying models in such domains inevitably involves uncertainty in both the model representation and in the input data. Uncertainty and sensitivity analysis techniques can be applied to study uncertainty in model predictions arising from imprecisely-known processes and input data. Sensitivity analysis involves determining the contribution of individual inputs to the uncertainty in model predictions. Global sensitivity analysis deals with uncertainty sources spanning over finite or infinite ranges of uncertainties and with the simultaneous variation of such sources. This in turn enables the identification of high-order interactions among inputs in determining the uncertainty in the output of interest. This paper applies global sensitivity analysis to the modeling of nuclear reactor applications using the Monte Carlo method. In particular, the tests of Exercise 1 (I-1), “Cell Physics”, of the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modeling (UAM) for Design, Operation and Safety Analysis of LWRs (OECD LWR UAM Benchmark), are analyzed.

The principal physical phenomenon underlying the computation of neutron spectra is the nuclear re... more The principal physical phenomenon underlying the computation of neutron spectra is the nuclear reaction in which neutrons lose or gain energy, i.e., the neutron scattering process. As long as neutrons only lose energy they are “slowing down”. The loss of energy by the neutrons is the dominant energy exchange mechanism for very fast (and hence very energetic) neutrons. In the past this fact led to the use of approximations in which the gain of energy by the neutron in collisions with the fuel lattice atoms or other materials, such as surrounding moderator, was assumed negligible in the energy range above thermal. This assumption was demonstrated to be inaccurate and unacceptable when scattering resonances are present at intermediate energies (the lower energy domain within the slowing down range). The purpose of this thesis is to contribute a method that allows the relaxation of the incorrect assumption. Namely, a method is developed that accounts for up-scattering by heavy nuclides ...

Nuclear Science and Engineering, 2014

Annals of Nuclear Energy, 2014

A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorp... more A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorporates the neutron up-scattering effects stemming from lattice atoms thermal motion and it accounts for them within the resulting effective nuclear cross-section data. The effects pertain essentially to resonant scattering off of heavy nuclei. The formulation, implemented into a standalone code, produces effective nuclear scattering data that are then supplied directly into the DRAGON lattice physics code where the effects on Doppler reactivity and neutron flux are demonstrated. The correct accounting for the crystal lattice effects influences the estimated values for the probability of neutron absorption and scattering, which in turn affect the estimation of core reactivity and burnup characteristics. The results show an increase in values of Doppler temperature feedback coefficients up to À10% for UOX and MOX LWR fuels compared to the corresponding values derived using the traditional asymptotic elastic scattering kernel. This paper also summarizes research performed to date on this topic.

Transactions of the American Nuclear Society, 2010

Nuclear Science and Engineering, 2014

Biotechnology Progress, 2008

Global sensitivity analysis (GSA) can be used to quantify the importance of model parameters and ... more Global sensitivity analysis (GSA) can be used to quantify the importance of model parameters and their interactions with respect to model output. In this study, the Sobol′ method for GSA is applied to a dynamic model of monoclonal antibody-producing mammalian cell cultures in order to identify the parameters that need to be accurately determined experimentally. Our results show that most parameters have low sensitivity indices and exhibit strong interactions with one another. These parameters can be set at their nominal values and unnecessary experimentation can therefore be avoided. In contrast, certain parameters are identified as sensitive, necessitating their estimation given sufficiently rich experimental data. Moreover, parameter sensitivity varies during culture time in a biologically meaningful manner. In conclusion, GSA can serve as an excellent precursor to optimal experiment design.

Annals of Nuclear Energy, 2011

An exact scattering kernel formulation for anisotropic scattering up to angular order 10 has been... more An exact scattering kernel formulation for anisotropic scattering up to angular order 10 has been developed and implemented into a deterministic code. The effects of accounting for lattice dynamics on the modeling of neutron scattering in 235U, 238U, 238Pu, and other nuclides have been demonstrated. The new formulation essentially reproduces other investigators previous results for isotropic scattering and quantifies the

Annals of Nuclear Energy, 2014

A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorp... more A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorporates the neutron up-scattering effects stemming from lattice atoms thermal motion and it accounts for them within the resulting effective nuclear cross-section data. The effects pertain essentially to resonant scattering off of heavy nuclei. The formulation, implemented into a standalone code, produces effective nuclear scattering data that are then supplied directly into the DRAGON lattice physics code where the effects on Doppler reactivity and neutron flux are demonstrated. The correct accounting for the crystal lattice effects influences the estimated values for the probability of neutron absorption and scattering, which in turn affect the estimation of core reactivity and burnup characteristics. The results show an increase in values of Doppler temperature feedback coefficients up to À10% for UOX and MOX LWR fuels compared to the corresponding values derived using the traditional asymptotic elastic scattering kernel. This paper also summarizes research performed to date on this topic.

PhDT, Jul 2, 2013

The principal physical phenomenon underlying the computation of neutron spectra is the nuclear re... more The principal physical phenomenon underlying the computation of neutron spectra is the nuclear reaction in which neutrons lose or gain energy, i.e., the neutron scattering process. As long as neutrons only lose energy they are "slowing down". The loss of energy by the neutrons is the dominant energy exchange mechanism for very fast (and hence very energetic) neutrons. In the past this fact led to the use of approximations in which the gain of energy by the neutron in collisions with the fuel lattice atoms or other materials, such as surrounding moderator, was assumed negligible in the energy range above thermal. This assumption was demonstrated to be inaccurate and unacceptable when scattering resonances are present at intermediate energies (the lower energy domain within the slowing down range). The purpose of this thesis is to contribute a method that allows the relaxation of the incorrect assumption. Namely, a method is developed that accounts for up-scattering by heavy nuclides in the resonance energy range. A multigroup formulation for the exact neutron elastic scattering kernel, taking into account up-scattering events, has been developed and verified. The formulation has been applied to elastic scattering cross section data of heavy nuclides for a very fine energy group structure and then supplied to a deterministic lattice physics code demonstrating its effects. Such resonance treatment provides a more accurate representation of the interaction between neutrons and nuclei and results in more realistic and higher fidelity neutron fluxes that reflect the effect of the temperature of the lattice. The correct accounting for the lattice effects influences the estimated values for the probability of neutron absorption and scattering, which in turn determine the core reactivity and consequent burnup characteristics. The slowing down process is important in thermal reactors because it results in the neutrons entering the thermal energy range in which the majority of fission events occur. Correctly modeling the slowing down and hence slowing down source into the thermal energy range and consequently allowing the correct modeling of iii Chapter 6 Conclusion 6.

In this project a comprehensive study was performed with a state-of-the-art multiphysics code sys... more In this project a comprehensive study was performed with a state-of-the-art multiphysics code system to examine the technical issues of a thorium-based matrix with fast reactors. The utilization of thorium-based fuels has been less developed than other fuels. The characteristics of thorium-based fuels in terms of their potential role in assisting the reduction of current plutonium stockpiles and proliferation resistance aspects are promising. The next generation nuclear reactor systems should reduce the inventory of longlived radioactive species, the radio-toxicity of discharged fuel elements, and the overall heat load on the final disposal systems, thus making nuclear power more sustainable. To achieve this goal, advanced technologies in recycling fuel and converting long-lived actinides into energy must be further investigated. There has been a renewed interest in sodium cooled fast reactors and thorium based fuels. Since advanced fast reactors are very effective at transmutation, their use will help to reduce such inventory by burning transuranics from Light Water Reactor (LWR) spent fuel. Improving the utilization of fertile material in fast reactors is vital. In order to ensure the projected expansion of nuclear power in conjunction with a reduced risk of nuclear weapons proliferation, new conventional sources of fuel will have to be made available. Thorium-based fuel is an attractive option due to the fact that fewer transuranics (TRU) are produced compared to uranium-based fuels. Fast spectrum reactors with plutonium-thorium or TRU-thorium fuel suggest that thorium-based iv fuels can efficiently reduce the plutonium stockpile while maintaining acceptable safety and control characteristics of the reactor system. A thorium-based fuel matrix allows effective burning of plutonium and minor actinides (Am, Cm, Np) since no plutonium and minor actinides (MA) are generated from the thorium.

Procedia - Social and Behavioral Sciences, 2010

When a vehicle equipped with tire is manoeuvred on the ground, the tires are submitted to a numbe... more When a vehicle equipped with tire is manoeuvred on the ground, the tires are submitted to a number of forces-longitudinal force when driving or braking torque is applied to the wheel and/or lateral force when the wheel is steered to turn at a corner. Pacejka model describes these forces that represent the reaction of the road onto the tire. This nonlinear model depends on correlated parameters such as the friction coefficient, the vertical load, the cornering stiffness,. .. which have to be identified from some measurements. The sensitivity of Pacejka model to these correlated parameters are studied using an approach based on polynomial chaos. It consists in decorrelating the parameters using the Nataf transformation and then, in expanding the model output onto polynomial chaos. The sensitivity indices are then obtained straightforwardly from the algebraic expression of the coefficients of the polynomial expansion.

In this project a comprehensive study was performed with a state-of-the-art multiphysics code sys... more In this project a comprehensive study was performed with a state-of-the-art multiphysics code system to examine the technical issues of a thorium-based matrix with fast reactors. The utilization of thorium-based fuels has been less developed than other fuels. The characteristics of thorium-based fuels in terms of their potential role in assisting the reduction of current plutonium stockpiles and proliferation resistance aspects are promising. The next generation nuclear reactor systems should reduce the inventory of longlived radioactive species, the radio-toxicity of discharged fuel elements, and the overall heat load on the final disposal systems, thus making nuclear power more sustainable. To achieve this goal, advanced technologies in recycling fuel and converting long-lived actinides into energy must be further investigated. There has been a renewed interest in sodium cooled fast reactors and thorium based fuels. Since advanced fast reactors are very effective at transmutation, their use will help to reduce such inventory by burning transuranics from Light Water Reactor (LWR) spent fuel. Improving the utilization of fertile material in fast reactors is vital. In order to ensure the projected expansion of nuclear power in conjunction with a reduced risk of nuclear weapons proliferation, new conventional sources of fuel will have to be made available. Thorium-based fuel is an attractive option due to the fact that fewer transuranics (TRU) are produced compared to uranium-based fuels. Fast spectrum reactors with plutonium-thorium or TRU-thorium fuel suggest that thorium-based iv fuels can efficiently reduce the plutonium stockpile while maintaining acceptable safety and control characteristics of the reactor system. A thorium-based fuel matrix allows effective burning of plutonium and minor actinides (Am, Cm, Np) since no plutonium and minor actinides (MA) are generated from the thorium.

Transactions of the American Nuclear Society, 2008

To study the improvement of fuel burnup for fast reactors, thorium based fuels are investigated. ... more To study the improvement of fuel burnup for fast reactors, thorium based fuels are investigated. In order to ensure the projected expansion of nuclear power is achieved in conjunction with reduced risk of nuclear weapons proliferation, new conventional sources of fuel will have to be made available. Thorium fuel cycles have many incentives such as the reduction of plutonium generation and consumption of LWR actinides, the provision of high performance burnup, and the conservation of 235 U resources. This work examined the burnup reactivity loss and depletion analysis of thorium versus uranium based metal fuels. When compared the thorium based metallic fuel outperformed uranium based fuel with respect to higher actinide burnup and higher depletion rate of plutonium isotopes.

Transactions of the American Nuclear Society, 2010

Models of varying complexity are developed to approximate or mimic systems and processes in diffe... more Models of varying complexity are developed to approximate or mimic systems and processes in different aspects of the real world (e.g. physical, environmental, social, or economic). Applying models in such domains inevitably involves uncertainty in both the model representation and in the input data. Uncertainty and sensitivity analysis techniques can be applied to study uncertainty in model predictions arising from imprecisely-known processes and input data. Sensitivity analysis involves determining the contribution of individual inputs to the uncertainty in model predictions. Global sensitivity analysis deals with uncertainty sources spanning over finite or infinite ranges of uncertainties and with the simultaneous variation of such sources. This in turn enables the identification of high-order interactions among inputs in determining the uncertainty in the output of interest. This paper applies global sensitivity analysis to the modeling of nuclear reactor applications using the Monte Carlo method. In particular, the tests of Exercise 1 (I-1), “Cell Physics”, of the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modeling (UAM) for Design, Operation and Safety Analysis of LWRs (OECD LWR UAM Benchmark), are analyzed.

The principal physical phenomenon underlying the computation of neutron spectra is the nuclear re... more The principal physical phenomenon underlying the computation of neutron spectra is the nuclear reaction in which neutrons lose or gain energy, i.e., the neutron scattering process. As long as neutrons only lose energy they are “slowing down”. The loss of energy by the neutrons is the dominant energy exchange mechanism for very fast (and hence very energetic) neutrons. In the past this fact led to the use of approximations in which the gain of energy by the neutron in collisions with the fuel lattice atoms or other materials, such as surrounding moderator, was assumed negligible in the energy range above thermal. This assumption was demonstrated to be inaccurate and unacceptable when scattering resonances are present at intermediate energies (the lower energy domain within the slowing down range). The purpose of this thesis is to contribute a method that allows the relaxation of the incorrect assumption. Namely, a method is developed that accounts for up-scattering by heavy nuclides ...

Nuclear Science and Engineering, 2014

Annals of Nuclear Energy, 2014

A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorp... more A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorporates the neutron up-scattering effects stemming from lattice atoms thermal motion and it accounts for them within the resulting effective nuclear cross-section data. The effects pertain essentially to resonant scattering off of heavy nuclei. The formulation, implemented into a standalone code, produces effective nuclear scattering data that are then supplied directly into the DRAGON lattice physics code where the effects on Doppler reactivity and neutron flux are demonstrated. The correct accounting for the crystal lattice effects influences the estimated values for the probability of neutron absorption and scattering, which in turn affect the estimation of core reactivity and burnup characteristics. The results show an increase in values of Doppler temperature feedback coefficients up to À10% for UOX and MOX LWR fuels compared to the corresponding values derived using the traditional asymptotic elastic scattering kernel. This paper also summarizes research performed to date on this topic.

Transactions of the American Nuclear Society, 2010

Nuclear Science and Engineering, 2014

Biotechnology Progress, 2008

Global sensitivity analysis (GSA) can be used to quantify the importance of model parameters and ... more Global sensitivity analysis (GSA) can be used to quantify the importance of model parameters and their interactions with respect to model output. In this study, the Sobol′ method for GSA is applied to a dynamic model of monoclonal antibody-producing mammalian cell cultures in order to identify the parameters that need to be accurately determined experimentally. Our results show that most parameters have low sensitivity indices and exhibit strong interactions with one another. These parameters can be set at their nominal values and unnecessary experimentation can therefore be avoided. In contrast, certain parameters are identified as sensitive, necessitating their estimation given sufficiently rich experimental data. Moreover, parameter sensitivity varies during culture time in a biologically meaningful manner. In conclusion, GSA can serve as an excellent precursor to optimal experiment design.

Annals of Nuclear Energy, 2011

An exact scattering kernel formulation for anisotropic scattering up to angular order 10 has been... more An exact scattering kernel formulation for anisotropic scattering up to angular order 10 has been developed and implemented into a deterministic code. The effects of accounting for lattice dynamics on the modeling of neutron scattering in 235U, 238U, 238Pu, and other nuclides have been demonstrated. The new formulation essentially reproduces other investigators previous results for isotropic scattering and quantifies the

Annals of Nuclear Energy, 2014

A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorp... more A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorporates the neutron up-scattering effects stemming from lattice atoms thermal motion and it accounts for them within the resulting effective nuclear cross-section data. The effects pertain essentially to resonant scattering off of heavy nuclei. The formulation, implemented into a standalone code, produces effective nuclear scattering data that are then supplied directly into the DRAGON lattice physics code where the effects on Doppler reactivity and neutron flux are demonstrated. The correct accounting for the crystal lattice effects influences the estimated values for the probability of neutron absorption and scattering, which in turn affect the estimation of core reactivity and burnup characteristics. The results show an increase in values of Doppler temperature feedback coefficients up to À10% for UOX and MOX LWR fuels compared to the corresponding values derived using the traditional asymptotic elastic scattering kernel. This paper also summarizes research performed to date on this topic.