Hugo Van Dam - Academia.edu (original) (raw)
Papers by Hugo Van Dam
Nuclear Technology, Feb 1, 2009
ABSTRACT This paper describes several modifications to the design of a fluidized bed nuclear reac... more ABSTRACT This paper describes several modifications to the design of a fluidized bed nuclear reactor in order to improve its performance. The goal of these modifications is to achieve a higher power output, requiring an excess reactivity of 4% at maximum expansion of the bed. The modifications are also intended to obtain a larger safety margin when the reactor does not operate; a shutdown margin of 4% is required when the bed is in a packed state. The modifications include installing an embedded side absorber, changing the reactor cross-section area, and modifying the moderator-to-fuel ratio. The new design based on the modifications related to the aforementioned parameters achieves the desired shutdown margin and the excess reactivity. A model describing the coupling of neutronics and thermal/fluid dynamics is developed, and it is used to study the behavior of the reactor at steady conditions. The results show that the reactor can achieve a high output temperature of 1163 K and produce a thermal power of ~120 MW. Further, the results indicate that the power level of the reactor can be controlled easily by adjusting the flow of helium into the core without any further use of control rods or other active control mechanisms.
Nucl Sci Eng, 1992
This paper reports on the sensitivity of a neutron detector to parametric fluctuations in the cor... more This paper reports on the sensitivity of a neutron detector to parametric fluctuations in the core of a reactor which depends on the position and the frequency of the perturbation. The basic neutron diffusion model for the calculation of this so-called field of view (FOV) of the detector is extended with respect to the dimensionality of the problem and the
Numerical simulations have been performed to investigate the possibility of passive decay heat re... more Numerical simulations have been performed to investigate the possibility of passive decay heat removal in a fluidized bed nuclear reactor. The conduction, convection and radiative heat transfer were included and the high Reynolds number k-ε turbulence model was applied for the flow calculations. The P 1 and S N approximation methods for participating media were used for the radiation model. The reactor was modeled as a 2D axisymmetric cylinder. Calculations were performed for an initial operating power of 60 MW. The results show that P 1 method is quite good to be applied in the particle bed but it fails in the freeboard. The high order S N method can be applied extremely good both in the particle bed and the freeboard. The drawback of the S N method is its long computational time. The invalidity of P 1 method leads to a high fuel particle temperature, exceeding its allowable maximum value. Such situation, however, does not occur in the S N method.
Progress in Nuclear Energy, 1988
ABSTRACT
Radiation Protection Dosimetry, 2005
A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a ... more A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a powerful white neutron source, designed for the high-energy resolution time-of-flight measurements. The main aim of this study is to reduce the time spread of neutrons of the given energy without compromising the neutron yield. Both time spread and neutron intensity influence the experimental accuracy of high-resolution neutron cross section measurements, which are particularly important in the resonance region. The quantities of interest have been simulated with coupled electron-photon-neutron steady state and transient MCNP4C3 calculations. Following benchmarking of the code to the properties of the existing target, neutron yield, energy spectra, resolution functions, and neutron and heat spatial distributions have been determined for various alternative geometries and materials. At a fixed accelerator power, actinides deliver the highest neutron yield and a small target provides the best time resolution. The resulting high-power density requires a joint optimisation of the thermal hydraulics and neutronics properties.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
ABSTRACT The Geel electron linear accelerator (GELINA) white neutron source is designed for time-... more ABSTRACT The Geel electron linear accelerator (GELINA) white neutron source is designed for time-of-flight (TOF) measurements with a high neutron energy resolution. A project has been launched in order to improve the accuracy of the high-resolution neutron cross-section measurements. The experimental accuracy is highly dependent on the neutron intensity and the time spread of the neutrons leaving the target. The main project objective is not only to design a new neutron producing target that reduces the time spread of the neutrons of a given energy, but also to maintain or possibly enhance the neutron production. The present GELINA target has been simulated recently with coupled electron–photon–neutron MCNP4C3 calculations and, subsequently, compared with experimental results. Based on the very good benchmarking results, this code is now used to design and optimise the new target and to assess all relevant parameters influencing the neutron flux and resolution functions. In this paper, the reader will find an explanation of the methodology on which the research of a new target is based. We compared the neutron fluxes of the compact geometries of various materials for different angles with the fluxes of the existing target. Further, we also made a comparison of the resolution functions for the present design versus a compact design. Finally, a dedicated figure of merit was used to make a qualitative comparison of various designs. The results presented in this paper reveal that there is a possibility to design a new target with superior characteristics so that all project objectives will be fulfilled.
Nuclear Engineering and Design, 2002
A dynamic model for natural circulation boiling water reactors (BWRs) under low-pressure conditio... more A dynamic model for natural circulation boiling water reactors (BWRs) under low-pressure conditions is developed. The motivation for this theoretical research is the concern about the stability of natural circulation BWRs during the low-pressure reactor start-up phase. There is experimental and theoretical evidence for the occurrence of void flashing in the unheated riser under these conditions. This flashing effect is
Medical Physics, 2007
This paper deals with the application of the adjoint transport theory in order to optimize Monte ... more This paper deals with the application of the adjoint transport theory in order to optimize Monte Carlo based radiotherapy treatment planning. The technique is applied to Boron Neutron Capture Therapy where most often mixed beams of neutrons and gammas are involved. In normal forward Monte Carlo simulations the particles start at a source and lose energy as they travel towards the region of interest, i.e., the designated point of detection. Conversely, with adjoint Monte Carlo simulations, the so-called adjoint particles start at the region of interest and gain energy as they travel towards the source where they are detected. In this respect, the particles travel backwards and the real source and real detector become the adjoint detector and adjoint source, respectively. At the adjoint detector, an adjoint function is obtained with which numerically the same result, e.g., dose or flux in the tumor, can be derived as with forward Monte Carlo. In many cases, the adjoint method is more efficient and by that is much quicker when, for example, the response in the tumor or organ at risk for many locations and orientations of the treatment beam around the patient is required. However, a problem occurs when the treatment beam is mono-directional as the probability of detecting adjoint Monte Carlo particles traversing the beam exit (detector plane in adjoint mode) in the negative direction of the incident beam is zero. This problem is addressed here and solved first with the use of next event estimators and second with the application of a Legendre expansion technique of the angular adjoint function. In the first approach, adjoint particles are tracked deterministically through a tube to a (adjoint) point detector far away from the geometric model. The adjoint particles will traverse the disk shaped entrance of this tube (the beam exit in the actual geometry) perpendicularly. This method is slow whenever many events are involved that are not contributing to the point detector, e.g., neutrons in a scattering medium. In the second approach, adjoint particles that traverse an adjoint shaped detector plane are used to estimate the Legendre coefficients for expansion of the angular adjoint function. This provides an estimate of the adjoint function for the direction normal to the detector plane. In a realistic head model, as described in this paper, which is surrounded by 1020 mono-directional neutron/gamma beams and from which the best ones are to be selected, the example calculates the neutron and gamma fluxes in ten tumors and ten organs at risk. For small diameter beams (5 cm), and with comparable relative errors, forward Monte Carlo is seen to be 1.5 times faster than the adjoint Monte Carlo techniques. For larger diameter neutron beams (10 and 15 cm), the Legendre technique is found to be 6 and 20 times faster, respectively. In the case of gammas alone, for the 10 and 15 cm diam beams, both adjoint Monte Carlo Legendre and point detector techniques are respectively 2 and 3 times faster than forward Monte Carlo.
Measurement, 1995
ABSTRACT A capacitive void fraction sensor for use in a rod-bundle geometry was designed using a ... more ABSTRACT A capacitive void fraction sensor for use in a rod-bundle geometry was designed using a new design criterion. This criterion states that the response of the sensor to small test bubbles of equal size should be independent of their positions. This so-called homogeneous sensor response replaces the principle of a homogeneous electric field which is usually used. It can be shown that the two methods yield different results. Calculations of the effect of test bubbles on the capacitance were done using the boundary element method. These calculations in combination with the measurement of several capacitances in a multi-electrode geometry make it possible to determine the void distribution in addition to the average void fraction. On the basis of the calculations the accuracy of the sensor was estimated to be 2–5% (relative) in most cases. Measurements using perspex models of the resulting designs show good agreement with the calculations and a good homogeneous response. Experiments on two-phase flow show the feasibility of fast measurements (4 ms) with low noise levels.
To investigate the influence of bubble formation on reactivity of the new design, some static cal... more To investigate the influence of bubble formation on reactivity of the new design, some static calculations were performed using KENO-Va code. The reactivity of the inhomogeneous core is compared with that of the corresponding homogeneous core. Further, a theoretical ...
Chemical Engineering Science, 1999
Annals of Nuclear Energy, 1996
Annals of Nuclear Energy, 2005
Annals of Nuclear Energy, 1998
Annals of Nuclear Energy, 2013
Nuclear …, 2006
This paper describes several modifications to the design of a fluidized bed nuclear reactor in or... more This paper describes several modifications to the design of a fluidized bed nuclear reactor in order to improve its performance. The goal of these modifications is to achieve a higher power output, requiring an excess reactivity of 4% at maximum expansion of the bed. The ...
Annals of Nuclear Energy, 1998
Nuclear Technology, Feb 1, 2009
ABSTRACT This paper describes several modifications to the design of a fluidized bed nuclear reac... more ABSTRACT This paper describes several modifications to the design of a fluidized bed nuclear reactor in order to improve its performance. The goal of these modifications is to achieve a higher power output, requiring an excess reactivity of 4% at maximum expansion of the bed. The modifications are also intended to obtain a larger safety margin when the reactor does not operate; a shutdown margin of 4% is required when the bed is in a packed state. The modifications include installing an embedded side absorber, changing the reactor cross-section area, and modifying the moderator-to-fuel ratio. The new design based on the modifications related to the aforementioned parameters achieves the desired shutdown margin and the excess reactivity. A model describing the coupling of neutronics and thermal/fluid dynamics is developed, and it is used to study the behavior of the reactor at steady conditions. The results show that the reactor can achieve a high output temperature of 1163 K and produce a thermal power of ~120 MW. Further, the results indicate that the power level of the reactor can be controlled easily by adjusting the flow of helium into the core without any further use of control rods or other active control mechanisms.
Nucl Sci Eng, 1992
This paper reports on the sensitivity of a neutron detector to parametric fluctuations in the cor... more This paper reports on the sensitivity of a neutron detector to parametric fluctuations in the core of a reactor which depends on the position and the frequency of the perturbation. The basic neutron diffusion model for the calculation of this so-called field of view (FOV) of the detector is extended with respect to the dimensionality of the problem and the
Numerical simulations have been performed to investigate the possibility of passive decay heat re... more Numerical simulations have been performed to investigate the possibility of passive decay heat removal in a fluidized bed nuclear reactor. The conduction, convection and radiative heat transfer were included and the high Reynolds number k-ε turbulence model was applied for the flow calculations. The P 1 and S N approximation methods for participating media were used for the radiation model. The reactor was modeled as a 2D axisymmetric cylinder. Calculations were performed for an initial operating power of 60 MW. The results show that P 1 method is quite good to be applied in the particle bed but it fails in the freeboard. The high order S N method can be applied extremely good both in the particle bed and the freeboard. The drawback of the S N method is its long computational time. The invalidity of P 1 method leads to a high fuel particle temperature, exceeding its allowable maximum value. Such situation, however, does not occur in the S N method.
Progress in Nuclear Energy, 1988
ABSTRACT
Radiation Protection Dosimetry, 2005
A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a ... more A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a powerful white neutron source, designed for the high-energy resolution time-of-flight measurements. The main aim of this study is to reduce the time spread of neutrons of the given energy without compromising the neutron yield. Both time spread and neutron intensity influence the experimental accuracy of high-resolution neutron cross section measurements, which are particularly important in the resonance region. The quantities of interest have been simulated with coupled electron-photon-neutron steady state and transient MCNP4C3 calculations. Following benchmarking of the code to the properties of the existing target, neutron yield, energy spectra, resolution functions, and neutron and heat spatial distributions have been determined for various alternative geometries and materials. At a fixed accelerator power, actinides deliver the highest neutron yield and a small target provides the best time resolution. The resulting high-power density requires a joint optimisation of the thermal hydraulics and neutronics properties.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
ABSTRACT The Geel electron linear accelerator (GELINA) white neutron source is designed for time-... more ABSTRACT The Geel electron linear accelerator (GELINA) white neutron source is designed for time-of-flight (TOF) measurements with a high neutron energy resolution. A project has been launched in order to improve the accuracy of the high-resolution neutron cross-section measurements. The experimental accuracy is highly dependent on the neutron intensity and the time spread of the neutrons leaving the target. The main project objective is not only to design a new neutron producing target that reduces the time spread of the neutrons of a given energy, but also to maintain or possibly enhance the neutron production. The present GELINA target has been simulated recently with coupled electron–photon–neutron MCNP4C3 calculations and, subsequently, compared with experimental results. Based on the very good benchmarking results, this code is now used to design and optimise the new target and to assess all relevant parameters influencing the neutron flux and resolution functions. In this paper, the reader will find an explanation of the methodology on which the research of a new target is based. We compared the neutron fluxes of the compact geometries of various materials for different angles with the fluxes of the existing target. Further, we also made a comparison of the resolution functions for the present design versus a compact design. Finally, a dedicated figure of merit was used to make a qualitative comparison of various designs. The results presented in this paper reveal that there is a possibility to design a new target with superior characteristics so that all project objectives will be fulfilled.
Nuclear Engineering and Design, 2002
A dynamic model for natural circulation boiling water reactors (BWRs) under low-pressure conditio... more A dynamic model for natural circulation boiling water reactors (BWRs) under low-pressure conditions is developed. The motivation for this theoretical research is the concern about the stability of natural circulation BWRs during the low-pressure reactor start-up phase. There is experimental and theoretical evidence for the occurrence of void flashing in the unheated riser under these conditions. This flashing effect is
Medical Physics, 2007
This paper deals with the application of the adjoint transport theory in order to optimize Monte ... more This paper deals with the application of the adjoint transport theory in order to optimize Monte Carlo based radiotherapy treatment planning. The technique is applied to Boron Neutron Capture Therapy where most often mixed beams of neutrons and gammas are involved. In normal forward Monte Carlo simulations the particles start at a source and lose energy as they travel towards the region of interest, i.e., the designated point of detection. Conversely, with adjoint Monte Carlo simulations, the so-called adjoint particles start at the region of interest and gain energy as they travel towards the source where they are detected. In this respect, the particles travel backwards and the real source and real detector become the adjoint detector and adjoint source, respectively. At the adjoint detector, an adjoint function is obtained with which numerically the same result, e.g., dose or flux in the tumor, can be derived as with forward Monte Carlo. In many cases, the adjoint method is more efficient and by that is much quicker when, for example, the response in the tumor or organ at risk for many locations and orientations of the treatment beam around the patient is required. However, a problem occurs when the treatment beam is mono-directional as the probability of detecting adjoint Monte Carlo particles traversing the beam exit (detector plane in adjoint mode) in the negative direction of the incident beam is zero. This problem is addressed here and solved first with the use of next event estimators and second with the application of a Legendre expansion technique of the angular adjoint function. In the first approach, adjoint particles are tracked deterministically through a tube to a (adjoint) point detector far away from the geometric model. The adjoint particles will traverse the disk shaped entrance of this tube (the beam exit in the actual geometry) perpendicularly. This method is slow whenever many events are involved that are not contributing to the point detector, e.g., neutrons in a scattering medium. In the second approach, adjoint particles that traverse an adjoint shaped detector plane are used to estimate the Legendre coefficients for expansion of the angular adjoint function. This provides an estimate of the adjoint function for the direction normal to the detector plane. In a realistic head model, as described in this paper, which is surrounded by 1020 mono-directional neutron/gamma beams and from which the best ones are to be selected, the example calculates the neutron and gamma fluxes in ten tumors and ten organs at risk. For small diameter beams (5 cm), and with comparable relative errors, forward Monte Carlo is seen to be 1.5 times faster than the adjoint Monte Carlo techniques. For larger diameter neutron beams (10 and 15 cm), the Legendre technique is found to be 6 and 20 times faster, respectively. In the case of gammas alone, for the 10 and 15 cm diam beams, both adjoint Monte Carlo Legendre and point detector techniques are respectively 2 and 3 times faster than forward Monte Carlo.
Measurement, 1995
ABSTRACT A capacitive void fraction sensor for use in a rod-bundle geometry was designed using a ... more ABSTRACT A capacitive void fraction sensor for use in a rod-bundle geometry was designed using a new design criterion. This criterion states that the response of the sensor to small test bubbles of equal size should be independent of their positions. This so-called homogeneous sensor response replaces the principle of a homogeneous electric field which is usually used. It can be shown that the two methods yield different results. Calculations of the effect of test bubbles on the capacitance were done using the boundary element method. These calculations in combination with the measurement of several capacitances in a multi-electrode geometry make it possible to determine the void distribution in addition to the average void fraction. On the basis of the calculations the accuracy of the sensor was estimated to be 2–5% (relative) in most cases. Measurements using perspex models of the resulting designs show good agreement with the calculations and a good homogeneous response. Experiments on two-phase flow show the feasibility of fast measurements (4 ms) with low noise levels.
To investigate the influence of bubble formation on reactivity of the new design, some static cal... more To investigate the influence of bubble formation on reactivity of the new design, some static calculations were performed using KENO-Va code. The reactivity of the inhomogeneous core is compared with that of the corresponding homogeneous core. Further, a theoretical ...
Chemical Engineering Science, 1999
Annals of Nuclear Energy, 1996
Annals of Nuclear Energy, 2005
Annals of Nuclear Energy, 1998
Annals of Nuclear Energy, 2013
Nuclear …, 2006
This paper describes several modifications to the design of a fluidized bed nuclear reactor in or... more This paper describes several modifications to the design of a fluidized bed nuclear reactor in order to improve its performance. The goal of these modifications is to achieve a higher power output, requiring an excess reactivity of 4% at maximum expansion of the bed. The ...
Annals of Nuclear Energy, 1998