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| 2. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Determination of the fuel heat transfer dynamics via CFD for the purpose of noise analysis
- 2006
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Ingår i: Proc. 5th Int. Topl. Mtg. Nuclear Plant Instrumentation, Controls, and Human Machine Interface Technology (NPIC&HMIT 2006), Albuquerque, New Mexico, USA, November 12-16, 2006, American Nuclear Society. - 0894480510
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Konferensbidrag (refereegranskat)abstract
- In this paper, a 3-dimensional CFD model of a PWR fuel pin surrounded by its cooling water was developed using the Fluent code. The full heterogeneity of the system was accounted for both radially and axially, and the temperature-dependence of the thermal properties of the different constituents was explicitly taken into account. The turbulent character of the flow was modeled via a k-e model. Thereafter, sinusoidal fluctuations of the power density around its mean value were induced for oscillation frequencies ranging from 0.01 Hz to 10 Hz. The transfer function between the fluctuations of the volume-averaged fuel temperature and the fluctuations of the volume-averaged power density, and the transfer function between the fluctuations of the volume-averaged moderator temperature and the fluctuations of the volume-averaged fuel temperature were then numerically determined. While the former can be approximated by a first-order system, the estimation of the analytical expression of the latter is rather complicated, due to the spatial dependence of the temperature and velocity fields in the coolant. This paper nevertheless gives numerical estimates of these transfer functions that can be used in any axially-homogenized lumped thermal-hydraulic model.
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| 4. |
- Mattsson, Håkan, 1969, et al.
(författare)
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Collimation and background in the pulsed neutron activation method for determination of water flow in pipes
- 2007
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Ingår i: International Journal of Nuclear Energy Science and Technology. - 1741-637X .- 1741-6361. ; 3:1, s. 12-
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Tidskriftsartikel (refereegranskat)abstract
- In a Pulsed Neutron Activation (PNA) flowmeter, the water in a pipe is bombarded with neutron pulses, which introduce activity into the pipe. The activity is mixed with the flow, and gamma radiation emitted from the activity is measured with a detector downstream. The average velocity of the water is then calculated using the time-resolved detector signal. In this paper, the effect of collimation of the neutron radiation has been investigated. Such a collimation would increase the accuracy of the measurement, but the use of a collimator requires the distance between the pipe and the neutron source to be increased, with a corresponding loss in count rate. The results show that this loss makes neutron collimators in PNA of little use. In addition, a method to identify and subtract the background originating from stationary sources in a PNA measurement was developed.
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| 7. |
- Mattsson, Håkan, 1969
(författare)
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Pulsed Neutron Activation for Determination of Water Flow in Pipes
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a Pulsed Neutron Activation (PNA) flowmeter neutron induced activity is used to measure water flow in pipes. The water in the pipe is bombarded with neutron pulses which introduce activity into the pipe. The activity is then transported and mixed with the flow. Gamma radiation emitted from the activity is measured with a detector downstream from the activations point. The average velocity of the water is calculated using the time-resolved detector signal. The ultimate purpose is to develop a portable and non-intrusive flowmeter that can be used as a calibration tool.The objectives of this work were to investigate some parameters that affect the accuracy of the measurement. Both experimental and numerical investigations have been performed.Developments were made in the transport and mixing of the activity. A Computational Fluid Dynamics (CFD) code was used for the first time in a model of the PNA flowmeter. With the CFD code it was examined how the activity distribution changes with time and its average velocity at different times after the neutron pulse was also calculated. The results showed that there is a substantial discrepancy between the average velocity of the water and the average velocity of the activity. One factor that influences this discrepancy is how the activity is distributed in the pipe directly after the neutron pulse. It is desirable that the initial activity distribution is homogeneous and in this work it was investigated if the homogeneity could be improved. A neutron collimator and an increased distance between the neutron source and the pipe wall were shown to improve the activity distribution in the pipe.Background radiation is a problem in many nuclear applications and the PNA flowmeter is no exception. The background in a PNA measurement changes both the shape and position of the peak and if not treated correctly it will decrease the accuracy of the flowmeter. A method for identifying the origin of the background as well as a method for subtracting it was developed in this work.
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| 9. |
- Mattsson, Håkan, 1969, et al.
(författare)
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Simulation of pulsed neutron activation for determination of water flow in pipes
- 2002
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Ingår i: Kerntechnik. - : Walter de Gruyter GmbH. - 0932-3902 .- 2195-8580. ; 67:2-3, s. 78-84
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the asymmetric distribution of activated water in PNA (pulsed neutron activation) measurements has been investigated experimentally by depositing a small amount of colour, simulating the activated water, in a transparent Plexiglas pipe. Based on the colour experiments, a semi-empirical model has been developed that describes the distribution of the activated water at different distances from the activation point. The model shows that the combination of inhomogeneous activation and a radial velocity profile makes the mean velocity of the activity lower than the mean velocity of the water. It can also be seen that the velocity of the activity increases as the distance from the activation point increases. The model has been compared with experimental values from PNA measurements and the measured mean velocity shows a similar dependence on the distance from the activation point.
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