The use radioactive tracers for flow rate measurement is applied to a great variety of situations, however the

accuracy of the technique is highly dependent of the adequate choice of the experimental measurement conditions.To measure flow rate of fluids in ducts partially filled, is necessary to measure the fluid flow velocity

and the fluid height. The flow velocity can be measured with the cross correlation function and the fluid level,

with a fluid level meter system. One of the error factors when measuring flow rate, is on the correct setting

of the source-detector of the fluid level meter system. The goal of the present work is to establish by mean

of MCNP-X code simulations the experimental parameters to measure the fluid level [3]. The experimental

tests will be realized in a flow rate system of 10 mm of diameter of acrylic tube for water and oil as fluids. The radioactive tracer to be used is the 82Br and for the detection will be employed two 1” NaI(Tl) scintillator

detectors, shielded with collimators of 0.5 cm and 1 cm of circular aperture diameter 

Brandão, Luis Eduardo

Salgado, Cesar Marques

Carpe dIEN

2015 International Nuclear Atlantic Conference - INAC 2015
Sa˜o Paulo, SP, Brazil, October 4-9, 2015
ASSOCIAC¸A˜O BRASILEIRA DE ENERGIA NUCLEAR - ABEN
ISBN: 978-85-99141-06-9
STUDY OF THE SOURCE-DETECTOR SYSTEM GEOMETRY
USING THE MCNP-X CODE IN THE FLOWRATE MEASUREMENT
WITH RADIOACTIVE TRACERS.
Eddie Avila´n P.1,2,3, Delson Braz2, Luis E. Brandao3 and Cesar M. Salgado3
1Universidad Central de Venezuela (UCV)
Facultad de Ingenierı´a, Departamento de Fı´sica Aplicada
Ciudad Universitaria, Los Chaguaramos
1050 Caracas, Venezuela
epuertas@nuclear.ufrj.br
2Programa de Engenharia Nuclear (PEN/COPPE)
Av. Pedro Calmon 550
Cidade Universita´ria, Ilha do Funda˜o 21941-901 Rio de Janeiro, RJ
delson@lin.ufrj.br
3Divisa˜o de Radiofa´rmacos - DIRA
Instituto de Engenharia Nuclear - (IEN/CNEN-RJ)
Rua He´lio de Almeida, 75
21941-906 Rio de Janeiro, RJ
brandao@ien.gov.br; otero@ien.gov.br
ABSTRACT
The use radioactive tracers for flow rate measurement is applied to a great variety of situations, however the
accuracy of the technique is highly dependent of the adequate choice of the experimental measurement con-
ditions. To measure flow rate of fluids in ducts partially filled, is necessary to measure the fluid flow velocity
and the fluid height. The flow velocity can be measured with the cross correlation function and the fluid level,
with a fluid level meter system. One of the error factors when measuring flow rate, is on the correct setting
of the source-detector of the fluid level meter system. The goal of the present work is to establish by mean
of MCNP-X code simulations the experimental parameters to measure the fluid level [3]. The experimental
tests will be realized in a flow rate system of 10 mm of diameter of acrylic tube for water and oil as fluids.
The radioactive tracer to be used is the 82Br and for the detection will be employed two 1” NaI(Tl) scintillator
detectors, shielded with collimators of 0.5 cm and 1 cm of circular aperture diameter .
1. INTRODUCTION
One of the most important measurement in industry is the accurate detection of the flow
rates of liquids, gases, and solids. The accuracy of the measurements is important due to the
economical profits are closely related to the uncertainty of this measurement. There are a
great variety of instruments and techniques designed to measure flow rate and the choice of
one of them is not an easy task because of the several physical and chemical parameter to be
to take into account. Each one has its advantages and disadvantages, and selecting a proper
technique depends on its specific applications.
The nuclear techniques has the advantages that can be applied to a great variety of situations
but in each case the accuracy must be considered in detail. When is measured flow rate in
pipes partially filled is needed to measure the fluid flow velocity and the fluid height.The fluid
flow velocity can be measured using the cross correlation function [5], equation 1, and the
fluid level, which is the measuring of height of the fluid, defining the position of the interface
with a level meter system consisting of an external 137Cs source that is the most commonly
used with a NaI(Tl) scintillator detector. The objective of this work is to establish by mean
of MCNP-X code simulations the experimental parameters to measure the fluid level.
Rxy(τ) = lim
T→∞
1
T
∫ T
0
x(t)y(t+ τ) dt (1)
2. LEVEL MEASUREMENT
Measure level is defined as “the determination of the position of an existing interface between
two media”, where the media are liquid/gas, solid/gas, immiscible liquid/liquid. Level is
simply a measuring of height, defining the position of the interface. The measure is often
converted to a gravimetric or volumetric quantity. Measuring the level is a way to determine
the volume fractions, eg. the gas fraction of the flow components. The void fraction is defined
as the gas volume fraction divided by the total volume of the flow [1].
There are two methods to measure level, Direct method and Indirect Method. In order to
measure a level of a substance, directly or indirectly the interface must be definite. For
instance, the point at which water meets air in an open channel, tank or pipe. If the liquids
that mix do not form clearly defined interfaces, the measure of level is a difficult task.
The direct method is simply, straightforward and economical, and it uses a direct measure-
ment of the distance (usually height) for local indication. Indirect method of level measure-
ment depend on the material having a physical property which can be measured and related
to level.
2.1. Gamma-ray Densitometer
Nuclear radiation devices used to measure level are fundamentally densitometers and their
basic components are: a radiation source and a detector with an associated electronic. When
a parallel beam of monoenergetic photons with intensity I0 strikes a target of a material of
thickness t and the linear attenuation coefficient µ, the number of photons I(t) emerging
without having interacted in the target is given by [4]
I(t) = I0.e
−µt (2)
The intensity of the radiation also decreases with r2 which is the distance between source
an the detector. For level measurements in tanks or pipes, the number of photons detected
depends upon the thickness of material between the source and the detector. To determine the
INAC 2015, Sa˜o Paulo, SP, Brazil.
fraction of volume is necessary to measure the linear attenuation coefficient on the measured
volume over the cross-section of the pipe. The most common measurement configuration for
single-beam gamma densitometer is shown on figure 1.
Figure 1: Cross section view of single-beam gamma densitometer with point source
and detector located diametrically opposite each other
When is used a single-beam densitometer as shown on figure 1, the results will vary with the
flow regime, since the measurement cross-section volume normally is less than that covered
by pipe cross-section [1].
3. FLOW REGIME DEPENDENCE OF THE GAMMA RAY DENSITOMETERS
In this work are examined the fluid level only for stratified flow regime. The measurement
volume depends of the collimation of the gamma ray beam and the area of the detector. The
linear attenuation coefficient is the same over the cross-section. Measuring the attenuation of
the gamma ray beam is possible to obtain the volume fraction of the flow.
When the detector diameter is smaller than the pipe diameter and the pipe wall is thin, and d1
is parallel d then the volume measurement can be defined as a cone in the flow as shown in
Fig. 2.
The volume fraction on the direction of the source-detector axis on the air-water interface is
not symmetrical and will vary for the stratified flow, it means, that the result if the source is
on top and the detector below (top-bottom configuration) will be different that for bottom-
top configuration. In the top-bottom configuration and stratified flow the void fraction in the
measurement volume for narrow beam can be written as [1]:
INAC 2015, Sa˜o Paulo, SP, Brazil.
Figure 2: Cross-sectional and lateral views of stratified flow
αw =
(2R− h)3
8R3
(3)
where h is the water level and R is the radius pipe.
The fraction volume for the bottom-top configuration is different to that top-bottom configu-
ration and the fraction of the measurement volume is calculated for the expression:
αw =
(2R− h)3
8R3
.(h2 + 2R.h+ 4R2) (4)
In the case of stratified flow and a parallel beam the fraction is:
αw = 1− h
2R
(5)
The single beam gamma-ray densitometer is based in the principle of express the volume
fraction in terms of transmitted intensity which is the number of photons detected in the full
energy peak in the measurement period time. The volume fraction can be calculated as [1]:
α =
ln( Imix
Iwater
)
ln( Iair
Iwater
)
(6)
where Iair and Iwater, correspond to 100% air and 100% water respectively. The results based
on the equation 6 assumes that the contribution of the scattered photons detected is negligible.
INAC 2015, Sa˜o Paulo, SP, Brazil.
4. MCNP-X CODE
The MCNP-X code is a general purpose Monte Carlo radiation transport code developed at
Los Alamos National Laboratory and designed to track different types of particles (neutrons,
electrons, gamma rays, etc). The code obtains the solutions of a problem simulating individ-
ual particles trajectories and recording some aspects of their average behaviour.
The probability distributions governing these events are statistically sampled to describe the
total phenomenon and the sample process is based on the selection of pseudo-random num-
bers. The process consists of following each of many particles since emission from source
until each reaches an energy threshold; the particle energy is transferred to the medium by
absorption, escape, etc.
The MCNP-X code can be used as in this work to simulate the interactions of the gamma-rays
with the different materials of the geometry that is been studied.
5. SIMULATIONS
This work is based on Monte Carlo simulations of a system source-detector to measure the
water level in an acrylic pipe with radius of 9.5 cm.
Three cases are simulated, two for a point source, a pencil beam in which the gamma-ray
beam of the source is very narrow and a second one where the gamma-ray beam is with an
angle of 10 rad in relation to the vertical incident axis (cone beam). Another one case for the
disc source in which the gamma-ray beam is parallel to vertical axis (parallel beam). Every
one of the cases simulated was realized with 106 histories in the MCNP-X code. The source
and the detector are placed diametrically opposite each other for every case, as shown on Fig.
3.
a) b)
Figure 3: Basic geometries used in this work. a) Pencil Beam cross-sectional view. b)
Cone Beam cross-sectional view.
INAC 2015, Sa˜o Paulo, SP, Brazil.
For the simulations was used a 137Cs source of 662 keV of energy and a modeled NaI(Tl)
detector of 1”x1” [2].
5.1. Point Source (Pencil beam)
In this simulation a gamma-ray beam is very narrow and were made 17 simulations, one
for each level of water, from 1cm until 17 cm. The number of counts are registered by the
scintillator detector of 1”x1” in the full energy peak region of 662 keV for each level of water.
All the results for this simulation are represented bellow in the figure 4:
5.2. Point Source (Cone beam)
This simulation consists as two cases before of 17 simulations for each level of water from
1 cm to 17 cm of height. In this simulation the gamma-ray beam is not a parallel one beam
but it has a little aperture simulating a conical beam. The number of counts are registered by
the scintillator detector of 1”x1” in the full energy peak region of 662 keV for each level of
water. All the results for this simulation are represented bellow in the Fig. 4:
5.3. Disc Source (Pencil beam)
This simulation consists as the case before of 17 simulations for each level of water from 1
cm to 17 cm. This simulations were made with a disc source of 5 mm diameter. The gamma-
ray beam is a parallel one as the pencil beam case. The number of counts are registered by
the scintillator detector of 1”x1” in the full energy peak region of 662 keV for each level of
water. All the results for this simulation are represented bellow in the Fig. 4:
INAC 2015, Sa˜o Paulo, SP, Brazil.
a) b)
c)
Figure 4: Counts vs water level for: a) Pencil Beam. b) Cone Beam. c) Disc source
Parallel Beam. In every case the result of the exponential negative fitting r2 is placed to
the right side of the figure
6. CONCLUSIONS
The three figures has a similar behaviour, the counting decreasing with the increment of level
water. The count recorded in the cone case for point source is lower than the other two cases.
In this case a source with low collimation will need a higher activity. A disc source register
few counts too and in the practice a source with a parallel beam is not possible to use.
This work is still running and we need to make more evaluations to reach a right source-
detector system to measure fluid level.
REFERENCES
1. E. A˚bro, G. A Johansen “Improved void fraction determination by means of multibeam
gamma-ray attenuation measurements”, Flow Measurement and Instrumentation, 10,
pp. 99–108, (1999).
INAC 2015, Sa˜o Paulo, SP, Brazil.
2. C.M. Salgado, L.E. Branda˜o “Validation of NaI(Tl) detector’s model developed with
MCNP-X code”, Progress in Nuclear Energy, 59, pp. 19–25, (2012).
3. C.M. Salgado, L.E. Branda˜o “Study of volume fractions for stratified and annular
regime in multiphase flows using gamma-rays and artificial neural network” , 5th In-
ternational Nuclear Atlantic Conference, Santos, SP,Brazil, (2007).
4. N. Tsoulfanidis and S. Landsberger, Measurement and Detection of Radiation, CRC
Press, Boca Raton, Florida, United States of America (2011).
5. E.J. Avilan, V. Reis “Evaluation of cross correlation technique to measure flow in Pipes
of the Oil industry”, 8th International Nuclear Atlantic Conference, Recife, PE, Brazil,
(2013).
INAC 2015, Sa˜o Paulo, SP, Brazil.


Study of the source-detector system geometry using the MCNP-X code in the flowrate measurement with radioactive tracers

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Study of the source-detector system geometry using the MCNP-X code in the flowrate measurement with radioactive tracers

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