ISO 24460:2023
(Main)Measurement of fluid flow rate in closed conduits — Radioactive tracer methods
Measurement of fluid flow rate in closed conduits — Radioactive tracer methods
This document defines the measurement of single phase fluid flow rate in closed conduits using radioactive tracer methods.
Mesure du débit des fluides dans des conduites fermées — Méthodes par traceur radioactif
Le présent document définit le mesurage du débit d’un fluide monophasique dans des conduites fermées à l’aide de méthodes par traceur radioactif.
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 24460
First edition
2023-09
Measurement of fluid flow rate in
closed conduits — Radioactive tracer
methods
Mesure du débit des fluides dans des conduites fermées — Méthodes
par traceur radioactif
Reference number
© ISO 2023
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ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles of radioactive tracer methods . 1
4.1 General . 1
4.2 Transit time method . 1
4.2.1 Principle . 1
4.2.2 Special recommendation for the transit time method . 3
4.2.3 Advantages of transit time method . 3
4.3 Constant rate injection method . 4
4.3.1 Principle . 4
4.3.2 Duration of injection . 4
4.3.3 Advantage of the constant rate injection method . 5
4.4 Integration method . 6
4.4.1 Principle . 6
4.4.2 Advantages of the integration method . 7
5 Choice of radioactive tracer .7
5.1 General . 7
5.1.1 Requirements . 7
5.1.2 Radioactive tracers . 7
5.2 Advantages of radioactive tracers . 8
5.3 Particular advantages of radionuclide generators . 8
5.4 Selection of radioactive tracer . 8
5.4.1 Type of emitted radiations . 8
5.4.2 Half-life . 9
6 Choice of adequate mixing length.9
6.1 General . 9
6.2 Consideration on the mixing length . 9
6.2.1 General . 9
6.2.2 Examples of injection techniques for reducing mixing length . 10
7 Detection of radioactive tracer .11
7.1 General . 11
7.2 Gamma radiation detector . 11
7.3 Detector arrangement . 11
7.4 Data acquisition system .12
8 Procedures for applying radioactive tracer methods .12
8.1 Transit time method . 12
8.1.1 Location of injection cross-section .12
8.1.2 Pulse injection of radioactive tracer . 13
8.1.3 Estimation of the activity to be injected . 14
8.1.4 Choice of measuring length . 15
8.1.5 Calculation of transit time . 15
8.2 Constant rate injection method . 16
8.2.1 Preparation of the radioactive tracer to be injected . 16
8.2.2 Injection of the radioactive tracer . 17
8.2.3 Measurement of injection rate . 17
8.3 Integration method . 17
9 Uncertainty .17
9.1 General . 17
iii
9.1.1 E valuation of uncertainty . 17
9.1.2 Procedures for evaluating the uncertainty of a measured flow rate . 18
9.1.3 Uncertainty propagation formula . 18
9.2 Uncertainty of flow rate measured using the transit time method . 19
9.3 Uncertainty of flow rate measured using the constant rate injection method .20
9.4 Uncertainty of flow rate measured using the integration method .22
Annex A (informative) Calculation of transit time and its standard uncertainty .25
Annex B (informative) Radiation dose considerations .31
Bibliography .32
iv
Foreword
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This document was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed
conduits, Subcommittee SC 5, Velocity and mass methods.
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v
Introduction
The accurate knowledge of fluid flow rates (liquid and gas) in industrial systems is an essential
requirement of processing industries. The fluid flow rate measurement is usually needed for various
reasons i.e. calibration of installed flow meters, fluid balance, measurement of efficacy of pumps or
turbines, distribution of flow in a network of pipes, etc. Generally, the industrial systems where the flow
rates are needed to be measured are classified into two categories, namely open channels and closed
conduits. Closed conduits are conveyance systems where the flow of fluid is confined on all boundaries
(i.e. pipe systems) while open channels are systems where the stream has a free surface open to the
atmosphere such as canals, rivers, streams, sewer lines, effluent channels, partly filled conduits.
This document deals with single phase fluid flow rate measurement in closed conduits only, by using
the radioactive tracer method. Flow in closed conduits is caused by an axial pressure difference.
Various types of flow meters, such as ultrasonic, electromagnetic, acoustic, Venturi, Pitot tube, and
gamma transmission, are routinely used for flow rate measurements in closed conduits in industry.
The selection of a suitable method for a particular application depends on the type and nature of the
system, physical properties of the flowing fluid, flow patterns of the fluid, limitations imposed by the
design and operating condition of the plant, cost and installation of the equipment. One advantage
of the radioactive tracer methods is that measurement can be carried out online in harsh industrial
environment, from outside of the conduits while the process is in operation, with no disruption, and
with a high accuracy. This document treats radioactive tracer methods only.
The use of radioactive tracer methods for the measurement of fluid flow rates in closed conduits is one
of the most common and well-established application of the radioactive tracer technology in industry.
The major methods that have been found to be particularly applicable for online flow rate measurement
and flowmeter calibration are the pulse velocity or transit time method, as well as dilution methods,
known as constant rate injection method and integration method.
This document is developed to fill the need for a generalized reference based on fundamental principles
to measure fluid flow using radioactive tracer methods.
For single phase steady-state flow of fluid in a closed conduit, the volumetric flow rate can be measured
using this method. If the mass density is known, the mass flow rate can be deduced from the volume
flow rate.
The accuracy of flow rate measurement with the radioactive tracer methods depends on how well the
injected tracer material mixes with the flowing fluid before the measuring section. It depends on the
amount of tracer injected and the accuracy of the measurement devices.
vi
INTERNATIONAL STANDARD ISO 24460:2023(E)
Measurement of fluid flow rate in closed conduits —
Radioactive tracer methods
1 Scope
This document defines the measurement of single phase fluid flow rate in closed conduits using
radioactive tracer methods.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
closed conduit
conveyance system where the flow of fluid is confined on all boundaries (i.e. pipe systems)
3.2
mixing length
l
m
shortest distance at which the variation in concentration of the tracer over the cross-section is less
than some pre-determined value (for example 0,5 %)
4 Principles of radioactive tracer methods
4.1 General
Three radioactive tracer methods for flow rate measurement have been used:
— transit time method;
— constant rate injection method;
— integration method.
Both the constant rate injection method and the integration method are part of the dilution methods.
Radiation dose considerations are given in Annex B.
4.2 Transit time method
4.2.1 Principle
In the transit time method, a quantity of a radioactive tracer is injected instantaneously into a flowing
stream. Two detection cross-sections downstream the injection cross-section are commonly used
for registration of the gamma radiation emitted from the radioactive tracer in the flow. Both cross-
sections are sufficiently far from the injection cross-section to allow adequate (homogeneous) mixing
of the tracer with the fluid flow. Each detector registers a response curve when the tracer cloud crosses
the detection cross-section. The two response curves are compared to provide the transit time of the
tracer or fluid between the two detection cross-sections. Under these conditions, the volumetric flow
rate Q is given by Formula (1):
V
Q= (1)
t
where
Q is the volumetric flow rate;
V is the volume of the conduit between the detection cross-sections;
t
is the transit time of the tracer between the two detection cross-sections.
The value of t is obtained by measuring the difference in the centre of gravity, i.e. the first moment of
the two response curves as shown in Figure 1.
Key
1 response curve of 1st detector
2 response curve of 2nd detector
t time
transit time of the tracer between the two detection cross-sections
t
Q volumetric flow rate
DAQ data acquisition system
S area of across-section
RI radioactive tracer injector
RD radiation detector
l mixing length
m
l distance between the two detection cross-sections
d inner diameter of conduit
N(t) measured radiation count rate
Figure 1 — Principle of transit time method
The volume of the measuring section, V, and the volume flow rate, Q, are given respectively by
Formulae (2) and (3):
VS=⋅l (2)
V Sl⋅
Q == (3)
t t
where
V is the volume of the conduit between the detection cross-sections;
S is the cross-section of the fluid in the closed conduit;
l is the distance between the two detection cross-sections;
t
is the transit time of the tracer between the two detection cross-sections.
The transit time, t , is calculated by the difference in the mean residence times (first moments) between
the two response curves, as given by Formula (4):
∑tn ∑tn
22ii 11ii
t =τ −τ= − (4)
∑n ∑n
2i 1i
where
t
is the transit time of the tracer between the two detection cross-sections;
τ
is the mean residence time, and the indexes 1 and 2 refer to the 1st and 2nd detector, respectively;
n is the corrected count per count time, and the indexes 1 and 2 refer to the 1st and 2nd detector,
respectively.
4.2.2 Special recommendation for the transit time method
For this method, a conduit length of constant cross-section between the two detection cross-sections
should be ensured, so that the flow parameters are constant over the measuring length. The internal
volume of the measuring section shall be determined with sufficient accuracy.
4.2.3 Advantages of transit time method
The radioactive tracer transit time method seems to provide the most effective field calibration method
for flow rate measurement in closed conduits. It is suitable for both liquid and gas flows and covers a
large range of flow rates with a small uncertainty (see Annex A).
The main advantages of this method are as follows:
— it is only necessary to determine the response curve at two detection cross-sections;
— it is not necessary to know activity, volume or flow rates of the injected radioactive tracer;
— it is not necessary to collect any samples;
— the activity of the radioactive tracer used by this method is considerably smaller than needed for
other methods.
4.3 Constant rate injection method
4.3.1 Principle
The constant rate injection method is based on the principle of conservation of tracer activity. A tracer
of activity concentration c is injected with constant volume flow rate q to the main flow with volume
flow rate Q. As there is no gain or loss of tracer in the measuring section, the injected tracer shall
eventually appear with the same total activity (but with a different activity concentration, C, because of
dilution in the main flow) at any downstream detection point, as given by Formula (5):
qc××=QC (5)
Figure 2 shows the principle of constant rate injection method.
Key
1 constant rate injection pump
Q volumetric flow rate in closed conduit
q volumetric flow rate of tracer solution
l mixing length
m
c activity concentration of tracer solution
C activity concentration of collected sample
Figure 2 — Principle of constant rate injection method
The volumetric flow rate of the mainstream can be calculated by Formula (6):
c
Qq= (6)
C
4.3.2 Duration of injection
The duration of injection shall be such that stable concentration conditions are established at all points
of the sampling cross-section over a sufficient period of time. A suitable duration of injection may
be determined by a preliminary investigation involving a pulse injection of a radioactive tracer. The
response curve (curve 2 of Figure 3) of the pulse injection is obtained at the sampling cross-section.
The curve starts at time t after the injection and the duration of the curve is t .
1 2
Key
1 pulse injection curve
2 response curve of the pulse injection
3 imaginary constant rate injection curve
4 response curve of the imaginary constant rate injection
Q volumetric flow rate
t time
t time for sampling
s
N(t) measured radiation count rate
RI radioactive tracer injector
RD radiation detector
l mixing length
m
a
Tracer injection curves at injection point.
b
Tracer response curves at measuring point.
Figure 3 — Determination of the duration of injection
In constant rate injection method, if it is required to achieve steady conditions for a period of time t in
s
a selected sampling cross-section, it is necessary to keep the constant rate injection for a period of time
t + t . Then, the measurement (detection or sampling) can be performed from the time t + t to time
2 s 1 2
t + t + t , after the start of the constant rate injection.
1 2 s
4.3.3 Advantage of the constant rate injection method
The main advantage of this method is:
— that it is not necessary to know the geometrical characteristics of the conduit.
4.4 Integration method
4.4.1 Principle
In integration (or total-count) method, it is assumed that if an activity A of tracer is injected, then this
amount — as there is no gain or loss of tracer in the measuring section — shall eventually pass any
downstream detection cross-section.
Pulse injection of tracer into closed conduit is applied. The flow rate is determined from the cumulative
response of a detector located externally on the closed conduit. Figure 4 shows the principle of the
integration method.
Key
1 response curve of injected radioactive tracer
RI radioactive tracer injector
Q volumetric flowrate
l mixing length
m
DAQ data acquisition system
N(t) measured radiation count rate
N integrated net radiation count
t time
Figure 4 — Principle of integration method
The integrated net radiation count, N, (corrected for background and decay) is registered, then the flow
rate Q is given by Formula (7)
A
QF= (7)
N
where
A is the total injected activity [Bq];
F is the calibration factor relating A to N [counts per unit time per Bq/l];
N is the integrated net radiation count.
The calibration factor, F, [counts per unit time per unit activity concentration] shall be determined
beforehand. For the calibration of detector placed external to a closed conduit a section of identical
conduit shall be set up. This section shall be longer than the field of view of the collimated detector.
Then, the net radiation count rate of an identically located detector to a known activity concentration
within the conduit shall be measured.
4.4.2 Advantages of the integration method
The main advantages of the integration method compared to the constant rate injection method are:
— a smaller amount of radioactive tracer can be used;
— less field operation time is needed.
5 Choice of radioactive tracer
5.1 General
5.1.1 Requirements
The radioactive tracer shall comply with the following requirements:
— have identical flow behaviour as the fluid being traced;
— mix easily and homogeneously with the fluid in the conduit;
— be measurable with sufficient sensitivity;
— have a suitable half-life for the examination;
— be sufficiently chemically stable under the conditions of use;
— be affordable.
5.1.2 Radioactive tracers
Tables 1 and 2 present the commonly used radioactive tracers for measurement of fluid flow rate. Only
gamma ray emitting tracers are considered here.
Table 1 — Tracers labelled with radionuclides produced in nuclear reactors or particle
accelerators
Gamma energy in
Chemical form of tracer/ Traced
keV
Radionuclide Half-life
form of carrier compound phase
(Probability in %)
1 368,6 (100) 24 +
Na /Sodium carbonate, Na CO or Sodium
24 2 3
Sodium-24 ( Na) 15 h Aqueous
bicarbonate, NaHCO
2 754,0 (100) 3
82 -
554,5 (71,7) Br /Ammonium bromide, NH Br Aqueous
Radiolabelled p-dibromobenzene, C H Br /
619,1 (43,7)
6 4 2
Organic
C H Br
6 4 2
698,4 (28,4)
Bromine-82
36 h
( Br)
776,5 (83,6)
CH Br/Methyl bromide, CH Br Gases
3 3
1 044,0 (25,6)
1 317,5 (26,9)
123 -
I /Potassium iodide, KI or sodium iodide,
Aqueous
123 NaI
Iodine-123 ( I) 13,2 h 159,0 (83,3)
Radiolabelled iodobenzene, C H I/C H I Organic
6 5 6 5
131 -
I /Potassium iodide, KI or sodium iodide,
Aqueous
131 NaI
Iodine-131 ( I) 8,03 d 364,5 (81,5)
Radiolabelled iodobenzene, C H I/C H I Organic
6 5 6 5
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Gamma energy in
Chemical form of tracer/ Traced
keV
Radionuclide Half-life
form of carrier compound phase
(Probability in %)
45,0 (52,8)
Xenon-133
133 0
5,27 d Xe /Xenon Gases
( Xe)
81,0 (36,9
261,3 (12,7)
Krypton-79
79 0
35 h Kr /Krypton Gases
( Kr)
511,0 (14,0)
41 41 0
Argon-41 ( Ar) 109,6 min 1 293,6 (99,22) Ar /Argon Gases
Table 2 — Radiotracers produced from radionuclides eluted from radionuclide generators
Gamma energy in
Half-life mother/
Radionuclide Traced
keV a b c d e
half-life Chemical form of tracer
generator phase
daughter
(Probability in %)
511,0 (177,8),
68 68 68 3+ 68 -
Ge → Ga 271 d/67,7 min Ga , Ga-[DOTA] Aqueous
1 077,3 (3,2)
99m -
99 99m
Mo → Tc 66 h/6 h 140,5 (89,0) Aqueous
TcO
113m 3+ 113m -
In , In-[EDTA] Aqueous
113 113m
Sn → In 115 d/99,5 min 391,7 (64,9)
113m
In-[D2EHPA] Organic
137m 2+ 137m n-
Ba , Ba-[EDTA] Aqueous
137 137m
Cs → Ba 30 y/2,55 min 661,7 (89,9)
137m
Ba-[DC18C6][HDNNS] Organic
a
DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid.
b
EDTA = ethylene-diamine tetra-acetic acid.
c
D2EHPA = di(2-ethylhexyl) phosphoric acid.
d
DC18C6 = di-cyclohexano-18-crown-6 or 2,3,11,12-dicyclohexano-1,4,7,10,13,16-hexaoxacyclo-octadecane.
e
HDNNS = di-nonyl naphthalene sulfonic acid.
5.2 Advantages of radioactive tracers
The main advantages of employing radioactive tracer are:
— these can be detected by means of detectors located outside the conduit (for tracers emitting
sufficiently energetic gamma radiation);
— with short half-life radioactive tracers, any contamination danger disappears quickly and there is
no permanent pollution.
5.3 Particular advantages of radionuclide generators
The main advantage of using radionuclide generator is, that practically useable quantity of radioactive
tracer of short half-life is available repeatedly at the measuring place.
5.4 Selection of radioactive tracer
5.4.1 Type of emitted radiations
Gamma ray emitting tracers are preferred to beta ray emitting tracers because the measurement of
this type of radiation can be made through conduit walls and the self-absorption of radiation by the
fluid is decreased.
5.4.2 Half-life
The transit time method makes it possible to use radioactive tracers with much shorter half-lives
than those required for constant rate injection and integration methods. A radioactive tracer shall be
chosen with the shortest possible half-life consistent with the above-mentioned conditions and with the
conditions of supply, storage and measurement of the radionuclide, in order to minimize any effect of
contamination and unnecessary radiological exposure associated with the handling of the tracer.
6 Choice of adequate mixing length
6.1 General
When a radioactive tracer is used to measure the flow of fluid in a conduit, there should be sufficient
distance between the injection cross-section and the detection or sampling cross-section.
Mixing length is defined as the distance beyond which the variation in the conduit cross-section of
tracer concentration is smaller than some previously chosen value. Therefore, the mixing length is not
a fixed value but varies according to the allowed concentration variations in the conduit cross-section:
the smaller the acceptable variation the greater the mixing length.
6.2 Consideration on the mixing length
6.2.1 General
The mixing length varies with Reynolds number Re, conduit friction and the injection technique
employed. Figure 5 shows variation in cross-section homogeneity of tracer as function of relative
mixing length for a Reynold number Re = 10 for a smooth pipe.
Key
L relative mixing length (ratio between length and diameter of pipe)
rel
maximum variation of tracer concentration in conduit cross-section (%)
σ
max
Figure 5 — Effect of variation in cross-section homogeneity of tracer on relative mixing length
for a smooth pipe
The length of conduit between the injection and first detector shall be equal to or greater than the
mixing length and should preferably contain no pipe fittings or sections likely to significantly increase
the longitudinal dispersion of the tracer at the detection cross-sections.
6.2.2 Examples of injection techniques for reducing mixing length
6.2.2.1 General
Experience has shown that good cross-sectional mixing, for central injection, may require as many as
100 pipe diameters downstream the injection cross-section to be achieved. It is often not possible to
inject the radioactive tracer at such a distance upstream of the measurement section. Therefore, it is
required to reduce that length by using appropriate radioactive tracer injection techniques and devices,
or to accept lower accuracy of the results of flow rate.
6.2.2.2 Multiple-orifice injectors
Substantial reduction in mixing length can be obtained by injecting the tracer through multiple orifices
uniformly distributed on the conduit wall or (if possible) concentrically inside the conduit. Figure 6
shows variation in cross-section homogeneity of tracer as function of relative mixing length for four
different types of injection.
Key
1 four orifices at r/R = 0,63
2 four orifices at the wall
3 one orifice at the centre of the pipe
4 one orifice at the wall
L relative mixing length (ratio between length and diameter of pipe)
rel
maximum variation of tracer concentration in conduit cross-section (%)
σ
max
Figure 6 — Effect of variation in cross-section homogeneity of tracer on relative mixing length
for four different types of injection
If multi-orifice injections are used, the device shall be designed so as to allow a simultaneous injection
with equal injection rate in every point.
6.2.2.3 High velocity jets
Injecting the tracer counter-currently at a velocity much larger than bulk flow velocity induces high
mixing at the end of the jet. The reduction in good mixing length depends on the number and momentum
of the jets and on their angle with respect to the main flow direction. A simple jet arrangement can
bring about 30 % reduction in the mixing length as compared to the single central injection point.
6.2.2.4 Vortex mixing
Incorporating obstacles within the conduit, just after tracer injection cross-section, produces turbulence
that enhances mixing and reduces the mixing length. As an example, injecting the tracer through three
triangular plates, at an angle of 40° to the main flow direction, reduces the mixing length by one third
with respect to a central single injection point.
6.2.2.5 Pumps and turbines
If tracer is injected upstream of a pump or a turbine, the mixing length is considerably reduced.
Centrifugal pumps reduce the mixing length by about 50 pipe diameters.
6.2.2.6 Bends, valves and other obstacles
Every singularity in the conduit promotes turbulence that tends to decrease good mixing length.
However, it is advisable to use straight lengths of conduit without obstacles whenever transit times are
to be measured.
7 Detection of radioactive tracer
7.1 General
For online radioactive tracer applications, detection system normally consists of a set of gamma
radiation detectors connected to a data acquisition system.
7.2 Gamma radiation detector
Gamma detectors have to be effective and ruggedized for rough industrial environments. Solid
inorganic scintillators meet most of the requirements. Two types of scintillation detectors, NaI(Tl) and
Bi Ge O (BGO), are common.
3 4 12
NaI(Tl)-detectors of 2 inch × 2 inch (length × diameter) are mostly used in field measurements.
Measurements can be carried out using single channel analysers where all gamma energies between a
lower and an upper limit are recorded.
If space is limited, BGO crystals of smaller size 1 inch × 1 inch but with approximately half detection
efficiency of 2 inch × 2 inch NaI(Tl)-detectors may be used. Their smaller sizes also need less collimator
weight, so they are easier to mount and handle, but somewhat more expensive.
7.3 Detector arrangement
Generally, detection of gamma activity in a detection cross-section can be carried out with only one
detector, supposing a sufficiently homogeneous tracer concentration in the detection cross-section of
the conduit as shown in Figure 7 (left).
Figure 7 — Typical arrangements of gamma detectors
In order to check the homogeneity of the tracer distribution in the flow, more detectors may be added,
for instance in a geometry like that suggested in Figure 7 (right). For a fully homogeneous tracer
distribution, all the detectors should give the same reading when corrected for their eventual difference
in total counting efficiency.
7.4 Data acquisition system
Radiation detectors are connected to a data acquisition system (DAQ). One, two or more radiation
detectors are used for flow rate measurement in closed conduits. The data acquisition system (see
Figure 8), which collects signals from the radiation detectors, is the basic equipment for online
radioactive tracer measurements. It ensures collection, treatment and visualization of the data in real
time.
Figure 8 — Example of a data acquisition system
8 Procedures for applying radioactive tracer methods
8.1 Transit time method
8.1.1 Location of injection cross-section
The location of injection cross-section depends mainly on the available length of conduit between the
injection cross-section and the first detection cross-section. The length of conduit between the injection
cross-section and the first detection cross-section, shall be equal or longer than the theoretical mixing
length.
When the available length of conduit between the injection cross-section and the first detection cross-
section is less than the theoretical mixing length, it is recommended to inject tracer upstream of a fan, a
pump or other turbulence-generating devices.
8.1.2 Pulse injection of radioactive tracer
Pulse injection of radioactive tracer is applied in the transit time method. In order to minimize
dispersion of the measured intensity/time distributions, the tracer shall be injected as rapidly as
possible, with no “tailing” of the injected tracer from the injection tubes within the conduit. This can be
achieved by any of the following means:
— by ensuring that the injected tracer is flushed into the conduit by a flow of radioactive tracer-free
material;
— by breaking with a suitable device an ampoule containing the radioactive tracer to be injected in the
conduit.
Injection systems are generally home-made, built and adapted for specific applications and field
conditions. They vary considerably in design from the simplest (a syringe) to the most complex (devices
for remote injection into pressure vessels). Figure 9 presents an example of a radioactive gas tracer
injection system for closed conduits and Figure 10 presents an example of a radioactive liquid tracer
injection system for closed conduits.
Key
Q gas flow in closed conduit
1 system valve
2 hammer
3 break rod
4 radioactive tracer ampoule
5 quick connector
6 pressure relief valve
7 compressed air/gas
Figure 9 — Example of radioactive gas tracer injection system
The operation procedure is carried out as follows:
a) insert the ampule with radioactive gas tracer;
b) connect the quick connector;
c) open the system valve;
d) break the ampoule;
e) open the pressure release valve;
f) close the system valve.
Key
1 radioactive tracer
2 lead container
3 compressed air tank
Q liquid flow in closed conduit
a
Liquid tracer injection setup.
b
Charging of tracer.
c
Injection of tracer.
Figure 10 — Example of radioactive liquid tracer injection system
8.1.3 Estimation of the activity to be injected
The amount of radioactivity is estimated based on efficiency of the detection system, required accuracy,
dilution between injection and detection points, and background radiation level.
A simplified calculation method is used to roughly estimating the radioactivity, A, to be injected. For a
conservative estimation of radioactivity, it is assumed that the volume, V, of the zone between injection
and second detector cross-sections is a perfect mixer with the radioactivity concentration, C = A/V. It
is recommended to inject an amount of radiotracer to get a radioactivity concentration equal to ten
times the lower detection limit or the minimal detectable concentration of the tracer, C , i.e. the
min
radioactivity to be injected is as given in Formula (8):
AC=10 V (8)
min
C depends on radiation background level, R , detection efficiency, ε, and count time, Δt. For a 95 %
min B
confidence limit, C can be delivered as given in Formula (9):
min
1/2
2R
2
B
C = (9)
min
ε Δt
where
R is the background count rate;
B
Δt is the count time;
ε is the detection efficiency.
Thus, the activity to be injected can be calculated using Formula (10):
1/2
R
B
A= ⋅ V (10)
ε Δt
−1
The detection efficiency is defined as the response ( s ) of the detector to the unit specific activity
−3 −−11 3
(Bq⋅m ) of the fluid inside the closed conduit at a given detection geometry. Its unit is [sB⋅⋅qm ].
The detection efficiency can be measured experimentally by simulating the field experimental
arrangement in the laboratory using a piece of pipe of the same diameter and wall thickness. The pipe
is plugged at both ends and an injection port is installed on the pipe. The background count rate is
measured at the beginning. The pipe is filled with radiotracer solution with known specific activity and
the count rate is measured.
8.1.4 Choice of measuring length
8.1.4.1 Mixing of radioactive tracer
The radioactive tracer shall be sufficiently mixed with the flow before the first detection cross-section
for the recorded response curves at both detectors to be adequately representative of the mean flow.
The tracer should be injected as rapidly as possible to minimize the longitudinal dispersion of the tracer.
8.1.4.2 Length of conduit between injection and first detector
The length of conduit between the injection and first detector shall be equal to or greater than the
mixing length and should preferably contain no pipe fittings or sections likely to significantly increase
the longitudinal dispersion of the tracer at the detection cross-sections.
8.1.4.3 Length of conduit between detection cross-sections
The length of conduit necessary between the detection cross-sections depends on the axial velocity of
the fluid, the spatial dispersion of the tracer at the detection cross-sections and the required accuracy
of the measurement of transit time.
8.1.5 Calculation of transit time
The transit time is calculated from the two corrected tracer response curves. This procedure is
introduced in Annex A.
When preliminary rough calculations are needed, the transit time
...
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