Application of thermoelectric cooling module for sampling of tritium in air

Abstract

The sampling and measurement of airborne tritium is an essential component of workplace monitoring at heavy water handling facilities and nuclear reactors using heavy water as coolant and moderator. Tritium being an internal hazard, its workplace monitoring and assessment of internal exposure of workers is a regulatory requirement for the facility. The conventional tritium air sample collection methods are condensation, bubbling, and trapping with appropriate media such as dry ice, water, and desiccants, respectively. A novel method for rapid collection of moisture in the air for the estimation of tritium is presented and discussed in this article. It involves condensation of tritium oxide in the air using a commercially available thermoelectric cooling module which has removed uncertainty in the availability of dry ice or desiccant. The instrument is capable of collecting 2–3 ml of sample in 30 min at a relative humidity level of about 60% and temperature of about 25.5°C. The quantity of sample collected is sufficient for the estimation of tritium concentration in air. The Peltier module-based low-cost, simple, and reliable system has been successfully implemented for workplace tritium in air sampling at radiological facilities.

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16 © 2022 Radiation Protection and Environment | Published by Wolters Kluwer - Medknow
Application of thermoelectric cooling module for sampling
of tritium in air
Lokesh Kumar, V. Shreenivas, Saurav Sood, P. Ashokkumar, Ranjit Sharma, M. S. Kulkarni
Health Physics Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
Original Article
INTRODUCTION
Tritium (T) is a radioactive isotope of hydrogen and it is
generally present as tritiated water molecule (HTO) or T as
a gas in the surrounding air. The higher concentration of
T is prevalent at heavy water (D2O)‑based nuclear reactors
and also it is being increasingly used at certain accelerators,
research, and industry. Tritium sampling and assessment of
its radioactivity levels at the workplace and environment is
an essential component of radiation protection as well as
a regulatory requirement. The continuous air monitoring
program is implemented to monitor airborne tritium at
the workplace to assess the need for appropriate personnel
protective equipment such as fresh airline respirators and
plastic suits. The quick detection and measurement of
unexpected airborne contamination in case of tritiated
heavy water spillage in the area can help in introducing
timely intervention and protective action for minimizing
internal exposure. The radiation workers are regularly
monitored for internal exposure to assess committed
effective dose due to tritium intake leading to appropriate
cautioning or removal from radioactive work.[1] Health
physicists collect the HTO vapor from the air especially
at plant occupancy areas of reactors and radioactive
facilities that handle tritium as well as in the environment
at the vicinity of all such facilities.[2,3] The sampling is
The sampling and measurement of airborne tritium is an essential component of workplace monitoring at
heavy water handling facilities and nuclear reactors using heavy water as coolant and moderator. Tritium being
an internal hazard, its workplace monitoring and assessment of internal exposure of workers is a regulatory
requirement for the facility. The conventional tritium air sample collection methods are condensation,
bubbling, and trapping with appropriate media such as dry ice, water, and desiccants, respectively. A novel
method for rapid collection of moisture in the air for the estimation of tritium is presented and discussed in
this article. It involves condensation of tritium oxide in the air using a commercially available thermoelectric
cooling module which has removed uncertainty in the availability of dry ice or desiccant. The instrument is
capable of collecting 2–3 ml of sample in 30 min at a relative humidity level of about 60% and temperature
of about 25.5°C. The quantity of sample collected is sufficient for the estimation of tritium concentration
in air. The Peltier module-based low-cost, simple, and reliable system has been successfully implemented
for workplace tritium in air sampling at radiological facilities.
Keywords: Air sampling, Peltier module, relative humidity, tritium
Abstract
Address for correspondence: Mr. Lokesh Kumar, Health Physics Division, Bhabha Atomic Research Centre, Mumbai ‑ 400 085, Maharashtra, India.
E‑mail: lokeshk@barc.gov.in
Submied: 28‑Mar‑2022 Accepted: 01‑Apr‑2022 Published: 28‑Jun‑2022
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DOI:
10.4103/rpe.rpe_10_22
How to cite this article: Kumar L, Shreenivas V, Sood S, Ashokkumar P,
Sharma R, Kulkarni MS. Application of thermoelectric cooling module for
sampling of tritium in air. Radiat Prot Environ 2022;45:16‑21.
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Kumar, et al.: Thermoelectric cooling module for sampling of tritium in air
Radiation Protection and Environment | Volume 45 | Issue 1 | Januar y-March 2022 17
carried out by applying convenient methods[4] such as
(i) passing the air through a desiccant, (ii) bubbling the air
through nontritiated water or other appropriate solvents,
and (iii) condensing or freezing. After sample collection,
the specic activity of T in the moisture condensate is
analyzed using liquid scintillation spectrometer (LSS) for
the estimation of tritium concentration in air.
Sampling by passing the air through desiccation agents
such as silica gels or molecular sieves involves the retention
of moisture present in the air on their surface. The water
is recovered by evaporation and condensation of water
from the desiccation agent to assay the T in the sample.
The requirement of the air sampling pump and a longer
sampling period due to the low water retention capacity
of desiccation agents is a disadvantage. Moreover, it
requires a bulky installation to recover tritium from the
desiccation agents. Another sampling method consists
of passing HTO vapor through water, which is free from
tritium contamination. The HTO vapor present in the air is
exchanged with the tritium‑free water in the bubbler bottles.
Tritium concentration in the water of bubbler bottles
is measured with LSS. A constant sample ow through
the bubbler has to be maintained using a pump. This
sampling method has drawback that it requires signicant
sampling time due to the required low airow in bubbler
bottles. The cold trap method consists of condensing or
freezing the HTO vapor on cold surfaces. Cold traps are
formed by the continuously cooling surface of copper
strips or aluminum plates or glass beakers with the use of
dry ice or liquid nitrogen. The moisture containing HTO
vapor condensed on the surface is recovered manually for
further analysis. The tritium concentration in the collected
water is measured using LSS. The cold trap requires the
constant availability of dry ice or liquid nitrogen for sample
collection. The nonavailability of dry ice due to breakdown
in supply from respective agencies and the problem of
long‑term storage may affect the sample collection during
any accidental heavy water spillage leading to an increase
in airborne tritium.
The Peltier effect is the cooling of one junction and heating
of the other one when an electric current is maintained in a
thermocouple of two dissimilar conductors. This effect is
the reverse of Seebeck effect, where two dissimilar materials
are joined together and their junctions are kept at different
temperatures. The voltage difference is developed across
the junctions which are proportional to the temperature
difference of the two junctions. The Peltier effect is
described as the heat extraction or absorption at the contact
of two dissimilar metals when a direct electric current ows
through it. If the hot junction is kept outside the insulated
area, the cold junction can be used to cool the specied
region. Peltier elements or thermoelectric cooling (TEC)
modules are available in various forms and shapes. Typically,
they consist of a larger amount of thermocouples arranged
in rectangular form and packaged between two thin ceramic
plates. Later, it has been evolved that the most prospective
materials for Peltier effect were semiconductors. A Peltier
device is generally fabricated using semiconductor material
such as bismuth telluride (Bi2Te3), lead telluride (PbTe), and
bismuth antimony telluride (PbSbTe).[5‑7] A Peltier material
exhibits very high electrical conductivity and relatively
low thermal conductivity, in contrast to normal metals
which have both high electrical and thermal conductivity.
A thermoelectric element is formed by making junction
between P‑ and N‑type semiconductor pallets using
copper tabs.[8] When an electric current is passed in the
appropriate direction through the junction, both types of
charge carriers, electrons in N‑type and holes in P‑type
semiconductor pallet, move away from the junction and
convey heat away, thus cooling the junction. Several such
elements are arranged between two rectangular plates with
connecting wires to form a TEC module which connects
the thermoelectric elements electrically in series and
thermally in parallel.
The Peltier effect has been utilized in this work to produce
cooling for moisture condensation. Peltier modules form
the electricity‑driven cold traps. We have developed a
novel device to quickly collect the T activity sample in
air using commercially available TEC or Peltier cooling
modules. The design, development, and implementation
of the TEC‑based T in air sampling device have been
described, along with the implementation of the device
and measurement results.
MATERIALS AND METHODS
An air sampling unit has been developed utilizing the Peltier
effect, which will be used for the moisture condensation
from the air using electricity instead of dry ice/liquid
nitrogen. To achieve the condensation of moisture in the
air, a suitable TEC module is selected to develop the tritium
in air sampling device.
Fabrication and assembly of T in air sampling system
The T in air sampling system to condense moisture from
air is a portable device which has been constructed using
a TEC module with an air‑cooled heat sink made of
copper connected at its hot surface. The air sampling
system design has been optimized to collect the required
amount of condensed moisture from the air in minimum
sampling time. The fabrication and assembly of various
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Kumar, et al.: Thermoelectric cooling module for sampling of tritium in air
18 Radiation Protection and Environment | Volume 45 | Issue 1 | Januar y-March 2022
parts of the Peltier effect‑based T in air sampling system
are discussed here.
The sampling device consists of four blocks, namely power
supply, TEC module, heat sink attached with fan for heat
removal and moisture sample collection surface. Figure 1
gives the TEC‑based T in air sampling device. A 12V
direct current power supply having 15 amperes current
rating which operates with 230V mains, has been used
to power the system. The efciency of moisture sample
collection depends on the effectiveness of heat removal
mechanism from the hot ceramic side of the TEC module.
The required cooling on the moisture condensing surface
could be achieved with an efcient heat dissipation unit.
We used a high performance, compact‑sized, heat removal
system with a precise combination of airow cooling coils
and heat sink having aluminum ns tted mechanically to
small (92 mm × 92 mm × 22 mm) high speed (2000 rpm)
fans connected to a 40 mm × 40 mm metallic plate. To
enhance the heat removal efciency, two fans are utilized.
A commercially available Peltier module TEC1‑12715[9] is
used as the cooling device [Figure 2].
This is a standard‑sized (40 mm × 40 mm × 3.6 mm),
single‑stage thermoelectric device having 127 numbers
of thermocouples with a rating current of 15 amperes for
operation. Table 1 gives the specications of TEC1‑12715.
The hot junction side of the TEC module is contact
coupled with the metallic surface of the fan/heat sink
combination with external ns for conduction cooling.
A conical‑shaped sample collection device is fabricated
using copper material to have an optimized and efcient
cooling surface. The schematic diagram of the sample
collection device is shown in Figure 3.
This sample collection device is mechanically tted with
the cold junction side of the TEC module. The moisture
condensate from the copper sample collecting surface is
collected in a sample holder kept below it. All the parts
of the system are assembled within an aluminum frame.
This frame has been designed open to ambient air to have
no restriction on air movement through the moisture
condensing surface tted to the TEC module. This ensures
the appropriate collection of a representative sample from
the surrounding air to assess T concentration in the work
environment.
Tritium sample collection method with thermoelectric
cooling module
When the power supply to the device is switched on, the
cooling is sensed on the cold ceramic side of the TEC
module instantaneously and it is followed by condensation
of moisture over the moisture collection surface [Figure 1].
The condensed moisture over the moisture collection
surface is collected in a glass Petri dish by placing it below
the moisture collection surface. The temperature, humidity,
and moisture content in the air were measured using the
dry‑ and wet‑bulb temperatures of a sling psychrometer
having two conventional side‑by‑side thermometers.
RESULTS AND DISCUSSION
T in air concentration was estimated using the sample
collected with the air sampling system and the results
have been compared with those obtained using the
conventional cold finger method. Air samples were
collected simultaneously at the same location using both
the methods. The sample collection time was 30 min for
each measurement. Dry‑bulb and wet‑bulb temperatures
were noted at the same time to estimate the moisture
content in the air. Tritium concentration in the air has been
estimated by measuring the tritium concentration in 1 ml
of collected moisture sample using a liquid scintillation
counter. The dew point, relative humidity (RH) (%), and
moisture content of air are also calculated using standard
psychometric methods. The amount of water vapor in
Figure 1: Thermoelectric cooling-based T in air sampling device
Table 1: Specifications of TEC1‑12715
Parameter Value
Operating voltage 12V
Vmax 15.4V
Imax 15.6A
Maximum power 136.8W
Temperature range −50‑100°C
Dimension (length×width×height) 40 mm×40 mm×3.6 mm
Weight 3.6 g
Vmax: Maximum voltage, Imax: Maximum current
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Kumar, et al.: Thermoelectric cooling module for sampling of tritium in air
Radiation Protection and Environment | Volume 45 | Issue 1 | Januar y-March 2022 19
the atmosphere varied from 16.3 g/m3 to 17.2 g/m3,
and this value has been utilized to estimate the accurate
T concentration in air. The details of the measurements
are given in Table 2. The deviations in measured tritium
concentration using the Peltier sampling method are within
6% of the cold nger method, which shows that the results
of the measurements are in agreement with each other.
The rate of sample collection depends on various factors
such as temperature, humidity of ambient environment,
and air movement. The sample collection efciency of
the system has been studied by collecting the samples
in different environmental conditions with respect to
temperature and humidity. The volume of sample collected
in 30 min with respect to the RH (%) of the environment
is plotted in Figure 4. The samples were collected in the
facility environment with the temperature ranging between
25°C and 26°C. The volume of sample collected varies
Figure 2: Peltier module, TEC1-12715
from 1.85 ml at 55% of RH to 3.6 ml at 92% of RH.
Figure 4 shows that the volume of the air sample collected
at a specic temperature is proportional to the prevailing
RH (%).
Approximately 2 ml of ambient atmospheric moisture
sample is collected at RH level of about 60% and
temperature of ~ 25.5°C for a collection time of 30 min.
The volume of sample required for analysis can be
collected within 20 min at the same ambient environmental
conditions, whereas at locations having higher RH values,
one can collect larger volume of sample in less time.
The consistency in sample collection efciency with
respect to the operating duration of the system has been
tested by measuring the sample collected in different
sample collection timing in the same environmental
conditions. The quantity of sample collected in 15 min–
120 min of collection duration varies from 0.7 ml to
Figure 3: Schematic diagram of copper sample collection device
Table 2: Comparison of the results of tritium in air concentration measured using Peltier effect‑based air sampling system and
the conventional cold finger method
Dry‑bulb
temperature (°C)
Wet‑bulb
temperature (°C)
Moisture content
in air (g/m3)
Relative
humidity (%)
Dew
point (°C)
Tritium concentration in
air (DAC)
Deviation in tritium
concentration (%)
Peltier Cold finger
26 21.5 16.3 67 19.43 0.0300±0.0005 0.0293±0.0005 −2.59
31. 5 23.5 16.7 51 20.1 0.0656±0.0008 0.0622±0.0008 −5.36
30 23 16.6 55 19.97 0.0555±0.0008 0.0565±0.0007 1.76
26 21.5 16.3 67 19.43 0.0386±0.0006 0.0373±0.0006 −3.49
30 23 16.6 55 19.97 0.3294±0.0018 0.3381±0.0018 2.58
29 23 17. 2 60 20.43 0.0960±0.001 0.0911±0.0001 −5.34
26 21.5 16.3 67 19.43 0.0909±0.001 0.0933±0.0008 2.61
26 21.5 16.3 67 19.43 0.0744±0.0009 0.0732±0.0015 −1.63
31. 5 23.5 16.7 51 20.1 0.2146±0.0015 0.209±0.0017 −2.41
30.5 23 16.4 53 19.74 0.2965±0.0017 0.3110±0.0013 4.65
30 23 16.6 55 19.97 0.1592±0.0013 0.1506±0.0024 −5.73
26 21.5 16.3 67 19.43 0.6277±0.0025 0.6006±0.0014 −4.50
30.5 23 16.4 53 19.74 0.2086±0.0014 0.1972±0.0014 −5.76
DAC: Derived air concentration
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Kumar, et al.: Thermoelectric cooling module for sampling of tritium in air
20 Radiation Protection and Environment | Volume 45 | Issue 1 | Januar y-March 2022
6.8 ml at temperature and humidity in the range of
24°C–25°C and 57%–62%, respectively, as shown in
Figure 5. The linear rise in the sample quantity with the
sample collection duration shows the consistency of
sampling efciency.
Comparison of sampling efficiency with respect to
conventional method
The condensed moisture sample from air with the
conventional condensation method, cold nger method
varies with the volume and surface area of the sampling
beaker. However, conventionally used 250 ml of beaker
lled with dry ice collets 1.65 ml of moisture on its outer
surface in half an hour of sampling duration at dry‑bulb
temperature and RH of 25°C and 57%, respectively. The
developed Peltier effect‑based tritium in air sampling
system also collects approximately the same amount of
moisture from air in the same ambient conditions.
As compared to the conventional method of bubbler
with water or cold strip condensation using dry ice,
the present device is faster and gathers direct air
condensation over the collection surface without using
any medium such as dry ice. This sampling method is
easy to implement and further this low‑cost device can
be fabricated using locally available components. This
system was successfully employed for the sampling of
T in air during nonavailability of dry ice and emergency
conditions. The only drawback that can be pointed out is
that it requires power supply instead of dry ice and hence
cannot be used for remote environmental sampling. It is
planned to employ the presently developed TEC‑based
T in air sampling device in various facilities handling
tritiated heavy water. A battery‑operated system can be
implemented for environmental sampling.
CONCLUSIONS
A low‑cost, portable TEC module‑based T in air sampling
system has been developed and tested in elevated levels
of airborne tritiated environment. The sampling and
activity analysis was carried out using TEC module and
dry ice‑based sampling technique to have a comparison
of the tritium activity measurements. The deviation in
the measured tritium concentration collected with Peltier
effect‑based air sampling system is within 6% of cold
finger method. Therefore, the tritium concentration
measured with Peltier effect‑based air sampling unit is in
good agreement with cold nger method. The required
sample for analysis can be collected in less than half an
hour duration and the use of electronic cooling devices
has removed the uncertainty in the availability of dry ice
or desiccant.
Acknowledgments
We acknowledge the guidance and encouragement given
by Dr. D K Aswal, Director, HS&E Group, BARC during
this developmental work. We are immensely thankful to
Dr. R. K. Gopalakrishnan, Ex‑Head RHCS, HPD, BARC
for encouragement and guidance to develop the sampling
system. The encouragement from Shri Kunal Chakrabarty
Head, Reactor Operation Division, Shri P. Sumanth,
Head of Research Reactor Maintenance Division, and
Shri S C Parida Head, Process Development Division is
gratefully acknowledged. We thank Shri B G Avhad, Head,
Engineering Service Section, RPhD, and colleagues at
RC&IG workshop for the fabrication of the mechanical
assembly. The valuable suggestions during the work from
Shri Sajin Prasad, Shri Lalit K Vajpyee, and Shri K. S. Babu
are gratefully acknowledged.
Figure 5: Quantity of sample collected for various sampling durations
at temperature and relative humidity ranging between 24°C and 25°C
and 57%–62%, respectively
Figure 4: Quantity of sample collected in sampling duration of 30 min
for various prevailing relative humidity values
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Kumar, et al.: Thermoelectric cooling module for sampling of tritium in air
Radiation Protection and Environment | Volume 45 | Issue 1 | Januar y-March 2022 21
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conicts of interest.
REFERENCES
1. AERB. Radiation Protection for Nuclear Facilities. Safety Manual,
AERB/NF/SM/O‑2 (Rev. 4). Mumbai: Atomic Energy Regulatory
Board; 2005.
2. Sundar SB, Chandrasekaran S, Ajoy KC, Yuvaraj N, Akila R,
Santhanam R, et al. Monitoring of tritium in CORAL reprocessing
facility. Radiat Prot Environ 2010;33:104‑5.
3. Varakhedkar VK, Baburajan A, Vanave SV, Rao DD, Ravi PM,
Tripathi RM. Evaluation of tritium dispersion in the atmosphere by Risψ
Mesoscale Puff modeling systems using on‑site meteorological parameters
for the nuclear site Tarapur, India. Radiat Prot Environ 2016;39:30‑7.
4. NCRP. Tritium Measurement Techniques. NCRP Report No. 47.
Bethesda, MD: National Council on Radiation Protection and
Measurement; 1995.
5. Poudel B, Hao Q, Ma Y, Lan Y, Minnich A, Yu B, et al. High‑ther moelectric
performance of nanostructured bismuth antimony telluride bulk alloys.
Science 2008;320:634‑8.
6. DiSalvo FJ. Thermoelectric cooling and power generation. Science
1999;285:703‑6.
7. Ghoshal US. Highly Reliable Thermoelectric Cooling Apparatus
and Method. United States Patent US 6,266,962 B1; 2001.
Available from: https://patentimages.storage.googleapis.com/8c/
a1/35/397b9120443c5a/US6266962.pdf.
8. Gurevich Y, Velazquez‑Perez J. Peltier effect in semiconductors. In:
Wiley Encyclopedia of Electrical and Electronics Engineering. New
Jersey, US: John Wiley & Sons; 2014. p. 1‑21. [doi: 10.1002/047134608X.
W8206].
9. Thermonamic. Specication of Thermoelectric Module TEC1‑12715.
Available from: http://www.thermonamic.com/TEC1‑12715‑English.
PDF. [Last accessed on 2022 Feb 02].
[Downloaded free from http://www.rpe.org.in on Wednesday, June 29, 2022, IP: 59.185.236.51]