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Radon mitigation system approach to avoid interferences at the
measurements room of a radioactive laboratory
Luis Alfonso Fernández-Serantes, Alberto Otero-Pazos, Alfonso Calleja-Garcı́a, Marı́a Isabel Fernández-Ibañez,
Andrés José Piñon-Pazos, José Luis Calvo-Rolle
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University of A Coruña,
Departamento de Ingenierı́a Industrial,
Avda. 19 de febrero s/n, 15495, Ferrol, A Coruña, España
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Tel.: +34 981 337400 ext. 3117 Fax.: +34 981 337401
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Abstract
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Radon gas is the second reason of lung cancer, causing thousands of deaths. It can be a problem for people or animals at houses,
workplaces, schools or any building. Due to this fact, its mitigation has become very important to avoid health problems, among
others. Also, radon interferes at radioactive measurements. This study describes how a radon mitigation system was carried out to
reduce interferences in the different works of a radioactivity laboratory. A large set of radon concentration samples is obtained from
measurements at the laboratory. Several mitigation methods were taken into account and the implemented solution is explained in
detail. With it, very good results have been obtained by reducing the radon concentration by 76 %.
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Keywords: Radon, mitigation, positive ventilation, sump system, sealing, radon reduction
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1. Introduction
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Radon is a gas that is produced by the natural radioactive decay of U 238 , which is a very active chemical element
capable of associating with many others and move with them [1]. Uranium exist in almost all rocks and soils of the
planet in small proportions (ppm) [2]. Galicia Autonomy (Spain) is a prone area to radon gas, due to the fact that
granites, one type of rock and soil that have great concentration of uranium, are very common [3].
Radon, which is an inert radioactive gas that is naturally occurring; is odorless, colorless and tasteless [4]. It
is easily released from the soil into the air, where it disintegrates forming various products of short duration which
are known as radon progeny [5]. As these are decay, radioactive and alpha particles are emitted and they adhere to
aerosols, dust and other airborne particles [6]. When people breathe, radon progeny is deposited on epithelial cells
lining the airways where alpha particles can damage DNA and, therefore, cause lung cancer [7] and thousands of
deaths all over the world each year [8]. According to the United States Environmental Protection Agency (EPA),
radon gas is the second cause of lung cancer, after smoking, causing 21 thousand of deaths per year in the United
States [9].
Due its accumulation, radon can be a problem at houses, workplaces, schools or any building where people or
animals are. It came from the soil basement where buildings are placed. Thus, it gets into them through cracks in the
floors, constructions joints, gaps in suspended floors, cavities inside walls or water supply. Normally, radon gas is not
produced by common building materials [8].
Email address: luis.alfonso.fernandez.serantes@udc.es (Luis Alfonso Fernández-Serantes)
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Usually, outdoors radon concentrations are very low. On average, it varies between 5 and 15Bq/m3 [6]. Conversely, indoor concentrations are higher and reach maximums in places like: mines, caves, treatment water plants
and so on [6]. Spanish legislation says that radon average concentration at work places should be less than 600Bq/m3
(300Bq/m3 if workplace with high permanence of workers). Over this value (> 600Bq/m3 ), a mitigation control
system with periodical tests should be implemented to keep radon concentration levels low [10].
With the aim of reducing radon gas concentration at working places there are several mitigation solutions depending on the case. The main generic solutions are:
• Sealing: trying to seal all obvious cracks, gaps and holes in floors or walls to prevent radon from entering the
building. However, in most cases reduction is not effective [11, 12].
• Positive ventilation: installing small fans to blow filtered fresh air into the building. The fundamental principle
is to increase the pressure inside the building in relation with outside pressure, so radon gas cannot flow inside
it[11, 12, 13].
• Sump systems: the purpose is to exhaust the air from inside the building when the concentration reaches a
set point value. Usually, the extraction is forced to improve the performance and to reduce the response time
[14, 12].
• Underfloor ventilation: installing vents at the foundations to provide natural or force ventilation underfloor to
suck or blow radon [12, 13].
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The proposed solutions explained on the present work are based on positive ventilation to mitigate radon concentration. The main aim is to avoid interferences with the working place equipment in a radioactivity laboratory. This
work is focused on the analysis of different steps that have been carried out at the mentioned case. For each step, a
change have been introduce and several measurement have been done. Finally, a comparative is made taken all cases
into account.
This paper begins with a description of the case of study, where the focused installation is described as well as all
the different components used to decrease radon concentration. It follows with the carried out process that analyses
the approach, step by step. Then, the results are shown and finally the conclusions are exposed.
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2. Case of study
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The Environmental Radioactive Laboratory carries out different works related to radioactive measurements and
the analysis of the obtained data. These tasks are made at a specific room (measurement room), where all the different
equipment is and where a radioactivity interference was found. The case of study is described in detail in the following
subsections.
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2.1. Environmental Radioactive Laboratory
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The proposal has been implemented at the “Laboratorio de Radiactividad Ambiental” (LRA) of the University of
A Coruña, located in Ferrol (Galicia Autonomy) at the Faculty of Engineering. The laboratory carries out different
researches about the radiological characterization of soils on the north coast of Galicia or an specific agreement with
the Nuclear Safety Council, on a program of Environmental Radiation Monitoring, for example.
The measurements of characterization of soils are done in a small room, which is presented after, where a concentration of radon gas has been detected. This laboratory measurement room was chosen because it is a small room,
closed and with few ventilation, an appropriated place where radon gas concentrations can be high.
Due to the fact that the presence of this gas could affect the measurements carried out in this laboratory, different
mitigation methods were studied. The studied method were proposed and, finally, some of them were implemented
with the consequently reduction of the radon gas.
The radon level was measure in the laboratory measurement room, showing an enough important activity that
could affect and disturb the measurements.
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2.2. Laboratory measurement room
The LRA measurement room is a small room of 20.60m2 where all radioactive measurements are done and where
the used equipment is placed. The room is located inside the LRA, second floor of the building. It is west-oriented
and its dimensions are, approximately, 3.20 meters high, 5.80 meters long and 3.55 meters wide. Figure 1 shows what
the room looks like.
Figure 1. Measurement room
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The building structure and the floor are made of reinforce concrete with the walls made of coated bricks and
painted. Due to the fact that the equipment is very heavy, it was necessary to install steel sheets on the floor with
the aim of distribute the weight uniformly. To get inside this room, there is a door that connects with the chemistry
laboratory and the office. Also, there is a window situated on the west wall where the different mitigation systems are
installed.
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3. Radon mitigation solution approach
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With the aim of reducing radon gas concentration and avoiding perturbations in the equipment, several mitigation
methods have been taken into account. The implemented solution had to consider building limitations and restrictions.
On the other hand, due to the fact that the measurement room is independent of the office, the applied solution does
not disturb the work environment.
The measurement room is on the second floor. Owing to this fact, some methods are impossible to carry out, such
as underfloor ventilation. Also, sealing cannot be implement due to the age of the building and because there are
different entrances to the room. Thus, for the same reason, sump systems could not be installed. In any case, radon
gas would have entered the measurement room through the cracks.
Instead, the positive ventilation could be a good solution because of its viability and low cost implementation.
Finally, due to the reasons described above, this is the chosen solution to mitigate radon.
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Figure 2. Measurement room with one fan
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For measuring radon concentrations the AlphaGuard PQ 2000PRO was used. This equipment measured the concentration of radon gas every ten minutes every day of the year. With the obtained values, the equipment do the
avarage as in equation 1.
n
1 X
Average = ·
xi
(1)
n i=1
It also calculates the uncertainty as the standard deviation using the equation 2.
sP
n
2
i=1 (xi − x)
Uncertainty =
(n − 1)
(2)
3.1. Positive ventilation solution
Positive ventilation consists of installing fans to blow fresh and filtered fresh air into the measurement room, by
pressurizing to prevent radon from entering and diluting it [11, 12]. To implement the selected solution, two fans and
an air conditioning system were installed. Different steps were followed to carried out this option.
The fans were installed with the aim of pressurizing and diluting radon gas. A second fan has been necessary
installed due to the fact that only one unit was not enough.
Also, an air conditioning system was installed to reduce air humidity, keep the temperature around the value
of 20 Celsius degrees and to weatherize the measurement room. Moreover, this system blows filtered air into the
measurement room, contributing to radon mitigation and its stability throughout the year. Air conditioning was
necessary to avoid variations at measurement conditions and because electronic device performance is better at a
constant temperature and low humidity.
These systems also benefits the installation because they reduce condensation.
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Figure 3. Measurement room with two fans
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They were installed at the unique window of the room, so the works done for their installation were minimal.
Figure 1 shows the measurement room where all the systems have been installed.
The components used to decrease radon concentration are the following:
• Fans: The used fans are the model HV-230 from S&P. These fans characteristics are:
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– Rotating speed of 1250 revolutions per second.
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– Extraction caudal at high speed of 600m3 /h and at low speed of 450m3 /h.
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– Impulsion caudal of 330m3 /h.
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The power that the fans consume is 34 watts each, and the absorbed current is 0.15 amperes.
• Air conditioning: The used air conditioning is the model PCA-RP50xB7KA from Mitsubishi Electric. The are
conditioning characteristics are:
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– For cold, 5 kW and 4300 kCal/h.
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– For hot, 5.5 kW and 4730 kCal/h.
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– Sound level, for low speed, around 32/40 dB.
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3.2. Steps followed until the final solution is reached
In this subsection, the steps carried out to get the desired results are explained:
a) The first step was the installation of one fan, to pressurize the measurement room, see figure 2. Radon concentration
was measured some time later, once its level had achieved a steady state, but the level did not decrease enough
with this action.
b) Due to this fact, as it is shown on figure 3, a second fan was installed to increase the pressure inside the measurement room. After several measurements, it was noticed that the introduced air was enough to reduce radon
concentrations, thus avoiding interferences in the measurements.
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Figure 4. Measurement room with all systems
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c) Once the fan systems were implemented, air conditioning was installed, see figure 4. Furthermore, it blows air
inside the measurement room and weathered it at constants condition during all time. The air conditioning helps
to have stable measurements and, thus, reducing the uncertainty. This fact is because of the temperature control of
the room and, also, because of the reduction in humidity.
d) In the end, all systems -fans and air conditioning- were working together with the aim to decrease radon concentration and to have repeatable conditions for the measurements. Also, different analysis were done periodically to
keep control of radon levels in order to know how it varies along the year.
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In this case, fans work in impulsion mode and the air conditioning works keeping the temperature around the value
of 20◦ C and controlling air humidity.
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4. Results
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In this section, the radon concentration measurements for the different cases mentioned above are shown. At first,
the radon concentration was measured on different days to quantify its level. Table 1 shows the average concentration
for the period from 25th of April to 23th of November of the previous year, without any mitigation solution.
Radon-222 activity
Average
Uncertainty
Maximum concentration
Number of measurements
Concentration (Bq/m3 )
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Table 1. Concentration before applying any solution
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Then, from the 30th of November of the previous year to the 25th of January of the next year, one fan was installed
and measurements were carried out. The next period of measuring was from the 25th of January to the 01 st of
December. During this period, a second fan was installed and several measurements were taken with both fans
working. Table 2 shows concentration during these times. The analysis of the concentration while the mitigation
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solutions were implemented, from 30th of November of the previous year to the 01 st of December, revealed how it
decrease to the values shown in table 2.
Radon-222 activity
Average
Uncertainty
Maximum concentration
Number of measurements
One fan (Bq/m3 )
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Two fans (Bq/m3 )
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One/Two fans (Bq/m3 )
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Table 2. Concentration after fans installation
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After the installation of the two fans, an air conditioning system was installing, thus achieving the results shown
in table 3. The period when this system (both fans and air conditioning) is on goes from the 01 st of December to
nowadays. At that moment, the value of radon concentration is very low. Finally, table 4 shows the concentration
reduction summary by using the different components of the mitigation solution.
Radon-222 activity
Average
Uncertainty
Maximum concentration
Number of measurements
Concentration (Bq/m3 )
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Table 3. Concentration after air conditioning installation
Radon-222 activity
Average
Uncertainty
Average
Uncertainty
Average
Uncertainty
Average
Uncertainty
Average
Uncertainty
Mitigation solution
One fan
One fan
Two fans
Two fans
Two fans
Two fans
One or two fans
One or two fans
Two fans and air conditioning
Two fans and air conditioning
Compared with
Any method
Any method
One fan
One fan
Any method
Any method
Any method
Any method
Any method
Any method
Reduction %
62.8
50.3
35.6
43.7
76.0
72.0
73.8
65.8
76.0
75.7
Table 4. Concentration reduction after mitigation systems installation
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The figure 5 is a picture of the measurement room with all the systems applied. It is possible to see the two fans
and the air conditioning system.
Also, the figure 6 shows a summary of the reduction of the radon gas with the different systems, showing how it
get reduced when the methods are implemented.
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Figure 5. Picture of the measurement room with all systems
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Figure 6. Evolution of radon gas measurement with the different systems
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5. Conclusion
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With the radon mitigation solution approach explained in this document, very good results have been obtained.
As it is shown in the results section, after the installation of the different removing systems, the radon concentration
decreased in a very significant way. It was reduced up to the value of 76 %. In this way, the implemented solution
avoids the interferences at the laboratory measurements.
Positive ventilation achieved good results by pressurizing the measurement room and avoiding radon entrance.
For this purpose, two fans were installed with the aim of reducing the radon concentration to a low value. Also, air
conditioning contributes slightly to radon mitigation and allows a very good repeatable condition performance for the
measurements.
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6. Acknowledgments
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This research has been funded by the University of A Coruña, and by the Spanish Ministry of Education, Culture
and Sport (grant for Collaboration in University Departments).
We would like to express our utmost gratitude to the Nuclear Security Council of Spain, without whose collaboration this research would not have been possible.
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7. References
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