FEASIBILITY STUDY OF VENTILATION DESIGN FOR UNDERGROUNDFACILITIES
Naoki Katsumata1, Ryoji Yahagi2, Hiromi Kurosaki2, Shigeru Kubota1
Nuclear Waste Management Organization of Japan (NUMO) 1
1-23, Shiba 4-chome, Minato-ku, Tokyo 108-0014 JapanSHIMIZU CORPORATION2
2-16-1, Kyobashi, Chuo-ku, Tokyo 104-8370 Japan
Key words; operational safety, ventilation system, underground facility layout
Abstract
NUMO considers not only post-closure safety but also pre-closure safety is important to ensure the safety ofDGR (Deep Geological Disposal). Radiation safety is important to ensure safety during the pre-closure phase,but occupational safety is also important as well. Functional requirements for ensuring occupational safety arethree requirements, such as maintaining the working environment, prevention of occurrence of accident and its
enlargement and securing of evacuation routes. In the DGR, in order to maintain the working environment,
supplying ventilation air flow rates to the underground and keeping the ambient temperature below 37°C should
be attained (Ordinance on Industrial Safety and Hearth). The underground facility has very long disposal tunnels
and it forms an extensive repository. Therefore, to confirm the feasibility of design for ventilation systemessential to the workers during construction and operation is important. NUMO conducted a case study toconfirm the feasibility of the ventilation system to the example of preliminary design in the underground facility
at the DGR, so the outline is introduced.

1.

Introduction

It is important to maintain a good working
environment by studying the preliminary design
method of ventilation system in the DGR (DeepGeological Repository). The ventilation systemshould satisfy the following three requirements tomaintain the working environment.
i. Supplying fresh air for the workers in tunnels.
ii. Dilution and elimination of harmful gas anddust.
iii. Cooling the air generated by geothermal andmechanical heat.
In order to satisfy the requirement i and ii, theminimum wind velocity is preset with reference tothe guidelines [1]. Also, it is necessary to note themaximum wind velocity prescribed by Enforcement
Ordinance of the Mine Safety Act (Ordinance No.16).
In order to satisfy the requirement iii, it is necessary
to maintain the temperature in the tunnel prescribedby Ordinance on Industrial Safety and Health(Ordinance No.611).
Table 1 shows the requirements and criteria fordesigning the ventilation system.

Table 1 Design requirements and criteria ofventilation system.

The ventilation air flow rates are the air quantity
required to dilute and eliminate the harmful gas anddust generated by the tunnel excavation work. The
detail setting methods are described in 3.3.
The maximum wind velocity is a requirement forsafety of the work environment. It was set to 7.5 m/sor less by reference to an Enforcement Ordinance ofthe Mine Safety Act (Ordinance No.16).
Temperature in the tunnel is a requirement for
maintaining a good working environment. It was set
to 37°C or less with reference to Ordinance on
Industrial Safety and Health (Ordinance No.611). The
ventilation system and the air cooling system shouldbe planned to satisfy these design requirements.
Firstly, the air quantity required to maintain theworking environment was calculated. It is required todilute the dust and to exhaust the gasses generated by

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanexcavation work and necessary for the exhalation ofworkers.
After conducting the ventilation network analysis,
the result should be checked whether the air quantity
satisfies its requirement or not. And the maximum
wind velocity should also be checked for its criteria.
If the temperature of working environment ishigher than its criteria, a cooling device should beinstalled in the tunnel.
2. Design method of ventilation system
2.1 DGR layout and ventilation access
DGR layout and the ventilation access in theexcavation area in crystalline rocks are shown in Fig.
1 and one in sedimentary rocks is shown in Fig. 2. An
excavation area is the target one of the case study.

Fig. 1 DGR layout and ventilation access for theperiod of construction in crystalline rocks.

depth of the underground facility was set at 1,000 mof crystalline rocks and 500 m of sedimentary rocks.
The surface temperature was preset to 15°C andthe geothermal gradient is set to 3°C/100m [2]. In
other words, it means the temperature of rocks in theunderground facility is estimated 45°C for crystallinerocks and 30°C for sedimentary rocks.
Furthermore, in the case of sedimentary rocks,
there is a possibility that methane gas will bedischarged.
Fig. 1 shows that panel No.6, the farthest panel
from the exhaust shaft, is under excavation. At thesame time, panel No.5 is under emplacement of HLW
and backfilling of the disposal tunnels. For the otherpanels backfilling are completed.
Fig. 2 shows that panel No.6 is under excavation.
At the same time, panel No.5 is under emplacementof HLW and backfilling of the disposal tunnel. For
the other panels backfilling are completed.
Although the excavation and emplacement works
are carried out in parallel, the work flow lines are set
in order that these works can be done separately.
2.2 Concept of basic design
In order to ventilate the working tunnels, it isnecessary that the ventilation access forms a circuit asshown in Fig. 3.
The underground facility is connected to thesurface through the air intake shaft and the exhaust
shaft. These tunnels and shafts form a circuit.
Therefore, it is possible to ventilate by installing an
exhaust fan at the outlet of the exhaust shaft.

Fig. 3 Conceptual diagram of ventilation circuit [3]Fig. 2 DGR layout and ventilation access for theperiod of construction in sedimentary rocks.
The final disposal plan requires to disposing
40,000 vitrified waste packages for HLW. NUMO
planned the conceptual DGR that consists of 6 panels.
The total extension of tunnels is about 30 km. It also
has 6 shafts and 1 ramp.
Two kinds of geological environment, crystalline
rocks and sedimentary rocks, was assumed. The

Ventilation fans should be installed not only at theoutlet of the exhaust shaft, but also in the tunnels. For
the reason mentioned above, the total extension of thetunnels and shafts which needs ventilation accessbecomes long and many fans have to be installed and
it is necessary to balance the air quantity, velocity
and direction (vector of wind velocity). This should
be studied by using ventilation network analysis.
2.3 Basic policy of dead-end disposal tunnel
Fig. 4 (a) shows the situation during excavating thedisposal tunnel. In this case, the disposal tunnel forms
a dead-end. In order to form a ventilation circuit, theventilation ducts and fans should be installed insidethe disposal tunnel as shown in Fig. 4 (b).

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

Table 2 Conditions of ventilation network analysis
for each caseFig. 4 Ventilation schematic illustration for dead-end
tunnel [3]2.4

Design of excavation completion disposal
tunnels
There is no person at always in the excavation
completion area. However, there is a possibility that
response to emergency works may occur, so it isnecessary to ventilate.
There are many excavation completion disposal
tunnels and a large air quantity is necessary due toabove reasons.
Therefore, the many disposal tunnels are connectedby a duct and ventilation by a high pressure fan. By
this ingenious ventilation policy setting, air quantity
can be reduced.

Fig.5 Ventilation access of a single stroke
3.
Analytical studies
3.1 Outline of Ventilation network analysis
The ventilation network analysis is used to checkthe ventilation air flow rates and the maximum windvelocity at the all tunnels and shafts of calculation
target area. Ventilation network analysis wasconducted by two types of analysis code,“KAZEMARU” and “ONTA”.
A one-dimensional pipeline calculation code
“KAZEMARU” is applied to the calculation of airquantity and wind velocity. In case of evaluating thethermal environment, “ONTA” is further applied. By
the way the validation of “KAZEMARU” has been
conducted and its applicability was verified in theactual mines [4].
“KAZEMARU” calculates the static pressure intunnels based on Bernoulli's principle and outputs theair quantity in the tunnel.
The parameters to be input are the tunnel
cross-sectional area, tunnel length, friction coefficient(parameters related to the roughness of the tunnel
wall surface), and the additional length (equivalenttunnel length considering pressure loss at the cornerof the tunnel, branching or confluent area) [5].
3.2 Condition of ventilation network analysis
Conditions of ventilation network analysis for eachcase were set as shown in Table 2.

The CASE-1 can be defined as the reference case.
The calculation results of the others were comparedwith CASE-1.
In the CASE-1, the ventilation access in theexcavation area is set as shown in Fig. 1. In thecrystalline rocks case, the disposal repository locatesat the depth of 1,000 m. The ventilation accessbecomes longer than the case of sedimentary rocks.
Because many construction machines are used atexcavation area, the large air quantity should berequired.
The CASE-2 represented the condition of an
emplacement area as shown in panel No. 5 of Fig. 1.
In accordance with our disposal plan, the process ofemplacement would be carried out by remote works.
The continuous ventilation is not necessary for theemplacement area. In this case, it is sufficient toventilate only the tunnel of backfill. In this kind ofsituation, it can be expected that the air quantity canbe reduced.
The CASE-3 represented the condition of aconstruction area as shown in panel No.6 of Fig. 2. In
this case, the length of the shaft is shorter than thecase of the crystalline rocks. It is expected that thecapacity can be reduced.
In the CASE-4, it is assumed that methane gas isgenerated in the same area as CASE-3. In this case,the minimum wind velocity would faster thanCASE-3.
3.3

Method for setting the ventilation air flowrates
In this section, the procedure for setting theventilation air flow rates would be indicated.
The ventilation air flow rates are calculated bysumming of the air quantity which is required todilute the gas and necessary for exhalation ofworkers.
The main cause of dust generation is thought to be
due to blasting and shotcreting. Exhaust gas isgenerated by drilling, chopping, mucking, haulage,shotcreting and installation of rock bolts. Thesevolumes are specified in the guideline [1]. For
information of guideline, because the dust is collectedby the electric dust collector, it is not counted as theventilation air flow rates.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

Each ventilation air flow rates are calculated basedon the method of the guideline. Fig. 6 shows the one
example of calculation result of the ventilation air
flow rates for CASE-1.
In this case, the ventilation air flow rates are thesum of the maximum value of the air quantity
necessary to dilute for gas and the air quantity
necessary for exhalation of workers.
The maximum value 6.7 m3/s should be chosen as
the ventilation air flow rates required to dilute thedust and gas. On the other hand, the ventilation air
flow rates required for exhalation of workers arecalculated to 0.5 m3/s.
Therefore, the ventilation air flow rates are set to
7.2 m3/s for each excavating tunnel in crystalline
rocks.
Finally, the total volume is calculated bymultiplying the ventilation air flow rates by thenumber of excavating tunnels.
In the same way, the ventilation air flow rates arecalculated for each case.

・ It is evident from the result of CASE-1 thatseveral fans enable to supply enough air eventhough the ventilation air flow rates are verylarge.
・ In the emplacement area, the capacity of the fan issmaller than the one in the excavation area. The
cause of this result is the difference of the numberof working tunnels (CASE-2).
・ Even at the same depth, in case of assuming
methane gas, should be required about doubled,
therefore, far more capacity by many fans areneeded for keeping the air flow.
4.2 Maximum wind velocity
CASE-1, 2 and 3 have resulted in that maximum
wind velocity satisfied with the design requirement,
below 7.5 m/s, as shown in Table 1.
CASE-4 has resulted in over the criteria ofmaximum wind velocity in this analysis condition.
The cause of this result is that the large air quantity isrequired to ventilate the methane gas.
In this case, we should expand the width of a crosssection of the tunnel from 5 m to 8 m.
It enable us to satisfy the maximum wind velocityas show in CASE-4’, Table 4.
Table 4 Results of the ventilation network analysis
for maximum wind velocity

Fig. 6 Example of ventilation air flow rates at thetime of excavation (crystalline rocks)
4. Results of Ventilation Network Analysis
4.1 Ventilation air flow rates
The results of the analysis are shown in Table 3.
After conducting the ventilation network analysis,
the result should be checked whether the air quantity
satisfies its requirement or not. And the maximum
wind velocity should also be checked against its
criteria.
Table 3 Results of the ventilation network analysis
for ventilation air flow rates

The results of the analysis suggested as follows.

4.3 Thermal environment analysis
In conducting the thermal environment analysis, it
is also important to consider the heats generated by
the construction machines in the tunnels.
Before conducting the thermal environment
analysis, the heats generation rates generated by theconstruction machines in the disposal tunnels arecalculated in accordance with the guideline.
In addition to the air quantity of tunnels obtainedby ventilation network analysis and the temperatureof the tunnel wall, the heats generated by theconstruction machines are preset on the “ONTA”
code.
As a result, the temperature of working
environment, increased to maximum 41°C as shownin Table 5, CASE-1.
Without considering the heats generated by theconstruction machines, the temperature in the tunnel
increased to maximum 40°C due to geothermal.
These results indicate that the influence ofgeothermal is dominant as compared with the heats
generated by the construction machines.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

The result of CASE-3 where the disposal tunnels
are located in the depth of 500 m and the thermal
environment is lower than CASE-1 supports the factthat geothermal influence is the maximum
consideration.
In order to maintain the good working environment,
the temperature in the tunnel where the workers areworking on must be kept below 37°C (Ordinance on
Industrial Safety and Health No. 611). Therefore, it isnecessary to install the air cooling system. The
capacity of the air cooling system was calculated byONTA. By the parameters input again based on theguidelines [1] relating to the air cooling system andthe temperature calculation was carried out. As aresult, it was possible to preliminary design an aircooling system to keep it below 37°C.
Table 5 Results of thermal environment analysis

REFERENCES
1. Japan Construction Occupational Safety and
Health Association, “Ventilation technicalguideline of tunnel construction” (2012) [InJapanese].
2. W. Taniguchi et al., “Fundamental Properties ofGeoenvironment for Design Study of Repository”,
JNC TN8400 99-053 (1999)[In Japanese].
3. Y. Hiramatsu, “Academic knowledge ofventilation studies for mines” (1974) [InJapanese].
4. M. Inoue, “Development and promotion of
Practical Use of the User Friendly Ventilation
Network Simulation Software”, Journal of MMIJ
Vol. 108(1) (1992) [In Japanese].
5. H. L. Hartman et al., “Mine Ventilation and air
conditioning, third edition”, John Wiley & Sons
Inc.(1997).

This study focused on maintaining a good working
environment in the disposal tunnels. If themaintenance or repair work is required in the accesstunnel, the local air cooling system or mobile rest
station should be installed to maintain the goodworking environment.
5.

CONCLUSIONS
Design method of ventilation system and air
cooling system were prepared in order to maintain theworking environment at excavation and operation ofunderground facilities. In this study of preliminary
design of ventilation system, it was available toconsider the balance of air quantity and position offans by using KAZEMARU.
In addition, it was confirmed that their systems
could be planned with generally equipment’s byanalytical studies of ventilation system and air
cooling system for underground facilities which weredesigned in an assumed geological environment.
ACKNOWLEDGMENTS

Advice and comments given by Dr. MasahiroInoue, associate professor of Kyushu University,
have been a great help in this study, and he kindly
offered the ventilation network analysis program“KAZEMARU Basic” he developed. Without hisguidance and persistent help this paper would nothave been possible. And we pay our heartfelt respects
and gratitude to those who worked so hard for us.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan