atw Vol. 63 (2018) | Issue 3 ı March
initial action, the detached lifted
coolant carrying by drone is similar in
the starting state. However, the non
in-site power is supplied by the battery
in the drone’s flying system. ‘Passive’
means that the power is not used from
the in-site system of the plant. The
battery is supplied from the external
energy source. So, the drone could be
considered as one for constructing the
passive system in NPPs. There are the
comparisons of the passive systems in
| | Tab. 1.
List of passive systems.
Non in-site electricity
Non in-site electricity
Non in-site electricity,
Battery or engine
installed in drones
| | Fig. 1.
Simplified configuration of NPPs in the accident.
| | Fig. 2.
Passive systems of NPPs.
ENVIRONMENT AND SAFETY 159
There are some passive safety
system related papers. Cho et al.
worked for the passive auxiliary feedwater
system (PAFS) [Cho et al. 2016].
In addition, Gou et al. studied that the
thermal hydraulic investigations were
done for a new type of passive residual
heat removal system (PRHRS) [Gou et
al. 2009]. Park et al. showed that the
advanced modular integral type rector
is investigated by the natural circulation
performance [Park et al. 2007].
Figure 1 shows the simplified configuration
of the NPPs in the accident
where the water tank is carried by the
drones. The water falls as the free-fall
for the water tank in which the water
are entering to the reactor building.
The passive action by the free-fall is
done completely, which could be used
in the case of the piping based
injection system failure. There are
some passive systems in Figure 2
where the natural circulation and
gravity are shown. In this paper, the
free-fall is described. There are the
conceptual comparisons of passive
systems of NPPs in Figure 3 that the
water falls down from flying drone
containing water tank and the water is
injected from the conventional water
tank attached to the reactor building.
This is revolutionary different from
the conventional passive system in
which the piping integrity should be
kept. Otherwise, in the free-fall
system, the reservoir could be an
active role on or after accident. So,
| | Fig. 3.
Conceptual comparisons of passive systems in NPPs.
this means that the post-accident
safety system is installed in this new
system. In the current commercial
NPPs, there is not any kind of the
post-accident safety system. It has
been experienced in Chernobyl as well
as Fukushima cases that it was impossible
to make the coolant enter into
the reactor core where the nuclear
fuels were continuing the nuclear
reactions and producing the heats.
Table 2 shows the specifications of
the condensate water storage tank as
the emergency water tank [The Virtual
Nuclear Tourist, 2016]. Newly developed
drone could supply 500 kg [Air-
Mule, 2016]. Therefore, it takes about
1,137 times supplies to carry the tank
water. If one uses 10 units of drone, it
reduced to about 113 times. However,
| | Fig. 4.
Major factors for the free fall of coolants.
(Condensate storage tank)
Mass flow rate
| | Tab. 2.
Specification of emergency water tank.
the coolant carrying quantity is
changeable by the situation and
2.2 Cooling by the free-fall
The modeling of this paper is to show
the capability of the free-fall coolant
in which this should make the
enhanced integrity to the piping based
injection systems. So, the major factor
of the fee-fall coolants is the coolant
quantity with mass flow rate which is
(567,812 liters, 568,500 kg water)
200 ~ 400 gallons/min.
Environment and Safety
Applied Reliability Assessment for the Passive Safety Systems of Nuclear Power Plants (NPPs) Using System Dynamics (SD) ı Yun Il Kim and Tae Ho Woo