atw Vol. 63 (2018) | Issue 3 ı March
ENVIRONMENT AND SAFETY 158
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Department of Nuclear
Science and Research Branch
Islamic Azad University, Tehran,
Reactor and Nuclear Safety
Nuclear Science and Technology
Research Institute (NSTRI), Tehran,
Applied Reliability Assessment for the
Passive Safety Systems of Nuclear Power
Plants (NPPs) Using System Dynamics (SD)
Yun Il Kim and Tae Ho Woo
1 Introduction A new kind of passive system is investigated in case of an accident in nuclear power plants
(NPPs). Conventional passive systems have the limitations in the conditional integrity like the piping system of the
coolants. In this paper, the free-falling of emergency coolants are proposed where the flying machine, drone, is imported
to carry out the coolants on the upper position of the containment building. In the cases of the Fukushima and Chernobyl,
the piping systems were blown away. So, the emergency coolants couldn’t flow into the reactor core position where the
reactor fuels were making continuous very high energy without stabilizing of the power level. Although the integrity of
the piping injection systems have been investigated as the good conditions, the previous history couldn’t give the
satisfactions to the public.
During the Fukushima disaster, the
operator had been seeking for the
prime minister to take a permission to
open the gas leak valve in the containment
building when the reactor pump
was out of order and the hydrogen
gases were produced continuously.
Eventually, the hydrogen explosion
happened and the four plants were
collapsed within several days after
East-Japan earthquake impact on the
Fukushima coast and its related areas.
Furthermore, even if there was an
opportunity to make use of the sea
water in order to cool down the
reactor core, the operator didn’t use it
for keeping the expensive reactor
structure from the saluted sea water
in which the material corrosions could
been happened and the material could
be in the significantly damaged situation.
Then, all kinds of the cooling
systems were gone permanently.
The dangerous radioactive contaminations
to the environment have been
done continuously. Considering the
case of the Fukushima nuclear accident,
the piping system has the crucial
fault that the safety system can’t
make any role in the post-accident or
on-accident. Piping in the NPPs should
be incorporated with the alternative
coolant supply method. So, the
detached system from plant building
could be imagined in this study.
The merit of the passive system is
operated without in-site electricity.
So, the natural circulation or gravity
could be acted for the designed system
by injection of the coolants. However,
even the action of switch of the system
operation should be done to start. So,
the manual based stating action is
needed for the operation of passive
system. As the same condition of the
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