Measures to Prevent Damages from Natural Disasters: The maximum seismic motion and height of tsunamis are reevaluated based on the up-to-date
knowledge of seismology, and the hazards of active faults close to the plant site are
reexamined. The seawalls are reconstructed and reinforcement structures are added
to the plant components, if necessary. Countermeasures are also taken against other
natural disasters such as tornados, volcanic eruptions, and external fires.
Installation of Watertight Structures and Countermeasures Against
Internal Flooding: Watertight doors are installed to the reactor building. The
structures of ventilation openings are redesigned to prevent water invasion.
Countermeasures against internal flooding are also taken by installing pipe and
cable penatration seals, water protection covers, weirs, and so on.
Reinforcement of Emergency Power Supply and Water Injection: Not only
permanent but also mobile equipment are installed for emergency power supply and
water injection considerig beyond-design-basis situations. The capacity of these
equipment are designed with enough margins to compensate for maintenance
outage and equipment failres. The storage locations and connection points for the
mobile equipment are diversified. Water injection to the spent fuel pits is also
reinforced.
Prevention of Reactor Containment Damage: Auxiliary containment spray
systems are installed, which can be supplied by permanent and mobile water
injection pumps. Water injection lines to the bottom of containment vessel are
considered for cooling core debris. Filtered containment venting systems are
installed to prevent damage of the containment vessel from overpressure. Measures
to prevent hydrogen explosion are taken by monitoring, evacuation, and recombination of hydrogen gas.
Preventing Dispersion of Radioactivity: Measures to prevent hydrogen
explosion in the reactor building are taken as well. Water cannon trucks are
equipped for mitigating dispersion of radioactivity in case the containment vessel or
the spent fuel pits are damaged. Pollution control screens are installed at the
drainage canal exits.
3 What Changed After Fukushima
3.1 All-Hazards and Multiple Disasters
Though the basis of nuclear safety did not change even after Fukushima, some
problems have emerged that caused the lack of defense-in-depth. We should learn
lessons on these points and reflect them in taking concrete measures for safety
enhancement.
Firstly, we must be concerned more about preparedness for all-hazards and
multiple disasters than had been. The safety barriers against tsunamis were very
fragile, because people in the nuclear industry were so concerned about seismic
38
K. Furuta and T. Kanno
knowledge of seismology, and the hazards of active faults close to the plant site are
reexamined. The seawalls are reconstructed and reinforcement structures are added
to the plant components, if necessary. Countermeasures are also taken against other
natural disasters such as tornados, volcanic eruptions, and external fires.
Installation of Watertight Structures and Countermeasures Against
Internal Flooding: Watertight doors are installed to the reactor building. The
structures of ventilation openings are redesigned to prevent water invasion.
Countermeasures against internal flooding are also taken by installing pipe and
cable penatration seals, water protection covers, weirs, and so on.
Reinforcement of Emergency Power Supply and Water Injection: Not only
permanent but also mobile equipment are installed for emergency power supply and
water injection considerig beyond-design-basis situations. The capacity of these
equipment are designed with enough margins to compensate for maintenance
outage and equipment failres. The storage locations and connection points for the
mobile equipment are diversified. Water injection to the spent fuel pits is also
reinforced.
Prevention of Reactor Containment Damage: Auxiliary containment spray
systems are installed, which can be supplied by permanent and mobile water
injection pumps. Water injection lines to the bottom of containment vessel are
considered for cooling core debris. Filtered containment venting systems are
installed to prevent damage of the containment vessel from overpressure. Measures
to prevent hydrogen explosion are taken by monitoring, evacuation, and recombination of hydrogen gas.
Preventing Dispersion of Radioactivity: Measures to prevent hydrogen
explosion in the reactor building are taken as well. Water cannon trucks are
equipped for mitigating dispersion of radioactivity in case the containment vessel or
the spent fuel pits are damaged. Pollution control screens are installed at the
drainage canal exits.
3 What Changed After Fukushima
3.1 All-Hazards and Multiple Disasters
Though the basis of nuclear safety did not change even after Fukushima, some
problems have emerged that caused the lack of defense-in-depth. We should learn
lessons on these points and reflect them in taking concrete measures for safety
enhancement.
Firstly, we must be concerned more about preparedness for all-hazards and
multiple disasters than had been. The safety barriers against tsunamis were very
fragile, because people in the nuclear industry were so concerned about seismic
38
K. Furuta and T. Kanno