2. 2011 Tōhoku Earthquake
9 on Richter scale,
with duration 140-
160s
Fukushima is 178 km
from the earthquake’s
epicentre
Power plants sustain
minor damage and go
into shutdown
(scram)
Power lines are
destroyed by the
earthquake
3. Anti-Seismic design
Design basis was for 7.9 Richters
Historically, earthquakes greater than the design values had been
recorded in the area
Damage from earthquake cannot be estimated due to ensuing events
5. Earthquake’s Aftermath
Workers evacuate plants after nationwide alert
Skeleton crew of 50 is left on Daiichi site to manage crisis
Devastating tsunami follow
7 waves of ~70mph
Peak wave height ~14m
Wave barriers (10m high) could not completely stop waves
Emergency backup power is lost due to flooding
9. BWR Mk.I Layout
Operating
conditions
600K 70 bar
Pictures source:
GE Hitachi Nuclear Energy
10. BWR Mk.I Layout
Operating
conditions
600K 70 bar
Pictures source:
GE Hitachi Nuclear Energy
11. BWR Mk.I Layout
Operating
conditions
600K 70 bar
Pictures source:
GE Hitachi Nuclear Energy
12. Reactor loss of cooling
Radioactive rods inside reactor heat up
The low-pressure core spray, residual
heat removal, low-pressure coolant
injection system main pumps and the
automatic depressurization systems all
require AC power
Reactor cannot contain
pressure/temperature and leaks in
several points
Release valves were assumed to be
working
Primary containment failure and
Unit 1 Units 2-3
gradual core meltdown
15. Spent fuel assemblies
• 1000-1500 tonnes of water required to fill
each pool
• The heat from each pool evaporates 70
tons per day
• Cladding triggers hydrogen explosions
after 500oC
20. Lack of H&S from operator
Lack of seismic and tsunami protection in Design Basis
Probabilistic Safety Analyses (PSA) underestimated dangers
Reactor upgrades were recommended by regulatory authorities,
including the Japanese government
Numerous studies found Fukushima prefecture power plants
inadequately protected
The company’s own engineers, nuclear safety experts and even
court orders were ignored, claiming all hazard reports were
unrealistic
21. Cause: deliberate oversight
TEPCO claimed that they had been afraid to consider the
risk of such a large tsunami, fearing admissions of risk could
result in public pressure to shut plants down
“There were concerns that if new countermeasures against severe
accidents were installed, concern would spread in host communities that
the current plants had safety problems,” the report said.
22. Nuclear & Industrial Safety Agency
NISA had deemed the plant operations as safe
Part of the ministry of trade, economy and industry
Ministry also responsible for promoting Nuclear Energy
Conflict of interests
"NISA’s lack of independence from the trade ministry, which promotes
the use of atomic power, hampered a quick response to the disaster at
Tokyo Electric Power Co.’s Fukushima Dai-Ichi plant this year“
Key people fired and NISA was disbanded on 2012
Nuclear Regulation Authority formed September 2012
23. References
Fukushima Nuclear Accident Interim Report, TEPCO, November 2011
Fukushima Dai-ichi NPP Accident, International Atomic Energy
Agency, June 2011
Lessons Learned and Recommendations from the Fukushima Dai‐ichi
Nuclear Accident, National Nuclear Security Administration, May
2012
Japanese earthquake and tsunami: Implications for the UK nuclear
industry Final Report, HSE, September 2011
Executive Summary of the Interim Report, Investigation Committee
on the Accidents at Fukushima Nuclear Power Stations of TEPCO,
December 2011
Reuters, NY Times
Allthingsnuclear.org, Wikipedia
