POWER March 2021 - 6

Fukushima's Decade-Long
Shadow Made Nuclear Safer
Koji Okamoto, director general of
the Japan Atomic Energy Agency's
(JAEA's) Collaborative Laboratories for
Advanced Decommissioning Science
(CLADS), can pinpoint the specific moment
that cemented his calling. Ten
years ago, he was a University of Tokyo
nuclear engineering professor working
on nuclear safety measures as part
of a government council. He was on a
business trip in the UK when he first
learned a 3-minute, magnitude 9.0 temblor
had rocked Japan's eastern coast
on March 11, 2011, inundating it with a
series of tsunami waves as tall as 38.9
meters (130 feet). The next day, though
his business took him to Germany, he
watched aghast on television as the crisis
amplified into a nuclear emergency
at Tokyo Electric Power Co.'s (TEPCO's)
six-unit Fukushima Daiichi Nuclear Station,
and prompted the first hydrogen
explosion at Unit 1, severely damaging
its reactor building.
" I never imagined that a reactor building
would be destroyed by a hydrogen
explosion, " Okamoto recalled. " I was
shocked, and at the same time decided
to dedicate the rest of my life to the handling
of this accident, " he said.
Okamoto was prescient. In the days
that followed, the catastrophe only
deepened, and in the decade since, it
has had vast, serious and complex implications.
As chronicled in myriad reports
over the past 10 years, the plant
was stricken by a 15-meter (49-foot) tsunami
that inundated most of its backup
power supply (12 of 13 emergency diesel
generators located in the basements
of the turbine buildings), and interrupted
critical cooling functions at the plant's
three units that were operating at the
time: Daichi 1, 2, and 3.
Despite efforts to maintain control,
the reactor cores of Units 1, 2, and 3
overheated, and their nuclear fuel melted.
A reaction between the zirconium of
the fuel-cladding tubes and water vapor
generated a large amount of hydrogen,
and the gas and radioactive materials
discharged into the primary containment
vessel (PCV) when TEPCO depressurized
the reactor pressure vessels (through
wet well venting). The gas containing the
hydrogen leaked and accumulated in the
upper area of the reactor buildings and
6
1. Inside the spent fuel pool of Fukushima
Daiichi Nuclear Power Station Unit 4. Courtesy:
Tokyo Electric Power Co. (TEPCO)
triggered an explosion at Unit 1 on March
12, and, two days later, at Unit 3. At Unit
4, which had been shut down for periodic
inspection, the nuclear fuel had been
transferred to a spent fuel pool (Figure
1). But after the tsunami, both cooling
and feedwater functions were lost, forcing
crews to spray water over the pool.
On March 15, the reactor building of that
unit also exploded.
Ten years later, fuel and debris removal
at Daichi is ongoing. While TEPCO
and the government continue to
grapple with contaminated water accumulation,
work is continuing-despite
COVID-19 challenges-to remove fuel
debris at Unit 2 (Figure 2) and Unit 3's
spent fuel pool. Decommissioning entities
have so far deployed various measures
to remove rubble accumulated in
the buildings and investigate the condition
inside the PCVs using robots. According
to Japan's July 2020-revised
long-term roadmap, fuel removal from
all spent fuel pools is expected by 2032.
Plans also entail installation of a " large
cover " at Unit 1 around 2023, enabling
removal of rubble at Unit 1, but actual
fuel removal is slated to begin at Unit 1
and 2 between 2024 and 2028.
The accident has been especially costly
to TEPCO. As of April 2020, the company
had paid $95 billion in compensation. A
district court in September 2019, however,
acquitted three TEPCO management
members accused of professional negligence
that led to the accident.
On a wider level, Japan, which continues
to be rattled by the Great East Japan
Earthquake and tsunamis that resulted in
at least 22,000 deaths including indirect
fatalities, has ramped up stringent oversight
on its nuclear industry. The toll on
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its nuclear generators has been steep. In
Fukushima's immediate aftermath, Japan
issued safety regulations and reviews
that affected its entire 50-reactor fleet.
Between September 2013-when Ohi
3 and 4 were shut down-and August
2015, when Sendai 1 and 2 restarted,
Japan's entire reactor fleet went black.
As of February 2021, only nine of 33 operable
reactors had restarted, though 16
others had garnered the Nuclear Regulatory
Authority's (NRA's) permission to
restart. Delays have been pegged on
lawsuits to general public distrust of the
nuclear industry-which was worsened
in 2020 by a bribery scandal allegedly involving
Kansai Electric Power Co.
But Fukushima's devastation
also
had wide implications for the global
power industry. In particular, it altered
the trajectory of global nuclear power
during a decade that many anticipated
would mark a " nuclear renaissance. "
In 2009, even as a global financial crisis
bore into investment decisions,
the Nuclear Energy Agency's (NEA's)
high-case scenario projected a 50% increase
in worldwide nuclear capacity-
up from 372 GWe to 616 GWe by 2025,
and virtually doubling to 781 GWe by
2035. In 2020-when total global nuclear
capacity stood at 393 GWe-the
sector's future remained uncertain.
Last year, NEA suggested it faced a
contraction to 354 GWe in a low case
or extraordinary growth to 626 GWe in
a high case.
Much of this uncertainty is driven by
policy. An international fallout began in
the immediate aftermath of the catastrophe,
as governments all over the world
issued a range of political decisions to
address nuclear safety. However, only
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2. A frame grab from an April 2018 video that
shows the inside of the containment vessel at
Unit 2. Courtesy: International Research Institute
for Nuclear Decommissioning (IRID)
POWER | March 2021
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POWER March 2021

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