Vannevar Bush Dean's
Medal Recipient Speaks about Fukushima
the lecture and Q&A
Richard A. Meserve, president of the Carnegie Institution,
international expert on nuclear energy and Tufts University alumnus
spoke about the impact of the Fukushima nuclear plant accident and
also received the first
Vannevar Bush Dean's Medal from Tufts School
of Engineering on Monday, April 4, 2011.
Meserve, A'66, addressed the failure and stabilization of the
Fukushima reactors; health effects; cleanup challenges; likely
impacts on nuclear engineering, construction and regulation; and the
need for planning for extreme events of all kinds.
Meserve chaired the U.S. Nuclear Regulatory Commission (NRC) prior
to becoming president of the Carnegie Institution in April 2003. He
is a member of President Obama's Blue Ribbon Commission on America's
Nuclear Future and chairman of the International Nuclear Safety
Group, which is chartered by the International Atomic Energy Agency.
On March 11, 2011 a 8.9 magnitude earthquake triggered a massive
tsunami to hit northeastern Japan where the Fukushima Daiichi
nuclear power plant is located.
At the time of this extreme event, the Fukushima nuclear power
plant had three of six nuclear
reactors in operation. The other three nuclear boiling water
reactors had been closed for maintenance, inspection, and refueling,
"which was very fortunate," Meserve said.
In a boiling water reactor system, the nuclear fuel assembly
contains uranium oxide fuel rods surrounded by a non-reactive
zirconium alloy. The fission of uranium fuel produces an enormous
amount of energy, as well as 200-300 different fission products,
such as Iodine-131 and Cesium-137, which also continue to fission to
produce additional energy.
"The problem you confront is that you can turn off the nuclear
reaction, but there are these fission products that are there that
are going to continue to produce energy and you need to be able to
deal with that energy getting somehow out of the reactor," said
The energy, as heat, converts water flowing through the reactor core
into steam that powers turbines and that also creates enormous
amounts of pressure in the system that must be released.
Even though the earthquake triggered the immediate shutdown of the
reactors, they were still were giving off about 6 percent of their
full power of approximately 2000 megawatts, said Meserve.
"If you were able to convert all of that 140 megawatts into
electricity, you could have enough power for a city of over 100,000
people," he said. "So, even if you've turned off the reactor, you've
still got a big problem of being able to get the heat out of the
If this heat isn't removed from the system, which normally operates
at about 280°C, the previously nonreactive zirconium alloy
surrounding the uranium fuel rods begins to react.
"At about 1000°C, there are really two reactions that you need to
worry about: If you're in air, zirconium and oxygen is going to
produce zirconium oxide and a lot of energy. And if you're in steam,
you're going to produce zirconium oxide and a lot of hydrogen, as
well as a lot of energy."
These reactions then cause the uranium fuel to burn, compromising
the integrity of the system, releasing radioactive noble gases and
the fission products. As the temperature climbs higher still, the
fuel begins to melt and additional radionuclide fission products are
According to "inconsistent stories" and news reports coming out of
the plant, said Meserve, the earthquake may have damaged the backup
power supply systems to keep the safety systems running properly to
ensure that the uranium fuel would continue to be kept cool after
Then, an hour after the earthquake, the tsunami hit. "You had a wall
of water 46 or 47 feet high that inundated all that area where all
the intake structures are that were bringing sea water into the
plant," said Meserve.
"The plant was designed to deal with a tsunami of 5.7 meters, so
they were completely overwhelmed with water. This was truly a six
As systems failed and the uranium fuel burned, the buildup of
hydrogen from the reacting zirconium alloy wasn't properly vented.
The hydrogen eventually reached explosive levels and blew off the
top of the reactors.
The nuclear power plant operators attempted to cool the burning
reactors with additional water, both salt and fresh water, but in
doing so "there's a lot of contaminated water all over the place,"
"And that's where we are today. The only way to cool these reactors
is pouring cold water over them," Meserve said. "And every day this
proceeds, they're contaminating the environment more."
"In one sense, their job is getting easier," Meserve said, adding
that the more time passes, the more energy and heat will have
dissipated. But dissipating energy also means an increase in
radioactive fission products. "The problem is with all this
contamination, the area is getting increasingly radioactively
contaminated, so it's very hard for humans to get in there to work."
Clean up crews can only work for a certain amount of time before
reaching a radiation exposure threshold.
In the United States, said Meserve, the NRC radiation dose limit for
a worker in a nuclear power plant is 50 millisievert (mSv). For
comparison, Americans receive an annual average background radiation
of about 6 mSv and person undergoing a full body CT scan receives 10
According to reports Meserve has read, the highest radiation dose
for a worker in Fukushima is 200 mSv, "which is obviously four times
the NRC annual dose limit."
"The doses are substantial," said Meserve, "But not yet at the
stage, for short periods of time, you have to worry."
Meserve concluded his talk by touching a number of points beyond
health effects and contamination that will need to be reassessed in
the wake of the Fukushima accident.
"One of the things that's going to come out of this activity in
Fukushima is there's going to be a huge assessment of lessons
learned," said Meserve, adding that disaster planning and
communication are key, especially in the face of the increased
likelihood of extreme events.
Following the lecture, an audience member asked, given the
consequences of the Fukushima incident, whether Meserve supports
Meserve responded affirmatively. "I do – but I am one of the few
people who believe in climate change," he said. "You need to not
take anything out of your weaponry to deal with the [energy]
challenge, and it's my view that nuclear has to be part of the
picture, but you have to do it safely."
—Julia C. Keller is Communications Manager at Tufts University School of Engineering
[This story was posted on April 6, 2011]
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