Image: Christine Daniloff |
Among the lessons to
be learned from the accident at Japan’s Fukushima Daichii nuclear powerplant,
according to a new report from the Massachusetts Institute of Technology (MIT),
are that emergency generators should be better protected from flooding and
other extreme natural events, and that increasing the spacing between reactors
at the same site would help prevent an incident at one reactor from damaging
others nearby.
These and other
lessons are contained in a report put out by MIT’s Department of Nuclear
Science and Engineering (NSE), based on its analysis of how events unfolded at
the troubled plant in the days and weeks following Japan’s devastating
earthquake and tsunami on March 13, 2011.
The specific
suggestions in this report are quite different from the response by some
governments—notably, Germany
and Japan,
which have halted or delayed expansion of nuclear power in the wake of the
meltdowns and radiation releases at the Japanese reactors. In fact, the report
says, health risks to the public, and even to workers at the plant, have been
negligible, despite the significant releases of radiation over the last few
months. There has been no loss of life associated with the accident, nor is
there expected to be, the report says.
The new report, an
update of a preliminary report issued in May, 2011, is available for download on the NSE website.
“A lot of information
that was not available when we started has become available,” says Jacopo
Buongiorno, the Carl Richard Soderberg Associate Professor of Power Engineering
and lead author of the new report, which was co-authored by eight other members
of the NSE faculty. However, he adds, there are some important areas where
information has still not come out.
During the first days
of the accident, he says, there were three critical delays that have not yet
been well explained—although the report says there is no evidence at this point
of any major human errors contributing to the unfolding problems. The delays
involved operating some safety-critical valves, injecting water into the
reactor cores and venting the containment buildings. “It’s not clear what the
cause of the delays was,” Buongiorno says, but it is unlikely that these were
caused by administrative delays in Japan’s control-and-command chain,
as had been initially suggested.
Rather, because of the
lack of power and the effects of the flooding, “there was disruption and
confusion around the site” during the crucial early hours, he says. “Things
that normally would take minutes, such as reading an instrument or connecting a
cable or a hose, took hours” because of the lack of power and the debris and
destruction. “Given the situation, they reacted as well as they could,” he
says.
Among the specific
suggestions the report makes:
- Emergency
backup generators, needed to keep the systems running when outside power
is cut off as it was in this case, should be well separated into at least
two locations—one situated high up, to protect against flooding, and the
other down low to protect against hazards such as an airplane crash. These
generators should also be housed in watertight rooms, as they already are
at many U.S.
plants. - In
future plants, spacing between reactor buildings located at the same site
should be increased—for example, by having other areas such as parking
lots or support buildings in between—and systems such as ventilation
shafts should be kept separate, in order to avoid a domino-like spread of
problems from one reactor to another. In the Fukushima accident, it seems that
hydrogen vented from reactor unit 3 may have reached unit 4 through the
ventilation system, causing an explosion there. - Officials
should be cautious about decisions to evacuate large areas around a
damaged nuclear plant in cases where the population has already been
devastated by a natural disaster. At Fukushima, “ironically, the biggest [health] consequences may be from the prolonged
evacuation,” Buongiorno says. - More
attention needs to be paid to how radiation risks are communicated to the
public, rather than the confusing mix of different measurements that were
disseminated in this case. The most useful standard is to relate radiation
releases to natural background levels, rather than using technical units unfamiliar to most people.
Perhaps the most obvious piece of advice—and one that is
already observed in the majority of new nuclear-plant installations worldwide—is
simply that in siting future plants it would be wise to “choose sites away from
highly seismic areas and coasts,” to reduce the risks from earthquakes,
tsunamis and floods. For existing plants located in areas at high risk of
earthquakes and tsunamis, it is important to re-evaluate the design basis for
such extreme natural events, incorporate the latest data and state-of-the-art
methodologies in the analysis, and ensure the plants are adequately protected.
But the report also emphasizes that all engineered
structures—bridges, powerplants, skyscrapers, dams—have their own risks,
especially when subjected to extreme conditions they were never designed to
withstand. The authors suggest it is important not to overreact to particular
high-profile cases.
“If you have an accident in your car, you don’t stop
driving a car, you learn from it,” Buongiorno says. Continuing the analogy, “in
this case, the accident was like a tree that fell on the car. It wasn’t the car
itself.”
But to fully absorb and learn from the lessons of this
accident may take years, Buongiorno cautions. “It took 20 years to fully absorb
the lessons of Three Mile Island,” he says. “Some of these questions are complex, requiring quantitative analysis to fully
evaluate the data and make rational decisions about how best to respond.”
Romney Duffey, a principal scientist at Atomic Energy of
Canada Ltd., says, “This report is both an excellent summary and provides
thoughtful suggestions. Of particular importance, the report addresses the
links to energy policy and comparative-risk aspects, in addition to the purely
technical and licensing considerations.” He adds that the suggestions regarding
better public communication about risks from radiation releases are especially
useful: “The concept of using easier-to-understand measures of risk is vital to
better communicating with everyone during such times of great stress and uncertainty.”
