Upload
da-kanne
View
220
Download
0
Embed Size (px)
Citation preview
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
1/9
34 NA EEE SEctr NvEbEr 2011 spectrum.ieee.org
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
2/9
NvEbEr 2011 EEE SEctr NA 35spectrum.ieee.org
Sometimes it takes a disaster
beore we humans reallyfgure out how to designsomething. In act, sometimesit takes more than one.
Millions o people hadto die on highways, orexample, beore governmentsorced auto companies to
get serious about saety inthe 1980s. But with nuclearpower, learning by disasterhas never really been anoption. Or so it seemed, untilocials ound themselvesgrappling with the worldsthird major accident at anuclear plant. On 11 March,a tidal wave set in motion asequence o events that led tomeltdowns in three reactorsat the Fukushima Dai-ichipower station, 250 kilometersnortheast o Tokyo.
After the DeLUGe: A fooded equipmen oom a uni 3
o he Fukushima Dai-ihi nulea powe plan. PHOTO: TEPCO
s
p
e
c
i
A
L
r
e
p
or
t
A bow-b-bow accoun of h wonuca accdn nc Chnob
By elizA striCklA
24 Hours atFukushima
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
3/9
Unlike the three Mile island accident in 1979 and
Chernobyl in 1986, the chain o ailures that led to disaster
at Fukushima was caused by an extreme event. It was pre-
cisely the kind o occurrence that nuclear-plant designers
strive to anticipate in their blueprints and emergency-
response ocials try to envision in their plans. The strug-
gle to control the stricken plant, with its remarkable heroism,
improvisational genius, and heartbreaking ailure, will keepthe experts busy or years to come. And in the end the calam-
ity will undoubtedly improve nuclear plant design.
True, the antinuclear orces will ind plenty in the
Fukushima saga to bolster their arguments. The interlocked
and cascading chain o mishaps seems to be a textbook vali-
dation o the normal accidents hypothesis developed by
Charles Perrow ater Three Mile Island. Perrow, a Yale
University sociologist, identifed the nuclear power plant
as the canonical tightly coupled system, in which the occa-
sional catastrophic ailure is inevitable.
On the other hand, close study o the disasters irst
24 hours, beore the cascade o ailures carried reactor 1
beyond any hope o salvation, reveals clear inection pointswhere minor dierences would have prevented events rom
spiraling out o control. Some o these are astonishingly sim-
ple: I the emergency generators had been installed on upper
oors rather than in basements, or example, the di saster
would have stopped beore it began. And i workers had
been able to vent g ases i n reactor 1 s ooner, the rest o the
plants destruction might well have been averted.
The worlds three major nuclear accidents had very di-
erent causes, but they have one important thing in com-
mon: In each case, the company or government agency in
charge withheld critical inormation rom the public. And
in the absence o inormation, the
panicked public began to associate
all nuclear power with horror and
radiation nightmares. The owner
o the Fukushima plant, the Tokyo
Electric Power Co. (TEPCO), has
only made the situation worse by
presenting the Japanese and globalpublic with obuscations instead o
a clear-eyed accounting.
Citing a government investi-
gation, TEPCO has steadastly
reused to make workers avail-
able or interviews and is barely
answering questions about the acci-
dent. By piecing together as best we
can the story o what happened dur-
ing the frst 24 hours, when reactor
1 was spiraling toward catastrophe,
we hope to acilitate the process o
learning-by-disaster.
When the 9.0-MagnitUde
earthquake struck o the east coast
o Japan, at 2:46 p.m. on 11 March,
the ground beneath the power plant
shook and alarms blared. In quiv-
ering control rooms, ceiling panels
ell open and dust loated down
onto instrument panels like snow.
Within 5 seconds, control rods
thrust upward into the three opera-
tional reactors and stopped the ission reac-
tions. It was a lawless automatic shutdown,
but the radioactive by-products in the reactors
uel rods continued to generate tremendous
amounts o heat.
Without adequate cooling, those rods
would become hot enough to melt through the
steel pressure vessel, and then through the
steel containment vessel. That would result in
the dreaded core-meltdown scenario, which
could lead to the release o clouds o radio-
activity that would be carried by winds to
sicken or kill masses o people.
But the heat wouldnt be a problem so longas Fukushima Dai-ichi had power to run the
pumps that circulate water rom the reactor
cores through heat-removal systems. The
mighty earthquake had toppled power trans-
mission towers and jumbled equipment at
nearby substations, but the interruption in
power to the plant was negligible: Within
10 seconds, the plants emergency power sys-
tem kicked in. Twelve diesel generators, most
o them installed in basement areas below the
turbines, were now responsible or the integ-
rity o the plants reactorsand the well-being
o its workers.
power AnD protection: n
Fukushima Dai-ihis oiling wae
eaos, nulea ssion eaions in he
uel ods geneaed hea, whih oiled he
wae inside he eao pessue essel.
the seam podued doe uines in he
uine uilding o geneae eleiiy. the
adioaie uel ods had hee leels o
poeion: he seel pessue essel, he
pimay onainmen essel, and he oue
eao uilding. E m i l y C O O P E r
TEPCOsassumedhighesttsunami:5.7 metersabove sealevel
Normalsea level
11 Marchtsunami:+14 meters
Site level:+10 meters
Turbineb
uilding
Emergencygenerators
Spent-fuelpool
Reactorpressurevessel
Primarycontainmentvessel
Reactor
buildin
g
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
4/9
NvEbEr 2011 EEE SEctr NA 37spectrum.ieee.org
At 3:27 p.m. the frst tsunami wave surged into the man-
made harbor protecting Fukushima Dai-ichi, rushing past
a tidal gauge that measured a water height o 4 meters above
normal. At 3:35 another set o much higher waves rolled
in and obliterated the gauge. The water rushed over the
seawalls and swept toward the plant. It smashed into the
seawater pumps used in the heat-removal systems, then
burst open the large doors on the turbine bui ldi ngs and
submerged power panels that controlled the operation o
pumps, valves, and other equipment. Weeks later, TEPCO
employees would measure the water stains on the buildings
and estimate the monstrous tsunamis height at 14 meters.
In the basements o turbine and
reactor buildings, 6 o the 12 dieselgenerators shuddered to a halt as the
oodwaters inundated them. Five other
generators cut out when their power
distribution panels were drenched.
Only one generator, on the frst oor o a
building near unit 6, kept going; unlike
the others, all o its equipment was
above the water line. Reactor 6 and its sister unit, reactor 5 ,
would weather the crisis without serious damage, thanks
in part to that generator.
The rest o Fukushima Dai-ichi now aced a cataclysmic
scenario that nuclear power plant operators have long eared
but never experienced: a complete station blackout.
At the time o the earthquake, three o the power stations
six reactors were operating; the other three were down or
scheduled maintenance. In the control rooms governing the
active reactorsunits 1, 2, and 3the sta checked the cool-
ing systems that remove residual heat rom the reactor cores
by cycling water through heat exchangers flled with seawater.
Everything seemed under control. Water also flled the spent-
uel pools on the top oors o all six reactor buildings to pre-
vent the pools rom overheating.
At 2:52 p.m., the shit supervisor overseeing the plants oldest
reactor, the 40-year-old unit 1, confrmed that a backup cooling
system called an isolation condenser (IC) had started up auto-
matically. This system didnt need electric
power to cycle steam through a cold-watertank on a higher oor, or to let the result-
ing water drop back down to the pressure
vessel. But operators soon noticed that the
IC was cooling the core too quickly, which
could stress the steel walls o the pressure
vessel. So they shut the system down. It
was a by-the-book decision, but the book
wasnt written or the extraordinary events o 11 March.
Tsunami alerts lashed on TV screens, predicting a
3-meter-high tsunami or Fukushima preecture. Although
the coastal Fukushima Dai-ichi plant was 10 meters above
sea level, nonessential personnel ollowed procedure and
began evacuating the site.
system fAiLUre: n 11 ah, a tEc woke
phoogaphed he sunami sweeping ino he Fukushima
Dai-ihi powe saion [op] and sumeging anks
and as [oom]. Ae he plan los elei powe,
opeaos ould ead insumens only y plugging
in empoay aeies [le]. PHOTOS: TEPCO (3)
This report is based on interviews with ocialsfrom the Tokyo Electric Power Co. (TEPCO), Japans
Nuclear and Industrial Safety Agency, the U.S.
Nuclear Regulatory Commission, the International
Atomic Energy Agenc y, local governments , and
with other experts in nuclear engineering, as well
as a review of hun dreds of pag es of ocial rep orts.
s
p
e
c
i
A
L
r
e
p
or
t
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
5/9
38 NA EEE SEctr NvEbEr 2011 spectrum.ieee.org
in the control rooM where operators managed reac-tor 1, the alarms went silent. The overhead lights blinked o,
and the indicator lights on the instrument panels aded away.
The oodwaters had even knocked out the con-
trol rooms batteries, the power source o last
resort. The operators would have to respond to
the emergency without working instruments.
With the power out, the pumps were no lon-
ger channeling water rom unit 1s pressure ves-sel through the cooling systems heat exchangers,
and the erociously hot uel rods were boiling the
water into steam. The water level in the nuclear
core was dropping, but, lacking power or their
instruments, the plant operators could only
guess at how ast the water was boiling away.
The isolation condenser, which relied on
convection and gravity to perorm its cooling
unction, should have helped keep the water
level high in unit 1s core through the crisis. But
operators had turned o the system just beore
the tsunami by closing its valvesand there
was no electric power to reopen them and let
steam and water ow. Workers struggled to manually open
the valves on the IC system, but experts believe the IC pro-
vided no help ater the tsunami struck.
As the operators surveyed the damage, they
quickly realized that the diesel generators
couldnt be salvaged and that external power
wouldnt be restored anytime soon. In the plants
parking lots, workers raised car hoods, grabbed
the batteries, and lugged them back to the controlrooms. They ound cables in storage rooms and
studied diagrams. I they could connect the bat-
teries to the instrument panels, they could at least
determine the water levels in the pressure vessels.
TEPCO did have a backup or the emergency
generators: power supply trucks outitted with
high-voltage dynamos. That aternoon, emergency
managers at TEPCOs Tokyo headquarters sent
11 power supply trucks racing toward Fukushima
Dai-ichi, 250 km away. They promptly got stuck
in trac. The roads that hadnt been damaged by
the earthquake or tsunami were clogged with resi-
dents eeing the disaster sites.
Lesson 1
Emergency gen-erators should
be installed at
high elevationsor in watertightchambers.
Lesson 2
If a cooling sys-tem is intendedto operate with-out power, makesure all of itsparts can bemanipulated
without power.
tUrbine bUiLDinG
seAwALL
reActor 2 reActor 3
tUrbine bUiLDinG
reActor 1
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
6/9
NvEbEr 2011 EEE SEctr NA 39spectrum.ieee.org
At 4:36 p.m., TEPCO ocially inormed the Japanese gov-
ernment about the increasingly dire situation at reactor 1.
The company declared that it could not confrm that any
water was being injected into the reactors core. The situa-
tion was better at the slightly more modern reactors 2 and 3,
where emergency cooling systems were operat-
ing, driven by the steam rom the reactors them-
selves. And the idled reactors 4, 5, and 6 didnt
pose an immediate threat.At 5:41, the sun set over the pools o seawater
and the mounds o debris scattered around the
power station. Work crews picked their way
through the gloom by ashlight.
At around 9 p.m., operators fnally plugged
the car batteries theyd collected into the instru-
ment panels and got a vital piece o inormation
the water level in reactor 1. The inormation
seemed reassuring. The gauge registered a water
level o 550 millimeters above the top o the uel
assembly, which, while ar below normal saety
standards, was enough to assure the operators
that no uel had melted yet.
But TEPCOs later analy-
sis ound that the gauges were
wrong. Months later, calcula-
tions would show that the
superheated water inside the
reactor 1 pressure vessel had
dropped all the way belowthe bottom o the uranium
uel rods shortly beore operators checked the gauge,
leaving the reactor core completely uncovered. Heat
pulsed through the exposed rods. When temperatures
passed 1300 C, the uel rods protective zirconium clad-
ding began to react with the steam inside the vessel, pro-
ducing highly volatile hydrogen gas. And the uranium
inside the uel rods began to melt, slump, and sag.
throUghoUt the night o 11 March, radiation lev-els rose around the plant. At 9:51 p.m. managers pro-
hibited entry into the unit 1 reactor building.
It was a wise decision, because in the bowels othe reactor, the meltdown had already begun. In the
reactors used at Fukushima, the control rods thrust
up into the pressure vessel rom below, and the hous-
ings around each control rods entry point were essen-
tially weak spots. When the melted uel began to pool
at the bottom o the pressure vessel, it likely melted
through those vulnerable seams. TEPCOs later anal-
ysis ound that the pressure vessel was damaged by
11 p.m., allowing highly radioactive water and gases
to leak into the primary containment vessel.
The containment vessel, which surrounds the pres-
sure vessel, is a crucial line o deense: Its a thick steel
hull meant to hold in any tainted materials that have
escaped rom the inner vessel. At 11:50 p.m. operators
in the control room fnally connected car batteries to
the pressure gauge or the primary containment ves-
sel. But the gauge revealed that the containment vessel had
already exceeded its maximum operating pressure, increas-
ing the likelihood that it would leak, crack, or even explode.
As 11 March turned into 12 March, TEPCO headquarters
told the sleepless operators that they must bring down the pres-
sure by venting the containment vessel. A venting
operation would jet the vessels radioactive gases
into the air; Fukushima Dai-ichis nightmare
would soon spread across the countryside.That night, the desperate struggle to con-
tain the peril at reactor 1 diverged into three
responses. Besides the team making prepara-
tions to vent the containment vessel, there was
also a group getting ready to receive the power
supply trucks, which were still making their
way to the plant. On arrival, they would supply
electricity to restart the pumps and reestablish
steady water circulation through the pressure
vessel. The third team ocused on another, short-
term plan or cooling the core: fre trucks, which
could inject water rom emergency tanks into
one o the reactors cooling systems.
Lesson 3
Keep powertrucks onor very closeto the powerplant site.
Lesson 4
Install indepen-dent and secure
battery systemsto power crucialinstrumentsduring emer-
gencies.
the DAmAGe: n he
days ollowing he
sunami, explosions oe
he oos o eaos 1, 3,
and 4, and an ineio
deonaion is hough o
hae damaged eao 2.
PHOTO: GAmmA/GETTy imAGES
reActor 4
s
p
e
c
i
A
L
r
e
p
or
t
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
7/9
40 NA EEE SEctr NvEbEr 2011 spectrum.ieee.org
It was ater midnight when the frst power supply trucks
began to arrive at the site, creeping along cracked roads. The
trucks parked outside the unit 2 turbine building, adjacent
to the troubled unit 1, where workers had ound one undam-
aged power control panel. In the darkness, they began snak-
ing a 200-meter-long power cable through the mud-caked
buildi ng i n order to connect it to the power control panel.
Usually trucks are used to lay such a cable, which weighedmore than a ton, but that night 40 workers did the job by
hand. It took them 5 hours.
Work continued at the power control panel all morn-
ing and into the aternoon o 12 March. Finally, at 3:30 p.m.,
everything was ready. Current lowed rom a power sup-
ply truck through the cable to the panel, which was ready
to switch on the pumps or a backup cooling system inside
the reactor 1 building. Workers prepared to start the ow
o reshwater into the pressure vessel, knowing that they
were about to take a crucial step toward stabilizing the plant.
Meanwhile, the fre engine team had been grappling with
diicult logistics all through the early morning hours. O
the three fre engines on site, one had been wrecked by thetsunami; another was stuck near reactors 5 and 6, trapped by
damaged roads. That let one fre engine to cool the overheat-
ing reactor 1. This truck was the best hope or getting water
into the pressure vessel quickly, but it took hours to maneuver
it through the plants wreckage. Finally the workers smashed
a lock on an electronic gate and drove the fre engine through.
In their initial, improvised response, the fre crew pumped
water into the trucks storage tanks, then drove close to the
side o the reactor building and injected the water into the fre
protection systems intake lines. It was 5:46 a.m. on 12 March
when the frst drops o water sprayed across the molten uel.
Then the workers drove back to the water tanks and began
the slow, arduous operation all over again. Eventually work-
ers managed to use the ire engines hoses to
connect the water tanks directly to the intake
lines and established a steady ow o water. By
midaternoon, they had injected 80 000 liters o
water into the pressure vessel using this make-
shit system. But it was too little, too late.
At 2:54 p.m., with reshwater supplies run-
ning short, TEPCO headquarters ordered the
fre truck crews to inject seawater into the pres-
sure vessel through the ire protection line.
Under normal conditions, saltwater is never
allowed in a reactor pressure vessel becauseit would corrode the vessels protective steel
walls and leave a mineral residue on the uel
rods. The decision was an admission that sav-
ing the reactor was no longer an option and that
operators could only hope to prevent a wide-
scale disaster. Fukushima Dai-ichi was now
beyond the point o no return.
Workers stretched long fre hoses rom a seaside pit that
had been flled with seawater by the tsunami; three newly
arrived ire engines lined up to pump the water through.
They connected the hose to the ire protection systems
intake line, and around 3:30 on 12 March they prepared to
blast the reactor with seawater.
It had been 24 hours since the tsunami roared into the har-
bor, and the desperate eorts o both the power crew and the
fre truck crew were about to pay o. It must have seemed that
their exhaustion and terror were nearly at an end.
the order to vent the containment vessel had come atmidnight. But without power to remotely operate the vent sys-
tems valves, it wouldnt be a simple task.And whether the workers knew it or not, time was o
the essence. While the venting team prepared or action
during the early morning hours o 12 March, gases were
bui lding up inside the primar y containment ves sel and
pushing on its weakest points, its gaskets and seals, and
they were starting to give. Hydrogen gas hissed through
the breaches and drited up to the top o the building. Hour
by hour, the gas collected there until it ormed a l ayer o
pure combustible menace.
The workers in charge o the venting operation took
iodine tablets. It was a eeble attempt at protection against
the radiation theyd soon encounter, but it was better than
nothing. They gathered protective head-to-toe suits andace masks connected to air tanks. At 3:45 a.m., the vent
crew tried to measure the radiation dose inside the reactor
building, which had been o limits or 6 hours. Armed with
handheld dosimeters, they opened the air lock, only to fnd
a malevolent white cloud o some gaseous substance bil-
lowing toward them. Fearing a radiation steam bath, they
slammed the door shut. They didnt get their reading, but
they had a good indication that things had already gone seri-
ously wrong inside the reactor.
I they could have looked inside the reactor pressure ves-
sel at around 6:30 a.m. on the morning o 12 March, they
would have seen a nuclear core transormed into molten
sludge. The melted mixture o uranium, zirconium, and
other metals had oozed to the bottom o the reac-
tor pressure vessel, where it was gradually eat-
ing through the steel oor.
But as the morning ticked on, the vent crew
were orced to sit and wait; they were standing
by or word that residents had been evacuated
and that it was sae to release the radioactive
gases into the air. The government had issued
an evacuation order or residents living within
3 km the night beore; in the early morning
hours ocials announced that everyone within
a 10 km radius o the plant should pack up andgo. Residents who had lived their whole lives
in the shadow o the Fukushima Dai-ichi plant
boarded buses, expecting to be gone or a couple
o days at most.
At 9:03 a.m. the message came: The last
buses had depa rted. At 9:04 workers set out
or the reactor building to open the valves that
would allow gas to ow out o the primary containment ves-
sel. They entered the reactor building and began a long, dark
trek around the periphery o the primary containment ves-
sel, guided only by ashlight beams. As they walked, their
handheld dosimeters lashed troubling numbers. In nor-
mal conditions, a nuclear plant employees radiation limit is
Lesson 5
Ensure that cat-alytic hydrogenrecombiners(power-freedevices thatturn dangeroushydrogen gasback into steam)
are positionedat the tops ofreactor build-ings where gaswould mostlikely collect.
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
8/9
spectrum.ieee.org NvEbEr 2011 EEE SEctr NA 41
in the rUins: the explosions duing he s days o he aiden saeed adioaie ule aound he sie. this pah o deis [op] has a
adiaion leel o 1000 millisiees pe hou; unde nomal ondiions, a nulea wokes adiaion limi is 50 mS pe yea. the dangeous
ondiions a he powe saion made oos [oom] a neessay addiion o leanup ews. PHOTOS: TEPCO (2)
rADiAtion AreA
s
p
e
c
i
A
L
r
e
p
or
t
7/28/2019 Strickland IEEE 24-Hours at Fukushima2
9/9
50 millisieverts per year; in an emergency situa-
tion it is 100 mSv. The workers had covered about
hal the distance to the valve when they realized
they had to turn backi they continued, they
would exceed the 100 mSv dose. They returned
to the control room at 9:30. They had ailed.
Over the next hours the operators scrambled
to fnd another way to open the valves; fnallythey decided to blast the valve open with air.
They used a crane truck to haul a portable air
compressor, the kind typically used at con-
struction sites, to the crucial valves location. At
2:00 p.m. the vent crew switched the compressor on, while
workers in the control room nervously watched the gauge.
By 3:30 p.m. on 1 2 March, it seemed that the venting
had worked and that the worst was over. The pressure had
dropped signifcantly in unit 1s primary containment ves-
sel, suggesting that the valve had opened and that gases had
rushed through the pipes to the ventilation stack near the
reactor building. The workers must have elt that the dan-
ger was ebbing. They had no idea that leaks rom the ventlines had added even more hydrogen to the gas collected
below the ceiling o unit 1s outer buildingand it was now
ready to blow.
at 3:36 p.M., a spark lashed in the darkness o the reactorbuilding, and hydrogen gas ignited. With a roar, the top o
the reactor building exploded.
The roo shattered and the walls splintered; ragments o
the building ew through the air. Chunks o rubble cut into
the cable leading rom the power truck, and the ow o current
stopped; now the pumps could not be turned on, and resh-
water could not cascade into the core. Other pieces o debris
sliced into the fre engine hoses leading rom the seawater pit.
postyourcommentsonline athttp://spectrum.ieee.org/24hours1111
Smoke billowed upward, radiation levels soared,
and the workers led F ukushimas i rst radio-
active ruin. It wouldnt be the last: The battle to
contain the catastrophe during the frst 24 hours
was lost, and the explosions would keep coming.
The ailure o reactor 1 made eorts to sta-
bili ze the other reactors exponentially more
diicult: Now workers would be laboring in aradioactive hot zone littered with debris. In addi-
tion, when work crews returned to the power
truck sometime ater the explosion, they couldnt
get the power owing. So the disaster continued.
At reactors 2 and 3, emergency cooling systems unctioned
or several days. When reactor 3s overtaxed system ailed
on 13 March, workers struggled to connect alternate water
supplies and to vent the primary containment vessel. But
work was slow, and soon reactor 3 ollowed reactor 1s exam-
ple. Leaking gas collected at the top o the building, and it
exploded on the morning o 14 March.
That blast urther impeded recovery
eorts at reactor 2, and on the morning o15 March some stil l-obscure explosive noise
resonated inside the unit 2 reactor building.
On that same day, an explosion tore the roo
o reactor building 4 and a ire broke out
inside. TEPCO reports say the problems in
reactor 4 were probably due to hydrogen gas
that leaked in rom reactor 3; despite early
reports to the contrary, the spent uel rods
stored in pools in reactors 4, 5, and 6 were
covered with water throughout the accident
and never posed a threat.
Each detonation made the eort to stabilize
the plant more hopeless. It is clear that i work-
ers had been able to gain control o reactor 1, the
whole terrible sequence o events would have
been dierent. But could the workers have
done anything dierently to speed up their
response? Could the ull scope o the catastro-
phe have been averted? So ar, TEPCO man-
agement hasnt answered those questions.
Weve learned a great deal about the
Fukushima accident in the past seven months.
But the nuclear industrys trial-and-error learning process
is a dreadul thing: The rare catastrophes advance the sci-
ence o nuclear power but also destroy lives and render entiretowns uninhabitable. Three Mile Island let the public terri-
fed o nuclear power; Chernobyl scattered allout across vast
swaths o Eastern Europe and is estimated to have caused
thousands o cancer deaths. So ar, the cost o Fukushima is
a dozen dead towns ringing the broken power station, more
than 80 000 reugees, and a traumatized Japan. We will learn
even more as TEPCO releases more details o what went
wrong in the frst days o the accident. But as we go orward,
we will also live with the knowledge that some uture catas-
trophe will have yet more lessons to teach us. o
broken sheLL: the uni 4 eao uilding was weked y an explosion and a e.
PHOTO: TEPCO
spectrum.ieee.org42 NA EEE SEctr NvEbEr 2011
Lesson 6
Install power-free filterson vent lines toremove radio-active materials
and allow forventing that wontharm nearbyresidents.
s
p
e
c
i
A
L
r
e
p
or
t