strickland ieee 24-hours at fukushima2

7/28/2019 Strickland IEEE 24-Hours at Fukushima2

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34 NA EEE SEctr NvEbEr 2011 spectrum.ieee.org


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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

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A bow-b-bow accoun of h wonuca accdn nc Chnob

By elizA striCklA

24 Hours atFukushima


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

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4/9


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.

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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


6/9


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

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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.


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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

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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.

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strickland ieee 24-hours at fukushima2

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