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Fallout from Fukushima
By Richard Broinowski Scribe Publications Pty Ltd
Copyright © 2012 Richard Broinowski
All rights reserved.
ISBN: 978-1-921942-93-8
CHAPTER 1
Meltdown
JAPAN'S NARROW ISLAND chain lies along an active geological fault line where two of the earth's tectonic plates collide. The circum-Pacific seismic belt, called the 'Ring of Fire', is highly prone to earthquakes. Particularly vulnerable is Japan's eastern seaboard, which slopes down into a very deep trench dominated by two currents, Kuroshio and Oyashio. The Oyashio Current flows south from Okhotsk and the Kuril Islands, past Hokkaido, and along Japan's eastern flank. Cold and rich in marine life, it has for centuries supplied the Japanese people with food.
Tohoku, the north-eastern region of Honshu, is a quiet part of Japan, less familiar to foreign visitors than are the megacities of Tokyo, Nagoya, and Kyoto-Osaka-Kobe. Its mountains and forests are rugged and beautiful, dotted with resorts positioned around hot springs and ski slopes. Its climate is hot and humid in summer, bitterly cold in winter. Short, fast-flowing rivers pour out of the steep gorges to reach the sea along an irregular coastline. The narrow and heavily indented flatlands of Miyagi and Fukushima, two of the region's six prefectures, face eastwards towards the Pacific Ocean, and are carpeted in a geometric pattern of rice paddies and orchards. Tohoku's rice wine is savoured by connoisseurs. Its high-grade beef is claimed to be better than that from Kobe, and comes from animals with individual certificates of pedigree. Its poultry, fish, and miso (bean paste) are prized by Japanese tourists as omiyage — souvenir gifts from places to which they have travelled. Its peaches, apples, pears, cherries, plums, apricots, chestnuts, persimmons, and grapes are renowned as the most luscious in Japan. The prefecture of Fukushima provides the markets of Sendai and the Tokyo-Yokohama region with 20 per cent of their rice and almost as much of their fruit and vegetables. Or at least it did until the day that soon came to be called 'Japan's 3/11'.
Friday 11 March 2011 was calm in Tohoku, slightly overcast and bitterly cold, for spring had not yet arrived. People went about their routine business: some working in sake breweries and food-processing factories; some in small- and medium-scale industrial plants producing semiconductors, optics, and car parts; some in factories making traditional lacquerware, pottery, and textiles; others shopping for the evening meal or engaged in household chores. As the afternoon sun slid towards the mountain rim to the west, primary-school children began filing in neat lines out of their classrooms, to wait for their mothers, to go to their juku cram-schools, or to catch afternoon buses home.
Without warning, at 2.46 p.m., a massive earthquake jolted the Pacific Ocean seabed 66 kilometres east of Sendai, the capital of Miyagi prefecture. For more than ten minutes, tall buildings swayed like bamboo. Severe shocks were felt as far away as Tokyo and the west coast of Honshu. Long inured against panic, and unaware that this was an unprecedented force-nine earthquake — a dai jishin — most people in the region waited out the tremors with a combination of apprehension and stoicism.
According to recordings at the Space Science Institute of the National Central University in Taiwan, the earthquake was so powerful that it rattled the ionosphere 350 kilometres above the planet, disrupted navigational signals above its epicentre, and caused a disk-shaped wave seven minutes after the event. The only other earthquake known to have done this was the magnitude 9.3 Sumatran earthquake of December 2004.
Within 40 minutes of the new earthquake, an event occurred for which Tohoku residents were less prepared. The earthquake had generated two massive oceanic upheavals which merged into a single gigantic swell, a 'double tsunami', that travelled west towards the Japanese coast at around 10 kilometres per minute — about the speed of a passenger jet when cruising. Packing an estimated 10 billion tonnes of water, the tsunami slowed to 4 kilometres per minute as it reached shallow water, and crashed as an immense wall of black water onto the coastline of Fukushima, Miyagi, and Iwate prefectures. A team of researchers, headed by University of Tokyo professor Shinji Sato, and the Fukushima prefectural government later concluded that the height of the wave had been 21.1 metres when it struck the Kobama district of Tomioka, just south of the Fukushima reactors. It varied in height at other coastal points — 16.5 metres at Futaba, 15.5 metres at Namie, and 12.2 metres at Minamisoma and Okuma. At all points, protective concrete walls were swept aside by its momentum as if they were doorstops. A Japanese television crew in the area managed to film fishing boats being rammed under bridges, rice paddies flooding, and long rows of vegetable-growing vinyl hothouses buried under liquid mud. The footage was broadcast over and over to appalled Japanese and international viewers.
Soon to follow were accounts of the horrendous human damage as entire towns and factories were flattened, villages washed away, and cars, buses, ferries, and trains engulfed in seawater, mud, and detritus. The tsunami acted like a battering ram, gathering weight and bulk from the thousands of buildings, motor vehicles, and boats that it carried before it. Its impetus took it several kilometres inland, further than any reasonable prediction would have suggested. Thousands of men, women, and children were carried inland, to be crushed against buildings and cliffs, or swept back out to sea to drown in the wave's reflux. By the end of March, 15,413 were counted as dead, and 8069 missing. Further deaths occurred among the tens of thousands of refugees, many of them old, most dying of hypothermia in the bitterly cold weather as they battled to survive in darkened schoolrooms and other temporary shelters, cut off from food and warmth.
To make things worse, the people then had to cope with a third calamity, the malfunction of a nuclear-power complex on the coast slightly south-east of Fukushima city.
Owned and run by the Tokyo Electric Power Company (TEPCO), what was then a smartly painted pale-blue and white facility is known as Fukushima Dai-ichi (Fukushima Number One). Built on the flat, seaside site of a Pacific War Japanese air base, it comprises six reactors and associated equipment in a sprawling complex of around four hectares. The oldest reactor, Unit One, is a General Electric–designed Mark I boiling-water reactor (BWR) of 439 megawatts (MW), operating since its construction in 1971. Units Two, Three, and Four are 760 MW BWRs, operating since 1974. Five and Six are larger capacity BWRs again, brought online after completion towards the end of the 1970s. General Electric designed all of the units, and built units One, Two, and Six. Toshiba built units Three and Five, and Hitachi built Unit Four. According to GE's website prior to the accident, all reactors met the Nuclear Regulatory Commission requirements for safe operation during and after an earthquake for the area where they were sited.
The Fukushima reactors are almost identical in design and age to many General Electric BWRs operating in the United States. In their centre is a pear-shaped steel containment building, or drywell, with a reactor pressure vessel suspended in its neck. Each vessel is an upright steel cylinder of about 7 metres in diameter and 21 metres in height, containing an average load of around 95 tonnes of nuclear fuel, comprising at least 25,000 3.6-metre-long zirconium fuel rods packed with pellets of slightly enriched uranium (3 per cent uranium-235). At the Fukushima Dai-ichi complex, Unit One is the smallest of the reactors, with about 70 tonnes of fuel-core load; Unit Six is the largest, with a 132-tonne fuel core. Before the accident, each core was cooled by a main feed line of fresh water, which circulated through the uranium rods in the vessel, heated, and exited as steam via a closed-loop primary circuit. The steam expanded to drive a high-pressure steam turbine, which was linked to an electricity generator. After passing through the turbine, the exhausted steam circulated to the wetwell, a giant doughnut-shaped seawater-cooled condensation chamber beneath the containment building, before being pumped once more as water back into the reactor vessel, where the process was repeated.
A peculiar feature of the General Electric–designed BWRs is the position of the pool of water, which holds spent fuel rods as they are rotated out of the reactor core when their thermal efficiency has been lost. In earlier GE BWRs, this pool sits high above and to one side of the reactor vessel, in a very exposed position. The designers placed it there for convenience, to allow gantries easy access to deposit their dangerous load of hot, spent fuel drawn from the adjacent open mouth of the reactor vessel. The reactor vessel, drywell containment, wetwell condensation chamber, and spent-fuel storage pool are all enclosed in a heavy concrete reactor building. On top sits a fully instrumented service floor in a lighter steel structure manned by plant operators.
Before the earthquake, units One, Two, and Three of the Dai-ichi plant were running, but units Four, Five, and Six were in cold shutdown for servicing. The fuel load of reactor four had been transferred to the water-filled spent-fuel storage pool located at the higher level of its reactor building. Time lines matter here if one is to chart the rising tide of chaos.
The earthquake at first seemed to have left the three operating reactors undamaged, as they were continually cooled by pumps powered by the regional grid. Suddenly, however, the power grid failed. A procedure known as SCRAM (see Appendix) was immediately initiated: neutron-absorbing control rods were rapidly inserted into the cores by electric motors, to halt the fission process and stop power generation. Simultaneously, emergency diesel generators, located on ground level behind the reactors, kicked in to pump fresh cooling water into the reactors. These actions kept things under control for another hour. At 3.41 p.m., however, the 21-metre-high tsunami generated by the earthquake rose out of the Pacific and struck the complex, flooding the generators. Only one battery-powered generator remained operational, but it did not have sufficient power to drive the cooling pumps, and all but one of three emergency core-cooling systems failed. A core isolation pump continued to operate, but it malfunctioned as the core temperature rose.
The situation deteriorated rapidly. As operators rushed around the control rooms in the hot, chaotic darkness, desperately trying to read instruments and decide what to do, heat from the fuel rods continued to produce steam in the reactors, which discharged into the condensation chamber beneath the reactor vessels. As heat and pressure rose, the water-coolant level in the reactors fell. The tops of the fuel rods in the reactor cores became exposed to the air. Temperature of the cladding around the rods rose to above 900 degrees Celsius. The cladding distorted and fractured, releasing fission products from the fuel rods, which were now half exposed. As the temperature rose to 1200 degrees, zirconium in the cladding began to burn. It also reacted to the water, producing zirconium oxide and releasing volatile hydrogen gas. The plant engineers were instructed to vent the steam and hydrogen from the containment building, but the venting system did not function because it depended on the same electricity sources that had failed and caused the crisis. None of the engineers had ever vented gas manually, and they had to search frantically through the dark control room to find the instruction books, and then slowly crank the vents open by hand — much too late to prevent what followed.
At 1800 degrees, the cladding and steel structures began to melt. At 2500 degrees, the fuel rods disintegrated, and radioactive debris formed inside the cores. At 2700 degrees, the fuel rods melted, releasing into the containment building a toxic stew of radioactive isotopes, including plutonium-239, uranium-235, americium, xenon, neptunium, caesium-137, iodine-131, and noble gases. Meanwhile, the hydrogen exploded sequentially in units One, Three, and Two, shattering the steel-framed concrete roofs of their reactor buildings, leading to the uncontrolled release of gases containing fission products into the atmosphere. Multiple leaks in pumps, pipes, and tanks released a similar stew of radioactivity into the sea close to the plant.
Worse was that, before the earthquake and tsunami, Unit Three had been fuelled with a trial batch of mixed-oxide fuel (MOX) containing about 230 kilograms of plutonium-239, which had been produced at the experimental nuclear complex in Rokkasho. Reprocessed from spent reactor fuel, MOX is richer in plutonium than conventional reactor fuel, and produces more radiation from plutonium-239. Sampling conducted around the complex within days of the explosions found five localities contaminated with plutonium-239, two of which were positively identified as being contaminated with plutonium from the Unit Three MOX fuel.
Meanwhile, even though shutdown and offline, Unit Four was having problems of its own. Its spent-fuel storage pool was holding 256 tonnes of spent fuel rods, 95 tonnes of which had been transferred from its reactor to the pool shortly before the earthquake. Under the lateral and vertical force of the earthquake, this heavy load had sloshed around the pool until cracks had appeared, releasing coolant (along with radiation) and raising the temperature of the rods. Another meltdown was possible. Mitsuhiko Tanaka, an engineer who helped design and supervise construction of the unit, was quoted in the Bloomberg News of 18 March 2011 as saying that the pool was damaged during the production process. Braces that should have been inside the vessel during manufacture were forgotten, and the walls became warped. This would indicate that this pool, at least, being too weak to withstand the lateral shaking from the tremors, was damaged by the earthquake, not the tsunami that later flooded the emergency generators.
TEPCO belatedly acknowledged that not all damage to the reactors was caused by the tsunami knocking out the emergency generators. They reluctantly admitted that the earthquake may have damaged the number four cooling pool, and also the high-pressure core flooder that provided emergency cooling to all of the reactor cores. Thus, even if the emergency generators had not been knocked out by the tsunami, the cores might not have been cooled properly. Both breakdowns carried safety implications concerning the supposedly 'quake-resistant' designs at Fukushima and all other Japanese reactors.
Back at the melted cores, Japanese emergency crews were attempting to pump in fresh water. But the heavy-lift military helicopters they used could not get low enough to dump their loads accurately because of the intensity of radiation bombarding their flight crews. Most of the water was blown away by fierce wind. They returned next morning with lead plates welded to the bellies of the choppers, but they still couldn't get close enough, and their loads of water again dispersed before hitting the target. Fire engines from the elite Tokyo Fire Brigade made an emergency dash to the site to pump sea water into the reactors, but they were only partially successful because the crews' vision was impeded by the height of the reactor buildings towering above them. In defiance of an order from his supervisor not to do so (because it was thought that this would destroy the reactors), one of the plant's senior technicians ordered sea water to be pumped from jury-rigged overhead jibs on the fire engines into the reactor and spent-fuel storage pool of Unit Four. But the sea water's cooling effects remained uncertain because salt in the water formed a crust around the hot fuel rods, insulating them from the coldness. Days passed, and these attempts either failed or were only partially successful in lowering core temperatures. TEPCO, humiliatingly, ordered in a 62-metre-long water pump from China, usually an export market for Japanese nuclear technology.
Another humiliation faced by TEPCO's management was that they had not seen fit to acquire industrial robots designed to resist high levels of radiation and climb over mounds of rubble to work in damaged reactor buildings. This was difficult to understand in a country with world-leading robotic technology, and robots that sing and dance. But like the other nine Japanese electric-power companies, TEPCO believed its own propaganda that nuclear power was safe, and that such technology was unnecessary and would send the wrong signals to the Japanese public. Hiroyuki Yoshikawa strongly criticised this complacency. In addition to being the director-general of the Centre for Research and Development Strategy at the Japanese Science and Technology Agency, and a former president of Tokyo University, he was an engineer himself, who at one stage had invented such a nuclear emergency robot, which TEPCO had declined to purchase. Humiliatingly again, the company was belatedly forced to import robots from iRobot, a company in Bedford, Massachusetts, to deal with the crisis.
(Continues...)
Excerpted from Fallout from Fukushima by Richard Broinowski. Copyright © 2012 Richard Broinowski. Excerpted by permission of Scribe Publications Pty Ltd.
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