Weeks after a massive magnitude 9.0 earthquake and subsequent 14-meter-high tsunami devastated Fukushima Prefecture in northeastern Japan, workers from the Tokyo Electric Power Co. (TEPCO) were still struggling to regain control of four severely damaged reactors at the six-unit Fukushima Daiichi nuclear power plant.

As of press time, more than 370 workers have been working around the clock to quell the crisis—the world’s worst since Ukraine’s Chernobyl disaster in 1986 (see the cover story). However, no end is in sight.

At the beginning of April, when 28,000 people were thought dead or missing in northeastern Japan, two TEPCO workers—Kazuhiko Kokubo, 24, and Yoshiki Terashima, 21—were the only confirmed fatalities at the plant. The workers, whose bodies were recovered in the basement level of Unit 4’s turbine hall, were thought to have died from multiple injuries sustained while conducting regular checks when the earthquake hit.

Twenty-one workers have so far been exposed to radiation doses of over 100 millisieverts—far exceeding the 50 millisieverts annually allowed by the U.S. Nuclear Regulatory Commission for adults working with radioactive material. Japanese authorities expanded the authorized threshold for radiation exposure to 250 millisieverts from the prior 100 millisieverts level set for emergency circumstances, but no one has been exposed to levels that high (Figure 1).

1. Suited up. In this photo, taken March 18, workers engaged in connecting the Fukushima Daiichi plant to the offsite power grid wear protective gear necessitated by elevated radiation levels near the damaged nuclear power facility. Courtesy: TEPCO

As of early April, engineers had managed to trace and plug a hole leaking highly radioactive water into the Pacific Ocean from a seaside pit at Unit 2, where, as in Units 1 and 3, fuel rods have partially melted.

Meanwhile, TEPCO continued disposal of 11,500 tons of water tainted with low levels of radioactivity from the radioactive waste treatment plant and sub-drain pits of Units 5 and 6 to make room for water with higher levels of radioactivity.

TEPCO also began injection of 6,000 cubic meters of nitrogen at Unit 1, where, 14 days after the disaster, temperatures reportedly surged to 400C, exceeding the unit’s design value of 302C. Nitrogen injection to displace oxygen and reduce the risk of another hydrogen explosion will also be carried out at Units 2 and 3.

At Unit 1—which was rocked by what TEPCO calls an “assumed” hydrogen explosion on March 12, a day after the massive quake—injections of seawater into the reactor have been replaced by freshwater additions, first via a temporary motor-driven pump and then by a motor-driven pump powered by an offsite transmission line.

At Unit 2—where the situation is more critical after an explosion is thought to have occurred on March 15 in the pressure suppression chamber, causing severe damage to the core and fuel integrity—TEPCO has replaced injections of seawater with boric acid–laced freshwater.

Freshwater is also being pumped into Unit 3, a reactor that has used mixed oxide fuel since September and where a March 14 explosion left the unit’s spent fuel tank exposed.

An explosion also occurred at Unit 4 on March 15. That unit had been shut down for routine inspection before the quake, but its fuel rods, stored in the spent fuel pool, were left without cooling water circulation to remove decay heat. For days, Japan’s defense force and TEPCO battled to cool down the spent fuel pools at Units 3 and 4, dumping seawater into the units by helicopter and riot-control water cannons. Periodic spraying continues at Unit 4’s spent fuel pool. The spent fuel pools at Units 5 and 6 are showing decreasing temperatures, and both units have reached cold shutdown.

The disaster has rattled Japan’s largest power utility, and its financial future is uncertain, as questions have been raised about its ability to pay mushrooming costs in the aftermath of the March 11 quake and tsunami. With the loss of Daiichi and other plants, TEPCO is struggling to meet power demand. Damage at four reactors of the crippled nuclear plant have rendered them useless; decommissioning could take three decades and cost up to 1 trillion yen (US$12 billion), TEPCO Chair Tsunehisa Katsumata has said.

Then, there are compensation costs. Though Japanese law exempts utilities from compensation for nuclear accidents caused by natural disasters, the government said it is “impossible” that TEPCO’s liability for the accident would be easily dismissed. And TEPCO itself in early April said it would consider payments to disaster victims, costs that could top US$130 billion if the crisis is prolonged, according to estimates from Bank of America–Merrill Lynch. TEPCO’s stock hit a 47-year low on April 6, at which point it had lost 82% of its pre-accident value.

It is unclear how much full cleanup will cost, though the consensus is that total costs will be staggering. The world’s top insurers have said the disaster will cost them $5 billion, although risk-modeling agencies suggest the overall cost to insurers could be as much as $30 billion. Calming fears of immediate bankruptcy, in early April, Japan’s major banks considered extending loans worth 2 trillion yen (US$24 billion) to TEPCO, and the Japanese government has not ruled out injecting capital into the beleaguered utility.

—Sonal Patel is POWER’s senior writer.