The last thing Japan needed was more bad news on its threatened nuclear reactors. But Monday and early today, that's just what this nation got.
By JiJi Press, AFP/Getty Images
An unprecedented series of crises in the reactors at three of Japan's 54 nuclear power reactors, triggered by Friday's massive quake and tsunami, is continuing to fuel fears of a fresh, enduring catastrophe of radioactive contamination — a prospect that is particularly alarming in the only nation to be attacked with atomic bombs.
In one reactor at the Fukushima Dai-ichi plant, nuclear fuel rods were exposed when they were dangerously depleted of cooling water. In two other reactors, hydrogen explosions have blown the roofs off their surrounding buildings. And early this morning, another explosion occurred. Like the others, it was the result of hydrogen building up in the outer building that surrounds the reactor.
Japan's Nuclear and Industrial Safety Agency acknowledged Monday that radiation levels at the plant had increased. Japan has evacuated nearly 200,000 people from areas near the Fukushima Dai-ichi plant and the Fukushima Daini nuclear plant nearby. The International Atomic Energy Agency said Japan had distributed 230,000 units of iodine — which can counter radiation's effects on the thyroid — to evacuation centers as a precaution.
Late Monday, Chief Cabinet Secretary Yukio Edano said a fire had started among spent fuel rods at the plant, sparking further radiation worries. The Associated Press reported that Japan's nuclear safety agency said the fire had been extinguished.
Edano said that "although we cannot directly check it, it's highly likely," that nuclear fuel rods were melting in the plant's three working reactors.
Even so, "the Japanese government's troubles are immense and unprecedented," says Peter Bradford, a former U.S. Nuclear Regulatory Commission official. Amid the damage from an earthquake and tsunami that the U.N. said has left more than 10,000 missing, nuclear engineers likely will spend the next several days — maybe weeks — battling to keep the reactors from overheating and melting.
"They do not have the situation under control," says nuclear safety specialist Robert Alvarez of the Institute for Policy Studies in Washington, D.C., a former Energy Department official. He warns that the reactor containment walls may have been breached in the disaster.
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Japanese nuclear agency official Naoki Kumagai says it is "impossible to say" whether such damage has occurred.
At the White House on Monday, Nuclear Regulatory Commission Chairman Greg Jaczko said, "We see a very low likelihood that there's any possibility of harmful radiation levels in the United States or in Hawaii." The commission sent two reactor experts to Japan on Sunday, as part of a U.S. Agency for International Development team helping with the quake crisis.
"Based on the information we have, we believe that the steps that the Japanese are taking to respond to this crisis are consistent with the approach that we would use here in the United States," Jaczko said.
The crisis has raised new concerns about the safety of nuclear reactors at a time when they've been enjoying a renaissance in a world looking for alternatives to fossil fuels.
So now the question is whether engineers can get the plants under control and prevent radioactive contamination.
'Three Three Mile Islands'
The crisis with Japan's reactors began Friday, when the quake cut power to the Fukushima Dai-ichi plant. Then the tsunami took out the plant's backup generators, which were being used to power the cooling systems for the reactor cores.
At the plant, two of three troubled reactors (Units 1 and 3), soon were in danger of catastrophically overheating. On Monday, the cooling system failed in a third reactor, Unit 2, leaving the nuclear fuel rods completely exposed and raising, at least temporarily, the threat of a total meltdown of the rods as plant engineers pumped in seawater in a desperate attempt to cool the rods.
Meanwhile, on Monday morning the roof on the containment building for Unit 3 blew off in an explosion caused by a mix of steam and hydrogen venting inside the building. Eleven workers were injured. The building that houses Unit 1 had blown apart on Saturday.
Then, this morning, the building housing Unit 2, with its dangerously overheating nuclear core, also experienced an explosion. Shigekazu Omukai, spokesman for Japan's nuclear safety agency, said the bottom of the container that surrounds the reactor might have been damaged. Another agency spokesman, Shinji Kinjo, says that "a leak of nuclear material is feared."
In all, it means officials are struggling to tame all three reactors, and it's difficult to tell how well they're doing so. Most analysts doubt the situation will create a scenario like that of Chernobyl in Soviet Ukraine in 1986, where a nuclear plant caught fire and sent dangerous levels of radiation over an area half the size of New Jersey.
They drew parallels to another iconic disaster in the history of nuclear power.
"This is going to be worse than Three Mile Island. We basically are looking at three Three Mile Islands," says nuclear consultant Lake Barrett, a former Energy Department and Nuclear Regulatory Commission engineer. However, Barrett and other analysts say the nightmare scenario of fuel rods melting through the steel floor of the reactor chambers is highly unlikely.
"We are three days into the shutdown of these reactors, so we are not looking at the total melting of the core," Barrett says.
In 1979, a stuck valve and operator error led to coolant water draining from a reactor at the Three Mile Island plant near Harrisburg, Pa. After officials initially told people not to worry, they ordered an evacuation in which 140,000 people temporarily left their homes.
Investigators learned weeks after the accident that the 16 hours the reactor went without cooling had led to the melting of the reactor's fuel rods. Plant operators were forced to vent radioactive gas from the overheated reactor for months to relieve pressure on the reactor chamber. No deaths or cancer cases have been tied directly to the release of those vent gases from Three Mile Island.
In Japan, plant operators face a similar dilemma, forced to vent radioactive gas from the overheating reactors at Fukushima Dai-ichi.
At the nearby Fukushima Daini facility, engineers have reported signs of three more reactors overheating, leading them to vent gas. A third facility, the Onagawa nuclear power plant, also is under a state of emergency.
"What we have here are reactors that are overheating, so we have to cool them," says radiation safety specialist Bruce Busby of the Fred Hutchison Cancer Research Center in Seattle.
The cooling challenge
On Friday, when the magnitude-9.0 earthquake rocked Japan, all of the reactors now in trouble automatically shut down. All are boiling water models. Normally, they generate steam to make electricity, which then cools and returns to the reactor chamber as water, ready to be boiled once more. Control rods that turn off the atomic reaction between the fuel rods automatically slid into place as soon as the quake started, sensed by motion detectors in the floor of the reactor facility.
Despite the shutdown, the rods didn't cool off immediately. Leftover radioactive heat remained inside the rods, perhaps 6% of their normal operating energy. In a normal shutdown, cooling systems and pumps would control those temperatures, dissipating them until the radioactive materials inside the rods finished cooking off most of their energy in the coming days to weeks.
Instead, the tsunami disrupted power for the pumps and cooling systems, leading the rods to heat up, boiling off the water that normally cools them. On Saturday, the Tokyo Electric Power Co., which owns all three power plants, alerted government officials to overheating in two reactors, triggering emergency declarations.
"The problem then, is removing that (radioactive) decay heat," says nuclear engineer John Gilligan of North Carolina State University in Raleigh.
Without cooling, Tokyo Electric Power Co. officials face a cascade of problems:
•The temperature in the rods rises, boiling off more water, exposing the rods to steam and air.
•Once exposed to steam and air, the rods begin heating, leading to blistering of the metal that covers them, letting radioactive elements escape.
•The blistering also creates a chemical reaction between the steam and metal, generating hydrogen gas that builds unsafe pressure in the reactor.
While generators were rushed to the power plants to restart power to the cooling system over the weekend, engineers needed to vent radioactive gas from the reactors to relieve this pressure. Desperate to cool the reactors, they turned to piping seawater into two reactors at the Dai-ichi plant. "That's an extraordinary thing to do," Alvarez says, because it means the reactors, billion-dollar machines in today's market, will be contaminated and never used again. Alvarez and others point to still more problems at the reactors:
•Plutonium fuel inside one reactor, different from the uranium used in the other reactors, may take longer to cool down than others, raising its risks. Barrett calls that a very small concern.
•Venting the hydrogen inside the reactors led to explosions that have injured 15 workers at the plants, and blew the roof off the outermost containment building housing two of the reactors.
•Used-up fuel rods are on-site, kept in water pools above the reactors. Leaks from those pools could lead to the release of radioactive elements in the old, used-up fuel rods.
If steps to cool the reactor proceed without further mishaps, the reactors should cool in the next few weeks, Gilligan says. Engineers will likely continue having to vent small amounts of radioactive gas from the reactors for months however, to keep the pressure off, even under the best of scenarios.
"That's how it was at Three Mile Island," Barrett says. "The weather report would say, 'Today will be sunny, and they will be venting gases today from the plant.' "
Contributing: The Associated Press
Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
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