Fukushima and Chernobyl

Japan’s nuclear crisis is worsening, with no water left in the spent fuel pool of one of the reactors at the Fukushima plant and radiation levels extremely high. Greg Jaczko, chairman of the US Nuclear Regulatory Commission (NRC), said attempts to cool reactors with sea water and prevent them from melting down appeared to be failing.

The worsening crisis at the Fukushima power station in Japan has led to inevitable comparisons with the 1986 Chernobyl nuclear disaster that killed workers at the plant instantly, caused cancers in the surrounding population and spread radioactive contamination so far that livestock restrictions are still in place at some farms around the UK.

The situation at Fukushima – which the French nuclear agency estimates to be a level six "serious accident" (two up from the one at Three Mile Island in 1979) – is certainly grave and immediately dangerous for those at the site who are fighting to make the crippled reactors and fuel storage ponds safe.

But whatever warnings are now being issued by foreign governments to their citizens in Japan, there are significant differences that set this apart from the catastrophe in Ukraine, even as the US Nuclear Regulatory Commission warned that a pool of spent fuel rods at Fukushima had boiled dry.

At Chernobyl the nuclear reactor exploded after a surge in power that blew the top off the power plant and sent hot fuel – and importantly, its more radioactive fission products – high into the upper atmosphere, where it floated across national borders.

A fire that broke out in the graphite core forced more radioactive material into the air, helping it spread further. The reactor had no containment facility to even slow the release of radiation from the plant.

The Fukushima boiling water reactor is a 40-year-old power plant and it has some glaring design flaws, but the reactors have been switched off for five days, so there is less fresh radioactive material around, and each core is contained within a 20cm-thick steel container, which is then protected by a steel-lined reinforced concrete outer structure. Even in the case of a meltdown, these measures should at least limit the amount of radiation released.

The most significant health effect from Chernobyl was a steep rise in children with thyroid cancer–more than 6000 cases, according to a recent United Nations report. To lessen the chances of such an increase, people living near the plant are reportedly being given potassium iodide tablets. The idea is to flood the thyroid with iodine and block any inhaled or ingested radioactive iodine-131 from entering the thyroid. But "timing is critical," says Fred Mettler, an radiology professor emeritus at the University of New Mexico who led an international team that investigated health effects from the accident. If taken 1 day before an exposure, the pills are 80% effective, he says; if taken during the point of exposure, 100% effective; 8 hours later, 30%. (Except for pregnant women, there’s not much reason for adults over 20 to take the tablets, Mettler adds, because their cancer risk is low.)

At Chernobyl, iodine-131 also got into the food supply via milk from cows that had fed in pastures tainted with radioactive iodine. Japan can avoid this consequence by barring cows from grazing in contaminated pastures, he said, or by storing any milk products or cheese for 80 days until the radioactivity is gone.

Another risk is cesium-137, which can also be spewed into the air from a nuclear plant. Its half-life is 30 years. In Chernobyl, it entered the food chain through soil and ended up in meat, berries, and mushrooms. One solution is to plow up a half-meter or more of soil, Mettler says. But the isotope also leaves the body within 2 months, so another option is to feed livestock clean food for a few months before slaughter, Mettler says. (People who accidentally ingest radioactive cesium are sometimes given a chemical called Prussian blue that binds to the cesium and helps the body to excrete it. But taking pills for weeks cuts exposure only by 50%, and levels in Japan will likely be too low to warrant such a step, Mettler says.)

Japan is also minimizing people’s exposure by evacuating the area 20 kilometers around the plant and advising people living within 10 kilometers outside that area to stay indoors. Those steps will reduce their exposure to both gamma rays (which are attenuated by walls) and to airborne radioactive particles.

The bottom line, Mettler says, is that radiation levels measured by monitors don’t equate with what actually enters people’s bodies. "The trick is to keep people from being exposed."

U.S. Energy Secretary Steven Chu said Wednesday he believes a "partial meltdown" occurred at the Japanese nuclear-power plant damaged by explosions, malfunctions and radiation leaks following a 9.0-magnitude earthquake.

Mr. Chu added, however, that Japan’s Fukushima Daiichi nuclear-power plant has containment systems to prevent leaks and that a partial meltdown doesn’t mean the "containment systems will fail."

Speaking before a U.S. House Energy and Commerce subcommittee, Mr. Chu said he believed the events unfolding in Japan "actually appear to be more serious than" the 1979 partial core meltdown at Three Mile Island in Pennsylvania.

Nuclear Regulatory Commission Chairman Gregory Jaczko called the incident in Japan a "very serious situation." Speaking at the same House energy committee hearing, Mr. Jaczko said the U.S. was monitoring at least four of the reactors at the Fukushima plant. The core cooling at the second unit "is not stable," but that the primary containment continues to function, he said.

At a third unit, Mr. Jaczko said he believes there could be a crack in the spent fuel pool, increasing the risk that water drains from the pool and leads to overheating.

At a fourth reactor, which was not operating at the time of the earthquake, Mr. Jaczko said there had been a hydrogen explosion and that the secondary containment "has been destroyed." The spent fuel pool at that unit has lost all or most of its water and radiation levels "are extremely high," Mr. Jaczko said.

Given the risks, Mr. Jaczko said the U.S. would recommend a "much larger radius" for evacuations than Japan had imposed.

The comments come as Japanese officials struggled to extinguish smoldering spent fuel at the Fukushima Daiichi plant amid reports of high radiation levels.

Meanwhile, the White House announced that U.S. citizens within 50 miles of Japanese reactors damaged during the disaster should evacuate.

Mr. Jaczko made the recommendation to President Barack Obama in light of the "deteriorating" situation at Japanese nuclear reactors, White House Press Secretary Jay Carney said.

U.S. citizens needing assistance to evacuate should contact the U.S. embassy in Japan, Mr. Carney said.

Mr. Chu, at the House hearing, told the committee the U.S. is "trying to monitor very closely" and is sorting through conflicting reports. "There are several reactors that are now at risk. I would not want to speculate on exactly what will happen," he said.

Both Mr. Chu and Mr. Jaczko said the U.S. government had sent experts and equipment to help the Japanese. The Energy Department has sent 39 staff to the country and deployed air and ground equipment to try to track radiation levels. The Nuclear Regulatory Commission has sent 11 staff.

Fukushima Daiichi: What went wrong

* Reactor 1: Was first to be rocked an explosion on Saturday; fuel rods reportedly 70% damaged
* Reactor 2: There are fears a blast on Tuesday breached a containment system; fuel rods reportedly 33% damaged
* Reactor 3: Explosion on Monday; smoke or steam seen rising on Wednesday; damage to roof and possibly also to a containment system
* Reactor 4: Hit by a major blaze on Tuesday and another fire on Wednesday