Challenges Mount at Fukushima, but Threat to Human Health Remains Low

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Each day seems to bring more news of the huge challenges facing the emergency workers at the Fukushima Daiichi nuclear power plant. As if adding insult to injury, a magnitude 7.4 earthquake hit the region on Thursday. Though Tokyo Electric Power Co. (TEPCO) reported no serious incidents as a result of the quake, the tremor was a reminder — as if one were needed — of how perilous the situation remains at the stricken plant. “The damage that has been done to date by the earthquake and tsunami has degraded the plant’s ability to withstand ground motion, so you have more chance of a containment breach with the next earthquake,” says Ed Lyman, a nuclear safety expert at the Union of Concerned Scientists. “The conditions at the plant are so fragile, it can’t really stand many more challenges.”

Four weeks after the 9.0 earthquake and tsunami damaged Fukushima, emergency workers continue to struggle to keep multiple hazards from spiraling out of control. Their effort will last months; eventual cleanup and decommissioning will take decades. Fukushima is already a messy, extremely costly nuclear disaster. But amid reports of cracked vessels and leaking radioactive water, it’s worth remembering that it will not necessarily be a harmful one to human health.

On Wednesday, Reuters reported that the head of a U.N. scientific body that focuses on the health effects of radiation said the Fukushima accident is not expected to have any serious impact — at least, barring any further radiation releases. Asked what health consequences he expected from Fukushima, Wolfgang Weiss, chairman of the U.N. Scientific Committee on the Effects of Atomic Radiation told a press conference in Vienna, “From what I know now, nothing, because levels are so low. We have seen traces of iodine in the air all over the world now, but they are much, much, much lower than traces we have seen at similar distances after Chernobyl.”

That, of course, would be a heroic outcome for the emergency personnel at Fukushima. But they have some serious work left to ensure that further radiation isn’t released. “It’s a bleak picture. The fact that they have to handle two spent fuel pools and two reactor cores … with no margin of error — it’s hard to say whether things are going to get better or worse,” says David Lochbaum, another nuclear safety expert with the Union of Concerned Scientists. “They are having to jury-rig solutions to problems that were never anticipated. And no one ever anticipated a problem on more than one reactor, which means you don’t have enough supplemental [emergency] equipment.”

The primary objective facing the Fukushima workers, according to Andrew Sherry, director of the Dalton Nuclear Institute at the University of Manchester, “is to cool the reactor fuel and the spent fuel in the storage ponds. All other activities at the plant are efforts to deal with the often unpredictable consequences of these cooling efforts.”

As an example, workers at Fukushima spent much of Wednesday injecting nitrogen into Reactor 1 to counter a buildup of hydrogen that had followed cooling of the fuel. That was necessary because as the reactor’s fuel rods cooled, steam inside the containment vessel condensed, reducing pressure inside the vessel. This encourages airflow back into the vessel, introducing oxygen that could react explosively with hydrogen.

TEPCO said the danger of another hydrogen explosion, like the one that blew the roof and upper walls off the reactor building on March 12, was “extremely low.” Nonetheless, it planned a similar nitrogen-injection procedure for Reactors 2 and 3, both of which are also suspected to have had hydrogen-oxygen explosions in the past.

Meanwhile, the U.S. Nuclear Regulatory Commission (NRC) believes that some of Reactor 2’s core has probably leaked from its steel pressure vessel into the bottom of the containment structure. The NRC did not disclose whether the fuel was in molten or solid form. If molten, it could potentially (in a worst-case scenario) burn through the cement containment structure around the reactor, through the ground and into the water table, from which it would spread and contaminate crops, livestock and land.

Reactors have five barriers to prevent the release of radioactive material: a fuel pellet, zirconium cladding around the fuel, the reactor pressure vessel, the containment vessel and the outer shell of the building. So, according to the NRC, all that remains to keep the fuel from the outside environment in Reactor 2 is the containment vessel and the outer shell of the building. Everything else has been breached.

Says Sherry: “It’s very difficult to know for sure what’s going on in the reactor cores because we can only make inferences from bits of evidence of radioactivity. Once they get the cores stable, they can go into the reactor cores and actually inspect them. I strongly suspect that these inspections will only reveal further complications and problems.”

The NRC believes that the fuel configuration in Reactors 1, 2 and 3 may be such that water can’t penetrate the fuel, either because salt from seawater has accumulated and blocked circulation or because the fuel itself has melted into a mass that prevents water from circulating through it. “This has been my concern, because if water can’t get in to cool the fuel, then boric acid [added by engineers to the water to prevent spontaneous fission] also can’t get in there to absorb neutrons and prevent criticality,” says Ferenc Dalnoki-Veress, a research scientist at the Monterey Institute of International Studies. (Read about Dalnoki-Veress’s work on the possibility of the reactors’ achieving re-criticality — which would cause grave danger to the emergency workers — here.)

Reports from Japan suggest that some of the challenges facing the workers may be a result of poor management by TEPCO. The government has repeatedly warned TEPCO about a shortage of working dosimeters, devices that measure doses of radiation. TEPCO has also reported several inaccurate isotopic concentration measurements, which scientists need to ascertain the condition of the fuel and the threat to the workers, leading to calls for an independent body to measure exactly what radioactive isotopes — and at what level — are present at the plant.

Says Dalnoki-Veress: “Sending workers into the nuclear power plant without dosimeters does not show that the company has the workers’ well-being prioritized. If TEPCO is unable to give the workers the needed resources, the world must move mountains to provide it to them.”