Second Explosion at Stricken Japanese Nuclear Plant; Radiation Risk Is Low

Zosia Chustecka

March 14, 2011

March 14, 2011 — Another explosion has hit the Japanese nuclear plant damaged by last Friday's earthquake and resultant tsunami, raising new fears about potential meltdown and radiation exposure.

Japanese prime minister Naoto Kan described the situation at the nuclear plant as "alarming" and said the earthquake has thrown Japan into "the most severe crisis since World War II."

The earthquake and tsunami on March 11 have wrought terrible destruction across northeast Japan, with tens of thousands of people missing and presumed dead. One town alone has officially listed more than 9500 missing — more than half of the total population of Minamisanriku. Situated on the coast nearest the epicenter of the earthquake, it was flattened by the tsunami, and only a few concrete structures, including the hospital, now remain standing.

Amid the devastation, there is increasing concern over a potential nuclear disaster, following explosions at the Fukushima Daiichi nuclear plant, also situated on the coast.

Map of nuclear power reactors in Japan.

Damage from the earthquake and tsunami, as well as from aftershocks, have resulted in failure of automatic cooling systems, leading to a build-up of heat and hydrogen, escape of radioactive steam, resulting in explosions.

According to the Tokyo Electric Power Company's (TEPCO) Web site, the Fukushima Daiichi plant has 6 functioning nuclear reactors. However, reactors 4, 5, and 6 were down because of regular inspections. The 3 reactors that were operating were all shut down after the earthquake, but soon afterward the Japanese government announced a nuclear emergency because of a reactor cooling system malfunction at reactor 1.

Even when reactors are shut down safely, they have to be cooled constantly to avoid a meltdown of the core. "Reactors are not like your car that you can turn off and walk away. They're going to continue generating a great amount of heat until the core is disassembled," explained Ron Chesser, PhD, director of the Center for Environmental Radiation Studies at Texas Tech University in Lubbock. "Without cooling water, then you stand a real chance of a meltdown of core that could result in a large release of radiation, potentially."

Despite efforts to cool the reactor, including pumping in seawater, there was an explosion at reactor 1 on Saturday afternoon, and another at reactor 3 today. TEPCO said that 4 people were injured in the first explosion, and 7 in the latest explosion.

In addition, reactor 2 is also has problems with its cooling system: water levels are falling, and sea water is being pumped in, said Japan's Chief Cabinet Secretary Yukio Edano. These were the same problems that preceded the explosions in the other 2 reactors.

The area around the nuclear plants has been evacuated — initially to a radius of 1.9 miles, affecting 3000 people, but after the first explosion that was increased to a radius of 12 miles, affecting 140,000 local residents.

The fear is that there will be a release of radiation if the problems at the nuclear plant cannot be contained.

The Japanese government was reported to be distributing potassium iodide tablets to prevent radiation sickness. This is a standard procedure in the event of a nuclear alarm. Ingestion of potassium iodide saturates the body with a stable form of iodine and protects the thyroid gland from taking up radioactive iodine, which may be released in a nuclear accident.

Understandably, this is a highly sensitive issue in the only country in the world to have suffered from widespread radiation sickness after the atomic bombs fell on Hiroshima and Nagasaki.

So far, however, there has been limited release of radiation. At a news conference on Sunday, Edano dismissed worries that the radiation posed a public-health threat, according to an article published today in the English-speaking version of The Japan Times.

Dr. Michael Corradini

An emergency status is triggered when the radiation released per hour amounts to more than one tenth of the natural background radiation, explained Michael Corradini, PhD, chair of engineering physics at the University of Wisconsin in Madison. Some radiation released on Friday after the earthquake reached this level, but since then the radiation levels have been decreasing continually, and as of Monday, the measurements are now below this trigger level, he said.

The radioactivity would have been released in steam escaping from the plant as the reactor was being cooled, he explained. This is part of the safety procedure, he continued, to vent the steam coming off the reactor into the building that surrounds it.

"The impression I get from reading the news reports is that they had a stoppage that allowed the coolant to fall to a level inside the reactor core such that the metal cladding of the core, which is made of zirconium, started to chemically react with the steam, which produced hydrogen," he told Medscape Medical News. Following safety procedures, they would have then vented the steam from the containment building, and the released hydrogen would have normally been inerted in containment, but it appears to have built up and ignited in the reactor building, and that exploded, blowing off the top of the building, he said.

Dr. Corradini emphasized that only the outer building was in the explosion. The nuclear material is in the reactor core, which is surrounded by metal cladding, and this is housed in a steel reactor vessel within a larger steel containment. "It's the building outside this containment that we see in the explosion," he said. The Japanese Nuclear and Industrial Safety Agency has made a point of emphasizing that the containment vessel is still intact, he noted.

These hydrogen combustion explosions themselves "are not a disaster," Dr. Corradini commented; what's gone is the "industrial building that keeps out the weather."

"That's not the safety issue," he said. "The issue is, has this promoted any radiation release, and the answer to that, as far as I can tell, is no."

From the reports both inside Japan and from measurements taken by US ships in nearby waters, the radiation release so far has been comparable to that seen in the 1979 disaster at Three Mile Island (TMI) in Pennsylvania, Dr. Corradini commented.

In that incident, which involved a partial meltdown, there was also a venting of gases, and there was release of small amounts of radioactivity and radioactive iodine, but there have been no documented health consequences — there were no early health effects, no genetic damage, and no latent cancers recorded in the 32 years since then, he pointed out.

"For me to say it's the same here [regarding Japan] is inappropriate, as we are only 3 days into this calamity, but as far as I can see from what I have read, they have the situation under control, and I would hope that the radiological consequences would be similar to that seen after TMI," he said.

"That's a million times less than after Chernobyl," Dr. Corradini added, referring to the 1986 disaster at Chernobyl in the former USSR, which resulted in widespread release of radioactivity and documented adverse health consequences for years afterward, including cancers.

A Chernobyl-like disaster is not possible in this case, he emphasized — this is a totally different type of reactor with a different design.

"Some news reports have been very misleading and causing inappropriate amounts of concern by suggesting that this may lead to another Chernobyl-like disaster," he said. "It's fair and rational to inform the general public that there has been radiation release, and to ask questions about the health consequences about that...but we should be fair and rational about this."

The medical aid group Doctors Without Borders (Médicins sans Frontières) said that they are "closely monitoring the situation around Fukushima nuclear power plants. If there is a serious nuclear incident, it is only the Japanese government that will be in a position to react."

"The longer-term impact of the tsunami and the resulting nuclear problem cannot really be understood at present. However, there are international teams of experts on the scene and so the world's expertise is being brought to bear on this serious issue," commented Kirby Kemper, PhD, professor of physics at Florida State University in Tallahassee.

"To me, it will be another 3 days before the reactors are fully under control, and then the assessment can begin," he told Medscape Medical News.

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