Alexander Sich, nuclear engineer and associate professor of physics at the Franciscan University of Steubenville, was the first Westerner permitted to live and work within the exclusion zone to investigate the Chernobyl accident. The results of his year-and -a-half research stint in the Exclusion Zone was published in three articles of the Nuclear Regulatory Commission's journal "Nuclear Safety" in 1994-95.

 

The world marks the 25th anniversary of the nuclear accident at Chernobyl on Tuesday, and with that will come continued incorrect -- sometimes sensationalist -- comparisons to the crisis at the Fukushima plant in Japan. Before the public can make sense of such claims, it needs to better understand what happened at Chernobyl.

Initial deaths numbering in the thousands were incorrectly reported by the Western press in Chernobyl's wake. Even with a complete meltdown of 75 percent of the plant's core and massive releases of radioactivity, the number of deaths directly attributable to the accident remains at 32. Notwithstanding the complexity of measuring radioactive exposure retrospectively, some estimates place the number of deaths from childhood thyroid cancers since then in the hundreds, with incidences in the thousands. Yet, curiously, no leukemia has been detected.

Soviet officials misrepresented the success of stopping major releases of radioactive material by dumping thousands of metric tons of sand, boron and clay from helicopters, in an attempt to smother the melted, burning core. Most of those materials didn't even make it into the reactor shaft. In fact, the melted fuel froze by itself.

If anything, Chernobyl demonstrated that a "China syndrome" -- the melting of nuclear fuel through the bottom of reactor structures and deep into the ground -- isn't even theoretically possible. For comparison, roughly one-third of the Three Mile Island core dropped to the bottom of its pressure vessel, and it only managed to melt through about 5/8 inch of its 6-inch thick wall.

None of this is intended to downplay the magnitude of Chernobyl: It was indeed a human and ecologic disaster for the former Soviet Union, whose dissolution few lament. Attempts to minimize Chernobyl's impact are nothing short of repugnant.

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Yet misguided comparisons of Fukushima to Chernobyl help no one. In recent weeks, for example, some have claimed that the Chernobyl vessel and roof blew out simultaneously. In fact, Chernobyl-type reactors have neither a reactor pressure vessel nor containment structure -- two of the most important barriers that strongly block the release of radioactivity at Fukushima.

Also, claims that Fukushima could be far worse than Chernobyl are incorrect. Even taking the four Fukushima units and the spent fuel pools together, this is nonsense -- as Japanese radioactivity release figures support. At Chernobyl, the melting core was exposed to the environment for almost 10 days and fueled a huge graphite fire. At Fukushima, the containment and vessel barriers are still functioning to a large extent, and there is no graphite to burn.

Most troubling is reckless advice for the Japanese attempt to dump material on Fukushima from helicopters. Leaving aside ignorance of the ineffectiveness of these attempts at Chernobyl, dropping tons of materials from high in the air might compromise the very structures designed to contain releases at Fukushima.

 

So let's set the record straight.

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Three general causes led to the disaster at Chernobyl: a flawed reactor design, a weak Soviet safety culture (which instigated multiple operational violations), and pressure to exceed planned electricity generation.

Just one cause led to Fukushima: an earthquake-induced tsunami that damaged backup cooling systems.

Chernobyl-type reactors -- 11 of which still operate in the Russian Federation -- have no reactor pressure vessel, no containment structure and comprise roughly 1,700 pressurized fuel channels embedded in about 1,900 metric tons of graphite, the latter of which burns ferociously in extreme accident conditions and spreads radioactive ash. These three features weren't the causes of the Chernobyl disaster, but they greatly exacerbated the release of radioactivity from the accident.

In contrast, Western light-water reactors are contained in robust vessels, themselves located inside very strong reinforced-concrete containment structures. They contain virtually no graphite.

They are also stable, while the Chernobyl-type reactors are not: For the former, if the core gets too hot and too much water boils, nuclear reactions are inhibited; at Chernobyl, boiling actually enhanced the nuclear reactions.

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Characterizations of Fukushima radioactivity releases being equivalent to 1/10 of Chernobyl -- with some even asserting they are "on par with" or "equal to" -- are extremely misleading.

First, to whatever extent they maybe damaged, Fukushima barriers are still greatly suppressing potential releases. Remember that at Chernobyl, there were no barriers. The entire core was exposed directly to the environment.

Second, while the Fukushima radioactivity-release data may be credible, they apply largely to a particular kind of radioactive material: the isotope iodine-131, with an eight-day half-life that escapes as a gas. Even if the relatively small release of the 30-year-half-life isotope cesium-137 is considered, only trace amounts of other isotopes have been reported.

At Chernobyl, literally hundreds of isotopes with widely-varying half-lives were released in many ways. For example, uranium and plutonium were ejected mechanically, cesium was released by combining chemically with iodine, and the remaining iodine was most likely released as a gas.

Fukushima is not on par with Chernobyl: even if all releases are considered, Fukushima will still be lower than Chernobyl's single reactor.

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The Japanese government has repeatedly cautioned that levels measured for iodine and cesium outside the Fukushima plant "pose no immediate threat to health," even if ingested. Chief Cabinet Secretary Yukio Edano emphasized that there is no "direct health hazard," and that most of the radioactivity has been contained in large concrete vessels -- although these may be leaking.

A health risk adviser at Fukushima has noted that radioactive iodine, the cause of future childhood thyroid cancers, has not been detected in the more than 1,000 children already screened.

In the United States, the Environmental Protection Agency and Department of Energy have stated "no radiation levels of concern have been detected." Massachusetts public health authorities noted that even drinking rain water is "still 25 times less risky than it would need to be in order to cause any kind of health concerns."

 

For Fukushima, the Japanese voluntarily and provisionally rated three reactors at level 5, one at level 3, and the situation as a whole at level 7 on the International Nuclear Event Scale. It is indeed a major accident. But Fukushima's complexity does not lend itself to single-number characterizations -- which are akin to defining a person by his age or weight.

At Chernobyl, the extent of the structural damage was known within four months, but the health ramifications are still unfolding. At Fukushima, until a proper assessment of structural damage has been made and detailed radiological surveys are conducted, prudence suggests eschewing the sensationalist rhetoric of panic mongers.