Japan reactor crisis no Chernobyl, Mac expert says

The crisis at a damaged Japanese nuclear power plant is serious but not as dangerous as the 1986 Chernobyl disaster, says a leading Canadian expert in nuclear safety.

Pressure inside one of six boiling water reactors at the Fukushima Daiichi plant is rising after Japan’s massive 8.9-magnitude earthquake knocked out primary and backup power to its cooling system.

Shutdown reactors remain very hot and must continue to be cooled to keep them from superheating steam and ultimately melting into radioactive slag if water levels fall to the point the reactor core itself is uncovered.

Because Japan is earthquake-prone, its 55 nuclear plants are built to very stringent seismic design requirements, said John Luxat, professor and NSERC industrial research chair in nuclear safety analysis at McMaster University’s Department of Engineering Physics. More importantly, unlike Chernobyl in Ukraine, Japanese nuclear power plants also have hardened containment structures over them.

“If cooling is not re-established, then, over time, the fuel in the reactor vessel becomes uncovered and you will get damage similar to what happened at Three Mile Island” in a Pennsylvania nuclear power plant accident in 1979.

It’s relatively easy to re-establish cooling, he said, even if it takes time because it can take many hours before enough water boils away to uncover the core.

Japan’s nuclear safety agency says pressure inside the disabled No. 1 reactor is now 1.5 times normal pressure and officials may vent slightly radioactive water vapour into the atmosphere to lower pressure. The agency says the release would not harm humans or the environment. “The containment structures are extremely strong reinforced concrete containment structures and I would anticipate they have not experienced much damage.”

Meanwhile, a top McMaster University mathematician who studies quantum and ocean waves was in California for a meeting Friday when the earthquake-generated tsunami that had crossed the Pacific Ocean with the speed of a jumbo jet struck North America’s West Coast.

“A tsunami is not a breaker multiplied by 100,” said Walter Craig, Canada research chair of mathematical analysis and its applications at McMaster University. A tsunami is generated when an earthquake displaces the sea bottom, which in turn displaces the water, transferring tremendous energy.
The earthquake that caused the Indian Ocean tsunami that killed 230,000 people in late 2004 thrust the sea bottom upwards about 60 centimetres, which was not particularly high, Craig said. The waves caused by the earthquake in Japan struck the California coast with enough power to crush boats in Crescent City, 500 kilometres north of San Francisco. “It impacted on a relatively low-lying, flat section of coast,” Craig said.

Radioactive iodine does not boost recurrence of thyroid cancer in Chernobyl survivors

A group of Russian and Japanese scientists has determined that people exposed to radiation during the Chernobyl disaster are unlikely to develop recurring papillary thyroid cancer as a result of subsequent treatment with radioactive iodine.

The team said this finding may have consequences both for people accidentally exposed to radiation and for those who have been medically irradiated as a treatment.

The disaster is still the only event to be rated with the highest level, a seven, on the International Nuclear and Radiological Event Scale, according to the International Atomic Energy Agency.

Researchers matched each participating survivor, all of whom were chosen because they had papillary thyroid cancer, with two patients who had papillary carcinomas unrelated to radiation exposure.

Each Chernobyl survivor had been exposed to between 50 milligrays and 3 grays of radiation. The latter exposure level can be fatal, even with medical care, in up to 50 percent of cases, the Merck Manual estimates.

Among these participants, this radiation was associated with the later development of thyroid cancer. The team conducted this study in order to determine if additional radiation - in the form of radioactive iodine therapy - would cause papillary thyroid cancer to recur among those who had previously been irradiated.

They found that the rate of papillary carcinoma recurrence among Chernobyl survivors was not significantly increased by radioactive iodine exposure.

Those treated according to the Revised American Thyroid Association Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer were most likely to stay free of papillary thyroid cancer.

In the U.S., nearly 45,000 people are diagnosed with thyroid cancer every year, according to the National Cancer Institute.