After reports of two explosions at a nuclear power plant in Japan following Friday’s devastating earthquake, experts say that the radiation risk to the public appears low; it’s looking “more like Three Mile Island than Chernobyl”, the director of the Center for Radiological Research at Columbia University in New York City, Dr David Brenner, told the New York Times.

Japanese authorities said the first blast on Saturday destroyed the concrete shell surrounding reactor number 1 at the Tokyo Electric Power Company nuclear power plant in Fukushima Dai-ichi, 150 miles (241 km) north of Tokyo.

Since then, a second hydrogen explosion has occurred at the plant but the Japanese authorities told the press the inner reactor container remains intact, reports Sky News.

11 people were injured, four members of the army and seven workers at the plant, after Unit 3 at the nuclear plant exploded on Monday. One of the injured is in a serious condition.

Yukio Edano, Japan’s chief cabinet secretary said the inner containment vessel that holds the nuclear fuel rods is safe and that the chances of a radioactive leak were “low”.

He said people within a 12 mile (20 km) radius of the plant were being ordered to stay indoors.

Earlier today, the US Seventh Fleet, which was positioned about 100 miles (160 km) off the coast of Japan said it had moved its ships and aircraft further away after its instruments detected low-level radiation.

According to a report from the Associatied Press, the fleet said the dose of radiation was around the equivalent of one month’s normal exposure to natural background radiation in the environment.

The explosions are thought to have occurred as a result of hydrogen build up from a chemical reaction between water and overheated metal sheaths surrounding the nuclear fuel rods. As a result of the earthquake, the normal cooling systems failed, and the authorities have taken emergency measures, including pumping in sea water, to cool the reactors.

A UK nuclear expert, Robin Grimes, director of the Center for Nuclear Engineering at Imperial College London, told Reuters that it does not look as bad as Three Mile Island:

“What’s clear because of the incidental radiation being released at the moment, which is significant but not overwhelming, is that the structure of the core is probably still intact”.

In the meantime, the Japanese authorities are focusing on a three-pronged strategy to stop the public from getting contaminated: evacuation, shelter and iodine pills.

These are the three weapons against civilian contamination, said Patrick Gourmelon, director of radioprotection at a French nuclear watchdog, the Institute for Radioprotection and Nuclear Safety (IRSN), according to an AFP agency report.

According to Sky News, the Japanese authorities are warning people not to drink tap water and to take iodine to prevent throat cancer.

The Chernobyl disaster occurred in April 1986 when an entire nuclear reactor blew up, vaporizing its radioactive fuel and sending up a radioactive cloud of dust over parts of Ukraine and Belarus.

This was followed by an epidemic of thyroid cancer and increases in cases of leukemia, said Brenner.

A UN estimate puts the death toll at 4,000, but other non-governmental groups say it was much higher than this.

The Three Mile Island accident was in 1979 in Pennsylvania in the US, when a partial core meltdown occurred in a pressurized water reactor. Brenner said the radiation released from Three Mile Island was about a millionth of that released by Chernobyl.

There is no evidence that anyone got sick as a result of Three Mile Island, said Brenner, “even decades later”.

Exposure to radiation interferes with DNA in cells, compromising their ability to divide and make healthy new cells. To keep us alive and healthy, our cells have to keep dividing, making new ones, allowing old ones to die, and get recycled. Especially in our gut, where the turnover rate is quite high, as in the cells in our bone marrow that make blood cells.

Fetuses and children are the most vulnerable groups.

The severity of medical symptoms from radiation exposure depend on two things: the strength of the radiation, and the duration of the exposure.

High levels of exposure cause severe radiation sickness with symptoms including fatigue, nausea and vomiting, hair loss, hemorrhage and diarrhea.

Very high doses eventually lead to death, which can occur up to several weeks later. Brenner said this is usually as a result of the lining of the gut being depleted.

However, the most likely risk to the public from what is happening in Japan, according to the current view from experts, which is highly dependent on the information being released by the Japanese authorities, is that of low-level exposure.

This can increase the risk of cancer many years later, but it depends on what types of radioactive materials people are exposed to and for how long. Some materials, like tritium, pass quickly through the body, while others travel to a particular part of the body and linger.

Most of the very dangerous substances, such as uranium and other heavy metals, would probably drop to the bottom of the containment vessel and not get released into the air, they would have to be recovered by nuclear hazard teams later.

The danger to the public is from the radioactive chemicals that are spewed into the air: smaller than a grain of sand, they can get into a person through their lungs, into their mouths and via the skin. And depending on the dose, they can lead to cancer years later.

These include for example, iodine-131 and strontium-90.

Iodine is normally present in our diet and travels to the thyroid. Strontium is not normally in our diet, but because it behaves chemically like calcium, it travels to bones and teeth.

According to the US Environmental Protection Agency, iodine-131 has a half life of eight days, which means after a year, it is no longer radioactive. Strontium-90 on the other hand, has a half-life of 29 years, which means basically, once in the body, it remains radioactive for most a person’s lifetime.

Brenner said while giving iodine tablets will help protect people against inhaling radioactive iodine, there is also a need to address the indirect route through which it gets into the body.

For instance, in the case of Chernobyl, many of the cancers that occurred years later came from eating dairy products contaminated with radioactive iodine that had fallen to the ground and been eaten by cows.

Brenner also said that another route was contaminated crops:

“I wouldn’t be eating an apple from a tree close to the [nuclear] plant,” he told the New York Times.

Sky News reported on Sunday that around 200,000 people have been evacuated from near the Fukushima Dai-ichi plant where the explosions have occurred, and also from near the Fukushima Daini plant nearby.

Sources: New York Times, AP, Wall Street Journal, AFP, BBC, Sky News, US Environmental Protection Agency.

Written by: Catharine Paddock, PhD