Causes and hazards of nuclear accidents

A handout image of Fukushima Daiichi nuclear plant located in the town of Okuma, Japan. Photo: AFP

A handout image of Fukushima Daiichi nuclear plant located in the town of Okuma, Japan. Photo: AFP

With the very recent news of a nuclear accident in an already devastated area of Japan, resembling the World War II atomic bomb devastation, there is growing concern about the present situation.

The nuclear reactor is like a sealed electric kettle element which, however, is inserted into a pressure cooker. By means of a pump, water is passed through the pressure cooker to be heated by the nuclear element or reactor. The hot water is converted to steam which goes to a turbine producing electricity. The speed and heat of the nuclear reaction is reduced by dipping control rods into the uranium fuel, mopping up the neutrons generated by uranium breakdown. The circulating water also functions as a coolant because it is designed to take some heat away from the nuclear reactor to prevent overheating.

As a result of the earthquake automatically switching off the electric power, there was no electricity to work the water circulation. The tsunami stopped an electric power backup a short time later. With no water circulation, the electric turbines failed, and the hot water/steam became hotter and more pressurised causing an explosion (“water explosion”) despite previous venting. While the venting should have contained steam only, some radioactive iodine and caesium contamination was observed, indicating a leak of these breakdown products from the nuclear reactor into the water circulatory system. Also with no water circulating, the temperature continued to rise causing the uranium neutrons to split water into hydrogen and oxygen which when they recombined produced a second explosion (“hydrogen explosion”).

Both these explosions have cracked the walls of the containments around the nuclear reactor which is inside another containment holding the water circulatory system which in turn is inside a third containment – like Chinese boxes. These cracks have allowed leakage of radioactivity from the uranium reactor and also chemicals (now radioactive) from the lining of the walls to the outside air.

In a desperate attempt to lower the ever increasing temperature, seawater has been poured over the uranium, so this of course means there is exposure of uranium and its radioactive products to the outside air adding to the pollutants.

If the temperature rise cannot be checked then melting of the walls of the nuclear reactor will occur with massive leakage of uranium and its many radioactive products into the air and soil contaminating the water table and crops and so entering the food chain. One of the worst is radioactive iodine which is picked up by the thyroid gland to produce cancer of it later. Another is strontium which is stored in the body long term.

In the 1950s, when I was a medical student on a walking tour, I was amazed to see stunted cows with asymmetric faces in fields near a nuclear reactor known as Winscale (now called Sellafield) where a little earlier there had been a meltdown causing a release of various radioactive chemicals which damaged the chromosomal DNA producing deformities, and which had contaminated the fields so that crops and milk had to be discarded for some years.

What is the treatment for the Japanese? If meltdown seems likely then draconian measures are commenced. The first is to remove the population as far away as possible from the radiation source with instructions to stay indoors and to remain well covered with clothes to avoid skin contamination by these radioactive chemicals.

One potassium iodide pill daily is taken to prevent the thyroid picking up the cancer-causing radioactive iodine. There is no pill for other radioactive contaminants.

Bottled drinks and uncontaminated food are all that is safe to ingest. If venturing outside, then wearing a respirator or a mask stops contamination droplets entering the body. Showering on return will wash away radioactive skin contaminants.

In Malta we are thousands of kilometres away so precautions are unnecessary apart from avoiding contaminated Japanese food. Hopefully reactor meltdown is prevented thus reducing the extensive, atmospheric, radioactive fallout which featured in the Chernobyl meltdown.

Several nuclear reactor accidents have revealed that when the cooling system fails, the inherent run-away tendency of uranium to overheat cannot be easily overcome, risking meltdown.


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