18 March 2011

Nuclear disaster: five questions

The nuclear disaster in Japan has prompted Health24 to ask a nuclear physics expert five important questions.


After the 9.0-magnitude earthquake and tsunami in Japan, four of the troubled Fukushima Daiichi plant's six reactor units have seen fires, explosions or partial meltdowns, and workers are risking their lives day and night to try and cool the overheating reactors.

Low levels of radiation have been detected well beyond Tokyo (220km south of Fukushima) and the zone within 20km of the plant has been evacuated, while people within 30km were told to stay indoors; and yet officials insist that hazardous levels are limited to the plant itself.

The World Health Organisation (WHO) has added its voice with reassurances on Friday that the radiation risk from Japan's nuclear crisis remains highly localised.

Health24 asked nuclear physics specialist Dr Shaun Wyngaardt from Stellenbosch University to shed some light on these questions.

1) There are so many conflicting reports. What exactly is going on at Fukushima, and should we be worried?

These higher levels of radiation are due to the cooling problems which were experienced at the time. The latest is that the levels are significantly lower that recorded on Wednesday. Fortunately the public measured radiation emitted directly from the plant drops as 1/ (distance)^2. This means that if one doubles the distance, the radiation levels are expected to drop by a factor of 4.

The main problem at the moment is the airborne radioactive contamination which is bubbling out of the reactor and which is currently moving in the upper layers of the atmosphere. As long as the atmospheric conditions are stable (such as no turbulence caused by strong winds) this radioactive cloud won't expose the larger population at ground level too much.

The largest concentration of radioactive material which is found in this cloud is Iodine-131, which has a half-life of 8 days. This means that the amount of this substance will be dropped by a factor of two in 8 days. [Half or it will have decayed after 8 days, and half of that in another 8 days etc.] 

2) Do you believe the experts will be able to contain the radiation leak and avoid a nuclear disaster? What is the long-term prognosis for Japan?

The last news report I saw mentioned that radiation workers have returned to the plant and that radiation levels have dropped to safer levels. Japan has always had a good track record in terms of its nuclear reactors. This dramatic turn of events, however, has shown some of the cracks in the safety aspect of the nuclear reactor industry which need to be addressed.

These reactors, Koeberg included, are well prepared for earthquakes of the magnitude experienced by the North Eastern part of Japan on Friday.  But no one comprehended the type of damage the tsumani would cause in the generators which ensure that a steady flow of coolant (in this case heavy water) gets pumped though the reactor core to prevent it from overheating (as was happening these past few days).          

3) According news reports, South Korea is planning to transfer its reserve boron to Japan, to help to stabilise the quake-damaged nuclear reactors. Can you please explain how the boron will help?

Boron is an element that acts as a "moderator" and dampens the nuclear fission reactions (splitting of uranium nuclei) which are taking place in the nuclear reactor's core reactor. It helps to slow it down in order to prevent further generation of heat, and the eventual overheating of the reactor core.

4) The nuclear crisis has reminded people of the possible dangers involved in nuclear energy- there is a new call for the closure of such facilities and a halt on any further plants to be built. What is your opinion of this? Is this an overreaction or are these fears justified?

Renewable energy is most certainly an option for the near future, however, the more realistic alternative for industrialised countries with a very heavy demand for electricity seems to be nuclear and coal. Coal power stations, of course, are not too popular at the moment because of concerns around climate change and global warming. 

The better compromise would be a well-balanced combination of renewable energy and the newer generations of inherently safer nuclear reactors (such as the Pebble Bed Modular reactor type of designed reactors).

As renewable energy sources improve in efficiency we should see more of this technology appear on the forefront.     

5) A website has reported that spent fuel bundles (used to generate the heat to drive the turbines) have been stored on site at the Fukushima plant for years instead of moving them to another location. Speculation is that these fuel bundles are very toxic - adding to the pollution and a potential natural disaster. What is your opinion of this?

The Japanese have, for the past decades, put enormous effort into ensuring that their spent fuel containers (which contain high level nuclear waste) survive the most stringent conditions or stress, corrosion, pressure, and heat. I do not see this as a potential risk at this stage.   

(Source: Dr Shaun Wyngaardt, nuclear physics specialist, Department of Physics, Stellenbosch University)

 - (Birgit Ottermann, Health24, March 2011)

Read more:

Nuclear meltdown
Radiation and you
17 quick facts on potassium iodide
Worse threats than radiation


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