Fukushima nuclear plant – frequently asked questions

There have been a lot of questions asked over the last few days as the Japanese try to control results of the damage from the Fukushima Dai-ichi nuclear plant.

Many people are concerned, but not sure what the true consequences are of the nuclear leak and the effects of the explosions which have occured at reactors 1 and 2 and the fire at reactor 4.

I will add to this FAQ list as and when I am asked more questions, but here are a few common ones:

I heard there was a release of radioactive material at one of the Fukushima plants, how much was released and is this dangerous?

The highest level of radiation was measured at the front gate of Fukushima number 1 plant during the radioactive release.  It was equal to 8217 microsieverts per hour.

To put this in perspective, if you went to hospital and had 1 abdominal CT scan, you would be exposed to 10,000 microsieverts.
We are exposed to radiation all the time and some medical procedures give high doses of radiation.  So, the current measured levels of radiation released from the Fukushima plants (as of Tuesday 15th March) were not at life threatening levels.

What Countries will be affected by the radiation? My son is in Hong Kong, will he be in danger?

It partly depends on which way the wind is blowing, and it depends on the amount of radioactive material released.

Right now the amount released is not large, and if you stood right by the exploding plant for 1 hour you would be exposed to no more radiation than if you went for a CT scan at the hospital.
The amount of radiation decreases significantly with increased distance from the Fukushima plant.
Currently the Japanese government has issued an evacuation of a 30km radius from the Fukushima plant – this is just as a precaution.
Hong Kong is over 3000km away from Fukushima, so your son is currently not at any risk from dangerous levels of radiation.

Should I be scared of radiation?

No, well not really.  You should be scared of radiation in large doses, but you could say that for pretty much anything – too much of most things will kill you.

The thing is that radiation is around us all the time, even in bananas!

If you have even been in an airplane then you were exposed to radiation from the galaxy.

If you have ever gone outside then you were exposed to radiation from the soil on the ground.

If you have eaten a Brazil nut, yes, you’ve guessed it, you were just nut irradiated.

So even though you have been exposed to all of this radiation, you are still alive and healthy.  Thats because it takes a lot of exposure to high levels of radiation to make you ill.

Currently, unless you are sitting on top of the nuclear power plant and have been for the last 4 days, you are probably safe from radiation poisoning.  If you are living within 30km from the Fukushima plant, then you should take precautions such as iodine tablets and keeping windows and doors closed and staying inside.  However if you are living further away such as in Tokyo, you can carry on as normal as radioactive iodine-131 is heavy with a short half-life of 8 days and won’t spread far in mild winds.

What is the impact on the ocean,  can I eat fish, will the marine life suffer?

The two main radioactive isotopes being emitted from the Fukushima power plants are caesium-137 and iodine-131.
Iodine has such a short half life of 8 days that it is not of concern to the marine environment.
Caesium-137 is soluble in sea water and was found to be in marine creatures after Chernobyl (remember Fukushima has not released anywhere near the amount of radiation that Chernobyl did), however
studies showed doses of caesium from eating marine food caught in the North Atlantic and Baltic seas were an order of magnitude lower than those due to naturally occurring isotope of polonium-210.
So, basically if the releases from Fukushima are contained and small like they are now, then the marine ecosystem impact will be minimal.

What is a normal nuclear reaction and how do we get power from it?

We create heat energy which is then converted to power by using nuclear fission of uranium.  By firing a neutron at uranium we can get the atom to split into lighter atoms, which are commonly Krypton and Barium, but can be other atoms too. This process generates heat and more neutrons which then go on to find more uranium atoms and the process continues.  The heat energy from the uranium bundles is surrounded by water which turn to steam and this steam drives a turbine.  The turbine spins a generator which then produces the power we need to supply our homes.

I heard that they were pumping seawater into the nuclear power plants – why?

When the earthquake hit, the safety systems kicked in for all nuclear reactors and automatically shut them down. This means that within a few seconds after the earthquake, the rods had been inserted into the core for safety and the nuclear chain reaction shown above had stopped.

However, the rods and the unit are still very hot and so water was still needed to keep the reactor cool.

Because of the earthquake, the external power supply to the nuclear reactor was lost and thus the power needed to push water past the reactor to keep it cool was lost.

As with all engineering projects, there was a contingency plan – and plan B was to use the emergency diesel powered generators to provide the electricity needed to pump the water for cooling.  This worked until the Tsunami (which was much bigger than ever anticipated) arrived and flooded the generators resulting in permanent damage.

Luckily the Japanese engineers had a plan C!

Fukushima nuclear plants were all equipped with emergency battery power which were switched on and enabled the core to be cooled for a further 8 hours.

Because some of the cooling water (which is usually very pure water) had been lost as steam, the engineers knew that as a last resort to keep the system cool they had to get a lot of water and fast, so they injected the nearest source of water available – seawater into the reactor.

For safety they also put in some boric acid which is a neutron absorber and would mop up any free floating neutrons to prevent further reaction, and hold on to any iodine that might be released.

This was a big sacrifice for the nuclear plant, as sea water is corrosive and would result in permanent damage to the reactor in the long term, which pretty much means the death of the power plant.  However it also means the safety of the environment and local population, and so sometimes engineering sacrifices have to be made to prevent potential human sacrifices.

The numerous contingency plans that were in place at the Fukushima plants are what prevented it from being a huge disaster and is an amazing showcase for how good planning and building can save lives.

I live in New Zealand, should I be worried?

No, New Zealand is in the Southern Hemisphere and thus our weather systems can be considered independent of those of the Northern Hemisphere.  The levels of radioactive material released so far are  not dangerous, and the intensity of radiation effects drops off with the second power of distance.

Should I buy Iodine tablets?

If you live within 30km of the Fukushima plant, then yes, it is probably a good idea to take 100 milligrams of potassium iodide.  The thyroid gland (in your throat) is the only part of the body that can absorb iodine. It usually takes it out of your food and converts it into the hormones thyroxine (T4) and triiodothyronine (T3) which are required for cell metabolism.  Your thyroid can only absorb a finite amount of iodine at a time, so if you take non-radioactive iodine and are exposed to radioactive iodine-131 then your body will not have any more space to absorb it and you are protected.

However its worth noting that iodine tablets will not protect you from caesium-137.  If you are not close to the nuclear zone then taking Potassium iodide is not a good idea, as it can be toxic in large doses and is in the FDA pregnancy category D meaning that it is known to be harmful to an unborn baby.

What are the symptoms of radiation poisoning?

At elevated doses of radioactive material, the first symptoms are usually nausea, vomiting and diarrhea. These symptoms can start within minutes to days after exposure, and last for minutes to days. This can progress to fever, and in some instances seizures and coma.

Chronic exposure is usually can cause medical problems such as cancer and premature aging, which may happen over a long period of time.

Has there been any further information regard the successive explosions? Surely if you have an explosion then you have a catastrophic failure of your contingencies/redundancies. Isolation, bypass,thermal relief have all been compromised. At that point (depending on what systems have failed) I find it hard to believe they can continue to continue to control the process.

Great question!  First lets talk about the explosions.  At units 1 and 3 there were huge hydrogen explosions which have been shown as amazing videos on the news.

In response to shutting down the nuclear reaction, the immediate task is to depressurise the reactor by opening the pressure relief systems on the reactor vessel.  The coolant water (which may be steam depending on how hot it is) is then poured down into a donut shaped pool which condenses back to fluid water from steam and keeps the pressure low in the containment system.

The pressure in the vessel is kept low as it is easier to push the water into it at lower pressures and this is done by venting the steam.  However as I have explained above, the Tsunami took out the diesel generators which prevented the pumps that pushed the water around from working which reduced the amount of cooling that that water could do.  Without cooling the water temperature started to rise rapidly creating a lot of steam in relation to liquid water which meant eventually there was not enough liquid covering the fuel rods.

The fuel rods are kept in zirconium tubes which were not getting really hot because of the lack of fluid cooling.  This caused the zirconium to react with the oxygen in the steam and produce hydrogen gas, so now there was a lot of hydrogen floating around in this donut pool.

Because of the lack of cooling facility, the pressure in the nuclear containment system started to rise.  Because the containment system is the part that holds the radioactive elements, it should be pretected at all costs and so the emergency response was to keep the pressure down within the containment system to protect it and any radioactive material inside it.  The only way to reduce the pressure was to vent some of the steam out, and it was decided to vent the steam (which now contains a lot of hydrogen) into upper level of the reactor building so that it did not contaminate the atmosphere.  It is thought that the colder temperature of this room caused some of the steam to become liquid again which resulted in a very high air concentration of hydrogen in this room.  Hydrogen gas is very explosive, and it would only take a small spark to cause the explosion which happened hence we see the video in the media.

This caused extensive damage to the top of the reactor building, where most of the steam had been vented to, however the containment structure was not damaged by the blast.

The nuclear rods are actually protected by three different containment systems and the external steel and concrete containment structure is designed to take impact from a plane crashing into it or a huge explosion.  Thankfully due to great engineering, it survived thehydrogen explosion and the radioactive material is still contained.

What happens to all that waste seawater they are pumping through the crippled reactor?

There are a couple of options, if it is just low levels of radiation, they could just pass the water through a specialised filter which will mop up the radioactivity and clean the water, afterwhich the filter will be carefully disposed of in the same way that spent nuclear fuel is.

Another option is to boil the seawater which can transform the radioactive material into a solid form, which can then be removed and carefully disposed of.

Japan has not yet given a statement as to how it will treat the water, but my guess is that it will be one of those two options.



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