Nuclear meltdown

Radiation levels near a quake-hit nuclear plant are now harmful to human health, Japan's government said after three explosions and a fire at the crippled facility. The crisis at the Fukushima No.1 plant, 250km northeast of Tokyo, has now spread to four out of its six reactors following Friday's earthquake and tsunami which knocked out cooling systems.

Tens of thousands have already been evacuated from a zone within a radius of 20km from the ageing plant, but Prime Minister Naoto Kan urged people living within 10km of the exclusion zone to stay indoors.

Edano said radiation levels as of 10:22 (01:22 GMT) on Tuesday were 30 millisieverts between the number-two and the number-three reactors, 400 millisieverts near number-three and 100 millisieverts near number-four. A single dose of 1 000 millisieverts - or one sievert - causes temporary radiation sickness such as nausea and vomiting. A dose of 5 000 millisieverts would kill about half those receiving it within a month.

Edano said radioactive substances might spread outside the 20-30km area but would dissipate the farther they spread.

It was still unclear whether the container sealing the number-two reactor had been breached.

What kind of danger will Japan face if the radiation cannot be contained?

Health effects of exposure to nuclear radiation
The following are the main health effects that have been studied with regard to Chernobyl (the worst nuclear accident in history), and which are likely to be seen with similar nuclear events:

Radiation sickness. People who receive a sudden very high dose of radiation, such as those working on the reactor at the time of the accident, or involved in clean-up operations afterwards, are at risk of acute radiation sickness (ARS), the result of damage to the body’s tissues and immune system.

Immediate ARS symptoms include nausea, diarrhoea and fatigue. This may be followed by symptoms such as hair loss, bleeding under the skin and mouth inflammation.

In severe cases death may occur within two to four weeks. Those who survive for six weeks after a large dose may generally be expected to recover, but are at risk for long-term effects.

Long-term effects. Radiation can also cause changes to the body's genes, which can lead to the development of diseases such as cancer later in life.

Radiation-related illnesses tend to emerge about 10 to 15 years after a radiation disaster. The most notable such illness attributable to Chernobyl is thyroid cancer: a large increase in incidence has been recorded in the most contaminated areas.

There is considerable uncertainty about many of the other possible health effects attributable to radiation from Chernobyl. The health effects of lower radiation doses are not well understood. The disaster has been implicated in following diseases, however: leukemia, breast cancer, cataracts and heart disease.

Nuclear emergency planning zones
All nuclear power stations have emergency plans in the event of a disaster. In the case of a ‘general emergency’ – one in which radiation cannot be contained within the site and threatens to contaminate the surrounding area, different ‘emergency planning zones’, depending on the level of risk, are recognised. These are as follows:

  • 5km radius of the source: people in this area would be at highest risk for radiation exposure.
  • 16km radius of the source: people could potentially be harmed by direct radiation exposure.
  • 80km radius of the source: radioactive materials may contaminate water supplies, crops and livestock

The above zones are, of course, only a model of most likely risk. There are multiple factors that affect the severity of a general emergency - the nature of the accident, the size of the radiation 'cloud', prevailing wind direction, rainfall and topography.

(Graphic: nuclear emergency planning zones - Koeberg nuclear plant)

Many power stations in the US and Europe have plans for up to the 16km radius. If a general emergency is declared, those living within the 16km radius (and even more so within the 5km radius) will hear sirens and loudspeakers advising them what to do. If you live in either of these zones, you should also be issued an ‘emergency calendar’ every year.

It’s not certain what the plan would be for anywhere beyond the 16-km zone. This probably wouldn’t be too problematic in the case of a small radiation leak. But a larger incident could have severe effects. The exclusion zone around Chernobyl – the area most contaminated, from which the population was evacuated -- was a 30km radius, and lower levels of radioactive material was deposited for hundreds of kilometres further than that.

Steps to take to reduce the radiation dose
The three factors to remember are distance, shielding and time.

Distance. The further away you can get from the source of the radiation, the better. If you’re told to evacuate, keep car windows and air vents closed; use re-circulating air. Keep your petrol tank full and your car serviced. Good in case of evacuation, or just a power outage that disables the petrol pumps.

Shielding. It may be better to stay put indoors when the accident happens. The aim is to put a ‘shield’ - a barrier of dense, heavy material like a wall or earth - between yourself and the radiation source. Ideally, get to a basement or other underground area. You should also:

Close off air intakes: doors, windows, air conditioners, fireplace flues etc.

Keep food in covered containers or in the fridge (though that's unlikely to be working at a time like this). Food not previously covered should be washed before being put in to containers.

If you think you’ve been exposed to radiation:

Take off any exposed clothing and shoes and put them in a plastic bag. Seal this and put it out of the way.

Have a shower and wash yourself really well.

Time. Radioactivity decreases over time, so the longer you can avoid going outside, the better. Radioactive fallout poses the greatest threat during the first two weeks, by which time it has reduced to about 1 percent of its initial level. So supplies will need to last for at least a fortnight.

It’s very important to be able to listen to broadcasts, which will advise as to the best course of action. So a battery-operated radio is a vital piece of equipment in any disaster that causes a power outage, as is a battery-operated torch.

- (Olivia Rose-Innes, EnviroHealth Editor, Health24, updated March 2011)

(Graphic: Denzil Daniels, Health24)

Information sources:
2nd blast rocks Japanese nuclear plant
Health Effects of the Chernobyl Accident and Special Health Care Programmes: Report of the UN Chernobyl Forum Health Expert Group World Health Organization, Geneva, 2006.

Read more about Chernobyl and radiation sickness

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