nuclear-news

Comparison of radiation levels before and after Fukushima nuclear catastrophe

when the accident struck, Konayashi and his colleagues were in a good position to measure exactly how things changed.

Japanese Physicist Publishes Fukushima Radiation Records, Technology Review, 14 Nov 11 The readings at the Fukushima Medical University, close to the damaged nuclear power plant, make for grim reading.

Today, an insight into the conditions in the region surrounding the Fukushima Nuclear Power plant soon after the magnitude 9 earthquake and resultant tsunami which caused the reactors to explode.

Fukushima Medical University sits some 60 kilometres northwest of the
power station. In the run up to the accident, a physicist at the
university, Tsuneo Konayashi, had been measuring the background levels
of gamma radiation, the numbers of secondary particles from cosmic ray
impacts and the amount of radon in the atmosphere.

So when the accident struck, Konayashi and his colleagues were in a
good position to measure exactly how things changed.

First, the background levels of gamma radiation changed little
immediately after the earthquake but then spiked, reaching 9.3 times
the usual levels on 16 March, five days after the quake and just hours
after a hydrogen explosion occurred at the plant That’s a level of
11.9 micro Seiverts per hour.

By August, Konayshi says the levels had dropped to 1.5 times the usual levels.

Indoor levels were significantly lower. The Japanese Self-Defense Force
screened people entering the university and anyone with more than
10,000 counts per minute had to be decontaminated at separate
decontamination tent before entering the campus.

“The maximum value found was 100,000 cpm,” says Konayashi. That’s a
significant level of contamination but it’s not possible to say
exactly how high because the number of counts for a given level of
radiation depends on the measuring apparatus. Other news reports on
the web mention a worker at the plant who was sprayed with highly
radioactive water while moving a hose leading to readings of 100,000
cpm.

Konayashi says his data can best be explained by fitting it to a model
in which there are two types of radiation with short and long half
lives. The best fit is for short-lived isotopes, such as iodine-131,
that decay with an average half life of about 3.6 days, and with the
longer-lived ones, such as cesium-134 and strontium-90, having a half
life of 181 days….
In some places the levels rose to 250 becquerels per cubic metre,
almost double the maximum allowable levels in the US. These places had
to be sealed off from normal use….
http://www.technologyreview.com/blog/arxiv/27335/

November 15, 2011 - Posted by Christina Macpherson | Japan, Reference, technology