Japan Update / Brief No. 71 / 17 March 2011
Japan Releases Radiation Data From More Than 50 Monitoring Posts
17 Mar (NucNet): A Japanese government ministry has released radiation data from more than 50 monitoring posts (MPs) around the Fukushima-Daiichi nuclear power plant in Japan that show transient high readings of up to 80 microsieverts per hour (microSv/hr) at two locations more than 20 kilometres from the plant.
The data, released today by the Ministry of Education, Culture, Sports, Science & Technology (MEXT), show the 80 microSv/hr readings at MP number 4, about 35 km northwest of the site, and MP number 21, about 30 km northwest of the site.
The first reading was taken at 11:30 yesterday (Wednesday) Japan time (03:20 central European time) and the second at 11:35 Japan time.
MEXT also released a map which shows radiation readings within the 20km - 30 km evacuation zone ranged from 2.1 to 40 microSv/hr. These readings were taken today between 09:20 and 17:43 Japan time.
Just outside the 30 km zone and to the west of the plant, today’s peak reading was 170 microSv/hr. Other readings outside the 30 km zone to the west of the plant ranged from 0.7 microSv/hr to 20 microSv/hr.
In most countries, the natural background radiation level is in the range of 0.2 to 0.5 microSv/hr, including the natural radon background radiation in buildings.
Many of the latest readings were taken during a period while venting was being carried out at the plant and when a fire broke out in unit 4, which resulted in peak readings caused by masses of contaminated air moving inland on a generally easterly wind.
At Fukushima-Daiichi’s main gate on 16 March readings varied from 8,000 microsieverts per hour (microSv/hr) early in the night down to 580 microSv/hr at around 09:30 Japan time. At 12:30 they increased to a peak value of 10,850 microSv/hr and since then have been falling steadily to about 350 microSv/hr late evening on 16 March Japan time.
Readings today (17 March) varied between about 350 microSv/hr at midnight and 310 microSv/hr at 15:30. These values do not represent too serious a problem for people working on the site.
Earlier today, Japanese authorities started using helicopters to drop water onto the spent fuel pools at Fukushima-Daiichi units 3 and 4 in an effort to counter what they called the “immediate threat” of damage to the fuel, the Japan Atomic Industrial Forum (JAIF) said.
In an update at 08:00 CET, JAIF said the helicopter operation had begun at
01:48 CET on 17 March.
The Nuclear and Industrial Safety Authority (NISA) said workers at the plant started to cool the unit 3 and 4 spent fuel pools using high pressure ground pumps at 08:10 CET .
NISA also said the temperature of fuel in the spent fuels pools at units 5 and 6 had reached about 65 degrees Celsius and 84 degrees Celsius at unit 4 this afternoon. According to JAIF spent fuel rods in unit 4’s fuel pool had probably been damaged.
There was no information on the condition of spent fuel in the spent fuel pools at units 1 and 2.
The MEXT table with radiation readings is online:
www.mext.go.jp/component/a_
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