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Evening Report

From NEI’s Japan earthquake launch page:


Restoration of electric power at reactors 1, 2 and 4 at the Fukushima Daiichi nuclear power plant has led to the reconnection of important reactor instrumentation, the International Atomic Energy Agency said.

Cooling water continues to be injected into reactors 1, 2 and 3. Reactors 5 and 6 at Fukushima Daiichi remain safely shut down. Both reactors were undergoing maintenance at the time of the earthquake.

Radiation dose rates inside the containment vessels of reactors 1 and 2 have decreased slightly, IAEA said.

External power has been reconnected to the common used fuel storage pool at the plant and cooling started on March 24 at 5:05 AM EDT, according to Japan’s Nuclear and Industrial Safety Agency.  About 60 percent of the used uranium fuel rods at Fukushima plant are stored at this facility.

Radiation monitoring continues

Air samples collected at on-site monitors at the Fukushima Daiichi plant March 19-23 show that only iodine-131 was found to be in excess of Japanese government limits. Radiation dose rates measured on site March 21-23 have decreased from 193 millirem to 21 millirem per hour. Radiation dose rates at the plant’s site boundary ranged from 1 millirem to 3 millirem per hour on Thursday.

At distances between 34 and 73 kilometers to the west of the Fukushima Daiichi nuclear power plant, the dose rate ranged from .06 millirem to .69 millirem per hour.

Considerable variation in the levels of reported iodine-131 and cesium-137 continues in 10 prefectures, IAEA said. Food, milk and drinking water sampling has been most thorough and extensive in the Fukushima and Ibaraki prefectures, IAEA said.

Seawater samples collected at several points 30 kilometers from the coastline near the Fukushima Daiichi nuclear power plant found measurable concentrations of iodine-131 and cesium-137, IAEA said. The iodine concentrations were at or above Japanese regulatory limits. The cesium levels were well below those limits.

For more information on iodine-131, see NEI’s fact sheet Health Impacts of Iodine-131


Martin Burkle said…
"Radiation dose rates inside the containment vessels of reactors 1 and 2 have decreased slightly, IAEA said."
Why would we care what the radiation level in the containment vessel is?
I think the containment vessel is a place where no one would be. Doesn't the reactor vessel vent to the containment vessel and the containment vessel vent to the suppression torus or optionally to the area under the roof (or the outside is the roof is gone)?
Mark C said…
What are the normal levels?

"At distances between 34 and 73 kilometers to the west of the Fukushima Daiichi nuclear power plant, the dose rate ranged from .06 millirem to .69 millirem per hour."

0.06 mr/hr. What is the normal background level and variation?

How can these help the public put it into perspective?
Peter said…
Regarding the I-131 fact sheet, every bit of news coming out of Japan is reporting dose in Seiverts and activity in Becquerels - why is NEI sticking to rem and picocuries??

Please consider changing your base units, or at least including both side by side.
Karen Street said…
I want to second Peter's recommendation. Being American means having to memorize two sets of numbers. We can use some help here. Yes, I know the conversion is easy.
David Bradish said…
To help put the radiation doses in perspective, check out page 7 in this pdf. One x-ray is 10 millirem, US background radiation is 300 millirem per year. 0.06 mrem/hr works out to 526 mrem/year. I talked with our radiation folks and the Japanese numbers are assumed to include their background radiation but we haven't seen numbers from what they were before the accident.

From searching news articles, it looks like the background radiation at Wako city next to Tokyo is 0.04 micro Sieverts/hr which works out to 0.004 mrem/hr. The average US background dose is 0.04 mrem/hr (310 mrem/8,760 hours in a year) so it looks Tokyo has quite a bit less background radiation than the US does.

As to why NEI is sticking with rem and picocuries, it's because the US hasn't adopted the SI system so that's why the NRC, EPA and industry use those numbers.

I recommend checking out our page on Japan's radiation. A lot of questions here about radiation can be found on that page.
David Bradish said…
correction: on page 7 of our sheet that I pointed folks to above, it should be Dose at the top of the table and not Annual Dose.
D Kosloff said…
There is radiation measuring equipment inside containments. Variations in containment radiation levels provide information that may be useful in evaluating reactor conditions. For the Japanese BWRs no one would be in the primary containment because it is filled with inert gas (nitrogen). The area under the roof is the secondary containment. Reporters generally do not know that there are two containments for each plant.
Karen Street said…
Dave, we all know that Americans use international units to send people to the moon and American units to talk to one another and two sets of tools so that we can fix either bike. But would it be unAmerican to include international units in ()? If we can see temperatures in °F and °C without violent protests, I'm thinking two sets of units, while a pain, would make life easier for us. And yes, I know the conversion is easy.

Also, I understand the premise behind not going to km from miles (it's too hard to change), but I would think that a fair percentage of those who rattle on and on and on about mrem could handle the shift to SI units. Probably not your decision.

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