57.5 Microsieverts/Hr in Kashiwa City, Chiba

After the Setagaya-ku, Tokyo's radiation scare turned out to be radium, what could this be this time in Kashiwa City, Chiba Prefecture, where the radiation level remains elevated?

From Nikkei Shinbun (11:24PM JST 10/21/2011):

千葉県柏市は21日、同市根戸の市有地で毎時57.5マイクロシーベルトの高い放射線量を計測したと発表した。原因は不明だが計測値が極端に高いため「福島第１原子力発電所事故の影響とは考えにくい」（総務部）としている。

Kashiwa City in Chiba Prefecture announced on October 21 that the very high radiation of 57.5 microsieverts/hour was detected on the land owned by the city in Nedo District. The cause of the high radiation is unknown. Since the measured number is extremely high, "It is hard to believe this is from the Fukushima I Nuclear Plant accident", says the city's general affairs department.

　現場は更地で、57.5マイクロシーベルトは地表から30センチ程度掘ったところで計測。10メートル離れると毎時0.3マイクロシーベルトまで低下した。市は半径３メートル以内を立ち入り禁止にし、24日以降に土の除去などを進める方針。

It is a vacant lot, and 57.5 microsieverts/hour radiation was detected 30 centimeter below the surface of the ground. The radiation dropped to 0.3 microsievert/hour at 10 meters from the spot. The city has designated the 3-meter radius from the spot as off-limit, and is planning to remove the soil sometime after October 24.

　18日に市民から高い放射線量を計測したとの連絡を受け調査した。

The city had received information from a citizen on October 18 that there was a high radiation spot, and the city tested on its own.

The city's announcement is here (in Japanese). According to the announcement,

• The city received a telephone call on October 18 from the neighborhood association that there was a high radiation spot;

• On October 19, the city measured the radiation at the location which is owned by the city. Radiation exceeding 10 microsieverts/hour was measured at a particular spot;

• On October 20, with the officials of the neighborhood association present, the city measured the radiation again. The radiation survey meter of the city couldn't not measure over 10 microsieverts/hour;

• On October 21, the city asked the Chiba Prefectural Environment Foundation to measure the radiation. After digging the soil at the location, maximum 57.5 microsieverts/hour at 30 centimeters below the surface was confirmed.

The yellow marker is where the spot is (from a tweet by a resident):

It's a thin strip of land in the middle of residential/commercial mixed neighborhood.

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Radionuclides Released into the Air from Fukushima I Nuke Plant, by NISA

as announced by Japan's Nuclear and Industrial Safety Agency (NISA) on June 6, 2011 (on page 13 of the PDF file). Click on the image below to view it in a separate window:

What's interesting about the numbers in the chart is:

1. Radioactive strontium came more from Reactor 2 and Reactor 3, 1 to 2-digit higher.

2. More plutonium came out from Reactor 2, 2-digit higher, not from Reactor 3 with MOX-fuel.

Strontium-89 (in becquerels)
Reactor 1： 8.2 x 10^13 (or 82 terabecquerels)
Reactor 2: 6.8 x 10^14 (or 680 terabecquerels)
Reactor 3: 1.2 x 10 ^15 (or 1,200 terabequerels)
Total: 2.0 x 10^15 (or 2,000 terabequerels)

Strontium-90 (in becquerels)
Reractor 1: 6.1 x 10^12 (or 6.1 terabecquerels)
Reactor 2: 4.8 x 10^13 (or 48 terabecquerels)
Reactor 3: 8.5 x 10^13 (or 85 terabecquerels)
Total: 1.4 x 10^14 (or 140 terabecquerels)

Plutonium-241 (in becquerels)
Reactor 1: 3.5 x 10^10 (or 35 billion becquerels)
Reactor 2: 1.2 x 10^12 (or 1.2 terabequerel)
Reactor 3: 1.6 x 10^10 (or 16 billion becquerels)
Total: 1.2 x 10^12 (or 1.2 terabequerel)

Neptunium-239, which decays to plutonium-239, was estimated at 7.6 x 10^13 becquerels, or 76 terabequerels, adding to 3.2 x 10^9 becquerels of plutonium-239 that came out. Again, most neptunium-239 came out of Reactor 2, whose reactor building is more or less intact and whose Suppression Chamber is said to have been damaged on March 15 morning.

In the PDF file linked above, NISA estimated 770,000 to 850,000 terabecquerels of radioactive materials have been released into the atmosphere from Fukushima I Nuke Plant (although they are now trying to lower that number), and additional 720,000 terabecquerels of radioactive materials are in the contaminated water at the plant.

(Thank you "Kyotoresident" for reminding me to put this up, which I did for my Japanese blog long time ago and forgot to do for this blog.)

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1 Billion Becquerels Per Hour Emission of Radioactive Materials from Fukushima I Nuke Plant at the End of June

That's an amazing reduction from the maximum emission of 2,000 terabecquerels per hour on March 15, it is actually one-2 millionth of the maximum, says TEPCO in the Reference No. 2 of the progress report on the "roadmap" to God knows where.

Is this number, 1 billion becquerels per hour emission, good? TEPCO's Matsumoto, in the press conference on July 19, avoided the judgment, and said he didn't know, but it was one-2 millionth of what it had been on March 15.

On closer reading of the document, though, I noticed one strange thing about this emission number. TEPCO is talking about the radiation emission measured in cesium (cesium-134 and -137), not in iodine equivalence.

To come up with the iodine-131 equivalence, you have to multiply cesium-134 by 3, and cesium-137 by 40 (according to INES handbook). TEPCO doesn't even give the breakdown of cesium 134 and -137 in its calculation of 1 billion becquerels/hour number. Other nuclides have even higher multiplier: americium-241 is 8,000, plutonium-239 is 10,000.

If half of 1 billion becquerels is cesium-134 and the other half is cesium-137, then in iodine-131 equivalence like in the previous calculations, the emission would be:

(0.5*3)+(0.5*40)=1.5+20=21.5 billion becquerels/hour

Instead of 1 billion becquerels/hour, it would be 21.4 billion becquerels/hour in iodine equivalence, or 516 billion becquerels in one day. In less than 2 days, we would be talking about over 1 terabecquerels.

Why TEPCO would do the calculation in cesium instead of iodine equivalent? To make a ready comparison with the previous emission calculations difficult and to give the impression that the number is low?

And what about iodine? They may not be detecting radioactive iodine at Fukushima I Nuke Plant, but iodine-131 is still being detected in sewage sludge in Tokyo and other parts of Kanto.

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