Thursday, September 1, 2011
Provisional evaluations of current emission rate of radioactive materials from the Unit 1 to 3 at Fukushima Daiichi
As a component of the Tokyo Electric Power Company’s Roadmap towards Restoration from the Accident (as of August 29, 2011), TEPCO has provided the following information about the estimated current emission rates from all point sources.
- March 15, 9 am – 15 pm: approx. two quadrillion Bq/hr (2.0 x 1015)
- March 25, 0 am – March 26 11 am: approx. 2.5 trillion Bq/hr (2.5 x 1012)
- April 4, 9 am – April 6 0 am: approx. 0.29 trillion Bq/hr (2.9 x 1012)
- June 20 – June 28: approx. 1 billion Bq/hr (1.0 x 109)
- July 26 – August 12: approx. 0.2 billion Bq/hr (2.0 x 108)
Any comments on these estimated accident emission rates would be appreciated. The question arises: since these emission rates derived from measurements taken at the site boundary, and there are seven emission point sources at Fukushima Daiichi, how accurate are the current release rate estimates? How do they compare with release rate estimates, which are done on a continuous basis by the National Security Agency? The July 26 – August 12 approximate estimate of 200 million Bq/hr indicates TEPCO has been successful in maintaining reduced temperatures in the melted fuel assemblies in their attempt to reach a cold shutdown status. Other TEPCO Roadmap summaries indicate significant success has been achieved in recovering and filtering fuel assembly coolant water, which is still being applied manually to avoid re-criticality. Easily accessible comprehensive analysis of the total contamination released in the form of high radiation level cooling waters is not yet available. An overview of major countermeasures undertaken at the accident site as of August 17th is available in the TEPCO Roadmap of August 29, 2011 (http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f12np-gaiyou_e_3.pdf).
“The measurements were taken June 6 to June 14, about three months after the Great East Japan Earthquake, by 780 members of 129 universities and specialized organizations from around the nation. Soil samples were collected from about 2,200 locations to identify the concentration levels of radioactive cesium… The map shows that areas with high radiation levels are concentrated in a zone to the northwest of the plant within a 40-km radius of the facility… The finding emerged in a map published Aug. 29 that for the first time shows contamination levels of areas within a 100-km radius of the plant. One location in the town of Okuma had the highest value at about 30 million becquerels of cesium of all types per square meter. About 8 percent of the measured areas recorded more than 555,000 becquerels, the figure that required forcible relocation by residents in the 1986 Chernobyl nuclear incident… Soil samples were collected for each 2-square-km area within an 80-km radius of the plant. Samples were also collected from each 10-square-km area within an 80- to 100-km radius of the facility. The number of sample locations total five for each radius zone. The sample was drawn from the soil 5 centimeters from the surface. The concentration levels of cesium-134 and cesium-137-the half-life periods of which are two years and 30 years, respectively-were estimated as of June 14 in this project.”
The contaminated soil map legend uses the following reporting units. Concentration level of cesium-137 per square meter unit becquerel: 3 million and over; 1 million – under 3 million; 0.6 million – under 1 million; 60,000 – under 0.6 million; and 10,000 – under 60,000. (http://ajw.asahi.com/article/0311disaster/fukushima/AJ201108308286).