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).

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