Sunday, June 5, 2011

Tepco provides wide dose-range estimates for its two over-the-limit employees

This is encouraging. Last week, Tepco finally dropped the compulsory 'may have exceeded' jargon and spelled it out for the public clearly - the workers in question have officially exceeded their maximum dose limits, and possibly by a wide margin.  From the Daily Mainichi:

"TEPCO said the minimum amount of radiation the two workers were exposed to stood between 284 and 289 millisieverts, while the maximum they could have been exposed to ranged between 654 and 659 millisieverts -- far more than the yearly limit of 250 millisieverts for workers handling the disaster"

With established external exposures of 74 and 89 milliSieverts respectively, internal exposures are estimated to be between 210-580 for one worker in his 30's, and 200-570 for another in his 40's.

Why the wide range?  I suspect it comes down to problems determining when these employees took their potassium iodide pills, or if they were even taken at all. The timing was crucial, and the benefit of taking the pills would be useless if their thyroids were already saturated with radioactive iodine.

Another Mainichi article points out that "at a measurement on May 23, their thyroid glands were found to have absorbed 7,690 and 9,760 becquerels of radioactive iodine-131 respectively".

If this is the limit of the two employee's exposures, they will probably be fine.  It's the kids within the exclusion zone who should concern us most.


  1. Your internal dose calculation methodology is incorrect. The calculated internal dose for the worst case worker is 1 millisievert:

    Days after Intake = 73 days
    (Intake 3/11/11 to Measurement 5/23/11)

    Measured = 9,760 Bq I-131
    (worst case worker)

    NUREG-4884 Fraction of Initial Intake in Thyroid = 0.116

    Initial Intake = 9,760 Bq / 0.116 = 84,138 Bq

    Federal Guide 11 Effective Dose Conversion Factor = 8.89E-9 Sv/Bq

    Total Body Dose Over 50 years =
    84,138 Bq x 8.89E-9 Sv/Bq =
    0.0007 Sv = 1 millisievert

    Federal Guide No. 11 page 136

    NUREG 4884 page B-104
    ( 84part09.pdf)”

  2. I've removed the calculation. will study how the govt calculates it asap. thanks for the info