Excess Absolute Risk (EAR)

[Mike Lantz <mlantz33@cybertrails.com>]

I'd like some help in understanding a risk term presented in a World Health Organization (WHO) draft document on KI guidance.  They say it comes from NCRP 80, which I couldn't find today.  The WHO took what they describe as an external radiation risk term, Excess Absolute Risk (EAR), and used it to calculate risk from internal exposures related to any nuclear accident; like Chernobyl thyroid cancers in children.  The problem I have, or question, is that this term was listed as 2.5 E-4 per Gy per year.  They then say that "if this risk persists unchanged for 40 to 50 years, the lifetime risk of cancer would be 1% per Gy".  They multiplied by 40 years to determine the total risk of thyroid cancers to children.  

Does that make any sense that you would assume an unchanged risk for 40 years following a nuclear power plant accident?  Or am I not understanding this EAR term?  

This isn't critical because we found an excellent document on the subject of KI, NUREG-1633, filled with wonderful insights by HPs such as Charlie Willis.  But I'd still like to understand the WHO's thinking here.

Thanks in advance.

Mike Lantz, CHP
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