Assessment of Doses from Nuclear Accidents

[DANIEL.WESTALL@HHLGCS.ausgovhhcs.telememo.au]

G'day y'all -

I've been wrestling with a couple of questions related to the assessment of
individual and collective radiation doses arising from hypothetical releases
from nuclear reactors. Has anyone any comments on the following:

1.  In ICRP60, Table B-20 shows the relative contribution of the thyroid to
the overall detriment as 0.021.  Paragraph (B120) explains that tissue
contributions to the overall detriment were rounded to give four groups of
tissue weighting factors.  The thyroid weighting factor assigned is  0.05,
which is 2.5 times the contribution to detriment.  Further, paragraph (B108)
notes that I-131 was estimated to be about one-fourth to one-third as
effective as external radiation in producing fatalities.  Therefore the
thyroid risk factor could be one quarter of the value used in Table B-20, and
the relative contribution for the thyroid could be 0.005, where internal
exposure of the thyroid from radioiodines is concerned.  This  is an order of
magnitude less than the thyroid weighting factor in ICRP60.  Has anyone else
thought about this?

2.  When calculating collective doses to the public due to airborne releases
of fission products, some sort of limit is almost always applied to the
extent of individual doses used in the calculation.  Most often this is a
distance from the point of release,  Has anyone applied dose cut-offs, below
which individual doses are not added to find collective dose?  If so, what
was the rationale behind the value chosen?

I realise these questions touch on some controversial issues, but I am
looking at dose assessments from a regulatory viewpoint, and need to use
methods which will withstand rigorous review.  Unless you feel compelled to
reply through RADSAFE, please reply to me directly (sorry about the long
address!).

Daniel Westall
Health Physicist, Nuclear Safety Bureau
PO Box 655, Miranda, NSW, 2228, AUSTRALIA
daniel.westall@hhlgcs.ausgovhhcs.telememo.au