20 mSv/a - 17 Sv/min - Chernobyl

["Dolf Brits" <dbrits@mepta.pwv.gov.za>]

RADSAFERS

Most of this may be old hat to you, but if you have time, I need some
comment on the following:

1. 20 mSv/a

This is the limit for worker exposure in our gold mines in South Africa.
Most of our gold ore also contain some U, about 1000 Bq U 238/kg (30 pCi/g).
One can  thus expect a radon problem in a gold mine.
Some of our older gold mines have worked-out areas that can be measured in
square km's
(or even square miles !).
Working areas in some mines are ventilated through these worked-out places.
Allthough the air supplied to the worker in such a case is of acceptable
quality (low in methane, dust, heat content etc.), it picks up significant
concentrations of radon progeny.
This scenario leads to large numbers of underground workers receiving doses
in excess of 20 mSv/a.
At great cost, various actions are implemented to bring dose levels of all
workers within limits.
(Interesting: The mass of air pumped down a mine per day is more than the
mass of rock and ore taken out.)

In the past few days a number of articles have appeared in our newspaper,
"Business Report", which has a country-wide circulation, on the issue of the
impact of radiation on workers and the public.

It has been stated in the paper that "low doses of radiation caused a much
larger risk of cancer than expected from the linear model". The (only)
researcher on this topic mentioned by name is Wolfgang Kohnlein who "argued
that the actual risks of radiation exposure may be 20 times higher than
predicted by the linear model".

Should we now plan for a future lowering of dose limits ?


2. 17 Sv/min

This may be the approximate dose rate that the unfortunate Japanese worker
was exposed to.
Hopefully he is still alive.
Now how do you explain spending money on a 20 mSv/a dose limit to a miner
who faces extremely though (and lethal) working conditions. ?
The person that received 1000 times the dose (in about a minute), against
which the miner is protected over a year, is not killed instantly.
100 mSv accrued while working in a mine subjects the miner to a
non-quantifiable (small) risk (the HPS position statement ?).

How does all this add up?


3. Chernobyl deaths

a). As it happens our "Business Report", which alerted us to the mining
issue, also carried an article on nuclear energy - South Africa is currently
developing an intrinsically safe helium-cooled reactor. In this highly
reliable newspaper, our "mining journalist" also states that
"Chernobyl....caused an estimated 25 000 deaths from cancer".

b). The Chernobyl report of the NEA Committee of the OECD (Nov 1995) refers
to 31 dead (p.12), a significant increase in carcinomas (no deaths ?) among
children (p.13) and not even "any increase in cancers" (p13) in the
population. This population however received significant doses - 120 people
received more than 200 mSv during 1986-89 (p. 51).

c). According to the Ukraine's ambassador, the "Chernobyl disaster killed 4
229 people" as reported on
http://www.chernobyl.com/health.htm.

How many Chernobyl deaths ?

Taking a geometric average (to give some credence to NEA Committee) yields 1
485 deaths.
There must be a better estimate ?

Thank you for your trouble

Dolf Brits
South Africa

dbrits@mepta.pwv.gov.za


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