FW: [ RadSafe ] DHS PLANNING SCENARIOS -Scenario 1: Nuclear Deton ation

[Minnema, Douglas]

Dear RADSAFErs,

I've been having offline discussions with regarding this, but it appears to
be time to go online.  I was not involved in the DHS studies, but have done
similar work and am quite familiar with the data and models.

First, let me point out that I think there is some confusion regarding the
DHS results.  One of the original postings here indicated that DHS had
considered impacts out to 3000 miles.  That appears to have been a
misunderstanding, the report actually claims that up to 3000 SQUARE MILES
could be contaminated to the point of needing some level of cleanup before
reuse.  This is the equivalent of a plume 100 miles long by 30 miles wide,
which is not unreasonable for a ground-level burst of the size postulated.
There is actually a strong basis in science and test data that supports
this, which I discuss further below.

The result is consistent with what I would expect, and that is even if you
relax the cleanup standards from what they are now.  From my estimates, the
early fallout from such a burst could result in external doses in excess of
100 rem at distances beyond 30 miles from the detonation.  It is unlikely
that you will be able to evacuate out to that distance in the first day, so
those are real doses.  The dose is not only cloud passage (cloud passage
would be in 2-3 hours at 30 miles, depending on wind speed), but a lot of
material deposited on the ground contributes also.  I don't have estimates
of deposition immediately available but I can give you an example: my
estimates indicate that at 50 miles downwind, the first 24-hour dose would
be 30 rem, and it would increase to 45 rem by the end of the 4th day.  The
cloud has long past, that remainder is only the material on the ground.
After the early decay and the long-lived stuff begins to dominate, these
areas will still probably exceed any realistic reuse scenario you can
establish without some type of remediation.  That is why I said that a 100
mile by 30 mile plume would not be unrealistic to expect.

There is one big difference between this scenario and essentially all of the
other tests that have been  mentioned - it is a ground-level burst.  I can't
emphasize that enough.  Also, the models that are being used are based on
historical experiences, as I will try to explain below.

The big difference is that at altitude, the bomb debris is the only
component of the fallout, and most of it has been vaporized to very small
particles so it gets lofted and dispersed long distances before settling.
Most of the leakage neutrons travel far before being captured in the
atmosphere, so what activation products there are not concentrated, and are
mostly short-lived gases like Argon-41 and Nitrogen-16.  At ground-level, a
10kT device will dig a crater 42' - 63' deep with a radius of 95' - 160',
depending on the hardness of the ground.  That is a lot of material, not to
mention all of the nearby building debris, and much of it is partially
vaporized and lofted by the fireball.  Besides being heavily activated,
these large particles form condensation nuclei for the finer bomb debris to
agglomerate on.  The result is a much larger total mass of debris and larger
particles; in other words, there are many more particles and they settle
faster.  It is an ugly mess.

Hiroshima and Nagasaki were both detonated at optimal altitudes exactly to
avoid this problem.  (Optimal altitude is designed to keep the fireball from
reaching the ground, it will vary by size of yield.)  The plowshare shots
were all underground, including the famous SEDAN crater shot.  That crater
was formed by the uplifting of the ground over the detonation, and not by
the bomb digging the crater - the bomb was detonated 300' below the crater's
final bottom (100 kT bomb was at 635', crater was 323' deep by 611' radius -
volume was 179 million cubic feet).  I'm not sure, but I believe that all of
the Nevada atmospheric shots were at or near optimal altitude or above, but
I'll have to check.

I believe that the only shots that the US has done (don't know about the
Russians) that were at or near ground-level were in the Pacific, and nobody
has mentioned these so far.  The idea was that the early fallout would
settle before the plume hit another island, but we were not always lucky.
The CASTLE BRAVO shot of March 1954 (the H-bomb test that was much higher
than expected) resulted in the exposures to the Marshall Islanders and the
Japanese fisherman.  Let me quote from the "Effects of Nuclear Weapons":

"The [BRAVO] device was detonated about 7 feet above the surface of a coral
reef and the resulting fallout, consisting of radioactive particles ranging
from about one-thousandth to one-fiftieth of an inch in diameter,
contaminated an elongated area extending over 330 (statute) miles downwind
and varying in width up to over 60 miles.  In addition, there was a severely
contaminated region upwind extending some 20 miles from the point of
detonation.  A total area of over 7,000 square miles was contaminated to
such an extent that avoidance of death or radiation injury would have
depended upon evacuation of the area or taking protective measures".

Granted, BRAVO was 15 MT and DHS's is a factor of 1000 lower, but they are
talking about potentially fatal doses over a 7000 square mile area, not
about the area that would require cleanup for free release.  In the DHS
case, we are only talking about an area for potentially lethal doses of
around something like 30-mile by 10-mile, or 300 square miles (my
guesstimates, not calculated).  This is actually comparable for two reasons.
First, weapons effects tend to scale by somewhere around the square root of
the ratio of the yields rather than the full ratio.  Also, the
fission/fusion ratio is important since the fusion yield creates a much
smaller fallout problem (don't know what the ratio was for BRAVO but I know
it was mostly fusion).

I've gone on longer than I intended, but I hope this helps.  My point is
that there is much more behind the DHS study than off-the-cuff estimates and
guesses.  If you haven't seen it you should look at the classic book "The
Effects of Nuclear Weapons" by Glasstone and Golan.  The most recent edition
is 1977.  I don't have the website at hand, but I know you can find all or
at least most of it online.  A simple Google search should find it for you.
It has some good discussions on early fallout and the tests where it was
observed.  Most of the current models are based directly on the same
evaluations discussed in this book, and it is firmly grounded in the test
experiences.  Another book of value is "The Effects of Nuclear War", which
was originally a Congressionally mandated study.

Doug Minnema, PhD, CHP

and yes, these are my own few thoughts and not necessarily those of my
employers.