Re[2]: Cassini and "60 Minutes"

["Dr. Marvin Goldman" <mgoldman@ucdavis.edu>]

>Putting aside for the moment that TV magazines are a form of entertainment and
>are an outlet for indiviudual and media opinion, the question raised on
>Cassini
>--but never answered on Radsafe or on "60 Minutes"--is not how safe or
>dangerous
>plutonium is but rather how much risk the government is allowed to take with
>citizens.  I believe the dangers of plutonium are well understood and
>exaggerated way out of proportion to other risks.  But to put the question in
>different terms, how would you feel about launching 72 pounds of liquid
>Saran or
>concentrated Ebola?  Assume, for the moment, that the scientific community had
>some reason to do this that was neither more nor less compelling than the
>Cassini mission.  Should the government bow to public concern by
>lay-people (how
>many), to informed concern by scientists (how many), to assurances from rocket
>scientists or HPs (how many), or scare tactics by the media?  Except for scare
>tactics, I've been pondering this question since the segment aired and I don't
>know the answer.
>
>bill
>william.kolb@faa.dot.gov
>_______________________________________________________________________________
>Subject: Re: Cassini and "60 Minutes"
>From:    Rick_Strickert@radian.com at Internet
>Date:    10/6/97  7:02 PM
>
>Sandy Perle asked:
>
>> Anyone else have different observations?

The answer is that there is no simple answer.  However, for what it is
worth, I'd like to share with you some personal observations about the Pu
in Space debate.  The issue is not taken lightly.  That's why the nuclear
issues regarding the Cassini mission to Saturn  first went through a SEVEN
year review of nuclear safety by all the agenies involved, plus an entirely
independent interagency review with some 50 national experts and finally a
critical review of the reviews by some more ad hoc experts, all feeding the
Administration their evaluation about Cassini's safety.  Finally the
President's Science advisor makes a recommendation to launch and the
Executive OK's it.  It's not perfect, but I think it is the best that can
be done with the facts.  It may not satisfy everyone, but it is the system
that's been evolved and in use for over two decades, for Pioneer,Voyager,
Apollo, Viking, Galileo, Ulysses deep space missions.

Much of the uproar is about the probability of a PuO2 release and the
subsequent concequences of a release.  As examples, there may also be
opposition to anything using radioactivity, anything that can have any kind
of risk, no matter what the numbers, and anything endorsed by agencies, or
experts, that may have the appearance of lack of enough public
participation and/or the issue of voluntary or involuntary risks.  I should
also include those who just think such expenditures are not appropriate.
RADSAFE may not be the place for that discussion,  but I am fully aware of
most of the arguments.  In a few paragraphs, I'd like to share with you
some insights on the issue and I hope that by being brief I convey the
essence of the scientific issues.  This comes from my own 25 year direct
experience in space nuclear safety.  The socio-economic issues I leave to
others.

That the Pu-238 in Cassini's three RTGs, [radioisotope thermoelectric
generators), is in high-fired ceramic oxide form, means it is not soluble
and only poses a risk if inhaled.  That the fuel is sturdily encased,
reduces the likelihood of any  post accident release having respirable Pu
particles as a major fraction of credible releases.  And unlike "liquid
saran and ebola" and botulina, plutonium is terribly poor and inefficient
about moving across any biological membranes or through the environment.
(I'm not talking about actually injecting it into experimental animals
where it mainly concentrates in bone and liver, and causes cancer as
predicted at the ususal doses; i.e., no surprises simply because it is Pu).
Of course it can "move", but PuO2 is no I-131, Cs-137 or Sr-90
environmental mimic.  Pu could pose a very local cleanup problem of the
"chunks" around the launch pad if there were  to be an accident with a
fireball powerful enough to rupture some of the fuel pellets.  The image of
"Pu pixie dust" all over Florida may be good media copy but it is
unacceptably poor science.   Because of what I just said my response is
that PuO2 is quite toxic, but not that hazardous.

If inhaled, as respirable particles, of less than 10 microns in diameter,
PuO2 delivers a lung dose, and as countless laboratory animals and a few
unfortunate Russian workers proved, it can cause lung cancer.  Again no
surprises just because it is plutonium; Pu acts like an alpha emitter.  In
my opinion, the real issue is not the 72+ pounds of Pu on Cassini, but
whether any of it could enter the environment in a respirable form
following a credible accident.  For me the issue is not whether the mission
could fail, but whether any postulated failure resulted in a "respirable
source term."  Those are very, very different numbers.  Perhaps analogous
to not whether an airplane can crash, but whether the crash totally
destroys the "black box-flight recorders." (I don't really know the air
crash numbers, but the comparative imagery may be useful).  Also a
respirable source term has to get to  where the lungs at risk are located.
If the radioactivity drifts out to sea, it is not the same as if it drifts
to population centers.  Depending on how you do the launch accident
calculations, one could postulate median lung cancer fatality rates from
insignificant up to a conservative possible one in a million chance of less
than five cases.

Another issue is the extremely remote possibility of the inadvertent burnup
of part of the fuel after an orbital reentry mishap, where the high
velocity of reentry produces sufficient heat friction to melt some fuel
many  miles above earth.  The Pu vapor could be inhaled, but it is so
dilute by the time any drifts to earth, that the doses, while calculable
are not measurable.  Here a worse case might possibly add about a single
millirem, [10 microSv] of lung dose to individuals over a 50 year period,
crudely similar to the alpha particle dose we each breath each day from
natural radon.  Again, an added dose of about 1/20,000 of the 50-year
natural background (Rn daughter) alpha dose to lung.

In the midst of all the "heat" about the issue, I hope I've added a bit of
"light" and that I've covered the essence of the scientific side of the
story.

Marvin Goldman
mgoldman@ucdavis.edu