The following is paraphrased by Peter Montague from 
the scientific Restoration of the Earth, published in 1973.
ASSUMPTION 1
We protect the earth by deciding how much of any destructive activity
the Earth (or any portion thereof) can safely absorb without harm.
We call this the "assimilative capacity" of an ecosystem... or a human
being...or a population of fish.
According to this assumption, scientists can reliably decide
how much damage a river or the Florida Panther or a human can absorb without
suffering irreversible harm.
The purpose of every risk assessment is to predict the limits of
this "assimilative capacity."
ASSUMPTION 2
Once the "assimilative capacity" of a person or system is established
for a particular toxicant or destructive activity, limits are imposed 
so that irreversible harm will not occur.  These restrictions are set,
river by river, forest by forest, factory by factory, chemical by chemical, 
everywhere on the planet, so that the total, cumulative effects do not 
exceed the "assimilative capacity" of the earth or any of its ecosystems
or inhabitants.

ASSUMPTION 3
 WE ALREADY KNOW which substances and activities are harmful.
In the case of substances or activities we never suspected of being harmful,
we ought to be warned of their possible dangers by traumatic
but sub-lethal (except for firemen) shocks that alert us to the danger
 before the thick smoke blacks out the sun.

Plutonium and fissile products of 
radioactive Uranium in process is 
3 billion more times radioactive 
than when first mined.

In the event of an accident, 
the amount of plutonium-235 and by-products continually generating would extend 
from the earth to the moon and back within three seconds.
 Because of the immense amount of waste, 
it is important to shut down a nuclear reactor
with control rods and moderators: steel beams, boron, cadmium
inserted into the reactor core
as soon as possible. 
Plutonium 235 in process is 3 million times
more radioactive than fuel first mined.
Modern Nuclear Reactors such as Chernoble 
contain enormous quantities of radioactive materials,
when the pressure builds - up to a thousand times
the amount released in one hiroshima-sized explosion.
   
Just 10 per cent of the core inventory escaping
into the environment would have 100 times the
eventual effects of one Hiroshima sized release.

The Chernoble accident showed that places as far away as
2,000 kilometers (1,250 miles) from the site 
could be environmentally affected.

It also showed that the 2-km (1 mile) evacuation zone 
around the reactor(s) to be grossly inadequate.

What is important about this book by Carolyn Raffensperger?
When an activity raises threats of harm to human health or the environment,
precautionary measures should be taken even if some cause and effect relationships
are not fully established scientifically.

In this context the proponent of an activity, rather than the public,
 should bear the burden of proof.
... if you have reason to believe that your building may be on fire, 
do you estimate the probability that the damage will be "acceptable" and
wait until you see flames shooting up into the sky? Or do you take
precautionary action based on incomplete evidence?