Pu at NTS - BBC perspective

["Sandy Perle" <sandyfl@earthlink.net>]

Wednesday, January 6, 1999 Published at 18:47 GMT - BBC

Nuclear waste travels fast and far  

The Nevada Test Sites experienced over 800 underground nuclear 
explosions between 1956 and 1992  

Plutonium waste has been detected 1.3 kilometres away from a 
1968 nuclear weapons test site in Nevada - carried much further 
and faster by groundwater than current theory would predict.  

The new research proves for the first time that this occurred 
because the plutonium attached itself to microscopic mineral 
fragments which were then carried along by flowing water 
underground.  

Plutonium hardly dissolves in water, which is why underground 
storage of nuclear waste has been seen as the most acceptable 
disposal option. But the new study shows that over 99% of the 
transported plutonium did not travel dissolved in groundwater but on 
particles - called colloids - carried in the flow.  

No complacency  

Nirex, the UK authority responsible for disposing of nuclear waste, 
told BBC News Online: "We agree with the scientific findings - 
colloids must not be neglected. But we have been aware of this 
transport mechanism and done our own research at a fractured 
slate mine in Cornwall.  

"This is factored into all the calculations we make about our rock 
repositories - we haven't been complacent," said Dr Alan Hooper, 
Science Director.  

The actual amount of plutonium moved in Nevada is very small and 
only a tiny fraction of the total waste present at the test site was 
mobilised. Nonetheless, the researchers from the Lawrence 
Livermore and Los Alamos National Laboratories, writing in the 
journal Nature, warn that ignoring this way in which contaminants 
can be dispersed may "significantly underestimate the extent of 
radionucleide migration."  

Vapourised rock  

The US researchers looked at the Nevada Test Sites where 828 
underground nuclear tests took place between 1956 and 1992. 
One, Benham, was the location of a 1,150 kiloton explosion just 
over 30 years ago. It reached a temperature of a million degrees 
and vapourised the rock 100 metres around.  

The scientists compared the ratio of the types of plutonium found in 
soil at Benham with that found in groundwater 1300 metres to the 
south. They matched perfectly, not only with each other but also 
with molten rock samples taken at the time of the blast.  

Filtering the very fine grit out of the groundwater samples showed 
that over 99% of the plutonium had been adsorbed onto the clay 
mineral particles. Professor Bruce Honeyman, at the Colorado 
School of Mines said in Nature that the study illustrated: "the 
striking influence colloids may have on contaminant transport."  

Plutonium - ideal candidate  

He stated that low solubility in water and a high tendency to stick 
to rock made plutonium "an ideal candidate" for this type of 
transport, along with thorium, cobalt and pesticides like DDT. 
However he told BBC News Online it was doubtful that it would 
provide a significant way in which people might be exposed to 
nuclear waste, because there the concentration of colloids is 
usually low.  

However, Professor Honeyman noted that pumping groundwater 
can create more colloids by pulling particles away from the rock, or 
changing the chemical environment, possibly increasing the 
transport of  pollutants. 

Sandy Perle
E-Mail: sandyfl@earthlink.net 
Personal Website: http://www.geocities.com/capecanaveral/1205

"The object of opening the mind, as of opening 
the mouth, is to close it again on something solid"
              - G. K. Chesterton -
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