🚀 go-pugleaf

On Fri, 09 Jun 2000 23:28:04 GMT, none (Quarks like a duck) wrote:

>
>
>>The nuke waste "quandery" has been solved from a technical
>>perspective.  But the politics of warm-inner-glow
>>pseudo-environmentalism and ignorant NIMBY attitudes, they will indeed
>>take some time to resolve.
>
>
>>...Greig
>
>Every time you repeat that lie, proves you are completely discredited.
>

[ from http://www.uic.com.au/wast.htm ]

Immobilising high-level waste 

Solidification processes have been developed in France, UK, US and
Germany over the past 35 years. Liquid high-level wastes are
evaporated, mixed with glass-forming materials, melted and poured into
robust stainless steel canisters which are then sealed by welding. 

Borosilicate glass from the first waste vitrification plant in UK in
the 1960s. This block contains material chemically identical to
high-level waste from reprocessing. A piece this size would contain
the total high-level waste arising from nuclear electricity generation
for one person throughout a normal lifetime.

The vitrified waste from the operation of a 1000 MWe reactor for one
year would fill about twelve canisters, each 1.3m high and 0.4m
diameter and holding 400 kg of glass. Commercial vitrification plants
in France, UK and Belgium produce about 1000 tonnes per year of such
vitrified waste (2500 canisters) and some have been operating for more
than 16 years. 

click to enlarge

Loading silos with canisters containing vitrified high-level waste in
UK, each disc on the floor covers a silo holding ten canisters 

A more sophisticated method of immobilising high-level radioactive
wastes has been developed in Australia. Called 'SYNROC' (synthetic
rock), the radioactive wastes are incorporated in the crystal lattices
of the naturally-stable minerals in a synthetic rock. In other words,
copying what happens in nature. This process is now being tested in
USA. 


Waste disposal 

Final disposal of high-level waste is delayed to allow its
radioactivity to decay. Forty years after removal from the reactor
less than one thousandth of its initial radioactivity remains, and it
is much easier to handle. Hence canisters of vitrified waste, or spent
fuel assemblies, are stored under water in special ponds, or in dry
concrete structures or casks. 

The ultimate disposal of vitrified wastes, or of spent fuel assemblies
without reprocessing, requires their isolation from the environment
for long periods. The most favoured method is burial in dry, stable
geological formations up to 600m deep. Several countries are
investigating sites that would be technically and publicly acceptable.
The USA is pushing ahead with a repository site in Nevada for all the
nations spent fuel. 

One purpose-built deep geological repository for long-lived nuclear
waste is in operation in New Mexico, though this only takes defence
wastes. 

There is a proposal for an international nuclear waste repository in
optimum geology, and this could be located in outback Australia. It
would be a commercial undertaking, generating some A$ 5 billion per
year in revenue. 

After being buried for about 1,000 years most of the radioactivity
will have decayed. The amount of radioactivity then remaining would be
similar to that of the naturally-occurring uranium ore from which the
fuel originated, though it would be more concentrated. 

Layers of protection 

Thus, to ensure that no significant environmental releases occur over
periods of tens of thousands of years after disposal, a 'multiple
barrier' disposal concept is used to immobilise the radioactive
elements in high-level (and some intermediate-level) wastes and to
isolate them from the biosphere. The principal barriers are: 

Immobilise waste in an insoluble matrix, eg borosilicate glass, Synroc
(or leave them as uranium oxide fuel pellets - a ceramic) 

Seal inside a corrosion-resistant container, eg stainless steel 
In wet rock: surround containers with bentonite clay to inhibit
groundwater movement 

Locate deep underground in a stable rock structure 

Site the repository in a remote location. 

For any of the radioactivity to reach human populations or the
environment, all of these barriers would need to be breached before
the radioactivity decayed. 

What happens in USA and Europe?

In USA high-level civil wastes all remain as spent fuel stored at the
reactor sites. It is planned to encapsulate these fuel assemblies and
dispose of them in an underground engineered repository about 2010,
probably at Yucca Mountain, Nevada. (Suggest search UIC Newsletters
for Yucca Mountain.) This is the program which has been funded by
electricity consumers to US$ 16 billion (ie @ 0.1 cent per kWh), of
which about US$ 6 billion has been spent.

In Europe some spent fuel is stored at reactor sites, similarly
awaiting disposal. However, much of the European spent fuel is sent
for reprocessing at either Sellafield in UK or La Hague in France. The
recovered U and Pu is then returned to the owners (the Pu via a MOX
fuel fabrication plant) and the separated wastes (c3% of the spent
fuel) are vitrified, sealed into stainless steel canisters, and either
stored or returned. Eventually they too will go to geological
disposal. 

Sweden represents the main difference, it has centralised spent fuel
storage, CLAB, near Oskarshamn, and will encapsulate spent fuel there
for geological disposal by about 2015. European funding is at similar
level to USA per kWh.

A natural precedent
We have an example in nature to suggest that final disposal of
high-level wastes underground is safe. Two billion years ago at Oklo
in Gabon, West Africa, chain reactions started spontaneously in
concentrated deposits of uranium ore. The reactions continued for
hundreds of thousands of years forming plutonium and all the highly
radioactive waste products created today in a nuclear power reactor.
Despite the existence at the time of large quantities of water in the
area, these materials stayed where they were formed and eventually
decayed into non-radioactive elements. The evidence is there.