Publicatie Laka-bibliotheek:
THORP. An in depth investigation
| Auteur | CORE |
| Datum | |
| Classificatie | 2.05.8.35/06 (GROOT-BRITTANNIË - SELLAFIELD - THORP) |
| Voorkant | 
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Uit de publicatie:
A BRIEF BACKGROUND TO REPROCESSING AND THE THERMAL OXIDE REPROCESSING PLANT (THORP)
Reprocessing is the physical and chemical separation of uranium and plutonium
from nuclear fuel after it has been used In a reactor ("spent" fuel). By weight, spent
fuel consists of 99.2% uranium, 0.3% plutonium and 0.5% "fission" products (other
radioactive elements, e.g. caesium, strontium, americium, etc). This small fission
product fraction, however, accounts for 97% of the radioactivity in the spent fuel.
Historically, Britain embarked upon reprocessing for the requirements of its military
programme. At the end of the Second World War the Government decided that the
Sellafleld TNT factory site, on the west coast of Cumbria, should be the place for
Britain's plutonium producing reactors for its atomic weapons programme. The two
characteristic plutonium 'piles started operating in 1950 and 1951. Along with the
two piles, a reprocessing plant (Building 204) was built to separate out the plutonium
from the spent nuclear fuel produced by the piles. This too was opened in 1951. By
1952 enough plutonium had been created at Sellafield to enable Britain to explode
its first atomic bomb at the Montebello Islands near NW Australia. The entire
Sellafleld site was owned and run by the United Kingdom Atomic Energy Authority
(UKAEA) until 1971 when responsibility for running Sellafield was handed over to
the newly formed Government owned company, British Nuclear Fuels Ltd (BNFL).
In 1956 and 1958 respectively, two new military Installations, comprising in all
eight nuclear reactors, were commissioned at Calder Hall (on the Sellafield site) and
Chapelcross in Dumfriesshire. These reactors became the main suppliers of military
plutonium after the disastrous fire at Sellafield In pile number one in 1957, which
led to the closure of both plutonium piles.
The Calder Hall and Chapelcross reactors were the first "Magnox" reactors and were
prototypes for the nine civil Magnox stations In the U.K. These reactors were named
after the type of fuel they use which Is natural uranium metal rods enclosed In
canisters (or "cladding") of a magnesium alloy called "Magnox". A plant (B205) to
reprocess this Magnox spent fuel was built at Sellafield and started operating in 1964
and continues to operate. Sellafield, at present, only reprocesses Magnox spent fuel.
Magnox spent fuel is reprocessed In two stages. In the first stage, the Magnox
cladding Is mechanically stripped off the uranium rods. This stripped cladding is
classed as Intermediate Level radioactive Waste (ILW). The uranium rods are then
dissolved in nitric acid and treated chemically, with organic solvents, to separate out
the unburned uranium and plutonium. The remaining hot, highly radioactive liquid
(which contains vast quantities of fission products) Is classed as High Level Waste
(HLW) and Is stored In large stainless steel silos. There are eleven of these silos at
Sellafield - each silo contains 444 million curies of radioactivity (for comparison, the
entire Chernobyl release is estimated to have been 50- 100 million curies). A plant is
currently being constructed at Sellafleld to "glassify" this liquid HLW (after a delay
period of five years to allow for cooling) through a process called vitrification.
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