As it took shape on the wild coast of Caithness during the late 1950s, the steel 'golf ball' housing the Dounreay fast reactor became one of Britain's most identifiable symbols of industrial progress. On Thursday, it will become a scientific gravestone.
It will not be Cecil Parkinson's finger on the button that extinguishes a 40-year dream of producing unlimited power from the heart of the atom. But it was he, who as Secretary of State for Energy in 1988, took the decision to shut the fast reactor programme, because it did not fit in the brave new commercial world of privatised electricity companies.
The reactor to be closed this week is the second on the site, housed in a concrete shoebox of a building, the successor to the one within the steel golf ball. This second reactor, the Prototype Fast Reactor (PFR), started up in 1974. Its predecessor shut in 1977 after 17 years.
This week, however, there will be no successor to the PFR. All that will remain to be done at Dounreay will be clearing up the debris, and reprocessing the spent fuel discharged from the reactor.
Fast breeder reactors had been the ultimate goal of the nuclear industry since the earliest days: reactors of the advanced gas cooled or pressurised water type were merely an intermediary stage to the final destination. In 1950, the nuclear pioneer and Nobel prize winner Sir John Cockroft said the primary task was to develop 'breeder piles'.
The attraction was the promise of squeezing virtually unlimited power out of nuclear fuel. A fast reactor can produce 60 times more useable energy from a given quantity of uranium than any of the so- called thermal reactors. Moreover, it can do so from depleted uranium, which is otherwise virtually useless.
Fast reactors were to have been the 20th-century version of the alchemical philosopher's stone transmuting base metals into gold. The design involves surrounding the reactor core (running on plutonium fuel) with a blanket of uranium which, as a result of nuclear irradiation, undergoes a transmutation of the elements and turns into plutonium. The effect is to turn the components of naturally occurring uranium, which cannot be used as nuclear fuel, into something that is a powerful energy source, and to produce more plutonium than the reactor core consumes.
In 1954, the Government backed the nuclear industry's vision and announced to the House of Commons that British scientists and engineers were ready to proceed with 'a powerful and dramatic project: the construction of a big test reactor of the breeder type' at Dounreay. The original reactor, within its golf ball, was generating electricity for the grid by 1959, even before Britain's first commercial nuclear power stations had started. In 1962, it became the world's first fast breeder reactor to produce power commercially. The future seemed assured when the prototype reactor started generating power in 1974 and the Arab oil embargo revealed the fragility of supplies of fossil fuels. The Atomic Energy Authority predicted that unless Britain built at least 20 fast reactors by 1990, the lights would go out. The Government authorised British Nuclear Fuels to build its Thermal Oxide Reprocessing Plant (Thorp) to produce the plutonium needed.
But reactors proved expensive to build and fast reactors even more so. Because of the high power levels within the core, neither gas nor water was suitable as a coolant. Instead the engineers turned to liquid metals, sodium and potassium. But while these were elegant solutions in the laboratory, they proved to be tricky when engineers tried to scale the process up.
In most reactors, the coolant takes the heat generated by the nuclear chain reaction in the core and transfers it, via a heat-exchanger, to an external water circuit, turning the water to steam to drive the turbine which produces the electricity. They thus have a primary and a secondary circuit.
In fast reactors, the sodium that circulates through the core gives up its heat to a secondary sodium circuit, which goes through a heat exchanger to raise steam in a tertiary circuit. The need to put in three rather than two circuits makes fast reactors too costly to build.
By the late 1980s, there was no longer an immediate energy shortage and the nuclear industry was proposing fast reactors as a long- term rather than a short-term solution. But while no one believes that the population of the world can both sustain its present standard of living and continue indefinitely to burn fossil fuels, the fast reactor in Britain began to appear an insurance policy that was too expensive.
In the run-up to privatisation of the electricity supply industry, neither Government nor private enterprise were willing to pay now for the promise of unlimited energy far in the future. The 'powerful and dramatic project' which the House of Commons greeted so enthusiastically in 1954, is now at an end.
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