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Source of power


The role of civil engineers in this century's diverse and rapidly changing power sector has been the one constant, ensuring its safe and reliable supply. David Hayward has the story.

Few of the responsibilities placed on Britain's civil engineers this century can have changed so dramatically as the challenge to provide power.

London was one of the first cities in the world to have a public electricity supply. But at the dawn of the century Government was describing the system as chaotic. Dozens of small private power companies were competing to sell electricity which offered a bewildering range of different and incompatible voltages.

As the century has progressed Britain's civil engineers have led the world in the development of power station structures. They have developed prestressed concrete for nuclear power station pressure vessels; have pioneered new cooling tower designs and have made it possible to eliminate acid rain chemicals from coal fired power stations.

By the 1920s London's public electricity supply had blossomed nationwide into 572 power companies. Government and industry were demanding reliability and in 1926 the newly formed Central Electricity Board was charged with creating what was arguably the world's first countrywide grid system.

As the larger power stations were linked into the new grid, civil engineers spearheaded what became known as the 'age of power' by building dozens of coal-fired power factories.

The electricity industry was nationalised in 1948 and the arrival of an all powerful Central Electricity Generating Board several years later. As Britain's coal-fired boiler and turbo generator technology led the world, its civil engineers did far more than cover the clever bits with a building shell.

The arrival of heavy, 60m high boilers, hung vertically to allow expansion of 250mm or more during use and exerting forces of around 12,000t down through support frames, triggered rapid advances in foundation designs and prestressed pile technology.

Rising global concern for the environment; worldwide declarations for reductions in sulphur dioxide emissions and, more specifically for Britain, Scandinavian complaints that their forests and lakes were being showered with acid rain all peaked at the same time threatening the future of coal- fired plants.

Again, civils consultants and steel fabricators were on hand, helping reduce acid rain by designing £700M flue gas desulphurisation units - boasting Channel Tunnel-sized ducting - to fit into live power stations just metres from operational turbines.

But such vast FGD units at Drax and Radcliffe power plants demanded their own operating power, further reducing their efficiency. In hindsight, it was inevitable that, when the lengthy moratorium on the use of that other fossil fuel - gas - was surprisingly lifted on the eve of industry's privatisation, it would signal coal's death warrant.

The discovery of offshore gas fields also helped shift the balance away from coal. Suddenly Britain had access to vast supplies of gas and in 1990, energy secretary Cecil Parkinson agreed to allow power companies to use gas for electricty generation for the first time. Gas-fired power stations could be built for a fraction of the cost and time needed for their now competing giants.

'The ban on gas meant we had ignored it as a power station fuel for decades,' recalls Bill Hannah who, with 45 years' experience in the power sector - 17 of them as CEGB chief civil engineer - can speak with some authority. 'Had we been allowed to consider it, the CEGB would have gone down that route ages before privatisation.'

According to Hannah, now retired, the politically triggered 'dash for gas', on top of the sudden, earlier than expected, privatisation announcement, pushed one of the world's most efficient power industries 'into total turmoil'.

Fast developing environmental concerns, plus the nuclear accidents at Chernobyl and at the US station Three Mile Island, left coal and nuclear power floundering. Gas fired power stations and, then even more efficient combined cycle gas turbine power stations, became not so much welcome competitors but sole and secure market leaders overnight.

Gas fired power stations were relatively simple to build compared with the complex coal and nuclear facilities that preceded them. As a result the challenges they presented to the civil engineering profession were less significant.

Civil engineering innovation did, however, dominate this century's third main power source. The once steady, now shaky, rise of nuclear power owes as much to the ingenuity of forward thinking civil engineers as it does to the innovations of nuclear scientists.

Hannah himself was involved in nuclear power station design during its infancy in the 1950s. Along with colleagues in the sector's pioneering contractors - Taylor Woodrow and Sir Robert McAlpine - he responded quickly to the need for more efficient protection around the nuclear cycle's nasty bits - its reactor core.

Such reactors in the original Magnox stations were encased in spherical steel enclosures. But as reactor cores grew in size, and the Magnox programme was replaced by advanced gas cooled reactors, so the safety and efficiency of steel pressure vessels decreased.

Insitu welding of 150mm thick spherical containment was difficult to quality check to nuclear standards, and in-service maintenance became problematic. Such vessels also still needed an outer concrete bioshield as a second defence line against radioactive releases.

It was much better, said civil engineers, to combine the two enclosures into a single concrete pressure vessel which, with thicknesses of 5m or more, rendered secondary outer shielding unnecessary. But loadings on the concrete of up to 400,000t called for those 1950s engineers to reach for their prestressing books.

The resulting prestressed concrete pressure vessels revolutionised nuclear power station design and economy. And consequent advances in the art of prestressing led directly to the creation of the North Sea's vast concrete gravity oil platforms and thus the protection of another vital energy fuel.

'Civil engineers and their skills were fundamental in the development of civil nuclear power in the UK,' claims Stephen Taylor, special projects manager for Sir Robert McAlpine and a pioneer in nuclear power station construction. 'Without the development of PCPVs we would not have had an AGR programme which, at the time, offered world leading technology.'

What though of the civil engineer's role in future power markets?

The CEGB's plan in the 1980s of commissioning at least five new nuclear power stations by the end of the century has been replaced by a seemingly closed order book.

Yet the civils nuclear work book is far from empty. There is still the £100bn legacy of decommissioning a varied portfolio of redundant structures and the storage of its radioactive waste products.

The government agency NIREX, charged with solving the storage problem, starts the millennium impotent and near destroyed. After years of research, the political plug has been pulled on agency plans for a vast underground repository - offering Channel Tunnel-sized project opportunities - which would have kept construction happy for years.

Though Government argued that ground stability risks remained too high, a powerful House of Lords committee concluded, earlier this year, that an underground store remained the best option and civils designers are again waiting for someone to press a green light.

This familiar political seesaw also rules the alternative power debate where construction of offshore wind farms and tidal barriers - specifically the £10bn Severn Barrage - remain poised to fall either way.

Taylor is involved in the nuclear and alternative energy sectors. A nuclear supporter, he also heads the Severn Barrage steering committee. He says future energy policy is shrouded in indecision. 'It seems governments are waiting for all the lights to go out before taking any decisions,' he says resignedly.

But he remains optimistic. 'The 1990 level of world energy demand is set to double by 2020. Our profession worldwide will be taking an ever increasing role in meeting that need and the real challenge to British civil engineers is ensuring we are up there helping to lead it.'

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