Geriatric nuclear power plants deserve our respect

Nuclear power in the UK received a boost in June. A deal was agreed with the Chinese to build a new generation of nuclear reactors on these shores. But there should be no room for complacency about the future of electricity supplies – they are still under threat says Dermot Martin The Government has long been doing the hokey-cokey on whether to press ahead with nuclear power. Now the options are diminishing. If it wants to secure the supply it will have to agree to growing requests to extend the life of existing advanced gas-cooled reactor (AGR) plants until the new-builds achieve their start-up dates and that’s likely to be many years hence. All round the world the governments and the nuclear industry are facing the fact that they will have to extend the life of existing reactors. By 2020, one third of the world’s fleet of nuclear power stations will be 40 or more years old. In 2030, this figure will have increased to 80%. Here in the UK all but one of the 16 reactors were due to be retired by 2023 but if they were pensioned off on schedule, the lights would go out. As a result, the trend of extending licensing of power stations is accelerating with requests to the Office of Nuclear Regulation stacking up. In May EDF, the French owned operator of the Dungeness B power station, asked for an extension of the life of its AGR facilities. EDF is planning life extensions averaging seven years for the AGR units and announced a seven-year life extension for Hinkley Point and Hunterston in November 2012 and a five-year extension for Hartlepool in November 2013. The company already spends about £350 million per year on plant upgrades to enable ongoing operation. Fears about the safety of these plants when the license extensions are granted will grow but is the public right to be concerned? Since short-term replacement of current generation capacity is not technically feasible, ensuring the safety of nuclear plant operations beyond 40 years is currently considered the better option. In 2008, EDF persuaded a group of plant operators to create the Materials Ageing Institute (MAI) which is proving valuable asset in understanding some of the reactor ageing processes. The sharing of research, experimental results, feedback and scientific information on materials degradation will contribute significantly to and life extension programmes at nuclear plants. In the US the strategy of extending the life of nuclear plants has been widely embraced. The US Nuclear Regulatory Commission has granted license extensions for 73 reactors and is currently reviewing 12 other applications, with approximately 30 more to be submitted in the next decade. The US re-licensing system has come in for criticism recently because most extensions went through based on reports written up by the operators. Critics say extensions of 20 years have been approved at some plants without proper independent checks. But the re-licensing system in the US is more rigorous that the UK because it is a prescriptive system in which the operators are told what they must do to ensure safety. In the UK the system is passive in that the licensee must make a case and the authority either accepts or rejects the plan. The loss of key personal with requisite skills means that often questions of safety are decided among a small and diminishing group of experts who can hardly be classed as independent. In the late 90s the stock of nuclear power was in serious decline. A series of high profile accidents, Three Mile Island and Chernobyl for example, together with unanswered questions on how to deal with radioactive waste materials with half life values measured in thousands of years bred suspicion. Governments turned away from nuclear and looked at other options. To many experts round the world it was obvious the so called green energy technologies such as wind and solar power would never be able to fill the gap. Nevertheless in the US several privately owned power plants went on the market and were sold off at ridiculously low prices. The country's oldest power plant, Oyster Creek near the New Jersey, went for $10 million — a paltry fraction of its $65 million construction cost in dollars adjusted for inflation. For these new plant owners the re-licensing system and the principal that extensions were acceptable was a godsend. It meant if they could convince the NRC that the plant was functioning within accepted safety parameters the life of a plant could be extended one twice three times and possible more. From an economic point of few it was fantastic for the owners. New plants would cost billions, but these older reactors suddenly became electricity generators but also cash generators because they had already paid for themselves many times over. In the UK we are coming to terms with the idea that geriatric nuclear reactors will have to go on producing electricity. Although there has been a glut of announcement about new reactors (Toshiba and Nu gen in Cumbria) new plant planned at Hinkley Point in Somerset the UK is moving ahead with incremental life extensions. [caption id="attachment_40245" align="alignleft" width="200"] The Chernobyl Nuclear power plant[/caption] To maintain demand our existing AGR’s will have to have their lives significantly extended. Even if the new Chinese deal becomes concrete – five new nuclear plants at a total costs of and estimated £35bn there is an uncertain the time frame. Energy strategists see the geopolitical situation as unpredictable in the longer term so it could be decades before these planned stations are built. So the crisis is already upon us The industry regulator, Ofgem, has already warned of the "unprecedented challenge" to secure UK power supplies. It said spare electricity power production capacity could fall to 2% by 2015, increasing the risk of black-outs. If part of the answer is to extend the life-time of all the functioning AGRs we need to know more about the life expectancy of a nuclear reactor. Can it in fact be predicted? When the first generation were build the predictions were based on the economic parameters and these were linked to simply how long it would take to pay off the construction loans. A time limit on construction materials and degradation of engineering systems was not really considered a factor. In the US In 2007, when Entergy Nuclear Operations sought a license extension for the Pilgrim reactor in Massachusetts, it wrote: "The original 40-year license term was selected on the basis of economic and anti-trust considerations rather than on technical limitations." Experts agree there were areas of weakness in all design features of a nuclear plant. But the debate on what constitutes the true life span of any reactor began to gain traction in about 2008. If you take a hydroelectricity project like the Hoover dam and predict a life expectancy what answer do you get? Eventually any dam will crumble if it is not used for the purpose it was built. If the use is continuous, studies show that it would take 10,000 years for serious defects to show-up. All that is needed is proper monitoring and maintenance for continued electricity production. There is no suggestion that a nuclear power plant falls into the same category as a Hoover dam, but if we are taking of extensions of 60 to 80 years why not 100 years or 150 years and beyond? One of the first clear signs of their intentions emerged in 2008 with an NRC-industry workshop on nuclear life beyond 60 years. Its summary said that "participants did not believe there is any compelling policy, regulatory, technical or industry issue precluding future extended plant operations". The next year, an issue paper by the industry-funded Electric Power Research Institute stated that "many experts believe ... that these plants can operate safely well beyond their initial or extended operating periods — possibly to 80 or 100 years." About 10 years ago a senior vice president of Constellation Energy Nuclear Group, indicated that her company may start applying for a second license extension within 10 years. Constellation owns two of the country's oldest reactors, Nine Mile Point and Ginna in upstate New York. It also owns Calvert Cliffs in Maryland, which acquired the industry's first renewed license in March 2000. She was warning then about the supply gap in the US which will develop if plants are decommissioned before replacements are built. Here in the UK that gap is already on us. In the UK the Office of Nuclear Regulation (ONR) assesses the safety cases for a limited extended operating period of say two or three years. There are various issues around the structure of reactor vessels, electric cables set in concrete, and underground piping. However it is not for ONR to predict whether the AGRs will achieve EDF’s anticipated lifetimes. The regulators only assess the adequacy of any submission provided by the operator, intended to justify a defined period of operation as above. One possible barrier to longevity, which is being studied in depth at MAI and in the UK, is graphite degeneration. A graphite nuclear core cannot in reality be fully replaced because the engineering difficulties are too great. The graphite not only acts as a moderator in the reactor to slow down the fission process when required but it provides channels for the control rods and the fuel, however the fuel has graphite sleeves that channel the main coolant flow. This fuel sleeve graphite is usually replaced at the time the nuclear fuel is replaced. Graphite is prone to significant weight loss caused by radiolytic oxidation. At the end of reactor life this maybe greater that 45% in parts of the peak rated bricks in the centre of the cores, but the mean brick weight loss will be less and the whole core mean weight loss less again. The main driver for this weight loss is gamma irradiation ionising the CO2 coolant. Only one serious graphite issue to date has caused the closure of a reactor in the UK and that was at Reactor 1 Oldbury. The graphite issue is the research area where EDF is pumping millions of Euros in research to gain a better understanding. Professor Barry Marsden, of the Nuclear Graphite Research Group acts as an independent adviser to the Office of Nuclear Regulation (ONR) and is a member of the ONR Graphite Technical Advisory Committee (GTAC). Among the ageing threats to older reactors face are boiler leaks. Any water entering the reactor core it would increase the moderation requirement. As the ageing graphite has lost some of its mass this increase in moderation would be greater than was the case when the reactor was new. Fast neutron damage is also a threat because it causes brick shrinkage and as this shrinkage is greater at the brick’s bore than the outside it causes brick stresses to develop. These stresses are tensile at the bore early in life and tensile at the outside of the bricks late in life. In addition there are stresses to the outside layers of the bricks. Extensive cracking is predicted late in reactor life. This brick cracking may cause extensive deformation of the fuel and control rod channels challenging the controllers the ability to shut down and cool the fuel, although if this proved to be an issue the reactors would be shut down long before an extreme conditions was reached. Says Professor Marsden: “We’ve got 14 AGRs in the UK but a very small pool of graphite experts. There is an incomplete graphite irradiation data base because of the premature break-up of the UKAEA. Reactor cores are unexpectedly cracking up. We need now to focus more research in this area.” “Both whole core graphite weight loss and brick cracking are of concern. Graphite cores will continue to lose weight as they operate and extensive brick cracking may start to occur late in life.” “EDF is investing significant amount of money on rigs, graphite material test programmes and analysis to try to pre-empt these problems and demonstrate the safety of the AGRs, in the hope of extending life times.” The ONR insists that extensive core monitoring, sampling and inspection is regularly carried out. The need for this monitoring, sampling and inspection is likely to increase and this in itself will affect the economics of reactor operations. There is no doubt that the UK owes a great debt to the engineers who built the country's first generations of nuclear power plants. Their caution manifests itself in the ability of so many plants to continue serving the UK’s needs decades later. The hope and expectation is that the new generation will inherit some of those qualities. The Author Dermot Martin is a writer on Chemistry and media adviser for Bournemouth and Poole College