SCHOTT develops and manufactures glass-to-metal electrical penetrations that stand up to high temperatures as well as overpressure in nuclear reactors.
Photo: SCHOTT/H.-R. Schulz
Meeting the highest standards
Nuclear power provides around 11 percent of the world’s electricity, and there has been increased focus on the safety of this energy generation source since the Fukushima Daiichi nuclear accident in Japan in 2011. With its electrical penetration assemblies (EPAs), SCHOTT provides a significant increase in nuclear safety.
After researching the accident, Fukushima’s operators TEPCO found that the tsunami, which cut off all power to the plant’s cooling system, led to the temperature inside the reactor containment rising significantly. Normal operating temperature was about 60 degrees Celsius and it rose to more than 250 degrees Celsius. The pressure was more than doubled. These extreme temperature and pressure levels are thought to have overstrained the organic epoxy seals of electrical penetration assemblies (EPAs) at Fukushima, which are suspected to have led to the leakage of explosive hydrogen. An EPA is a key part of the reactor containment, or safety barrier system, where electrical conductors pass through the containment to relay measurement data or supply high currents to operate reactor systems. If EPAs cannot withstand the same or greater conditions as the reactor containment, then they can become weak points that could fail during operation or an accident.
SCHOTT designs and manufactures unique glass-to-metal EPAs which have ground-breaking performance in what is known as severe accident conditions, including high temperatures and pressures. Around 10,550 SCHOTT EPAs are used at nuclear sites and other safety-critical locations, such as liquefied natural gas installations and submarines, around the world. In terms of nuclear plants, SCHOTT EPAs have been used in over 50 nuclear power plants worldwide since the 1960s, for example Borssele in the Netherlands, Loviisa in Finland, and Forsmark in Sweden. It is a proven technology which has been improved and adapted over many years. Due to their high performance, the EPAs are now leading the field in the context of higher nuclear safety standards for components, which are aimed for after Fukushima. SCHOTT’s glass-to-metal EPAs avoid the problems suffered by components that utilize organic epoxy and Teflon material, which degrade over time in reactors. The high temperature, pressure and radiation in a reactor cause these materials to age and degrade, which does not happen with glass-to-metal seals.
Nuclear component manufacturers are raising their safety specifications as a result of Fukushima, but there has been a consensus view in the nuclear industry, addressed at recent symposia, that standard-setting bodies should provide higher uniform standards to be applied globally. Organizations such as the International Atomic Energy Agency (IAEA), the US Nuclear Regulatory Commission (NRC), the Institute of Electrical and Electronic Engineers (IEEE), and the American Society of Mechanical Engineers (ASME), are key bodies that set nuclear standards.
Nuclear power booms in China
Around the world, there are over 430 commercial nuclear power reactors in 31 countries, with over 370,000 MWe of total capacity, according to the World Nuclear Association (WNA). Sixteen countries use nuclear reactors for at least 25 percent of their electricity. France gets around three quarters of its power from nuclear energy, while Belgium, Czech Republic, Hungary, Slovakia, Sweden, Switzerland, Slovenia and the Ukraine get one third or more. South Korea, Bulgaria and Finland normally get more than 30 percent of there power from nuclear, whereas in the USA, UK, Spain and Russia almost one fifth is nuclear energy, according to WNA. Some countries, such as India and China, are building more reactors to supply electricity, whereas others, such as Germany and Scotland, are phasing out nuclear power. The Chinese government plans to increase nuclear generating capacity to 58 GWe, with 30 GWe more under construction by 2020. China has completed construction and started running 17 new nuclear power reactors from 2002 to 2013, and 28 are currently under construction. <
Cable feedthroughs from SCHOTT are tested carefully and meet high standards. They are designed to last for decades. Photo: SCHOTT/H.-R. Schulz
Specially developed cable feedthroughs from SCHOTT were installed in the nuclear reactor Forsmark 3 located just north of Stockholm. Photo: Vattenfall
There will undoubtedly be a significant market for nuclear reactor components for many years to come, both in retrofitting and new build, and the ongoing global aim is likely to be for increased safety standards, both after Fukushima and beyond. SCHOTT is leading the way with its glass-to-metal EPAs that withstand severe accident conditions, and this places the company at the forefront of nuclear component manufacture due to proactive application of stringent safety standards. <
Electrical Penetration Assemblies for Nuclear Power Plants
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