SCHOTT solutions no. 2/2014 > Energy
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.
SCHOTT EPAs were recently installed at Forsmark 3, a nuclear reactor north of Stockholm. The EPAs for this project were designed and stringently tested to provide the higher standards that were key to plant operator Forsmarks Kraftgrupp’s (a company of the Vattenfall Group) upgrading of the reactor, which included modified safety scenarios. The EPAs were designed to withstand submerged conditions under 13 meters of water for at least 30 days, together with pressures of up to 8.3 bar, and temperatures up to 185 degrees Celsius. In addition, the radiological exposure of the EPA during a severe accident scenario had to reach 1.7 MGy at a dose rate of 2360 Gy/h. SCHOTT Nuclear Safety Division General Manager Thomas Fink said: ”Our EPAs have been thoroughly tested and meet a number of high standards, which means that the EPAs will last for the Forsmark 3 life extension of 30 years.” EPAs are also a small part of the total cost of a new nuclear plant. Fink: ”In terms of new build, the cost of these safety-critical components is only 0.1 % of the entire budget, which is a small investment for a very significant increase in safety in a key part of the reactor.”
Cable feedthroughs from SCHOTT are tested carefully and meet high standards. They are designed to last for decades. Photo: SCHOTT/H.-R. Schulz
Vattenfall has stated that the modernization of its plants in Sweden will mean longer operational lives for the reactors. Torbjörn Wahlborg, Chairman of the Board for Forsmarks Kraftgrupp AB, said: ”Vattenfall is currently conducting the most extensive modernization program in the history of Swedish nuclear power, and the company is planning to invest SEK 16 billion (1.75 billion euros) over a five-year period between 2013 and 2017. From a technical standpoint, the modernization process will lay the way to operating these plants for many more decades to come.”
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
Electrical Penetration Assemblies for Nuclear Power Plants