China receives first glass-to-metal sealed hermetic penetration from SCHOTT

China’s first commercial High Temperature Reactor (HTR) in the province of Shandong will be one of the most modern nuclear power plants in the world. Employing only the safest and most reliable technology available today, SCHOTT has been selected to supply its hermetic glass-to-metal sealed Electrical Penetration Assemblies (EPAs). The first feedthrough has now been delivered to the Institute of Nuclear and New Energy Technology (INET) at Tsinghua University for testing and training purposes.

China, the world’s largest energy consumer, is focused on creating its independence in energy generation through scientific and technological advancements, in a safe and environmentally-friendly manner. Hence, the country has been described as developing into a leading center for new nuclear reactor designs. The high temperature reactor with pebble bed modules (HTR-PM), for example, is considered to be one of the most promising next generation reactors with its inherent safety features. A demonstration plant is currently under construction at Shidaowan, in the Shandong province of China. SCHOTT has been selected to equip the reactor with its unique glass-to-metal sealed Electrical Penetration Assemblies (EPAs).

The outstanding performance of the glass-to-metal sealing technology from SCHOTT has convinced Xu Yuanhui, Deputy General Manager of Chinergy, “Based on our investigations and comparisons, EPAs from SCHOTT can meet the high requirements for precision and quality of high temperature reactors. This is why we chose them over many other suppliers for the demonstrator reactor. In addition, SCHOTT has an extremely good reputation and is a reliable supplier. This is of great importance to our HTR project. The successful completion of the demonstration HTR plant would pave the way for future nuclear reactor modules.”

Fukushima drastically underlined the imperative of safety

Following the Fukushima accident in March 2011, the Chinese government temporarily suspended its review and approval of new nuclear power projects. Safety checks at existing reactors and those under construction were also commissioned. In late July, a team of more than 40 representatives and experts from various government bodies, scientific community and nuclear related institutes conducted the safety review at Shidaowan.

TEPCO, the operator of the facility in Fukushima, has recently reconstructed the natural catastrophe that led to a breakdown of all available power supplies for the boiling water reactor’s cooling system. TEPCO’s analysis shows that the temperature inside the containment structure must have risen from a normal operating temperature of approximately 60 degrees Celsius to above 250 degrees Celsius while the design pressure was exceeded by more than twofold. The extreme temperature and pressure levels seemed to have overstrained the epoxy seals of the electrical penetrations at the Fukushima facility which are suspected to have led to the leakage of explosive hydrogen, according to TEPCO (also see for more details from TEPCO; Japanese only).

Next generation High Temperature Reactor is going through extensive testing phases

“The conditions inside the HTR are very demanding. The pressure in the nuclear reactor is about 80 bar and the temperature of the coolant can climb to as high as 1000 degrees Celsius. The temperature is already around 150 degrees Celsius even along the inside wall of the reactor pressure vessel,” Professor Zhou Huizhong from the Institute of Nuclear and New Energy Technology (INET) at Tsinghua University explains. “SCHOTT’s unique expertise in the area of glass-to-metal sealing, particularly in the nuclear industry, convinced us that this is the right technology for our advanced nuclear design.”

“Our standard glass-to-metal sealed penetrations are able to comfortably withstand temperatures in the range of -200 to +240 degrees Celsius. Special material combinations can even tolerate up to 1000 degrees Celsius for a period of time”, says Dr. Oliver Fritz, Head of Technology for the Nuclear Safety Division at SCHOTT Electronic Packaging. “As latest tests have shown, our EPAs remain completely airtight even at pressure peaks above 100 bar – it is the safest and most reliable sealing technology for EPAs available today.”

SCHOTT’s electrical penetrations, based on glass-to-metal sealing, withstand even higher pressures and offer the highest safety standards world-wide

The international technology company SCHOTT is supplying its glass-to-metal sealed electrical penetration assemblies (EPAs) to the Swedish Nuclear Power Plant Forsmark 3 which is undergoing renewed investment to improve its safety and reliability. SCHOTT especially developed a new type of EPA to meet the safety requirements of the Swedish Nuclear Power Plant.

“EPAs are important safety equipment at nuclear power plants”, states Thomas Fink, General Manager Nuclear Safety Division of SCHOTT. “Our electrical penetrations are already being used in more than 50 active nuclear power plants throughout the world: They are all uniquely and exclusively based on the unparalleled robustness of our glass-to-metal seal technology which provides considerable advantages over organic epoxy seals. For Forsmark 3, we designed a new generation EPA which can withstand latest Severe Accident (SA) requirements.”

This became necessary as the operator of the power plant had defined new and modified safety scenarios, i.e. the EPAs have to be 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 °C. In addition, the radiological exposure of the penetration during the SA amounts to 1.7 MGy at a dose rate of 2360 Gy/h. The use of inorganic sealing material like SCHOTT glass for the pressure boundary of the EPA minimizes the effect of high radiological exposures.

“For these higher requirements, we designed our new optimized EPAs. They are ready to undergo a complete equipment qualification process, witnessed by TÜV Nord. This includes endurance tests simulating a lifespan of 30 years as well as simulations of Design Based Accidents (DBA) and Severe Accidents (SA) such as flooding and earthquakes”; Fink adds. Once the testing is completed, SCHOTT will be able to offer these high-tech EPAs to other operators of nuclear power plants as well.

Electrical penetration assemblies are the vital conduits for power, control, and instrumentation circuits in nuclear power plant reactor pressure vessels. Their performance is critical to running core functions within the reactor, and their seals must be strong enough to maintain the pressure boundary integrity of the containment vessel in all accident conditions.

SCHOTT’s EPAs, designed with superior, redundant, and safer glass-to-metal seal technology, provide considerable safety advantages over organic epoxy seals to ensure the integrity of electrical penetration seals and containment vessels by incorporating inorganic, non-aging glass seals with significant heat- and radiation-resistant properties.

At SCHOTT’s own request, their glass-to-metal sealed EPA underwent stringent testing at Wyle Laboratories in Huntsville, Alabama (USA) in 2012 The SCHOTT EPA successfully passed an extensive qualification test program per IEEE Standards 317 and 344, including full survivability in conditions analogous to an earthquake reaching a magnitude of 12 on the Richter Scale.

SCHOTT glass-to-metal sealed electrical penetrations are already protecting nuclear reactors worldwide and are qualified for 60 years of use. The performance range of these electrical penetrations is staggering, having withstood over 400 bar (5,800 psi) and 400 degrees Celsius (752 degrees Fahrenheit) in previous tests.

In contrast, epoxy seals may break down under extreme temperatures and pressures, such as experienced at the Fukushima Daiichi nuclear power plant disaster. While electrical penetrations using organic polymer seals, such as epoxy, meet the current design basis specifications for electrical penetration assemblies in first and second-generation nuclear power plants, nuclear experts have voiced concern that the effects of severe accidents which have exceeded the design basis conditions could compromise the integrity of the seal.

VISOLA and SCHOTT supply enhanced Electrical Penetration Assemblies for Nuclear Power Plant

Hungary’s only Nuclear Power Plant (NPP) located in Paks plays a significant role in the country’s economy. The NPP, which houses four nuclear reactor units, accounts for more than 40 percent of the energy that the nation consumes. According to the International Atomic Energy Agency (IAEA), Paks NPP has an operational safety record on par with the best in the world. To raise this to an even higher level, 347 Electrical Penetration Assemblies (EPA) have been replaced. The new EPAs manufactured by VISOLA Ltd. ensure the highest safety thanks to the glass-to-metal sealed feedthroughs from SCHOTT Electronic Packaging GmbH.

Paks NPP is extremely important to the Hungarian electric power market. After all, it helps ensure that consumers have access to a reliable and affordable supply of safe and environmentally-friendly electricity. To achieve this, all four units of the power plant that were put into service between 1982 and 1987 are constantly being modernized. This effort has certainly paid off: IAEA awarded Paks the highest scores for its safety performance.

”The Soviet designed VVER-440 type, V-213 model, second generation pressurized water reactors are still functioning reliably. This can be attributed to the skilled maintenance work and a series of measures implemented for improving the level of safety,” says Mr. István Mittler, Communication Director for Paks NPP Ltd. “However, in addition to the reconstruction of the reactor protection system, a lot of obsolete equipment had to be either replaced or refurbished,” he adds.

Safety upgrade to enable extension of service lifetime

As agreed to with the IAEA, the Hungarian government decided to upgrade the infrastructure of the NPP even further. The goal is to lay the foundation for an extended service life of 20 years, in addition to its original 30 years of operation. This means that several of the NPP’s components need to be replaced, especially safety-critical parts like the Electrical Penetration Assemblies (EPAs), which were insulated with plastic that has since aged. EPAs from VISOLA in Hungary that contain glass-to-metal sealed feedthroughs manufactured by SCHOTT Electronic Packaging in Germany, offered the ideal solution.

“We prefer these products over other imported EPAs because they combine reliable feedthroughs with gamma screening and other constructional components required by our power plant,” explains Mr. Géza Pekárik, Technical Director of Paks NPP Ltd. “The quality management system of both suppliers also passed our qualification standard. There was no defective product in the shipments and no failure occurred during operation. Both the electrical and sealing properties of the VISOLA-SCHOTT EPAs are excellent,” he notes.

Glass-to-metal sealed penetrations with gamma screening

“We developed a complete family of EPAs based on these reliable glass-to-metal sealed feedthroughs that are equipped with gamma screening in order to be able to meet the rigid requirements of the VVER-440 type reactors at Paks NPP,” says Dr. Endre Zelenyánszki, Managing Director of VISOLA Ltd. “The development of the design, manufacturing technology and quality assurance system took four years. Domestic research laboratories were also involved in the testing of the design and qualification of the products,” adds Mr. Habib Naderi, Technical Adviser for VISOLA Ltd.

“Glass-to-metal sealed penetrations provide pass-through for power, control and instrumentation cables to the thousands of instruments, control panels, electric motors and many other electric and electronic devices in a nuclear power plant,” explains Dr. Oliver Fritz, Technology Expert from SCHOTT Electronic Packaging. “They maintain the pressure boundary integrity of the containment structure for periods well in excess of the 60 years design lifetime and enhance the safety levels of the nuclear reactor,” he concludes.

“The installed EPAs will definitely be able to meet the requirements of the extended service time,” Mr. Pekárik says. “Uninterrupted operation of the existing four units over the next two decades will also serve as proof of concept for the construction of new reactors. According to the plan currently under preparation, two new units are to go into operation between 2020 and 2025 and thus providethe cornerstone for the national strategy on minimizing risks with respect to the country’s power supply,” he concludes.