Approximately 17% of all worldwide electric generation is produced by nuclear power plants. In these plants, a controlled nuclear fission is used as a high-energy source of heat to turn water into steam, which spins an electricity generating turbine.
SCHOTT Eternaloc™ - Small component. Big impact.
SCHOTT Eternaloc™ Electrical Penetrations, based on Glass-to-Metal Sealing Technology, allow the safe conduction of electricity through the fire-protective, pressure-resistant and hermetically sealed containment walls of nuclear power plants. The performance of electrical penetrations 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. In case of an accident, these glass-to-metal sealed penetrations also prevent steam, pressure and radioactivity from escaping.
Eternaloc™ penetrations are sealed by non-aging glass that remains pressure- and vacuum-proof for many decades. All around the world, our glass-to-metal-seals have been proving their durability and reliability in power plants – maintenance-free – since the early 1960s.
A penetration module for nuclear power plants mainly consists of:
Our latest generation penetrations use receptive modules with mountable connectors, which allow smaller construction sizes and easy installation at the site.
Eternaloc™ electrical penetrations assemblies (EPA) are designed with superior, redundant, and safer glass-to-metal seal technology. They 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, the Eternaloc™ glass-to-metal sealed penetrations 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.
Eternaloc™ 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.
Eternaloc™ hermetically sealed penetration modules have:
The benefit of Eternaloc™ Glass-to-Metal Sealed (GTMS) penetrations is that they are not only inherently more stable and safe, they are also based upon proven technology.
SCHOTT has successfully applied this technology to a range of critical applications including nuclear submarines, air bags for cars and in high pressure and extreme temperature applications in the oil and gas industry, such as for Liquefied Natural Gas (LNG) vessels.
Within the nuclear industry itself, SCHOTT has 12,000 GTMS EPAs installed in more than 50 active nuclear power plants, including Pressurized Water Reactors (PWR), High Temperature Reactors (HTR) - also known as Pebble Bed Reactors (PBR), Boiling Water Reactors (BWR) and Fast Breeder Reactors (FBR).
Meeting the central requirement for longevity, some of these EPAs remain in operation - maintenance-free - after almost 50 years of service. Key to this is the inorganic and non-aging nature of the glass-to-metal seal which offers a virtually unlimited lifespan at the pressure boundary.
For Forsmark 3, SCHOTT designed a new generation electrical penetration which can withstand the latest Severe Accident (SA) requirements (e.g. submerged conditions at higher pressure levels and higher temperatures).
Compression Glass-to-Metal Sealing Technology
Compression glass-to-metal sealed feedthroughs comprise a metal housing, a glass sealant and metal conductors. The preassembled component is heated to a temperature where the glass melts to the metal. During the cooling process, the metal housing contracts at a rate much higher than that of the glass. This compression creates a highly pressure-resistant and hermetically sealed unit that offers the highest safety.
The glass preform, metal shell and conductor pins, made of nickel-iron or oxygen-free copper (low-ohmic), are assembled on a fixture. The complete assembly is heated to a temperature where the glass becomes free-flowing and fills the space between the main body and the conductor pin or bolt.
During the cooling process, the glass solidifies at its set point. Upon further cooling, the outer metal housing shrinks more than the sealing glass and the conductor (due to its higher coefficient of thermal expansion), leading to a compressive radial force onto the glass body. This leads to a very high hermeticity and tightness even under high temperature or gas pressure and thermal cyclic conditions.
Finally, corrosion-protective layers are deposited on the metal shell; whereas the nickel-iron conductor pins are plated with a gold layer.
The cable tails are connected to the pins by plugs, crimping or soldering and then insulated by shrinking sleeve and potting with elastomer to ensure the electrical function even during extreme environmental conditions (important during Loss of Coolant Accident, LOCA).
Stainless steel housings are mounted to the ends, providing mechanical protection and strain relief at the cable inlet. Junction boxes inside and outside containment give an additional protection for this electrical system. For receptacle modules, the connectors can be either provided cabled according to the customer’s requirements or can be finished on site.
Besides power and regular control/instrumentation penetrations we also produce coax and triax penetrations in single or double barrier version.
Features / Specifications
Our penetration modules are manufactured according to KTA 3403 or based upon IEEE317 (Standard for Electric Penetration Assemblies in Containment Structures for Nuclear Power Generating Stations).
For more information about our quality assurance process, please refer to this page.
This case study by Visola Electric Insulation Technology Ltd illustrates the use of SCHOTT's EPAs in the PAKS NPP (Hungary) since 1995 with no incidents of failure.
"Electrical Penetration Assemblies for VVER type Nuclear Power Plants, Role and Behaviour of Electrical Penetration Assemblies in a Nuclear Power Plant"