Electrical Penetration Assemblies for Nuclear Power Plants

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.

In order to keep the radioactive high-energy source controlled, electricity is needed inside the containment structure to supply thousands of instruments, control panels, electric motors and many other electric and electronic devices. Glass-to-metal sealed penetrations allow the safe conduction of electricity through the fire-protective, pressure-resistant and hermetically sealed containment walls of nuclear power plants. In case of an accident, these glass-to-metal sealed penetrations also prevent steam, pressure and radioactivity from escaping.

Our feedthroughs 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.

Product Description

A penetration module for nuclear power plants mainly consists of:
  • A metal housing with the sealed-in conductors
  • The glass-to-metal seal (in compression technique)
  • Connections to tail cables (LOCA-proof sealed by shrinking tubes and or elastomer sealing)
  • Tail cables (length and type according to customers' specification)
  • Metal housing for protection and strain relief of the cable connections
Our latest generation penetrations use receptive modules with mountable connectors, which allow smaller construction sizes and easy installation at the site.

Product Advantages

Our hermetically sealed penetration modules have:
  • High packing density of up to 118 poles at connector solutions and more than 500 pins at flange types enabling a reduction of the required embedded pipes for nuclear power plants
  • Virtually no aging of the used conductor and seal material – leading to the fact, that other types of penetrations (i.e. epoxy-to-metal bonds) with signs of aging have been replaced by glass-to-metal type penetrations.
  • Penetration which also includes connections between conductor pins of the hermetically sealed feedthrough and oncoming cables for use in nuclear power plants and under seismic stress. These plugs are easy to connect, allow easy exchange of modules in case of system modification and offer high stress resistance.


Our glass-to-metal sealed (GTMS) penetrations are used in Pressurized Water Reactors (PWR), High Temperature Reactors (HTR) - also known as Pebble Bed Reactors (PBR), Boiling Water Reactors (BWR) and Fast Breeder Reactors (FBR).


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
  • Degree of Protection: IP 54
  • Temperature Resistance: up to ≥ 200 °C / 8h
  • Pressure: up to ≥ 20 bar
  • Radiation Dose: 0.5 x 106 Gray Gamma (up to 5 x 106 Gray is possible)
  • Leakage Rate (penetration only): < 1 x 10-6 cm3 / sec. He (at ΔP=1 bar)
  • Leakage Rate (penetraton installed): < 1 x 10-3 cm3 / sec. He (at ΔP=1 bar)
  • Seismic Test: up to 5g / 5... 100 Hz at 3 axes

Forms of Supply and Product Packaging

We can deliver products in accordance to customers’ specifications and / or completely pre-assembled. The penetration assembly usually includes junction boxes, as well.

Our products are delivered in dust-safe, moisture-safe, impact-proof transportation boxes.

Quality Assurance

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.
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Case Study

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"