Material Selection for Tritium Sealing Environments

As global investment in fusion energy, nuclear research and isotope handling systems grows, the need for reliable sealing solutions for tritium environments is increasing.

However, tritium, a radioactive isotope of hydrogen commonly used for nuclear fusion fuel , presents unique engineering challenges. It is one of the smallest and most permeable molecules and is capable of diffusing through many elastomers and polymers. At the same time, systems handling tritium often operate in radiation environments, meaning sealing materials must maintain their properties over long service periods.

Selecting the correct sealing material, therefore, requires careful consideration of permeation behaviour, radiation resistance, and application conditions.

This article outlines the key considerations when specifying elastomer seals for tritium environments and explains how hydrogen testing and nuclear material data can inform the selection of the correct elastomer material.

Why tritium sealing is challenging

Tritium (³H) is a radioactive isotope of hydrogen that behaves chemically very similarly to hydrogen and deuterium. However, from a sealing perspective, it introduces several important challenges:

High Gas Permeation

Hydrogen isotopes have extremely small molecular sizes, allowing them to diffuse through many elastomer materials. This can result in gradual gas leakage, permeation into surrounding environments, and loss of system efficiency in containment systems

Radiation exposure

Many tritium systems operate within nuclear facilities where materials may be exposed to gamma radiation or other ionising sources. Radiation can affect elastomers through crosslinking, chain scission, and changes in hardness, elasticity, and sealing capability

Long-term containment requirements

Tritium systems are often designed for long service intervals, meaning seals for use with tritium must maintain performance over extended periods without significant degradation.

Elastomer behaviour with hydrogen isotopes

Although tritium testing is limited due to the complexity of handling radioactive materials, the behaviour of hydrogen isotopes in elastomers is well understood. Hydrogen, deuterium, and tritium all exhibit similar diffusion mechanisms within polymer structures.

As a result, hydrogen permeation testing is widely used as an indicator of tritium compatibility. Testing conducted on sealing materials in high-purity hydrogen environments can therefore provide valuable insights into how materials may behave in tritium systems. Our blog on gaskets for hydrogen electrolysis contains valuable insight into the capabilities of various elastomers in hydrogen environments.

For example, permeation testing conducted at 80 °C using 99.995 % hydrogen demonstrates how elastomer structures influence hydrogen diffusion rates. Materials designed with lower gas permeability can significantly reduce gas migration through sealing components.

If you have any further questions about our testing, don’t hesitate to contact TRP directly.

Key sealing challenges in tritium systems

When specifying seals for tritium service, several engineering factors should be considered, such as the following:

Gas permeation

Gas permeation occurs when hydrogen isotopes diffuse through elastomer networks. Materials with dense polymer structures or specialised formulations can help reduce this effect.

Radiation degradation

Exposure to radiation can cause changes in elastomer properties, including hardness, elasticity and compression set. For example, nuclear-grade EPDM materials tested under controlled radiation environments demonstrate gradual hardness change.

Material stability in process environments

In addition to tritium itself, sealing materials are all commonly exposed to process gases, oils and lubricants, cleaning chemicals, and temperature fluctuations. As a result, the compatibility of materials within the seal’s specific environments needs to be carefully considered.

Materials commonly used for seals for use with tritium

Several elastomer families are commonly used in nuclear and hydrogen isotope environments due to their balance of chemical resistance, permeation performance and radiation tolerance. See TRP’s quick reference guide below for more info:

Table 1. a comparison of elastomers for radiation environments

Specifically, the radiation-resistant rubbers below are among the most suitable for tritium applications:

EPDM – Nuclear-grade elastomers

EPDM materials are widely used in nuclear applications due to their excellent resistance to water, steam, and many chemicals, as well as good radiation tolerance. For example, our EPDM 30H material is nuclear-grade and tested in accordance with Sellafield Ltd engineering standard ES_0_5331_2. The key characteristics of this material include:

• Temperature range: –40 °C to +150 °C
• Compatibility with hot water and steam
• Suitability for radiation environments

Radiation exposure testing for this material has demonstrated stable performance over extended exposure periods, with gradual changes in hardness observed at increasing radiation doses. As a result, these properties make EPDM materials particularly suitable for containment systems, gloveboxes, and processing equipment.

Nitrile (NBR)

Nitrile elastomers remain a common choice for sealing against oils and greases within nuclear environments.

Our material, Nitrile 18L, tested in accordance with Sellafield Ltd engineering standard ES_0_5332_2, offers:

• Temperature range: –25 °C to +125 °C
• Compatibility with oils and greases
• Resistance to radiation environments

As such, nitrile materials are suitable for mechanical equipment and lubricated systems within nuclear facilities.

Fluoroelastomers (FKM)

Fluoroelastomers (FKM) provide excellent chemical resistance and high temperature performance, making them widely used in demanding sealing environments. Examples include materials meeting the Daisy specification, such as Daisy 50, 60, 70, 80, and 90.

FKM typically operates between –15 °C to +200 °C and provides strong resistance to oils, fuels, and many aggressive chemicals. In addition, Daisy fluoroelastomers demonstrate good resistance to radiation environments, making them suitable for many nuclear sealing applications. Below is a graph showing the predicted sealing life vs radiation exposure at different temperatures:

Designing seals for tritium environments

Though choosing the right materials for tritium systems is essential for successful sealing, a seal’s geometry and system design also have an important role. Common sealing solutions for these environments include:

• O-rings
• Bonded seals
• Static gaskets
• Valve seats
• Custom rubber mouldings

Our engineering tools, such as finite element analysis (FEA), can be used to optimise seal geometry, contact pressure, and deformation behaviour to ensure reliable sealing performance with tritium use. 

Additionally, it’s important to verify the compatibility between sealing materials and lubricants or assembly aids to avoid contamination or degradation within your application.

The importance of permeation control

As hydrogen isotopes can diffuse through elastomers, permeation resistance is a critical factor when selecting materials for tritium systems. Our material development efforts continually focus on low-permeation elastomer formulations, particularly for applications such as hydrogen electrolysers and transport systems, and nuclear containment equipment.

Through testing these materials under hydrogen environments, TRP can help to evaluate how formulation changes influence gas permeability.

Supporting nuclear applications through materials expertise

Reliable sealing in nuclear environments requires more than just selecting a material, as successful projects often require:

• Traceable material batches
• Controlled manufacturing processes
• Documented quality control plans
• Customer or end-user audits

Our advanced manufacturing systems can provide full material traceability from raw ingredients through to finished components, ensuring compliance with the stringent requirements within nuclear industry supply chains.

Supporting the Future of Fusion and Tritium Handling at TRP Polymer Solutions

As research into fusion energy and advanced nuclear technologies accelerates, the demand for sealing materials capable of performing in hydrogen isotope environments will continue to grow.

While tritium testing itself remains specialised, our combination of hydrogen permeation testing, radiation exposure studies, and nuclear-grade elastomer development provides valuable insight into how materials may perform in these demanding environments.

By combining materials science, testing expertise, and seal design, we can develop sealing solutions that support the next generation of nuclear and fusion systems.

If you’d like to find out more about our seals for use with tritium and our dependable rubber materials for our custom rubber seals, custom rubber gaskets, and rubber diaphragms within nuclear fusion and many other industries, contact us today, and we can discuss your ideal solution in further detail.