Weakest link: the small components that keep nuclear safe

23 November 2017 (Last Updated June 9th, 2020 14:57)

Even the smallest components in a nuclear plant must be maintained for the plant to run as safely and efficiently as possible. Thomas Fink, head of nuclear safety at glass and ceramics technology company Schott, lends his insight.

Weakest link: the small components that keep nuclear safe
“The components within the reactor casing can almost be the weak link in the whole chain,” says Fink. Credit: Courtesy of SCHOTT

Effective operation and maintenance of a nuclear plant lead to cost savings and improved safety, and often it is the smallest components that are overlooked.  Hatches, seals, electrical penetrations and hydrogen sensors all failed during the 2011 Fukushima disaster.

According to an International Atomic Energy Agency (IAEA) report released in July, “failures of components not designed to withstand a severe accident played a role in the rapid degradation of the plant infrastructure.” While regulation of large-scale nuclear safety features such as flood walls have seen dramatic change in the last few years, little has changed regarding these components.

These should not be overlooked, explained Schott head of nuclear safety Thomas Fink during the UK Nuclear New Builds Conference in September. Fink highlighted that during severe events, pressure and temperature can exceed normal ranges by as much as 300%. As such, the strength, reliability and maintenance of these components must be considered right from construction.

Schott has recently installed more of its Eternaloc electrical penetrations at the Forsmark Plant in Sweden. Not only can these withstand temperatures of up to 400°C, they also require no maintenance for 60 years.

As the UK embarks on a new phase of nuclear, it must look into operations and maintenance alternative for every component to ensure that plants are as safe and cost-effective as possible.

Molly Lempriere: Could you tell me a little about Schott?

Thomas Fink: Schott has a 135-year history in speciality glass. Everything started with optical glasses for lenses and from that we developed into a technology company. The division I work for is the nuclear safety division. We’ve been in the nuclear field since the early 60s.

We started with the Otto Hahn nuclear-powered ship in Germany, and then developed, working at German nuclear power plants and then moving into the international sector.

ML: Could you tell me about Schott’s Eternaloc component?

TF: The Eternaloc manages electric penetration through the containment wall of a nuclear reactor. So wherever you have to bring the cable through the steel and concrete containment you somehow have to make a penetration but at the same time keep the whole thing hermetic.

We have based it on glass-to-metal seal technology; this means we are sealing in the electric conductors with glass into a metal flange. The glass acts as an electrical insulator, and at the same time it’s absolutely hermetic and there is a pressure boundary. The good thing with glass, and also with the metal materials that we’re using, is that these are inorganic materials so they do not breach under radiation or stress.

ML: Because they’re inorganic do you find that even operating over a long period of time the materials remain safe?

TF: Exactly. I think a very good example from daily life is if you look at something that’s made of plastic, an organic material. If you have it in the sun over the summer, in your garden, it will change colour and it gets brittle. This is because the carbon chains within it are quick to oxidise; this shows the aging process that you have with organic materials. But if you look at the windows on your house, they are made of glass which doesn’t change its properties over hundreds of years.

This glass-to-metal sealing is actually, probably, the safest technology that you can use for electrical penetration components that go into the reactors. They’ve got a life expectancy of around 60-80 years and they need no maintenance, so there’s no costly replacement after a few years like you have to expect with the organic alternatives.

We’ve had equipment working for 50 years without any maintenance and without replacement so far, so we have proven technology.

ML: As a company, you’re involved in many different areas of industry. Do you think that has helped with your work in nuclear?

TF: Yes of course, the first thing is we are coming from a glass background so we are able to modify the glass that we use for our sealing technology. We have the capability in-house to adjust our glass to different kinds of applications.

Working in a range of fields on technical applications has helped. For example working in the oil exploration industry, where you have extremely high pressure requirements of up to 5000bars, which is a thousand times what you’d usually need for a nuclear power plant, has developed the resistance of the glass. These types of challenges further develop the technology in the nuclear sector too, giving us a much higher degree of safety for the products that we’re using.

ML: Many people remain unconvinced about the safety of nuclear. Do you think this could change?

TF: I think what we see now is a very positive trend, with people becoming more accepting of the new generation of reactor types, this Generation III+. Also, small modular reactors have created publicity with their increased safety.

We have also seen very good practical lessons learned from Fukushima, but more on big equipment, like extra diesel generators, flood walls, these kinds of things. What is still missing is a drilling down to smaller equipment. We have a lot of small components that are safety-critical.

I was talking yesterday about a new report by the IAEA which was published in July this year, and they highlight all the components that are safety-critical in the case of an accident, and give clear recommendations. These recommendations are something that we were missing, and that needs to go further, that needs to go into national and international standards. There is still room for improvement.

The components within the reactor casing can almost be the weak link in the whole chain and Schott’s components have been tested and perform to a much higher level than, say, the ones used in the Fukushima reactor.

ML: Have you faced many challenges getting your Eternaloc technology out there?

TF: It’s been a bit of a challenge getting our components specified for new build reactors. I think we do expect that the requirements for these kinds of components will rise in the future. The lessons that were learnt from Fukushima are still a little bit behind, so the requirements will increase which definitely works in favour of our technology because we are meeting much higher standards for other applications already.

We are using these inorganic materials, so the product itself might be a little bit more costly compared to others at the beginning but over the lifetime of the reactor, you do not have any maintenance, you don’t have any replacements so the total cost of ownership is much lower.

There are some conflicts of interest between the EPCs [engineering, procurement and construction]. They usually have the tendency to build using equipment they can buy for lower costs. The utility companies are not always aware of all the small components they may later have to replace costly after just 20 years, so there are hidden costs.

And of course, you can have additional shut down time if you have to replace components. As a utility you can easily lose a million euros a day if your reactor is not operating, and that immediately consumes all the savings in the purchasing price at the beginning.

I think the total cost of ownership, and the transparency to the end-customers, is blocking us a little bit at the moment.