NUCLEAR POWER STATIONS REPRESENT A significant investment and are designed to last: the new EPR reactors, for example, will have a design life in excess of 60 years. This presents a number of challenges for those tasked with maintaining critical equipment, which may require repair or replacement several times during a power station’s lifetime.

Let us take pumps as an example. They perform an essential role in moving fluids around the site and also have a critical function as part of the core’s cooling system, designed to operate if the reactor temperature becomes too high. Whether they are in use daily or in an emergency, they must be ready to go into service and working at their best all the time.

Safety-related pumps are generally operated for one hour per month to ensure they to function as required in an emergency. Even after 40 years, this is less than 2000 hours of operation. These pumps therefore require a strip down every two to ten years, to ensure they still comply in every detail with the original drawings and tolerances.

The nuclear sector requires a number of key attributes from supply chain partners, particularly those involved in the supply and maintenance of critical equipment and components. These include:

  • Long-term commitment, with a business model that supports the longevity of service required for nuclear applications;
  • Knowledge of the regulatory framework and how to operate within it, including documentary procedures;
  • Expertise at technical and industry level that is constantly kept up to date and shared with the client;
  • Facilities and personnel that are fully accredited to undertake maintenance and servicing work that cannot be performed on-site.

On the record

In such a highly regulated industry, the chain of supply required to maintain each piece of equipment is considerable. Documentation is key to compliance: validation of materials, processes and consumables requires a recorded history to ensure integrity. The original equipment specification must be immaculate, with any changes logged, so it is possible to re-engineer components over time. This includes ensuring continuity of supply for the materials from which the components are made, whether that is steel for housings or rubber composites for seals.

Documentation also plays a key role in the ongoing safety and reliability of critical equipment. Its importance was amply illustrated in 1979, when the investigation into the Three Mile Island accident found that the previous holder had let certificates lapse, making it difficult to apportion responsibility for the reactor meltdown. In response, the USA developed a specific code for documentation for nuclear programmes that is still in use today.

Recent events in Korea have further stressed the importance of accurate documentation and traceability for nuclear operators. In this instance, a substandard material entered the supply chain when a supplier deliberately altered documentation. This shut down the country’s nuclear programme for some time, while comprehensive checks were made to establish the extent of the problem. The final ruling clarified that legal responsibility rests with the certificate holder to ensure traceability through the entire supply chain.

While the legal position is clear, in practice the retention of documents and records over the lifetime of a nuclear site has to be a collaborative effort between the equipment suppliers, the operator and the maintenance team. The ability to demonstrate due diligence in creating and retaining the necessary documentation is therefore a key attribute to consider when selecting a life-cycle partner.

Planning for obsolescence

The lifetime of a nuclear plant and its components and equipment can be quite different — the average life of a pump is 35 years, for example. So obsolescence is a key consideration for maintenance regimes. Where original parts are no longer available, it is necessary to prove that replacements can perform the same task and to the same standards as the original certified product, which may be a considerable undertaking.

Most clients have their own boards of obsolescence, who want full details of likely parts going out of production so that shortfalls and lack of availability can be predicted as far as possible. The ability of a lifecycle partner to work with the client and provide transparency in this regard is a key competence to look for.

Celeros FT combines manufacturing with aftermarket services, so we are able to make a commitment that critical equipment such as pumps and their constituent components will not become obsolete, with parts availability guaranteed for the lifetime of the plant.

Sharing knowledge

It is not only physical plant that may become obsolete over time. It is very unlikely that the engineer who originally installed the equipment will be on hand 40 years later to maintain it; he or she certainly will not be available when the power station is due for decommissioning. So the ability to capture knowledge and ensure continuity of expertise is another key part of good nuclear asset management.

Our own employees are continuously improving their knowledge and we also host training courses for client employees. Key to these sessions is ensuring everyone involved is speaking a common language, with no jargon and no company slang or abbreviations. This approach greatly reduces the likelihood of misunderstanding between site personnel and external suppliers in times of crisis.

Topics for training should not be limited to a specific site’s requirements: sessions to update people on regulations and responsibilities, or to share new technical developments and best practice are also very useful. Around 200 people per year from external organisations attend our courses, including representatives from safety authorities who are keen to keep abreast of the latest flow control solutions.

Responsiveness to change

In safety-critical industries, it is vital that all parties respond swiftly to any incident, learn lessons and contribute positively to finding a lasting solution. Fukushima is a case in point. Here, the tsunami flooded the site and prevented the operation of safety pumps that were supposed to kick in and cool the reactor core.

This prompted global nuclear safety authorities to ask site operators what would happen if they lost all power? In Europe, the response has been to house the emergency diesel engine for the reactor cooling system in an entirely separate and elevated building, to prevent it being flooded. However this solution does not solve the fundamental problem: safety-critical pumps rely on an external power source and may not operate properly if submerged.

Celeros FT has reassessed the pump design, using its inhouse ASME-accredited facilities, to develop a solution – the CUP TWL pump. Rather than rely on an external power source, the CUP TWL uses the steam produced as a byproduct of the nuclear generation process to pump cooling water into the core should it overheat. The pump requires no external electrical supply, cooling water or oil system and provides an independent, robust and reliable solution. Validation tests have proved that the TWL pump will perform reliably for extended periods, even when fully submerged.

The current global pandemic is another challenge. Lockdown has had a big impact on materials availability and it will take time to get the supply chain working again. For example, the qualification process for foundries takes time, so finding and validating alternative sources will be arduous. Celeros FT is working on ways to fast-track materials in order to control timelines for customers.

Author details: Christophe Borgeois, Regional sales director for nuclear aftermarket, Europe and Africa at Celeros Flow Technology; Yohann Valla, Aftermarket director, Celeros Flow Technology