Overcoming obsolescence24 December 2019
The UK is embarking on a renaissance of its nuclear infrastructure. But for the foreseeable future, the technology of an earlier generation will continue to underpin its civil sector. Peter Langan explains how operators overcome the challenge of obsolescence.
EVERY NEW PLANT IS STATE-of-the-art, a technological marvel of its time. But age and human innovation march on and today’s technical dream becomes tomorrow’s challenge in an industry unable to reap the benefit of mass production of spare parts.
Through acquisition and merger, a lot of Britain’s nuclear heritage and specialist knowledge sits within Cavendish Nuclear, the country’s largest nuclear services business with a presence across every tier of the civil sector.
This includes our specialist obsolescence service, which performs a critical role in the repair and replacement of electronic assemblies no longer available from the original equipment manufacturer (OEM).
Cavendish Nuclear provides a fault-finding, refurbishment and re-manufacturing service for OEM assemblies and individual printed circuit boards (PCB), to ensure availability of critical spares for all makes and models of any age, saving our customers time and money against complete system replacement.
This service typically removes the requirement for costly engineering activities such as system replacement justification exercises (including safety and technical reviews), procurement, installation, commissioning and training.
Delivering a lower cost solution
Replacing electronics systems is expensive and Cavendish Nuclear has to use its expertise to provide a more cost-effective solution to obsolescence for its customers, through its repair and re-manufacturing service.
- A re-manufacturing service that prevents the need for costly plant modifications.
- Reverse engineering of obsolete or unsupported items, often when no design information is available.
- Detailed assessment of an assembly for repair, refurbishment or remanufacture, down to individual component level.
- Analysis of components, including transformers and inductors
- Services fully accredited to ISO 9001, ISO 14001 and ISO 18001.
- Staff accredited to IPC-7711 and IPC-7721 for rework and repair of electronic assemblies.
To decide on the best approach in dealing with an obsolete system, we carry out a detailed assessment down to individual component level. New PCB manufacturing data (gerber files) are produced via high resolution scanning of the OEM’s PCB to produce exact ‘like for like’ circuit tracks and silk-screen-printing information. Once the gerber set has been created, it is possible to edit these files to incorporate any changes required. For example, we can change the PCB profile to match new mechanical keyway requirements or design modifications, such as component footprints or additional components.
Anti-counterfeit screening of replacement components to AS6081:2012 is a key part of the process. X-ray fluorescence (XRF) analysis of original assembly, for solder alloys and PCB substrate, ensures identical alloys are used during fault-finding, repair, refurbishment or remanufacture, eliminating future failure routes and subsequent system failure. Assembly testing requirements and a technical file for engineering justification are agreed with the customer.
In addition, we also provide our customers with off-line test rigs that can simulate their environment. These are a safer, faster, lower cost option for certifying operation, fault finding and training of plant personnel including calibration and configuration, providing solution.
EDF Energy’s requirement
One of our major customers is EDF Energy, whose fleet of advanced gas-cooled reactors were built in the 1960s and 1970s. More of the technology is becoming obsolete and sourcing replacement parts has been critical to the success of recent plant life extensions.
An example of how Cavendish Nuclear is helping EDF Energy overcome the challenge of obsolescence is our support for EDF Energy’s inlet gas vane (IGV) motor controller system. The IGV controls the cooling gas across the reactor core and each reactor relies on four units.
There was a critical spares challenge. The OEM no longer supported the IGV system and this was compounded by the fact that in previous years several different repair contractors had been engaged to fault-find and repair. This created issues with version control, unknown origins and quality of replacement parts, varying degrees of testing prior to installation, minimal rectification records and no traceability back to the repair engineer.
In addition, replacing the existing system with a modern equivalent posed a number of constraints. The replacement had to be installed and commissioned within a standard 12-week scheduled maintenance outage and had to interface with existing plant constraints such as cabinet footprints and existing control system signals. The safety case and engineering justification effort to sanction a replacement system would have been expensive.
Cavendish Nuclear was issued three IGV assemblies, each presenting different physical degradation as well as unknown faults.
Each had previously been condemned by EDF Energy repair suppliers as “beyond economic repair”.
Our first task was to baseline each PCB within the assembly. This involved:
- Establishing the latest PCB modification revision.
- Establishing a detailed bill-of-materials (BoM) and detailing component availability and source to ensure like-for-like components are used during the repair service, to reduce the requirement for individual component engineering justification for use.
- Identifying and sourcing obsolete components, ensuring full anti-counterfeit component screening to AS 6081:2012.
- Establishing minimum order quantities to enable a ‘lifetime buy’ to facilitate the repair service.
- Identifying any component that requires re-manufacture, for example transformers.
- Establishing minimum order quantities and price for any re-manufactured parts.
The output from this was an obsolescence report. This report detailed:
- PCB re-manufacture recommendations — in this case, the Power 1 CCT and associated daughter board assemblies.
- The ability to effect a repair to ‘rework and repair’ standard.
- Assumptions made during the assessment.
- Obsolete part recommendations.
- Testing requirements to fully exercise all board functions.
- Basic considerations (visual board inspection). For example, any conformal coatings, engineered links, programmable elements etc.
- Details of re-work equipment, materials and processes.
- XRF analysis of the PCB substrate and solder composition used by the OEM, to determine its chemistry.
The report provided all the information needed to enable EDF Energy to agree the way forward in terms of the options to repair or re-manufacture, including identification of risk.
Cavendish Nuclear recognised that the trigger module was the weakest part in the overall IGV design. Based on the Cavendish Nuclear recommendations EDF Energy agreed to remanufacture the Power 1 CCT and the trigger modules (there are six trigger modules mounted on each Power 1 CCT board).
Following discussions with EDF Energy, a decision was made to progressively test each PCB in isolation following fault finding, refurbishment and repair of each board, to ensure each board worked as it was designed to do.
After individual board testing, combination testing of the three boards at low power took place, again de-risking the testing, culminating with a full power system test driving a 415V motor. This final test regime fully simulated the on-plant conditions.
Individual board test harnesses, a full system test harness and a full test rig were designed and manufactured by Cavendish Nuclear to simulate the plant conditions. A suite of detailed test documentation was developed to record the set-by-step test results and calibration set-up details.
As a result, Cavendish Nuclear was able to provide EDF Energy with a supply of reliable IGVs, which could be swapped in when needed and which contributed to the safe, effective and reliable operation of the reactors. Refurbishing the IGVs, rather than the more complex and expensive option of completely replacing the system, saved EDF Energy time and money. Cavendish Nuclear continues to support EDF Energy in refurbishing IGVs and managing other areas of obsolescence.
Author information: Peter Langan, Project manager, Cavendish Nuclear