Severn Unival has been handling valve overhauls during Sizewell B’s refuelling outages since 2004. The longevity of the relationship is rooted in Severn’s exacting engineering standards and in-depth understanding of the safety regimes associated with nuclear plant.

Sizewell B is a critical baseload nuclear power station for the UK and its statutory periodic shutdowns for maintenance, inspection and refuelling are expertly orchestrated. Severn Unival has handled valve and actuator overhauls during the power station’s scheduled outages for more than ten years. Valves are small but vital components in the context of a nuclear power plant. They play an important role across applications such as pollution control, feedwater, cooling water, chemical treatment and steam turbine control systems.

Sizewell B

Sophisticated project management
Statutory shutdowns are scheduled every 18 months at Sizewell B. The safe, competent and efficient overhaul of valves during these outages is essential. Any upgrades or repairs need to be completed to exacting standards within a strict timeframe. It is crucial that the plant restarts on time and that all necessary measures are taken to minimise the risk of an unplanned shutdown before the next scheduled outage.

Severn Unival has a strong pedigree in the intelligent maintenance of valve populations to enhance long-term performance and reliability. This is married with rigorous, safety-led procedures and an appreciation of the underlying need to complete tasks in a systematic and timely manner during shutdowns.

Maintenance shutdowns on large nuclear plants typically involve in excess of 1,000 engineers conducting more than 10,000 separate pieces of work. This requires careful management and execution at a macro level by the operator, and at a micro level by contracted service providers.

A large plant uses hundreds of valves to manage the flow of water and steam. Ensuring the entire population works reliably and efficiently requires shrewd prioritisation of outage work lists. Valve reliability and safety go hand-in-hand on any processing plant. In the context of nuclear power this has even greater significance.

A meticulous approach
A blend of standard maintenance routines and performance monitoring is used to determine which valves will be overhauled during a given outage. Severn Unival is briefed on the scope of work 12 months in advance, and a team of around 18 instrument technicians is deployed onsite for 8 – 10 weeks.

A reliable, highly-skilled team is the cornerstone of any valve maintenance project. This is especially true on nuclear plants which require a meticulous approach and scrupulous safety standards. Each member of the team is fully audited and receives bespoke training ahead of the outage, regardless of how many times they have previously worked in a nuclear facility.

Training is conducted by Jonathan Jones, one of Severn Glocon Group’s Business Directors, who says there are three core principles to the programme:

  1. Safety
  2. Competency (ability to calibrate)
  3. Following procedures and processes verbatim

Practical skills such as calibration are vital to ensure valves are optimised for safe and reliable performance between outages. However, general safety tops the list of training priorities. Failure to follow basic safety procedures onsite can have wide repercussions that risk jeopardising the entire maintenance project.

Attention to detail – and an ability to work in a process-driven manner – is also important. Each piece of work is allocated its own job card with activities outlined in prescribed stages. The assigned technician needs to complete each stage systematically, physically signing off each item on completion. This paper trail reduces the risk of human error and boosts efficiency. It also enables team leaders and site operators to conduct spot-checks as required.

Inevitably, there are occasions when instrument technicians identify additional maintenance requirements that are not detailed on the job card. The ability to detect these and competently realign resources to handle them is central to Severn Unival’s offering.

“Maintenance routines and performance monitoring enable most valve overhaul requirements to be predicted accurately,” explains Jonathan Jones. “However, some low level wear and tear of internal components can’t be picked up until the equipment is disassembled. Our instrument technicians have a high level of expertise and can quickly ascertain if a component is unlikely to last until the next scheduled outage. They flag such issues with team leaders, who in turn use their project management skills to ensure the situation is resolved. A capacity to take the unexpected in our stride without compromising standards or timeliness underpins the strength of our relationship with Sizewell B.”

When a baseload power station goes offline for maintenance, detailed planning is required to avoid disruption to the UK national grid. A fine balancing act needs to be achieved to maintain an adequate ‘spare margins’ buffer between electricity supply and demand. This puts acute pressure on power station operators to ensure outage maintenance is efficient enough to finish on time and effective enough to minimise the risk of unplanned shutdown between routine outages. Every service contractor has an important role to play taking responsibility for their own area and working collaboratively to ensure the best possible outcome for the plant as a whole.

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