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The Dry Store Cells are used to provide a storage facility for irradiated fuel elements for a period after removal from the reactor, until their radioactivity level and heat levels have decayed to a sufficiently low level to permit dispatch from site for reprocessing.

The Secondary Dry Store Cells (DSC) 4 and 5 were constructed during the late 1970s to supplement the three original CO2 filled Primary DSCs 1, 2 & 3, to provide fuel storage for a prolonged period. DSC 4 and 5 are near identical systems and each system comprises a Control Desk, Auxiliary Equipment, Contactor and PLC Cubicles.

Each system controls movement, loading and unloading of fuel elements in an array of skips. The main system functions are:

  • Skip shuffling within the Secondary Dry Store Cells
  • Skip positioning prior to loading or unloading
  • Skip loading from the Skip Loading Chute at the East end of the DSCs
  • Skip unloading from the Skip Loading Chute via the Primary Discharge Route
  • Skip unloading via the Diverse Discharge Route (DDR) Transfer Chute at the West end

Restoration of the DSC4 and 5 systems to a high level of reliability and maintainability was required in order to continue the process of removing fuel elements which are currently stored in skips, and in order to discharge all fuel from the reactor, as de-commissioning of the Wylfa reactors approaches.

In addition, the existing PLC based control system equipment did not comply with current safety integrity standards. The SDSCs are very large enclosed structures, held at negative pressure due to the presence of contaminants. The mechanical components within the cell are impractical to access.

Any mechanical damage would result in significant delay and cost to repair, as well as increasing the risk of loss of fuel element integrity or containment.

A new Siemens S7 controller was deployed to provide a site standard PES solution.

Magnox Limited Requirements

  • To ensure and demonstrate compliance with current safety standards.
  • To meet and demonstrate the specified safety integrity targets.
  • To provide a well documented, modern system.
  • To improve maintainability throughout generation and de-fuelling.
  • To ensure high system functional availability.
  • To avoid or minimise modification and disruption to existing mechanical plant items
  • To avoid or minimise modification and disruption to existing electrical power and control cabling.
  • To provide improved operator information and controls.
  • To minimise DSC unavailability during the refurbishment project.
  • To enable integrated commissioning with the refurbished Transfer Machine at a later date.
  • To utilise proven technologies, common with other systems on site.

Case Study: Secondary Dry Fuel Store - Magnox Limited, Wylfa Power Station



Download the Wylfa Power Station case study here

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