Hot standby at Dounreay
A 'hot standby' process control system supplied by Mitsubishi is taking
care of operations at Dounreay's new Sodium Disposal Plant - a key
element in the decommissioning of this venerable nuclear research
facility
Though not a producer of nuclear powered energy anymore, activity at the
United Kingdom Atomic Energy Authority (UKAEA) installation at Dounreay
is far from over. Work is now underway to decommission the former
research facility and return it back to a natural landscape by the year
2060. The contract to design, construct and commission a system for the
disposal of the bulk liquid metals (sodium and sodium/potassium alloy) at
the Prototype Fast Reactor (PFR) was recently awarded, with the main
contractor choosing to use Mitsubishi Electric's Automation products to
control the entire application.
Cornerstone of the contract, the Sodium Disposal Plant (SDP), recently
completed five days continuous operation, effectively bringing to a
successful close the inactive commissioning of the plant. The next
(active) stage of the work will proceed when consent is given by the
Nuclear Installations Inspectorate.
Commissioning of the SDP and the associated equipment provided to supply
the sodium to the SDP started late in 1999. The combined commissioning
team comprises UKAEA, NNC (the main contractor) and RWE Nukem (who will
provide the operations team for the plant). The scale of the SDP is
unparalleled and as decommissioning of other liquid metal cooled reactors
progresses around the world, there is significant international interest
in its operation.
The central processing plant and the fluid systems have been integrated
through the application of a Mitsubishi Q4AR 'Hot standby' process system
connected to a central SCADA based control system. Although backed up by
hardwired safety circuits, this automatic system is key to maintaining
the reaction conditions. Commissioning experience so far has demonstrated
that the control system has easily met the design requirements set for it.
Mitsubishi Control products are fully IEC 61131-3 compliant - a standard
that allows the systems programs to be created in a standard format,
using coding terminology and symbols that are universally recognisable.
Extraction of the sodium from its various locations at the PFR and its
transfer to the SDP presented a number of other challenges. The original
design for the PFR, like most other older nuclear plants, did not include
many facilities for decommissioning. This has imposed some significant
design constraints on the equipment used for the liquid metals disposal
project. Typically, the equipment to extract sodium from the reactor
vessel can only be deployed through existing penetrations in the
structure - and it will only be used once!
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